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Sample records for integrable many-body systems

  1. Spreading in integrable and non-integrable many-body systems

    NASA Astrophysics Data System (ADS)

    Freese, Johannes; Gutkin, Boris; Guhr, Thomas

    2016-11-01

    We consider a finite, closed and selfbound many-body system in which a collective degree of freedom is excited. The redistribution of energy and momentum into a finite number of the non-collective degrees of freedom is referred to as spreading as opposed to damping in open systems. Spreading closely relates to thermalization, but while thermalization requires non-integrability, spreading can also present in integrable systems. We identify subtle features which determine the onset of spreading in an integrable model and compare the result with a non-integrable case.

  2. Introduction to the Statistical Physics of Integrable Many-body Systems

    NASA Astrophysics Data System (ADS)

    Šamaj, Ladislav Å.; Bajnok, Zoltán

    2013-05-01

    Preface; Part I. Spinless Bose and Fermi Gases: 1. Particles with nearest-neighbour interactions: Bethe ansatz and the ground state; 2. Bethe ansatz: zero-temperature thermodynamics and excitations; 3. Bethe ansatz: finite-temperature thermodynamics; 4. Particles with inverse-square interactions; Part II. Quantum Inverse Scattering Method: 5. QISM: Yang-Baxter equation; 6. QISM: transfer matrix and its diagonalization; 7. QISM: treatment of boundary conditions; 8. Nested Bethe ansatz for spin-1/2 fermions with delta interactions; 9. Thermodynamics of spin-1/2 fermions with delta interactions; Part III. Quantum Spin Chains: 10. Quantum Ising chain in a transverse field; 11. XXZ Heisenberg chain: Bethe ansatz and the ground state; 12. XXZ Heisenberg chain: ground state in the presence of magnetic field; 13. XXZ Heisenberg chain: excited states; 14. XXX Heisenberg chain: thermodynamics with strings; 15. XXZ Heisenberg chain: thermodynamics without strings; 16. XYZ Heisenberg chain; 17. Integrable isotropic chains with arbitrary spin; Part IV. Strongly Correlated Electrons: 18. Hubbard model; 19. Kondo effect; 20. Luttinger many-fermion model; 21. Integrable BCS superconductors; Part V. Sine-Gordon Model: 22. Classical sine-Gordon theory; 23. Conformal quantization; 24. Lagrangian quantization; 25. Bootstrap quantization; 26. UV-IR relation; 27. Exact finite volume description from XXZ; 28. Two-dimensional Coulomb gas; Appendix A. Spin and spin operators on chain; Appendix B. Elliptic functions; References; Index.

  3. Semiclassical Methods for Many-Body Systems

    NASA Astrophysics Data System (ADS)

    Landry, Brian Robert

    Semiclassical methods are some of the most effective for tackling the notorious many-body problem. We follow up on some inspired work in the field of semiclassical physics including the Berry random wave conjecture and its connection to statistical mechanics, and the Thomas-Fermi approximation. The main thrust of the work is a new semiclassical method based on the Thomas-Fermi approximation that shows positive results especially for highly correlated systems. A new way of looking at particle exchange symmetry is central to our new method, and as such we take a fresh look at permutation symmetry in many-body systems of identical particles.

  4. Dynamical many-body localization in an integrable model

    NASA Astrophysics Data System (ADS)

    Keser, Aydin Cem; Ganeshan, Sriram; Refael, Gil; Galitski, Victor

    2016-08-01

    We investigate dynamical many-body localization and delocalization in an integrable system of periodically-kicked, interacting linear rotors. The linear-in-momentum Hamiltonian makes the Floquet evolution operator analytically tractable for arbitrary interactions. One of the hallmarks of this model is that depending on certain parameters, it manifests both localization and delocalization in momentum space. We present a set of "emergent" integrals of motion, which can serve as a fundamental diagnostic of dynamical localization in the interacting case. We also propose an experimental scheme, involving voltage-biased Josephson junctions, to realize such many-body kicked models.

  5. Dynamical many-body localization in an integrable model

    NASA Astrophysics Data System (ADS)

    Keser, Ayin C.; Ganeshan, Sriram; Refael, Gil; Galitski, Victor

    We investigate dynamical many-body localization and delocalization in an integrable system of periodically-kicked, interacting linear rotors. The linear-in-momentum Hamiltonian makes the Floquet evolution operator analytically tractable for arbitrary interactions. One of the hallmarks of this model is that depending on certain parameters, it manifest both localization and delocalization in momentum space. We explicitly show that, for this model, the energy being bounded at long times is neither a necessary nor a sufficient condition for dynamical localization. We present a set of integrals of motion, which can serve as a fundamental diagnostic of dynamical localization. We also propose an experimental scheme, involving voltage-biased Josephson junctions, to realize such many-body kicked models.

  6. Understanding quantum work in a quantum many-body system

    NASA Astrophysics Data System (ADS)

    Wang, Qian; Quan, H. T.

    2017-03-01

    Based on previous studies in a single-particle system in both the integrable [Jarzynski, Quan, and Rahav, Phys. Rev. X 5, 031038 (2015), 10.1103/PhysRevX.5.031038] and the chaotic systems [Zhu, Gong, Wu, and Quan, Phys. Rev. E 93, 062108 (2016), 10.1103/PhysRevE.93.062108], we study the the correspondence principle between quantum and classical work distributions in a quantum many-body system. Even though the interaction and the indistinguishability of identical particles increase the complexity of the system, we find that for a quantum many-body system the quantum work distribution still converges to its classical counterpart in the semiclassical limit. Our results imply that there exists a correspondence principle between quantum and classical work distributions in an interacting quantum many-body system, especially in the large particle number limit, and further justify the definition of quantum work via two-point energy measurements in quantum many-body systems.

  7. Understanding quantum work in a quantum many-body system.

    PubMed

    Wang, Qian; Quan, H T

    2017-03-01

    Based on previous studies in a single-particle system in both the integrable [Jarzynski, Quan, and Rahav, Phys. Rev. X 5, 031038 (2015)2160-330810.1103/PhysRevX.5.031038] and the chaotic systems [Zhu, Gong, Wu, and Quan, Phys. Rev. E 93, 062108 (2016)1539-375510.1103/PhysRevE.93.062108], we study the the correspondence principle between quantum and classical work distributions in a quantum many-body system. Even though the interaction and the indistinguishability of identical particles increase the complexity of the system, we find that for a quantum many-body system the quantum work distribution still converges to its classical counterpart in the semiclassical limit. Our results imply that there exists a correspondence principle between quantum and classical work distributions in an interacting quantum many-body system, especially in the large particle number limit, and further justify the definition of quantum work via two-point energy measurements in quantum many-body systems.

  8. Logarithmic entanglement lightcone in many-body localized systems

    NASA Astrophysics Data System (ADS)

    Deng, Dong-Ling; Li, Xiaopeng; Pixley, J. H.; Wu, Yang-Le; Das Sarma, S.

    2017-01-01

    We theoretically study the response of a many-body localized system to a local quench from a quantum information perspective. We find that the local quench triggers entanglement growth throughout the whole system, giving rise to a logarithmic lightcone. This saturates the modified Lieb-Robinson bound for quantum information propagation in many-body localized systems previously conjectured based on the existence of local integrals of motion. In addition, near the localization-delocalization transition, we find that the final states after the local quench exhibit volume-law entanglement. We also show that the local quench induces a deterministic orthogonality catastrophe for highly excited eigenstates, where the typical wave-function overlap between the pre- and postquench eigenstates decays exponentially with the system size.

  9. A semiclassical approach to the dynamics of many-body Bose/Fermi systems by the path integral centroid molecular dynamics

    NASA Astrophysics Data System (ADS)

    Kinugawa, Kenichi; Nagao, Hidemi; Ohta, Koji

    2001-01-01

    We present a formalism of the path integral centroid molecular dynamics (CMD) extended to Bose and Fermi statistics as a semiclassical approach to explore the dynamics of quantum many-body systems. The validity of the method is examined in relation to the time correlation functions. The presently proposed scheme, refined from our previous derivation [Chem. Phys. Lett. 307, 187 (1999)], is aimed at the calculations of not the exact quantum-mechanical dynamics but the semiclassical dynamics under certain approximations. The formalism is based on the projection operator with which the Bose/Fermi system is mapped onto a particular type of pseudo-Boltzmann system. In the pseudo-Boltzmann system the correlation due to the Bose/Fermi statistics is introduced via an extra pseudopotential called the permutation potential and its relevant operator. Using the present semiclassical formalism, the time correlation function of centroid position, which is evaluated from the CMD trajectories in the pseudo-Boltzmann system, is an approximation to the Kubo canonical correlation function of position operator of the exact quantum-statistical system composed of bosons or fermions. There is no such apparent relation between the momentum operator and the corresponding momentum centroid.

  10. Many-body localization in imperfectly isolated quantum systems.

    PubMed

    Johri, Sonika; Nandkishore, Rahul; Bhatt, R N

    2015-03-20

    We use numerical exact diagonalization to analyze which aspects of the many-body localization phenomenon survive in an imperfectly isolated setting, when the system of interest is weakly coupled to a thermalizing environment. We show that widely used diagnostics (such as many-body level statistics and expectation values in exact eigenstates) cease to show signatures of many-body localization above a critical coupling that is exponentially small in the size of the environment. However, we also identify alternative diagnostics for many-body localization, in the spectral functions of local operators. Diagnostics include a discrete spectrum and a hierarchy of energy gaps, including a universal gap at zero frequency. These alternative diagnostics are shown to be robust, and continue to show signatures of many-body localization as long as the coupling to the bath is weaker than the characteristic energy scales in the system. We also examine how these signatures disappear when the coupling to the environment becomes larger than the characteristic energy scales of the system.

  11. Measuring entanglement entropy in a quantum many-body system.

    PubMed

    Islam, Rajibul; Ma, Ruichao; Preiss, Philipp M; Tai, M Eric; Lukin, Alexander; Rispoli, Matthew; Greiner, Markus

    2015-12-03

    Entanglement is one of the most intriguing features of quantum mechanics. It describes non-local correlations between quantum objects, and is at the heart of quantum information sciences. Entanglement is now being studied in diverse fields ranging from condensed matter to quantum gravity. However, measuring entanglement remains a challenge. This is especially so in systems of interacting delocalized particles, for which a direct experimental measurement of spatial entanglement has been elusive. Here, we measure entanglement in such a system of itinerant particles using quantum interference of many-body twins. Making use of our single-site-resolved control of ultracold bosonic atoms in optical lattices, we prepare two identical copies of a many-body state and interfere them. This enables us to directly measure quantum purity, Rényi entanglement entropy, and mutual information. These experiments pave the way for using entanglement to characterize quantum phases and dynamics of strongly correlated many-body systems.

  12. Drude weight fluctuations in many-body localized systems

    NASA Astrophysics Data System (ADS)

    Filippone, Michele; Brouwer, Piet W.; Eisert, Jens; von Oppen, Felix

    2016-11-01

    We numerically investigate the distribution of Drude weights D of many-body states in disordered one-dimensional interacting electron systems across the transition to a many-body localized phase. Drude weights are proportional to the spectral curvatures induced by magnetic fluxes in mesoscopic rings. They offer a method to relate the transition to the many-body localized phase to transport properties. In the delocalized regime, we find that the Drude weight distribution at a fixed disorder configuration agrees well with the random-matrix-theory prediction P (D ) ∝(γ2+D2) -3 /2 , although the distribution width γ strongly fluctuates between disorder realizations. A crossover is observed towards a distribution with different large-D asymptotics deep in the many-body localized phase, which however differs from the commonly expected Cauchy distribution. We show that the average distribution width <γ >, rescaled by L Δ ,Δ being the average level spacing in the middle of the spectrum and L the systems size, is an efficient probe of the many-body localization transition, as it increases (vanishes) exponentially in the delocalized (localized) phase.

  13. Entanglement dynamics in quantum many-body systems

    NASA Astrophysics Data System (ADS)

    Ho, Wen Wei; Abanin, Dmitry A.

    2017-03-01

    The dynamics of entanglement has recently been realized as a useful probe in studying ergodicity and its breakdown in quantum many-body systems. In this paper, we study theoretically the growth of entanglement in quantum many-body systems and propose a method to measure it experimentally. We show that entanglement growth is related to the spreading of local operators in real space. We present a simple toy model for ergodic systems in which linear spreading of operators results in a universal, linear-in-time growth of entanglement for initial product states, in contrast with the logarithmic growth of entanglement in many-body localized (MBL) systems. Furthermore, we show that entanglement growth is directly related to the decay of the Loschmidt echo in a composite system comprised of several copies of the original system, in which connections are controlled by a quantum switch (two-level system). By measuring only the switch's dynamics, the growth of the Rényi entropies can be extracted. Our work provides a way of understanding entanglement dynamics in many-body systems and to directly measure its growth in time via a single local measurement.

  14. Ultracold atoms for simulation of many body quantum systems

    NASA Astrophysics Data System (ADS)

    Hutchinson, David A. W.

    2017-01-01

    Feynman famously proposed simulating quantum physics using other, better controlled, quantum systems. This vision is now a reality within the realm of ultracold atomic physics. We discuss how these systems can be used to simulate many body physics, concentrating the Berezinskii-Kosterlitz-Thouless transition in 2D physics and the role of disorder.

  15. Nonequilibrium quantum dynamics and transport: from integrability to many-body localization

    NASA Astrophysics Data System (ADS)

    Vasseur, Romain; Moore, Joel E.

    2016-06-01

    We review the non-equilibrium dynamics of many-body quantum systems after a quantum quench with spatial inhomogeneities, either in the Hamiltonian or in the initial state. We focus on integrable and many-body localized systems that fail to self-thermalize in isolation and for which the standard hydrodynamical picture breaks down. The emphasis is on universal dynamics, non-equilibrium steady states and new dynamical phases of matter, and on phase transitions far from thermal equilibrium. We describe how the infinite number of conservation laws of integrable and many-body localized systems lead to complex non-equilibrium states beyond the traditional dogma of statistical mechanics.

  16. Topological structure of an anharmonically coupled many-body system.

    NASA Technical Reports Server (NTRS)

    Rasetti, M.

    1971-01-01

    It has been proposed recently that the description of a many-body system with anharmonic coupling could be achieved through the use of the generalized Bose operators of Brandt and Greenberg (1969) directly in a second quantized form. The present study describes a new formulation of the generalized Bose operators which exploits the group theoretical content of these operators.

  17. Material properties of one-dimensional systems studied by path-integral quantum Monte Carlo simulations and an analytical many-body model

    NASA Astrophysics Data System (ADS)

    Böhm, Michael C.; Schulte, Joachim; Utrera, Luis

    Feynman path-integral quantum Monte Carlo (QMC) simulations and an analytic many-body approach are used to study the ground state properties of one-dimensional (1D) chains in the theoretical framework of model Hamiltonians of the Hubbard type. The QMC algorithm is employed to derive position-space quantities, while band structure properties are evaluated by combining QMC data with expressions derived in momentum (k) space. Bridging link between both representations is the quasi-chemical approximation (QCA). Electronic charge fluctuations <(Δn2i)> and the fluctuations of the magnetic local moments <(Δs2i)> are studied as a function of the on-site density and correlation strength, which is given by the ratio between two-electron interaction and kinetic hopping. Caused by the non-analytic behaviour of the chemical potential μ = ∂E/∂ (with E denoting the electronic energy), strict 1D systems with an on-site density of 1·0 do not exhibit the properties of a conductor for any non-zero interaction beyond the mean-field approximation. The QMC simulations lead to straightforward access to the probabilities Pi(n) of finding n = 0, 1, 2 electrons at the ith lattice site. The Pi(n) elements allow to calculate the enhancement factors on the electron spin susceptibility χ, effective electronic mass m* and Knight shift κ. m* is enhanced by a bandwidth renormalization factor D-10, κ by an element ηK mapping the additional localization of the correlated electrons in the presence of an external magnetic field B and χ by the product D-10 ηK. Available experimental data are discussed in the light of the present theoretical findings.

  18. Periodically driven ergodic and many-body localized quantum systems

    SciTech Connect

    Ponte, Pedro; Chandran, Anushya; Papić, Z.; Abanin, Dmitry A.

    2015-02-15

    We study dynamics of isolated quantum many-body systems whose Hamiltonian is switched between two different operators periodically in time. The eigenvalue problem of the associated Floquet operator maps onto an effective hopping problem. Using the effective model, we establish conditions on the spectral properties of the two Hamiltonians for the system to localize in energy space. We find that ergodic systems always delocalize in energy space and heat up to infinite temperature, for both local and global driving. In contrast, many-body localized systems with quenched disorder remain localized at finite energy. We support our conclusions by numerical simulations of disordered spin chains. We argue that our results hold for general driving protocols, and discuss their experimental implications.

  19. Theory of many-body localization in periodically driven systems

    SciTech Connect

    Abanin, Dmitry A.; De Roeck, Wojciech; Huveneers, François

    2016-09-15

    We present a theory of periodically driven, many-body localized (MBL) systems. We argue that MBL persists under periodic driving at high enough driving frequency: The Floquet operator (evolution operator over one driving period) can be represented as an exponential of an effective time-independent Hamiltonian, which is a sum of quasi-local terms and is itself fully MBL. We derive this result by constructing a sequence of canonical transformations to remove the time-dependence from the original Hamiltonian. When the driving evolves smoothly in time, the theory can be sharpened by estimating the probability of adiabatic Landau–Zener transitions at many-body level crossings. In all cases, we argue that there is delocalization at sufficiently low frequency. We propose a phase diagram of driven MBL systems.

  20. Theory of many-body localization in periodically driven systems

    NASA Astrophysics Data System (ADS)

    Abanin, Dmitry A.; De Roeck, Wojciech; Huveneers, François

    2016-09-01

    We present a theory of periodically driven, many-body localized (MBL) systems. We argue that MBL persists under periodic driving at high enough driving frequency: The Floquet operator (evolution operator over one driving period) can be represented as an exponential of an effective time-independent Hamiltonian, which is a sum of quasi-local terms and is itself fully MBL. We derive this result by constructing a sequence of canonical transformations to remove the time-dependence from the original Hamiltonian. When the driving evolves smoothly in time, the theory can be sharpened by estimating the probability of adiabatic Landau-Zener transitions at many-body level crossings. In all cases, we argue that there is delocalization at sufficiently low frequency. We propose a phase diagram of driven MBL systems.

  1. Nonlinear Quantum Metrology of Many-Body Open Systems

    NASA Astrophysics Data System (ADS)

    Beau, M.; del Campo, A.

    2017-07-01

    We introduce general bounds for the parameter estimation error in nonlinear quantum metrology of many-body open systems in the Markovian limit. Given a k -body Hamiltonian and p -body Lindblad operators, the estimation error of a Hamiltonian parameter using a Greenberger-Horne-Zeilinger state as a probe is shown to scale as N-[k -(p /2 )], surpassing the shot-noise limit for 2 k >p +1 . Metrology equivalence between initial product states and maximally entangled states is established for p ≥1 . We further show that one can estimate the system-environment coupling parameter with precision N-(p /2 ), while many-body decoherence enhances the precision to N-k in the noise-amplitude estimation of a fluctuating k -body Hamiltonian. For the long-range Ising model, we show that the precision of this parameter beats the shot-noise limit when the range of interactions is below a threshold value.

  2. Entanglement replication in driven dissipative many-body systems.

    PubMed

    Zippilli, S; Paternostro, M; Adesso, G; Illuminati, F

    2013-01-25

    We study the dissipative dynamics of two independent arrays of many-body systems, locally driven by a common entangled field. We show that in the steady state the entanglement of the driving field is reproduced in an arbitrarily large series of inter-array entangled pairs over all distances. Local nonclassical driving thus realizes a scale-free entanglement replication and long-distance entanglement distribution mechanism that has immediate bearing on the implementation of quantum communication networks.

  3. Boundary driven open quantum many-body systems

    SciTech Connect

    Prosen, Tomaž

    2014-01-08

    In this lecture course I outline a simple paradigm of non-eqjuilibrium quantum statistical physics, namely we shall study quantum lattice systems with local, Hamiltonian (conservative) interactions which are coupled to the environment via incoherent processes only at the system's boundaries. This is arguably the simplest nontrivial context where one can study far from equilibrium steady states and their transport properties. We shall formulate the problem in terms of a many-body Markovian master equation (the so-called Lindblad equation, and some of its extensions, e.g. the Redfield eqaution). The lecture course consists of two main parts: Firstly, and most extensively we shall present canonical Liouville-space many-body formalism, the so-called 'third quantization' and show how it can be implemented to solve bi-linear open many-particle problems, the key peradigmatic examples being the XY spin 1/2 chains or quasi-free bosonic (or harmonic) chains. Secondly, we shall outline several recent approaches on how to approach exactly solvable open quantum interacting many-body problems, such as anisotropic Heisenberg ((XXZ) spin chain or fermionic Hubbard chain.

  4. On microstates counting in many body polymer quantum systems

    SciTech Connect

    Chacon-Acosta, Guillermo; Morales-Tecotl, Hugo A.; Dagdug, Leonardo

    2011-10-14

    Polymer quantum systems are mechanical models quantized in a similar way as loop quantum gravity but in which loops/graphs resembling polymers are replaced by discrete sets of points. Such systems have allowed to study in a simpler context some novel aspects of loop quantum gravity. Although thermal aspects play a crucial role in cosmology and black hole physics little attention has been given to the thermostatistics of many body polymer quantum systems. In this work we explore how the features of a one-dimensional effective polymer gas, affect its microstate counting and hence the corresponding thermodynamical quantities.

  5. Many-body energy localization transition in periodically driven systems

    SciTech Connect

    D’Alessio, Luca; Polkovnikov, Anatoli

    2013-06-15

    According to the second law of thermodynamics the total entropy of a system is increased during almost any dynamical process. The positivity of the specific heat implies that the entropy increase is associated with heating. This is generally true both at the single particle level, like in the Fermi acceleration mechanism of charged particles reflected by magnetic mirrors, and for complex systems in everyday devices. Notable exceptions are known in noninteracting systems of particles moving in periodic potentials. Here the phenomenon of dynamical localization can prevent heating beyond certain threshold. The dynamical localization is known to occur both at classical (Fermi–Ulam model) and at quantum levels (kicked rotor). However, it was believed that driven ergodic systems will always heat without bound. Here, on the contrary, we report strong evidence of dynamical localization transition in both classical and quantum periodically driven ergodic systems in the thermodynamic limit. This phenomenon is reminiscent of many-body localization in energy space. -- Highlights: •A dynamical localization transition in periodically driven ergodic systems is found. •This phenomenon is reminiscent of many-body localization in energy space. •Our results are valid for classical and quantum systems in the thermodynamic limit. •At critical frequency, the short time expansion for the evolution operator breaks down. •The transition is associated to a divergent time scale.

  6. Measuring entanglement entropies in many-body systems

    SciTech Connect

    Klich, Israel; Refael, Gil; Silva, Alessandro

    2006-09-15

    We explore the relation between entanglement entropy of quantum many-body systems and the distribution of corresponding, properly selected, observables. Such a relation is necessary to actually measure the entanglement entropy. We show that, in general, the Shannon entropy of the probability distribution of certain symmetry observables gives a lower bound to the entropy. In some cases this bound is saturated and directly gives the entropy. We also show other cases in which the probability distribution contains enough information to extract the entropy: we show how this is done in several examples including BEC wave functions, the Dicke model, XY spin chain, and chains with strong randomness.

  7. Continuum mechanics for quantum many-body systems

    NASA Astrophysics Data System (ADS)

    Vignale, Giovanni; Tao, Jianmin; Gao, Xianlong; Tokatly, Ilya

    2010-03-01

    Continuum mechanics is a theory of the dynamics of classical liquids and solids in which the state of the body is described by a small set of collective, such as density and current. A similar description is possible for quantum many-body systems, and indeed its existence is guaranteed by the basic theorems of time-dependent current density functional theory. In this paper we show how the exact Heisenberg equation of motion for the current density of a many-body system can be closed by expressing the quantum stress tensor as a functional of the current density. Several approximation schemes for this functional are discussed. The simplest scheme allows us to bypass the solution of the time-dependent Schr"odinger equation, resulting in an equation of motion for the current that requires only ground-state properties as an input. We illustrate the formalism by applying it to the calculation of excitation energies in simple one- and two-electron systems.

  8. Measuring entanglement entropy in a quantum many-body system

    NASA Astrophysics Data System (ADS)

    Rispoli, Matthew; Preiss, Philipp; Tai, Eric; Lukin, Alex; Schittko, Robert; Kaufman, Adam; Ma, Ruichao; Islam, Rajibul; Greiner, Markus

    2016-05-01

    The presence of large-scale entanglement is a defining characteristic of exotic quantum phases of matter. It describes non-local correlations between quantum objects, and is at the heart of quantum information sciences. However, measuring entanglement remains a challenge. This is especially true in systems of interacting delocalized particles, for which a direct experimental measurement of spatial entanglement has been elusive. Here we measure entanglement in such a system of itinerant particles using quantum interference of many-body twins. We demonstrate a novel approach to the measurement of entanglement entropy of any bosonic system, using a quantum gas microscope with tailored potential landscapes. This protocol enables us to directly measure quantum purity, Rényi entanglement entropy, and mutual information. In general, these experiments exemplify a method enabling the measurement and characterization of quantum phase transitions and in particular would be apt for studying systems such as magnetic ordering within the quantum Ising model.

  9. Quantum order, entanglement and localization in many-body systems

    NASA Astrophysics Data System (ADS)

    Khemani, Vedika

    The interplay of disorder and interactions can have remarkable effects on the physics of quantum systems. A striking example is provided by the long conjectured--and recently confirmed--phenomenon of many-body localization. Many-body localized (MBL) phases violate foundational assumptions about ergodicity and thermalization in interacting systems, and represent a new frontier for non-equilibrium quantum statistical mechanics. We start with a study of the dynamical response of MBL phases to time-dependent perturbations. We find that that an asymptotically slow, local perturbation induces a highly non-local response, a surprising result for a localized insulator. A complementary calculation in the linear-response regime elucidates the structure of many-body resonances contributing to the dynamics of this phase. We then turn to a study of quantum order in MBL systems. It was shown that localization can allow novel high-temperature phases and phase transitions that are disallowed in equilibrium. We extend this idea of "localization protected order'' to the case of symmetry-protected topological phases and to the elucidation of phase structure in periodically driven Floquet systems. We show that Floquet systems can display nontrivial phases, some of which show a novel form of correlated spatiotemporal order and are absolutely stable to all generic perturbations. The next part of the thesis addresses the role of quantum entanglement, broadly speaking. Remarkably, it was shown that even highly-excited MBL eigenstates have low area-law entanglement. We exploit this feature to develop tensor-network based algorithms for efficiently computing and representing highly-excited MBL eigenstates. We then switch gears from disordered, localized systems and examine the entanglement Hamiltonian and its low energy spectrum from a statistical mechanical lens, particularly focusing on issues of universality and thermalization. We close with two miscellaneous results on topologically

  10. General coordinate invariance in quantum many-body systems

    NASA Astrophysics Data System (ADS)

    Brauner, Tomáš; Endlich, Solomon; Monin, Alexander; Penco, Riccardo

    2014-11-01

    We extend the notion of general coordinate invariance to many-body, not necessarily relativistic, systems. As an application, we investigate nonrelativistic general covariance in Galilei-invariant systems. The peculiar transformation rules for the background metric and gauge fields, first introduced by Son and Wingate in 2005 and refined in subsequent works, follow naturally from our framework. Our approach makes it clear that Galilei or Poincaré symmetry is by no means a necessary prerequisite for making the theory invariant under coordinate diffeomorphisms. General covariance merely expresses the freedom to choose spacetime coordinates at will, whereas the true, physical symmetries of the system can be separately implemented as "internal" symmetries within the vielbein formalism. A systematic way to implement such symmetries is provided by the coset construction. We illustrate this point by applying our formalism to nonrelativistic s -wave superfluids.

  11. Typical fast thermalization processes in closed many-body systems

    PubMed Central

    Reimann, Peter

    2016-01-01

    The lack of knowledge about the detailed many-particle motion on the microscopic scale is a key issue in any theoretical description of a macroscopic experiment. For systems at or close to thermal equilibrium, statistical mechanics provides a very successful general framework to cope with this problem. However, far from equilibrium, only very few quantitative and comparably universal results are known. Here a quantum mechanical prediction of this type is derived and verified against various experimental and numerical data from the literature. It quantitatively describes the entire temporal relaxation towards thermal equilibrium for a large class (in a mathematically precisely defined sense) of closed many-body systems, whose initial state may be arbitrarily far from equilibrium. PMID:26926224

  12. Typical fast thermalization processes in closed many-body systems

    NASA Astrophysics Data System (ADS)

    Reimann, Peter

    2016-03-01

    The lack of knowledge about the detailed many-particle motion on the microscopic scale is a key issue in any theoretical description of a macroscopic experiment. For systems at or close to thermal equilibrium, statistical mechanics provides a very successful general framework to cope with this problem. However, far from equilibrium, only very few quantitative and comparably universal results are known. Here a quantum mechanical prediction of this type is derived and verified against various experimental and numerical data from the literature. It quantitatively describes the entire temporal relaxation towards thermal equilibrium for a large class (in a mathematically precisely defined sense) of closed many-body systems, whose initial state may be arbitrarily far from equilibrium.

  13. Classical simulation of quantum many-body systems

    NASA Astrophysics Data System (ADS)

    Huang, Yichen

    Classical simulation of quantum many-body systems is in general a challenging problem for the simple reason that the dimension of the Hilbert space grows exponentially with the system size. In particular, merely encoding a generic quantum many-body state requires an exponential number of bits. However, condensed matter physicists are mostly interested in local Hamiltonians and especially their ground states, which are highly non-generic. Thus, we might hope that at least some physical systems allow efficient classical simulation. Starting with one-dimensional (1D) quantum systems (i.e., the simplest nontrivial case), the first basic question is: Which classes of states have efficient classical representations? It turns out that this question is quantitatively related to the amount of entanglement in the state, for states with "little entanglement'' are well approximated by matrix product states (a data structure that can be manipulated efficiently on a classical computer). At a technical level, the mathematical notion for "little entanglement'' is area law, which has been proved for unique ground states in 1D gapped systems. We establish an area law for constant-fold degenerate ground states in 1D gapped systems and thus explain the effectiveness of matrix-product-state methods in (e.g.) symmetry breaking phases. This result might not be intuitively trivial as degenerate ground states in gapped systems can be long-range correlated. Suppose an efficient classical representation exists. How can one find it efficiently? The density matrix renormalization group is the leading numerical method for computing ground states in 1D quantum systems. However, it is a heuristic algorithm and the possibility that it may fail in some cases cannot be completely ruled out. Recently, a provably efficient variant of the density matrix renormalization group has been developed for frustration-free 1D gapped systems. We generalize this algorithm to all (i.e., possibly frustrated) 1D

  14. Monte Carlo Studies of Quantum Many-Body Systems

    NASA Astrophysics Data System (ADS)

    Zhang, Shiwei

    1993-01-01

    This thesis describes studies of the ground-state properties of quantum many-body systems by Monte Carlo techniques. In the first part, an algorithm is described to address the fundamental "sign problem" in quantum Monte Carlo when applied to fermion systems. Implementation of this algorithm in a parallel distributed environment is then discussed. The last part presents variational calculations of the ground states of ^4 He clusters. The sign problem prevents exact simulations of large many-fermion systems without uncontrolled approximations. It arises because of the antisymmetric nature of wavefunctions of fermion systems, and because of the use of random sampling. The proposed new algorithm is within the framework of the Green's function Monte Carlo method. To attack the difficulties associated with the sign problem, several new ideas are introduced to improve the Monte Carlo sampling techniques. As tests, the energies of an excited state of the He atom and of the ground states of the Li, Be, and N atoms are calculated. The algorithm remained stable and the results were in excellent agreement with the experimental values for the energies. The fermion algorithm was parallelized and implemented on a coupled cluster of workstations using a message-passing environment. The method of parallelization maintains large granularity and therefore low overhead. Despite the stochastic nature of the algorithm, good load-balancing can be accomplished and reproducibility is ensured. Droplets of ^4He atoms, as an example of simple inhomogeneous quantum many-body systems, are of interest to condensed-matter physics as well as nuclear physics. Previous variational studies of their ground states were unsatisfactory as unphysical one-body form factors had to be used to enforce a bound state. The new trial wavefunction, based on the shadow wavefunction for bulk helium, has a modified shadow-shadow correlation that reflects the varying local density in the system. A bound state is

  15. Critical quasienergy states in driven many-body systems

    NASA Astrophysics Data System (ADS)

    Bastidas Valencia, Victor Manuel; Engelhardt, Georg; Perez-Fernandez, Pedro; Vogl, Malte; Brandes, Tobias

    2015-03-01

    A quantum phase transition (QPT) is characterized by non-analyticities of ground-state properties at the critical points. Recently it has been shown that quantum criticality emerges also in excited states of the system, which is referred to as an excited-state quantum phase transition (ESQPT). This kind of quantum criticality is intimately related to a level clustering at critical energies, which results in a logarithmic singularity in the density of states. Most of the previous studies on quantum criticality in excited states have been focused on time independent systems. Here we study spectral singularities that appear in periodically-driven many-body systems and show how the external control allows one to engineer geometrical features of the quasienergy landscape. In particular, we study singularities in the quasienergy spectrum of a fully-connected network consisting of two-level systems with time-dependent interactions. We discuss the characteristic signatures of these singularities in observables like the magnetization, which should be measurable with current technology. The authors gratefully acknowledge financial support by the DFG via grants BRA 1528/7, BRA 1528/8, SFB 910 (V.M.B., T.B.), the Spanish Ministerio de Ciencia e Innovacion (Grants No. FIS2011-28738-C02-01) and Junta de Andalucia (Grants No. FQM160).

  16. Many-body effects in coupled light-matter systems

    NASA Astrophysics Data System (ADS)

    Bordyuh, Mykola

    Interaction between light and matter is one of the most basic processes in nature and represents a cornerstone in our understanding of a broad range of physical phenom- ena. The increasing level of control over light-matter interactions with atomic and solid-state systems has brought forth a new class of quantum many-body systems realized on photon lattices where light and matter play equally important roles in emergent phenomena. Systems of strongly interacting atoms and photons, that can be realized by wiring up individual cavity QED systems into lattices, are perceived as a new platform for engineering synthetic hybrid light-matter systems. While sharing important properties with other systems of interacting quantum particles, here we argue that the nature of light-matter interaction gives rise to unique features with no analogs in condensed matter or atomic physics setups. The central topic of the thesis is a lattice of cavity QED systems described by the Rabi-Hubbard model. We de- scribe the most prominent features of the model associated with quantum criticality. We consider a realistic case of the system open to the environment and investigate thermal radiation from a lattice of cavity QED systems. Next, we demonstrate that the output radiation displays unique features associated with collective excitations of light and matter. Further, we consider a non-equilibrium lattice of cavity QED systems and demonstrate exotic attractors in the phase diagram, associated with the action of the environment, not present in the equilibrium analogs. We conclude the discussions with a theory of measurement applied to the non-equilibrium Dicke model and compare our findings to a recent experiment.

  17. Petascale Many Body Methods for Complex Correlated Systems

    NASA Astrophysics Data System (ADS)

    Pruschke, Thomas

    2012-02-01

    Correlated systems constitute an important class of materials in modern condensed matter physics. Correlation among electrons are at the heart of all ordering phenomena and many intriguing novel aspects, such as quantum phase transitions or topological insulators, observed in a variety of compounds. Yet, theoretically describing these phenomena is still a formidable task, even if one restricts the models used to the smallest possible set of degrees of freedom. Here, modern computer architectures play an essential role, and the joint effort to devise efficient algorithms and implement them on state-of-the art hardware has become an extremely active field in condensed-matter research. To tackle this task single-handed is quite obviously not possible. The NSF-OISE funded PIRE collaboration ``Graduate Education and Research in Petascale Many Body Methods for Complex Correlated Systems'' is a successful initiative to bring together leading experts around the world to form a virtual international organization for addressing these emerging challenges and educate the next generation of computational condensed matter physicists. The collaboration includes research groups developing novel theoretical tools to reliably and systematically study correlated solids, experts in efficient computational algorithms needed to solve the emerging equations, and those able to use modern heterogeneous computer architectures to make then working tools for the growing community.

  18. Quantifying fermionic decoherence in many-body systems

    NASA Astrophysics Data System (ADS)

    Kar, Arnab; Franco, Ignacio

    2017-06-01

    Practical measures of electronic decoherence, called distilled purities, that are applicable to many-body systems are introduced. While usual measures of electronic decoherence such as the purity employ the full N-particle density matrix which is generally unavailable, the distilled purities are based on the r-body reduced density matrices (r-RDMs) which are more accessible quantities. The r-body distilled purities are derivative quantities of the previously introduced r-body reduced purities [I. Franco and H. Appel, J. Chem. Phys. 139, 094109 (2013)] that measure the non-idempotency of the r-RDMs. Specifically, the distilled purities exploit the structure of the reduced purities to extract coherences between Slater determinants with integer occupations defined by a given single-particle basis that compose an electronic state. In this way, the distilled purities offer a practical platform to quantify coherences in a given basis that can be used to analyze the quantum dynamics of many-electron systems. Exact expressions for the one-body and two-body distilled purities are presented and the utility of the approach is exemplified via an analysis of the dynamics of oligo-acetylene as described by the Su-Schrieffer-Heeger Hamiltonian. Last, the advantages and limitations of the purity, reduced purity, and distilled purity as measures of electronic coherence are discussed.

  19. Lattice methods for strongly interacting many-body systems

    NASA Astrophysics Data System (ADS)

    Drut, Joaquín E.; Nicholson, Amy N.

    2013-04-01

    Lattice field theory methods, usually associated with non-perturbative studies of quantum chromodynamics, are becoming increasingly common in the calculation of ground-state and thermal properties of strongly interacting non-relativistic few- and many-body systems, blurring the interfaces between condensed matter, atomic and low-energy nuclear physics. While some of these techniques have been in use in the area of condensed matter physics for a long time, others, such as hybrid Monte Carlo and improved effective actions, have only recently found their way across areas. With this topical review, we aim to provide a modest overview and a status update on a few notable recent developments. For the sake of brevity we focus on zero-temperature, non-relativistic problems. After a short introduction, we lay out some general considerations and proceed to discuss sampling algorithms, observables, and systematic effects. We show selected results on ground- and excited-state properties of fermions in the limit of unitarity. The appendix contains technical details on group theory on the lattice.

  20. Dissipation and dynamics in quantum many-body systems

    NASA Astrophysics Data System (ADS)

    Barker, Brent Wendolyn

    In this thesis, we simulate the time evolution of quantum many-body systems and use comparisons to experimental data in order to learn more about the properties of nuclear matter and understand better the dynamical processes in central nuclear collisions. We further advance the development of a nonequilibrium Green's function description of both central nuclear collisions and Bose-Einstein Condensates. First in the thesis, we determine the viscosity of nuclear matter by adjusting the in-medium nucleon-nucleon cross section (IMNNCS) in our BUU transport model until the simulation results match experimental data on nuclear stopping in central nuclear collisions at intermediate energies. Then we use that cross section to calculate the viscosity self-consistently. We also calculate the ratio of shear viscosity to entropy density to determine how close the system is to the proposed universal quantum lower limit. Next, we use the same BUU transport model to isolate the protons emitted early in a central nuclear collision at intermediate energy, as predicted in the model, using a filter on high transverse momentum, and we show the effect on the source function. We predict a recontraction of protons at late times in the central collision of 112Sn+112Sn at 50 MeV/nucleon that results in a resurgence of emission of protons and show how to use the transverse momentum filter and the source function to test this prediction in experiment. Next, we develop an early implementation of a more fully quantal transport model than the BUU equations, with our sights set on solving central nuclear collisions in 3D using nonequilibrium Green's functions. In our 1D, mean field, density matrix model, we demonstrate the initial state preparation and collision of 1D nuclear "slabs". With the aim of reducing the computational cost of the calculation, we show that we can neglect far off-diagonal elements in the density matrix without affecting the one-body observables. Further, we describe a

  1. Aspects of Strongly Correlated Many-Body Fermi Systems

    NASA Astrophysics Data System (ADS)

    Porter, William J., III

    which we use to characterize the entanglement properties of the two-body sector across a broad range of attractive couplings. In the many-body case, we determine universal scaling properties of this system, and for the two-body case, we compute the entanglement spectrum exactly, successfully characterizing a vast range of entanglement behavior across the BCS-BEC crossover.

  2. Quantum phase transition in strongly correlated many-body system

    NASA Astrophysics Data System (ADS)

    You, Wenlong

    The past decade has seen a substantial rejuvenation of interest in the study of quantum phase transitions (QPTs), driven by experimental advance on the cuprate superconductors, the heavy fermion materials, organic conductors, Quantum Hall effect, Fe-As based superconductors and other related compounds. It is clear that strong electronic interactions play a crucial role in the systems of current interest, and simple paradigms for the behavior of such systems near quantum critical points remain unclear. Furthermore, the rapid progress in Feshbach resonance and optical lattice provides a flexible platform to study QPT. Quantum Phase Transition (QPT) describes the non-analytic behaviors of the ground-state properties in a many-body system by varying a physical parameter at absolute zero temperature - such as magnetic field or pressure, driven by quantum fluctuations. Such quantum phase transitions can be first-order phase transition or continuous. The phase transition is usually accompanied by a qualitative change in the nature of the correlations in the ground state, and describing this change shall clearly be one of our major interests. We address this issue from three prospects in a few strong correlated many-body systems in this thesis, i.e., identifying the ordered phases, studying the properties of different phases, characterizing the QPT points. In chapter 1, we give an introduction to QPT, and take one-dimensional XXZ model as an example to illustrate the QPT therein. Through this simple example, we would show that when the tunable parameter is varied, the system evolves into different phases, across two quantum QPT points. The distinct phases exhibit very different behaviors. Also a schematic phase diagram is appended. In chapter 2, we are engaged in research on ordered phases. Originating in the work of Landau and Ginzburg on second-order phase transition, the spontaneous symmetry breaking induces nonzero expectation of field operator, e.g., magnetization M

  3. Vibrational many-body methods for molecules and extended systems

    NASA Astrophysics Data System (ADS)

    Keceli, Murat

    Vibrational many-body methods for molecules and extended systems have been developed that can account for the effects of anharmonicity in the potential energy surfaces (PESs) on energies and other observable properties. For molecules, we present a general scheme to calculate anharmonic vibrational frequencies and vibrationally-averaged structures along with applications to some key species in hydrocarbon combustion chemistry: HCO+, HCO, HNO, HOO, HOO--, CH3+, and CH3. We propose a hybrid, compact representation of PESs that combines the merits of two existing representations, which are a quartic force field (QFF) and numerical values on a rectilinear grid. We employed a combination of coupled-cluster singles and doubles (CCSD), CCSD with a second-order perturbation correction in the space of triples [CCSD(2)T] and in the space of triples and quadruples [CCSD(2)TQ], and a correlation-consistent basis set series to achieve the complete-correlation, complete-basis-set limits of the potential energy surfaces. The mean absolute deviation between the predicted and the observed frequencies is 11 cm --1. For extended systems, we generalized the formulations of the vibrational self-consistent field (VSCF), vibrational Moller--Plesset perturbation (VMP), and vibrational coupled-cluster (VCC) methods on the basis of a QFF in normal coordinates. We have identified algebraically and eliminated several terms in the formalisms of VSCF that have nonphysical size dependence, leading to compact and strictly size-extensive equations. This size-extensive VSCF method (XVSCF) thus defined has no contributions from cubic force constants and alters only the transition energies of the underlying harmonic-oscillator reference from a subset of quartic force constants. The mean-field potential of XVSCF felt by each mode is shown to be effectively harmonic, making the XVSCF equations subject to a self-consistent analytical solution without a basis-set expansion and matrix diagonalization

  4. Quantum many-body systems with short-range interactions

    NASA Astrophysics Data System (ADS)

    Yin, Jun

    In this dissertation, the central theme is evaluation of the ground energy and the first few excited energies of Bose or Fermi gas system in continuum R3 or lattice Z3 with short-range interactions. In Chapter 2 and 3, we carry out an analysis on low-dimensional behaviors of dilute Bose gas in traps. In Chapter 4 and 5, we generalize the results on the ground state energies of dilute Bose or Fermi gases in thermodynamic limit. In quantum mechanics, many-body quantum system is completely described by the Hamiltonian, which is a self-adjoint operator on a suitable Hilbert space. In proper scaling limits and parameter regimes, these three-dimensional Hamiltonians can be rigorously described by effective low-dimensional Hamiltonians or equations. In Chapter 2 we show that the Lieb-Liniger model for one-dimensional bosons with repulsive Delta function interaction can be rigorously derived from a dilute three-dimensional Bose gas with arbitrary repulsive interaction potential of finite scattering length. In Chapter 3 we prove that the two dimensional rotating Gross-Pitaevskii (GP) equation correctly describes the ground state energy and corresponding one-particle density matrix of rotating, dilute, interacting Bose gas in three dimensions in a potential that is strongly confining in one direction. Another one of the most remarkable recent developments in study of dilute Bose gases is the rigorous proofs on the leading terms of the effect of the repulsive interaction potential on the ground state energy or the free energy in the thermodynamic limit. For interacting Bose gases, in [44], Lieb and Yngvason proved the correction per volume on ground energy is 4pi aϱ2, where a is the scattering length of interaction potential and ϱ is the density. In this dissertation we generalize this result as follows, we prove that the upper bound part holds for all interaction potentials of positive scattering length, i.e., a > 0, and the lower bound part holds for some interaction

  5. Fokker Planck equations for globally coupled many-body systems with time delays

    NASA Astrophysics Data System (ADS)

    Frank, T. D.; Beek, P. J.

    2005-10-01

    A Fokker-Planck description for globally coupled many-body systems with time delays was developed by integrating previously derived Fokker-Planck equations for many-body systems and for time-delayed systems. By means of the Fokker-Planck description developed, we examined the dependence of the variability of many-body systems on attractive coupling forces and time delays. For a fundamental class of systems exemplified by a time-delayed Shimizu-Yamada model for muscular contractions, we established that the variability is an invertible one-to-one mapping of coupling forces and time delays and that coupling forces and time delays have opposite effects on system variability, allowing time delays to annihilate the impact of coupling forces. Furthermore, we showed how variability measures could be used to determine coupling parameters and time delays from experimental data.

  6. Numerical approaches to isolated many-body quantum systems

    NASA Astrophysics Data System (ADS)

    Kolodrubetz, Michael H.

    Ultracold atoms have revolutionized atomic and condensed matter physics. In addition to having clean, controllable Hamiltonians, ultracold atoms are near-perfect realizations of isolated quantum systems, in which weak environmental coupling can be neglected on experimental time scales. This opens new opportunities to explore these systems not just in thermal equilibrium, but out of equilibrium as well. In this dissertation, we investigate some properties of closed quantum systems, utilizing a combination of numerical and analytical techniques. We begin by applying full configuration-interaction quantum Monte Carlo (FCIQMC) to the Fermi polaron, which we use as a test bed to improve the algorithm. In addition to adapting standard QMC techniques, we introduce novel controlled approximations that allow mitigation of the sign problem and simulation directly in the thermodynamic limit. We also contrast the sign problem of FCIQMC with that of more standard techniques, focusing on FCIQMC's capacity to work in a second quantized determinant space. Next, we discuss nonequilibrium dynamics near a quantum critical point, focusing on the one-dimensional transverse-field Ising (TFI) chain. We show that the TFI dynamics exhibit critical scaling, within which the spin correlations exhibit qualitatively athermal behavior. We provide strong numerical evidence for the universality of dynamic scaling by utilizing time-dependent matrix product states to simulate a non-integrable model in the same equilibrium universality class. As this non-integrable model has been realized experimentally, we investigate the robustness of our predictions against the presence of open boundary conditions and disorder. We find that the qualitatively athermal correlations remain visible, although other phenomena such as even/odd effects become relevant within the finite size scaling theory. Finally, we investigate the properties of the integrable TFI model upon varying the strength of a non-integrable

  7. Theory of Transport for Interacting Many-Body Systems

    DTIC Science & Technology

    1992-06-15

    A novel approach to quantum transport in coupled electron-phonon systems has been developed. Application to the polaron problem, two-level systems...This model has been successfully applied to ternary alloys, as well as amorphous semiconductor quantum wells. Quantum transport theory, dissipation, electronic density of states.

  8. Characterizing and quantifying frustration in quantum many-body systems.

    PubMed

    Giampaolo, S M; Gualdi, G; Monras, A; Illuminati, F

    2011-12-23

    We present a general scheme for the study of frustration in quantum systems. We introduce a universal measure of frustration for arbitrary quantum systems and we relate it to a class of entanglement monotones via an exact inequality. If all the (pure) ground states of a given Hamiltonian saturate the inequality, then the system is said to be inequality saturating. We introduce sufficient conditions for a quantum spin system to be inequality saturating and confirm them with extensive numerical tests. These conditions provide a generalization to the quantum domain of the Toulouse criteria for classical frustration-free systems. The models satisfying these conditions can be reasonably identified as geometrically unfrustrated and subject to frustration of purely quantum origin. Our results therefore establish a unified framework for studying the intertwining of geometric and quantum contributions to frustration.

  9. Quantum control of infinite-dimensional many-body systems

    NASA Astrophysics Data System (ADS)

    Bliss, Roger S.; Burgarth, Daniel

    2014-03-01

    A major challenge to the control of infinite-dimensional quantum systems is the irreversibility which is often present in the system dynamics. Here we consider systems with discrete-spectrum Hamiltonians operating over a Schwartz space domain and show that by utilizing the implications of the quantum recurrence theorem this irreversibility may be overcome, in the case of individual states more generally, but also in certain specified cases over larger subsets of the Hilbert space. We discuss briefly the possibility of using these results in the control of infinite-dimensional coupled harmonic oscillators and also draw attention to some of the issues and open questions arising from this and related work.

  10. Theory of entropy production in quantum many-body systems

    NASA Astrophysics Data System (ADS)

    Solano-Carrillo, E.; Millis, A. J.

    2016-06-01

    We define the entropy operator as the negative of the logarithm of the density matrix, give a prescription for extracting its thermodynamically measurable part, and discuss its dynamics. For an isolated system we derive the first, second, and third laws of thermodynamics. For weakly coupled subsystems of an isolated system, an expression for the long-time limit of the expectation value of the rate of change of the thermodynamically measurable part of the entropy operator is derived and interpreted in terms of entropy production and entropy transport terms. The interpretation is justified by comparison to the known expression for the entropy production in an aged classical Markovian system with Gaussian fluctuations and by a calculation of the current-induced entropy production in a conductor with electron-phonon scattering.

  11. Many-body force and mobility measurements in colloidal systems

    NASA Astrophysics Data System (ADS)

    Merrill, Jason W.

    We have extended a sensitive probe of colloidal interparticle forces, blinking optical tweezers, to allow measurements of forces among groups of more than two particles. This dissertation focuses on bridging the gap between microscopic pair interactions and bulk behavior in colloidal systems by using this technique to explore the regime of few-body interactions between micron-size polymer beads suspended in oil. Electrostatic forces and each component of the mobility tensor of small groups of colloidal particles are simultaneously measured using blinking optical tweezers. When the electrostatic screening length is longer than the inter-particle separation, forces are found to be non-pairwise additive. Both pair and multi-particle forces are well described by the linearized Poisson-Boltzmann equation with constant potential boundary conditions. These findings may play an important role in understanding the structure and stability of a wide variety of systems, from micron-sized particles in oil to aqueous nanocolloids. The measurement technique presented here should be simple to further extend to systems of heterogeneous, non-spherical particles arranged in arbitrary three dimensional geometries.

  12. Dissipative effects in dipolar, quantum many-body systems

    NASA Astrophysics Data System (ADS)

    Safavi-Naini, Arghavan; Capogrosso-Sansone, Barbara; Rey, Ana Maria

    2015-03-01

    We use Quantum Monte Carlo simulations, by the Worm algorithm, to study the ground state phase diagram of two-dimensional, dipolar lattice bosons where each site is coupled, via density operators, to an external reservoir. A recent related study of the XXZ model with ohmic coupling to an external reservoir reported the existence of a bath-induced Bose metal phase in the ground state phase diagram away from half filling, and a Luttinger liquid and a charge density wave at half-filling. Our work extends this methodology to higher dimensional systems with long-range interactions. In the case of hard-core bosons, our method can be applied to experimental systems featuring dipolar fermionic molecules in the presence of losses. This work utilized the Janus supercomputer, which is supported by the NSF (award number CNS-0821794) and the University of Colorado Boulder, and is a joint effort with the University of Colorado Denver and the National Center for Atmospheric Research, as well as OU Supercomputing Center for Education and Research (OSCER) at the University of Oklahoma. NIST, JILA-NSF-PFC-1125844, NSF-PIF-1211914, NSF-PHY11-25915, ARO, ARO-DARPA-OLE, AFOSR, AFOSR-MURI.

  13. Generation of squeezing in a driven many-body system

    NASA Astrophysics Data System (ADS)

    Hebbe Madhusudhana, Bharath; Boguslawski, Matthew; Anquez, Martin; Robbins, Bryce; Barrios, Maryrose; Hoang, Thai; Chapman, Michael

    2016-05-01

    In a spin-1 Bose-Einstein condensate, the non-linear spin-dependent collisional interactions can create entanglement and squeezing. Typically, the condensate is initialized at an unstable fixed point of the phase space, and subsequent free evolution under a time-independent Hamiltonian creates the squeezed state. Alternatively, it is possible to generate squeezing by driving the system localized at a stable fixed point. Here, we demonstrate that periodic modulation of the Hamiltonian can generate highly squeezed states. Our measurements show -5 dB of squeezing, limited by the detection, but calculations indicate that a theoretical potential of -20 dB of squeezing. We discuss the advantages of this method compared with the typical techniques.

  14. Efficient Representation of Fully Many-Body Localized Systems Using Tensor Networks

    NASA Astrophysics Data System (ADS)

    Wahl, Thorsten B.; Pal, Arijeet; Simon, Steven H.

    2017-04-01

    We propose a tensor network encoding the set of all eigenstates of a fully many-body localized system in one dimension. Our construction, conceptually based on the ansatz introduced in Phys. Rev. B 94, 041116(R) (2016), 10.1103/PhysRevB.94.041116, is built from two layers of unitary matrices which act on blocks of ℓ contiguous sites. We argue that this yields an exponential reduction in computational time and memory requirement as compared to all previous approaches for finding a representation of the complete eigenspectrum of large many-body localized systems with a given accuracy. Concretely, we optimize the unitaries by minimizing the magnitude of the commutator of the approximate integrals of motion and the Hamiltonian, which can be done in a local fashion. This further reduces the computational complexity of the tensor networks arising in the minimization process compared to previous work. We test the accuracy of our method by comparing the approximate energy spectrum to exact diagonalization results for the random-field Heisenberg model on 16 sites. We find that the technique is highly accurate deep in the localized regime and maintains a surprising degree of accuracy in predicting certain local quantities even in the vicinity of the predicted dynamical phase transition. To demonstrate the power of our technique, we study a system of 72 sites, and we are able to see clear signatures of the phase transition. Our work opens a new avenue to study properties of the many-body localization transition in large systems.

  15. Radiative heat transfer in anisotropic many-body systems: Tuning and enhancement

    SciTech Connect

    Nikbakht, Moladad

    2014-09-07

    A general formalism for calculating the radiative heat transfer in many body systems with anisotropic component is presented. Our scheme extends the theory of radiative heat transfer in isotropic many body systems to anisotropic cases. In addition, the radiative heating of the particles by the thermal bath is taken into account in our formula. It is shown that the radiative heat exchange (HE) between anisotropic particles and their radiative cooling/heating (RCH) could be enhanced several order of magnitude than that of isotropic particles. Furthermore, we demonstrate that both the HE and RCH can be tuned dramatically by particles relative orientation in many body systems.

  16. Many-body localization in spin chain systems with quasiperiodic fields

    NASA Astrophysics Data System (ADS)

    Lee, Mac; Look, Thomas R.; Lim, S. P.; Sheng, D. N.

    2017-08-01

    We study the many-body localization of spin chain systems with quasiperiodic fields. We identify the lower bound for the critical disorder necessary to drive the transition between the thermal and many-body localized phase to be Wc>1.85 , based on finite-size scaling of entanglement entropy and fluctuations of the bipartite magnetization. We also examine the time evolution of the entanglement entropy of an initial product state where we find power-law and logarithmic growth for the thermal and many-body localized phases, respectively, with a transition point Wc˜2.5 . For larger disorder strength, both imbalance and spin-glass order are preserved at long times, while spin-glass order shows dependence on system size. Quasiperiodic fields have been applied in different experimental systems, and our study finds that such fields are very efficient at driving the many-body localized phase transition.

  17. Role of the Initial State in the Nonequilibrium Quantum Dynamics of Many-Body Systems

    NASA Astrophysics Data System (ADS)

    Santos, Lea F.; Torres-Herrera, Eduardo J.

    2014-03-01

    We show that the dynamics of isolated many-body quantum systems after a quench depends on the interplay between the initial state and the Hamiltonian dictating the evolution. The systems considered are in the nonperturbative regime. The relaxation process is controlled by the width of the energy distribution of the initial state and may be very similar for both chaotic and integrable Hamiltonians. Our analytical expression for the fidelity decay displays excellent agreement with our numerical results. This decay is Gaussian and may persist until saturation. We also provide analytical expressions that describe very well the initial evolution of the Shannon entropy and of few-body observables. The analyses are developed for deterministic one-dimensional systems and initial states of interest to current experiments with cold atoms in optical lattices. This work was supported by the NSF grant No. DMR-1147430. E.J.T.H. acknowledges partial support by CONACyT, México.

  18. Powerlaw Decays and Thermalization in Isolated Many-Body Quantum Systems

    NASA Astrophysics Data System (ADS)

    Tavora, Marco; Torres-Herrera, E. J.; Santos, Lea

    2016-05-01

    We propose a new criterion for thermalization in isolated many-body quantum systems. It is based on the powerlaw behavior of the survival probability at long times. The value of the powerlaw exponent depends on the shape and filling of the energy distribution of the initial state. Exponents larger than or equal to 2 correspond to ergodic filling and consequent thermalization. We show that the algebraic behavior, which occurs in both integrable and chaotic systems, may be caused by bounds in the spectrum or by the presence of correlations between the eigenstates of the Hamiltonian. Numerical and analytical results as well as comparisons with existing rigorous mathematical derivations are presented. Our focus are on initial states that can be prepared experimentally using cold atoms in optical lattices. NSF Grant No. DMR-1147430.

  19. Floquet–Magnus theory and generic transient dynamics in periodically driven many-body quantum systems

    SciTech Connect

    Kuwahara, Tomotaka; Mori, Takashi; Saito, Keiji

    2016-04-15

    This work explores a fundamental dynamical structure for a wide range of many-body quantum systems under periodic driving. Generically, in the thermodynamic limit, such systems are known to heat up to infinite temperature states in the long-time limit irrespective of dynamical details, which kills all the specific properties of the system. In the present study, instead of considering infinitely long-time scale, we aim to provide a general framework to understand the long but finite time behavior, namely the transient dynamics. In our analysis, we focus on the Floquet–Magnus (FM) expansion that gives a formal expression of the effective Hamiltonian on the system. Although in general the full series expansion is not convergent in the thermodynamics limit, we give a clear relationship between the FM expansion and the transient dynamics. More precisely, we rigorously show that a truncated version of the FM expansion accurately describes the exact dynamics for a certain time-scale. Our theory reveals an experimental time-scale for which non-trivial dynamical phenomena can be reliably observed. We discuss several dynamical phenomena, such as the effect of small integrability breaking, efficient numerical simulation of periodically driven systems, dynamical localization and thermalization. Especially on thermalization, we discuss a generic scenario on the prethermalization phenomenon in periodically driven systems. -- Highlights: •A general framework to describe transient dynamics for periodically driven systems. •The theory is applicable to generic quantum many-body systems including long-range interacting systems. •Physical meaning of the truncation of the Floquet–Magnus expansion is rigorously established. •New mechanism of the prethermalization is proposed. •Revealing an experimental time-scale for which non-trivial dynamical phenomena can be reliably observed.

  20. Code C# for chaos analysis of relativistic many-body systems with reactions

    NASA Astrophysics Data System (ADS)

    Grossu, I. V.; Besliu, C.; Jipa, Al.; Stan, E.; Esanu, T.; Felea, D.; Bordeianu, C. C.

    2012-04-01

    . Object oriented solution, easy to reuse, extend and customize, in any development environment which accepts .Net assemblies or COM components. Treatment of two particles reactions and decays. For each particle, calculation of the time measured in the particle reference frame, according to the instantaneous velocity. Possibility to dynamically add particle properties (spin, isospin, etc.), and reactions/decays, using a specific XML input file. Basic support for Monte Carlo simulations. Implementation of: Lyapunov exponent, “fragmentation level”, “average system radius”, “virial coefficient”, “clusterization map”, and energy conservation precision test. As an example of use, we implemented a toy-model for nuclear relativistic collisions at 4.5 A GeV/c. Reasons for new version: Following our goal of applying chaos theory to nuclear relativistic collisions at 4.5 A GeV/c, we developed a reaction module integrated with the Chaos Many-Body Engine. In the previous version, inheriting the Particle class was the only possibility of implementing more particle properties (spin, isospin, and so on). In the new version, particle properties can be dynamically added using a dictionary object. The application was improved in order to calculate the time measured in the own reference frame of each particle. two particles reactions: a+b→c+d, decays: a→c+d, stimulated decays, more complicated schemas, implemented as various combinations of previous reactions. Following our goal of creating a flexible application, the reactions list, including the corresponding properties (cross sections, particles lifetime, etc.), could be supplied as parameter, using a specific XML configuration file. The simulation output files were modified for systems with reactions, assuring also the backward compatibility. We propose the “Clusterization Map” as a new investigation method of many-body systems. The multi-dimensional Lyapunov Exponent was adapted in order to be used for systems

  1. Quantum many-body system in presence of time-dependent potential and electric field

    NASA Astrophysics Data System (ADS)

    Sobhani, Hadi; Hassanabadi, Hassan

    2017-07-01

    In this article, a quantum many-body system is considered. Then two time-dependent interactions have been added to the system. Changing of them is assumed in general form. After that, by using algebraic method, time evolution of this many-body system has been investigated. In order to study the time evolution, Lewis-Riesenfeld dynamical invariant and time evolution operator method have been used. Appropriate dynamical invariants are constructed and their Eigenvalues are derived as well as appropriate time evolution operators are constructed. These calculations have been done in general form so there are no limiting assumptions on changing of time-dependent functions.

  2. Positive Tensor Network Approach for Simulating Open Quantum Many-Body Systems

    NASA Astrophysics Data System (ADS)

    Werner, A. H.; Jaschke, D.; Silvi, P.; Kliesch, M.; Calarco, T.; Eisert, J.; Montangero, S.

    2016-06-01

    Open quantum many-body systems play an important role in quantum optics and condensed matter physics, and capture phenomena like transport, the interplay between Hamiltonian and incoherent dynamics, and topological order generated by dissipation. We introduce a versatile and practical method to numerically simulate one-dimensional open quantum many-body dynamics using tensor networks. It is based on representing mixed quantum states in a locally purified form, which guarantees that positivity is preserved at all times. Moreover, the approximation error is controlled with respect to the trace norm. Hence, this scheme overcomes various obstacles of the known numerical open-system evolution schemes. To exemplify the functioning of the approach, we study both stationary states and transient dissipative behavior, for various open quantum systems ranging from few to many bodies.

  3. Positive Tensor Network Approach for Simulating Open Quantum Many-Body Systems.

    PubMed

    Werner, A H; Jaschke, D; Silvi, P; Kliesch, M; Calarco, T; Eisert, J; Montangero, S

    2016-06-10

    Open quantum many-body systems play an important role in quantum optics and condensed matter physics, and capture phenomena like transport, the interplay between Hamiltonian and incoherent dynamics, and topological order generated by dissipation. We introduce a versatile and practical method to numerically simulate one-dimensional open quantum many-body dynamics using tensor networks. It is based on representing mixed quantum states in a locally purified form, which guarantees that positivity is preserved at all times. Moreover, the approximation error is controlled with respect to the trace norm. Hence, this scheme overcomes various obstacles of the known numerical open-system evolution schemes. To exemplify the functioning of the approach, we study both stationary states and transient dissipative behavior, for various open quantum systems ranging from few to many bodies.

  4. Exponential orthogonality catastrophe in single-particle and many-body localized systems

    NASA Astrophysics Data System (ADS)

    Deng, Dong-Ling; Pixley, J. H.; Li, Xiaopeng; Das Sarma, S.

    2015-12-01

    We investigate the statistical orthogonality catastrophe (STOC) in single-particle and many-body localized systems by studying the response of the many-body ground state to a local quench. Using scaling arguments and exact numerical calculations, we establish that the STOC gives rise to a wave function overlap between the pre- and postquench ground states that has an exponential decay with the system size, in sharp contrast to the well-known power law Anderson orthogonality catastrophe in metallic systems. This exponential decay arises from a statistical charge transfer process where a particle can be effectively "transported" to an arbitrary lattice site. In a many-body localized phase, this nonlocal transport and the associated exponential STOC phenomenon persist in the presence of interactions. We study the possible experimental consequences of the exponential STOC on the Loschmidt echo and spectral function, establishing that this phenomenon might be observable in cold atomic experiments through Ramsey interference and radio-frequency spectroscopy.

  5. Physics in one dimension: theoretical concepts for quantum many-body systems.

    PubMed

    Schönhammer, K

    2013-01-09

    Various sophisticated approximation methods exist for the description of quantum many-body systems. It was realized early on that the theoretical description can simplify considerably in one-dimensional systems and various exact solutions exist. The focus in this introductory paper is on fermionic systems and the emergence of the Luttinger liquid concept.

  6. Editorial: Focus on Dynamics and Thermalization in Isolated Quantum Many-Body Systems

    NASA Astrophysics Data System (ADS)

    Cazalilla, M. A.; Rigol, M.

    2010-05-01

    The dynamics and thermalization of classical systems have been extensively studied in the past. However, the corresponding quantum phenomena remain, to a large extent, uncharted territory. Recent experiments with ultracold quantum gases have at last allowed exploration of the coherent dynamics of isolated quantum systems, as well as observation of non-equilibrium phenomena that challenge our current understanding of the dynamics of quantum many-body systems. These experiments have also posed many new questions. How can we control the dynamics to engineer new states of matter? Given that quantum dynamics is unitary, under which conditions can we expect observables of the system to reach equilibrium values that can be predicted by conventional statistical mechanics? And, how do the observables dynamically approach their statistical equilibrium values? Could the approach to equilibrium be hampered if the system is trapped in long-lived metastable states characterized, for example, by a certain distribution of topological defects? How does the dynamics depend on the way the system is perturbed, such as changing, as a function of time and at a given rate, a parameter across a quantum critical point? What if, conversely, after relaxing to a steady state, the observables cannot be described by the standard equilibrium ensembles of statistical mechanics? How would they depend on the initial conditions in addition to the other properties of the system, such as the existence of conserved quantities? The search for answers to questions like these is fundamental to a new research field that is only beginning to be explored, and to which researchers with different backgrounds, such as nuclear, atomic, and condensed-matter physics, as well as quantum optics, can make, and are making, important contributions. This body of knowledge has an immediate application to experiments in the field of ultracold atomic gases, but can also fundamentally change the way we approach and

  7. Measuring entanglement entropy of a generic many-body system with a quantum switch.

    PubMed

    Abanin, Dmitry A; Demler, Eugene

    2012-07-13

    Entanglement entropy has become an important theoretical concept in condensed matter physics because it provides a unique tool for characterizing quantum mechanical many-body phases and new kinds of quantum order. However, the experimental measurement of entanglement entropy in a many-body system is widely believed to be unfeasible, owing to the nonlocal character of this quantity. Here, we propose a general method to measure the entanglement entropy. The method is based on a quantum switch (a two-level system) coupled to a composite system consisting of several copies of the original many-body system. The state of the switch controls how different parts of the composite system connect to each other. We show that, by studying the dynamics of the quantum switch only, the Rényi entanglement entropy of the many-body system can be extracted. We propose a possible design of the quantum switch, which can be realized in cold atomic systems. Our work provides a route towards testing the scaling of entanglement in critical systems as well as a method for a direct experimental detection of topological order.

  8. Floquet-Magnus theory and generic transient dynamics in periodically driven many-body quantum systems

    NASA Astrophysics Data System (ADS)

    Kuwahara, Tomotaka; Mori, Takashi; Saito, Keiji

    2016-04-01

    This work explores a fundamental dynamical structure for a wide range of many-body quantum systems under periodic driving. Generically, in the thermodynamic limit, such systems are known to heat up to infinite temperature states in the long-time limit irrespective of dynamical details, which kills all the specific properties of the system. In the present study, instead of considering infinitely long-time scale, we aim to provide a general framework to understand the long but finite time behavior, namely the transient dynamics. In our analysis, we focus on the Floquet-Magnus (FM) expansion that gives a formal expression of the effective Hamiltonian on the system. Although in general the full series expansion is not convergent in the thermodynamics limit, we give a clear relationship between the FM expansion and the transient dynamics. More precisely, we rigorously show that a truncated version of the FM expansion accurately describes the exact dynamics for a certain time-scale. Our theory reveals an experimental time-scale for which non-trivial dynamical phenomena can be reliably observed. We discuss several dynamical phenomena, such as the effect of small integrability breaking, efficient numerical simulation of periodically driven systems, dynamical localization and thermalization. Especially on thermalization, we discuss a generic scenario on the prethermalization phenomenon in periodically driven systems.

  9. How an interacting many-body system tunnels through a potential barrier to open space.

    PubMed

    Lode, Axel U J; Streltsov, Alexej I; Sakmann, Kaspar; Alon, Ofir E; Cederbaum, Lorenz S

    2012-08-21

    The tunneling process in a many-body system is a phenomenon which lies at the very heart of quantum mechanics. It appears in nature in the form of α-decay, fusion and fission in nuclear physics, and photoassociation and photodissociation in biology and chemistry. A detailed theoretical description of the decay process in these systems is a very cumbersome problem, either because of very complicated or even unknown interparticle interactions or due to a large number of constituent particles. In this work, we theoretically study the phenomenon of quantum many-body tunneling in a transparent and controllable physical system, an ultracold atomic gas. We analyze a full, numerically exact many-body solution of the Schrödinger equation of a one-dimensional system with repulsive interactions tunneling to open space. We show how the emitted particles dissociate or fragment from the trapped and coherent source of bosons: The overall many-particle decay process is a quantum interference of single-particle tunneling processes emerging from sources with different particle numbers taking place simultaneously. The close relation to atom lasers and ionization processes allows us to unveil the great relevance of many-body correlations between the emitted and trapped fractions of the wave function in the respective processes.

  10. How an interacting many-body system tunnels through a potential barrier to open space

    PubMed Central

    Lode, Axel U.J.; Streltsov, Alexej I.; Sakmann, Kaspar; Alon, Ofir E.; Cederbaum, Lorenz S.

    2012-01-01

    The tunneling process in a many-body system is a phenomenon which lies at the very heart of quantum mechanics. It appears in nature in the form of α-decay, fusion and fission in nuclear physics, and photoassociation and photodissociation in biology and chemistry. A detailed theoretical description of the decay process in these systems is a very cumbersome problem, either because of very complicated or even unknown interparticle interactions or due to a large number of constituent particles. In this work, we theoretically study the phenomenon of quantum many-body tunneling in a transparent and controllable physical system, an ultracold atomic gas. We analyze a full, numerically exact many-body solution of the Schrödinger equation of a one-dimensional system with repulsive interactions tunneling to open space. We show how the emitted particles dissociate or fragment from the trapped and coherent source of bosons: The overall many-particle decay process is a quantum interference of single-particle tunneling processes emerging from sources with different particle numbers taking place simultaneously. The close relation to atom lasers and ionization processes allows us to unveil the great relevance of many-body correlations between the emitted and trapped fractions of the wave function in the respective processes. PMID:22869703

  11. Dynamics of isolated quantum systems: many-body localization and thermalization

    NASA Astrophysics Data System (ADS)

    Torres-Herrera, E. Jonathan; Tavora, Marco; Santos, Lea F.

    2016-05-01

    We show that the transition to a many-body localized phase and the onset of thermalization can be inferred from the analysis of the dynamics of isolated quantum systems taken out of equilibrium abruptly. The systems considered are described by one-dimensional spin-1/2 models with static random magnetic fields and by power-law band random matrices. We find that the short-time decay of the survival probability of the initial state is faster than exponential for sufficiently strong perturbations. This initial evolution does not depend on whether the system is integrable or chaotic, disordered or clean. At long-times, the dynamics necessarily slows down and shows a power-law behavior. The value of the power-law exponent indicates whether the system will reach thermal equilibrium or not. We present how the properties of the spectrum, structure of the initial state, and number of particles that interact simultaneously affect the value of the power-law exponent. We also compare the results for the survival probability with those for few-body observables. EJTH aknowledges financial support from PRODEP-SEP and VIEP-BUAP, Mexico.

  12. Spectrum of quantum transfer matrices via classical many-body systems

    NASA Astrophysics Data System (ADS)

    Gorsky, A.; Zabrodin, A.; Zotov, A.

    2014-01-01

    In this paper we clarify the relationship between inhomogeneous quantum spin chains and classical integrable many-body systems. It provides an alternative (to the nested Bethe ansatz) method for computation of spectra of the spin chains. Namely, the spectrum of the quantum transfer matrix for the inhomogeneous n -invariant XXX spin chain on N sites with twisted boundary conditions can be found in terms of velocities of particles in the rational N -body Ruijsenaars-Schneider model. The possible values of the velocities are to be found from intersection points of two Lagrangian submanifolds in the phase space of the classical model. One of them is the Lagrangian hyperplane corresponding to fixed coordinates of all N particles and the other one is an N -dimensional Lagrangian submanifold obtained by fixing levels of N classical Hamiltonians in involution. The latter are determined by eigenvalues of the twist matrix. To support this picture, we give a direct proof that the eigenvalues of the Lax matrix for the classical Ruijsenaars-Schneider model, where velocities of particles are substituted by eigenvalues of the spin chain Hamiltonians, calculated through the Bethe equations, coincide with eigenvalues of the twist matrix, with certain multiplicities. We also prove a similar statement for the n Gaudin model with N marked points (on the quantum side) and the Calogero-Moser system with N particles (on the classical side). The realization of the results obtained in terms of branes and supersymmetric gauge theories is also discussed.

  13. Effective Hamiltonians, prethermalization, and slow energy absorption in periodically driven many-body systems

    NASA Astrophysics Data System (ADS)

    Abanin, Dmitry A.; De Roeck, Wojciech; Ho, Wen Wei; Huveneers, François

    2017-01-01

    We establish some general dynamical properties of quantum many-body systems that are subject to a high-frequency periodic driving. We prove that such systems have a quasiconserved extensive quantity H*, which plays the role of an effective static Hamiltonian. The dynamics of the system (e.g., evolution of any local observable) is well approximated by the evolution with the Hamiltonian H* up to time τ*, which is exponentially large in the driving frequency. We further show that the energy absorption rate is exponentially small in the driving frequency. In cases where H* is ergodic, the driven system prethermalizes to a thermal state described by H* at intermediate times t ≲τ* , eventually heating up to an infinite-temperature state after times t ˜τ* . Our results indicate that rapidly driven many-body systems generically exhibit prethermalization and very slow heating. We briefly discuss implications for experiments which realize topological states by periodic driving.

  14. Intermolecular Singlet and Triplet Exciton Transfer Integrals from Many-Body Green's Functions Theory.

    PubMed

    Wehner, Jens; Baumeier, Björn

    2017-03-08

    A general approach to determine orientation and distance-dependent effective intermolecular exciton transfer integrals from many-body Green's functions theory is presented. On the basis of the GW approximation and the Bethe-Salpeter equation (BSE), a projection technique is employed to obtain the excitonic coupling by forming the expectation value of a supramolecular BSE Hamiltonian with electron-hole wave functions for excitations localized on two separated chromophores. Within this approach, accounting for the effects of coupling mediated by intermolecular charge transfer (CT) excitations is possible via perturbation theory or a reduction technique. Application to model configurations of pyrene dimers shows an accurate description of short-range exchange and long-range Coulomb interactions for the coupling of singlet and triplet excitons. Computational parameters, such as the choice of the exchange-correlation functional in the density-functional theory (DFT) calculations that underly the GW-BSE steps and the convergence with the number of included CT excitations, are scrutinized. Finally, an optimal strategy is derived for simulations of full large-scale morphologies by benchmarking various approximations using pairs of dicyanovinyl end-capped oligothiophenes (DCV5T), which are used as donor material in state-of-the-art organic solar cells.

  15. Simulation of Quantum Many-Body Systems with Strings of Operators and Monte Carlo Tensor Contractions

    SciTech Connect

    Schuch, Norbert; Wolf, Michael M.; Cirac, J. Ignacio; Verstraete, Frank

    2008-02-01

    We introduce string-bond states, a class of states obtained by placing strings of operators on a lattice, which encompasses the relevant states in quantum information. For string-bond states, expectation values of local observables can be computed efficiently using Monte Carlo sampling, making them suitable for a variational algorithm which extends the density matrix renormalization group to higher dimensional and irregular systems. Numerical results demonstrate the applicability of these states to the simulation of many-body systems.0.

  16. Realistic Many-Body Quantum Systems vs. Full Random Matrices: Static and Dynamical Properties

    NASA Astrophysics Data System (ADS)

    Torres-Herrera, Eduardo; Karp, Jonathan; Távora, Marco; Santos, Lea

    2016-10-01

    We study the static and dynamical properties of isolated many-body quantum systems and compare them with the results for full random matrices. In doing so, we link concepts from quantum information theory with those from quantum chaos. In particular, we relate the von Neumann entanglement entropy with the Shannon information entropy and discuss their relevance for the analysis of the degree of complexity of the eigenstates, the behavior of the system at different time scales and the conditions for thermalization. A main advantage of full random matrices is that they enable the derivation of analytical expressions that agree extremely well with the numerics and provide bounds for realistic many-body quantum systems.

  17. NON-EQUILIBRIUM DYNAMICS OF MANY-BODY QUANTUM SYSTEMS: FUNDAMENTALS AND NEW FRONTIER

    SciTech Connect

    DeMille, David; LeHur, Karyn

    2013-11-27

    Rapid progress in nanotechnology and naofabrication techniques has ushered in a new era of quantum transport experiments. This has in turn heightened the interest in theoretical understanding of nonequilibrium dynamics of strongly correlated quantum systems. This project has advanced the frontiers of understanding in this area along several fronts. For example, we showed that under certain conditions, quantum impurities out of equilibrium can be reformulated in terms of an effective equilibrium theory; this makes it possible to use the gamut of tools available for quantum systems in equilibrium. On a different front, we demonstrated that the elastic power of a transmitted microwave photon in circuit QED systems can exhibit a many-body Kondo resonance. We also showed that under many circumstances, bipartite fluctuations of particle number provide an effective tool for studying many-body physics—particularly the entanglement properties of a many-body system. This implies that it should be possible to measure many-body entanglement in relatively simple and tractable quantum systems. In addition, we studied charge relaxation in quantum RC circuits with a large number of conducting channels, and elucidated its relation to Kondo models in various regimes. We also extended our earlier work on the dynamics of driven and dissipative quantum spin-boson impurity systems, deriving a new formalism that makes it possible to compute the full spin density matrix and spin-spin correlation functions beyond the weak coupling limit. Finally, we provided a comprehensive analysis of the nonequilibrium transport near a quantum phase transition in the case of a spinless dissipative resonant-level model. This project supported the research of two Ph.D. students and two postdoctoral researchers, whose training will allow them to further advance the field in coming years.

  18. Nonlocality in many-body quantum systems detected with two-body correlators

    SciTech Connect

    Tura, J.; Augusiak, R.; Sainz, A.B.; Lücke, B.; Klempt, C.; Lewenstein, M.; Acín, A.

    2015-11-15

    Contemporary understanding of correlations in quantum many-body systems and in quantum phase transitions is based to a large extent on the recent intensive studies of entanglement in many-body systems. In contrast, much less is known about the role of quantum nonlocality in these systems, mostly because the available multipartite Bell inequalities involve high-order correlations among many particles, which are hard to access theoretically, and even harder experimentally. Standard, “theorist- and experimentalist-friendly” many-body observables involve correlations among only few (one, two, rarely three...) particles. Typically, there is no multipartite Bell inequality for this scenario based on such low-order correlations. Recently, however, we have succeeded in constructing multipartite Bell inequalities that involve two- and one-body correlations only, and showed how they revealed the nonlocality in many-body systems relevant for nuclear and atomic physics [Tura et al., Science 344 (2014) 1256]. With the present contribution we continue our work on this problem. On the one hand, we present a detailed derivation of the above Bell inequalities, pertaining to permutation symmetry among the involved parties. On the other hand, we present a couple of new results concerning such Bell inequalities. First, we characterize their tightness. We then discuss maximal quantum violations of these inequalities in the general case, and their scaling with the number of parties. Moreover, we provide new classes of two-body Bell inequalities which reveal nonlocality of the Dicke states—ground states of physically relevant and experimentally realizable Hamiltonians. Finally, we shortly discuss various scenarios for nonlocality detection in mesoscopic systems of trapped ions or atoms, and by atoms trapped in the vicinity of designed nanostructures.

  19. Chaos Many-Body Engine v03: A new version of code C# for chaos analysis of relativistic many-body systems with reactions

    NASA Astrophysics Data System (ADS)

    Grossu, I. V.; Besliu, C.; Jipa, Al.; Felea, D.; Esanu, T.; Stan, E.; Bordeianu, C. C.

    2013-04-01

    In this paper we present a new version of the Chaos Many-Body Engine C# application (Grossu et al. 2012 [1]). In order to benefit from the latest technological advantages, we migrated the application from .Net Framework 2.0 to .Net Framework 4.0. New tools were implemented also. Trying to estimate the particle interactions dependence on initial conditions, we considered a new distance, which takes into account only the structural differences between two systems. We used this distance for implementing the “Structural Lyapunov” function. We propose also a new precision test based on temporal reversed simulations. New version program summaryProgram title: Chaos Many-Body Engine v03 Catalogue identifier: AEGH_v3_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AEGH_v3_0.html Program obtainable from: CPC Program Library, Queen’s University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 214429 No. of bytes in distributed program, including test data, etc.: 9512380 Distribution format: tar.gz Programming language: Visual C# .Net 2010 Computer: PC Operating system: .Net Framework 4.0 running on MS Windows RAM: 128 MB Classification: 24.60.Lz, 05.45.a Catalogue identifier of previous version: AEGH_v2_0 Journal reference of previous version: Computer Physics Communications 183 (2012) 1055-1059 Does the new version supersede the previous version?: Yes Nature of problem: Chaos analysis of three-dimensional, relativistic many-body systems with reactions. Solution method: Second order Runge-Kutta algorithm. Implementation of temporal reversed simulation precision test, and “Structural Lyapunov” function. In order to benefit from the advantages involved in the latest technologies (e.g. LINQ Queries [2]), Chaos Many-Body Engine was migrated from .Net Framework 2.0 to .Net Framework 4.0. In addition to existing energy conservation

  20. INTRODUCTION: Many-Body Theory of Atomic Systems: Proceedings of the Nobel Symposium 46

    NASA Astrophysics Data System (ADS)

    Lindgren, Ingvar; Lundqvist, Stig

    1980-01-01

    A Nobel Symposium provides an excellent opportunity to bring together a group of prominent scientists for a stimulating meeting. The Nobel Symposia are very small meetings by invitation only and the number of key participants is usually in the range 20-40. These symposia are organized through a special Nobel Symposium Committee after proposals from individuals. They have been made possible through a major grant from the Tri-Centennial Fund of the Bank of Sweden. Our first ideas to arrange a Nobel Symposium on many-body theory of atomic systems came up more than two years ago. It was quite obvious to us that a major break-through was happening in this field. Very accurate schemes have been available for some time for studying the static properties of small closed-shell atomic systems. By "atomic" systems we understand here atoms as well as free molecules, which can be treated by the same formalism, although the technical approaches might be quite different. The conceptual and computational developments in recent years, however, have made it possible to apply the many-body formalism also to heavier systems. Although no rigorous relativistic many-body theory yet exists, there seems to be a general agreement about the way relativistic calculations should be performed on normal atoms and molecules. Schemes based on relativistic perturbation theory as well as on relativistic multi- configurational Hartree-Fock are now in operation and a rapid development is expected in this area. Another field of atomic theory, where significant progress has been made recently, is in the application of many-body formalism to open-shell systems. General schemes, applicable to systems with one or several open shells, are now available, which will make it possible to apply many-body formalism to a much larger group of atomic systems and, in particular, to systems of more physical interest, A number of atomic properties - not only the correlation energy - can then be compared with the

  1. Entanglement Holographic Mapping of Many-Body Localized System by Spectrum Bifurcation Renormalization Group

    NASA Astrophysics Data System (ADS)

    You, Yi-Zhuang; Qi, Xiao-Liang; Xu, Cenke

    We introduce the spectrum bifurcation renormalization group (SBRG) as a generalization of the real-space renormalization group for the many-body localized (MBL) system without truncating the Hilbert space. Starting from a disordered many-body Hamiltonian in the full MBL phase, the SBRG flows to the MBL fixed-point Hamiltonian, and generates the local conserved quantities and the matrix product state representations for all eigenstates. The method is applicable to both spin and fermion models with arbitrary interaction strength on any lattice in all dimensions, as long as the models are in the MBL phase. In particular, we focus on the 1 d interacting Majorana chain with strong disorder, and map out its phase diagram using the entanglement entropy. The SBRG flow also generates an entanglement holographic mapping, which duals the MBL state to a fragmented holographic space decorated with small blackholes.

  2. Non-Kondo many-body physics in a Majorana-based Kondo type system

    NASA Astrophysics Data System (ADS)

    van Beek, Ian J.; Braunecker, Bernd

    2016-09-01

    We carry out a theoretical analysis of a prototypical Majorana system, which demonstrates the existence of a Majorana-mediated many-body state and an associated intermediate low-energy fixed point. Starting from two Majorana bound states, hosted by a Coulomb-blockaded topological superconductor and each coupled to a separate lead, we derive an effective low-energy Hamiltonian, which displays a Kondo-like character. However, in contrast to the Kondo model which tends to a strong- or weak-coupling limit under renormalization, we show that this effective Hamiltonian scales to an intermediate fixed point, whose existence is contingent upon teleportation via the Majorana modes. We conclude by determining experimental signatures of this fixed point, as well as the exotic many-body state associated with it.

  3. General variational many-body theory with complete self-consistency for trapped bosonic systems

    SciTech Connect

    Streltsov, Alexej I.; Alon, Ofir E.; Cederbaum, Lorenz S.

    2006-06-15

    In this work we develop a complete variational many-body theory for a system of N trapped bosons interacting via a general two-body potential. The many-body solution of this system is expanded over orthogonal many-body basis functions (configurations). In this theory both the many-body basis functions and the respective expansion coefficients are treated as variational parameters. The optimal variational parameters are obtained self-consistently by solving a coupled system of noneigenvalue--generally integro-differential--equations to get the one-particle functions and by diagonalizing the secular matrix problem to find the expansion coefficients. We call this theory multiconfigurational Hartree theory for bosons or MCHB(M), where M specifies explicitly the number of one-particle functions used to construct the configurations. General rules for evaluating the matrix elements of one- and two-particle operators are derived and applied to construct the secular Hamiltonian matrix. We discuss properties of the derived equations. We show that in the limiting cases of one configuration the theory boils down to the well-known Gross-Pitaevskii and the recently developed multi-orbital mean fields. The invariance of the complete solution with respect to unitary transformations of the one-particle functions is utilized to find the solution with the minimal number of contributing configurations. In the second part of our work we implement and apply the developed theory. It is demonstrated that for any practical computation where the configurational space is restricted, the description of trapped bosonic systems strongly depends on the choice of the many-body basis set used, i.e., self-consistency is of great relevance. As illustrative examples we consider bosonic systems trapped in one- and two-dimensional symmetric and asymmetric double well potentials. We demonstrate that self-consistency has great impact on the predicted physical properties of the ground and excited states

  4. Quantum statistical gravity: time dilation due to local information in many-body quantum systems

    NASA Astrophysics Data System (ADS)

    Sels, Dries; Wouters, Michiel

    2017-08-01

    We propose a generic mechanism for the emergence of a gravitational potential that acts on all classical objects in a quantum system. Our conjecture is based on the analysis of mutual information in many-body quantum systems. Since measurements in quantum systems affect the surroundings through entanglement, a measurement at one position reduces the entropy in its neighbourhood. This reduction in entropy can be described by a local temperature, that is directly related to the gravitational potential. A crucial ingredient in our argument is that ideal classical mechanical motion occurs at constant probability. This definition is motivated by the analysis of entropic forces in classical systems.

  5. Equivalent dynamical complexity in a many-body quantum and collective human system

    NASA Astrophysics Data System (ADS)

    Johnson, Neil F.; Ashkenazi, Josef; Zhao, Zhenyuan; Quiroga, Luis

    2011-03-01

    Proponents of Complexity Science believe that the huge variety of emergent phenomena observed throughout nature, are generated by relatively few microscopic mechanisms. Skeptics however point to the lack of concrete examples in which a single mechanistic model manages to capture relevant macroscopic and microscopic properties for two or more distinct systems operating across radically different length and time scales. Here we show how a single complexity model built around cluster coalescence and fragmentation, can cross the fundamental divide between many-body quantum physics and social science. It simultaneously (i) explains a mysterious recent finding of Fratini et al. concerning quantum many-body effects in cuprate superconductors (i.e. scale of 10-9 - 10-4 meters and 10-12 - 10-6 seconds), (ii) explains the apparent universality of the casualty distributions in distinct human insurgencies and terrorism (i.e. scale of 103 - 106 meters and 104 - 108 seconds), (iii) shows consistency with various established empirical facts for financial markets, neurons and human gangs and (iv) makes microscopic sense for each application. Our findings also suggest that a potentially productive shift can be made in Complexity research toward the identification of equivalent many-body dynamics in both classical and quantum regimes.

  6. Isolated many-body quantum systems far from equilibrium: Relaxation process and thermalization

    SciTech Connect

    Torres-Herrera, E. J.; Santos, Lea F.

    2014-10-15

    We present an overview of our recent numerical and analytical results on the dynamics of isolated interacting quantum systems that are taken far from equilibrium by an abrupt perturbation. The studies are carried out on one-dimensional systems of spins-1/2, which are paradigmatic models of many-body quantum systems. Our results show the role of the interplay between the initial state and the post-perturbation Hamiltonian in the relaxation process, the size of the fluctuations after equilibration, and the viability of thermalization.

  7. Fluctuations and Stochastic Processes in One-Dimensional Many-Body Quantum Systems

    SciTech Connect

    Stimming, H.-P.; Mauser, N. J.; Mazets, I. E.

    2010-07-02

    We study the fluctuation properties of a one-dimensional many-body quantum system composed of interacting bosons and investigate the regimes where quantum noise or, respectively, thermal excitations are dominant. For the latter, we develop a semiclassical description of the fluctuation properties based on the Ornstein-Uhlenbeck stochastic process. As an illustration, we analyze the phase correlation functions and the full statistical distributions of the interference between two one-dimensional systems, either independent or tunnel-coupled, and compare with the Luttinger-liquid theory.

  8. Detecting ground-state degeneracy in many-body systems through qubit decoherence

    NASA Astrophysics Data System (ADS)

    Cui, Hai-Tao; Yi, Xue-Xi

    2017-02-01

    By coupling with a qubit, we demonstrate that qubit decoherence can unambiguously detect the occurrence of ground-state degeneracy in many-body systems. We first demonstrate universality using the two-band model. Consequently, several exemplifications, focused on topological condensed matter systems in one, two, and three dimensions, are presented to validate our proposal. The key point is that qubit decoherence varies significantly when energy bands touch each other at the Fermi surface. In addition, it can partially reflect the degeneracy inside the band. This feature implies that qubit decoherence can be used for reliable diagnosis of ground-state degeneracy.

  9. Atomistic formulas for local properties in systems with many-body interactions

    NASA Astrophysics Data System (ADS)

    Hardy, Robert J.

    2016-11-01

    Atomistic formulas are derived for the local densities and fluxes used in the continuum description of energy and momentum transport. Two general methods for the distribution of potential energy among a system's constituent particles are presented and analyzed. The resulting formulas for the heat flux and stress tensor and the equations for energy and momentum transport are exact consequences of the definitions of the densities and the equations of classical mechanics. The formulas and equations obtained are valid for systems with very general types of many-body interactions.

  10. Real-space decoupling transformation for quantum many-body systems.

    PubMed

    Evenbly, G; Vidal, G

    2014-06-06

    We propose a real-space renormalization group method to explicitly decouple into independent components a many-body system that, as in the phenomenon of spin-charge separation, exhibits separation of degrees of freedom at low energies. Our approach produces a branching holographic description of such systems that opens the path to the efficient simulation of the most entangled phases of quantum matter, such as those whose ground state violates a boundary law for entanglement entropy. As in the coarse-graining transformation of Vidal [Phys. Rev. Lett. 99, 220405 (2007).

  11. Calculation of local pressure tensors in systems with many-body interactions.

    PubMed

    Heinz, Hendrik; Paul, Wolfgang; Binder, Kurt

    2005-12-01

    Local pressures are important in the calculation of interface tensions and in analyzing micromechanical behavior. The calculation of local pressures in computer simulations has been limited to systems with pairwise interactions between the particles, which is not sufficient for chemically detailed systems with many-body potentials such as angles and torsions. We introduce a method to calculate local pressures in systems with n-body interactions (n=2,3,4,) based on a micromechanical definition of the pressure tensor. The local pressure consists of a kinetic contribution from the linear momentum of the particles and an internal contribution from dissected many-body interactions by infinitesimal areas. To define dissection by a small area, respective n-body interactions are divided into two geometric centers, effectively reducing them to two-body interactions. Consistency with hydrodynamics-derived formulas for systems with two-body interactions [J. H. Irving and J. G. Kirkwood, J. Chem. Phys. 18, 817 (1950)], for average cross-sectional pressures [B. D. Todd, D. J. Evans, and P. J. Daivis, Phys. Rev. E 52, 1627 (1995)], and for volume averaged pressures (virial formula) is shown. As a simple numerical example, we discuss liquid propane in a cubic box. Local, cross-sectional, and volume-averaged pressures as well as relative contributions from two-body and three-body forces are analyzed with the proposed method, showing full numerical equivalence with the existing approaches. The method allows computing local pressures in the presence of many-body interactions in atomistic simulations of complex materials and biological systems.

  12. Experimental characterization of a quantum many-body system via higher-order correlations

    NASA Astrophysics Data System (ADS)

    Schweigler, Thomas; Kasper, Valentin; Erne, Sebastian; Mazets, Igor; Rauer, Bernhard; Cataldini, Federica; Langen, Tim; Gasenzer, Thomas; Berges, Jürgen; Schmiedmayer, Jörg

    2017-05-01

    Quantum systems can be characterized by their correlations. Higher-order (larger than second order) correlations, and the ways in which they can be decomposed into correlations of lower order, provide important information about the system, its structure, its interactions and its complexity. The measurement of such correlation functions is therefore an essential tool for reading, verifying and characterizing quantum simulations. Although higher-order correlation functions are frequently used in theoretical calculations, so far mainly correlations up to second order have been studied experimentally. Here we study a pair of tunnel-coupled one-dimensional atomic superfluids and characterize the corresponding quantum many-body problem by measuring correlation functions. We extract phase correlation functions up to tenth order from interference patterns and analyse whether, and under what conditions, these functions factorize into correlations of lower order. This analysis characterizes the essential features of our system, the relevant quasiparticles, their interactions and topologically distinct vacua. From our data we conclude that in thermal equilibrium our system can be seen as a quantum simulator of the sine-Gordon model, relevant for diverse disciplines ranging from particle physics to condensed matter. The measurement and evaluation of higher-order correlation functions can easily be generalized to other systems and to study correlations of any other observable such as density, spin and magnetization. It therefore represents a general method for analysing quantum many-body systems from experimental data.

  13. Quasiparticle engineering and entanglement propagation in a quantum many-body system.

    PubMed

    Jurcevic, P; Lanyon, B P; Hauke, P; Hempel, C; Zoller, P; Blatt, R; Roos, C F

    2014-07-10

    The key to explaining and controlling a range of quantum phenomena is to study how information propagates around many-body systems. Quantum dynamics can be described by particle-like carriers of information that emerge in the collective behaviour of the underlying system, the so-called quasiparticles. These elementary excitations are predicted to distribute quantum information in a fashion determined by the system's interactions. Here we report quasiparticle dynamics observed in a quantum many-body system of trapped atomic ions. First, we observe the entanglement distributed by quasiparticles as they trace out light-cone-like wavefronts. Second, using the ability to tune the interaction range in our system, we observe information propagation in an experimental regime where the effective-light-cone picture does not apply. Our results will enable experimental studies of a range of quantum phenomena, including transport, thermalization, localization and entanglement growth, and represent a first step towards a new quantum-optic regime of engineered quasiparticles with tunable nonlinear interactions.

  14. Density of states of many-body quantum systems from tensor networks

    NASA Astrophysics Data System (ADS)

    Schrodi, Fabian; Silvi, Pietro; Tschirsich, Ferdinand; Fazio, Rosario; Montangero, Simone

    2017-09-01

    We present a technique to compute the microcanonical thermodynamical properties of a many-body quantum system using tensor networks. The density of States, and more general spectral properties, are evaluated by means of a Hubbard-Stratonovich transformation performed on top of a real-time evolution, which is carried out via numerical methods based on tensor networks. As a consequence, the free energy and thermal averages can be also calculated. We test this approach on the one-dimensional Ising and Fermi-Hubbard models. Using matrix product states, we show that the thermodynamical quantities as a function of temperature are in very good agreement with the exact results.

  15. Variational principle for steady states of dissipative quantum many-body systems.

    PubMed

    Weimer, Hendrik

    2015-01-30

    We present a novel generic framework to approximate the nonequilibrium steady states of dissipative quantum many-body systems. It is based on the variational minimization of a suitable norm of the quantum master equation describing the dynamics. We show how to apply this approach to different classes of variational quantum states and demonstrate its successful application to a dissipative extension of the Ising model, which is of importance to ongoing experiments on ultracold Rydberg atoms, as well as to a driven-dissipative variant of the Bose-Hubbard model. Finally, we identify several advantages of the variational approach over previously employed mean-field-like methods.

  16. Many-body mobility edges in a one-dimensional system of interacting fermions

    NASA Astrophysics Data System (ADS)

    Nag, Sabyasachi; Garg, Arti

    2017-08-01

    We study many-body localization (MBL) in an interacting one-dimensional system with a deterministic aperiodic potential. Below the threshold potential h system has single particle mobility edges (MEs) at ±Ec while for h >hc all the single particle states are localized. We demonstrate that even in the presence of single particle MEs, interactions do not always delocalize the system and the interacting system can have MBL. Our numerical calculation of energy level spacing statistics, participation ratio in the Fock space, and Shannon entropy shows that for some regime of particle densities, even for h many-body states at the top (with E >E2 ) and the bottom of the spectrum (with E

  17. Open-system many-body dynamics through interferometric measurements and feedback

    NASA Astrophysics Data System (ADS)

    Lammers, Jonas; Weimer, Hendrik; Hammerer, Klemens

    2016-11-01

    Light-matter interfaces enable the generation of entangled states of light and matter which can be exploited to steer the quantum state of matter through measurement of light and feedback. Here we consider continuous-time, interferometric homodyne measurements of light on an array of light-matter interfaces followed by local feedback acting on each material system individually. While the systems are physically noninteracting, the feedback master equation we derive describes driven-dissipative, interacting many-body quantum dynamics, and comprises pairwise Hamiltonian interactions and collective jump operators. We characterize the general class of driven-dissipative many-body systems which can be engineered in this way, and derive necessary conditions on models supporting nontrivial quantum dynamics beyond what can be generated by local operations and classical communication. We provide specific examples of models which allow for the creation of stationary many-particle entanglement, and the emulation of dissipative Ising models. Since the interaction between the systems is mediated via feedback only, there is no intrinsic limit on the range or geometry of the interaction, making the scheme quite versatile.

  18. Observation of discrete time-crystalline order in a disordered dipolar many-body system

    NASA Astrophysics Data System (ADS)

    Choi, Soonwon; Choi, Joonhee; Landig, Renate; Kucsko, Georg; Zhou, Hengyun; Isoya, Junichi; Jelezko, Fedor; Onoda, Shinobu; Sumiya, Hitoshi; Khemani, Vedika; von Keyserlingk, Curt; Yao, Norman Y.; Demler, Eugene; Lukin, Mikhail D.

    2017-03-01

    Understanding quantum dynamics away from equilibrium is an outstanding challenge in the modern physical sciences. Out-of-equilibrium systems can display a rich variety of phenomena, including self-organized synchronization and dynamical phase transitions. More recently, advances in the controlled manipulation of isolated many-body systems have enabled detailed studies of non-equilibrium phases in strongly interacting quantum matter; for example, the interplay between periodic driving, disorder and strong interactions has been predicted to result in exotic ‘time-crystalline’ phases, in which a system exhibits temporal correlations at integer multiples of the fundamental driving period, breaking the discrete time-translational symmetry of the underlying drive. Here we report the experimental observation of such discrete time-crystalline order in a driven, disordered ensemble of about one million dipolar spin impurities in diamond at room temperature. We observe long-lived temporal correlations, experimentally identify the phase boundary and find that the temporal order is protected by strong interactions. This order is remarkably stable to perturbations, even in the presence of slow thermalization. Our work opens the door to exploring dynamical phases of matter and controlling interacting, disordered many-body systems.

  19. Griffiths effects and slow dynamics in nearly many-body localized systems

    NASA Astrophysics Data System (ADS)

    Gopalakrishnan, Sarang; Agarwal, Kartiek; Demler, Eugene A.; Huse, David A.; Knap, Michael

    2016-04-01

    The low-frequency response of systems near a many-body localization transition can be dominated by rare regions that are locally critical or "in the other phase." It is known that in one dimension, these rare regions can cause the dc conductivity and diffusion constant to vanish even inside the delocalized thermal phase. Here, we present a general analysis of such Griffiths effects in the thermal phase near the many-body localization transition: we consider both one-dimensional and higher-dimensional systems, subject to quenched randomness, and discuss both linear response (including the frequency- and wave-vector-dependent conductivity) and more general dynamics. In all the regimes we consider, we identify observables that are dominated by rare-region effects. In some cases (one-dimensional systems and Floquet systems with no extensive conserved quantities), essentially all long-time local observables are dominated by rare-region effects; in others, generic observables are instead dominated by hydrodynamic long-time tails throughout the thermal phase, and one must look at specific probes, such as spin echo, to see Griffiths behavior.

  20. Topological order of mixed states in correlated quantum many-body systems

    NASA Astrophysics Data System (ADS)

    Grusdt, F.

    2017-02-01

    Topological order has become a new paradigm to distinguish ground states of interacting many-body systems without conventional long-range order. Here, we discuss possible extensions of this concept to density matrices describing statistical ensembles. For a large class of quasithermal states, which can be realized as thermal states of some quasilocal Hamiltonian, we generalize earlier definitions of density-matrix topology to generic many-body systems with strong correlations. We point out that the robustness of topological order, defined as a pattern of long-range entanglement, depends crucially on the perturbations under consideration. While it is intrinsically protected against local perturbations of arbitrary strength in an infinite closed quantum system, purely local perturbations can destroy topological order in open systems coupled to baths if the coupling is sufficiently strong. We discuss our classification scheme using the finite-temperature quantum Hall states and point out that the classical Hall effect can be understood as a finite-temperature topological phase.

  1. Artificial quantum thermal bath: Engineering temperature for a many-body quantum system

    NASA Astrophysics Data System (ADS)

    Shabani, Alireza; Neven, Hartmut

    2016-11-01

    Temperature determines the relative probability of observing a physical system in an energy state when that system is energetically in equilibrium with its environment. In this paper we present a theory for engineering the temperature of a quantum system different from its ambient temperature. We define criteria for an engineered quantum bath that, when coupled to a quantum system with Hamiltonian H , drives the system to the equilibrium state e/-H/TTr (e-H /T) with a tunable parameter T . This is basically an analog counterpart of the digital quantum metropolis algorithm. For a system of superconducting qubits, we propose a circuit-QED approximate realization of such an engineered thermal bath consisting of driven lossy resonators. Our proposal opens the path to simulate thermodynamical properties of many-body quantum systems of size not accessible to classical simulations. Also we discuss how an artificial thermal bath can serve as a temperature knob for a hybrid quantum-thermal annealer.

  2. Exponential series expansion for correlation functions of many-body systems.

    PubMed

    Barocchi, Fabrizio; Guarini, Eleonora; Bafile, Ubaldo

    2014-09-01

    We demonstrate that in Hamiltonian many-body systems at equilibrium, any kind of time dependent correlation function c(t) can always be expanded in a series of (complex) exponential functions of time when its Laplace transform C̃(z) has single poles. The characteristic frequencies can be identified as the eigenfrequencies of the correlation. This is done without introducing the concepts of fluctuating forces and memory functions, due to Mori and Zwanzig and extensively used in the literature in the last decades. Our method is based on a different projection technique in the Hilbert space S of the system and shows that appropriate approximations of the exponential series are related to the contraction of S to a finite, usually small, number of dimensions. The time dependence of correlation functions is always described in detail by a multiple-exponential functionality also at long times. This result is therefore also valid for correlation functions of many-body Hamiltonian systems for which a power-law dependence, observed in restricted time ranges and predicted to be the asymptotic one, can be considered at most as a useful approximate modeling of long-time behavior.

  3. Theory of the Many-Body Localization Transition in One-Dimensional Systems

    NASA Astrophysics Data System (ADS)

    Vosk, Ronen; Huse, David A.; Altman, Ehud

    2015-07-01

    We formulate a theory of the many-body localization transition based on a novel real-space renormalization group (RG) approach. The results of this theory are corroborated and intuitively explained with a phenomenological effective description of the critical point and of the "badly conducting" state found near the critical point on the delocalized side. The theory leads to the following sharp predictions: (i) The delocalized state established near the transition is a Griffiths phase, which exhibits subdiffusive transport of conserved quantities and sub-ballistic spreading of entanglement. The anomalous diffusion exponent α <1 /2 vanishes continuously at the critical point. The system does thermalize in this Griffiths phase. (ii) The many-body localization transition is controlled by a new kind of infinite-randomness RG fixed point, where the broadly distributed scaling variable is closely related to the eigenstate entanglement entropy. Dynamically, the entanglement grows as ˜log t at the critical point, as it does in the localized phase. (iii) In the vicinity of the critical point, the ratio of the entanglement entropy to the thermal entropy and its variance (and, in fact, all moments) are scaling functions of L /ξ , where L is the length of the system and ξ is the correlation length, which has a power-law divergence at the critical point.

  4. Role of interactions in a dissipative many-body localized system

    NASA Astrophysics Data System (ADS)

    Everest, Benjamin; Lesanovsky, Igor; Garrahan, Juan P.; Levi, Emanuele

    2017-01-01

    Recent experimental and theoretical efforts have focused on the effect of dissipation on quantum many-body systems in their many-body localized (MBL) phase. While in the presence of dephasing noise such systems reach a unique ergodic state, their dynamics is characterized by slow relaxation manifested in nonexponential decay of self-correlations. Here we shed light on a currently much debated issue, namely, the role of interactions for this relaxation dynamics. We focus on the experimentally relevant situation of the evolution from an initial charge density wave in the presence of strong dephasing noise. We find a crossover from a regime dominated by disorder to a regime dominated by interactions, with an accompanying change of time correlators from stretched exponential to compressed exponential form. The strongly interacting regime can be explained in terms of nucleation and growth dynamics of relaxing regions—reminiscent of the kinetics of crystallization in soft matter systems—and should be observable experimentally. This interaction-driven crossover suggests that the competition between interactions and noise gives rise to a much richer structure of the MBL phase than anticipated so far.

  5. PREFACE: Advanced many-body and statistical methods in mesoscopic systems

    NASA Astrophysics Data System (ADS)

    Anghel, Dragos Victor; Sabin Delion, Doru; Sorin Paraoanu, Gheorghe

    2012-02-01

    It has increasingly been realized in recent times that the borders separating various subfields of physics are largely artificial. This is the case for nanoscale physics, physics of lower-dimensional systems and nuclear physics, where the advanced techniques of many-body theory developed in recent times could provide a unifying framework for these disciplines under the general name of mesoscopic physics. Other fields, such as quantum optics and quantum information, are increasingly using related methods. The 6-day conference 'Advanced many-body and statistical methods in mesoscopic systems' that took place in Constanta, Romania, between 27 June and 2 July 2011 was, we believe, a successful attempt at bridging an impressive list of topical research areas: foundations of quantum physics, equilibrium and non-equilibrium quantum statistics/fractional statistics, quantum transport, phases and phase transitions in mesoscopic systems/superfluidity and superconductivity, quantum electromechanical systems, quantum dissipation, dephasing, noise and decoherence, quantum information, spin systems and their dynamics, fundamental symmetries in mesoscopic systems, phase transitions, exactly solvable methods for mesoscopic systems, various extension of the random phase approximation, open quantum systems, clustering, decay and fission modes and systematic versus random behaviour of nuclear spectra. This event brought together participants from seventeen countries and five continents. Each of the participants brought considerable expertise in his/her field of research and, at the same time, was exposed to the newest results and methods coming from the other, seemingly remote, disciplines. The talks touched on subjects that are at the forefront of topical research areas and we hope that the resulting cross-fertilization of ideas will lead to new, interesting results from which everybody will benefit. We are grateful for the financial and organizational support from IFIN-HH, Ovidius

  6. Entanglement scaling of excited states in large one-dimensional many-body localized systems

    NASA Astrophysics Data System (ADS)

    Kennes, D. M.; Karrasch, C.

    2016-06-01

    We study the properties of excited states in one-dimensional many-body localized (MBL) systems using a matrix product state algorithm. First, the method is tested for a large disordered noninteracting system, where for comparison we compute a quasiexact reference solution via a Monte Carlo sampling of the single-particle levels. Thereafter, we present extensive data obtained for large interacting systems of L ˜100 sites and large bond dimensions χ ˜1700 , which allows us to quantitatively analyze the scaling behavior of the entanglement S in the system. The MBL phase is characterized by a logarithmic growth S (L )˜log(L ) over a large scale separating the regimes where volume and area laws hold. We check the validity of the eigenstate thermalization hypothesis. Our results are consistent with the existence of a mobility edge.

  7. Universal Chiral Quasisteady States in Periodically Driven Many-Body Systems

    NASA Astrophysics Data System (ADS)

    Lindner, Netanel H.; Berg, Erez; Rudner, Mark S.

    2017-01-01

    We investigate many-body dynamics in a one-dimensional interacting periodically driven system, based on a partially filled version of Thouless's topologically quantized adiabatic pump. The corresponding single-particle Floquet bands are chiral, with the Floquet spectrum realizing nontrivial cycles around the quasienergy Brillouin zone. For generic filling, with either bosons or fermions, the system is gapless and is expected to rapidly absorb energy from the driving field. We identify parameter regimes where scattering between Floquet bands of opposite chirality is exponentially suppressed, opening a long time window in which the system prethermalizes to an infinite-temperature state restricted to a single Floquet band. In this quasi-steady state, the time-averaged current takes a universal value determined solely by the density of particles and the topological winding number of the populated Floquet band. This remarkable behavior may be readily studied experimentally in recently developed cold atom systems.

  8. Quantum phase transitions in the collective degrees of freedom: nuclei and other many-body systems

    NASA Astrophysics Data System (ADS)

    Cejnar, Pavel; Stránský, Pavel

    2016-08-01

    Quantum phase transitions (QPTs) represent a quickly developing subject of theoretical and experimental research. Nuclear physics contributed to the formation of the QPT concept in the 1970s and remains an area where new viewpoints and original approaches to criticality in many-body systems can be created. In this review, we present a comprehensible introduction to the subject, with an emphasis on the role of nuclear physics, and point out some specific features of QPTs in the systems that exhibit an effective separation of some collective degrees of freedom. The focus on collectivity, which stems from the nuclear context, is an essential ingredient of our treatise. It leads to some consequences that find application in nuclei as well as in a wide spectrum of non-nuclear systems.

  9. Quantum simulation. Coherent imaging spectroscopy of a quantum many-body spin system.

    PubMed

    Senko, C; Smith, J; Richerme, P; Lee, A; Campbell, W C; Monroe, C

    2014-07-25

    Quantum simulators, in which well-controlled quantum systems are used to reproduce the dynamics of less understood ones, have the potential to explore physics inaccessible to modeling with classical computers. However, checking the results of such simulations also becomes classically intractable as system sizes increase. Here, we introduce and implement a coherent imaging spectroscopic technique, akin to magnetic resonance imaging, to validate a quantum simulation. We use this method to determine the energy levels and interaction strengths of a fully connected quantum many-body system. Additionally, we directly measure the critical energy gap near a quantum phase transition. We expect this general technique to become a verification tool for quantum simulators once experiments advance beyond proof-of-principle demonstrations and exceed the resources of conventional computers. Copyright © 2014, American Association for the Advancement of Science.

  10. Quantum thermalization through entanglement in an isolated many-body system.

    PubMed

    Kaufman, Adam M; Tai, M Eric; Lukin, Alexander; Rispoli, Matthew; Schittko, Robert; Preiss, Philipp M; Greiner, Markus

    2016-08-19

    Statistical mechanics relies on the maximization of entropy in a system at thermal equilibrium. However, an isolated quantum many-body system initialized in a pure state remains pure during Schrödinger evolution, and in this sense it has static, zero entropy. We experimentally studied the emergence of statistical mechanics in a quantum state and observed the fundamental role of quantum entanglement in facilitating this emergence. Microscopy of an evolving quantum system indicates that the full quantum state remains pure, whereas thermalization occurs on a local scale. We directly measured entanglement entropy, which assumes the role of the thermal entropy in thermalization. The entanglement creates local entropy that validates the use of statistical physics for local observables. Our measurements are consistent with the eigenstate thermalization hypothesis. Copyright © 2016, American Association for the Advancement of Science.

  11. Quantum thermalization through entanglement in an isolated many-body system

    NASA Astrophysics Data System (ADS)

    Kaufman, Adam M.; Tai, M. Eric; Lukin, Alexander; Rispoli, Matthew; Schittko, Robert; Preiss, Philipp M.; Greiner, Markus

    2016-08-01

    Statistical mechanics relies on the maximization of entropy in a system at thermal equilibrium. However, an isolated quantum many-body system initialized in a pure state remains pure during Schrödinger evolution, and in this sense it has static, zero entropy. We experimentally studied the emergence of statistical mechanics in a quantum state and observed the fundamental role of quantum entanglement in facilitating this emergence. Microscopy of an evolving quantum system indicates that the full quantum state remains pure, whereas thermalization occurs on a local scale. We directly measured entanglement entropy, which assumes the role of the thermal entropy in thermalization. The entanglement creates local entropy that validates the use of statistical physics for local observables. Our measurements are consistent with the eigenstate thermalization hypothesis.

  12. Investigation of short-time many-body dynamics in multilevel Rydberg systems.

    NASA Astrophysics Data System (ADS)

    Bracamontes, Carlos; Young, Jeremy; Goldschmidt, Elizabeth; Boulier, Thomas; Gorshkov, Alexey; Rolston, Steve; Porto, James

    2016-05-01

    We present follow-up work to previous results in which we observe anomalous broadening in a driven-dissipative system of Rydberg atoms. We address rubidium atoms in a 3D optical lattice on 5s-18s transition and see substantial broadening of this line with increasing excitation strength and atomic density. We attribute the broadening mechanism to dipole-dipole interactions with spontaneously populated nearby Rydberg states. This mechanism implies complex dynamics at early times as the contaminant population is built up. A full microscopic model of this many-body multilevel system has proved elusive, but initial experiments to study these dynamics using single photon counting provided qualitative information that was consistent with simple theoretical estimates. We implement optical heterodyne detection for short probe pulses to study this dynamics in depth and gain further understanding of the system.

  13. Seniority in quantum many-body systems. I. Identical particles in a single shell

    SciTech Connect

    Van Isacker, P.

    2014-10-15

    A discussion of the seniority quantum number in many-body systems is presented. The analysis is carried out for bosons and fermions simultaneously but is restricted to identical particles occupying a single shell. The emphasis of the paper is on the possibility of partial conservation of seniority which turns out to be a peculiar property of spin-9/2 fermions but prevalent in systems of interacting bosons of any spin. Partial conservation of seniority is at the basis of the existence of seniority isomers, frequently observed in semi-magic nuclei, and also gives rise to peculiar selection rules in one-nucleon transfer reactions. - Highlights: • Unified derivation of conditions for the total and partial conservation of seniority. • General analysis of the partial conservation of seniority in boson systems. • Why partial conservation of seniority is crucial for seniority isomers in nuclei. • The effect of partial conservation of seniority on one-nucleon transfer intensities.

  14. Image method for induced surface charge from many-body system of dielectric spheres

    NASA Astrophysics Data System (ADS)

    Qin, Jian; de Pablo, Juan J.; Freed, Karl F.

    2016-09-01

    Charged dielectric spheres embedded in a dielectric medium provide the simplest model for many-body systems of polarizable ions and charged colloidal particles. We provide a multiple scattering formulation for the total electrostatic energy for such systems and demonstrate that the polarization energy can be rapidly evaluated by an image method that generalizes the image methods for conducting spheres. Individual contributions to the total electrostatic energy are ordered according to the number of polarized surfaces involved, and each additional surface polarization reduces the energy by a factor of (a/R)3ɛ, where a is the sphere radius, R the average inter-sphere separation, and ɛ the relevant dielectric mismatch at the interface. Explicit expressions are provided for both the energy and the forces acting on individual spheres, which can be readily implemented in Monte Carlo and molecular dynamics simulations of polarizable charged spheres, thereby avoiding costly computational techniques that introduce a surface charge distribution that requires numerical solution.

  15. IImage method for induced surface charge from many-body system of dielectric spheres

    SciTech Connect

    Qin, Jian; de Pablo, Juan J.; Freed, Karl F.

    2016-09-28

    Charged dielectric spheres embedded in a dielectric medium provide the simplest model for many-body systems of polarizable ions and charged colloidal particles. We provide a multiple scattering formulation for the total electrostatic energy for such systems and demonstrate that the polarization energy can be rapidly evaluated by an image method that generalizes the image methods for conducting spheres. Individual contributions to the total electrostatic energy are ordered according to the number of polarized surfaces involved, and each additional surface polarization reduces the energy by a factor of (a/R)(3) epsilon, where a is the sphere radius, R the average inter-sphere separation, and. the relevant dielectric mismatch at the interface. Explicit expressions are provided for both the energy and the forces acting on individual spheres, which can be readily implemented in Monte Carlo and molecular dynamics simulations of polarizable charged spheres, thereby avoiding costly computational techniques that introduce a surface charge distribution that requires numerical solution.

  16. Regimes of heating and dynamical response in driven many-body localized systems

    NASA Astrophysics Data System (ADS)

    Gopalakrishnan, Sarang; Knap, Michael; Demler, Eugene

    2016-09-01

    We explore the response of many-body localized (MBL) systems to periodic driving of arbitrary amplitude, focusing on the rate at which they exchange energy with the drive. To this end, we introduce an infinite-temperature generalization of the effective "heating rate" in terms of the spread of a random walk in energy space. We compute this heating rate numerically and estimate it analytically in various regimes. When the drive amplitude is much smaller than the frequency, this effective heating rate is given by linear response theory with a coefficient that is proportional to the optical conductivity; in the opposite limit, the response is nonlinear and the heating rate is a nontrivial power law of time. We discuss the mechanisms underlying this crossover in the MBL phase. We comment on implications for the subdiffusive thermal phase near the MBL transition, and for response in imperfectly isolated MBL systems.

  17. The Interplay of Localization and Interactions in Quantum Many-Body Systems

    NASA Astrophysics Data System (ADS)

    Iyer, Shankar

    systems with high energy density (i.e., far from the usual low energy limit of condensed matter physics). Recent theoretical and numerical work indicates that localization can survive in this regime, provided that interactions are sufficiently weak. Stronger interactions can destroy localization, leading to a so-called many-body localization transition. This dynamical phase transition is relevant to questions of thermalization in isolated quantum systems: it separates a many-body localized phase, in which localization prevents transport and thermalization, from a conducting ("ergodic") phase in which the usual assumptions of quantum statistical mechanics hold. Here, we present evidence that many-body localization also occurs in quasiperiodic systems that lack true disorder.

  18. Quantum variance: A measure of quantum coherence and quantum correlations for many-body systems

    NASA Astrophysics Data System (ADS)

    Frérot, Irénée; Roscilde, Tommaso

    2016-08-01

    Quantum coherence is a fundamental common trait of quantum phenomena, from the interference of matter waves to quantum degeneracy of identical particles. Despite its importance, estimating and measuring quantum coherence in generic, mixed many-body quantum states remains a formidable challenge, with fundamental implications in areas as broad as quantum condensed matter, quantum information, quantum metrology, and quantum biology. Here, we provide a quantitative definition of the variance of quantum coherent fluctuations (the quantum variance) of any observable on generic quantum states. The quantum variance generalizes the concept of thermal de Broglie wavelength (for the position of a free quantum particle) to the space of eigenvalues of any observable, quantifying the degree of coherent delocalization in that space. The quantum variance is generically measurable and computable as the difference between the static fluctuations and the static susceptibility of the observable; despite its simplicity, it is found to provide a tight lower bound to most widely accepted estimators of "quantumness" of observables (both as a feature as well as a resource), such as the Wigner-Yanase skew information and the quantum Fisher information. When considering bipartite fluctuations in an extended quantum system, the quantum variance expresses genuine quantum correlations among the two parts. In the case of many-body systems, it is found to obey an area law at finite temperature, extending therefore area laws of entanglement and quantum fluctuations of pure states to the mixed-state context. Hence the quantum variance paves the way to the measurement of macroscopic quantum coherence and quantum correlations in most complex quantum systems.

  19. Quantum versus mean-field collapse in a many-body system

    NASA Astrophysics Data System (ADS)

    Astrakharchik, G. E.; Malomed, B. A.

    2015-10-01

    The recent analysis, based on the mean-field approximation (MFA), has predicted that the critical quantum collapse of the bosonic wave function, pulled to the center by the inverse-square potential in the three-dimensional space, is suppressed by the repulsive cubic nonlinearity in the bosonic gas, the collapsing ground state being replaced by a regular one. We demonstrate that a similar stabilization acts in a quantum many-body system, beyond the MFA. While the collapse remains possible, repulsive two-particle interactions give rise to a metastable gaseous state, which is separated by a potential barrier from the collapsing regime. The stability of this state improves with the increase of the number of particles. The results are produced by calculations of the variational energy, with the help of the Monte Carlo method.

  20. Dynamics and asymptotics of correlations in a many-body localized system

    NASA Astrophysics Data System (ADS)

    Campbell, Steve; Power, Matthew J. M.; De Chiara, Gabriele

    2017-08-01

    We examine the dynamics of nearest-neighbor bipartite concurrence and total correlations in the spin-1/2 XXZ model with random fields. We show, starting from factorized random initial states, that the concurrence can suffer entanglement sudden death in the long time limit and therefore may not be a useful indicator of the properties of the system. In contrast, we show that the total correlations capture the dynamics more succinctly, and further reveal a fundamental difference in the dynamics governed by the ergodic versus many-body localized phases, with the latter exhibiting dynamical oscillations. Finally, we consider an initial state composed of several singlet pairs and show that by fixing the correlation properties, while the dynamics do not reveal noticeable differences between the phases, the long-time values of the correlation measures appear to indicate the critical region.

  1. Understanding the many-body expansion for large systems. II. Accuracy considerations

    NASA Astrophysics Data System (ADS)

    Lao, Ka Un; Liu, Kuan-Yu; Richard, Ryan M.; Herbert, John M.

    2016-04-01

    To complement our study of the role of finite precision in electronic structure calculations based on a truncated many-body expansion (MBE, or "n-body expansion"), we examine the accuracy of such methods in the present work. Accuracy may be defined either with respect to a supersystem calculation computed at the same level of theory as the n-body calculations, or alternatively with respect to high-quality benchmarks. Both metrics are considered here. In applications to a sequence of water clusters, (H2O)N=6-55 described at the B3LYP/cc-pVDZ level, we obtain mean absolute errors (MAEs) per H2O monomer of ˜1.0 kcal/mol for two-body expansions, where the benchmark is a B3LYP/cc-pVDZ calculation on the entire cluster. Three- and four-body expansions exhibit MAEs of 0.5 and 0.1 kcal/mol/monomer, respectively, without resort to charge embedding. A generalized many-body expansion truncated at two-body terms [GMBE(2)], using 3-4 H2O molecules per fragment, outperforms all of these methods and affords a MAE of ˜0.02 kcal/mol/monomer, also without charge embedding. GMBE(2) requires significantly fewer (although somewhat larger) subsystem calculations as compared to MBE(4), reducing problems associated with floating-point roundoff errors. When compared to high-quality benchmarks, we find that error cancellation often plays a critical role in the success of MBE(n) calculations, even at the four-body level, as basis-set superposition error can compensate for higher-order polarization interactions. A many-body counterpoise correction is introduced for the GMBE, and its two-body truncation [GMBCP(2)] is found to afford good results without error cancellation. Together with a method such as ωB97X-V/aug-cc-pVTZ that can describe both covalent and non-covalent interactions, the GMBE(2)+GMBCP(2) approach provides an accurate, stable, and tractable approach for large systems.

  2. Efficient calculation of many-body induced electrostatics in molecular systems.

    PubMed

    McLaughlin, Keith; Cioce, Christian R; Pham, Tony; Belof, Jonathan L; Space, Brian

    2013-11-14

    Potential energy functions including many-body polarization are in widespread use in simulations of aqueous and biological systems, metal-organics, molecular clusters, and other systems where electronically induced redistribution of charge among local atomic sites is of importance. The polarization interactions, treated here via the methods of Thole and Applequist, while long-ranged, can be computed for moderate-sized periodic systems with extremely high accuracy by extending Ewald summation to the induced fields as demonstrated by Nymand, Sala, and others. These full Ewald polarization calculations, however, are expensive and often limited to very small systems, particularly in Monte Carlo simulations, which may require energy evaluation over several hundred-thousand configurations. For such situations, it shall be shown that sufficiently accurate computation of the polarization energy can be produced in a fraction of the central processing unit (CPU) time by neglecting the long-range extension to the induced fields while applying the long-range treatments of Ewald or Wolf to the static fields; these methods, denoted Ewald E-Static and Wolf E-Static (WES), respectively, provide an effective means to obtain polarization energies for intermediate and large systems including those with several thousand polarizable sites in a fraction of the CPU time. Furthermore, we shall demonstrate a means to optimize the damping for WES calculations via extrapolation from smaller trial systems.

  3. Signatures of Many-Body Localization in a Controlled Open Quantum System

    NASA Astrophysics Data System (ADS)

    Lüschen, Henrik P.; Bordia, Pranjal; Hodgman, Sean S.; Schreiber, Michael; Sarkar, Saubhik; Daley, Andrew J.; Fischer, Mark H.; Altman, Ehud; Bloch, Immanuel; Schneider, Ulrich

    2017-01-01

    In the presence of disorder, an interacting closed quantum system can undergo many-body localization (MBL) and fail to thermalize. However, over long times, even weak couplings to any thermal environment will necessarily thermalize the system and erase all signatures of MBL. This presents a challenge for experimental investigations of MBL since no realistic system can ever be fully closed. In this work, we experimentally explore the thermalization dynamics of a localized system in the presence of controlled dissipation. Specifically, we find that photon scattering results in a stretched exponential decay of an initial density pattern with a rate that depends linearly on the scattering rate. We find that the resulting susceptibility increases significantly close to the phase transition point. In this regime, which is inaccessible to current numerical studies, we also find a strong dependence on interactions. Our work provides a basis for systematic studies of MBL in open systems and opens a route towards extrapolation of closed-system properties from experiments.

  4. Many-body localization in disorder-free systems: The importance of finite-size constraints

    SciTech Connect

    Papić, Z.; Stoudenmire, E. Miles; Abanin, Dmitry A.

    2015-11-15

    Recently it has been suggested that many-body localization (MBL) can occur in translation-invariant systems, and candidate 1D models have been proposed. We find that such models, in contrast to MBL systems with quenched disorder, typically exhibit much more severe finite-size effects due to the presence of two or more vastly different energy scales. In a finite system, this can artificially split the density of states (DOS) into bands separated by large gaps. We argue for such models to faithfully represent the thermodynamic limit behavior, the ratio of relevant coupling must exceed a certain system-size depedent cutoff, chosen such that various bands in the DOS overlap one another. Setting the parameters this way to minimize finite-size effects, we study several translation-invariant MBL candidate models using exact diagonalization. Based on diagnostics including entanglement and local observables, we observe thermal (ergodic), rather than MBL-like behavior. Our results suggest that MBL in translation-invariant systems with two or more very different energy scales is less robust than perturbative arguments suggest, possibly pointing to the importance of non-perturbative effects which induce delocalization in the thermodynamic limit.

  5. Transport properties across the many-body localization transition in quasiperiodic and random systems

    NASA Astrophysics Data System (ADS)

    Setiawan, F.; Deng, Dong-Ling; Pixley, J. H.

    2017-09-01

    We theoretically study transport properties in one-dimensional interacting quasiperiodic systems at infinite temperature. We compare and contrast the dynamical transport properties across the many-body localization (MBL) transition in quasiperiodic and random models. Using exact diagonalization we compute the optical conductivity σ (ω ) and the return probability R (τ ) and study their average low-frequency and long-time power-law behavior, respectively. We show that the low-energy transport dynamics is markedly distinct in both the thermal and MBL phases in quasiperiodic and random models and find that the diffusive and MBL regimes of the quasiperiodic model are more robust than those in the random system. Using the distribution of the dc conductivity, we quantify the contribution of sample-to-sample and state-to-state fluctuations of σ (ω ) across the MBL transition. We find that the activated dynamical scaling ansatz works poorly in the quasiperiodic model but holds in the random model with an estimated activation exponent ψ ≈0.9 . We argue that near the MBL transition in quasiperiodic systems, critical eigenstates give rise to a subdiffusive crossover regime on finite-size systems.

  6. Stochastic many-body problems in ecology, evolution, neuroscience, and systems biology

    NASA Astrophysics Data System (ADS)

    Butler, Thomas C.

    Using the tools of many-body theory, I analyze problems in four different areas of biology dominated by strong fluctuations: The evolutionary history of the genetic code, spatiotemporal pattern formation in ecology, spatiotemporal pattern formation in neuroscience and the robustness of a model circadian rhythm circuit in systems biology. In the first two research chapters, I demonstrate that the genetic code is extremely optimal (in the sense that it manages the effects of point mutations or mistranslations efficiently), more than an order of magnitude beyond what was previously thought. I further show that the structure of the genetic code implies that early proteins were probably only loosely defined. Both the nature of early proteins and the extreme optimality of the genetic code are interpreted in light of recent theory [1] as evidence that the evolution of the genetic code was driven by evolutionary dynamics that were dominated by horizontal gene transfer. I then explore the optimality of a proposed precursor to the genetic code. The results show that the precursor code has only limited optimality, which is interpreted as evidence that the precursor emerged prior to translation, or else never existed. In the next part of the dissertation, I introduce a many-body formalism for reaction-diffusion systems described at the mesoscopic scale with master equations. I first apply this formalism to spatially-extended predator-prey ecosystems, resulting in the prediction that many-body correlations and fluctuations drive population cycles in time, called quasicycles. Most of these results were previously known, but were derived using the system size expansion [2, 3]. I next apply the analytical techniques developed in the study of quasi-cycles to a simple model of Turing patterns in a predator-prey ecosystem. This analysis shows that fluctuations drive the formation of a new kind of spatiotemporal pattern formation that I name "quasi-patterns." These quasi

  7. Dynamics of entanglement among the environment oscillators of a many-body system

    NASA Astrophysics Data System (ADS)

    de Paula, A. L.; Freitas, Dagoberto S.

    2016-06-01

    In this work, we extend the discussion that began in Ref. 16 [A. L. de Paula, Jr., J. G. G. de Oliveira, Jr., J. G. P. de Faria, D. S. Freitas and M. C. Nemes, Phys. Rev. A 89 (2014) 022303] to deal with the dynamics of the concurrence of a many-body system. In that previous paper, the discussion was focused on the residual entanglement between the partitions of the system. The purpose of the present contribution is to shed some light on the dynamical properties of entanglement among the environment oscillators. We consider a system consisting of a harmonic oscillator linearly coupled to N others and solve the corresponding dynamical problem analytically. We divide the environment into two arbitrary partitions and the entanglement dynamics between any of these partitions is quantified and it shows that in the case when excitations in each partition are equal, the concurrence reaches the value 1 and the two partitions of the environment are maximally entangled. For long times, the excitations of the main oscillator are completely transferred to environment and the environment oscillators are found entangled.

  8. Quantum Correlations, Separability, and Quantum Coherence Length in Equilibrium Many-Body Systems

    NASA Astrophysics Data System (ADS)

    Malpetti, Daniele; Roscilde, Tommaso

    2016-09-01

    Nonlocality is a fundamental trait of quantum many-body systems, both at the level of pure states, as well as at the level of mixed states. Because of nonlocality, mixed states of any two subsystems are correlated in a stronger way than what can be accounted for by considering the correlated probabilities of occupying some microstates. In the case of equilibrium mixed states, we explicitly build two-point quantum correlation functions, which capture the specific, superior correlations of quantum systems at finite temperature, and which are directly accessible to experiments when correlating measurable properties. When nonvanishing, these correlation functions rule out a precise form of separability of the equilibrium state. In particular, we show numerically that quantum correlation functions generically exhibit a finite quantum coherence length, dictating the characteristic distance over which degrees of freedom cannot be considered as separable. This coherence length is completely disconnected from the correlation length of the system—as it remains finite even when the correlation length of the system diverges at finite temperature—and it unveils the unique spatial structure of quantum correlations.

  9. Measuring the dynamic structure factor of a dissipative quantum many-body system

    NASA Astrophysics Data System (ADS)

    Donner, Tobias; Landig, Renate; Mottl, Rafael; Hruby, Lorenz; Brennecke, Ferdinand; Esslinger, Tilman

    2014-05-01

    A Bose-Einstein condensate whose motional degrees of freedom are coupled to a high-finesse optical cavity via a transverse pump beam constitutes a dissipative quantum many-body system with long range interactions. These interactions can induce a structural phase transition from a flat to a density-modulated state. The transverse pump field simultaneously represents a probe of the atomic density via cavity-enhanced Bragg scattering. By spectrally analysing the light field leaking out of the cavity, we measure non-destructively the dynamic structure factor of the fluctuating atomic density while the system undergoes the phase transition. An observed asymmetry in the dynamic structure factor is attributed to the coupling to dissipative baths. Critical exponents for both sides of the phase transition can be extracted from the data. We further discuss our progress in adding strong short-range interactions to this system, in order to explore Bose-Hubbard physics with cavity-mediated long-range interactions and self-organization in lower dimensions.

  10. Experimental demonstration of Rydberg dressing in a many-body system

    NASA Astrophysics Data System (ADS)

    Zeiher, Johannes; Schauss, Peter; Hild, Sebastian; Rubio-Abadal, Antonio; Choi, Jae-Yoon; van Bijnen, Rick; Pohl, Thomas; Bloch, Immanuel; Gross, Christian

    2016-05-01

    Rydberg atoms offer the possibility to study long range interacting systems of ultracold atoms due to their strong van der Waals interactions. Admixture of a Rydberg state to a ground state, known as Rydberg dressing, allows for increased experimental tunability of these interactions and promises to study novel phases of matter. Here we report on our results of the realization of Rydberg dressing in a many-body spin system. Starting from a two-dimensional spin-polarized Mott insulator of an ultracold gas of rubidium-87, we optically couple one spin component to a Rydberg p-state on a single photon ultra-violet transition at 297 nm. Using microwave Ramsey interferometry in the ground state manifold, we measure the spin-spin correlations emerging due to the admixture of long range interactions to the ground state. To show the predicted versatility of Rydberg dressing, we tune the range and anisotropy of the interaction. We furthermore discuss loss processes affecting our dressed ensembles and present initial indications of improved lifetimes in our system. Our results constitute an important step towards the realization of novel spin models with Rydberg dressed interactions.

  11. Local Convertibility and the Quantum Simulation of Edge States in Many-Body Systems

    NASA Astrophysics Data System (ADS)

    Franchini, Fabio; Cui, Jian; Amico, Luigi; Fan, Heng; Gu, Mile; Korepin, Vladimir; Kwek, Leong Chuan; Vedral, Vlatko

    2014-10-01

    In some many-body systems, certain ground-state entanglement (Rényi) entropies increase even as the correlation length decreases. This entanglement nonmonotonicity is a potential indicator of nonclassicality. In this work, we demonstrate that such a phenomenon, known as lack of local convertibility, is due to the edge-state (de)construction occurring in the system. To this end, we employ the example of the Ising chain, displaying an order-disorder quantum phase transition. Employing both analytical and numerical methods, we compute entanglement entropies for various system bipartitions (A |B ) and consider ground states with and without Majorana edge states. We find that the thermal ground states, enjoying the Hamiltonian symmetries, show lack of local convertibility if either A or B is smaller than, or of the order of, the correlation length. In contrast, the ordered (symmetry-breaking) ground state is always locally convertible. The edge-state behavior explains all these results and could disclose a paradigm to understand local convertibility in other quantum phases of matter. The connection we establish between convertibility and nonlocal, quantum correlations provides a clear criterion of which features a universal quantum simulator should possess to outperform a classical machine.

  12. Electrostatically Embedded Many-Body Expansion for Neutral and Charged Metalloenzyme Model Systems.

    PubMed

    Kurbanov, Elbek K; Leverentz, Hannah R; Truhlar, Donald G; Amin, Elizabeth A

    2012-01-10

    The electrostatically embedded many-body (EE-MB) method has proven accurate for calculating cohesive and conformational energies in clusters, and it has recently been extended to obtain bond dissociation energies for metal-ligand bonds in positively charged inorganic coordination complexes. In the present paper, we present four key guidelines that maximize the accuracy and efficiency of EE-MB calculations for metal centers. Then, following these guidelines, we show that the EE-MB method can also perform well for bond dissociation energies in a variety of neutral and negatively charged inorganic coordination systems representing metalloenzyme active sites, including a model of the catalytic site of the zinc-bearing anthrax toxin lethal factor, a popular target for drug development. In particular, we find that the electrostatically embedded three-body (EE-3B) method is able to reproduce conventionally calculated bond-breaking energies in a series of pentacoordinate and hexacoordinate zinc-containing systems with an average absolute error (averaged over 25 cases) of only 0.98 kcal/mol.

  13. Self-similar nonequilibrium dynamics of a many-body system with power-law interactions

    NASA Astrophysics Data System (ADS)

    Gutiérrez, Ricardo; Garrahan, Juan P.; Lesanovsky, Igor

    2015-12-01

    The influence of power-law interactions on the dynamics of many-body systems far from equilibrium is much less explored than their effect on static and thermodynamic properties. To gain insight into this problem we introduce and analyze here an out-of-equilibrium deposition process in which the deposition rate of a given particle depends as a power law on the distance to previously deposited particles. This model draws its relevance from recent experimental progress in the domain of cold atomic gases, which are studied in a setting where atoms that are excited to high-lying Rydberg states interact through power-law potentials that translate into power-law excitation rates. The out-of-equilibrium dynamics of this system turns out to be surprisingly rich. It features a self-similar evolution which leads to a characteristic power-law time dependence of observables such as the particle concentration, and results in a scale invariance of the structure factor. Our findings show that in dissipative Rydberg gases out of equilibrium the characteristic distance among excitations—often referred to as the blockade radius—is not a static but rather a dynamic quantity.

  14. Self-similar nonequilibrium dynamics of a many-body system with power-law interactions.

    PubMed

    Gutiérrez, Ricardo; Garrahan, Juan P; Lesanovsky, Igor

    2015-12-01

    The influence of power-law interactions on the dynamics of many-body systems far from equilibrium is much less explored than their effect on static and thermodynamic properties. To gain insight into this problem we introduce and analyze here an out-of-equilibrium deposition process in which the deposition rate of a given particle depends as a power law on the distance to previously deposited particles. This model draws its relevance from recent experimental progress in the domain of cold atomic gases, which are studied in a setting where atoms that are excited to high-lying Rydberg states interact through power-law potentials that translate into power-law excitation rates. The out-of-equilibrium dynamics of this system turns out to be surprisingly rich. It features a self-similar evolution which leads to a characteristic power-law time dependence of observables such as the particle concentration, and results in a scale invariance of the structure factor. Our findings show that in dissipative Rydberg gases out of equilibrium the characteristic distance among excitations-often referred to as the blockade radius-is not a static but rather a dynamic quantity.

  15. Extracting signatures of quantum criticality in the finite-temperature behavior of many-body systems

    NASA Astrophysics Data System (ADS)

    Cuccoli, Alessandro; Taiti, Alessio; Vaia, Ruggero; Verrucchi, Paola

    2007-08-01

    We face the problem of detecting and featuring footprints of quantum criticality in the finite-temperature behavior of quantum many-body systems. Our strategy is that of comparing the phase diagram of a system displaying a T=0 quantum phase transition with that of its classical limit, in order to single out the genuinely quantum effects. To this aim, we consider the one-dimensional Ising model in a transverse field: while the quantum S=1/2 Ising chain is exactly solvable and extensively studied, results for the classical limit (S→∞) of such model are lacking, and we supply them here. They are obtained numerically, via the transfer-matrix method, and their asymptotic low-temperature behavior is also derived analytically by self-consistent spin-wave theory. We draw the classical phase diagram according to the same procedure followed in the quantum analysis, and the two phase diagrams are found unexpectedly similar: Three regimes are detected also in the classical case, each characterized by a functional dependence of the correlation length on temperature and field analogous to that of the quantum model. What discriminates the classical from the quantum case are the different values of the exponents entering such dependencies, a consequence of the different nature of zero-temperature quantum fluctuations with respect to the thermal ones.

  16. Reduced-density-matrix spectrum and block entropy of permutationally invariant many-body systems.

    PubMed

    Salerno, Mario; Popkov, Vladislav

    2010-07-01

    Spectral properties of the reduced density matrix (RDM) of permutational invariant quantum many-body systems are investigated. The RDM block diagonalization which accounts for all symmetries of the Hamiltonian is achieved. The analytical expression of the RDM spectrum is provided for arbitrary parameters and rigorously proved in the thermodynamical limit. The existence of several sum rules and recurrence relations among RDM eigenvalues is also demonstrated and the distribution function of RDM eigenvalues (including degeneracies) characterized. In particular, we prove that the distribution function approaches a two-dimensional Gaussian in the limit of large subsystem sizes n>1. As a physical application we discuss the von Neumann entropy (VNE) of a block of size n for a system of hard-core bosons on a complete graph, as a function of n and of the temperature T. The occurrence of a crossover of VNE from purely logarithmic behavior at T=0 to a purely linear behavior in n for T≥Tc, is demonstrated.

  17. Rahman Prize Talk: Pushing the frontier in the simulation of correlated quantum many body systems

    NASA Astrophysics Data System (ADS)

    Troyer, Matthias

    Amazing progress in the simulation of correlated quantum many body systems has been achieved in the past two decades by combining significant advances in new algorithms with efficient implementations on ever faster supercomputers. This has enabled the accurate simulation of an increasing number of problems and helped settle many open questions. I will review a selection of results that my collaborators and I have worked on, from quantum phase transitions in quantum magnets, over supersolidity of bosons in lattice models and Helium-4 to recent simulations of correlated fermions and quantum gases. I will then provide an outlook to the future and discuss how in the short term analog quantum simulators can help tackle problems for which no efficient simulation algorithms exist and how in the longer term quantum computers can be used to solve many of the still open questions in the field. I will finally connect to the topic of the remainder of this symposium by touching on how the design of new topological materials will help in the construction of these quantum computers.

  18. Many-body quantum dynamics by adiabatic path-integral molecular dynamics: Disordered Frenkel Kontorova models

    NASA Astrophysics Data System (ADS)

    Krajewski, Florian R.; Müser, Martin H.

    2005-07-01

    The spectral density of quantum mechanical Frenkel Kontorova chains moving in disordered, external potentials is investigated by means of path-integral molecular dynamics. If the second moment of the embedding potential is well defined (roughness exponent H=0), there is one regime in which the chain is pinned (large masses m of chain particles) and one in which it is unpinned (small m). If the embedding potential can be classified as a random walk on large length scales ( H=1/2), then the chain is always pinned irrespective of the value of m. For H=1/2, two phonon-like branches appear in the spectra.

  19. PREFACE: Many-body correlations from dilute to dense nuclear systems

    NASA Astrophysics Data System (ADS)

    Otsuka, Takaharu; Urban, Michael; Yamada, Taiichi

    2011-09-01

    The International EFES-IN2P3 conference on "Many body correlations from dilute to dense nuclear systems" was held at the Institut Henri Poincaré (IHP), Paris, France, from 15-18 February 2011, on the occasion of the retirement of our colleague Peter Schuck. Correlations play a decisive role in various many-body systems such as nuclear systems, condensed matter and quantum gases. Important examples include: pairing correlations (Cooper pairs) which give rise to nuclear superfluidity (analogous to superconductivity in condensed matter); particle-hole (RPA) correlations in the description of the ground state beyond mean-field theory; clusters; and α-particle correlations in certain nuclei. Also, the nucleons themselves can be viewed as clusters of three quarks. During the past few years, researchers have started to study how the character of these correlations changes with the variation of the density. For instance, the Cooper pairs in dense matter can transform into a Bose-Einstein condensate (BEC) of true bound states at low density (this is the BCS-BEC crossover studied in ultracold Fermi gases). Similar effects play a role in neutron matter at low density, e.g., in the "neutron skin" of exotic nuclei. The α-cluster correlation becomes particularly important at lower density, such as in the excited states of some nuclei (e.g., the α-condensate-like structure in the Hoyle state of 12C) or in the formation of compact stars. In addition to nuclear physics, topics from astrophysics (neutron stars), condensed matter, and quantum gases were discussed in 48 talks and 19 posters, allowing the almost 90 participants from different communities to exchange their ideas, experiences and methods. The conference dinner took place at the Musée d'Orsay, and all the participants enjoyed the very pleasant atmosphere. One session of the conference was dedicated to the celebration of Peter's retirement. We would like to take this opportunity to wish Peter all the best and we hope

  20. Electrostatically Embedded Many-Body Expansion for Large Systems, with Applications to Water Clusters.

    PubMed

    Dahlke, Erin E; Truhlar, Donald G

    2007-01-01

    The use of background molecular charge to incorporate environmental effects on a molecule or active site is widely employed in quantum chemistry. In the present article we employ this practice in conjunction with many-body expansions. In particular, we present electrostatically embedded two-body and three-body expansions for calculating the energies of molecular clusters. The system is divided into fragments, and dimers or trimers of fragments are calculated in a field of point charges representing the electrostatic potential of the other fragments. We find that including environmental point charges can lower the errors in the electrostatically embedded pairwise additive (EE-PA) energies for a series of water clusters by as much as a factor of 10 when compared to the traditional pairwise additive approximation and that for the electrostatically embedded three-body (EE-3B) method the average mean unsigned error over nine different levels of theory for a set of six tetramers and one pentamer is only 0.05 kcal/mol, which is only 0.4% of the mean unsigned net interaction energy. We also test the accuracy of the EE-PA and EE-3B methods for a cluster of 21 water molecules and find that the errors relative to a full MP2/aug'-cc-pVTZ calculation to be only 2.97 and 0.38 kcal/mol, respectively, which are only 1.5% and 0.2%, respectively, of the net interaction energy. This method offers the advantage over some other fragment-based methods in that it does not use an iterative method to determine the charges and thus provides substantial savings for large clusters. The method is convenient to adapt to a variety of electronic structure methods and program packages, it has N(2) or N(3) computational scaling for large systems (where N is the number of fragments), it is easily converted to an O(N) method, and its linearity allows for convenient analytic gradients.

  1. More many-body perturbation theory for an electron-ion system

    SciTech Connect

    Baker, G.A. Jr.; Johnson, J.D.

    1997-10-01

    From previous finite-temperature, quantum, many-body perturbation theory results for the grand partition function of an electron-ion fluid through order {epsilon}{sup 4}, we compute the electron and ion fugacities in terms of the volume per ion and the temperature to that same order in perturbation theory. From these results we also give the pressure, again to the same order in perturbation theory about the values for the non-interacting fluid.

  2. Tensor-optimized antisymmetrized molecular dynamics as a successive variational method in nuclear many-body system

    NASA Astrophysics Data System (ADS)

    Myo, Takayuki; Toki, Hiroshi; Ikeda, Kiyomi; Horiuchi, Hisashi; Suhara, Tadahiro

    2017-06-01

    We study the tensor-optimized antisymmetrized molecular dynamics (TOAMD) as a successive variational method in many-body systems with strong interaction for nuclei. In TOAMD, the correlation functions for the tensor force and the short-range repulsion and their multiples are operated to the AMD state as the variational wave function. The total wave function is expressed as the sum of all the components and the variational space can be increased successively with the multiple correlation functions to achieve convergence. All the necessary matrix elements of many-body operators, consisting of the multiple correlation functions and the Hamiltonian, are expressed analytically using the Gaussian integral formula. In this paper we show the results of TOAMD with up to the double products of the correlation functions for the s-shell nuclei, 3H and 4He, using the nucleon-nucleon interaction AV8‧. It is found that the energies and Hamiltonian components of two nuclei converge rapidly with respect to the multiple of correlation functions. This result indicates the efficiency of TOAMD for the power series expansion in terms of the tensor and short-range correlation functions.

  3. Negative differential gain in quantum dot systems: Interplay of structural properties and many-body effects

    SciTech Connect

    Goldmann, E. Jahnke, F.; Lorke, M.; Frauenheim, T.

    2014-06-16

    The saturation behaviour of optical gain with increasing excitation density is an important factor for laser device performance. For active materials based on self-organized InGaAs/GaAs quantum dots, we study the interplay between structural properties of the quantum dots and many-body effects of excited carriers in the optical properties via a combination of tight-binding and quantum-kinetic calculations. We identify regimes where either phase-space filling or excitation-induced dephasing dominates the saturation behavior of the optical gain. The latter can lead to the emergence of a negative differential material gain.

  4. Radiative heat transfer in many-body systems: Coupled electric and magnetic dipole approach

    NASA Astrophysics Data System (ADS)

    Dong, Jian; Zhao, Junming; Liu, Linhua

    2017-03-01

    The many-body radiative heat transfer theory [P. Ben-Abdallah, S.-A. Biehs, and K. Joulain, Phys. Rev. Lett. 107, 114301 (2011), 10.1103/PhysRevLett.107.114301] considered only the contribution from the electric dipole moment. For metal particles, however, the magnetic dipole moment due to eddy current plays an important role, which can further couple with the electric dipole moment to introduce crossed terms. In this paper, we develop the coupled electric and magnetic dipole (CEMD) approach for the radiative heat transfer in a collection of objects in mutual interaction. Due to the coupled electric and magnetic interactions, four terms, namely the electric-electric, the electric-magnetic, the magnetic-electric, and the magnetic-magnetic terms, contribute to the radiative heat flux and the local energy density. The CEMD is applied to study the radiative heat transfer between various dimers of nanoparticles. It is found that each of the four terms can dominate the radiative heat transfer depending on the position and composition of particles. Moreover, near-field many-body interactions are studied by CEMD considering both dielectric and metallic nanoparticles. The near-field radiative heat flux and local energy density can be greatly increased when the particles are in coupled resonances. Surface plasmon polariton and surface phonon polariton can be coupled to enhance the radiative heat flux.

  5. Multiconfigurational time-dependent Hartree method for bosons: Many-body dynamics of bosonic systems

    NASA Astrophysics Data System (ADS)

    Alon, Ofir E.; Streltsov, Alexej I.; Cederbaum, Lorenz S.

    2008-03-01

    The evolution of Bose-Einstein condensates is amply described by the time-dependent Gross-Pitaevskii mean-field theory which assumes all bosons to reside in a single time-dependent one-particle state throughout the propagation process. In this work, we go beyond mean field and develop an essentially exact many-body theory for the propagation of the time-dependent Schrödinger equation of N interacting identical bosons. In our theory, the time-dependent many-boson wave function is written as a sum of permanents assembled from orthogonal one-particle functions, or orbitals, where both the expansion coefficients and the permanents (orbitals) themselves are time-dependent and fully determined according to a standard time-dependent variational principle. By employing either the usual Lagrangian formulation or the Dirac-Frenkel variational principle we arrive at two sets of coupled equations of motion, one for the orbitals and one for the expansion coefficients. The first set comprises of first-order differential equations in time and nonlinear integrodifferential equations in position space, whereas the second set consists of first-order differential equations with time-dependent coefficients. We call our theory multiconfigurational time-dependent Hartree for bosons, or MCTDHB(M) , where M specifies the number of time-dependent orbitals used to construct the permanents. Numerical implementation of the theory is reported and illustrative numerical examples of many-body dynamics of trapped Bose-Einstein condensates are provided and discussed. The convergence of the method with a growing number M of orbitals is demonstrated in a specific example of four interacting bosons in a double well.

  6. Scrambling and thermalization in a diffusive quantum many-body system

    NASA Astrophysics Data System (ADS)

    Bohrdt, A.; Mendl, C. B.; Endres, M.; Knap, M.

    2017-06-01

    Out-of-time ordered (OTO) correlation functions describe scrambling of information in correlated quantum matter. They are of particular interest in incoherent quantum systems lacking well defined quasi-particles. Thus far, it is largely elusive how OTO correlators spread in incoherent systems with diffusive transport governed by a few globally conserved quantities. Here, we study the dynamical response of such a system using high-performance matrix-product-operator techniques. Specifically, we consider the non-integrable, one-dimensional Bose-Hubbard model in the incoherent high-temperature regime. Our system exhibits diffusive dynamics in time-ordered correlators of globally conserved quantities, whereas OTO correlators display a ballistic, light-cone spreading of quantum information. The slowest process in the global thermalization of the system is thus diffusive, yet information spreading is not inhibited by such slow dynamics. We furthermore develop an experimentally feasible protocol to overcome some challenges faced by existing proposals and to probe time-ordered and OTO correlation functions. Our study opens new avenues for both the theoretical and experimental exploration of thermalization and information scrambling dynamics.

  7. Scrambling and thermalization in a diffusive quantum many-body system

    DOE PAGES

    Bohrdt, A.; Mendl, C. B.; Endres, M.; ...

    2017-06-02

    Out-of-time ordered (OTO) correlation functions describe scrambling of information in correlated quantum matter. They are of particular interest in incoherent quantum systems lacking well defined quasi-particles. Thus far, it is largely elusive how OTO correlators spread in incoherent systems with diffusive transport governed by a few globally conserved quantities. Here, we study the dynamical response of such a system using high-performance matrix-product-operator techniques. Specifically, we consider the non-integrable, one-dimensional Bose–Hubbard model in the incoherent high-temperature regime. Our system exhibits diffusive dynamics in time-ordered correlators of globally conserved quantities, whereas OTO correlators display a ballistic, light-cone spreading of quantum information. Themore » slowest process in the global thermalization of the system is thus diffusive, yet information spreading is not inhibited by such slow dynamics. We furthermore develop an experimentally feasible protocol to overcome some challenges faced by existing proposals and to probe time-ordered and OTO correlation functions. As a result, our study opens new avenues for both the theoretical and experimental exploration of thermalization and information scrambling dynamics.« less

  8. Coherent Imaging Spectroscopy of a Quantum Many-Body Spin System

    NASA Astrophysics Data System (ADS)

    Smith, Jacob; Senko, Crystal; Richerme, Phil; Lee, Aaron; Campbell, Wes; Monroe, Chris

    2014-05-01

    Trapped-ion quantum simulators are a promising candidate for exploring quantum-many-body physics, such as quantum magnetism, that are difficult to examine in condensed-matter experiments or using classical simulation. We demonstrate a coherent imaging spectroscopic technique to validate a quantum simulation. In this work, we study fully-connected transverse Ising models with a chain of up to 18 171Yb+ ions. Here, We resolve the state of each spin by collecting the spin-dependent fluorescence on a camera in order to map the complete energy spectrum and fully characterize the spin-spin couplings, while also engineering entangled states and measuring the critical gap near a quantum phase transition. We expect this general technique to become an important verification tool for quantum simulators. This work is supported by grants from the U.S. Army Research Office with funding from the DARPA OLE program, IARPA, and the MURI program; and the NSF Physics Frontier Center at JQI.

  9. Quantum phases and transitions of many-body systems realized using cold atomic gases

    NASA Astrophysics Data System (ADS)

    Powell, Stephen Christopher

    In recent years, new advances in techniques for trapping and cooling atoms have allowed the production of atomic gases at low-enough temperatures and high-enough densities for collective quantum-mechanical effects to become important. This thesis describes theoretical investigations of certain many-body physics problems motivated by these experimental developments. It consists of two main parts. In the first, I investigate the array of phases exhibited by degenerate mixtures of bosons and fermions with a Feshbach resonance, a bound molecular state whose energy can be tuned with a magnetic field. These phases are distinguished by the presence or absence of a bosonic condensate and also by the different Luttinger constraints that are shown to apply to the Fermi surface(s). The second part is concerned with bosons in an optical lattice, in which a periodic potential is produced by counterpropagating lasers. Spinless bosons are known to exhibit a quantum phase transition between a Mott insulator and a superfluid state, while bosons with spin have a much richer phase structure. I consider, in particular, a phase transition with a spinless order parameter, and show that the long-time dynamics of spin-carrying excitations is governed by a nontrivial fixed point. The corresponding anomalous exponents are found using a renormalization-group calculation.

  10. Understanding the many-body expansion for large systems. I. Precision considerations

    SciTech Connect

    Richard, Ryan M.; Lao, Ka Un; Herbert, John M.

    2014-07-07

    Electronic structure methods based on low-order “n-body” expansions are an increasingly popular means to defeat the highly nonlinear scaling of ab initio quantum chemistry calculations, taking advantage of the inherently distributable nature of the numerous subsystem calculations. Here, we examine how the finite precision of these subsystem calculations manifests in applications to large systems, in this case, a sequence of water clusters ranging in size up to (H{sub 2}O){sub 47}. Using two different computer implementations of the n-body expansion, one fully integrated into a quantum chemistry program and the other written as a separate driver routine for the same program, we examine the reproducibility of total binding energies as a function of cluster size. The combinatorial nature of the n-body expansion amplifies subtle differences between the two implementations, especially for n ⩾ 4, leading to total energies that differ by as much as several kcal/mol between two implementations of what is ostensibly the same method. This behavior can be understood based on a propagation-of-errors analysis applied to a closed-form expression for the n-body expansion, which is derived here for the first time. Discrepancies between the two implementations arise primarily from the Coulomb self-energy correction that is required when electrostatic embedding charges are implemented by means of an external driver program. For reliable results in large systems, our analysis suggests that script- or driver-based implementations should read binary output files from an electronic structure program, in full double precision, or better yet be fully integrated in a way that avoids the need to compute the aforementioned self-energy. Moreover, four-body and higher-order expansions may be too sensitive to numerical thresholds to be of practical use in large systems.

  11. Understanding the many-body expansion for large systems. I. Precision considerations

    NASA Astrophysics Data System (ADS)

    Richard, Ryan M.; Lao, Ka Un; Herbert, John M.

    2014-07-01

    Electronic structure methods based on low-order "n-body" expansions are an increasingly popular means to defeat the highly nonlinear scaling of ab initio quantum chemistry calculations, taking advantage of the inherently distributable nature of the numerous subsystem calculations. Here, we examine how the finite precision of these subsystem calculations manifests in applications to large systems, in this case, a sequence of water clusters ranging in size up to (H_2O)_{47}. Using two different computer implementations of the n-body expansion, one fully integrated into a quantum chemistry program and the other written as a separate driver routine for the same program, we examine the reproducibility of total binding energies as a function of cluster size. The combinatorial nature of the n-body expansion amplifies subtle differences between the two implementations, especially for n ⩾ 4, leading to total energies that differ by as much as several kcal/mol between two implementations of what is ostensibly the same method. This behavior can be understood based on a propagation-of-errors analysis applied to a closed-form expression for the n-body expansion, which is derived here for the first time. Discrepancies between the two implementations arise primarily from the Coulomb self-energy correction that is required when electrostatic embedding charges are implemented by means of an external driver program. For reliable results in large systems, our analysis suggests that script- or driver-based implementations should read binary output files from an electronic structure program, in full double precision, or better yet be fully integrated in a way that avoids the need to compute the aforementioned self-energy. Moreover, four-body and higher-order expansions may be too sensitive to numerical thresholds to be of practical use in large systems.

  12. Understanding the many-body expansion for large systems. I. Precision considerations.

    PubMed

    Richard, Ryan M; Lao, Ka Un; Herbert, John M

    2014-07-07

    Electronic structure methods based on low-order "n-body" expansions are an increasingly popular means to defeat the highly nonlinear scaling of ab initio quantum chemistry calculations, taking advantage of the inherently distributable nature of the numerous subsystem calculations. Here, we examine how the finite precision of these subsystem calculations manifests in applications to large systems, in this case, a sequence of water clusters ranging in size up to (H₂O)₄₇. Using two different computer implementations of the n-body expansion, one fully integrated into a quantum chemistry program and the other written as a separate driver routine for the same program, we examine the reproducibility of total binding energies as a function of cluster size. The combinatorial nature of the n-body expansion amplifies subtle differences between the two implementations, especially for n ⩾ 4, leading to total energies that differ by as much as several kcal/mol between two implementations of what is ostensibly the same method. This behavior can be understood based on a propagation-of-errors analysis applied to a closed-form expression for the n-body expansion, which is derived here for the first time. Discrepancies between the two implementations arise primarily from the Coulomb self-energy correction that is required when electrostatic embedding charges are implemented by means of an external driver program. For reliable results in large systems, our analysis suggests that script- or driver-based implementations should read binary output files from an electronic structure program, in full double precision, or better yet be fully integrated in a way that avoids the need to compute the aforementioned self-energy. Moreover, four-body and higher-order expansions may be too sensitive to numerical thresholds to be of practical use in large systems.

  13. Experimental observation of the Poincaré-Birkhoff scenario in a driven many-body quantum system

    NASA Astrophysics Data System (ADS)

    Tomkovič, J.; Muessel, W.; Strobel, H.; Löck, S.; Schlagheck, P.; Ketzmerick, R.; Oberthaler, M. K.

    2017-01-01

    Accessing the connection between classical chaos and quantum many-body systems has been a long-standing experimental challenge. Here, we investigate the onset of chaos in periodically driven two-component Bose-Einstein condensates, whose small quantum uncertainties allow for exploring the phase space with high resolution. By analyzing the uncertainties of time-evolved many-body states, we find signatures of elliptic and hyperbolic periodic orbits generated according to the Poincaré-Birkhoff theorem, and the formation of a chaotic region at increasing driving strengths. The employed fluctuation analysis allows for probing the phase-space structure by use of only short-time quantum dynamics.

  14. Inevitable power-law behavior of isolated many-body quantum systems and how it anticipates thermalization

    NASA Astrophysics Data System (ADS)

    Távora, Marco; Torres-Herrera, E. J.; Santos, Lea F.

    2016-10-01

    Despite being ubiquitous, out-of-equilibrium quantum systems are much less understood than systems at equilibrium. Progress in the field has benefited from a symbiotic relationship between theoretical studies and new experiments on coherent dynamics. The present work strengthens this connection by providing a general picture of the relaxation process of isolated lattice many-body quantum systems that are routinely studied in experiments with cold atoms, ions traps, and nuclear magnetic resonance. We show numerically and analytically that the long-time decay of the probability for finding the system in its initial state necessarily shows a power-law behavior ∝t-γ . This happens independently of the details of the system, such as integrability, level repulsion, and the presence or absence of disorder. Information about the spectrum, the structure of the initial state, and the number of particles that interact simultaneously is contained in the value of γ . From it, we can anticipate whether the initial state will or will not thermalize.

  15. Effects of the interplay between initial state and Hamiltonian on the thermalization of isolated quantum many-body systems.

    PubMed

    Torres-Herrera, E J; Santos, Lea F

    2013-10-01

    We explore the role of the initial state on the onset of thermalization in isolated quantum many-body systems after a quench. The initial state is an eigenstate of an initial Hamiltonian H(I) and it evolves according to a different final Hamiltonian H(F). If the initial state has a chaotic structure with respect to H(F), i.e., if it fills the energy shell ergodically, thermalization is certain to occur. This happens when H(I) is a full random matrix, because its states projected onto H(F), are fully delocalized. The results for the observables then agree with those obtained with thermal states at infinite temperature. However, finite real systems with few-body interactions, as the ones considered here, are deprived of fully extended eigenstates, even when described by a nonintegrable Hamiltonian. We examine how the initial state delocalizes as it gets closer to the middle of the spectrum of H(F), causing the observables to approach thermal averages, be the models integrable or chaotic. Our numerical studies are based on initial states with energies that cover the entire lower half of the spectrum of one-dimensional Heisenberg spin-1/2 systems.

  16. Convergence of the many-body expansion of interaction potentials: From van der Waals to covalent and metallic systems

    SciTech Connect

    Hermann, Andreas; Krawczyk, Robert P.; Lein, Matthias; Schwerdtfeger, Peter; Hamilton, I. P.; Stewart, James J. P.

    2007-07-15

    The many-body expansion of the interaction potential between atoms and molecules is analyzed in detail for different types of interactions involving up to seven atoms. Elementary clusters of Ar, Na, Si, and, in particular, Au are studied, using first-principles wave-function- and density-functional-based methods to obtain the individual n-body contributions to the interaction energies. With increasing atom number the many-body expansion converges rapidly only for long-range weak interactions. Large oscillatory behavior is observed for other types of interactions. This is consistent with the fact that Au clusters up to a certain size prefer planar structures over the more compact three-dimensional Lennard-Jones-type structures. Several Au model potentials and semiempirical PM6 theory are investigated for their ability to reproduce the quantum results. We further investigate small water clusters as prototypes of hydrogen-bonded systems. Here, the many-body expansion converges rapidly, reflecting the localized nature of the hydrogen bond and justifying the use of two-body potentials to describe water-water interactions. The question of whether electron correlation contributions can be successfully modeled by a many-body interaction potential is also addressed.

  17. Many-body effects in intermolecular forces.

    PubMed

    Elrod, M J; Saykally, R J

    1994-11-01

    The authors provide a review and literature survey of many-body effects in intermolecular forces. Topics include experimental methods, theoretical methods, many-body effects in atomic systems, and many-body effects in aqueous and nonaqueous molecular systems.

  18. Preparing ground States of quantum many-body systems on a quantum computer.

    PubMed

    Poulin, David; Wocjan, Pawel

    2009-04-03

    Preparing the ground state of a system of interacting classical particles is an NP-hard problem. Thus, there is in general no better algorithm to solve this problem than exhaustively going through all N configurations of the system to determine the one with lowest energy, requiring a running time proportional to N. A quantum computer, if it could be built, could solve this problem in time sqrt[N]. Here, we present a powerful extension of this result to the case of interacting quantum particles, demonstrating that a quantum computer can prepare the ground state of a quantum system as efficiently as it does for classical systems.

  19. Preparing Ground States of Quantum Many-Body Systems on a Quantum Computer

    SciTech Connect

    Poulin, David; Wocjan, Pawel

    2009-04-03

    Preparing the ground state of a system of interacting classical particles is an NP-hard problem. Thus, there is in general no better algorithm to solve this problem than exhaustively going through all N configurations of the system to determine the one with lowest energy, requiring a running time proportional to N. A quantum computer, if it could be built, could solve this problem in time {radical}(N). Here, we present a powerful extension of this result to the case of interacting quantum particles, demonstrating that a quantum computer can prepare the ground state of a quantum system as efficiently as it does for classical systems.

  20. (The physics of cellular automata and coherence and chaos in classical many-body systems)

    SciTech Connect

    Not Available

    1992-06-24

    This report contains short discussions on the following topics: non-variational effects in a Ginzburg-Landau equation; algebraic correlations in conserved chaotic systems; chaotic interface models of turbulence; algebraic correlations in coupled order parameter systems; and dynamics of Josephson Junction arrays. (LSP)

  1. Universal Features of the Nonequilibrium Dynamics of Many-Body Quantum Systems

    NASA Astrophysics Data System (ADS)

    Santos, Lea; Torres-Herrera, Eduardo

    2014-05-01

    We describe the nonequilibrium dynamics of isolated quantum systems with two-body interactions. In these systems, the energy shell is a Gaussian of width σ and it gives the maximum possible spreading of the energy distribution of any initial state. When the distribution achieves this shape, the fidelity decay is Gaussian until saturation. This establishes a lower bound for the fidelity decay in realistic systems. We find excellent agreement between our numerics and the analytical expression for the fidelity. We also provide the general conditions under which the short-time dynamics of few-body observables is controlled by σ. The analyses are developed for systems, initial states, and observables accessible to experiments with cold atoms in optical lattices. This work was supported by the NSF grant No. DMR-1147430 and CONACyT, Mexico.

  2. Quantum Simulations of Many-Body Systems with Ultra-Cold Atoms

    DTIC Science & Technology

    2009-02-28

    Preparation of strongly correlated quantum phases, such as antiferromagnetic insulating or d-wave paired states of fcrmions in optical lattices. Approaches...d-wave paired states of fermions in optical lattices. Approaches studied included the dynamic changes of systems parameters, cooling, or their...blocks to construct a d-wave superfluid state . We described how to use the coherent dynamical evolution in such a system to experimentally probe the

  3. A Rigorous Theory of Many-Body Prethermalization for Periodically Driven and Closed Quantum Systems

    NASA Astrophysics Data System (ADS)

    Abanin, Dmitry; De Roeck, Wojciech; Ho, Wen Wei; Huveneers, François

    2017-09-01

    Prethermalization refers to the transient phenomenon where a system thermalizes according to a Hamiltonian that is not the generator of its evolution. We provide here a rigorous framework for quantum spin systems where prethermalization is exhibited for very long times. First, we consider quantum spin systems under periodic driving at high frequency {ν}. We prove that up to a quasi-exponential time {τ_* ˜ e^{c ν/log^3 ν}}, the system barely absorbs energy. Instead, there is an effective local Hamiltonian {\\widehat D} that governs the time evolution up to {τ_*}, and hence this effective Hamiltonian is a conserved quantity up to {τ_*}. Next, we consider systems without driving, but with a separation of energy scales in the Hamiltonian. A prime example is the Fermi-Hubbard model where the interaction U is much larger than the hopping J. Also here we prove the emergence of an effective conserved quantity, different from the Hamiltonian, up to a time {τ_*} that is (almost) exponential in {U/J}.

  4. Ergodicity in a two-dimensional self-gravitating many-body system

    NASA Astrophysics Data System (ADS)

    Silvestre, C. H.; Rocha Filho, T. M.

    2016-01-01

    We study the ergodic properties of a two-dimensional self-gravitating system using molecular dynamics simulations. We apply three different tests for ergodicity: a direct method comparing the time average of a particle momentum and position to the respective ensemble average, sojourn times statistics and the dynamical functional method. For comparison purposes they are also applied to a short-range interacting system and to the Hamiltonian mean-field model. Our results show that a two-dimensional self-gravitating system takes a very long time to establish ergodicity. If a Kac factor is used in the potential energy, such that the total energy is extensive, then this time is independent of particle number, and diverges with √{ N} without a Kac factor.

  5. Diffusive and Subdiffusive Spin Transport in the Ergodic Phase of a Many-Body Localizable System.

    PubMed

    Žnidarič, Marko; Scardicchio, Antonello; Varma, Vipin Kerala

    2016-07-22

    We study high temperature spin transport in a disordered Heisenberg chain in the ergodic regime. By employing a density matrix renormalization group technique for the study of the stationary states of the boundary-driven Lindblad equation we are able to study extremely large systems (400 spins). We find both a diffusive and a subdiffusive phase depending on the strength of the disorder and on the anisotropy parameter of the Heisenberg chain. Studying finite-size effects, we show numerically and theoretically that a very large crossover length exists that controls the passage of a clean-system dominated dynamics to one observed in the thermodynamic limit. Such a large length scale, being larger than the sizes studied before, explains previous conflicting results. We also predict spatial profiles of magnetization in steady states of generic nondiffusive systems.

  6. Many-body GW calculations of ground-state properties: quasi-2D electron systems and van der Waals forces.

    PubMed

    García-González, P; Godby, R W

    2002-02-04

    We present GW many-body results for ground-state properties of two simple but very distinct families of inhomogeneous systems in which traditional implementations of density-functional theory (DFT) fail drastically. The GW approach gives notably better results than the well-known random-phase approximation, at a similar computational cost. These results establish GW as a superior alternative to standard DFT schemes without the expensive numerical effort required by quantum Monte Carlo simulations.

  7. Dynamical scaling in infinitely correlated many-body systems through a quantum phase transition

    NASA Astrophysics Data System (ADS)

    Acevedo, Oscar Leonardo; Quiroga, Luis; Rodriguez, Ferney Javier; Johnson, Neil

    2013-03-01

    We assess dynamical scaling of many two-level systems (TLSs) infinitely correlated, either through a mediating radiation mode as in the Dicke Model, or through a direct interaction between TLSs as in the Lipkin-Meshkov-Glick model. Those models are characterized by the presence of a Quantum Phase Transition (QPT) in the thermodynamic limit, and they belong to the same universality class. The assessment is done by means of exact computational simulations of finite-size systems under linear rampings of the interaction parameter crossing the quantum critical point. Our results exhibit significant differences with respect to previous works on dynamical scaling across QPTs in the near-adiabatic regime, which have focused on spin-chain models where correlation lengths can be defined. We have confirmed that in infinitely correlated models an effective system size can play the role of the correlation length in traditional scaling arguments. However, due to the infinite correlation among TLSs, the standard Kibble-Zurek mechanism is not realized as the system cannot fully enter an adiabatic evolution during the ordered phase. Also, in the two-level approximation, a suitable deviation from the standard Landau-Zener protocol must be performed in order to obtain scaling collapse.

  8. Stability, diffusion and interactions of nonlinear excitations in a many body system

    NASA Astrophysics Data System (ADS)

    Coste, Christophe; Jean, Michel Saint; Dessup, Tommy

    2017-04-01

    When repelling particles are confined in a quasi-one-dimensional trap by a transverse potential, a configurational phase transition happens. All particles are aligned along the trap axis at large confinement, but below a critical transverse confinement they adopt a staggered row configuration (zigzag phase). This zigzag transition is a subcritical pitchfork bifurcation in extended systems and in systems with cyclic boundary conditions in the longitudinal direction. Among many evidences, phase coexistence is exhibited by localized nonlinear patterns made of a zigzag phase embedded in otherwise aligned particles. We give the normal form at the bifurcation and we show that these patterns can be described as solitary wave envelopes that we call bubbles. They are stable in a large temperature range and can diffuse as quasi-particles, with a diffusion coefficient that may be deduced from the normal form. The potential energy of a bubble is found to be lower than that of the homogeneous bifurcated phase, which explains their stability. We observe also metastable states, that are pairs of solitary wave envelopes which spontaneously evolve toward a stable single bubble. We evidence a strong effect of the discreteness of the underlying particles system and introduce the concept of topological frustration of a bubble pair. A configuration is frustrated when the particles between the two bubbles are not organized in a modulated staggered row. For a nonfrustrated (NF) bubble pair configuration, the bubbles interaction is attractive so that the bubbles come closer and eventually merge as a single bubble. In contrast, the bubbles interaction is found to be repulsive for a frustrated (F) configuration. We describe a model of interacting solitary wave that provides all qualitative characteristics of the interaction force: it is attractive for NF-systems, repulsive for F-systems, and decreases exponentially with the bubbles distance.

  9. A Deterministic Projector Configuration Interaction Approach for the Ground State of Quantum Many-Body Systems.

    PubMed

    Zhang, Tianyuan; Evangelista, Francesco A

    2016-09-13

    In this work we propose a novel approach to solve the Schrödinger equation which combines projection onto the ground state with a path-filtering truncation scheme. The resulting projector configuration interaction (PCI) approach realizes a deterministic version of the full configuration interaction quantum Monte Carlo (FCIQMC) method [Booth, G. H.; Thom, A. J. W.; Alavi, A. J. Chem. Phys. 2009, 131, 054106]. To improve upon the linearized imaginary-time propagator, we develop an optimal projector scheme based on an exponential Chebyshev expansion in the limit of an infinite imaginary time step. After writing the exact projector as a path integral in determinant space, we introduce a path filtering procedure that truncates the size of the determinantal basis and approximates the Hamiltonian. The path filtering procedure is controlled by one real threshold that determines the accuracy of the PCI energy and is not biased toward any determinant. Therefore, the PCI approach can equally well describe static and dynamic electron correlation effects. This point is illustrated in benchmark computations on N2 at both equilibrium and stretched geometries. In both cases, the PCI achieves chemical accuracy with wave functions that contain less than 0.5% determinants of full CI space. We also report computations on the ground state of C2 with up to quaduple-ζ basis sets and wave functions as large as 200 million determinants, which allow a direct comparison of the PCI, FCIQMC, and density matrix renormalization group (DMRG) methods. The size of the PCI wave function grows modestly with the number of unoccupied orbitals, and its accuracy may be tuned to match that of FCIQMC and DMRG.

  10. Slow dynamics in many-body quantum systems with long range interactions

    NASA Astrophysics Data System (ADS)

    Santos, Lea; Perez-Bernal, Francisco

    2016-05-01

    In recent experiments with ion traps the range of the interactions between spins-1/2 can be controlled. In the limit of infinite-range interaction the system may be described by the Lipkin model, which exhibits an excited state quantum phase transition (ESQPT). The latter corresponds to a singularity in the spectrum that occurs at the ground state and propagates to higher energies as the control parameter increases beyond the ground state critical point. We show that the evolution of an initial state with energy close to the ESQPT critical point may be extremely slow. This result is surprising, since the dynamics is usually expected to be very fast in systems with long-range interactions. This behavior is justified with the analysis of the structures of the eigenstates. This work was supported by the NSF Grant No. DMR-1147430.

  11. Distributed thermal tasks on many-body systems through a single quantum machine

    NASA Astrophysics Data System (ADS)

    Leggio, Bruno; Doyeux, Pierre; Messina, Riccardo; Antezza, Mauro

    2015-11-01

    We propose a configuration of a single three-level quantum emitter embedded in a non-equilibrium steady electromagnetic environment, able to stabilize and control the local temperatures of a target system it interacts with, consisting of a collection of coupled two-level systems. The temperatures are induced by dissipative processes only, without the need of further external couplings for each qubit. Moreover, by acting on a set of easily tunable geometric parameters, we demonstrate the possibility to manipulate and tune each qubit temperature independently over a remarkably broad range of values. These findings address one standard problem in quantum-scale thermodynamics, providing a way to induce a desired distribution of temperature among interacting qubits and to protect it from external noise sources.

  12. Cooperative Shielding in Many-Body Systems with Long-Range Interaction.

    PubMed

    Santos, Lea F; Borgonovi, Fausto; Celardo, Giuseppe Luca

    2016-06-24

    In recent experiments with ion traps, long-range interactions were associated with the exceptionally fast propagation of perturbation, while in some theoretical works they have also been related with the suppression of propagation. Here, we show that such apparently contradictory behavior is caused by a general property of long-range interacting systems, which we name cooperative shielding. It refers to shielded subspaces that emerge as the system size increases and inside of which the evolution is unaffected by long-range interactions for a long time. As a result, the dynamics strongly depends on the initial state: if it belongs to a shielded subspace, the spreading of perturbation satisfies the Lieb-Robinson bound and may even be suppressed, while for initial states with components in various subspaces, the propagation may be quasi-instantaneous. We establish an analogy between the shielding effect and the onset of quantum Zeno subspaces. The derived effective Zeno Hamiltonian successfully describes the short-ranged dynamics inside the subspaces up to a time scale that increases with system size. Cooperative shielding can be tested in current experiments with trapped ions.

  13. Nonlinear entangled quantum dynamics in many-body systems with strong electron correlation

    NASA Astrophysics Data System (ADS)

    Hong, Jongbae

    2017-04-01

    A quantum impurity system out of equilibrium comprises two metallic reservoirs with different chemical potentials and one mediating spin impurity between them. We study the highly nonlinear tunneling conductance of this system, and clarify that three coherent peaks, one zero-bias peak and two side peaks, naturally appear in the tunneling conductance. We use the Liouvillian approach, in which a complete set of basis operators is available, and construct a Liouville matrix to obtain Green’s function at the mediating site. We show that the two coherent side peaks are the outcome of steady-state nonequilibrium combined with strong electron correlation at the mediating site. Tunneling in the quantum impurity system out of equilibrium is performed by an entangled state which is a linear combination of two Kondo singlets formed by the spin at the mediating site and the coherent spins in each reservoir. The fluctuation by incoherent spins is also included. The spectral weights and positions of the three coherent peaks are analytically discussed via atomic limit analysis. Our theoretical results well fit experimental data obtained for quantum point contacts with symmetric and asymmetric Kondo couplings.

  14. Order-disorder transitions in a sheared many-body system

    NASA Astrophysics Data System (ADS)

    Pfeifer, Jens C.; Bischoff, Tobias; Ehlers, Georg; Eckhardt, Bruno

    2015-12-01

    Motivated by experiments on sheared suspensions that show a transition between ordered and disordered phases, we here study the long-time behavior of a sheared and overdamped two-dimensional system of particles interacting by repulsive forces. As a function of interaction strength and shear rate we find transitions between phases with vanishing and large single-particle diffusion. In the phases with vanishing single-particle diffusion, the system evolves towards regular lattices, usually on very slow time scales. Different lattices can be approached, depending on interaction strength and forcing amplitude. The disordered state appears in parameter regions where the regular lattices are unstable. Correlation functions between the particles reveal the formation of shear bands. In contrast to single-particle densities, the spatially resolved two-particle correlation functions vary with time and allow to determine the phase within a period. As in the case of the suspensions, motion in the state with low diffusivity is essentially reversible, whereas in the state with strong diffusion it is not.

  15. Image method for Coulomb energy for many-body system of charged dielectric spheres

    NASA Astrophysics Data System (ADS)

    Qin, Jian; de Pablo, Juan; Freed, Karl

    2015-03-01

    Ion polarization is important for understanding ion solvation and the stability of ion clusters in polymeric materials which typically exhibit a low and spatially inhomogeneous dielectric permittivity. The simplest approach for modeling ion polarization involves treating the ions as charged spheres with an internal dielectric permittivity differing from that of the medium. The surface polarization contribution to the electrostatic energy for a system of such dielectric spheres can be evaluated perturbatively. We derived closed-form expressions for this energy as a function of the positions of an arbitrary number of polarized surfaces. Our approach is a generalization of the image method for conducting spheres. Using this approach, we calculated the polarization corrections to the cohesion energy for ion clusters and for densely packed ionic crystals. The method can be readily adapted for investigating ion polarization effects in both Monte Carlo and molecular dynamics simulations.

  16. Chord-length and free-path distribution functions for many-body systems

    NASA Astrophysics Data System (ADS)

    Lu, Binglin; Torquato, S.

    1993-04-01

    We study fundamental morphological descriptors of disordered media (e.g., heterogeneous materials, liquids, and amorphous solids): the chord-length distribution function p(z) and the free-path distribution function p(z,a). For concreteness, we will speak in the language of heterogeneous materials composed of two different materials or ``phases.'' The probability density function p(z) describes the distribution of chord lengths in the sample and is of great interest in stereology. For example, the first moment of p(z) is the ``mean intercept length'' or ``mean chord length.'' The chord-length distribution function is of importance in transport phenomena and problems involving ``discrete free paths'' of point particles (e.g., Knudsen diffusion and radiative transport). The free-path distribution function p(z,a) takes into account the finite size of a simple particle of radius a undergoing discrete free-path motion in the heterogeneous material and we show that it is actually the chord-length distribution function for the system in which the ``pore space'' is the space available to a finite-sized particle of radius a. Thus it is shown that p(z)=p(z,0). We demonstrate that the functions p(z) and p(z,a) are related to another fundamentally important morphological descriptor of disordered media, namely, the so-called lineal-path function L(z) studied by us in previous work [Phys. Rev. A 45, 922 (1992)]. The lineal path function gives the probability of finding a line segment of length z wholly in one of the ``phases'' when randomly thrown into the sample. We derive exact series representations of the chord-length and free-path distribution functions for systems of spheres with a polydispersivity in size in arbitrary dimension D. For the special case of spatially uncorrelated spheres (i.e., fully penetrable spheres) we evaluate exactly the aforementioned functions, the mean chord length, and the mean free path. We also obtain corresponding analytical formulas for the case

  17. Feature Article: Understanding strongly correlated many-body systems with quantum Monte Carlo simulations

    NASA Astrophysics Data System (ADS)

    Lavalle, Catia; Rigol, Marcos; Muramatsu, Alejandro

    2005-08-01

    The cover picture of the current issue, taken from the Feature Article [1], depicts the evolution of local density (a) and its quantum fluctuations (b) in trapped fermions on one-dimensional optical lattices. As the number of fermions in the trap is increased, figure (a) shows the formation of a Mott-insulating plateau (local density equal to one) whereas the quantum fluctuations - see figure (b) - are strongly suppressed, but nonzero. For a larger number of fermions new insulating plateaus appear (this time with local density equal to two), but no density fluctuations. Regions with non-constant density are metallic and exhibit large quantum fluctuations of the density.The first author Catia Lavalle is a Postdoc at the University of Stuttgart. She works in the field of strongly correlated quantum systems by means of Quantum Monte Carlo methods (QMC). While working on her PhD thesis at the University of Stuttgart, she developed a new QMC technique that allows to study dynamical properties of the t-J model.

  18. D¯0D0* (D0D¯0*) system in QCD-improved many body potential

    NASA Astrophysics Data System (ADS)

    Jamil, M. Imran; Masud, Bilal; Akram, Faisal; Sohail Gilani, S. M.

    2017-01-01

    For a system of current interest (composed of charm, anticharm and a pair of light quarks), we show trends in phenomenological implications of QCD-based improvements to a simple quark model treatment. We employ a resonating group method to render this difficult four-body problem manageable. We use a quadratic confinement so as to be able to improve beyond the Born approximation. We report the position of the pole corresponding to the D¯0D0* molecule for the best fit of a model parameter to the relevant QCD simulations. We point out the interesting possibility that the pole can be shifted to 3872 MeV by introducing another parameter I 0 that changes the strength of the interaction in this one component of X(3872). The revised value of this second parameter can guide future trends in modeling of the full exotic meson X(3872). We also report the changes with I 0 in the S-wave spin averaged cross sections for D¯0D0* ⟶ ωJ/ψ and D¯0D0* ⟶ ρJ/ψ. These cross sections are important regarding the study of QGP (quark gluon plasma). BM and FA acknowledge the support of PU research (D/605/Est.I Sr. 20 Project 2014-15, D/34/Est.1 Sr. 109 Project 2013-14), SG is thankful to the Higher Education Commission (HEC) of Pakistan for its financial support through (17-5-4(Ps3-128) HEC/Sch/2006)

  19. Many-body effects on optical gain in GaAsPN/GaPN quantum well lasers for silicon integration

    SciTech Connect

    Park, Seoung-Hwan

    2014-02-14

    Many-body effects on the optical gain in GaAsPN/GaP QW structures were investigated by using the multiband effective-mass theory and the non-Markovian gain model with many-body effects. The free-carrier model shows that the optical gain peak slightly increases with increasing N composition. In addition, the QW structure with a larger As composition shows a larger optical gain than that with a smaller As composition. On the other hand, in the case of the many-body model, the optical gain peak decreases with increasing N composition. Also, the QW structure with a smaller As composition is observed to have a larger optical gain than that with a larger As composition. This can be explained by the fact that the QW structure with a smaller As or N composition shows a larger Coulomb enhancement effect than that with a larger As or N composition. This means that it is important to consider the many-body effect in obtaining guidelines for device design issues.

  20. Out-of-equilibrium evolution of kinetically constrained many-body quantum systems under purely dissipative dynamics.

    PubMed

    Olmos, Beatriz; Lesanovsky, Igor; Garrahan, Juan P

    2014-10-01

    We explore the relaxation dynamics of quantum many-body systems that undergo purely dissipative dynamics through non-classical jump operators that can establish quantum coherence. Our goal is to shed light on the differences in the relaxation dynamics that arise in comparison to systems evolving via classical rate equations. In particular, we focus on a scenario where both quantum and classical dissipative evolution lead to a stationary state with the same values of diagonal or "classical" observables. As a basis for illustrating our ideas we use spin systems whose dynamics becomes correlated and complex due to dynamical constraints, inspired by kinetically constrained models (KCMs) of classical glasses. We show that in the quantum case the relaxation can be orders of magnitude slower than the classical one due to the presence of quantum coherences. Aspects of these idealized quantum KCMs become manifest in a strongly interacting Rydberg gas under electromagnetically induced transparency (EIT) conditions in an appropriate limit. Beyond revealing a link between this Rydberg gas and the rather abstract dissipative KCMs of quantum glassy systems, our study sheds light on the limitations of the use of classical rate equations for capturing the non-equilibrium behavior of this many-body system.

  1. Out-of-equilibrium evolution of kinetically constrained many-body quantum systems under purely dissipative dynamics

    NASA Astrophysics Data System (ADS)

    Olmos, Beatriz; Lesanovsky, Igor; Garrahan, Juan P.

    2014-10-01

    We explore the relaxation dynamics of quantum many-body systems that undergo purely dissipative dynamics through non-classical jump operators that can establish quantum coherence. Our goal is to shed light on the differences in the relaxation dynamics that arise in comparison to systems evolving via classical rate equations. In particular, we focus on a scenario where both quantum and classical dissipative evolution lead to a stationary state with the same values of diagonal or "classical" observables. As a basis for illustrating our ideas we use spin systems whose dynamics becomes correlated and complex due to dynamical constraints, inspired by kinetically constrained models (KCMs) of classical glasses. We show that in the quantum case the relaxation can be orders of magnitude slower than the classical one due to the presence of quantum coherences. Aspects of these idealized quantum KCMs become manifest in a strongly interacting Rydberg gas under electromagnetically induced transparency (EIT) conditions in an appropriate limit. Beyond revealing a link between this Rydberg gas and the rather abstract dissipative KCMs of quantum glassy systems, our study sheds light on the limitations of the use of classical rate equations for capturing the non-equilibrium behavior of this many-body system.

  2. Time-dependent restricted-active-space self-consistent-field theory for bosonic many-body systems

    NASA Astrophysics Data System (ADS)

    Lévêque, Camille; Bojer Madsen, Lars

    2017-04-01

    We develop an ab initio time-dependent wavefunction based theory for the description of a many-body system of cold interacting bosons. Like the multi-configurational time-dependent Hartree method for bosons (MCTDHB), the theory is based on a configurational interaction Ansatz for the many-body wavefunction with time-dependent self-consistent-field orbitals. The theory generalizes the MCTDHB method by incorporating restrictions on the active space of the orbital excitations. The restrictions are specified based on the physical situation at hand. The equations of motion of this time-dependent restricted-active-space self-consistent-field (TD-RASSCF) theory are derived. The similarity between the formal development of the theory for bosons and fermions is discussed. The restrictions on the active space allow the theory to be evaluated under conditions where other wavefunction based methods due to exponential scaling in the numerical effort cannot, and to clearly identify the excitations that are important for an accurate description, significantly beyond the mean-field approach. For ground state calculations we find it to be important to allow a few particles to have the freedom to move in many orbitals, an insight facilitated by the flexibility of the restricted-active-space Ansatz. Moreover, we find that a high accuracy can be obtained by including only even excitations in the many-body self-consistent-field wavefunction. Time-dependent simulations of harmonically trapped bosons subject to a quenching of their noncontact interaction, show failure of the mean-field Gross-Pitaevskii approach within a fraction of a harmonic oscillation period. The TD-RASSCF theory remains accurate at much reduced computational cost compared to the MCTDHB method. Exploring the effect of changes of the restricted-active-space allows us to identify that even self-consistent-field excitations are mainly responsible for the accuracy of the method.

  3. Radiative heat transfer and nonequilibrium Casimir-Lifshitz force in many-body systems with planar geometry

    NASA Astrophysics Data System (ADS)

    Latella, Ivan; Ben-Abdallah, Philippe; Biehs, Svend-Age; Antezza, Mauro; Messina, Riccardo

    2017-05-01

    A general theory of photon-mediated energy and momentum transfer in N -body planar systems out of thermal equilibrium is introduced. It is based on the combination of the scattering theory and the fluctuational-electrodynamics approach in many-body systems. By making a Landauer-like formulation of the heat transfer problem, explicit formulas for the energy transmission coefficients between two distinct slabs as well as the self-coupling coefficients are derived and expressed in terms of the reflection and transmission coefficients of the single bodies. We also show how to calculate local equilibrium temperatures in such systems. An analogous formulation is introduced to quantify momentum transfer coefficients describing Casimir-Lifshitz forces out of thermal equilibrium. Forces at thermal equilibrium are readily obtained as a particular case. As an illustration of this general theoretical framework, we show on three-body systems how the presence of a fourth slab can impact equilibrium temperatures in heat-transfer problems and equilibrium positions resulting from the forces acting on the system.

  4. Exploring Interacting Quantum Many-Body Systems by Experimentally Creating Continuous Matrix Product States in Superconducting Circuits

    NASA Astrophysics Data System (ADS)

    Eichler, C.; Mlynek, J.; Butscher, J.; Kurpiers, P.; Hammerer, K.; Osborne, T. J.; Wallraff, A.

    2015-10-01

    Improving the understanding of strongly correlated quantum many-body systems such as gases of interacting atoms or electrons is one of the most important challenges in modern condensed matter physics, materials research, and chemistry. Enormous progress has been made in the past decades in developing both classical and quantum approaches to calculate, simulate, and experimentally probe the properties of such systems. In this work, we use a combination of classical and quantum methods to experimentally explore the properties of an interacting quantum gas by creating experimental realizations of continuous matrix product states—a class of states that has proven extremely powerful as a variational ansatz for numerical simulations. By systematically preparing and probing these states using a circuit quantum electrodynamics system, we experimentally determine a good approximation to the ground-state wave function of the Lieb-Liniger Hamiltonian, which describes an interacting Bose gas in one dimension. Since the simulated Hamiltonian is encoded in the measurement observable rather than the controlled quantum system, this approach has the potential to apply to a variety of models including those involving multicomponent interacting fields. Our findings also hint at the possibility of experimentally exploring general properties of matrix product states and entanglement theory. The scheme presented here is applicable to a broad range of systems exploiting strong and tunable light-matter interactions.

  5. Microwave Spectroscopy of Wigner crystals in 2DES and Bilayer Systems: Many-body correlation in electronic quantum solids

    NASA Astrophysics Data System (ADS)

    Chen, Yong P.

    2007-03-01

    It is generally known that in high quality two dimensional electron systems (2DES, similarly for 2D hole systems and bilayer systems) under sufficiently large perpendicular magnetic field B, the quantum Hall (QH) states terminate into an electronic solid --- a Wigner crystal (WC) pinned by disorder. After a brief review of solid phases in QH systems (including several recently discovered ones [1]) as known from microwave spectroscopy (measuring a characteristic pinning mode resonance of the solid), I will discuss two of our experiments that highlight the importance of many-body quantum correlation in the high-B WC. In one experiment [2], we measured the melting temperature (Tc) of the high-B WC at many different B and densities n and in multiple 2DES samples. The data show unambiguously that in a given sample, Tc is controlled by Landau filling ν=nh/eB instead of by n. This demonstrates the quantum nature of the high-B WC and that its melting is dependent on many-body quantum correlation (via ν). Such behavior contrasts with any other known solids (in particular, a classical electron solid), whose Tc are determined by n. In addition, we found that stronger pinning disorder in samples with tighter vertical confinement led to an enhancement of Tc. In another experiment [3], we studied bilayer WC (BWC) in bilayer hole systems (in low inter-layer tunneling limit). We found that in samples with a bilayer exciton condensate (BEC) QH state at ν=1, the pinning mode frequency of the BWC (ν1) is systematically enhanced from what would be expected from two classically interacting single-layer WC. The enhancement decreases with increasing effective layer separation and is not observed for samples without the ν=1 state. We suggest that our results give evidence for a pseudospin (layer index) ferromagnetic BWC, which possesses interlayer quantum correlation and long range in-plane phase coherence similar to that in the ν=1 BEC state and can experience enhanced pinning [4

  6. A charge-optimized many-body potential for the U-UO2-O2 system

    NASA Astrophysics Data System (ADS)

    Li, Yangzhong; Liang, Tao; Sinnott, Susan B.; Phillpot, Simon R.

    2013-12-01

    Building on previous charge-optimized many-body (COMB) potentials for metallic α-U and gaseous O2, we have developed a new potential for UO2, which also allows the simulation of U-UO2-O2 systems. The UO2 lattice parameter, elastic constants and formation energies of stoichiometric and non-stoichiometric intrinsic defects are well reproduced. Moreover, this is the first rigid-ion potential that produces the correct deviation of the Cauchy relation, as well as the first classical interatomic potential that is able to determine the defect energies of non-stoichiometric intrinsic point defects in UO2 with an appropriate reference state. The oxygen molecule interstitial in the α-U structure is shown to decompose, with some U-O bonds approaching the natural bond length of perfect UO2. Finally, we demonstrate the capability of this COMB potential to simulate a complex system by performing a simulation of the α-U + O2 → UO2 phase transformation. We also identify a possible mechanism for uranium oxidation and the orientation of the resulting fluorite UO2 structure relative to the coordinate system of orthorhombic α-U.

  7. A charge-optimized many-body potential for the U-UO2-O2 system.

    PubMed

    Li, Yangzhong; Liang, Tao; Sinnott, Susan B; Phillpot, Simon R

    2013-12-18

    Building on previous charge-optimized many-body (COMB) potentials for metallic α-U and gaseous O2, we have developed a new potential for UO2, which also allows the simulation of U-UO2-O2 systems. The UO2 lattice parameter, elastic constants and formation energies of stoichiometric and non-stoichiometric intrinsic defects are well reproduced. Moreover, this is the first rigid-ion potential that produces the correct deviation of the Cauchy relation, as well as the first classical interatomic potential that is able to determine the defect energies of non-stoichiometric intrinsic point defects in UO2 with an appropriate reference state. The oxygen molecule interstitial in the α-U structure is shown to decompose, with some U-O bonds approaching the natural bond length of perfect UO2. Finally, we demonstrate the capability of this COMB potential to simulate a complex system by performing a simulation of the α-U + O2 → UO2 phase transformation. We also identify a possible mechanism for uranium oxidation and the orientation of the resulting fluorite UO2 structure relative to the coordinate system of orthorhombic α-U.

  8. Signatures of many-body localisation in a system without disorder and the relation to a glass transition

    NASA Astrophysics Data System (ADS)

    Hickey, James M.; Genway, Sam; Garrahan, Juan P.

    2016-05-01

    We study a quantum spin system—adapted from a facilitated spin model for classical glasses—with local bilinear interactions and without quenched disorder which seems to display characteristic signatures of a many-body localisation (MBL) transition. From direct diagonalisation of small systems, we find a change in certain dynamical and spectral properties at a critical value of a coupling, from those characteristic of a thermalising phase to those characteristic of a MBL phase. The system we consider is known to have a quantum phase transition in its ground-state in the limit of large size, related to a first-order active-to-inactive phase transition in the stochastic trajectories of an associated classical model of glasses. Our results here suggest that this first-order transition in the low-lying spectrum may influence the rest of the spectrum of the system in the large size limit. These findings may help understand the connection between MBL and structural glass transitions.

  9. Real-time observation of fluctuations in a driven-dissipative quantum many-body system undergoing a phase transition

    NASA Astrophysics Data System (ADS)

    Donner, Tobias

    2015-03-01

    A Bose-Einstein condensate whose motional degrees of freedom are coupled to a high-finesse optical cavity via a transverse pump beam constitutes a dissipative quantum many-body system with long range interactions. These interactions can induce a structural phase transition from a flat to a density-modulated state. The transverse pump field simultaneously represents a probe of the atomic density via cavity- enhanced Bragg scattering. By spectrally analyzing the light field leaking out of the cavity, we measure non-destructively the dynamic structure factor of the fluctuating atomic density while the system undergoes the phase transition. An observed asymmetry in the dynamic structure factor is attributed to the coupling to dissipative baths. Critical exponents for both sides of the phase transition can be extracted from the data. We further discuss our progress in adding strong short-range interactions to this system, in order to explore Bose-Hubbard physics with cavity-mediated long-range interactions and self-organization in lower dimensions.

  10. Accurate and efficient quantum chemistry calculations for noncovalent interactions in many-body systems: the XSAPT family of methods.

    PubMed

    Lao, Ka Un; Herbert, John M

    2015-01-15

    We present an overview of "XSAPT", a family of quantum chemistry methods for noncovalent interactions. These methods combine an efficient, iterative, monomer-based approach to computing many-body polarization interactions with a two-body version of symmetry-adapted perturbation theory (SAPT). The result is an efficient method for computing accurate intermolecular interaction energies in large noncovalent assemblies such as molecular and ionic clusters, molecular crystals, clathrates, or protein-ligand complexes. As in traditional SAPT, the XSAPT energy is decomposable into physically meaningful components. Dispersion interactions are problematic in traditional low-order SAPT, and two new approaches are introduced here in an attempt to improve this situation: (1) third-generation empirical atom-atom dispersion potentials, and (2) an empirically scaled version of second-order SAPT dispersion. Comparison to high-level ab initio benchmarks for dimers, water clusters, halide-water clusters, a methane clathrate hydrate, and a DNA intercalation complex illustrate both the accuracy of XSAPT-based methods as well as their limitations. The computational cost of XSAPT scales as O(N(3))-O(N(5)) with respect to monomer size, N, depending upon the particular version that is employed, but the accuracy is typically superior to alternative ab initio methods with similar scaling. Moreover, the monomer-based nature of XSAPT calculations makes them trivially parallelizable, such that wall times scale linearly with respect to the number of monomer units. XSAPT-based methods thus open the door to both qualitative and quantitative studies of noncovalent interactions in clusters, biomolecules, and condensed-phase systems.

  11. Many-body wave functions

    SciTech Connect

    Chasman, R.R.

    1995-08-01

    In the past few years, we developed many-body variational wave functions that allow one to treat pairing and particle-hole two-body interactions on an equal footing. The complexity of these wave functions depends on the number of levels included in the valence space, but does not depend on the number of nucleons in the system. By using residual interaction strengths (e.g. the quadrupole interaction strength or pairing interaction strength) as generator coordinates, one gets many different wave functions, each having a different expectation value for the relevant interaction mode. These wave functions are particularly useful when one is dealing with a situation in which the mean-field approximation is inadequate. Because the same basis states are used in the construction of the many-body wave functions, it is possible to calculate overlaps and interaction matrix elements for the many-body wave functions (which are not in general orthogonal) easily. The valence space can contain a large number of single-particle basis states, when there are constants of motion that can be used to break the levels up into groups. We added a cranking term to the many-body Hamiltonian and modified the projection procedure to get states of good signature before variation. In our present implementation, each group is limited to eight pairs of single-particle levels. We are working on ways of increasing the number of levels that can be included in each group. We are also working on including particle-particle residual interaction modes, in addition to pairing, in our Hamiltonian.

  12. Brillouin-zone integration scheme for many-body density of states: Tetrahedron method combined with cluster perturbation theory

    NASA Astrophysics Data System (ADS)

    Seki, K.; Yunoki, S.

    2016-06-01

    By combining the tetrahedron method with the cluster perturbation theory (CPT), we present an accurate method to numerically calculate the density of states of interacting fermions without introducing the Lorentzian broadening parameter η or the numerical extrapolation of η →0 . The method is conceptually based on the notion of the effective single-particle Hamiltonian which can be subtracted in the Lehmann representation of the single-particle Green's function within the CPT. Indeed, we show the general correspondence between the self-energy and the effective single-particle Hamiltonian which describes exactly the single-particle excitation energies of interacting fermions. The detailed formalism is provided for two-dimensional multiorbital systems and a benchmark calculation is performed for the two-dimensional single-band Hubbard model. The method can be adapted straightforwardly to symmetry-broken states, three-dimensional systems, and finite-temperature calculations.

  13. Many-Body Switches

    NASA Astrophysics Data System (ADS)

    MacDonald, Allan H.

    2014-03-01

    Most current electronic devices use gate voltages to switch individual electron transport channels or off. This architecture necessarily leads to operating voltages that are much larger than the temperature thermal energy, and places lower bounds on power consumption that are becoming. I will discuss strategies for achieving devices in which gates are used to collective many-electron states, in principle allowing charge transport to be switched by smaller voltage changes and both operating voltages and power consumption to reduced. I will specifically address devices based on the properties of itinerant electroninsulating magnetic systems, and devices based on bilayer exciton condensation. This work is based on work performed in collaboration with Sanjay Banerjee and Frank Register.

  14. Many body physics with light

    NASA Astrophysics Data System (ADS)

    Tureci, Hakan E.

    2013-03-01

    Systems of strongly interacting atoms and photons, which can be realized wiring up individual Cavity QED (CQED) systems into lattices, are perceived as a new platform for quantum simulation. While sharing important properties with other systems of interacting quantum particles, the nature of light-matter interaction gives rise to unique features with no analogs in condensed matter or atomic physics setups. Such Lattice CQED systems operate on polaritonic quasi-particles that are hybrids of light and matter in a controllable proportion, combining long-range coherence of photons and strong interactions typically displayed by massive particles. In this talk, I will discuss our recent efforts on the possibility of observing quantum many body physics and quantum phase transitions in Lattice CQED systems. Unavoidable photon loss coupled with the ease of feeding in additional photons through continuous external driving renders such lattices open quantum systems. Another key aspect of many body physics with light that I will focus on is the particle number non-conserving nature of the fundamental light-matter interaction and the question of what quantity, if not the chemical potential, can stabilize finite density quantum phases of correlated photons. Work supported by the NSF and the Swiss NSF. Work reported is a collaboration with M. Biondi, G. Blatter, M. Bordyuh, D. Gerace, A. Houck, J. Keeling, F. Nissen, B. Oztop, M. Schiro, S. Schmidt.

  15. New successive variational method of tensor-optimized antisymmetrized molecular dynamics for nuclear many-body systems

    NASA Astrophysics Data System (ADS)

    Myo, Takayuki; Toki, Hiroshi; Ikeda, Kiyomi; Horiuchi, Hisashi; Suhara, Tadahiro

    2017-07-01

    We recently proposed a new variational theory of "tensor-optimized antisymmetrized molecular dynamics" (TOAMD), which treats the strong interaction explicitly for finite nuclei [T. Myo et al., Prog. Theor. Exp. Phys. 2015, 073D02 (2015)]. In TOAMD, the correlation functions for the tensor force and the short-range repulsion and their multiple products are successively operated to the AMD state. The correlated Hamiltonian is expanded into many-body operators by using the cluster expansion and all the resulting operators are taken into account in the calculation without any truncation. We show detailed results for TOAMD with the nucleon-nucleon interaction AV8' for s-shell nuclei. The binding energy and the Hamiltonian components are successively converged to exact values of the few-body calculations. We also apply TOAMD to the Malfliet-Tjon central potential having a strong short-range repulsion. TOAMD can treat the short-range correlation and provided accurate energies of s-shell nuclei, reproducing the results of few-body calculations. It turns out that the numerical accuracy of TOAMD with double products of the correlation functions is beyond the variational Monte Carlo method with Jastrow's product-type correlation functions.

  16. Macroscopic transport equations in many-body systems from microscopic exclusion processes in disordered media: a review

    NASA Astrophysics Data System (ADS)

    Galanti, Marta; Fanelli, Duccio; Piazza, Francesco

    2016-08-01

    Describing particle transport at the macroscopic or mesoscopic level in non-ideal environments poses fundamental theoretical challenges in domains ranging from inter and intra-cellular transport in biology to diffusion in porous media. Yet, often the nature of the constraints coming from many-body interactions or reflecting a complex and confining environment are better understood and modeled at the microscopic level. In this paper we review the subtle link between microscopic exclusion processes and the mean-field equations that ensue from them in the continuum limit. We show that in an inhomogeneous medium, i.e. when jumps are controlled by site-dependent hopping rates, one can obtain three different nonlinear advection-diffusion equations in the continuum limit, suitable for describing transport in the presence of quenched disorder and external fields, depending on the particular rule embodying site inequivalence at the microscopic level. In a situation that might be termed point-like scenario, when particles are treated as point-like objects, the effect of crowding as imposed at the microscopic level manifests in the mean-field equations only if some degree of inhomogeneity is enforced into the model. Conversely, when interacting agents are assigned a finite size, under the more realistic extended crowding framework, exclusion constraints persist in the unbiased macroscopic representation.

  17. Nearest-neighbor distributions and tunneling splittings in interacting many-body two-level boson systems.

    PubMed

    Hernández-Quiroz, Saúl; Benet, Luis

    2010-03-01

    We study the nearest-neighbor distributions of the k -body embedded ensembles of random matrices for n bosons distributed over two-degenerate single-particle states. This ensemble, as a function of k , displays a transition from harmonic-oscillator behavior (k=1) to random-matrix-type behavior (k=n) . We show that a large and robust quasidegeneracy is present for a wide interval of values of k when the ensemble is time-reversal invariant. These quasidegenerate levels are Shnirelman doublets which appear due to the integrability and time-reversal invariance of the underlying classical systems. We present results related to the frequency in the spectrum of these degenerate levels in terms of k and discuss the statistical properties of the splittings of these doublets.

  18. Many-body Study of Core-valence Partitioning and Correlation in Systems with Large-Z Element

    NASA Astrophysics Data System (ADS)

    Zehtabi-Oskuie, Ana

    This thesis presents optical trapping of various single nanoparticles, and the method for integrating the optical trap system into a microfluidic channel to examine the trapping stiffness and to study binding at the single molecule level. Optical trapping is the capability to immobilize, move, and manipulate small objects in a gentle way. Conventional trapping methods are able to trap dielectric particles with size greater than 100 nm. Optical trapping using nanostructures has overcome this limitation so that it has been of interest to trap nanoparticles for bio-analytical studies. In particular, aperture optical trapping allows for trapping at low powers, and easy detection of the trapping events by noting abrupt jumps in the transmission intensity of the trapping beam through the aperture. Improved trapping efficiency has been achieved by changing the aperture shape from a circle; for example, to a rectangle, double nanohole (DNH), or coaxial aperture. The DNH has the advantage of a well-defined trapping region between the two cusps where the nanoholes overlap, which typically allows only single particle trapping due to steric hindrance. Trapping of 21 nm encapsulated quantum dot has been achieved which shows optical trapping can be used in technologies that seek to place a quantum dot at a specific location in a plasmonic or nanophotonic structure. The DNH has been used to trap and unfold a single protein. The high signal-to-noise ratio of 33 in monitoring single protein trapping and unfolding shows a tremendous potential for using the double nanohole as a sensor for protein binding events at a single molecule level. The DNH integrated in a microfluidic chip with flow to show that stable trapping can be achieved under reasonable flow rates of a few microL/min. With such stable trapping under flow, it is possible to envision co-trapping of proteins to study their interactions. Co-trapping is achieved for the case where we flow in a protein (bovine serum albumin

  19. Gravitational Many-Body Problem

    SciTech Connect

    Makino, J.

    2008-04-29

    In this paper, we briefly review some aspects of the gravitational many-body problem, which is one of the oldest problems in the modern mathematical science. Then we review our GRAPE project to design computers specialized to this problem.

  20. Gravitational Many-Body Problem

    NASA Astrophysics Data System (ADS)

    Makino, J.

    2008-04-01

    In this paper, we briefly review some aspects of the gravitational many-body problem, which is one of the oldest problems in the modern mathematical science. Then we review our GRAPE project to design computers specialized to this problem.

  1. [The physics of cellular automata and coherence and chaos in classical many-body systems]. Progress report, May 1991--present

    SciTech Connect

    Not Available

    1992-06-24

    This report contains short discussions on the following topics: non-variational effects in a Ginzburg-Landau equation; algebraic correlations in conserved chaotic systems; chaotic interface models of turbulence; algebraic correlations in coupled order parameter systems; and dynamics of Josephson Junction arrays. (LSP)

  2. Excited-state quantum phase transitions in many-body systems with infinite-range interaction: Localization, dynamics, and bifurcation

    NASA Astrophysics Data System (ADS)

    Santos, Lea F.; Távora, Marco; Pérez-Bernal, Francisco

    2016-07-01

    Excited-state quantum phase transitions (ESQPTs) are generalizations of quantum phase transitions to excited levels. They are associated with local divergences in the density of states. Here, we investigate how the presence of an ESQPT can be detected from the analysis of the structure of the Hamiltonian matrix, the level of localization of the eigenstates, the onset of bifurcation, and the speed of the system evolution. Our findings are illustrated for a Hamiltonian with infinite-range Ising interaction in a transverse field. This is a version of the Lipkin-Meshkov-Glick (LMG) model and the limiting case of the one-dimensional spin-1/2 system with tunable interactions realized with ion traps. From our studies for the dynamics, we uncover similarities between the LMG and the noninteracting XX models.

  3. Many-body theory for systems with particle conversion: Extending the multiconfigurational time-dependent Hartree method

    NASA Astrophysics Data System (ADS)

    Alon, Ofir E.; Streltsov, Alexej I.; Cederbaum, Lorenz S.

    2009-02-01

    We derive a multiconfigurational time-dependent Hartree theory for systems with particle conversion. In such systems particles of one kind can convert to another kind and the total number of particles varies in time. The theory thus extends the scope of the available and successful multiconfigurational time-dependent Hartree methods—which were solely formulated for and applied to systems with a fixed number of particles—to a broader class of physical systems and problems. As a guiding example we treat explicitly a system where bosonic atoms can combine to form bosonic molecules and vice versa. In the theory for particle conversion, the time-dependent many-particle wave function is written as a sum of configurations made of a different number of particles, and assembled from sets of atomic and molecular orbitals. Both the expansion coefficients and the orbitals forming the configurations are time-dependent quantities that are fully determined according to the Dirac-Frenkel time-dependent variational principle. By employing the Lagrangian formulation of the Dirac-Frenkel variational principle we arrive at two sets of coupled equations of motion, one for the atomic and molecular orbitals and one for the expansion coefficients. The first set is comprised of first-order differential equations in time and nonlinear integrodifferential equations in position space, whereas the second set consists of first-order differential equations with coefficients forming a time-dependent Hermitian matrix. Particular attention is paid to the reduced density matrices of the many-particle wave function that appear in the theory and enter the equations of motion. There are two kinds of reduced density matrices: particle-conserving reduced density matrices which directly only couple configurations with the same number of atoms and molecules, and particle nonconserving reduced density matrices which couple configurations with a different number of atoms and molecules. Closed-form and

  4. Atomistic simulations of stainless steels: a many-body potential for the Fe-Cr-C system.

    PubMed

    Henriksson, K O E; Björkas, C; Nordlund, K

    2013-11-06

    Stainless steels found in real-world applications usually have some C content in the base Fe-Cr alloy, resulting in hard and dislocation-pinning carbides-Fe3C (cementite) and Cr23C6-being present in the finished steel product. The higher complexity of the steel microstructure has implications, for example, for the elastic properties and the evolution of defects such as Frenkel pairs and dislocations. This makes it necessary to re-evaluate the effects of basic radiation phenomena and not simply to rely on results obtained from purely metallic Fe-Cr alloys. In this report, an analytical interatomic potential parameterization in the Abell-Brenner-Tersoff form for the entire Fe-Cr-C system is presented to enable such calculations. The potential reproduces, for example, the lattice parameter(s), formation energies and elastic properties of the principal Fe and Cr carbides (Fe3C, Fe5C2, Fe7C3, Cr3C2, Cr7C3, Cr23C6), the Fe-Cr mixing energy curve, formation energies of simple C point defects in Fe and Cr, and the martensite lattice anisotropy, with fair to excellent agreement with empirical results. Tests of the predictive power of the potential show, for example, that Fe-Cr nanowires and bulk samples become elastically stiffer with increasing Cr and C concentrations. High-concentration nanowires also fracture at shorter relative elongations than wires made of pure Fe. Also, tests with Fe3C inclusions show that these act as obstacles for edge dislocations moving through otherwise pure Fe.

  5. Quantum-classical transition for an analog of the double-slit experiment in complex collisions: Dynamical decoherence in quantum many-body systems

    SciTech Connect

    Benet, L.; Chadderton, L. T.; Kun, S. Yu.; Qi Wang

    2007-06-15

    We study coherent superpositions of clockwise and anticlockwise rotating intermediate complexes with overlapping resonances formed in bimolecular chemical reactions. Disintegration of such complexes represents an analog of a famous double-slit experiment. The time for disappearance of the interference fringes is estimated from heuristic arguments related to fingerprints of chaotic dynamics of a classical counterpart of the coherently rotating complex. Validity of this estimate is confirmed numerically for the H+D{sub 2} chemical reaction. Thus we demonstrate the quantum-classical transition in temporal behavior of highly excited quantum many-body systems in the absence of external noise and coupling to an environment.

  6. Driving induced many-body localization

    NASA Astrophysics Data System (ADS)

    Bairey, Eyal; Refael, Gil; Lindner, Netanel H.

    2017-07-01

    Subjecting a many-body localized system to a time-periodic drive generically leads to delocalization and a transition to ergodic behavior if the drive is sufficiently strong or of sufficiently low frequency. Here we show that a specific drive can have an opposite effect, taking a static delocalized system into the many-body localized phase. We demonstrate this effect using a one-dimensional system of interacting hard-core bosons subject to an oscillating linear potential. The system is weakly disordered, and is ergodic absent the driving. The time-periodic linear potential leads to a suppression of the effective static hopping amplitude, increasing the relative strengths of disorder and interactions. Using numerical simulations, we find a transition into the many-body localized phase above a critical driving frequency and in a range of driving amplitudes. Our findings highlight the potential of driving schemes exploiting the coherent destruction of tunneling for engineering long-lived Floquet phases.

  7. Loschmidt echo in many-body localized phases

    NASA Astrophysics Data System (ADS)

    Serbyn, Maksym; Abanin, Dmitry A.

    2017-07-01

    The Loschmidt echo, defined as the overlap between quantum wave function evolved with different Hamiltonians, quantifies the sensitivity of quantum dynamics to perturbations and is often used as a probe of quantum chaos. In this work we consider the behavior of the Loschmidt echo in the many-body localized phase, which is characterized by emergent local integrals of motion and provides a generic example of nonergodic dynamics. We demonstrate that the fluctuations of the Loschmidt echo decay as a power law in time in the many-body localized phase, in contrast to the exponential decay in few-body ergodic systems. We consider the spin-echo generalization of the Loschmidt echo and argue that the corresponding correlation function saturates to a finite value in localized systems. Slow, power-law decay of fluctuations of such spin-echo-type overlap is related to the operator spreading and is present only in the many-body localized phase, but not in a noninteracting Anderson insulator. While most of the previously considered probes of dephasing dynamics could be understood by approximating physical spin operators with local integrals of motion, the Loschmidt echo and its generalizations crucially depend on the full expansion of the physical operators via local integrals of motion operators, as well as operators which flip local integrals of motion. Hence these probes allow one to get insights into the relation between physical operators and local integrals of motion and access the operator spreading in the many-body localized phase.

  8. Many-Body Atomic Physics

    NASA Astrophysics Data System (ADS)

    Boyle, J. J.; Pindzola, M. S.

    1998-09-01

    Preface; Contributors; Introduction; Part I. Atomic Structure: 1. Development of atomic many-body theory Ingvar Lindgren; 2. Relativistic MBPT for highly charged ions W. R. Johnson; 3. Parity nonconservation in atoms S. A. Blundell, W. R. Johnson, and J. Sapirstein; Part II. Photoionization of Atoms: 4. Single photoionization processes J. J. Boyle, and M. D. Kutzner; 5. Photoionization dominated by double excitation T. N. Chang; 6. Direct double photoionization in atoms Z. W. Liu; 7. Photoelectron angular distributions Steven T. Manson; Part III. A. Atomic Scattering - General Considerations: 8. The many-body approach to electron-atom collisions M. Ya Amusia; 9. Theoretical aspects of electron impact ionization P. L. Altick; Part III. B. Atomic Scattering - Low-Order Applications: 10. Perturbation series methods D. H. Madison; 11. Target dependence of the triply differential cross section Cheng Pan and Anthony F. Starace; 12. Overview of Thomas processes for fast mass transfer J. H. McGuire, Jack C. Straton and T. Ishihara; Part III. C. Atomic Scattering - All-Order Applications: 13. R-matrix Theory: Some Recent Applications Philip G. Burke: 14. Electron scattering: application of Dirac R-matrix theory Wasantha Wijesundera, Ian Grant and Patrick Norrington; 15. Close coupling and distorted-wave theory D. C. Griffin and M. S. Pindzola; Appendix: Units and notation; References; Index.

  9. Many-Body Atomic Physics

    NASA Astrophysics Data System (ADS)

    Boyle, J. J.; Pindzola, M. S.

    2005-11-01

    Preface; Contributors; Introduction; Part I. Atomic Structure: 1. Development of atomic many-body theory Ingvar Lindgren; 2. Relativistic MBPT for highly charged ions W. R. Johnson; 3. Parity nonconservation in atoms S. A. Blundell, W. R. Johnson, and J. Sapirstein; Part II. Photoionization of Atoms: 4. Single photoionization processes J. J. Boyle, and M. D. Kutzner; 5. Photoionization dominated by double excitation T. N. Chang; 6. Direct double photoionization in atoms Z. W. Liu; 7. Photoelectron angular distributions Steven T. Manson; Part III. A. Atomic Scattering - General Considerations: 8. The many-body approach to electron-atom collisions M. Ya Amusia; 9. Theoretical aspects of electron impact ionization P. L. Altick; Part III. B. Atomic Scattering - Low-Order Applications: 10. Perturbation series methods D. H. Madison; 11. Target dependence of the triply differential cross section Cheng Pan and Anthony F. Starace; 12. Overview of Thomas processes for fast mass transfer J. H. McGuire, Jack C. Straton and T. Ishihara; Part III. C. Atomic Scattering - All-Order Applications: 13. R-matrix Theory: Some Recent Applications Philip G. Burke: 14. Electron scattering: application of Dirac R-matrix theory Wasantha Wijesundera, Ian Grant and Patrick Norrington; 15. Close coupling and distorted-wave theory D. C. Griffin and M. S. Pindzola; Appendix: Units and notation; References; Index.

  10. Complexity of controlling quantum many-body dynamics

    NASA Astrophysics Data System (ADS)

    Caneva, T.; Silva, A.; Fazio, R.; Lloyd, S.; Calarco, T.; Montangero, S.

    2014-04-01

    We demonstrate that arbitrary time evolutions of many-body quantum systems can be reversed even in cases when only part of the Hamiltonian can be controlled. The reversed dynamics obtained via optimal control—contrary to standard time-reversal procedures—is extremely robust to external sources of noise. We provide a lower bound on the control complexity of a many-body quantum dynamics in terms of the dimension of the manifold supporting it, elucidating the role played by integrability in this context.

  11. Connecting Few-Body Inelastic Decay to Quantum Correlations in a Many-Body System: A Weakly Coupled Impurity in a Resonant Fermi Gas

    NASA Astrophysics Data System (ADS)

    Laurent, Sébastien; Pierce, Matthieu; Delehaye, Marion; Yefsah, Tarik; Chevy, Frédéric; Salomon, Christophe

    2017-03-01

    We study three-body recombination in an ultracold Bose-Fermi mixture. We first show theoretically that, for weak interspecies coupling, the loss rate is proportional to Tan's contact. Second, using a Li 7 /Li 6 mixture we probe the recombination rate in both the thermal and dual superfluid regimes. We find excellent agreement with our model in the BEC-BCS crossover. At unitarity where the fermion-fermion scattering length diverges, we show that the loss rate is proportional to nf4 /3 , where nf is the fermionic density. This unusual exponent signals nontrivial two-body correlations in the system. Our results demonstrate that few-body losses can be used as a quantitative probe of quantum correlations in many-body ensembles.

  12. Connecting Few-Body Inelastic Decay to Quantum Correlations in a Many-Body System: A Weakly Coupled Impurity in a Resonant Fermi Gas.

    PubMed

    Laurent, Sébastien; Pierce, Matthieu; Delehaye, Marion; Yefsah, Tarik; Chevy, Frédéric; Salomon, Christophe

    2017-03-10

    We study three-body recombination in an ultracold Bose-Fermi mixture. We first show theoretically that, for weak interspecies coupling, the loss rate is proportional to Tan's contact. Second, using a ^{7}Li/^{6}Li mixture we probe the recombination rate in both the thermal and dual superfluid regimes. We find excellent agreement with our model in the BEC-BCS crossover. At unitarity where the fermion-fermion scattering length diverges, we show that the loss rate is proportional to n_{f}^{4/3}, where n_{f} is the fermionic density. This unusual exponent signals nontrivial two-body correlations in the system. Our results demonstrate that few-body losses can be used as a quantitative probe of quantum correlations in many-body ensembles.

  13. Understanding the many-body expansion for large systems. III. Critical role of four-body terms, counterpoise corrections, and cutoffs

    NASA Astrophysics Data System (ADS)

    Liu, Kuan-Yu; Herbert, John M.

    2017-10-01

    Papers I and II in this series [R. M. Richard et al., J. Chem. Phys. 141, 014108 (2014); K. U. Lao et al., ibid. 144, 164105 (2016)] have attempted to shed light on precision and accuracy issues affecting the many-body expansion (MBE), which only manifest in larger systems and thus have received scant attention in the literature. Many-body counterpoise (CP) corrections are shown to accelerate convergence of the MBE, which otherwise suffers from a mismatch between how basis-set superposition error affects subsystem versus supersystem calculations. In water clusters ranging in size up to (H2O)37, four-body terms prove necessary to achieve accurate results for both total interaction energies and relative isomer energies, but the sheer number of tetramers makes the use of cutoff schemes essential. To predict relative energies of (H2O)20 isomers, two approximations based on a lower level of theory are introduced and an ONIOM-type procedure is found to be very well converged with respect to the appropriate MBE benchmark, namely, a CP-corrected supersystem calculation at the same level of theory. Results using an energy-based cutoff scheme suggest that if reasonable approximations to the subsystem energies are available (based on classical multipoles, say), then the number of requisite subsystem calculations can be reduced even more dramatically than when distance-based thresholds are employed. The end result is several accurate four-body methods that do not require charge embedding, and which are stable in large basis sets such as aug-cc-pVTZ that have sometimes proven problematic for fragment-based quantum chemistry methods. Even with aggressive thresholding, however, the four-body approach at the self-consistent field level still requires roughly ten times more processors to outmatch the performance of the corresponding supersystem calculation, in test cases involving 1500-1800 basis functions.

  14. On the ground state calculation of a many-body system using a self-consistent basis and quasi-Monte Carlo: an application to water hexamer.

    PubMed

    Georgescu, Ionuţ; Jitomirskaya, Svetlana; Mandelshtam, Vladimir A

    2013-11-28

    Given a quantum many-body system, the Self-Consistent Phonons (SCP) method provides an optimal harmonic approximation by minimizing the free energy. In particular, the SCP estimate for the vibrational ground state (zero temperature) appears to be surprisingly accurate. We explore the possibility of going beyond the SCP approximation by considering the system Hamiltonian evaluated in the harmonic eigenbasis of the SCP Hamiltonian. It appears that the SCP ground state is already uncoupled to all singly- and doubly-excited basis functions. So, in order to improve the SCP result at least triply-excited states must be included, which then reduces the error in the ground state estimate substantially. For a multidimensional system two numerical challenges arise, namely, evaluation of the potential energy matrix elements in the harmonic basis, and handling and diagonalizing the resulting Hamiltonian matrix, whose size grows rapidly with the dimensionality of the system. Using the example of water hexamer we demonstrate that such calculation is feasible, i.e., constructing and diagonalizing the Hamiltonian matrix in a triply-excited SCP basis, without any additional assumptions or approximations. Our results indicate particularly that the ground state energy differences between different isomers (e.g., cage and prism) of water hexamer are already quite accurate within the SCP approximation.

  15. The Bogolyubov-Born-Green-Kirkwood-Yvon hierarchy and Fokker-Planck equation for many-body dissipative randomly driven systems

    SciTech Connect

    Sliusarenko, O. Yu.; Chechkin, A. V.; Slyusarenko, Yu. V.

    2015-04-15

    By generalizing Bogolyubov’s reduced description method, we suggest a formalism to derive kinetic equations for many-body dissipative systems in external stochastic field. As a starting point, we use a stochastic Liouville equation obtained from Hamilton’s equations taking dissipation and stochastic perturbations into account. The Liouville equation is then averaged over realizations of the stochastic field by an extension of the Furutsu-Novikov formula to the case of a non-Gaussian field. As the result, a generalization of the classical Bogolyubov-Born-Green-Kirkwood-Yvon (BBGKY) hierarchy is derived. In order to get a kinetic equation for the single-particle distribution function, we use a regular cutoff procedure of the BBGKY hierarchy by assuming weak interaction between the particles and weak intensity of the field. Within this approximation, we get the corresponding Fokker-Planck equation for the system in a non-Gaussian stochastic field. Two particular cases are discussed by assuming either Gaussian statistics of external perturbation or homogeneity of the system.

  16. Introduction to Many-Body Physics

    NASA Astrophysics Data System (ADS)

    Coleman, Piers

    2015-11-01

    Introduction; 1. Scales and complexity; 2. Quantum fields; 3. Conserved particles; 4. Simple examples of second-quantization; 5. Green's functions; 6. Landau Fermi liquid theory; 7. Zero temperature Feynman diagrams; 8. Finite temperature many-body physics; 9. Fluctuation dissipation and linear response theory; 10. Electron transport theory; 11. Phase transitions and broken symmetry; 12. Path integrals; 13. Path integrals and itinerant magnetism; 14. Superconductivity and BCS theory; 15. Retardation and anisotrophic pairing; 16. Local moments and the Kondo effect; 17. Heavy electrons; 18. Mixed valence, fluctuations and topology; 19. Epilogue: the challenge of the future; Index.

  17. Self-consistent phonons: An accurate and practical method to account for anharmonic effects in equilibrium properties of general classical or quantum many-body systems

    NASA Astrophysics Data System (ADS)

    Brown, Sandra E.; Mandelshtam, Vladimir A.

    2016-12-01

    The self-consistent phonons (SCP) method is a practical approach for computing structural and dynamical properties of a general quantum or classical many-body system while incorporating anharmonic effects. However, a convincing demonstration of the accuracy of SCP and its advantages over the standard harmonic approximation is still lacking. Here we apply SCP to classical Lennard-Jones (LJ) clusters and compare with numerically exact results. The close agreement between the two reveals that SCP accurately describes structural properties of the classical LJ clusters from zero-temperature (where the method is exact) up to the temperatures at which the chosen cluster conformation becomes unstable. Given the similarities between thermal and quantum fluctuations, both physically and within the SCP ansatz, the accuracy of classical SCP over a range of temperatures suggests that quantum SCP is also accurate over a range of quantum de Boer parameter Λ = ℏ / (σ√{ mε }) , which describes the degree of quantum character of the system.

  18. Quantum Annealing and Many-Body Localization

    NASA Astrophysics Data System (ADS)

    Bray-Ali, Noah

    The quantum phase transition separating the Ising spin glass from the quantum paramagnet phase in one-dimension is many-body localized. We study quantum annealing across this transition using the recently developed, dynamical strong-disorder renormalization group approach. The probability of successful adiabatic quantum computation of the spin glass ground-state obeys a universal scaling function of system size, anneal rate, and strength of disorder, which we obtain. Measurement of this universal scaling behavior in a quantum annealing device, for example, would be the first direct test of the activated dynamics of a many-body localized quantum phase transition. Support provided by National Research Council Post-Doctoral Research Associateship.

  19. A Many-Body RAGE Theorem

    NASA Astrophysics Data System (ADS)

    Lampart, Jonas; Lewin, Mathieu

    2015-12-01

    We prove a generalized version of the RAGE theorem for N-body quantum systems. The result states that only bound states of systems with {0 ≤slant n ≤slant N} particles persist in the long time average. The limit is formulated by means of an appropriate weak topology for many-body systems, which was introduced by the second author in a previous work, and is based on reduced density matrices. This topology is connected to the weak-* topology of states on the algebras of canonical commutation or anti-commutation relations, and we give a formulation of our main result in this setting.

  20. Emergent equilibrium in many-body optical bistability

    NASA Astrophysics Data System (ADS)

    Foss-Feig, M.; Niroula, P.; Young, J. T.; Hafezi, M.; Gorshkov, A. V.; Wilson, R. M.; Maghrebi, M. F.

    2017-04-01

    Many-body systems constructed of quantum-optical building blocks can now be realized in experimental platforms ranging from exciton-polariton fluids to ultracold Rydberg gases, establishing a fascinating interface between traditional many-body physics and the driven-dissipative, nonequilibrium setting of cavity QED. At this interface, the standard techniques and intuitions of both fields are called into question, obscuring issues as fundamental as the role of fluctuations, dimensionality, and symmetry on the nature of collective behavior and phase transitions. Here, we study the driven-dissipative Bose-Hubbard model, a minimal description of numerous atomic, optical, and solid-state systems in which particle loss is countered by coherent driving. Despite being a lattice version of optical bistability, a foundational and patently nonequilibrium model of cavity QED, the steady state possesses an emergent equilibrium description in terms of a classical Ising model. We establish this picture by making new connections between traditional techniques from many-body physics (functional integrals) and quantum optics (the system-size expansion). To lowest order in a controlled expansion—organized around the experimentally relevant limit of weak interactions—the full quantum dynamics reduces to nonequilibrium Langevin equations, which support a phase transition described by model A of the Hohenberg-Halperin classification. Numerical simulations of the Langevin equations corroborate this picture, revealing that canonical behavior associated with the Ising model manifests readily in simple experimental observables.

  1. Revisiting a many-body model for water based on a single polarizable site: from gas phase clusters to liquid and air/liquid water systems.

    PubMed

    Réal, Florent; Vallet, Valérie; Flament, Jean-Pierre; Masella, Michel

    2013-09-21

    We present a revised version of the water many-body model TCPE [M. Masella and J.-P. Flament, J. Chem. Phys. 107, 9105 (1997)], which is based on a static three charge sites and a single polarizable site to model the molecular electrostatic properties of water, and on an anisotropic short range many-body energy term specially designed to accurately model hydrogen bonding in water. The parameters of the revised model, denoted TCPE/2013, are here developed to reproduce the ab initio energetic and geometrical properties of small water clusters (up to hexamers) and the repulsive water interactions occurring in cation first hydration shells. The model parameters have also been refined to reproduce two liquid water properties at ambient conditions, the density and the vaporization enthalpy. Thanks to its computational efficiency, the new model range of applicability was validated by performing simulations of liquid water over a wide range of temperatures and pressures, as well as by investigating water liquid/vapor interfaces over a large range of temperatures. It is shown to reproduce several important water properties at an accurate enough level of precision, such as the existence liquid water density maxima up to a pressure of 1000 atm, the water boiling temperature, the properties of the water critical point (temperature, pressure, and density), and the existence of a "singularity" temperature at about 225 K in the supercooled regime. This model appears thus to be particularly well-suited for characterizing ion hydration properties under different temperature and pressure conditions, as well as in different phases and interfaces.

  2. Symmetry constraints on many-body localization

    NASA Astrophysics Data System (ADS)

    Potter, Andrew C.; Vasseur, Romain

    2016-12-01

    We derive general constraints on the existence of many-body localized (MBL) phases in the presence of global symmetries, and show that MBL is not possible with symmetry groups that protect multiplets (e.g., all non-Abelian symmetry groups). Based on simple representation theoretic considerations, we derive general Mermin-Wagner-type principles governing the possible alternative fates of nonequilibrium dynamics in isolated, strongly disordered quantum systems. Our results rule out the existence of MBL symmetry-protected topological phases with non-Abelian symmetry groups, as well as time-reversal symmetry-protected electronic topological insulators, and in fact all fermion topological insulators and superconductors in the 10-fold way classification. Moreover, extending our arguments to systems with intrinsic topological order, we rule out MBL phases with non-Abelian anyons as well as certain classes of symmetry-enriched topological orders.

  3. Intermittent many-body dynamics at equilibrium

    NASA Astrophysics Data System (ADS)

    Danieli, C.; Campbell, D. K.; Flach, S.

    2017-06-01

    The equilibrium value of an observable defines a manifold in the phase space of an ergodic and equipartitioned many-body system. A typical trajectory pierces that manifold infinitely often as time goes to infinity. We use these piercings to measure both the relaxation time of the lowest frequency eigenmode of the Fermi-Pasta-Ulam chain, as well as the fluctuations of the subsequent dynamics in equilibrium. The dynamics in equilibrium is characterized by a power-law distribution of excursion times far off equilibrium, with diverging variance. Long excursions arise from sticky dynamics close to q -breathers localized in normal mode space. Measuring the exponent allows one to predict the transition into nonergodic dynamics. We generalize our method to Klein-Gordon lattices where the sticky dynamics is due to discrete breathers localized in real space.

  4. Many-body physics via machine learning

    NASA Astrophysics Data System (ADS)

    Arsenault, Louis-Francois; von Lilienfeld, O. Anatole; Millis, Andrew J.

    We demonstrate a method for the use of machine learning (ML) to solve the equations of many-body physics, which are functional equations linking a bare to an interacting Green's function (or self-energy) offering transferable power of prediction for physical quantities for both the forward and the reverse engineering problem of materials. Functions are represented by coefficients in an orthogonal polynomial expansion and kernel ridge regression is used. The method is demonstrated using as an example a database built from Dynamical Mean Field theory (DMFT) calculations on the three dimensional Hubbard model. We discuss the extension to a database for real materials. We also discuss some new area of investigation concerning high throughput predictions for real materials by offering a perspective of how our scheme is general enough for applications to other problems involving the inversion of integral equations from the integrated knowledge such as the analytical continuation of the Green's function and the reconstruction of lattice structures from X-ray spectra. Office of Science of the U.S. Department of Energy under SubContract DOE No. 3F-3138 and FG-ER04169.

  5. Electrostatically Embedded Many-Body Approximation for Systems of Water, Ammonia, and Sulfuric Acid and the Dependence of Its Performance on Embedding Charges.

    PubMed

    Leverentz, Hannah R; Truhlar, Donald G

    2009-06-09

    This work tests the capability of the electrostatically embedded many-body (EE-MB) method to calculate accurate (relative to conventional calculations carried out at the same level of electronic structure theory and with the same basis set) binding energies of mixed clusters (as large as 9-mers) consisting of water, ammonia, sulfuric acid, and ammonium and bisulfate ions. This work also investigates the dependence of the accuracy of the EE-MB approximation on the type and origin of the charges used for electrostatically embedding these clusters. The conclusions reached are that for all of the clusters and sets of embedding charges studied in this work, the electrostatically embedded three-body (EE-3B) approximation is capable of consistently yielding relative errors of less than 1% and an average relative absolute error of only 0.3%, and that the performance of the EE-MB approximation does not depend strongly on the specific set of embedding charges used. The electrostatically embedded pairwise approximation has errors about an order of magnitude larger than EE-3B. This study also explores the question of why the accuracy of the EE-MB approximation shows such little dependence on the types of embedding charges employed.

  6. Quantum thermalization and many-body Anderson localization

    NASA Astrophysics Data System (ADS)

    Huse, David

    2016-05-01

    The out-of-equilibrium dynamics of closed quantum many-body systems can now be explored in a variety of laboratories using a variety of different physical systems, and as a consequence have received a lot of recent theoretical attention. When such systems do go to thermal equilibrium under their own unitary time evolution, this is what is called thermalization. Thermalization is what happens at long times in many large interacting and closed quantum systems, and one way of understanding part of how this happens is via the eigenstate thermalization hypothesis (ETH). The main generic exception to thermalization is many-body localization (MBL), where the system fails to act as a bath to thermalize itself, in spite of being strongly interacting. Instead, the quantum state of a MBL system remains localized near its initial state. MBL is now understood as a new type of quantum integrability, with localized conserved operators. There is a new type of quantum phase transition between MBL and thermalization as one decreases the static randomness in the system; this phase transition remains poorly understood.

  7. Observing a self-thermalizing many-body state

    NASA Astrophysics Data System (ADS)

    Lukin, Alexander; Tai, Eric; Preiss, Philipp; Rispoli, Matthew; Robert, Schittko; Kaufman, Adam; Greiner, Markus

    2016-05-01

    There is a clear intuition for the dynamics of a classical many-body system that is suddenly displaced from thermal equilibrium: Unless there are conserved quantities, the system re-thermalizes and reaches a new equilibrium distribution constrained by only a few thermodynamic variables. In contrast, an isolated quantum many-body system subject to a sudden perturbation undergoes unitary evolution. The dynamics is reversible and preserves memory of the microscopic details of the initial state. Yet, the long-time behavior of local observables in quenched, non-integrable systems is very well described by thermal ensembles. This thermalization within globally pure quantum states is mediated by the growth of entanglement entropy, which takes on the role of thermodynamic entropy. We use recently developed methods to study the global and local quantum purity in the dynamics of quenched Bose-Hubbard systems. We observe a rapid growth and saturation of the entanglement entropy, during which the full system remains verifiably pure. Using number-resolved measurements in a quantum gas microscope, we show that local observables thermalize in agreement with the Eigenstate Thermalization Hypothesis, and we detect a near-volume law in the entanglement entropy.

  8. Many-body localization in infinite chains

    NASA Astrophysics Data System (ADS)

    Enss, T.; Andraschko, F.; Sirker, J.

    2017-01-01

    We investigate the phase transition between an ergodic and a many-body localized phase in infinite anisotropic spin-1 /2 Heisenberg chains with binary disorder. Starting from the Néel state, we analyze the decay of antiferromagnetic order ms(t ) and the growth of entanglement entropy Sent(t ) during unitary time evolution. Near the phase transition we find that ms(t ) decays exponentially to its asymptotic value ms(∞ ) ≠0 in the localized phase while the data are consistent with a power-law decay at long times in the ergodic phase. In the localized phase, ms(∞ ) shows an exponential sensitivity on disorder with a critical exponent ν ˜0.9 . The entanglement entropy in the ergodic phase grows subballistically, Sent(t ) ˜tα , α ≤1 , with α varying continuously as a function of disorder. Exact diagonalizations for small systems, on the other hand, do not show a clear scaling with system size and attempts to determine the phase boundary from these data seem to overestimate the extent of the ergodic phase.

  9. Many body topics in condensed matter physics

    NASA Astrophysics Data System (ADS)

    Anduaga, Inaki Pablo

    Two different problems involving many-body systems are presented. A hydrodynamic version of the Calogero system of one-dimensional particles interacting on the line is derived using a classical field formalism, and the results are contrasted to a derivation starting from first quantum mechanical principles. This new classical approach is shown to help in understanding subtleties occurring in the latter, such as the conditions for chiral motion, the decomposition of the Hamiltonian in terms of chiral currents and the nature of the physical velocity and density operators. Explicit collective solitonic excitations in the linear and non-linear limits are also presented. Additionally, we overview the possibility of expanding this formalism to the study of the Fractional Quantum Hall Effect. The second problem involves a simple two-dimensional model of a px + ipy superfluid in which the mass flow that gives rise to the intrinsic angular momentum is easily calculated by numerical diagonalization of the Bogoliubovde Gennes operator. The results confirm theoretical predictions such as the Thomas-Fermi approximation and the Ishikawa formula, in which the mass flow at zero-temperature and for a constant director l follows jmass = ½curl(rhohl/2).

  10. Many-body localization due to random interactions

    NASA Astrophysics Data System (ADS)

    Sierant, Piotr; Delande, Dominique; Zakrzewski, Jakub

    2017-02-01

    The possibility of observing many-body localization of ultracold atoms in a one-dimensional optical lattice is discussed for random interactions. In the noninteracting limit, such a system reduces to single-particle physics in the absence of disorder, i.e., to extended states. In effect, the observed localization is inherently due to interactions and is thus a genuine many-body effect. In the system studied, many-body localization manifests itself in a lack of thermalization visible in temporal propagation of a specially prepared initial state, in transport properties, in the logarithmic growth of entanglement entropy, and in statistical properties of energy levels.

  11. Power-Law Entanglement Spectrum in Many-Body Localized Phases

    NASA Astrophysics Data System (ADS)

    Serbyn, Maksym; Michailidis, Alexios A.; Abanin, Dmitry A.; Papić, Z.

    2016-10-01

    The entanglement spectrum of the reduced density matrix contains information beyond the von Neumann entropy and provides unique insights into exotic orders or critical behavior of quantum systems. Here, we show that strongly disordered systems in the many-body localized phase have power-law entanglement spectra, arising from the presence of extensively many local integrals of motion. The power-law entanglement spectrum distinguishes many-body localized systems from ergodic systems, as well as from ground states of gapped integrable models or free systems in the vicinity of scale-invariant critical points. We confirm our results using large-scale exact diagonalization. In addition, we develop a matrix-product state algorithm which allows us to access the eigenstates of large systems close to the localization transition, and discuss general implications of our results for variational studies of highly excited eigenstates in many-body localized systems.

  12. Power-Law Entanglement Spectrum in Many-Body Localized Phases.

    PubMed

    Serbyn, Maksym; Michailidis, Alexios A; Abanin, Dmitry A; Papić, Z

    2016-10-14

    The entanglement spectrum of the reduced density matrix contains information beyond the von Neumann entropy and provides unique insights into exotic orders or critical behavior of quantum systems. Here, we show that strongly disordered systems in the many-body localized phase have power-law entanglement spectra, arising from the presence of extensively many local integrals of motion. The power-law entanglement spectrum distinguishes many-body localized systems from ergodic systems, as well as from ground states of gapped integrable models or free systems in the vicinity of scale-invariant critical points. We confirm our results using large-scale exact diagonalization. In addition, we develop a matrix-product state algorithm which allows us to access the eigenstates of large systems close to the localization transition, and discuss general implications of our results for variational studies of highly excited eigenstates in many-body localized systems.

  13. Many-Body Interactions in Ice

    DOE PAGES

    Pham, C. Huy; Reddy, Sandeep K.; Chen, Karl; ...

    2017-02-28

    Many-body effects in ice are investigated through a systematic analysis of the lattice energies of several proton ordered and disordered phases, which are calculated with different flexible water models, ranging from pairwise additive (q-TIP4P/F) to polarizable (TTM3-F and AMOE-BA BA) and explicit many-body (MB-pol) potential energy functions. Comparisons with available experimental and diffusion Monte Carlo data emphasize the importance of an accurate description of the individual terms of the many-body expansion of the interaction energy between water molecules for the correct prediction of the energy ordering of the ice phases. Further analysis of the MB-pol results, in terms of fundamentalmore » energy contributions, demonstrates that the differences in lattice energies between different ice phases are sensitively dependent on the subtle balance between short-range two-body and three-body interactions, many-body induction, and dispersion energy. Here, by correctly reproducing many-body effects at both short range and long range, it is found that MB-pol accurately predicts the energetics of different ice phases, which provides further support for the accuracy of MB-pol in representing the properties of water from the gas to the condensed phase.« less

  14. Many-body electron correlations in graphene

    NASA Astrophysics Data System (ADS)

    Neilson, David; Perali, Andrea; Zarenia, Mohammad

    2016-03-01

    The conduction electrons in graphene promise new opportunities to access the region of strong many-body electron-electron correlations. Extremely high quality, atomically flat two-dimensional electron sheets and quasi-one-dimensional electron nanoribbons with tuneable band gaps that can be switched on by gates, should exhibit new many-body phenomena that have long been predicted for the regions of phase space where the average Coulomb repulsions between electrons dominate over their Fermi energies. In electron nanoribbons a few nanometres wide etched in monolayers of graphene, the quantum size effects and the van Hove singularities in their density of states further act to enhance electron correlations. For graphene multilayers or nanoribbons in a double unit electron-hole geometry, it is possible for the many-body electron-hole correlations to be made strong enough to stabilise high-temperature electron-hole superfluidity.

  15. Spectral statistics across the many-body localization transition

    NASA Astrophysics Data System (ADS)

    Serbyn, Maksym; Moore, Joel E.

    2016-01-01

    The many-body localization transition (MBLT) between ergodic and many-body localized phases in disordered interacting systems is a subject of much recent interest. The statistics of eigenenergies is known to be a powerful probe of crossovers between ergodic and integrable systems in simpler examples of quantum chaos. We consider the evolution of the spectral statistics across the MBLT, starting with mapping to a Brownian motion process that analytically relates the spectral properties to the statistics of matrix elements. We demonstrate that the flow from Wigner-Dyson to Poisson statistics is a two-stage process. First, a fractal enhancement of matrix elements upon approaching the MBLT from the delocalized side produces an effective power-law interaction between energy levels, and leads to a plasma model for level statistics. At the second stage, the gas of eigenvalues has local interactions and the level statistics belongs to a semi-Poisson universality class. We verify our findings numerically on the XXZ spin chain. We provide a microscopic understanding of the level statistics across the MBLT and discuss implications for the transition that are strong constraints on possible theories.

  16. Spatially-partitioned many-body vortices

    NASA Astrophysics Data System (ADS)

    Klaiman, S.; Alon, O. E.

    2016-02-01

    A vortex in Bose-Einstein condensates is a localized object which looks much like a tiny tornado storm. It is well described by mean-field theory. In the present work we go beyond the current paradigm and introduce many-body vortices. These are made of spatially- partitioned clouds, carry definite total angular momentum, and are fragmented rather than condensed objects which can only be described beyond mean-field theory. A phase diagram based on a mean-field model assists in predicting the parameters where many-body vortices occur. Implications are briefly discussed.

  17. Molecular Interactions with Many-Body Methods.

    DTIC Science & Technology

    1982-12-30

    359 (1981). R.J. Bartlett and G.D. Purvis, "Electron Correlation in Large Molecules with Many-Body Methods," Annals N.Y. Acadeny of Sciences 367, 62...the predominant criticism of NBPT /CCM has been the practical limitation to a single reference function, particularly in a region of bond breaking when

  18. Accessing Many-Body Localized States through the Generalized Gibbs Ensemble.

    PubMed

    Inglis, Stephen; Pollet, Lode

    2016-09-16

    We show how the thermodynamic properties of large many-body localized systems can be studied using quantum Monte Carlo simulations. We devise a heuristic way of constructing local integrals of motion of high quality, which are added to the Hamiltonian in conjunction with Lagrange multipliers. The ground state simulation of the shifted Hamiltonian corresponds to a high-energy state of the original Hamiltonian in the case of exactly known local integrals of motion. The inevitable mixing between eigenstates as a consequence of nonperfect integrals of motion is weak enough such that the characteristics of many-body localized systems are not averaged out, unlike the standard ensembles of statistical mechanics. Our method paves the way to study higher dimensions and indicates that a fully many-body localized phase in 2D, where (nearly) all eigenstates are localized, is likely to exist.

  19. Accessing Many-Body Localized States through the Generalized Gibbs Ensemble

    NASA Astrophysics Data System (ADS)

    Inglis, Stephen; Pollet, Lode

    2016-09-01

    We show how the thermodynamic properties of large many-body localized systems can be studied using quantum Monte Carlo simulations. We devise a heuristic way of constructing local integrals of motion of high quality, which are added to the Hamiltonian in conjunction with Lagrange multipliers. The ground state simulation of the shifted Hamiltonian corresponds to a high-energy state of the original Hamiltonian in the case of exactly known local integrals of motion. The inevitable mixing between eigenstates as a consequence of nonperfect integrals of motion is weak enough such that the characteristics of many-body localized systems are not averaged out, unlike the standard ensembles of statistical mechanics. Our method paves the way to study higher dimensions and indicates that a fully many-body localized phase in 2D, where (nearly) all eigenstates are localized, is likely to exist.

  20. Many-body Bose systems and the hard-sphere model: dynamic properties from the weak to the strong interaction regime

    NASA Astrophysics Data System (ADS)

    Rota, R.; Tramonto, F.; Galli, D. E.; Giorgini, S.

    2014-08-01

    We obtain ab-initio estimations of the dynamic structure factor, S(q,ω), of Bose gases at zero temperature. More precisely, we use the Genetic Inversion via Falsification of Theories (GIFT) algorithm to perform analytic continuations of imaginary time correlation functions computed via an exact Path Integral projector method. Using the hard-sphere potential to model the two-body interactions between the atoms, we compute S(q,ω) changing the gas parameter from the dilute regime (na3 = 10-4) up to the density corresponding to superfluid 4He at equilibrium (na3 = 0.2138). With increasing density, we observe the emergence of a broad multiphonon contribution accompanying the quasiparticle peak and a crossover of the dispersion of elementary excitations from a Bogoliubov-like spectrum to a phonon-maxon- roton curve. Apart from the low wave vector region, for na3 = 0.2138 the energy-momentum dispersion relation and the static density response function, χ(q), turns out to be in good agreement with the superfluid 4He experimental data at equilibrium density.

  1. Many-body physics using cold atoms

    NASA Astrophysics Data System (ADS)

    Sundar, Bhuvanesh

    Advances in experiments on dilute ultracold atomic gases have given us access to highly tunable quantum systems. In particular, there have been substantial improvements in achieving different kinds of interaction between atoms. As a result, utracold atomic gases oer an ideal platform to simulate many-body phenomena in condensed matter physics, and engineer other novel phenomena that are a result of the exotic interactions produced between atoms. In this dissertation, I present a series of studies that explore the physics of dilute ultracold atomic gases in different settings. In each setting, I explore a different form of the inter-particle interaction. Motivated by experiments which induce artificial spin-orbit coupling for cold fermions, I explore this system in my first project. In this project, I propose a method to perform universal quantum computation using the excitations of interacting spin-orbit coupled fermions, in which effective p-wave interactions lead to the formation of a topological superfluid. Motivated by experiments which explore the physics of exotic interactions between atoms trapped inside optical cavities, I explore this system in a second project. I calculate the phase diagram of lattice bosons trapped in an optical cavity, where the cavity modes mediates effective global range checkerboard interactions between the atoms. I compare this phase diagram with one that was recently measured experimentally. In two other projects, I explore quantum simulation of condensed matter phenomena due to spin-dependent interactions between particles. I propose a method to produce tunable spin-dependent interactions between atoms, using an optical Feshbach resonance. In one project, I use these spin-dependent interactions in an ultracold Bose-Fermi system, and propose a method to produce the Kondo model. I propose an experiment to directly observe the Kondo effect in this system. In another project, I propose using lattice bosons with a large hyperfine spin

  2. [The physics of cellular automata and coherence and chaos in classical many-body dynamical systems]. Progress report, May 1992--present

    SciTech Connect

    Hayot, F.; Jayaprakash, C.

    1993-08-01

    Brief summaries are given of work on the following topics: universal properties of the two-dimensional Kuramoto-Sivashinsky (K-S) equation, dynamic scaling in the K-S equation, chaotic interface models of turbulence, self-organized criticality in nonconserving systems, and local dynamics of Josephson junction arrays. 8 refs.

  3. Recent Developments in the Nuclear Many-Body Problem

    NASA Astrophysics Data System (ADS)

    Furnstahl, R. J.

    The study of quantum chromodynamics (QCD) over the past quarter century has had relatively little impact on the traditional approach to the low-energy nuclear many-body problem. Recent developments are changing this situation. New experimental capabilities and theoretical approaches are opening windows into the richness of many-body phenomena in QCD. A common theme is the use of effective field theory (EFT) methods, which exploit the separation of scales in physical systems. At low energies, effective field theory can explain how existing phenomenology emerges from QCD and how to refine it systematically. More generally, the application of EFT methods to many-body problems promises insight into the analytic structure of observables, the identification of new expansion parameters, and a consistent organisation of many-body corrections, with reliable error estimates.

  4. Recent Developments in the Nuclear Many-Body Problem

    NASA Astrophysics Data System (ADS)

    Furnstahl, R. J.

    2002-12-01

    The study of quantum chromodynamics (QCD) over the past quarter century has had relatively little impact on the traditional approach to the low-energy nuclear many-body problem. Recent developments are changing this situation. New experimental capabilities and theoretical approaches are opening windows into the richness of many-body phenomena in QCD. A common theme is the use of effective field theory (EFT) methods, which exploit the separation of scales in physical systems. At low energies, effective field theory can explain how existing phenomenology emerges from QCD and how to refine it systematically. More generally, the application of EFT methods to many-body problems promises insight into the analytic structure of observables, the identification of new expansion parameters, and a consistent organisation of many-body corrections, with reliable error estimates.

  5. Natural orbitals for a two-particle system in one dimension as a testbed for use in the nuclear many-body problem

    NASA Astrophysics Data System (ADS)

    McNanna, Mitch A.; Caprio, Mark A.

    2014-09-01

    Natural orbitals have been applied in atomic and molecular electronic-structure theory to increase the accuracy of calculations of observables for a many-particle system. However, unlike the electron-structure problem, the nuclear problem is translationally invariant. We created a testbed code to test the usefulness of natural orbitals as they may apply to translationally invariant problems. The relative Hamiltonian matrix of a two-particle system in one dimension is first calculated in a basis of antisymmetrized products of the harmonic oscillator eigenfunctions. The natural orbitals are then calculated for the resulting ground state, and the Hamiltonian matrix is recalculated using a two-particle basis built from the natural orbitals. The effect of basis size on the accuracy of the ground state energy calculation is explored. Natural orbitals have been applied in atomic and molecular electronic-structure theory to increase the accuracy of calculations of observables for a many-particle system. However, unlike the electron-structure problem, the nuclear problem is translationally invariant. We created a testbed code to test the usefulness of natural orbitals as they may apply to translationally invariant problems. The relative Hamiltonian matrix of a two-particle system in one dimension is first calculated in a basis of antisymmetrized products of the harmonic oscillator eigenfunctions. The natural orbitals are then calculated for the resulting ground state, and the Hamiltonian matrix is recalculated using a two-particle basis built from the natural orbitals. The effect of basis size on the accuracy of the ground state energy calculation is explored. Supported by the US NSF under grant NSF-PHY05-52843, the US DOE under grant DE-FG02-95ER-4093 and the Research Corporation for Science Advancement under a Cottrell Scholar Award.

  6. Boltzmann-Gibbs states in topological quantum walks and associated many-body systems: fidelity and Uhlmann parallel transport analysis of phase transitions

    NASA Astrophysics Data System (ADS)

    Mera, Bruno; Vlachou, Chrysoula; Paunković, Nikola; Vieira, Vítor R.

    2017-09-01

    We perform the fidelity analysis for Boltzmann-Gibbs-like states in order to investigate whether the topological order of 1D fermionic systems at zero temperature is maintained at finite temperatures. We use quantum walk protocols that are known to simulate topological phases and the respective quantum phase transitions for chiral symmetric Hamiltonians. Using the standard approaches of the fidelity analysis and the study of edge states, we conclude that no thermal-like phase transitions occur as temperature increases, i.e. the topological behaviour is washed out gradually. We also show that the behaviour of the Uhlmann geometric factor associated to the considered fidelity exhibits the same behaviour as the latter, thus confirming the results obtained using the previously established approaches.

  7. A two-dimensional many-body system with competing interactions as a model for segregation of photosystems in thylakoids of green plants.

    PubMed

    Rojdestvenski, I; Ivanov, A G; Cottam, M G; Oquist, G

    2000-01-01

    We address the segregation of photosystems I (PSI) and II (PSII) in thylakoid membranes by means of a molecular dynamics method. We assume a two-dimensional (in-plane) problem with PSI and PSII being represented by particles with different values of negative charge. The pair interactions between particles include a screened Coulomb repulsive part and am exponentially decaying attractive part. Our modeling results suggest that the system may have a complicated phase behavior, including a quasi-crystalline phase at low ionic screening, a disordered phase and, in addition, a possible "clotting" agglomerate phase at high screening where the photosystems tend to clot together. The relevance of the observed phenomena to the stacking of thylakoid membranes is discussed.

  8. Convergence of many-body wave-function expansions using a plane-wave basis: From homogeneous electron gas to solid state systems

    NASA Astrophysics Data System (ADS)

    Shepherd, James J.; Grüneis, Andreas; Booth, George H.; Kresse, Georg; Alavi, Ali

    2012-07-01

    Using the finite simulation-cell homogeneous electron gas (HEG) as a model, we investigate the convergence of the correlation energy to the complete-basis-set (CBS) limit in methods utilizing plane-wave wave-function expansions. Simple analytic and numerical results from second-order Møller-Plesset theory (MP2) suggest a 1/M decay of the basis-set incompleteness error where M is the number of plane waves used in the calculation, allowing for straightforward extrapolation to the CBS limit. As we shall show, the choice of basis-set truncation when constructing many-electron wave functions is far from obvious, and here we propose several alternatives based on the momentum transfer vector, which greatly improve the rate of convergence. This is demonstrated for a variety of wave-function methods, from MP2 to coupled-cluster doubles theory and the random-phase approximation plus second-order screened exchange. Finite basis-set energies are presented for these methods and compared with exact benchmarks. A transformation can map the orbitals of a general solid state system onto the HEG plane-wave basis and thereby allow application of these methods to more realistic physical problems. We demonstrate this explicitly for solid and molecular lithium hydride.

  9. Absence of many-body mobility edges

    NASA Astrophysics Data System (ADS)

    De Roeck, Wojciech; Huveneers, Francois; Müller, Markus; Schiulaz, Mauro

    2016-01-01

    Localization transitions as a function of temperature require a many-body mobility edge in energy, separating localized from ergodic states. We argue that this scenario is inconsistent because local fluctuations into the ergodic phase within the supposedly localized phase can serve as mobile bubbles that induce global delocalization. Such fluctuations inevitably appear with a low but finite density anywhere in any typical state. We conclude that the only possibility for many-body localization to occur is lattice models that are localized at all energies. Building on a close analogy with a model of assisted two-particle hopping, where interactions induce delocalization, we argue why hot bubbles are mobile and do not localize upon diluting their energy. Numerical tests of our scenario show that previously reported mobility edges cannot be distinguished from finite-size effects.

  10. Local conservation laws and the structure of the many-body localized states.

    PubMed

    Serbyn, Maksym; Papić, Z; Abanin, Dmitry A

    2013-09-20

    We construct a complete set of local integrals of motion that characterize the many-body localized (MBL) phase. Our approach relies on the assumption that local perturbations act locally on the eigenstates in the MBL phase, which is supported by numerical simulations of the random-field XXZ spin chain. We describe the structure of the eigenstates in the MBL phase and discuss the implications of local conservation laws for its nonequilibrium quantum dynamics. We argue that the many-body localization can be used to protect coherence in the system by suppressing relaxation between eigenstates with different local integrals of motion.

  11. Non-equilibrium many body dynamics

    SciTech Connect

    Creutz, M.; Gyulassy, M.

    1997-09-22

    This Riken BNL Research Center Symposium on Non-Equilibrium Many Body Physics was held on September 23-25, 1997 as part of the official opening ceremony of the Center at Brookhaven National Lab. A major objective of theoretical work at the center is to elaborate on the full spectrum of strong interaction physics based on QCD, including the physics of confinement and chiral symmetry breaking, the parton structure of hadrons and nuclei, and the phenomenology of ultra-relativistic nuclear collisions related to the up-coming experiments at RHIC. The opportunities and challenges of nuclear and particle physics in this area naturally involve aspects of the many body problem common to many other fields. The aim of this symposium was to find common theoretical threads in the area of non-equilibrium physics and modern transport theories. The program consisted of invited talks on a variety topics from the fields of atomic, condensed matter, plasma, astrophysics, cosmology, and chemistry, in addition to nuclear and particle physics. Separate abstracts have been indexed into the database for contributions to this workshop.

  12. Many-body localization and thermalization in disordered Hubbard chains

    NASA Astrophysics Data System (ADS)

    Mondaini, Rubem; Rigol, Marcos

    Recently, a lot of attention has been given to the aspects that lead isolated interacting quantum systems to thermalize. In the presence of disorder, however, the thermalization process fails resulting in a phenomena where transport is suppressed known as many-body localization. Unlike the standard Anderson localization for non-interacting systems, the delocalized (ergodic) phase is very robust against disorder even for moderate values of interaction. Another interesting aspect of the many-body localization phase is that under the time evolution of the quenched disorder, information present in the initial state may survive for arbitrarily long times. This was recently used as a probe of many-body localization of ultracold fermions in optical lattices with quasi-periodic disorder. Here, we will use numerical results in one-dimensional Hubbard chains to show that this analysis may suffer from substantial finite-size effects. We will also compare different types of disorder to see how the ergodicity is affected.

  13. Many body theory in hadronic physics

    NASA Astrophysics Data System (ADS)

    Llanes-Estrada, Felipe Jose

    2000-11-01

    This dissertation presents the development of several many body techniques of widespread use in Atomic, Nuclear and Solid State to Hadronic, the low energy Particle Physics that studies strong interactions. For the high energy, asymptotically free, quarks and gluons described by Quantum Chromodynamics, a canonical (BCS) transformation is performed to generate effective low energy degrees of freedom. Then a model Hamiltonian is approximately diagonalized in Fock space using the TDA and RPA formulations. The relativistic wave equations resulting in each sector are numerically solved, yielding mass eigenvalues for the hadronic spectrum. The TDA provides a reasonable approximation for the glueball and meson spectra, with the exception of the light pseudoscalar mesons, where only the RPA correctly incorporates chiral symmetry and the Goldstone boson nature of the pion. Particular attention is devoted to charmed and hybrid mesons, especially exotic states, given the existing data from BNL and prospects of detection at both TJNAF (Hall D) and CERN (Compass).

  14. Many-body quantum interference on hypercubes

    NASA Astrophysics Data System (ADS)

    Dittel, Christoph; Keil, Robert; Weihs, Gregor

    2017-03-01

    Beyond the regime of distinguishable particles, many-body quantum interferences influence quantum transport in an intricate manner. However, symmetries of the single-particle transformation matrix alleviate this complexity and even allow the analytic formulation of suppression laws, which predict final states to occur with a vanishing probability due to total destructive interference. Here we investigate the symmetries of hypercube graphs and their generalisations with arbitrary identical subgraphs on all vertices. We find that initial many-particle states, which are invariant under self-inverse symmetries of the hypercube, lead to a large number of suppressed final states. The condition for suppression is determined solely by the initial symmetry, while the fraction of suppressed states is given by the number of independent symmetries of the initial state. Our findings reveal new insights into particle statistics for ensembles of indistinguishable bosons and fermions and may represent a first step towards many-particle quantum protocols in higher-dimensional structures.

  15. Many-body phenomena in QED-cavity arrays [Invited

    SciTech Connect

    Tomadin, A.; Fazio, Rosario

    2010-06-15

    Coupled quantum electrodynamics (QED) cavities have been recently proposed as new systems to simulate a variety of equilibrium and nonequilibrium many-body phenomena. We present a brief review of their main properties together with a survey of the latest developments of the field and some perspectives concerning their experimental realizations and possible new theoretical directions.

  16. Exploring many body interactions with Raman spectroscopy

    NASA Astrophysics Data System (ADS)

    Tian, Yao

    Many-body interactions are cornerstones of contemporary solid state physics research. Especially, phonon related interactions such as phonon-phonon coupling, spin-phonon coupling and electron-phonon coupling constantly present new challenges. To study phonon related many-body interactions, temperature dependent Raman spectroscopy is employed. Firstly, a new design and construction of a Raman microscope aimed at high collection eciency, positional and thermal stability is discussed. The application of the home-built Raman microscope is shown in the context of two types of novel materials; Cr2Ge2Te6 (spin-phonon coupling) and Bi2Te3-xSex (phonon-phonon coupling). Cr2Ge2Te6 is one of the rare class of ferromagnetic semiconductors and recent thermal transport studies suggest the spin and lattice are strongly coupled in its cousin compound Cr2Si2Te6. In this work, the spin-phonon coupling in Cr2Ge2Te6 has been revealed in multiple ways: we observed a split of two phonon modes due to the breaking of time reversal symmetry; the anomalous hardening of an additional three modes; and a dramatic enhancement of the phonon lifetimes. It is well-known that the phonon-phonon interaction plays a signicant role in determining the thermal transport properties of thermoelectrics. A comprehensive study of the phonon dynamics of Bi2Te3-xSex has been performed. We found that the unusual temperature dependence of dierent phonon modes originates from both cubic and quartic anharmonicity. These results are consistent with the resonance bonding mechanism, suggesting that the resonance bonding may be a common feature for conventional thermoelectrics. In the Raman spectra of Bi2Te2Se, the origin of the extra Raman feature has been debated for decades. Through a temperature dependent Raman study, we were able to prove the feature is generated by a Te-Se antisite induced local mode. The anomalous linewidth of the local mode as well as the anharmonic behavior were explained through a statistical

  17. Pair-potential approximations for many-body plasma physics

    NASA Astrophysics Data System (ADS)

    Marciante, M.; Stanton, L. G.; Murillo, M. S.

    2016-10-01

    Predicting properties of dense plasmas across wide parameters regimes requires the numerical solution of a many-body dynamical system whose properties depend on various underlying quantum processes. For this reason, high fidelity physics codes (e.g. DFT (orbital-free or Kohn-Sham), classical-map HNC and path integral MC) yield accurate information about the microphysical properties of dense matter. However, their computational cost restricts the simulations to a few tens to few hundreds of ions. To simulate larger systems while retaining an accurate kinetic description of ions, classical MD simulations make use of quantum-effective pair-potentials between the ions. Such potentials involve a small set of parameters, whose values are obtained from DFT calculations, and allow to simulate multi-species systems at much lower computational cost. In these models, bound electrons are usually approximated by an effective charge and free electrons are described as a continuous density. We have undertaken a detailed comparison of our DFT-informed pair-potentials, with results from higher-fidelity physics codes, including g(r), VACF Z(t), and interdiffusion coefficients, in order to determine the physical regimes in which the simpler accurate and very large-scale simulations are possible. Contract DE-AC52-06NA25396.

  18. Exploring many-body physics with deep networks

    NASA Astrophysics Data System (ADS)

    Torlai, Giacomo; Carrasquilla, Juan; Schwab, David; Melko, Roger

    The introduction of neural networks with deep architecture has led to a revolution, giving rise to a new wave of technologies empowering our modern society. Although data science has been the main focus, the idea of generic algorithms which automatically extract features and representations from raw data is quite general and applicable in multiple scenarios. Motivated by the effectiveness of deep learning algorithms in revealing complex patterns and structures underlying data, we are interested in exploiting such tool in the context of many-body physics. In this talk we will focus on how to extract information about the physics of a many-body system from the generative training of a deep network, and ultimately consider discriminative tasks, such as phase diagrams estimation and critical points detection. We will discuss results for different classical spin systems, including models with quenched disorder.

  19. Efficient variational diagonalization of fully many-body localized Hamiltonians

    NASA Astrophysics Data System (ADS)

    Pollmann, Frank; Khemani, Vedika; Cirac, J. Ignacio; Sondhi, S. L.

    2016-07-01

    We introduce a variational unitary matrix product operator based variational method that approximately finds all the eigenstates of fully many-body localized one-dimensional Hamiltonians. The computational cost of the variational optimization scales linearly with system size for a fixed depth of the UTN ansatz. We demonstrate the usefulness of our approach by considering the Heisenberg chain in a strongly disordered magnetic field for which we compare the approximation to exact diagonalization results.

  20. Lattice Methods and the Nuclear Few- and Many-Body Problem

    NASA Astrophysics Data System (ADS)

    Lee, Dean

    This chapter builds upon the review of lattice methods and effective field theory of the previous chapter. We begin with a brief overview of lattice calculations using chiral effective field theory and some recent applications. We then describe several methods for computing scattering on the lattice. After that we focus on the main goal, explaining the theory and algorithms relevant to lattice simulations of nuclear few- and many-body systems. We discuss the exact equivalence of four different lattice formalisms, the Grassmann path integral, transfer matrix operator, Grassmann path integral with auxiliary fields, and transfer matrix operator with auxiliary fields. Along with our analysis we include several coding examples and a number of exercises for the calculations of few- and many-body systems at leading order in chiral effective field theory.

  1. Simulating typical entanglement with many-body Hamiltonian dynamics

    SciTech Connect

    Nakata, Yoshifumi; Murao, Mio

    2011-11-15

    We study the time evolution of the amount of entanglement generated by one-dimensional spin-1/2 Ising-type Hamiltonians composed of many-body interactions. We investigate sets of states randomly selected during the time evolution generated by several types of time-independent Hamiltonians by analyzing the distributions of the amount of entanglement of the sets. We compare such entanglement distributions with that of typical entanglement, entanglement of a set of states randomly selected from a Hilbert space with respect to the unitarily invariant measure. We show that the entanglement distribution obtained by a time-independent Hamiltonian can simulate the average and standard deviation of the typical entanglement, if the Hamiltonian contains suitable many-body interactions. We also show that the time required to achieve such a distribution is polynomial in the system size for certain types of Hamiltonians.

  2. Universal Properties of Many-Body Delocalization Transitions

    NASA Astrophysics Data System (ADS)

    Potter, Andrew C.; Vasseur, Romain; Parameswaran, S. A.

    2015-07-01

    We study the dynamical melting of "hot" one-dimensional many-body localized systems. As disorder is weakened below a critical value, these nonthermal quantum glasses melt via a continuous dynamical phase transition into classical thermal liquids. By accounting for collective resonant tunneling processes, we derive and numerically solve an effective model for such quantum-to-classical transitions and compute their universal critical properties. Notably, the classical thermal liquid exhibits a broad regime of anomalously slow subdiffusive equilibration dynamics and energy transport. The subdiffusive regime is characterized by a continuously evolving dynamical critical exponent that diverges with a universal power at the transition. Our approach elucidates the universal long-distance, low-energy scaling structure of many-body delocalization transitions in one dimension, in a way that is transparently connected to the underlying microscopic physics. We discuss experimentally testable signatures of the predicted scaling properties.

  3. Many-body Green functions in nuclear physics

    NASA Astrophysics Data System (ADS)

    Speth, J.; Lyutorovich, N.

    Many-body Green functions are a very efficient formulation of the many-body problem. We review the application of this method to nuclear physics problems. The formulas which can be derived are of general applicability, e.g., in self-consistent as well as in nonself-consistent calculations. With the help of the Landau renormalization, one obtains relations without any approximations. This allows to apply conservation laws which lead to important general relations. We investigate the one-body and two-body Green functions as well as the three-body Green function and discuss their connection to nuclear observables. The generalization to systems with pair correlations are also presented. Numerical examples are compared with experimental data.

  4. Probing many-body localization with neural networks

    NASA Astrophysics Data System (ADS)

    Schindler, Frank; Regnault, Nicolas; Neupert, Titus

    2017-06-01

    We show that a simple artificial neural network trained on entanglement spectra of individual states of a many-body quantum system can be used to determine the transition between a many-body localized and a thermalizing regime. Specifically, we study the Heisenberg spin-1/2 chain in a random external field. We employ a multilayer perceptron with a single hidden layer, which is trained on labeled entanglement spectra pertaining to the fully localized and fully thermal regimes. We then apply this network to classify spectra belonging to states in the transition region. For training, we use a cost function that contains, in addition to the usual error and regularization parts, a term that favors a confident classification of the transition region states. The resulting phase diagram is in good agreement with the one obtained by more conventional methods and can be computed for small systems. In particular, the neural network outperforms conventional methods in classifying individual eigenstates pertaining to a single disorder realization. It allows us to map out the structure of these eigenstates across the transition with spatial resolution. Furthermore, we analyze the network operation using the dreaming technique to show that the neural network correctly learns by itself the power-law structure of the entanglement spectra in the many-body localized regime.

  5. Renormalization group studies of many-body localization

    NASA Astrophysics Data System (ADS)

    Altman, Ehud

    2015-03-01

    Quantum correlations do not usually persist for long in systems at finite energy density and disappear once the system thermalizes. But many-body localization offers an alternative paradigm, whereby quantum matter can evade the usual fate of thermal equilibrium and retain retrievable quantum correlations even at high energies. I will survey a dynamical renormalization group (RG) approach used to characterize the novel dynamics and entanglement structures, which develop in the localized phase in lieu of classical thermalization. Then I will present a theory of the transition between the ergodic and the many-body localized phase based on a novel RG framework. Here eigenstate entanglement entropy emerges as a natural scaling variable; the RG describes a change from area-law to volume law entanglement through an intriguing critical point, where the distribution of entanglement entropy becomes maximally broad. The ergodic phase established near the critical point is a Griffiths phase, which exhibits sub-diffusive energy transport and sub-ballistic entanglement propagation. The anomalous diffusion exponent vanishes continuously at the critical point. Before closing I will discuss recent progress in confronting the emerging theoretical understanding of many-body localization with experimental tests. This research is supported in part by the ERC synergy grant UQUAM.

  6. Probing many-body interactions in an optical lattice clock

    SciTech Connect

    Rey, A.M.; Gorshkov, A.V.; Kraus, C.V.; Martin, M.J.; Bishof, M.; Swallows, M.D.; Zhang, X.; Benko, C.; Ye, J.; Lemke, N.D.; Ludlow, A.D.

    2014-01-15

    We present a unifying theoretical framework that describes recently observed many-body effects during the interrogation of an optical lattice clock operated with thousands of fermionic alkaline earth atoms. The framework is based on a many-body master equation that accounts for the interplay between elastic and inelastic p-wave and s-wave interactions, finite temperature effects and excitation inhomogeneity during the quantum dynamics of the interrogated atoms. Solutions of the master equation in different parameter regimes are presented and compared. It is shown that a general solution can be obtained by using the so called Truncated Wigner Approximation which is applied in our case in the context of an open quantum system. We use the developed framework to model the density shift and decay of the fringes observed during Ramsey spectroscopy in the JILA {sup 87}Sr and NIST {sup 171}Yb optical lattice clocks. The developed framework opens a suitable path for dealing with a variety of strongly-correlated and driven open-quantum spin systems. -- Highlights: •Derived a theoretical framework that describes many-body effects in a lattice clock. •Validated the analysis with recent experimental measurements. •Demonstrated the importance of beyond mean field corrections in the dynamics.

  7. Many-body effects for critical Casimir forces.

    PubMed

    Mattos, T G; Harnau, L; Dietrich, S

    2013-02-21

    Within mean-field theory we calculate the scaling functions associated with critical Casimir forces for a system consisting of two spherical colloids immersed in a binary liquid mixture near its consolute point and facing a planar, homogeneous substrate. For several geometrical arrangements and boundary conditions we analyze the normal and the lateral critical Casimir forces acting on one of the two colloids. We find interesting features such as a change of sign of these forces upon varying either the position of one of the colloids or the temperature. By subtracting the pairwise forces from the total force we are able to determine the many-body forces acting on one of the colloids. We have found that the many-body contribution to the total critical Casimir force is more pronounced for small colloid-colloid and colloid-substrate distances, as well as for temperatures close to criticality, where the many-body contribution to the total force can reach up to 25%.

  8. Many body generalization of the Landau-Zener problem.

    PubMed

    Altland, Alexander; Gurarie, V

    2008-02-15

    We formulate and approximately solve a specific many body generalization of the Landau-Zener problem. Unlike with the single particle Landau-Zener problem, our system does not abide in the adiabatic ground state, even at very slow driving rates. The structure of the theory suggests that this finding reflects a more general phenomenon in the physics of adiabatically driven many particle systems. Our solution can be used to understand, for example, the behavior of two-level systems coupled to an electromagnetic field, as realized in cavity QED experiments.

  9. Probing many body effects in semiconductor nanostructures

    NASA Astrophysics Data System (ADS)

    Potok, Ron M.

    This thesis describes two sets of experiments performed in quantum dots and quantum point contacts fabricated in GaAs/AlGaAs 2D electron gases. First, we investigate the role of interactions in determining the ground state of a quantum dot. Transport spectroscopy reveals both spin-increasing and spin-decreasing transitions, as well as higher-spin ground states. We then compare ground and excited state transport spectroscopy to direct measurements of the spin polarization of emitted current by developing the first mesoscopic spin polarizer/analyzer system using spin-selective transverse electron focusing. A transverse electron focusing geometry is used to couple current from an emitter (either a quantum point contact or quantum dot) into a collector point contact. In a magnetic field, the collector point contact can be biased to transmit only a single spin, which allows a direct measure of spin polarization of the current incident on it. Spin polarization of >70% is found for a quantum point contact, while the spin of emitted current in the Coulomb blockade regime of a quantum dot is found to be polarized along the direction of the applied magnetic field regardless of the ground state spin transition. In the second set of experiments, we realize a highly correlated electron system, the two channel Kondo system, in a specific geometry of coupled quantum dots. The two channel Kondo model, in which a local magnetic moment is screened by two independent conduction reservoirs, is created in a double quantum dot system based on a proposal by Oreg and Goldhaber-Gordon [1]. Using electrostatic gates we demonstrate in situ control of the parameters of the two channel Kondo model. We tune continuously between two distinct Fermi-liquid regimes, which are characterized by different values of conductance through the nanostructure. We investigate the properties of this quantum phase transition and the associated two channel Kondo quantum critical point. [1]Y. Oreg and D

  10. Many-body formalism for fermions: The partition function

    NASA Astrophysics Data System (ADS)

    Watson, D. K.

    2017-09-01

    The partition function, a fundamental tenet in statistical thermodynamics, contains in principle all thermodynamic information about a system. It encapsulates both microscopic information through the quantum energy levels and statistical information from the partitioning of the particles among the available energy levels. For identical particles, this statistical accounting is complicated by the symmetry requirements of the allowed quantum states. In particular, for Fermi systems, the enforcement of the Pauli principle is typically a numerically demanding task, responsible for much of the cost of the calculations. The interplay of these three elements—the structure of the many-body spectrum, the statistical partitioning of the N particles among the available levels, and the enforcement of the Pauli principle—drives the behavior of mesoscopic and macroscopic Fermi systems. In this paper, we develop an approach for the determination of the partition function, a numerically difficult task, for systems of strongly interacting identical fermions and apply it to a model system of harmonically confined, harmonically interacting fermions. This approach uses a recently introduced many-body method that is an extension of the symmetry-invariant perturbation method (SPT) originally developed for bosons. It uses group theory and graphical techniques to avoid the heavy computational demands of conventional many-body methods which typically scale exponentially with the number of particles. The SPT application of the Pauli principle is trivial to implement since it is done "on paper" by imposing restrictions on the normal-mode quantum numbers at first order in the perturbation. The method is applied through first order and represents an extension of the SPT method to excited states. Our method of determining the partition function and various thermodynamic quantities is accurate and efficient and has the potential to yield interesting insight into the role played by the Pauli

  11. Quantum power functional theory for many-body dynamics

    SciTech Connect

    Schmidt, Matthias

    2015-11-07

    We construct a one-body variational theory for the time evolution of nonrelativistic quantum many-body systems. The position- and time-dependent one-body density, particle current, and time derivative of the current act as three variational fields. The generating (power rate) functional is minimized by the true current time derivative. The corresponding Euler-Lagrange equation, together with the continuity equation for the density, forms a closed set of one-body equations of motion. Space- and time-nonlocal one-body forces are generated by the superadiabatic contribution to the functional. The theory applies to many-electron systems.

  12. Exploring flocking via quantum many-body physics techniques

    NASA Astrophysics Data System (ADS)

    Souslov, Anton; Loewe, Benjamin; Goldbart, Paul M.

    2015-03-01

    Flocking refers to the spontaneous breaking of spatial isotropy and time-reversal symmetries in collections of bodies such as birds, fish, locusts, bacteria, and artificial active systems. The transport of matter along biopolymers using molecular motors also involves the breaking of these symmetries, which in some cases are known to be broken explicitly. We study these classical nonequilibrium symmetry-breaking phenomena by means of models of many strongly interacting particles that hop on a periodic lattice. We employ a mapping between the classical and quantum dynamics of many-body systems, combined with tools from many-body theory. In particular, we examine the formation and properties of nematic and polar order in low-dimensional, strongly-interacting active systems using techniques familiar from fermionic systems, such as self-consistent field theory and bosonization. Thus, we find that classical active systems can exhibit analogs of quantum phenomena such as spin-orbit coupling, magnetism, and superconductivity. The models we study connect the physics of asymmetric exclusion processes to the spontaneous emergence of transport and flow, and also provide a soluble cousin of Vicsek's model system of self-propelled particles.

  13. Chiral Floquet Phases of Many-Body Localized Bosons

    NASA Astrophysics Data System (ADS)

    Po, Hoi Chun; Fidkowski, Lukasz; Morimoto, Takahiro; Potter, Andrew C.; Vishwanath, Ashvin

    2016-10-01

    We construct and classify chiral topological phases in driven (Floquet) systems of strongly interacting bosons, with finite-dimensional site Hilbert spaces, in two spatial dimensions. The construction proceeds by introducing exactly soluble models with chiral edges, which in the presence of many-body localization (MBL) in the bulk are argued to lead to stable chiral phases. These chiral phases do not require any symmetry and in fact owe their existence to the absence of energy conservation in driven systems. Surprisingly, we show that they are classified by a quantized many-body index, which is well defined for any MBL Floquet system. The value of this index, which is always the logarithm of a positive rational number, can be interpreted as the entropy per Floquet cycle pumped along the edge, formalizing the notion of quantum-information flow. We explicitly compute this index for specific models and show that the nontrivial topology leads to edge thermalization, which provides an interesting link between bulk topology and chaos at the edge. We also discuss chiral Floquet phases in interacting fermionic systems and their relation to chiral bosonic phases.

  14. The many-body expansion combined with neural networks

    NASA Astrophysics Data System (ADS)

    Yao, Kun; Herr, John E.; Parkhill, John

    2017-01-01

    Fragmentation methods such as the many-body expansion (MBE) are a common strategy to model large systems by partitioning energies into a hierarchy of decreasingly significant contributions. The number of calculations required for chemical accuracy is still prohibitively expensive for the ab initio MBE to compete with force field approximations for applications beyond single-point energies. Alongside the MBE, empirical models of ab initio potential energy surfaces have improved, especially non-linear models based on neural networks (NNs) which can reproduce ab initio potential energy surfaces rapidly and accurately. Although they are fast, NNs suffer from their own curse of dimensionality; they must be trained on a representative sample of chemical space. In this paper we examine the synergy of the MBE and NN's and explore their complementarity. The MBE offers a systematic way to treat systems of arbitrary size while reducing the scaling problem of large systems. NN's reduce, by a factor in excess of 106, the computational overhead of the MBE and reproduce the accuracy of ab initio calculations without specialized force fields. We show that for a small molecule extended system like methanol, accuracy can be achieved with drastically different chemical embeddings. To assess this we test a new chemical embedding which can be inverted to predict molecules with desired properties. We also provide our open-source code for the neural network many-body expansion, Tensormol.

  15. Factorization in large-scale many-body calculations

    DOE PAGES

    Johnson, Calvin W.; Ormand, W. Erich; Krastev, Plamen G.

    2013-08-07

    One approach for solving interacting many-fermion systems is the configuration-interaction method, also sometimes called the interacting shell model, where one finds eigenvalues of the Hamiltonian in a many-body basis of Slater determinants (antisymmetrized products of single-particle wavefunctions). The resulting Hamiltonian matrix is typically very sparse, but for large systems the nonzero matrix elements can nonetheless require terabytes or more of storage. An alternate algorithm, applicable to a broad class of systems with symmetry, in our case rotational invariance, is to exactly factorize both the basis and the interaction using additive/multiplicative quantum numbers; such an algorithm recreates the many-body matrix elementsmore » on the fly and can reduce the storage requirements by an order of magnitude or more. Here, we discuss factorization in general and introduce a novel, generalized factorization method, essentially a ‘double-factorization’ which speeds up basis generation and set-up of required arrays. Although we emphasize techniques, we also place factorization in the context of a specific (unpublished) configuration-interaction code, BIGSTICK, which runs both on serial and parallel machines, and discuss the savings in memory due to factorization.« less

  16. Factorization in large-scale many-body calculations

    SciTech Connect

    Johnson, Calvin W.; Ormand, W. Erich; Krastev, Plamen G.

    2013-08-07

    One approach for solving interacting many-fermion systems is the configuration-interaction method, also sometimes called the interacting shell model, where one finds eigenvalues of the Hamiltonian in a many-body basis of Slater determinants (antisymmetrized products of single-particle wavefunctions). The resulting Hamiltonian matrix is typically very sparse, but for large systems the nonzero matrix elements can nonetheless require terabytes or more of storage. An alternate algorithm, applicable to a broad class of systems with symmetry, in our case rotational invariance, is to exactly factorize both the basis and the interaction using additive/multiplicative quantum numbers; such an algorithm recreates the many-body matrix elements on the fly and can reduce the storage requirements by an order of magnitude or more. Here, we discuss factorization in general and introduce a novel, generalized factorization method, essentially a ‘double-factorization’ which speeds up basis generation and set-up of required arrays. Although we emphasize techniques, we also place factorization in the context of a specific (unpublished) configuration-interaction code, BIGSTICK, which runs both on serial and parallel machines, and discuss the savings in memory due to factorization.

  17. Exploring many-body localization and thermalization using semiclassical methods

    NASA Astrophysics Data System (ADS)

    Acevedo, O. L.; Safavi-Naini, A.; Schachenmayer, J.; Wall, M. L.; Nandkishore, R.; Rey, A. M.

    2017-09-01

    The discrete truncated Wigner approximation (DTWA) is a semiclassical phase-space method useful for the exploration of many-body quantum dynamics. In this work we investigate many-body localization (MBL) and thermalization using DTWA and compare its performance to exact numerical solutions. By taking as a benchmark case a one-dimensional random field Heisenberg spin chain with short-range interactions, and by comparing to numerically exact techniques, we show that DTWA is able to reproduce dynamical signatures that characterize both the thermal and the MBL phases. It exhibits the best quantitative agreement at short times deep in each of the phases and larger mismatches close to the phase transition. The DTWA captures the logarithmic growth of entanglement in the MBL phase, even though a pure classical mean-field analysis would lead to no dynamics at all. Our results suggest the DTWA can become a useful method to investigate MBL and thermalization in experimentally relevant settings intractable with exact numerical techniques, such as systems with long-range interactions and/or systems in higher dimensions.

  18. Probing many-body interactions in an optical lattice clock

    NASA Astrophysics Data System (ADS)

    Rey, A. M.; Gorshkov, A. V.; Kraus, C. V.; Martin, M. J.; Bishof, M.; Swallows, M. D.; Zhang, X.; Benko, C.; Ye, J.; Lemke, N. D.; Ludlow, A. D.

    2014-01-01

    We present a unifying theoretical framework that describes recently observed many-body effects during the interrogation of an optical lattice clock operated with thousands of fermionic alkaline earth atoms. The framework is based on a many-body master equation that accounts for the interplay between elastic and inelastic p-wave and s-wave interactions, finite temperature effects and excitation inhomogeneity during the quantum dynamics of the interrogated atoms. Solutions of the master equation in different parameter regimes are presented and compared. It is shown that a general solution can be obtained by using the so called Truncated Wigner Approximation which is applied in our case in the context of an open quantum system. We use the developed framework to model the density shift and decay of the fringes observed during Ramsey spectroscopy in the JILA 87Sr and NIST 171Yb optical lattice clocks. The developed framework opens a suitable path for dealing with a variety of strongly-correlated and driven open-quantum spin systems.

  19. Aiming for benchmark accuracy with the many-body expansion.

    PubMed

    Richard, Ryan M; Lao, Ka Un; Herbert, John M

    2014-09-16

    Conspectus The past 15 years have witnessed an explosion of activity in the field of fragment-based quantum chemistry, whereby ab initio electronic structure calculations are performed on very large systems by decomposing them into a large number of relatively small subsystem calculations and then reassembling the subsystem data in order to approximate supersystem properties. Most of these methods are based, at some level, on the so-called many-body (or "n-body") expansion, which ultimately requires calculations on monomers, dimers, ..., n-mers of fragments. To the extent that a low-order n-body expansion can reproduce supersystem properties, such methods replace an intractable supersystem calculation with a large number of easily distributable subsystem calculations. This holds great promise for performing, for example, "gold standard" CCSD(T) calculations on large molecules, clusters, and condensed-phase systems. The literature is awash in a litany of fragment-based methods, each with their own working equations and terminology, which presents a formidable language barrier to the uninitiated reader. We have sought to unify these methods under a common formalism, by means of a generalized many-body expansion that provides a universal energy formula encompassing not only traditional n-body cluster expansions but also methods designed for macromolecules, in which the supersystem is decomposed into overlapping fragments. This formalism allows various fragment-based methods to be systematically classified, primarily according to how the fragments are constructed and how higher-order n-body interactions are approximated. This classification furthermore suggests systematic ways to improve the accuracy. Whereas n-body approaches have been thoroughly tested at low levels of theory in small noncovalent clusters, we have begun to explore the efficacy of these methods for large systems, with the goal of reproducing benchmark-quality calculations, ideally meaning complete

  20. Scalable Dissipative Preparation of Many-Body Entanglement.

    PubMed

    Reiter, Florentin; Reeb, David; Sørensen, Anders S

    2016-07-22

    We present a technique for the dissipative preparation of highly entangled multiparticle states of atoms coupled to common oscillator modes. By combining local spontaneous emission with coherent couplings, we engineer many-body dissipation that drives the system from an arbitrary initial state into a Greenberger-Horne-Zeilinger state. We demonstrate that using our technique highly entangled steady states can be prepared efficiently in a time that scales polynomially with the system size. Our protocol assumes generic couplings and will thus enable the dissipative production of multiparticle entanglement in a wide range of physical systems. As an example, we demonstrate the feasibility of our scheme in state-of-the-art trapped-ion systems.

  1. PREFACE: 17th International Conference on Recent Progress in Many-Body Theories (MBT17)

    NASA Astrophysics Data System (ADS)

    Reinholz, Heidi; Boronat, Jordi

    2014-08-01

    These are the proceedings of the XVII International Conference on Recent Progress in Many-Body Theories, which was held from 8-13 September 2013 in Rostock, Germany. The conference continued the triennial series initiated in Trieste in 1978 and was devoted to new developments in the field of many-body theories. The conference series encourages the exchange of ideas between physicists working in such diverse areas as nuclear physics, quantum chemistry, lattice Hamiltonians or quantum uids. Many-body theories are an integral part in different fields of theoretical physics such as condensed matter, nuclear matter and field theory. Phase transitions and macroscopic quantum effects such as magnetism, Bose-Einstein condensation, super uidity or superconductivity have been investigated within ultra-cold gases, finite systems or various nanomaterials. The conference series on Recent Progress in Many-Body Theories is devoted to foster the interaction and to cross-fertilize between different fields and to discuss future lines of research. The topics of the 17th meeting were Cluster Physics Cold Gases High Energy Density Matter and Intense Lasers Magnetism New Developments in Many-Body Techniques Nuclear Many-Body and Relativistic Theories Quantum Fluids and Solids Quantum Phase Transitions Topological Insulators and Low Dimensional Systems. 109 participants from 20 countries participated. 44 talks and 61 posters werde presented. As a particular highlight of the conference, The Eugene Feenberg Memorial Medal for outstanding results in the field of many-body theory and The Hermann Kümmel Early Achievement Award in Many-Body Physics for young scientists in that field were awarded. The Feenberg Medal went jointly to Patrick Lee (MIT, USA) for his fundamental contributions to condensed-matter theory, especially in regard to the quantum Hall effect, to universal conductance uctuations, and to the Kondo effect in quantum dots, and Douglas Scalapino (UC Santa Barbara, USA) for his

  2. Fermions in Two Dimensions: Scattering and Many-Body Properties

    NASA Astrophysics Data System (ADS)

    Galea, Alexander; Zielinski, Tash; Gandolfi, Stefano; Gezerlis, Alexandros

    2017-08-01

    Ultracold atomic Fermi gases in two dimensions (2D) are an increasingly popular topic of research. The interaction strength between spin-up and spin-down particles in two-component Fermi gases can be tuned in experiments, allowing for a strongly interacting regime where the gas properties are yet to be fully understood. We have probed this regime for 2D Fermi gases by performing T = 0 ab initio diffusion Monte Carlo calculations. The many-body dynamics are largely dependent on the two-body interactions; therefore, we start with an in-depth look at scattering theory in 2D. We show the partial-wave expansion and its relation to the scattering length and effective range. Then, we discuss our numerical methods for determining these scattering parameters. We close out this discussion by illustrating the details of bound states in 2D. Transitioning to the many-body system, we use variationally optimized wave functions to calculate ground-state properties of the gas over a range of interaction strengths. We show results for the energy per particle and parametrize an equation of state. We then proceed to determine the chemical potential for the strongly interacting gas.

  3. Nonequilibrium many-body steady states via Keldysh formalism

    NASA Astrophysics Data System (ADS)

    Maghrebi, Mohammad F.; Gorshkov, Alexey V.

    2016-01-01

    Many-body systems with both coherent dynamics and dissipation constitute a rich class of models which are nevertheless much less explored than their dissipationless counterparts. The advent of numerous experimental platforms that simulate such dynamics poses an immediate challenge to systematically understand and classify these models. In particular, nontrivial many-body states emerge as steady states under nonequilibrium dynamics. While these states and their phase transitions have been studied extensively with mean-field theory, the validity of the mean-field approximation has not been systematically investigated. In this paper, we employ a field-theoretic approach based on the Keldysh formalism to study nonequilibrium phases and phase transitions in a variety of models. In all cases, a complete description via the Keldysh formalism indicates a partial or complete failure of the mean-field analysis. Furthermore, we find that an effective temperature emerges as a result of dissipation, and the universal behavior including the dynamics near the steady state is generically described by a thermodynamic universality class.

  4. Fluctuation Theorem for Many-Body Pure Quantum States

    NASA Astrophysics Data System (ADS)

    Iyoda, Eiki; Kaneko, Kazuya; Sagawa, Takahiro

    2017-09-01

    We prove the second law of thermodynamics and the nonequilibrium fluctuation theorem for pure quantum states. The entire system obeys reversible unitary dynamics, where the initial state of the heat bath is not the canonical distribution but is a single energy eigenstate that satisfies the eigenstate-thermalization hypothesis. Our result is mathematically rigorous and based on the Lieb-Robinson bound, which gives the upper bound of the velocity of information propagation in many-body quantum systems. The entanglement entropy of a subsystem is shown connected to thermodynamic heat, highlighting the foundation of the information-thermodynamics link. We confirmed our theory by numerical simulation of hard-core bosons, and observed dynamical crossover from thermal fluctuations to bare quantum fluctuations. Our result reveals a universal scenario that the second law emerges from quantum mechanics, and can be experimentally tested by artificial isolated quantum systems such as ultracold atoms.

  5. Dynamical stability of a many-body Kapitza pendulum

    SciTech Connect

    Citro, Roberta; Dalla Torre, Emanuele G.; D’Alessio, Luca; Polkovnikov, Anatoli; Babadi, Mehrtash; Oka, Takashi; Demler, Eugene

    2015-09-15

    We consider a many-body generalization of the Kapitza pendulum: the periodically-driven sine–Gordon model. We show that this interacting system is dynamically stable to periodic drives with finite frequency and amplitude. This finding is in contrast to the common belief that periodically-driven unbounded interacting systems should always tend to an absorbing infinite-temperature state. The transition to an unstable absorbing state is described by a change in the sign of the kinetic term in the Floquet Hamiltonian and controlled by the short-wavelength degrees of freedom. We investigate the stability phase diagram through an analytic high-frequency expansion, a self-consistent variational approach, and a numeric semiclassical calculation. Classical and quantum experiments are proposed to verify the validity of our results.

  6. Field Theory Approach to Many-Body Localization

    NASA Astrophysics Data System (ADS)

    Altland, Alexander; Micklitz, Tobias

    2017-03-01

    We introduce an analytic approach to many-body localization (MBL) in random spin chains. We consider MBL within a first quantized framework where it becomes a localization phenomenon in the high-dimensional lattice defined by the Hilbert space of the clean system. Designed in analogy with the field-theory description of single particle localization, our approach describes wave package propagation on that lattice after a disorder average has been performed and the system is controlled by only a few universal parameters. We discuss the stability of an ergodic weak disorder and a localized strong disorder phase, respectively, and demonstrate that the latter is protected by mechanisms which put MBL outside the universality class of Anderson localization.

  7. Estimation of many-body quantum Hamiltonians via compressive sensing

    SciTech Connect

    Shabani, A.; Rabitz, H.; Mohseni, M.; Lloyd, S.; Kosut, R. L.

    2011-07-15

    We develop an efficient and robust approach for quantum measurement of nearly sparse many-body quantum Hamiltonians based on the method of compressive sensing. This work demonstrates that with only O(sln(d)) experimental configurations, consisting of random local preparations and measurements, one can estimate the Hamiltonian of a d-dimensional system, provided that the Hamiltonian is nearly s sparse in a known basis. The classical postprocessing is a convex optimization problem on the total Hilbert space which is generally not scalable. We numerically simulate the performance of this algorithm for three- and four-body interactions in spin-coupled quantum dots and atoms in optical lattices. Furthermore, we apply the algorithm to characterize Hamiltonian fine structure and unknown system-bath interactions.

  8. A Floquet model for the many-body localization transition

    NASA Astrophysics Data System (ADS)

    Zhang, Liangsheng; Khemani, Vedika; Huse, David A.

    2016-12-01

    The nature of the dynamical quantum phase transition between the many-body localized (MBL) phase and the thermal phase remains an open question, and one line of attack on this problem is to explore this transition numerically in finite-size systems. To maximize the contrast between the MBL phase and the thermal phase in such finite-size systems, we argue one should choose a Floquet model with no local conservation laws and rapid thermalization to "infinite temperature" in the thermal phase. Here we introduce and explore such a Floquet spin chain model and show that standard diagnostics of the MBL-to-thermal transition behave well in this model even at modest sizes. We also introduce a physically motivated space-time correlation function, which peaks at the transition in the Floquet model, but is strongly affected by conservation laws in Hamiltonian models.

  9. Many-body theory of surface-enhanced Raman scattering

    NASA Astrophysics Data System (ADS)

    Masiello, David J.; Schatz, George C.

    2008-10-01

    A many-body Green’s function approach to the microscopic theory of surface-enhanced Raman scattering is presented. Interaction effects between a general molecular system and a spatially anisotropic metal particle supporting plasmon excitations in the presence of an external radiation field are systematically included through many-body perturbation theory. Reduction of the exact effects of molecular-electronic correlation to the level of Hartree-Fock mean-field theory is made for practical initial implementation, while description of collective oscillations of conduction electrons in the metal is reduced to that of a classical plasma density; extension of the former to a Kohn-Sham density-functional or second-order Møller-Plesset perturbation theory is discussed; further specialization of the latter to the random-phase approximation allows for several salient features of the formalism to be highlighted without need for numerical computation. Scattering and linear-response properties of the coupled system subjected to an external perturbing electric field in the electric-dipole interaction approximation are investigated. Both damping and finite-lifetime effects of molecular-electronic excitations as well as the characteristic fourth-power enhancement of the molecular Raman scattering intensity are elucidated from first principles. It is demonstrated that the presented theory reduces to previous models of surface-enhanced Raman scattering and leads naturally to a semiclassical picture of the response of a quantum-mechanical molecular system interacting with a spatially anisotropic classical metal particle with electronic polarization approximated by a discretized collection of electric dipoles.

  10. Solving a quantum many-body problem by experiment

    NASA Astrophysics Data System (ADS)

    Schweigler, Thomas; Kasper, Valentin; Erne, Sebastian; Rauer, Bernhard; Langen, Tim; Gasenzer, Thomas; Berges, Jürgen; Schmiedmayer, Jörg

    We experimentally study a pair of tunnel-coupled one-dimensional atomic superfluids, which realize the quantum sine-Gordon/massive Thirring models relevant for a wide variety of disciplines from particle to condensed-matter physics. From measured interference patterns we extract phase correlation functions and analyze if, and under which conditions, the higher-order correlation functions factorize into lower ones. This allows us to characterize the essential features of the model solely from our experimental measurements, detecting the relevant quasiparticles, their interactions and the topologically distinct vacua. Our method provides comprehensive insights into a non-trivial quantum field theory and establishes a general method to analyze quantum many-body systems through experiments. The method is also used to investigate the non-equilibrium dynamics following a quench in the tunnel-coupling between the superfluids.

  11. Particle diagrams and embedded many-body random matrix theory.

    PubMed

    Small, R A; Müller, S

    2014-07-01

    We present a method which uses Feynman-like diagrams to calculate the statistical quantities of embedded many-body random matrix problems. The method provides a promising alternative to existing techniques and offers many important simplifications. We use it here to find the fourth, sixth, and eighth moments of the level density of an m-body system with k fermions or bosons interacting through a random Hermitian potential (k ≤ m) in the limit where the number of possible single-particle states is taken to infinity. All share the same transition, starting immediately after 2k = m, from moments arising from a semicircular level density to Gaussian moments. The results also reveal a striking feature; the domain of the 2nth moment is naturally divided into n subdomains specified by the points 2k = m,3 k = m,...,nk = m.

  12. Breakdown of Traditional Many-Body Theories for Correlated Electrons

    NASA Astrophysics Data System (ADS)

    Gunnarsson, O.; Rohringer, G.; Schäfer, T.; Sangiovanni, G.; Toschi, A.

    2017-08-01

    Starting from the (Hubbard) model of an atom, we demonstrate that the uniqueness of the mapping from the interacting to the noninteracting Green function, G →G0, is strongly violated, by providing numerous explicit examples of different G0 leading to the same physical G . We argue that there are indeed infinitely many such G0, with numerous crossings with the physical solution. We show that this rich functional structure is directly related to the divergence of certain classes of (irreducible vertex) diagrams, with important consequences for traditional many-body physics based on diagrammatic expansions. Physically, we ascribe the onset of these highly nonperturbative manifestations to the progressive suppression of the charge susceptibility induced by the formation of local magnetic moments and/or resonating valence bond (RVB) states in strongly correlated electron systems.

  13. Many-body lattice wave functions from conformal blocks

    NASA Astrophysics Data System (ADS)

    Montes, Sebastián; Rodríguez-Laguna, Javier; Tu, Hong-Hao; Sierra, Germán

    2017-02-01

    We introduce a general framework to construct many-body lattice wave functions starting from the conformal blocks (CBs) of rational conformal field theories (RCFTs). We discuss the different ways of encoding the physical degrees of freedom of the lattice system using both the internal symmetries of the theory and the fusion channels of the CBs. We illustrate this construction both by revisiting the known Haldane-Shastry model and by providing a novel implementation for the Ising RCFT. In the latter case, we find a connection to the Ising transverse field (ITF) spin chain via the Kramers-Wannier duality and the Temperley-Lieb-Jones algebra. We also find evidence that the ground state of the finite-size critical ITF Hamiltonian corresponds exactly to the wave function obtained from CBs of spin fields.

  14. Optimal Control Technique for Many-Body Quantum Dynamics

    NASA Astrophysics Data System (ADS)

    Doria, Patrick; Calarco, Tommaso; Montangero, Simone

    2011-05-01

    We present an efficient strategy for controlling a vast range of nonintegrable quantum many-body one-dimensional systems that can be merged with state-of-the-art tensor network simulation methods such as the density matrix renormalization group. To demonstrate its potential, we employ it to solve a major issue in current optical-lattice physics with ultracold atoms: we show how to reduce by about 2 orders of magnitude the time needed to bring a superfluid gas into a Mott insulator state, while suppressing defects by more than 1 order of magnitude as compared to current experiments [T. Stöferle , Phys. Rev. Lett. 92, 130403 (2004)PRLTAO0031-900710.1103/PhysRevLett.92.130403]. Finally, we show that the optimal pulse is robust against atom number fluctuations.

  15. Particle diagrams and embedded many-body random matrix theory

    NASA Astrophysics Data System (ADS)

    Small, R. A.; Müller, S.

    2014-07-01

    We present a method which uses Feynman-like diagrams to calculate the statistical quantities of embedded many-body random matrix problems. The method provides a promising alternative to existing techniques and offers many important simplifications. We use it here to find the fourth, sixth, and eighth moments of the level density of an m-body system with k fermions or bosons interacting through a random Hermitian potential (k ≤m) in the limit where the number of possible single-particle states is taken to infinity. All share the same transition, starting immediately after 2k=m, from moments arising from a semicircular level density to Gaussian moments. The results also reveal a striking feature; the domain of the 2nth moment is naturally divided into n subdomains specified by the points 2k=m,3k=m,...,nk=m.

  16. Many-body dynamics of chemically propelled nanomotors

    NASA Astrophysics Data System (ADS)

    Colberg, Peter H.; Kapral, Raymond

    2017-08-01

    The collective behavior of chemically propelled sphere-dimer motors made from linked catalytic and noncatalytic spheres in a quasi-two-dimensional confined geometry is studied using a coarse-grained microscopic dynamical model. Chemical reactions at the catalytic spheres that convert fuel to product generate forces that couple to solvent degrees of freedom as a consequence of momentum conservation in the microscopic dynamics. The collective behavior of the many-body system is influenced by direct intermolecular interactions among the motors, chemotactic effects due to chemical gradients, hydrodynamic coupling, and thermal noise. Segregation into high and low density phases and globally homogeneous states with strong fluctuations are investigated as functions of the motor characteristics. Factors contributing to this behavior are discussed in the context of active Brownian models.

  17. Many-body dynamics of a BEC quenched to unitarity

    NASA Astrophysics Data System (ADS)

    Corson, John; Sykes, Andrew; D'Incao, Jose; Koller, Andrew; Greene, Chris; Rey, Ana Maria; Hazzard, Kaden; Bohn, John

    2014-03-01

    The dynamics of a dilute BEC quenched to unitarity are studied using a variational ansatz for the many-body quantum state. Despite the resonant atom-atom interactions, the condensate does not deplete instantaneously, and this allows for a self-consistent mean-field-like description of the system at short (but experimentally-accessible) times. At infinite scattering length and zero temperature, the dynamics are found to scale universally with the number density, as reported in the experiment of Makotyn et al, arXiv1308.3696. We predict the time evolution of observables such as the momentum distribution nk(t) , the contact C(t) , and the density nm(t) of Feshbach molecules generated by the interaction quench. We observe a saturation of large-momentum populations on a time scale that is consistent with recent measurements.

  18. Many-body-localization transition: sensitivity to twisted boundary conditions

    NASA Astrophysics Data System (ADS)

    Monthus, Cécile

    2017-03-01

    For disordered interacting quantum systems, the sensitivity of the spectrum to twisted boundary conditions depending on an infinitesimal angle ϕ can be used to analyze the many-body-localization transition. The sensitivity of the energy levels {{E}n}(φ ) is measured by the level curvature {{K}n}=En\\prime \\prime(0) , or more precisely by the Thouless dimensionless curvature {{k}n}={{K}n}/{{ Δ }n} , where {{ Δ }n} is the level spacing that decays exponentially with the size L of the system. For instance {{ Δ }n}\\propto {{2}-L} in the middle of the spectrum of quantum spin chains of L spins, while the Drude weight {{D}n}=L{{K}n} studied recently by Filippone et al (arxiv:1606.07291v1) involves a different rescaling. The sensitivity of the eigenstates |{{\\psi}n}(φ )> is characterized by the susceptibility {χn}=-Fn\\prime \\prime(0) of the fidelity {{F}n}= |<{{\\psi}n}(0)|{{\\psi}n}(φ )>| . Both observables are distributed with probability distributions displaying power-law tails {{P}β}(k)≃ {{A}β}|k{{|}-(2+β )} and Q(χ )≃ {{B}β}{χ-\\frac{3+β{2}}} , where β is the level repulsion index taking the values {β\\text{GOE}}=1 in the ergodic phase and {β\\text{loc}}=0 in the localized phase. The amplitudes {{A}β} and {{B}β} of these two heavy tails are given by some moments of the off-diagonal matrix element of the local current operator between two nearby energy levels, whose probability distribution has been proposed as a criterion for the many-body-localization transition by Serbyn et al (2015 Phys. Rev. X 5 041047).

  19. Global characteristics of all eigenstates of local many-body Hamiltonians: participation ratio and entanglement entropy

    NASA Astrophysics Data System (ADS)

    Beugeling, W.; Andreanov, A.; Haque, Masudul

    2015-02-01

    In the spectrum of many-body quantum systems appearing in condensed matter physics, the low-energy eigenstates were the traditional focus of research. The interest in the statistical properties of the full eigenspectrum has grown more recently, in particular in the context of non-equilibrium questions. Wave functions of interacting lattice quantum systems can be characterized either by local observables or by global properties such as the participation ratio (PR) in a many-body basis or the entanglement between various partitions. We present a study of the PR and of the entanglement entropy (EE) between two roughly equal spatial partitions of the system, in all the eigenfunctions of local Hamiltonians. Motivated by the similarity of the PR and EE—both are generically larger in the bulk and smaller near the edges of the spectrum—we quantitatively analyze the correlation between them. We elucidate the effect of (proximity to) integrability, showing how low-entanglement and low-PR states appear also in the middle of the spectrum as one approaches integrable points. We also determine the precise scaling behaviour of the eigenstate-to-eigenstate fluctuations of the PR and EE with respect to system size and characterize the statistical distribution of these quantities near the middle of the spectrum.

  20. Many-body effect in ion binding to RNA

    PubMed Central

    Zhu, Yuhong; Chen, Shi-Jie

    2014-01-01

    Ion-mediated electrostatic interactions play an important role in RNA folding stability. For a RNA in a solution with higher Mg2+ ion concentration, more counterions in the solution can bind to the RNA, causing a strong many-body coupling between the bound ions. The many-body effect can change the effective potential of mean force between the tightly bound ions. This effect tends to dampen ion binding and lower RNA folding stability. Neglecting the many-body effect leads to a systematic error (over-estimation) of RNA folding stability at high Mg2+ ion concentrations. Using the tightly bound ion model combined with a conformational ensemble model, we investigate the influence of the many-body effect on the ion-dependent RNA folding stability. Comparisons with the experimental data indicate that including the many-body effect led to much improved predictions for RNA folding stability at high Mg2+ ion concentrations. The results suggest that the many-body effect can be important for RNA folding in high concentrations of multivalent ions. Further investigation showed that the many-body effect can influence the spatial distribution of the tightly bound ions and the effect is more pronounced for compact RNA structures and structures prone to the formation of local clustering of ions. PMID:25106614

  1. Measurement of many-body chaos using a quantum clock

    NASA Astrophysics Data System (ADS)

    Zhu, Guanyu; Hafezi, Mohammad; Grover, Tarun

    2016-12-01

    There has been recent progress in understanding chaotic features in many-body quantum systems. Motivated by the scrambling of information in black holes, it has been suggested that the time dependence of out-of-time-ordered (OTO) correlation functions such as is a faithful measure of quantum chaos. Experimentally, these correlators are challenging to access since they apparently require access to both forward and backward time evolution with the system Hamiltonian. Here we propose a protocol to measure such OTO correlators using an ancilla that controls the direction of time. Specifically, by coupling the state of the ancilla to the system Hamiltonian of interest, we can emulate the forward and backward time propagation, where the ancilla plays the role of a quantum clock. Within this scheme, the continuous evolution of the entire system (the system of interest and the ancilla) is governed by a time-independent Hamiltonian. We discuss the implementation of our protocol with current circuit-QED technology for a class of interacting Hamiltonians. Our protocol is immune to errors that could occur when the direction of time evolution is externally controlled by a classical switch.

  2. Many body population trapping in ultracold dipolar gases

    NASA Astrophysics Data System (ADS)

    Dutta, Omjyoti; Lewenstein, Maciej; Zakrzewski, Jakub

    2014-05-01

    A system of interacting dipoles is of paramount importance for understanding many-body physics. The interaction between dipoles is anisotropic and long-range. While the former allows one to observe rich effects due to different geometries of the system, long-range (1/{{r}^{3}}) interactions lead to strong correlations between dipoles and frustration. In effect, interacting dipoles in a lattice form a paradigmatic system with strong correlations and exotic properties with possible applications in quantum information technologies, and as quantum simulators of condensed matter physics, material science, etc. Notably, such a system is extremely difficult to model due to a proliferation of interaction induced multi-band excitations for sufficiently strong dipole-dipole interactions. In this article we develop a consistent theoretical model of interacting polar molecules in a lattice by applying the concepts and ideas of ionization theory which allows us to include highly excited Bloch bands. Additionally, by involving concepts from quantum optics (population trapping), we show that one can induce frustration and engineer exotic states, such as Majumdar-Ghosh state, or vector-chiral states in such a system.

  3. Stochastic many-body perturbation theory for anharmonic molecular vibrations

    SciTech Connect

    Hermes, Matthew R.; Hirata, So

    2014-08-28

    A new quantum Monte Carlo (QMC) method for anharmonic vibrational zero-point energies and transition frequencies is developed, which combines the diagrammatic vibrational many-body perturbation theory based on the Dyson equation with Monte Carlo integration. The infinite sums of the diagrammatic and thus size-consistent first- and second-order anharmonic corrections to the energy and self-energy are expressed as sums of a few m- or 2m-dimensional integrals of wave functions and a potential energy surface (PES) (m is the vibrational degrees of freedom). Each of these integrals is computed as the integrand (including the value of the PES) divided by the value of a judiciously chosen weight function evaluated on demand at geometries distributed randomly but according to the weight function via the Metropolis algorithm. In this way, the method completely avoids cumbersome evaluation and storage of high-order force constants necessary in the original formulation of the vibrational perturbation theory; it furthermore allows even higher-order force constants essentially up to an infinite order to be taken into account in a scalable, memory-efficient algorithm. The diagrammatic contributions to the frequency-dependent self-energies that are stochastically evaluated at discrete frequencies can be reliably interpolated, allowing the self-consistent solutions to the Dyson equation to be obtained. This method, therefore, can compute directly and stochastically the transition frequencies of fundamentals and overtones as well as their relative intensities as pole strengths, without fixed-node errors that plague some QMC. It is shown that, for an identical PES, the new method reproduces the correct deterministic values of the energies and frequencies within a few cm{sup −1} and pole strengths within a few thousandths. With the values of a PES evaluated on the fly at random geometries, the new method captures a noticeably greater proportion of anharmonic effects.

  4. Stochastic many-body perturbation theory for anharmonic molecular vibrations

    NASA Astrophysics Data System (ADS)

    Hermes, Matthew R.; Hirata, So

    2014-08-01

    A new quantum Monte Carlo (QMC) method for anharmonic vibrational zero-point energies and transition frequencies is developed, which combines the diagrammatic vibrational many-body perturbation theory based on the Dyson equation with Monte Carlo integration. The infinite sums of the diagrammatic and thus size-consistent first- and second-order anharmonic corrections to the energy and self-energy are expressed as sums of a few m- or 2m-dimensional integrals of wave functions and a potential energy surface (PES) (m is the vibrational degrees of freedom). Each of these integrals is computed as the integrand (including the value of the PES) divided by the value of a judiciously chosen weight function evaluated on demand at geometries distributed randomly but according to the weight function via the Metropolis algorithm. In this way, the method completely avoids cumbersome evaluation and storage of high-order force constants necessary in the original formulation of the vibrational perturbation theory; it furthermore allows even higher-order force constants essentially up to an infinite order to be taken into account in a scalable, memory-efficient algorithm. The diagrammatic contributions to the frequency-dependent self-energies that are stochastically evaluated at discrete frequencies can be reliably interpolated, allowing the self-consistent solutions to the Dyson equation to be obtained. This method, therefore, can compute directly and stochastically the transition frequencies of fundamentals and overtones as well as their relative intensities as pole strengths, without fixed-node errors that plague some QMC. It is shown that, for an identical PES, the new method reproduces the correct deterministic values of the energies and frequencies within a few cm-1 and pole strengths within a few thousandths. With the values of a PES evaluated on the fly at random geometries, the new method captures a noticeably greater proportion of anharmonic effects.

  5. Stochastic many-body perturbation theory for anharmonic molecular vibrations.

    PubMed

    Hermes, Matthew R; Hirata, So

    2014-08-28

    A new quantum Monte Carlo (QMC) method for anharmonic vibrational zero-point energies and transition frequencies is developed, which combines the diagrammatic vibrational many-body perturbation theory based on the Dyson equation with Monte Carlo integration. The infinite sums of the diagrammatic and thus size-consistent first- and second-order anharmonic corrections to the energy and self-energy are expressed as sums of a few m- or 2m-dimensional integrals of wave functions and a potential energy surface (PES) (m is the vibrational degrees of freedom). Each of these integrals is computed as the integrand (including the value of the PES) divided by the value of a judiciously chosen weight function evaluated on demand at geometries distributed randomly but according to the weight function via the Metropolis algorithm. In this way, the method completely avoids cumbersome evaluation and storage of high-order force constants necessary in the original formulation of the vibrational perturbation theory; it furthermore allows even higher-order force constants essentially up to an infinite order to be taken into account in a scalable, memory-efficient algorithm. The diagrammatic contributions to the frequency-dependent self-energies that are stochastically evaluated at discrete frequencies can be reliably interpolated, allowing the self-consistent solutions to the Dyson equation to be obtained. This method, therefore, can compute directly and stochastically the transition frequencies of fundamentals and overtones as well as their relative intensities as pole strengths, without fixed-node errors that plague some QMC. It is shown that, for an identical PES, the new method reproduces the correct deterministic values of the energies and frequencies within a few cm(-1) and pole strengths within a few thousandths. With the values of a PES evaluated on the fly at random geometries, the new method captures a noticeably greater proportion of anharmonic effects.

  6. Investigation of many-body forces in krypton and xenon

    NASA Astrophysics Data System (ADS)

    Salacuse, J. J.; Egelstaff, P. A.

    1988-10-01

    The simplicity of the state dependence at relatively high temperatures of the many-body potential contribution to the pressure and energy has been pointed out previously [J. Ram and P. A. Egelstaff, J. Phys. Chem. Liq. 14, 29 (1984); A. Teitsima and P. A. Egelstaff, Phys. Rev. A 21, 367 (1980)]. In this paper, we investigate how far these many-body potential terms may be represented by simple models in the case of krypton on the 423-, 273-, 190-, and 150-K isotherms, and xenon on the 170-, 210-, and 270-K isotherms. At the higher temperatures the best agreement is found for the mean-field type of theory, and some consequences are pointed out. On the lower isotherms a state point is found where the many-body energy vanishes, and large departures from mean-field behavior are observed. This is attributed to the influence of short-ranged many-body forces.

  7. Investigation of many-body forces in krypton and xenon

    SciTech Connect

    Salacuse, J.J.; Egelstaff, P.A.

    1988-10-15

    The simplicity of the state dependence at relatively high temperatures ofthe many-body potential contribution to the pressure and energy has been pointed out previously (J. Ram and P. A. Egelstaff, J. Phys. Chem. Liq. 14, 29 (1984); A. Teitsima and P. A. Egelstaff, Phys. Rev. A 21, 367 (1980)). In this paper, we investigate how far these many-body potential terms may be represented by simple models in the case of krypton on the 423-, 273-, 190-, and 150-K isotherms, and xenon on the 170-, 210-, and 270-K isotherms. At the higher temperatures the best agreement is found for the mean-field type of theory, and some consequences are pointed out. On the lower isotherms a state point is found where the many-body energy vanishes, and large departures from mean-field behavior are observed. This is attributed to the influence of short-ranged many-body forces.

  8. Communication: Random phase approximation renormalized many-body perturbation theory

    SciTech Connect

    Bates, Jefferson E.; Furche, Filipp

    2013-11-07

    We derive a renormalized many-body perturbation theory (MBPT) starting from the random phase approximation (RPA). This RPA-renormalized perturbation theory extends the scope of single-reference MBPT methods to small-gap systems without significantly increasing the computational cost. The leading correction to RPA, termed the approximate exchange kernel (AXK), substantially improves upon RPA atomization energies and ionization potentials without affecting other properties such as barrier heights where RPA is already accurate. Thus, AXK is more balanced than second-order screened exchange [A. Grüneis et al., J. Chem. Phys. 131, 154115 (2009)], which tends to overcorrect RPA for systems with stronger static correlation. Similarly, AXK avoids the divergence of second-order Møller-Plesset (MP2) theory for small gap systems and delivers a much more consistent performance than MP2 across the periodic table at comparable cost. RPA+AXK thus is an accurate, non-empirical, and robust tool to assess and improve semi-local density functional theory for a wide range of systems previously inaccessible to first-principles electronic structure calculations.

  9. Communication: Random phase approximation renormalized many-body perturbation theory

    NASA Astrophysics Data System (ADS)

    Bates, Jefferson E.; Furche, Filipp

    2013-11-01

    We derive a renormalized many-body perturbation theory (MBPT) starting from the random phase approximation (RPA). This RPA-renormalized perturbation theory extends the scope of single-reference MBPT methods to small-gap systems without significantly increasing the computational cost. The leading correction to RPA, termed the approximate exchange kernel (AXK), substantially improves upon RPA atomization energies and ionization potentials without affecting other properties such as barrier heights where RPA is already accurate. Thus, AXK is more balanced than second-order screened exchange [A. Grüneis et al., J. Chem. Phys. 131, 154115 (2009)], which tends to overcorrect RPA for systems with stronger static correlation. Similarly, AXK avoids the divergence of second-order Møller-Plesset (MP2) theory for small gap systems and delivers a much more consistent performance than MP2 across the periodic table at comparable cost. RPA+AXK thus is an accurate, non-empirical, and robust tool to assess and improve semi-local density functional theory for a wide range of systems previously inaccessible to first-principles electronic structure calculations.

  10. EDITORIAL: Focus on Quantum Information and Many-Body Theory

    NASA Astrophysics Data System (ADS)

    Eisert, Jens; Plenio, Martin B.

    2010-02-01

    Quantum many-body models describing natural systems or materials and physical systems assembled piece by piece in the laboratory for the purpose of realizing quantum information processing share an important feature: intricate correlations that originate from the coherent interaction between a large number of constituents. In recent years it has become manifest that the cross-fertilization between research devoted to quantum information science and to quantum many-body physics leads to new ideas, methods, tools, and insights in both fields. Issues of criticality, quantum phase transitions, quantum order and magnetism that play a role in one field find relations to the classical simulation of quantum systems, to error correction and fault tolerance thresholds, to channel capacities and to topological quantum computation, to name but a few. The structural similarities of typical problems in both fields and the potential for pooling of ideas then become manifest. Notably, methods and ideas from quantum information have provided fresh approaches to long-standing problems in strongly correlated systems in the condensed matter context, including both numerical methods and conceptual insights. Focus on quantum information and many-body theory Contents TENSOR NETWORKS Homogeneous multiscale entanglement renormalization ansatz tensor networks for quantum critical systems M Rizzi, S Montangero, P Silvi, V Giovannetti and Rosario Fazio Concatenated tensor network states R Hübener, V Nebendahl and W Dür Entanglement renormalization in free bosonic systems: real-space versus momentum-space renormalization group transforms G Evenbly and G Vidal Finite-size geometric entanglement from tensor network algorithms Qian-Qian Shi, Román Orús, John Ove Fjærestad and Huan-Qiang Zhou Characterizing symmetries in a projected entangled pair state D Pérez-García, M Sanz, C E González-Guillén, M M Wolf and J I Cirac Matrix product operator representations B Pirvu, V Murg, J I Cirac

  11. Charge optimized many body (COMB) potentials for Pt and Au

    NASA Astrophysics Data System (ADS)

    Antony, A. C.; Akhade, S. A.; Lu, Z.; Liang, T.; Janik, M. J.; Phillpot, S. R.; Sinnott, S. B.

    2017-06-01

    Interatomic potentials for Pt and Au are developed within the third generation charge optimized many-body (COMB3) formalism. The potentials are capable of reproducing phase order, lattice constants, and elastic constants of Pt and Au systems as experimentally measured or calculated by density functional theory. We also fit defect formation energies, surface energies and stacking fault energies for Pt and Au metals. The resulting potentials are used to map a 2D contour of the gamma surface and simulate the tensile test of 16-grain polycrystalline Pt and Au structures at 300 K. The stress-strain behaviour is investigated and the primary slip systems {1 1 1}<1 \\bar{1}  0> are identified. In addition, we perform high temperature (1800 K for Au and 2300 K for Pt) molecular dynamics simulations of 30 nm Pt and Au truncated octahedron nanoparticles and examine morphological changes of each particle. We further calculate the activation energy barrier for surface diffusion during simulations of several nanoseconds and report energies of 0.62+/- 0.16 eV for Pt and 1.44+/- 0.06 eV for Au. This initial parameterization and application of the Pt and Au potentials demonstrates a starting point for the extension of these potentials to multicomponent systems within the COMB3 framework.

  12. Critical Properties of the Many-Body Localization Transition

    NASA Astrophysics Data System (ADS)

    Khemani, Vedika; Lim, S. P.; Sheng, D. N.; Huse, David A.

    2017-04-01

    The transition from a many-body localized phase to a thermalizing one is a dynamical quantum phase transition that lies outside the framework of equilibrium statistical mechanics. We provide a detailed study of the critical properties of this transition at finite sizes in one dimension. We find that the entanglement entropy of small subsystems looks strongly subthermal in the quantum critical regime, which indicates that it varies discontinuously across the transition as the system size is taken to infinity, even though many other aspects of the transition look continuous. We also study the variance of the half-chain entanglement entropy, which shows a peak near the transition, and find substantial variation in the entropy across eigenstates of the same sample. Furthermore, the sample-to-sample variations in this quantity are strongly growing and are larger than the intrasample variations. We posit that these results are consistent with a picture in which the transition to the thermal phase is driven by an eigenstate-dependent sparse resonant "backbone" of long-range entanglement, which just barely gains enough strength to thermalize the system on the thermal side of the transition as the system size is taken to infinity. This discontinuity in a global quantity—the presence of a fully functional bath—in turn implies a discontinuity even for local properties. We discuss how this picture compares with existing renormalization group treatments of the transition.

  13. Interferometric measurements of many-body topological invariants using mobile impurities.

    PubMed

    Grusdt, F; Yao, N Y; Abanin, D; Fleischhauer, M; Demler, E

    2016-06-17

    Topological quantum phases cannot be characterized by Ginzburg-Landau type order parameters, and are instead described by non-local topological invariants. Experimental platforms capable of realizing such exotic states now include synthetic many-body systems such as ultracold atoms or photons. Unique tools available in these systems enable a new characterization of strongly correlated many-body states. Here we propose a general scheme for detecting topological order using interferometric measurements of elementary excitations. The key ingredient is the use of mobile impurities that bind to quasiparticles of a host many-body system. Specifically, we show how fractional charges can be probed in the bulk of fractional quantum Hall systems. We demonstrate that combining Ramsey interference with Bloch oscillations can be used to measure Chern numbers characterizing the dispersion of individual quasiparticles, which gives a direct probe of their fractional charges. Possible extensions of our method to other many-body systems, such as spin liquids, are conceivable.

  14. Interferometric measurements of many-body topological invariants using mobile impurities

    NASA Astrophysics Data System (ADS)

    Grusdt, F.; Yao, N. Y.; Abanin, D.; Fleischhauer, M.; Demler, E.

    2016-06-01

    Topological quantum phases cannot be characterized by Ginzburg-Landau type order parameters, and are instead described by non-local topological invariants. Experimental platforms capable of realizing such exotic states now include synthetic many-body systems such as ultracold atoms or photons. Unique tools available in these systems enable a new characterization of strongly correlated many-body states. Here we propose a general scheme for detecting topological order using interferometric measurements of elementary excitations. The key ingredient is the use of mobile impurities that bind to quasiparticles of a host many-body system. Specifically, we show how fractional charges can be probed in the bulk of fractional quantum Hall systems. We demonstrate that combining Ramsey interference with Bloch oscillations can be used to measure Chern numbers characterizing the dispersion of individual quasiparticles, which gives a direct probe of their fractional charges. Possible extensions of our method to other many-body systems, such as spin liquids, are conceivable.

  15. Dynamics close to the many-body localization transition

    NASA Astrophysics Data System (ADS)

    Bar Lev (Krivolapov), Yevgeny; Reichman, David R.

    2014-03-01

    It has recently been suggested that in a generic class of disordered and (short-ranged) interacting quantum systems a dynamical metal-insulator transition may occur at finite temperatures. This proposed phenomenon is called many-body localization (MBL). In this work we study the real-time dynamics of this transition for a range of parameters where the transition should manifest according to theory and recent numerical studies. For this purpose, we numerically solve the non-equilibrium quantum kinetic equations in the self-consistent second-Born approximation, the same approximation used in the original prediction of MBL. For accessible times, we observe a complex sequence of dynamical regimes. Surprisingly we find little change of behavior upon crossing the putative dynamical phase boundary as determined by previous numerical studies. This work used the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by National Science Foundation grant number OCI-1053575. The work was supported by grant NSF-CHE-1213247.

  16. Two Universality Classes for the Many-Body Localization Transition

    NASA Astrophysics Data System (ADS)

    Khemani, Vedika; Sheng, D. N.; Huse, David A.

    2017-08-01

    We provide a systematic comparison of the many-body localization (MBL) transition in spin chains with nonrandom quasiperiodic versus random fields. We find evidence suggesting that these belong to two separate universality classes: the first dominated by "intrinsic" intrasample randomness, and the second dominated by external intersample quenched randomness. We show that the effects of intersample quenched randomness are strongly growing, but not yet dominant, at the system sizes probed by exact-diagonalization studies on random models. Thus, the observed finite-size critical scaling collapses in such studies appear to be in a preasymptotic regime near the nonrandom universality class, but showing signs of the initial crossover towards the external-randomness-dominated universality class. Our results provide an explanation for why exact-diagonalization studies on random models see an apparent scaling near the transition while also obtaining finite-size scaling exponents that strongly violate Harris-Chayes bounds that apply to disorder-driven transitions. We also show that the MBL phase is more stable for the quasiperiodic model as compared to the random one, and the transition in the quasiperiodic model suffers less from certain finite-size effects.

  17. Correlation energy extrapolation by many-body expansion

    DOE PAGES

    Boschen, Jeffery S.; Theis, Daniel; Ruedenberg, Klaus; ...

    2017-01-09

    Accounting for electron correlation is required for high accuracy calculations of molecular energies. The full configuration interaction (CI) approach can fully capture the electron correlation within a given basis, but it does so at a computational expense that is impractical for all but the smallest chemical systems. In this work, a new methodology is presented to approximate configuration interaction calculations at a reduced computational expense and memory requirement, namely, the correlation energy extrapolation by many-body expansion (CEEMBE). This method combines a MBE approximation of the CI energy with an extrapolated correction obtained from CI calculations using subsets of the virtualmore » orbitals. The extrapolation approach is inspired by, and analogous to, the method of correlation energy extrapolation by intrinsic scaling. Benchmark calculations of the new method are performed on diatomic fluorine and ozone. Finally, the method consistently achieves agreement with CI calculations to within a few mhartree and often achieves agreement to within ~1 millihartree or less, while requiring significantly less computational resources.« less

  18. Fermionic Many-Body States Under the Microscope

    NASA Astrophysics Data System (ADS)

    Mazurenko, Anton; Greif, Daniel; Parsons, Maxwell F.; Chiu, Christie S.; Blatt, Sebastian; Huber, Florian; Ji, Geoffrey; Greiner, Markus

    2016-05-01

    We demonstrate the site-resolved observation of two component, fermionic Mott insulators, band insulators and metals of ultracold 6 Li in a single layer of a three-dimensional optical lattice. Site-resolved imaging enables measurements of local observables, including the local occupation variance. A comparison with predictions of the high temperature series expansion of the Fermi-Hubbard model is consistent with thermally equilibrated samples, with local entropies as low as 0 . 7kB per particle in the Mott insulator, and 0 . 5kB per particle in the band insulator. The phase diagram in the Mott regime is studied, exploiting the fact that the underlying harmonic potential enables measurements across a wide range of chemical potentials in a single experimental shot. Our experiments provide a starting point for implementing entropy redistribution based cooling schemes. Furthermore, we report on our recent progress towards measuring site-resolved spin correlations for low temperature samples, opening the door for studying many-body systems in theoretically intractable regimes. Current address: Max-Planck-Institut für Quantenoptik, 85748 Garching, Germany.

  19. On the representation of many-body interactions in water

    SciTech Connect

    Medders, Gregory R.; Gotz, Andreas W.; Morales, Miguel A.; Bajaj, Pushp; Paesani, Francesco

    2015-09-09

    Our recent work has shown that the many-body expansion of the interactionenergy can be used to develop analytical representations of global potential energy surfaces (PESs) for water. In this study, the role of short- and long-range interactions at different orders is investigated by analyzing water potentials that treat the leading terms of the many-body expansion through implicit (i.e., TTM3-F and TTM4-F PESs) and explicit (i.e., WHBB and MB-pol PESs) representations. Moreover, it is found that explicit short-range representations of 2-body and 3-body interactions along with a physically correct incorporation of short- and long-range contributions are necessary for an accurate representation of the waterinteractions from the gas to the condensed phase. Likewise, a complete many-body representation of the dipole moment surface is found to be crucial to reproducing the correct intensities of the infrared spectrum of liquid water.

  20. Using optical clock to probe quantum many-body physics

    NASA Astrophysics Data System (ADS)

    Ye, Jun

    2016-05-01

    The progress of optical lattice clock has benefited greatly from the understanding of atomic interactions. At the same time, the precision of clock spectroscopy has been applied to explore many-body spin interactions including SU(N) symmetry. Our recent work on this combined front of quantum metrology and many-body physics includes the probe of spin-orbital physics in the lattice clock and the investigation of a Fermi degenerate gas of 105 87Sr atoms in a three-dimensional magic-wavelength optical lattice.

  1. Many-body transitions in a single molecule visualized by scanning tunnelling microscopy

    NASA Astrophysics Data System (ADS)

    Schulz, Fabian; Ijäs, Mari; Drost, Robert; Hämäläinen, Sampsa K.; Harju, Ari; Seitsonen, Ari P.; Liljeroth, Peter

    2015-03-01

    Many-body effects arise from the collective behaviour of large numbers of interacting particles, for example, electrons, and the properties of such a system cannot be understood considering only single or non-interacting particles. Despite the generality of the many-body picture, there are only a few examples of experimentally observing such effects in molecular systems. Measurements of the local density of states of single molecules by scanning tunnelling spectroscopy is usually interpreted in terms of single-particle molecular orbitals. Here, we show that the simple single-particle picture fails qualitatively to account for the resonances in the tunnelling spectra of different charge states of cobalt phthalocyanine molecules. Instead, these resonances can be understood as a series of many-body excitations of the different ground states of the molecule. Our theoretical approach opens an accessible route beyond the single-particle picture in quantifying many-body states in molecules.

  2. Molecular Interactions with Many-Body Perturbation Theory.

    DTIC Science & Technology

    1981-09-11

    Medcine , Ne. York, York, June 4, 1979. R. J. Bartlett, "Many-Body Perturbation Thery", Aarhus University, Aarhus, Denmark, June 18, 1979. R. J. Bartlett...editor can be accepted for speedy publication. Permission is granted to authors of scientific articles and books to quote from this journal provided

  3. Many-body localization in one dimension as a dynamical renormalization group fixed point.

    PubMed

    Vosk, Ronen; Altman, Ehud

    2013-02-08

    We formulate a dynamical real space renormalization group (RG) approach to describe the time evolution of a random spin-1/2 chain, or interacting fermions, initialized in a state with fixed particle positions. Within this approach we identify a many-body localized state of the chain as a dynamical infinite randomness fixed point. Near this fixed point our method becomes asymptotically exact, allowing analytic calculation of time dependent quantities. In particular, we explain the striking universal features in the growth of the entanglement seen in recent numerical simulations: unbounded logarithmic growth delayed by a time inversely proportional to the interaction strength. This is in striking contrast to the much slower entropy growth as loglogt found for noninteracting fermions with bond disorder. Nonetheless, even the interacting system does not thermalize in the long time limit. We attribute this to an infinite set of approximate integrals of motion revealed in the course of the RG flow, which become asymptotically exact conservation laws at the fixed point. Hence we identify the many-body localized state with an emergent generalized Gibbs ensemble.

  4. Particle diagrams and statistics of many-body random potentials

    NASA Astrophysics Data System (ADS)

    Small, Rupert A.; Müller, Sebastian

    2015-05-01

    We present a method using Feynman-like diagrams to calculate the statistical properties of random many-body potentials. This method provides a promising alternative to existing techniques typically applied to this class of problems, such as the method of supersymmetry and the eigenvector expansion technique pioneered in Benet et al. (2001). We use it here to calculate the fourth, sixth and eighth moments of the average level density for systems with m bosons or fermions that interact through a random k-body Hermitian potential (k ≤ m); the ensemble of such potentials with a Gaussian weight is known as the embedded Gaussian Unitary Ensemble (eGUE) (Mon and French, 1975). Our results apply in the limit where the number l of available single-particle states is taken to infinity. A key advantage of the method is that it provides an efficient way to identify only those expressions which will stay relevant in this limit. It also provides a general argument for why these terms have to be the same for bosons and fermions. The moments are obtained as sums over ratios of binomial expressions, with a transition from moments associated to a semi-circular level density for m < 2 k to Gaussian moments in the dilute limit k ≪ m ≪ l. Regarding the form of this transition, we see that as m is increased, more and more diagrams become relevant, with new contributions starting from each of the points m = 2 k , 3 k , … , nk for the 2 nth moment.

  5. Solving the Quantum Many-Body Problem via Correlations Measured with a Momentum Microscope.

    PubMed

    Hodgman, S S; Khakimov, R I; Lewis-Swan, R J; Truscott, A G; Kheruntsyan, K V

    2017-06-16

    In quantum many-body theory, all physical observables are described in terms of correlation functions between particle creation or annihilation operators. Measurement of such correlation functions can therefore be regarded as an operational solution to the quantum many-body problem. Here, we demonstrate this paradigm by measuring multiparticle momentum correlations up to third order between ultracold helium atoms in an s-wave scattering halo of colliding Bose-Einstein condensates, using a quantum many-body momentum microscope. Our measurements allow us to extract a key building block of all higher-order correlations in this system-the pairing field amplitude. In addition, we demonstrate a record violation of the classical Cauchy-Schwarz inequality for correlated atom pairs and triples. Measuring multiparticle momentum correlations could provide new insights into effects such as unconventional superconductivity and many-body localization.

  6. Many-body interactions in quasi-freestanding graphene

    PubMed Central

    Siegel, David A.; Park, Cheol-Hwan; Hwang, Choongyu; Deslippe, Jack; Fedorov, Alexei V.; Louie, Steven G.; Lanzara, Alessandra

    2011-01-01

    The Landau–Fermi liquid picture for quasiparticles assumes that charge carriers are dressed by many-body interactions, forming one of the fundamental theories of solids. Whether this picture still holds for a semimetal such as graphene at the neutrality point, i.e., when the chemical potential coincides with the Dirac point energy, is one of the long-standing puzzles in this field. Here we present such a study in quasi-freestanding graphene by using high-resolution angle-resolved photoemission spectroscopy. We see the electron–electron and electron–phonon interactions go through substantial changes when the semimetallic regime is approached, including renormalizations due to strong electron–electron interactions with similarities to marginal Fermi liquid behavior. These findings set a new benchmark in our understanding of many-body physics in graphene and a variety of novel materials with Dirac fermions. PMID:21709258

  7. Many-body interactions in quasi-freestanding graphene

    SciTech Connect

    Siegel, David; Park, Cheol-Hwan; Hwang, Choongyu; Deslippe, Jack; Fedorov, Alexei; Louie, Steven; Lanzara, Alessandra

    2011-06-03

    The Landau-Fermi liquid picture for quasiparticles assumes that charge carriers are dressed by many-body interactions, forming one of the fundamental theories of solids. Whether this picture still holds for a semimetal such as graphene at the neutrality point, i.e., when the chemical potential coincides with the Dirac point energy, is one of the long-standing puzzles in this field. Here we present such a study in quasi-freestanding graphene by using high-resolution angle-resolved photoemission spectroscopy. We see the electron-electron and electron-phonon interactions go through substantial changes when the semimetallic regime is approached, including renormalizations due to strong electron-electron interactions with similarities to marginal Fermi liquid behavior. These findings set a new benchmark in our understanding of many-body physics in graphene and a variety of novel materials with Dirac fermions.

  8. Many-Body Electronic Structure of Curium metal

    NASA Astrophysics Data System (ADS)

    Toropova, Antonina; Haule, Kristjan; Kotliar, Gabriel

    2006-03-01

    We report computer-based simulations for the many-body electronic structure of Curium metal. Cm belongs to the actinide series and has a half-filled shell with seven 5f electrons. As a function of pressure, curium exhibits five different crystallographic phases. At low temperatures all phases demonstrate either antiferromagnetic or ferrimagnetic ordering. In this study we perform LDA+DMFT calculations for the antiferromagnetic state of high-pressure fcc modification of Curium metal.

  9. Automatic Generation of Vacuum Amplitude Many-Body Perturbation Series

    NASA Astrophysics Data System (ADS)

    Stevenson, P. D.

    An algorithm and a computer program in Fortran 95 are presented which enumerate the Hugenholtz diagram representation of the many-body perturbation series for the ground state energy with a two-body interaction. The output is in a form suitable for post-processing such as automatic code generation. The result of a particular application, generation of LATEX code to draw the diagrams, is shown.

  10. Many-Body Effects in Quantum-Well Intersubband Transitions

    NASA Technical Reports Server (NTRS)

    Li, Jian-Zhong; Ning, Cun-Zheng

    2003-01-01

    Intersubband polarization couples to collective excitations of the interacting electron gas confined in a semiconductor quantum well (Qw) structure. Such excitations include correlated pair excitations (repellons) and intersubband plasmons (ISPs). The oscillator strength of intersubband transitions (ISBTs) strongly varies with QW parameters and electron density because of this coupling. We have developed a set of kinetic equations, termed the intersubband semiconductor Bloch equations (ISBEs), from density matrix theory with the Hartree-Fock approximation, that enables a consistent description of these many-body effects. Using the ISBEs for a two-conduction-subband model, various many-body effects in intersubband transitions are studied in this work. We find interesting spectral changes of intersubband absorption coefficient due to interplay of the Fermi-edge singularity, subband renormalization, intersubband plasmon oscillation, and nonparabolicity of bandstructure. Our results uncover a new perspective for ISBTs and indicate the necessity of proper many-body theoretical treatment in order for modeling and prediction of ISBT line shape.

  11. Many-Body Effects in Quantum-Well Intersubband Transitions

    NASA Technical Reports Server (NTRS)

    Li, Jian-Zhong; Ning, Cun-Zheng

    2003-01-01

    Intersubband polarization couples to collective excitations of the interacting electron gas confined in a semiconductor quantum well (Qw) structure. Such excitations include correlated pair excitations (repellons) and intersubband plasmons (ISPs). The oscillator strength of intersubband transitions (ISBTs) strongly varies with QW parameters and electron density because of this coupling. We have developed a set of kinetic equations, termed the intersubband semiconductor Bloch equations (ISBEs), from density matrix theory with the Hartree-Fock approximation, that enables a consistent description of these many-body effects. Using the ISBEs for a two-conduction-subband model, various many-body effects in intersubband transitions are studied in this work. We find interesting spectral changes of intersubband absorption coefficient due to interplay of the Fermi-edge singularity, subband renormalization, intersubband plasmon oscillation, and nonparabolicity of bandstructure. Our results uncover a new perspective for ISBTs and indicate the necessity of proper many-body theoretical treatment in order for modeling and prediction of ISBT line shape.

  12. On the representation of many-body interactions in water

    DOE PAGES

    Medders, Gregory R.; Gotz, Andreas W.; Morales, Miguel A.; ...

    2015-09-09

    Our recent work has shown that the many-body expansion of the interactionenergy can be used to develop analytical representations of global potential energy surfaces (PESs) for water. In this study, the role of short- and long-range interactions at different orders is investigated by analyzing water potentials that treat the leading terms of the many-body expansion through implicit (i.e., TTM3-F and TTM4-F PESs) and explicit (i.e., WHBB and MB-pol PESs) representations. Moreover, it is found that explicit short-range representations of 2-body and 3-body interactions along with a physically correct incorporation of short- and long-range contributions are necessary for an accurate representationmore » of the waterinteractions from the gas to the condensed phase. Likewise, a complete many-body representation of the dipole moment surface is found to be crucial to reproducing the correct intensities of the infrared spectrum of liquid water.« less

  13. Persistent Directional Current at Equilibrium in Nonreciprocal Many-Body Near Field Electromagnetic Heat Transfer

    NASA Astrophysics Data System (ADS)

    Zhu, Linxiao; Fan, Shanhui

    2016-09-01

    We consider the consequence of nonreciprocity in near-field heat transfer by studying systems consisting of magneto-optical nanoparticles. We demonstrate that, in thermal equilibrium, a nonreciprocal many-body system in heat transfer can support a persistent directional heat current, without violating the second law of thermodynamics. Such a persistent directional heat current cannot occur in reciprocal systems, and can only arise in many-body systems in heat transfer. The use of nonreciprocity therefore points to a new regime of near-field heat transfer for the control of heat flow in the nanoscale.

  14. Studying non-equilibrium many-body dynamics using one-dimensional Bose gases

    SciTech Connect

    Langen, Tim; Gring, Michael; Kuhnert, Maximilian; Rauer, Bernhard; Geiger, Remi; Mazets, Igor; Smith, David Adu; Schmiedmayer, Jörg; Kitagawa, Takuya; Demler, Eugene

    2014-12-04

    Non-equilibrium dynamics of isolated quantum many-body systems play an important role in many areas of physics. However, a general answer to the question of how these systems relax is still lacking. We experimentally study the dynamics of ultracold one-dimensional (1D) Bose gases. This reveals the existence of a quasi-steady prethermalized state which differs significantly from the thermal equilibrium of the system. Our results demonstrate that the dynamics of non-equilibrium quantum many-body systems is a far richer process than has been assumed in the past.

  15. Thouless energy and multifractality across the many-body localization transition

    NASA Astrophysics Data System (ADS)

    Serbyn, Maksym; Papić, Z.; Abanin, Dmitry A.

    2017-09-01

    Thermal and many-body localized phases are separated by a dynamical phase transition of a new kind. We analyze the distribution of off-diagonal matrix elements of local operators across this transition in two different models of disordered spin chains. We show that the behavior of matrix elements can be used to characterize the breakdown of thermalization and to extract the many-body Thouless energy. We find that upon increasing the disorder strength the system enters a critical region around the many-body localization transition. The properties of the system in this region are: (i) the Thouless energy becomes smaller than the level spacing, (ii) the matrix elements show critical dependence on the energy difference, and (iii) the matrix elements, viewed as amplitudes of a fictitious wave function, exhibit strong multifractality. This critical region decreases with the system size, which we interpret as evidence for a diverging correlation length at the many-body localization transition. Our findings show that the correlation length becomes larger than the accessible system sizes in a broad range of disorder strength values and shed light on the critical behavior near the many-body localization transition.

  16. Parametric excitation and squeezing in a many-body spinor condensate

    PubMed Central

    Hoang, T. M.; Anquez, M.; Robbins, B. A.; Yang, X. Y.; Land, B. J.; Hamley, C. D.; Chapman, M. S.

    2016-01-01

    Atomic spins are usually manipulated using radio frequency or microwave fields to excite Rabi oscillations between different spin states. These are single-particle quantum control techniques that perform ideally with individual particles or non-interacting ensembles. In many-body systems, inter-particle interactions are unavoidable; however, interactions can be used to realize new control schemes unique to interacting systems. Here we demonstrate a many-body control scheme to coherently excite and control the quantum spin states of an atomic Bose gas that realizes parametric excitation of many-body collective spin states by time varying the relative strength of the Zeeman and spin-dependent collisional interaction energies at multiples of the natural frequency of the system. Although parametric excitation of a classical system is ineffective from the ground state, we show that in our experiment, parametric excitation from the quantum ground state leads to the generation of quantum squeezed states. PMID:27044675

  17. Parametric excitation and squeezing in a many-body spinor condensate

    NASA Astrophysics Data System (ADS)

    Hoang, T. M.; Anquez, M.; Robbins, B. A.; Yang, X. Y.; Land, B. J.; Hamley, C. D.; Chapman, M. S.

    2016-04-01

    Atomic spins are usually manipulated using radio frequency or microwave fields to excite Rabi oscillations between different spin states. These are single-particle quantum control techniques that perform ideally with individual particles or non-interacting ensembles. In many-body systems, inter-particle interactions are unavoidable; however, interactions can be used to realize new control schemes unique to interacting systems. Here we demonstrate a many-body control scheme to coherently excite and control the quantum spin states of an atomic Bose gas that realizes parametric excitation of many-body collective spin states by time varying the relative strength of the Zeeman and spin-dependent collisional interaction energies at multiples of the natural frequency of the system. Although parametric excitation of a classical system is ineffective from the ground state, we show that in our experiment, parametric excitation from the quantum ground state leads to the generation of quantum squeezed states.

  18. Absence of many-body localization in a single Landau level

    NASA Astrophysics Data System (ADS)

    Geraedts, Scott D.; Bhatt, R. N.

    2017-02-01

    The localization properties of the highly excited states of a system projected into a single Landau level are analyzed. An analysis of level spacing ratios for finite size systems shows a clear crossover from extended (GUE) to localized (Poisson) statistics, indicating a many-body localization transition. However, the location of this transition depends very strongly on system size, and appears to scale to infinite disorder in the thermodynamic limit. This result does not depend on the properties of the ground state (such as whether the ground state exhibits topological order), as expected for a transition of highly excited eigenstates. We therefore conclude that many-body localization does not exist in these systems. Our results demonstrate that a subthermodynamic number of single particle effectively extended states is sufficient to cause all many-body states to become extended.

  19. Towards Efficient and General Method for Many-Body van-der-Waals Interactions

    NASA Astrophysics Data System (ADS)

    Tkatchenko, Alexandre

    2012-02-01

    Van der Waals interactions are intrinsically many-body phenomena, arising from collective electron fluctuations in a given material. Adiabatic connection fluctuation-dissipation theorem (ACFDT) allows to compute the many-body vdW interactions accurately. However, the ACFDT computational cost is prohibitive for real materials, even when the random-phase approximation is employed for the response function. We show how the problem of computing the long-range many-body vdW energy for real systems can be solved efficiently by mapping the system (molecule or condensed matter) onto a collection of quantum harmonic oscillators. Currently, our method, which couples density-functional theory with the many-body dispersion energy (DFT+MBD), is developed for non-metallic system [A. Tkatchenko, R. A. DiStasio Jr., R. Car, M. Scheffler, submitted]. The DFT+MBD method includes the hybridization effects by using the Tkatchenko-Scheffler approach [PRL 102, 073005 (2009)], the long-range Coulomb screening through classical electrodynamics [B. U. Felderhof, Physica 29, 1569 (1974)], and the many-body vdW energy from the coupled-fluctuating dipole model [M. W. Cole et al., Mol. Simul. 35, 849 (2009)]. The successes of the DFT+MBD approach and the many challenges that lie ahead will be discussed.

  20. Meson Structure in a Relativistic Many-Body Approach

    SciTech Connect

    Llanes-Estrada, Felipe J.; Cotanch, Stephen R.

    2000-02-07

    Results from an extensive relativistic many-body analysis utilizing a realistic effective QCD Hamiltonian are presented for the meson spectrum. A comparative numerical study of the BCS, Tamm-Dancoff (TDA), and RPA treatments provides new, significant insight into the condensate structure of the vacuum, the chiral symmetry governance of the pion, and the meson spin, orbital, and flavor mass splitting contributions. In contrast to a previous glueball application, substantial quantitative differences are computed between TDA and RPA for the light quark sector with the pion emerging as a Goldstone boson only in the RPA. (c) 2000 The American Physical Society.

  1. Computational nuclear quantum many-body problem: The UNEDF project

    SciTech Connect

    Fann, George I

    2013-01-01

    The UNEDF project was a large-scale collaborative effort that applied high-performance computing to the nuclear quantum many-body problem. The primary focus of the project was on constructing, validating, and applying an optimized nuclear energy density functional, which entailed a wide range of pioneering developments in microscopic nuclear structure and reactions, algorithms, high-performance computing, and uncertainty quantification. UNEDF demonstrated that close associations among nuclear physicists, mathematicians, and computer scientists can lead to novel physics outcomes built on algorithmic innovations and computational developments. This review showcases a wide range of UNEDF science results to illustrate this interplay.

  2. Understanding many-body physics in one dimension from the Lieb-Liniger model

    NASA Astrophysics Data System (ADS)

    Jiang, Yu-Zhu; Chen, Yang-Yang; Guan, Xi-Wen

    2015-05-01

    This article presents an elementary introduction on various aspects of the prototypical integrable model the Lieb-Liniger Bose gas ranging from the cooperative to the collective features of many-body phenomena. In 1963, Lieb and Liniger first solved this quantum field theory many-body problem using Bethe’s hypothesis, i.e., a particular form of wavefunction introduced by Bethe in solving the one-dimensional Heisenberg model in 1931. Despite the Lieb-Liniger model is arguably the simplest exactly solvable model, it exhibits rich quantum many-body physics in terms of the aspects of mathematical integrability and physical universality. Moreover, the Yang-Yang grand canonical ensemble description for the model provides us with a deep understanding of quantum statistics, thermodynamics, and quantum critical phenomena at the many-body physical level. Recently, such fundamental physics of this exactly solved model has been attracting growing interest in experiments. Since 2004, there have been more than 20 experimental papers that reported novel observations of different physical aspects of the Lieb-Liniger model in the laboratory. So far the observed results are in excellent agreement with results obtained using the analysis of this simplest exactly solved model. Those experimental observations reveal the unique beauty of integrability. Project supported by the National Basic Research Program of China (Grant No. 2012CB922101) and the National Natural Science Foundation of China (Grant Nos. 11374331 and 11304357).

  3. Ideal quantum glass transitions: Many-body localization without quenched disorder

    SciTech Connect

    Schiulaz, M.; Müller, M.

    2014-08-20

    We explore the possibility for translationally invariant quantum many-body systems to undergo a dynamical glass transition, at which ergodicity and translational invariance break down spontaneously, driven entirely by quantum effects. In contrast to analogous classical systems, where the existence of such an ideal glass transition remains a controversial issue, a genuine phase transition is predicted in the quantum regime. This ideal quantum glass transition can be regarded as a many-body localization transition due to self-generated disorder. Despite their lack of thermalization, these disorder-free quantum glasses do not possess an extensive set of local conserved operators, unlike what is conjectured for many-body localized systems with strong quenched disorder.

  4. Direct observation of ultrafast many-body electron dynamics in an ultracold Rydberg gas

    NASA Astrophysics Data System (ADS)

    Takei, Nobuyuki; Sommer, Christian; Genes, Claudiu; Pupillo, Guido; Goto, Haruka; Koyasu, Kuniaki; Chiba, Hisashi; Weidemüller, Matthias; Ohmori, Kenji

    2016-11-01

    Many-body correlations govern a variety of important quantum phenomena such as the emergence of superconductivity and magnetism. Understanding quantum many-body systems is thus one of the central goals of modern sciences. Here we demonstrate an experimental approach towards this goal by utilizing an ultracold Rydberg gas generated with a broadband picosecond laser pulse. We follow the ultrafast evolution of its electronic coherence by time-domain Ramsey interferometry with attosecond precision. The observed electronic coherence shows an ultrafast oscillation with a period of 1 femtosecond, whose phase shift on the attosecond timescale is consistent with many-body correlations among Rydberg atoms beyond mean-field approximations. This coherent and ultrafast many-body dynamics is actively controlled by tuning the orbital size and population of the Rydberg state, as well as the mean atomic distance. Our approach will offer a versatile platform to observe and manipulate non-equilibrium dynamics of quantum many-body systems on the ultrafast timescale.

  5. Direct observation of ultrafast many-body electron dynamics in an ultracold Rydberg gas.

    PubMed

    Takei, Nobuyuki; Sommer, Christian; Genes, Claudiu; Pupillo, Guido; Goto, Haruka; Koyasu, Kuniaki; Chiba, Hisashi; Weidemüller, Matthias; Ohmori, Kenji

    2016-11-16

    Many-body correlations govern a variety of important quantum phenomena such as the emergence of superconductivity and magnetism. Understanding quantum many-body systems is thus one of the central goals of modern sciences. Here we demonstrate an experimental approach towards this goal by utilizing an ultracold Rydberg gas generated with a broadband picosecond laser pulse. We follow the ultrafast evolution of its electronic coherence by time-domain Ramsey interferometry with attosecond precision. The observed electronic coherence shows an ultrafast oscillation with a period of 1 femtosecond, whose phase shift on the attosecond timescale is consistent with many-body correlations among Rydberg atoms beyond mean-field approximations. This coherent and ultrafast many-body dynamics is actively controlled by tuning the orbital size and population of the Rydberg state, as well as the mean atomic distance. Our approach will offer a versatile platform to observe and manipulate non-equilibrium dynamics of quantum many-body systems on the ultrafast timescale.

  6. Direct observation of ultrafast many-body electron dynamics in an ultracold Rydberg gas

    PubMed Central

    Takei, Nobuyuki; Sommer, Christian; Genes, Claudiu; Pupillo, Guido; Goto, Haruka; Koyasu, Kuniaki; Chiba, Hisashi; Weidemüller, Matthias; Ohmori, Kenji

    2016-01-01

    Many-body correlations govern a variety of important quantum phenomena such as the emergence of superconductivity and magnetism. Understanding quantum many-body systems is thus one of the central goals of modern sciences. Here we demonstrate an experimental approach towards this goal by utilizing an ultracold Rydberg gas generated with a broadband picosecond laser pulse. We follow the ultrafast evolution of its electronic coherence by time-domain Ramsey interferometry with attosecond precision. The observed electronic coherence shows an ultrafast oscillation with a period of 1 femtosecond, whose phase shift on the attosecond timescale is consistent with many-body correlations among Rydberg atoms beyond mean-field approximations. This coherent and ultrafast many-body dynamics is actively controlled by tuning the orbital size and population of the Rydberg state, as well as the mean atomic distance. Our approach will offer a versatile platform to observe and manipulate non-equilibrium dynamics of quantum many-body systems on the ultrafast timescale. PMID:27849054

  7. Emergence of stationary many-body entanglement in driven-dissipative Rydberg lattice gases

    NASA Astrophysics Data System (ADS)

    Lee, Sun Kyung; Cho, Jaeyoon; Choi, K. S.

    2015-11-01

    Non-equilibrium quantum dynamics represents an emerging paradigm for condensed matter physics, quantum information science, and statistical mechanics. Strongly interacting Rydberg atoms offer an attractive platform to examine driven-dissipative dynamics of quantum spin models with long-range order. Here, we explore the conditions under which stationary many-body entanglement persists with near-unit fidelity and high scalability. In our approach, coherent many-body dynamics is driven by Rydberg-mediated laser transitions, while atoms at the lattice boundary locally reduce the entropy of the many-body system. Surprisingly, the many-body entanglement is established by continuously evolving a locally dissipative Rydberg system towards the steady state, precisely as with optical pumping. We characterize the dynamics of multipartite entanglement in an one-dimensional lattice by way of quantum uncertainty relations, and demonstrate the long-range behavior of the stationary entanglement with finite-size scaling. Our work opens a route towards dissipative preparation of many-body entanglement with unprecedented scaling behavior.

  8. Evolution of regulatory complexes: a many-body system

    NASA Astrophysics Data System (ADS)

    Nouemohammad, Armita; Laessig, Michael

    2013-03-01

    In eukaryotes, many genes have complex regulatory input, which is encoded by multiple transcription factor binding sites linked to a common function. Interactions between transcription factors and site complexes on DNA control the production of protein in cells. Here, we present a quantitative evolutionary analysis of binding site complexes in yeast. We show that these complexes have a joint binding phenotype, which is under substantial stabilizing selection and is well conserved within Saccharomyces paradoxus populations and between three species of Saccharomyces. At the same time, individual low-affinity sites evolve near-neutrally and show considerable affinity variation even within one population. Thus, functionality of and selection on regulatory complexes emerge from the entire cloud of sites, but cannot be pinned down to individual sites. Our method is based on a biophysical model, which determines site occupancies and establishes a joint affinity phenotype for binding site complexes. We infer a fitness landscape depending on this phenotype using yeast whole-genome polymorphism data and a new method of quantitative trait analysis. Our fitness landscape predicts the amount of binding phenotype conservation, as well as ubiquitous compensatory changes between sites in the cloud. Our results open a new avenue to understand the regulatory ``grammar'' of eukaryotic genomes based on quantitative evolution models. Carl-Icahn Laboratory, Washington Road, Princeton 08544 NJ

  9. Quantum simulations and many-body physics with light.

    PubMed

    Noh, Changsuk; Angelakis, Dimitris G

    2017-01-01

    In this review we discuss the works in the area of quantum simulation and many-body physics with light, from the early proposals on equilibrium models to the more recent works in driven dissipative platforms. We start by describing the founding works on Jaynes-Cummings-Hubbard model and the corresponding photon-blockade induced Mott transitions and continue by discussing the proposals to simulate effective spin models and fractional quantum Hall states in coupled resonator arrays (CRAs). We also analyse the recent efforts to study out-of-equilibrium many-body effects using driven CRAs, including the predictions for photon fermionisation and crystallisation in driven rings of CRAs as well as other dynamical and transient phenomena. We try to summarise some of the relatively recent results predicting exotic phases such as super-solidity and Majorana like modes and then shift our attention to developments involving 1D nonlinear slow light setups. There the simulation of strongly correlated phases characterising Tonks-Girardeau gases, Luttinger liquids, and interacting relativistic fermionic models is described. We review the major theory results and also briefly outline recent developments in ongoing experimental efforts involving different platforms in circuit QED, photonic crystals and nanophotonic fibres interfaced with cold atoms.

  10. Padé resummation of many-body perturbation theories.

    PubMed

    Pavlyukh, Y

    2017-03-29

    In a typical scenario the diagrammatic many-body perturbation theory generates asymptotic series. Despite non-convergence, the asymptotic expansions are useful when truncated to a finite number of terms. This is the reason for the popularity of leading-order methods such as the GW approximation in condensed matter, molecular and atomic physics. Appropriate truncation order required for the accurate description of strongly correlated materials is, however, not known a priori. Here an efficient method based on the Padé approximation is introduced for the regularization of perturbative series allowing to perform higher-order self-consistent calculations and to make quantitative predictions on the convergence of many-body perturbation theories. The theory is extended towards excited states where the Wick theorem is not directly applicable. Focusing on the plasmon-assisted photoemission from graphene, we treat diagrammatically electrons coupled to the excited state plasmons and predict new spectral features that can be observed in the time-resolved measurements.

  11. Giant many-body effects in liquid ammonia absorption spectrum

    NASA Astrophysics Data System (ADS)

    Ziaei, Vafa; Bredow, Thomas

    2016-11-01

    In the present work, we accurately calculate the absorption spectrum of liquid ammonia up to 13 eV using many-body perturbation approach. The electronic bandgap of liquid NH3 is perfectly described as the combination of density functional theory, Coulomb-hole screened exchange, and G0W0 approximation to the electronic self-energy, yielding a direct gap (Γ → Γ) of 7.71 eV, fully consistent with the experimentally measured gap from photo-emission spectroscopy. With respect to the NH3 optical properties, the entire spectrum in particular the low lying first absorption band is extremely affected by electron-hole interactions, leading to a fundamental redistribution of spectral weights of the independent-particle spectrum. Three well separated but broad main peaks are identified at 7.0, 9.8, and 11.8 eV with steadily increasing intensities in excellent agreement with the experimental data. Furthermore, we observe a giant net blue-shift of the first absorption peak of about 1.4 eV from gaseous to liquid phase as the direct consequence of many-body effects, allowing the associated liquid ammonia absorption band exciton to delocalize and feel more effectively the repulsion effects imposed by the surrounding solvent shells. Further, the spectrum is insensitive to the coupling of resonant and anti-resonant contributions. Concerning electronic response structure of liquid NH3, it is most sensitive to excitations at energies lower than its electronic gap.

  12. Quantum simulations and many-body physics with light

    NASA Astrophysics Data System (ADS)

    Noh, Changsuk; Angelakis, Dimitris G.

    2017-01-01

    In this review we discuss the works in the area of quantum simulation and many-body physics with light, from the early proposals on equilibrium models to the more recent works in driven dissipative platforms. We start by describing the founding works on Jaynes-Cummings-Hubbard model and the corresponding photon-blockade induced Mott transitions and continue by discussing the proposals to simulate effective spin models and fractional quantum Hall states in coupled resonator arrays (CRAs). We also analyse the recent efforts to study out-of-equilibrium many-body effects using driven CRAs, including the predictions for photon fermionisation and crystallisation in driven rings of CRAs as well as other dynamical and transient phenomena. We try to summarise some of the relatively recent results predicting exotic phases such as super-solidity and Majorana like modes and then shift our attention to developments involving 1D nonlinear slow light setups. There the simulation of strongly correlated phases characterising Tonks-Girardeau gases, Luttinger liquids, and interacting relativistic fermionic models is described. We review the major theory results and also briefly outline recent developments in ongoing experimental efforts involving different platforms in circuit QED, photonic crystals and nanophotonic fibres interfaced with cold atoms.

  13. Many-body localization in the presence of a small bath

    NASA Astrophysics Data System (ADS)

    Hyatt, Katharine; Garrison, James R.; Potter, Andrew C.; Bauer, Bela

    2017-01-01

    In the presence of strong disorder and weak interactions, closed quantum systems can enter a many-body localized phase where the system does not conduct, does not equilibrate even for arbitrarily long times, and robustly violates quantum statistical mechanics. The starting point for such a many-body localized phase is usually taken to be an Anderson insulator where, in the limit of vanishing interactions, all degrees of freedom of the system are localized. Here, we instead consider a model where in the noninteracting limit, some degrees of freedom are localized while others remain delocalized. Such a system can be viewed as a model for a many-body localized system brought into contact with a small bath of a comparable number of degrees of freedom. We numerically and analytically study the effect of interactions on this system and find that generically, the entire system delocalizes. However, we find certain parameter regimes where results are consistent with localization of the entire system, an effect recently termed many-body proximity effect.

  14. Semiconductor laser theory with many-body effects

    SciTech Connect

    Haug, H.; Gayg, G.; Koch, S.W.

    1989-02-15

    A description of the electron-hole plasma of a semiconductor laser is developed that includes the many-body effects due to the Coulomb interactions. In particular, the plasma density-dependent band-gap renormalization, the broadening due to intraband scattering, and the Coulomb enhancement are included and evaluated for three- and two-dimensional semiconductor structures. Because of the short intraband scattering relaxation time one can eliminate the interband polarization adiabatically and at the same time introduce a hydrodynamic description of the interband kinetics. From this general formulation a diffusion equation for the carrier density is derived. The resulting ambipolar diffusion coefficient decreases with the laser intensity due to the reduction of the electron drift. The present semiclassical theory is completed by the laser field equations and by the addition of Langevin fluctuations.

  15. Many-body tight-binding model for aluminum nanoparticles

    SciTech Connect

    Staszewska, Grazyna; Staszewski, Przemyslaw; Schultz, Nathan E.; Truhlar, Donald G.

    2005-01-15

    A new, parametrized many-body tight-binding model is proposed for calculating the potential energy surface for aluminum nanoparticles. The parameters have been fitted to reproduce the energies for a variety of aluminum clusters (Al{sub 2}, Al{sub 3}, Al{sub 4}, Al{sub 7}, Al{sub 13}) calculated recently by the PBE0/MG3 method as well as the experimental face-centered-cubic cohesive energy, lattice constant, and a small set of Al cluster ionization potentials. Several types of parametrization are presented and compared. The mean unsigned error per atom for the best model is less than 0.03 eV.

  16. Many-body theory and Energy Density Functionals

    NASA Astrophysics Data System (ADS)

    Baldo, M.

    2016-07-01

    In this paper a method is first presented to construct an Energy Density Functional on a microscopic basis. The approach is based on the Kohn-Sham method, where one introduces explicitly the Nuclear Matter Equation of State, which can be obtained by an accurate many-body calculation. In this way it connects the functional to the bare nucleon-nucleon interaction. It is shown that the resulting functional can be performing as the best Gogny force functional. In the second part of the paper it is shown how one can go beyond the mean-field level and the difficulty that can appear. The method is based on the particle-vibration coupling scheme and a formalism is presented that can handle the correct use of the vibrational degrees of freedom within a microscopic approach.

  17. Many-body localization protected quantum state transfer

    NASA Astrophysics Data System (ADS)

    Laumann, Chris R.; Yao, Norman Y.; Vishwanath, Ashvin

    In thermal phases, the quantum coherence of individual degrees of freedom is rapidly lost to the environment. Many-body localized (MBL) phases limit the spread of this coherence and appear promising for quantum information applications. However, such applications require not just long coherence times but also a means to transport and manipulate information. We demonstrate that this can be done in a one dimensional model of interacting spins at infinite temperature. Our protocol utilizes protected qubits which emerge at the boundary between topological and trivial phases. State transfer occurs via dynamic shifts of this boundary and is shown to preserve quantum information. As an example, we discuss the implementation of a universal, two-qubit gate based upon MBL-protected quantum state transfer.

  18. Novel simulation model for many-body multipole dispersion interactions

    NASA Astrophysics Data System (ADS)

    van der Hoef Paul, Martin A.; Madden, A.

    We present a novel simulation technique, within the framework of a molecular dynamics simulation, which accounts for both two- and three-body dispersion interactions, up to the triple-quadrupole interaction. This technique involves a unification of molecular dynamics and quantum-mechanical variational methods, in the spirit of the Car-Parrinello method. The advantage of this new method compared to existing techniques for simulating three-body dispersion forces, is that it allows for a consistent treatment of both dispersion damping and periodic boundary conditions at the pair and three-body level. The latter means that it would be possible, for the first time, to include many-body dispersion effects in the simulation of bulk properties of materials, without making use of effective pair potentials.

  19. Many-body theory of magnetoelasticity in one dimension

    NASA Astrophysics Data System (ADS)

    Tsyplyatyev, O.; Kopietz, P.; Tsui, Y.; Wolf, B.; Cong, P. T.; van Well, N.; Ritter, F.; Krellner, C.; Aßmus, W.; Lang, M.

    2017-01-01

    We construct a many-body theory of magnetoelasticity in one dimension and show that the dynamical correlation functions of the quantum magnet, connecting the spins with phonons, involve all energy scales. Accounting for all magnetic states nonperturbatively via the exact diagonalization techniques of Bethe ansatz, we find that the renormalization of the phonon velocity is a nonmonotonous function of the external magnetic field and identify a new mechanism for attenuation of phonons—via hybridization with the continuum of excitations at high energy. We conduct ultrasonic measurements on a high-quality single crystal of the frustrated spin-1/2 Heisenberg antiferromagnet Cs2CuCl4 in its nearly one-dimensional regime and confirm the theoretical predictions, demonstrating that ultrasound can be used as a powerful probe of strong correlations in one dimension.

  20. Encoding the structure of many-body localization with matrix product operators

    NASA Astrophysics Data System (ADS)

    Pekker, David; Clark, Bryan K.

    2017-01-01

    Anderson insulators are noninteracting disordered systems which have localized single-particle eigenstates. The interacting analog of Anderson insulators are the many-body localized (MBL) phases. The spectrum of the many-body eigenstates of an Anderson insulator is efficiently represented as a set of product states over the single-particle modes. We show that product states over matrix product operators of small bond dimension is the corresponding efficient description of the spectrum of an MBL insulator. In this language all of the many-body eigenstates are encoded by matrix product states (i.e., density matrix renormalization group wave functions) consisting of only two sets of low bond dimension matrices per site: the Gi matrices corresponding to the local ground state on site i and the Ei matrices corresponding to the local excited state. All 2n eigenstates can be generated from all possible combinations of these sets of matrices.

  1. Giant many-body effects in liquid ammonia absorption spectrum.

    PubMed

    Ziaei, Vafa; Bredow, Thomas

    2016-11-07

    In the present work, we accurately calculate the absorption spectrum of liquid ammonia up to 13 eV using many-body perturbation approach. The electronic bandgap of liquid NH3 is perfectly described as the combination of density functional theory, Coulomb-hole screened exchange, and G0W0 approximation to the electronic self-energy, yielding a direct gap (Γ → Γ) of 7.71 eV, fully consistent with the experimentally measured gap from photo-emission spectroscopy. With respect to the NH3 optical properties, the entire spectrum in particular the low lying first absorption band is extremely affected by electron-hole interactions, leading to a fundamental redistribution of spectral weights of the independent-particle spectrum. Three well separated but broad main peaks are identified at 7.0, 9.8, and 11.8 eV with steadily increasing intensities in excellent agreement with the experimental data. Furthermore, we observe a giant net blue-shift of the first absorption peak of about 1.4 eV from gaseous to liquid phase as the direct consequence of many-body effects, allowing the associated liquid ammonia absorption band exciton to delocalize and feel more effectively the repulsion effects imposed by the surrounding solvent shells. Further, the spectrum is insensitive to the coupling of resonant and anti-resonant contributions. Concerning electronic response structure of liquid NH3, it is most sensitive to excitations at energies lower than its electronic gap.

  2. Effects of pairwise versus many-body forces on high-stress plastic deformation

    NASA Astrophysics Data System (ADS)

    Holian, B. L.; Voter, A. F.; Wagner, N. J.; Ravelo, R. J.; Chen, S. P.; Hoover, W. G.; Hoover, C. G.; Hammerberg, J. E.; Dontje, T. D.

    1991-03-01

    We propose a model embedded-atom (many-body) potential and test it against an effective, density-independent, pairwise-additive potential in a variety of nonequilibrium molecular-dynamics simulations of plastic deformation under high stress. Even though both kinds of interactions have nearly the same equilibrium equation of state, the defect energies (i.e., vacancy formation and surface energies) are quite different. As a result, we observe significant qualitative differences in flow behavior between systems characterized by purely pairwise interactions versus higher-order many-body forces.

  3. Relativistic many-body perturbation theory for general open-shell multiplet states of atoms

    NASA Astrophysics Data System (ADS)

    Ishikawa, Yasuyuki; Koc, Konrad

    1996-06-01

    A relativistic many-body perturbation theory, which accounts for relativistic and electron-correlation effects for general open-shell multiplet states of atoms and molecules, is developed and implemented with analytic basis sets of Gaussian spinors. The theory retains the essential aspects of Mo/ller-Plesset perturbation theory by employing the relativistic single-Fock-operator method of Koc and Ishikawa [Phys. Rev. A 49, 794 (1994)] for general open-shell systems. Open-shell Dirac-Fock and relativistic many-body perturbation calculations are reported for the ground and low-lying excited states of Li, B2+, Ne7+, and Ca11+.

  4. Many-body computations by stochastic sampling in Hartree-Fock-Bogoliubov space

    NASA Astrophysics Data System (ADS)

    Shi, Hao; Zhang, Shiwei

    2017-01-01

    We describe the computational ingredients for an approach to treat interacting fermion systems with pairing fields, based on path integrals in the space of Hartree-Fock-Bogoliubov (HFB) wave functions. The path integrals can be evaluated by Monte Carlo, via random walks of HFB wave functions whose orbitals evolve stochastically. The approach combines the advantage of HFB theory in paired fermion systems and many-body quantum Monte Carlo techniques. The properties of HFB states, written in the form of either product states or Thouless states, are discussed. The states preserve forms when propagated by generalized one-body operators. They can be stabilized for numerical iteration. Overlaps and one-body Green's functions between two such states can be computed. A constrained-path or phaseless approximation can be applied to the random walks of the HFB states if a sign problem or phase problem is present. The method is illustrated with an exact numerical projection in the Kitaev model, and in the Hubbard model with attractive interaction under an external pairing field.

  5. Effect of SU(2) symmetry on many-body localization and thermalization

    NASA Astrophysics Data System (ADS)

    Protopopov, Ivan V.; Ho, Wen Wei; Abanin, Dmitry A.

    2017-07-01

    The many-body localized (MBL) phase is characterized by a complete set of quasilocal integrals of motion and area-law entanglement of excited eigenstates. We study the effect of non-Abelian continuous symmetries on MBL, considering the case of SU(2 ) symmetric disordered spin chains. The SU(2 ) symmetry imposes strong constraints on the entanglement structure of the eigenstates, precluding conventional MBL. We construct a fixed-point Hamiltonian, which realizes a nonergodic (but non-MBL) phase characterized by eigenstates having logarithmic scaling of entanglement with the system size, as well as an incomplete set of quasilocal integrals of motion. We study the response of such a phase to local symmetric perturbations, finding that even weak perturbations induce multispin resonances. We conclude that the nonergodic phase is generally unstable and that SU(2 ) symmetry implies thermalization. The approach introduced in this Rapid Communication can be used to study dynamics in disordered systems with non-Abelian symmetries, and provides a starting point for searching nonergodic phases beyond conventional MBL.

  6. Interferometric measurements of many-body topological invariants using mobile impurities

    PubMed Central

    Grusdt, F.; Yao, N. Y.; Abanin, D.; Fleischhauer, M.; Demler, E.

    2016-01-01

    Topological quantum phases cannot be characterized by Ginzburg–Landau type order parameters, and are instead described by non-local topological invariants. Experimental platforms capable of realizing such exotic states now include synthetic many-body systems such as ultracold atoms or photons. Unique tools available in these systems enable a new characterization of strongly correlated many-body states. Here we propose a general scheme for detecting topological order using interferometric measurements of elementary excitations. The key ingredient is the use of mobile impurities that bind to quasiparticles of a host many-body system. Specifically, we show how fractional charges can be probed in the bulk of fractional quantum Hall systems. We demonstrate that combining Ramsey interference with Bloch oscillations can be used to measure Chern numbers characterizing the dispersion of individual quasiparticles, which gives a direct probe of their fractional charges. Possible extensions of our method to other many-body systems, such as spin liquids, are conceivable. PMID:27312285

  7. From Discrete Breathers to Many Body Localization and Flatbands

    NASA Astrophysics Data System (ADS)

    Flach, Sergej

    Discrete breathers (DB) and intrinsic localized modes (ILM) are synonymic dynamical states on nonlinear lattices - periodic in time and localized in space, and widely observed in many applications. I will discuss the connections between DBs and many-body localization (MBL) and the properties of DBs on flatband networks. A dense quantized gas of strongly excited DBs can lead to a MBL phase in a variety of different lattice models. Its classical counterpart corresponds to a 'nonergodic metal' in the MBL language, or to a nonGibbsean selftrapped state in the language of nonlinear dynamics. Flatband networks are lattices with small amplitude waves exhibiting macroscopic degeneracy in their band structure due to local symmetries, destructive interference, compact localized eigenstates and horizontal flat bands. DBs can preserve the compactness of localization in the presence of nonlinearity with properly tuned internal phase relationships, making them promising tools for control of the phase coherence of waves. Also at New Zealand Institute of Advanced Study, Massey University, Auckland, New Zealand.

  8. Uncovering many-body correlations in nanoscale nuclear spin baths by central spin decoherence

    PubMed Central

    Ma, Wen-Long; Wolfowicz, Gary; Zhao, Nan; Li, Shu-Shen; Morton, John J.L.; Liu, Ren-Bao

    2014-01-01

    Central spin decoherence caused by nuclear spin baths is often a critical issue in various quantum computing schemes, and it has also been used for sensing single-nuclear spins. Recent theoretical studies suggest that central spin decoherence can act as a probe of many-body physics in spin baths; however, identification and detection of many-body correlations of nuclear spins in nanoscale systems are highly challenging. Here, taking a phosphorus donor electron spin in a 29Si nuclear spin bath as our model system, we discover both theoretically and experimentally that many-body correlations in nanoscale nuclear spin baths produce identifiable signatures in decoherence of the central spin under multiple-pulse dynamical decoupling control. We demonstrate that under control by an odd or even number of pulses, the central spin decoherence is principally caused by second- or fourth-order nuclear spin correlations, respectively. This study marks an important step toward studying many-body physics using spin qubits. PMID:25205440

  9. Many-body effects in low-order optical nonlinearities of semiconductor quantum wells

    NASA Astrophysics Data System (ADS)

    Roumiantsev, Ilia

    This dissertation addresses both fundamental aspects of Coulomb correlations in semiconductor quantum wells and more practical aspects of theoretical analysis of semiconductor optoelectronic devices. After introducing the subject, we present and evaluate a state-of-the-art theory of the third order coherent optical response of a semiconductor quantum well based on the Dynamics Controlled Truncation (DCT) scheme. Already in the third order (the so-called chi (3)) regime, semiconductors exhibit a number of many-body Coulomb correlation effects. Their manifestation in various multi-pulse experimental configurations, customarily used in ultrafast semiconductor spectroscopy, has been an important component of this thesis. Coherent optical effects in a semiconductor 3-band system based on the heavy-hole, light-hole and conduction bands were investigated. The quantum beats in the time-integrated differential transmission signal were analyzed and compared with experimental data obtained at the University of Iowa. Fundamental differences from corresponding quantum beats in atomic 3-level systems were found. Also, the analysis of experimental data (obtained at the University of Arizona) of the coupled heavy-hole-light-hole optical Stark shift revealed evidence of intervalence band coherences, an analog of Raman coherences in atomic 3-levels systems. A scheme for realization of electromagnetically-induced transparency (EIT) based on the interference of excitonic and biexcitonic coherences was proposed. Corresponding experiments performed at the University of Oregon showed indeed a considerable coherent reduction of excitonic absorption. Furthermore, an extension of the chi(3) analysis revealed an energy renormalization of the biexciton, in good agreement with the corresponding experiment. A microscopic analysis of polarization dynamics in time-resolved four-wave mixing signals was performed, revealing interesting implications for the biexciton dephasing in addition to the

  10. Explicit schemes for time propagating many-body wave functions

    NASA Astrophysics Data System (ADS)

    Frapiccini, Ana Laura; Hamido, Aliou; Schröter, Sebastian; Pyke, Dean; Mota-Furtado, Francisca; O'Mahony, Patrick F.; Madroñero, Javier; Eiglsperger, Johannes; Piraux, Bernard

    2014-02-01

    Accurate theoretical data on many time-dependent processes in atomic and molecular physics and in chemistry require the direct numerical ab initio solution of the time-dependent Schrödinger equation, thereby motivating the development of very efficient time propagators. These usually involve the solution of very large systems of first-order differential equations that are characterized by a high degree of stiffness. In this contribution, we analyze and compare the performance of the explicit one-step algorithms of Fatunla and Arnoldi. Both algorithms have exactly the same stability function, therefore sharing the same stability properties that turn out to be optimum. Their respective accuracy, however, differs significantly and depends on the physical situation involved. In order to test this accuracy, we use a predictor-corrector scheme in which the predictor is either Fatunla's or Arnoldi's algorithm and the corrector, a fully implicit four-stage Radau IIA method of order 7. In this contribution, we consider two physical processes. The first one is the ionization of an atomic system by a short and intense electromagnetic pulse; the atomic systems include a one-dimensional Gaussian model potential as well as atomic hydrogen and helium, both in full dimensionality. The second process is the decoherence of two-electron quantum states when a time-independent perturbation is applied to a planar two-electron quantum dot where both electrons are confined in an anharmonic potential. Even though the Hamiltonian of this system is time independent the corresponding differential equation shows a striking stiffness which makes the time integration extremely difficult. In the case of the one-dimensional Gaussian potential we discuss in detail the possibility of monitoring the time step for both explicit algorithms. In the other physical situations that are much more demanding in term of computations, we show that the accuracy of both algorithms depends strongly on the degree

  11. Many-body localization in Ising models with random long-range interactions

    NASA Astrophysics Data System (ADS)

    Li, Haoyuan; Wang, Jia; Liu, Xia-Ji; Hu, Hui

    2016-12-01

    We theoretically investigate the many-body localization phase transition in a one-dimensional Ising spin chain with random long-range spin-spin interactions, Vi j∝|i-j |-α , where the exponent of the interaction range α can be tuned from zero to infinitely large. By using exact diagonalization, we calculate the half-chain entanglement entropy and the energy spectral statistics and use them to characterize the phase transition towards the many-body localization phase at infinite temperature and at sufficiently large disorder strength. We perform finite-size scaling to extract the critical disorder strength and the critical exponent of the divergent localization length. With increasing α , the critical exponent experiences a sharp increase at about αc≃1.2 and then gradually decreases to a value found earlier in a disordered short-ranged interacting spin chain. For α <αc , we find that the system is mostly localized and the increase in the disorder strength may drive a transition between two many-body localized phases. In contrast, for α >αc , the transition is from a thermalized phase to the many-body localization phase. Our predictions could be experimentally tested with an ion-trap quantum emulator with programmable random long-range interactions, or with randomly distributed Rydberg atoms or polar molecules in lattices.

  12. Variational and Diffusion Monte Carlo Approaches to the Nuclear Few- and Many-Body Problem

    NASA Astrophysics Data System (ADS)

    Pederiva, Francesco; Roggero, Alessandro; Schmidt, Kevin E.

    We review Quantum Monte Carlo methods, a class of stochastic methods allowing for solving the many-body Schrödinger equation for an arbitrary Hamiltonian. The basic elements of the stochastic integration theory are first presented, followed by the implementation to the variational solution of the quantum many-body problem. Projection algorithms are then introduced, beginning with a formulation in coordinate space for central potentials, in order to illustrate the fundamental ideas. The extension to Hamiltonians with an explicit dependence on the spin-isospin degrees of freedom is then presented by making use of auxiliary fields (Auxiliary Field Diffusion Monte Carlo, AFDMC). Finally, we present the Configuration Interaction Monte Carlo algorithm (CIMC) a method to compute the ground state of general, local or non-local, Hamiltonians based on the configuration space sampling.

  13. Monte Carlo explicitly correlated second-order many-body perturbation theory

    NASA Astrophysics Data System (ADS)

    Johnson, Cole M.; Doran, Alexander E.; Zhang, Jinmei; Valeev, Edward F.; Hirata, So

    2016-10-01

    A stochastic algorithm is proposed and implemented that computes a basis-set-incompleteness (F12) correction to an ab initio second-order many-body perturbation energy as a short sum of 6- to 15-dimensional integrals of Gaussian-type orbitals, an explicit function of the electron-electron distance (geminal), and its associated excitation amplitudes held fixed at the values suggested by Ten-no. The integrals are directly evaluated (without a resolution-of-the-identity approximation or an auxiliary basis set) by the Metropolis Monte Carlo method. Applications of this method to 17 molecular correlation energies and 12 gas-phase reaction energies reveal that both the nonvariational and variational formulas for the correction give reliable correlation energies (98% or higher) and reaction energies (within 2 kJ mol-1 with a smaller statistical uncertainty) near the complete-basis-set limits by using just the aug-cc-pVDZ basis set. The nonvariational formula is found to be 2-10 times less expensive to evaluate than the variational one, though the latter yields energies that are bounded from below and is, therefore, slightly but systematically more accurate for energy differences. Being capable of using virtually any geminal form, the method confirms the best overall performance of the Slater-type geminal among 6 forms satisfying the same cusp conditions. Not having to precompute lower-dimensional integrals analytically, to store them on disk, or to transform them in a nonscalable dense-matrix-multiplication algorithm, the method scales favorably with both system size and computer size; the cost increases only as O(n4) with the number of orbitals (n), and its parallel efficiency reaches 99.9% of the ideal case on going from 16 to 4096 computer processors.

  14. Many-body perturbation theory using the density-functional concept: beyond the GW approximation.

    PubMed

    Bruneval, Fabien; Sottile, Francesco; Olevano, Valerio; Del Sole, Rodolfo; Reining, Lucia

    2005-05-13

    We propose an alternative formulation of many-body perturbation theory that uses the density-functional concept. Instead of the usual four-point integral equation for the polarizability, we obtain a two-point one, which leads to excellent optical absorption and energy-loss spectra. The corresponding three-point vertex function and self-energy are then simply calculated via an integration, for any level of approximation. Moreover, we show the direct impact of this formulation on the time-dependent density-functional theory. Numerical results for the band gap of bulk silicon and solid argon illustrate corrections beyond the GW approximation for the self-energy.

  15. Ultrafast many-body interferometry of impurities coupled to a Fermi sea

    NASA Astrophysics Data System (ADS)

    Cetina, Marko; Jag, Michael; Lous, Rianne S.; Fritsche, Isabella; Walraven, Jook T. M.; Grimm, Rudolf; Levinsen, Jesper; Parish, Meera M.; Schmidt, Richard; Knap, Michael; Demler, Eugene

    2016-10-01

    The fastest possible collective response of a quantum many-body system is related to its excitations at the highest possible energy. In condensed matter systems, the time scale for such “ultrafast” processes is typically set by the Fermi energy. Taking advantage of fast and precise control of interactions between ultracold atoms, we observed nonequilibrium dynamics of impurities coupled to an atomic Fermi sea. Our interferometric measurements track the nonperturbative quantum evolution of a fermionic many-body system, revealing in real time the formation dynamics of quasi-particles and the quantum interference between attractive and repulsive states throughout the full depth of the Fermi sea. Ultrafast time-domain methods applied to strongly interacting quantum gases enable the study of the dynamics of quantum matter under extreme nonequilibrium conditions.

  16. Stretched exponential decay of Majorana edge modes in many-body localized Kitaev chains under dissipation

    NASA Astrophysics Data System (ADS)

    Carmele, Alexander; Heyl, Markus; Kraus, Christina; Dalmonte, Marcello

    2015-11-01

    We investigate the resilience of symmetry-protected topological edge states at the boundaries of Kitaev chains in the presence of a bath which explicitly introduces symmetry-breaking terms. Specifically, we focus on single-particle losses and gains, violating the protecting parity symmetry, which could generically occur in realistic scenarios. For homogeneous systems we show that the Majorana mode decays exponentially fast. By the inclusion of strong disorder, where the closed system enters a many-body localized phase, we find that the Majorana mode can be stabilized substantially. The decay of the Majorana converts into a stretched exponential form for particle losses or gains occurring in the bulk. In particular, for pure loss dynamics we find a universal exponent α ≃2 /3 . We show that this holds both in the Anderson and many-body localized regimes. Our results thus provide a first step to stabilize edge states even in the presence of symmetry-breaking environments.

  17. Dielectric many-body effects in arrays of charged cylindrical macromolecules

    NASA Astrophysics Data System (ADS)

    Sinkovits, Daniel W.; Barros, Kipton; Dobnikar, Jure; Kandu&{Caron; C}, Matej; Naji, Ali; Podgornik, Rudolf; Luijten, Erik

    2012-02-01

    Nonuniform dielectric constants are a ubiquitous aspect of condensed-matter systems, but nevertheless widely ignored in simulations. Analytical work suggests that the polarization effects resulting from these inhomogeneities can produce many-body interactions that qualitatively alter the behavior of systems driven by electrostatic interactions, but such work relies on approximations. Recently, we have developed an algorithm that computes the fluctuating polarization charge at the interface between dielectric materials during a molecular dynamics simulation, without approximation. Here, we apply this approach to investigate arrays of charged cylindrical macromolecules in the presence of explicit counterions. We study the dielectric many-body effects as a function of separation, dielectric constant variation, and counterion valency. Our findings have implications for the aggregation of polyelectrolytes such as F-actin or DNA.

  18. Many-Body for Anybody: An Interactive Exploration of the Physics of More Than One Thing

    NASA Astrophysics Data System (ADS)

    Panoff, Robert M.

    2002-08-01

    Computational science continues to advance the accurate description and prediction of the dynamics of many-body systems with new applications, algorithms, and architectures. Moving from the researcher's workbench to the classroom, real-time model solutions and simulations now used in most every area of physics research can and should be incorporated into most every aspect of physics education. The result will be the development and deployment of interactive learning environments to help us to understand complex systems, while opening up new areas of learner-centered, group-oriented, discovery-based learning. Several examples from recent work in a range of many-body problems will be presented to demonstrate the full impact of numerical modeling and scientific visualization on physics education.

  19. Robustness of Many-Body Localization in the Presence of Dissipation

    NASA Astrophysics Data System (ADS)

    Levi, Emanuele; Heyl, Markus; Lesanovsky, Igor; Garrahan, Juan P.

    2016-06-01

    Many-body localization (MBL) has emerged as a novel paradigm for robust ergodicity breaking in closed quantum many-body systems. However, it is not yet clear to which extent MBL survives in the presence of dissipative processes induced by the coupling to an environment. Here we study heating and ergodicity for a paradigmatic MBL system—an interacting fermionic chain subject to quenched disorder—in the presence of dephasing. We find that, even though the system is eventually driven into an infinite-temperature state, heating as monitored by the von Neumann entropy can progress logarithmically slowly, implying exponentially large time scales for relaxation. This slow loss of memory of initial conditions makes signatures of nonergodicity visible over a long, but transient, time regime. We point out a potential controlled realization of the considered setup with cold atomic gases held in optical lattices.

  20. Quantum Drude oscillator model of atoms and molecules: Many-body polarization and dispersion interactions for atomistic simulation

    NASA Astrophysics Data System (ADS)

    Jones, Andrew P.; Crain, Jason; Sokhan, Vlad P.; Whitfield, Troy W.; Martyna, Glenn J.

    2013-04-01

    Treating both many-body polarization and dispersion interactions is now recognized as a key element in achieving the level of atomistic modeling required to reveal novel physics in complex systems. The quantum Drude oscillator (QDO), a Gaussian-based, coarse grained electronic structure model, captures both many-body polarization and dispersion and has linear scale computational complexity with system size, hence it is a leading candidate next-generation simulation method. Here, we investigate the extent to which the QDO treatment reproduces the desired long-range atomic and molecular properties. We present closed form expressions for leading order polarizabilities and dispersion coefficients and derive invariant (parameter-free) scaling relationships among multipole polarizability and many-body dispersion coefficients that arise due to the Gaussian nature of the model. We show that these “combining rules” hold to within a few percent for noble gas atoms, alkali metals, and simple (first-row hydride) molecules such as water; this is consistent with the surprising success that models with underlying Gaussian statistics often exhibit in physics. We present a diagrammatic Jastrow-type perturbation theory tailored to the QDO model that serves to illustrate the rich types of responses that the QDO approach engenders. QDO models for neon, argon, krypton, and xenon, designed to reproduce gas phase properties, are constructed and their condensed phase properties explored via linear scale diffusion Monte Carlo (DMC) and path integral molecular dynamics (PIMD) simulations. Good agreement with experimental data for structure, cohesive energy, and bulk modulus is found, demonstrating a degree of transferability that cannot be achieved using current empirical models or fully ab initio descriptions.

  1. Adiabatic many-body state preparation and information transfer in quantum dot arrays

    NASA Astrophysics Data System (ADS)

    Farooq, Umer; Bayat, Abolfazl; Mancini, Stefano; Bose, Sougato

    2015-04-01

    Quantum simulation of many-body systems are one of the most interesting tasks of quantum technology. Among them is the preparation of a many-body system in its ground state when the vanishing energy gap makes the cooling mechanisms ineffective. Adiabatic theorem, as an alternative to cooling, can be exploited for driving the many-body system to its ground state. In this paper, we study two most common disorders in quantum dot arrays, namely exchange coupling fluctuations and hyperfine interaction, in adiabatic preparation of ground state in such systems. We show that the adiabatic ground-state preparation is highly robust against those disorder effects making it a good analog simulator. Moreover, we also study the adiabatic quantum information transfer, using singlet-triplet states, across a spin chain. In contrast to ground-state preparation the transfer mechanism is highly affected by disorder and in particular, the hyperfine interaction is very destructive for the performance. This suggests that for communication tasks across such arrays adiabatic evolution is not as effective and quantum quenches could be preferable.

  2. Toward Hamiltonian Adaptive QM/MM: Accurate Solvent Structures Using Many-Body Potentials.

    PubMed

    Boereboom, Jelle M; Potestio, Raffaello; Donadio, Davide; Bulo, Rosa E

    2016-08-09

    Adaptive quantum mechanical (QM)/molecular mechanical (MM) methods enable efficient molecular simulations of chemistry in solution. Reactive subregions are modeled with an accurate QM potential energy expression while the rest of the system is described in a more approximate manner (MM). As solvent molecules diffuse in and out of the reactive region, they are gradually included into (and excluded from) the QM expression. It would be desirable to model such a system with a single adaptive Hamiltonian, but thus far this has resulted in distorted structures at the boundary between the two regions. Solving this long outstanding problem will allow microcanonical adaptive QM/MM simulations that can be used to obtain vibrational spectra and dynamical properties. The difficulty lies in the complex QM potential energy expression, with a many-body expansion that contains higher order terms. Here, we outline a Hamiltonian adaptive multiscale scheme within the framework of many-body potentials. The adaptive expressions are entirely general, and complementary to all standard (nonadaptive) QM/MM embedding schemes available. We demonstrate the merit of our approach on a molecular system defined by two different MM potentials (MM/MM'). For the long-range interactions a numerical scheme is used (particle mesh Ewald), which yields energy expressions that are many-body in nature. Our Hamiltonian approach is the first to provide both energy conservation and the correct solvent structure everywhere in this system.

  3. Remanent Magnetization: Signature of Many-Body Localization in Quantum Antiferromagnets.

    PubMed

    Ros, V; Müller, M

    2017-06-09

    We study the remanent magnetization in antiferromagnetic, many-body localized quantum spin chains, initialized in a fully magnetized state. Its long time limit is an order parameter for the localization transition, which is readily accessible by standard experimental probes in magnets. We analytically calculate its value in the strong-disorder regime exploiting the explicit construction of quasilocal conserved quantities of the localized phase. We discuss analogies in cold atomic systems.

  4. Simulations of dipolar fluids using effective many-body isotropic interactions

    NASA Astrophysics Data System (ADS)

    Sindt, Julien O.; Camp, Philip J.

    2015-07-01

    The partition function of a system with pairwise-additive anisotropic dipole-dipole interactions is equal to that of a hypothetical system with many-body isotropic interactions [G. Stell, Phys. Rev. Lett. 32, 286 (1974)]. The effective many-body interactions contain n-body contributions of all orders. Each contribution is known as an expansion in terms of the particle-particle distances r, and the coefficients are temperature dependent. The leading-order two-body term is the familiar -r-6 attraction, and the leading-order three-body term is equivalent to the Axilrod-Teller interaction. In this work, a fluid of particles with the leading-order two-body and three-body interactions is compared to an equivalent dipolar soft-sphere fluid. Molecular simulations are used to determine the conditions under which the effective many-body interactions reproduce the fluid-phase structures of the dipolar system. The effective many-body interaction works well at moderately high temperatures but fails at low temperatures where particle chaining is expected to occur. It is shown that an adjustment of the coefficients of the two-body and three-body terms leads to a good description of the structure of the dipolar fluid even in the chaining regime, due primarily to the ground-state linear configuration of the three-body Axilrod-Teller interaction. The vapor-liquid phase diagrams of systems with different Axilrod-Teller contributions are determined. As the strength of the three-body interaction is increased, the critical temperature and density both decrease and disappear completely above a threshold strength, where chaining eventually suppresses the condensation transition.

  5. Importance of many-body correlations in glass transition: An example from polydisperse hard spheres

    NASA Astrophysics Data System (ADS)

    Leocmach, Mathieu; Russo, John; Tanaka, Hajime

    2013-03-01

    Most of the liquid-state theories, including glass-transition theories, are constructed on the basis of two-body density correlations. However, we have recently shown that many-body correlations, in particular, bond orientational correlations, play a key role in both the glass transition and the crystallization transition. Here we show, with numerical simulations of supercooled polydisperse hard spheres systems, that the length-scale associated with any two-point spatial correlation function does not increase toward the glass transition. A growing length-scale is instead revealed by considering many-body correlation functions, such as correlators of orientational order, which follows the length-scale of the dynamic heterogeneities. Despite the growing of crystal-like bond orientational order, we reveal that the stability against crystallization with increasing polydispersity is due to an increasing population of icosahedral arrangements of particles. Our results suggest that, for this type of systems, many-body correlations are a manifestation of the link between the vitrification and the crystallization phenomena. Whether a system is vitrified or crystallized can be controlled by the degree of frustration against crystallization, polydispersity in this case.

  6. Quantum many-body theory for electron spin decoherence in nanoscale nuclear spin baths

    NASA Astrophysics Data System (ADS)

    Yang, Wen; Ma, Wen-Long; Liu, Ren-Bao

    2017-01-01

    Decoherence of electron spins in nanoscale systems is important to quantum technologies such as quantum information processing and magnetometry. It is also an ideal model problem for studying the crossover between quantum and classical phenomena. At low temperatures or in light-element materials where the spin-orbit coupling is weak, the phonon scattering in nanostructures is less important and the fluctuations of nuclear spins become the dominant decoherence mechanism for electron spins. Since the 1950s, semi-classical noise theories have been developed for understanding electron spin decoherence. In spin-based solid-state quantum technologies, the relevant systems are in the nanometer scale and nuclear spin baths are quantum objects which require a quantum description. Recently, quantum pictures have been established to understand the decoherence and quantum many-body theories have been developed to quantitatively describe this phenomenon. Anomalous quantum effects have been predicted and some have been experimentally confirmed. A systematically truncated cluster-correlation expansion theory has been developed to account for the many-body correlations in nanoscale nuclear spin baths that are built up during electron spin decoherence. The theory has successfully predicted and explained a number of experimental results in a wide range of physical systems. In this review, we will cover this recent progress. The limitations of the present quantum many-body theories and possible directions for future development will also be discussed.

  7. Quantum many-body theory for electron spin decoherence in nanoscale nuclear spin baths.

    PubMed

    Yang, Wen; Ma, Wen-Long; Liu, Ren-Bao

    2017-01-01

    Decoherence of electron spins in nanoscale systems is important to quantum technologies such as quantum information processing and magnetometry. It is also an ideal model problem for studying the crossover between quantum and classical phenomena. At low temperatures or in light-element materials where the spin-orbit coupling is weak, the phonon scattering in nanostructures is less important and the fluctuations of nuclear spins become the dominant decoherence mechanism for electron spins. Since the 1950s, semi-classical noise theories have been developed for understanding electron spin decoherence. In spin-based solid-state quantum technologies, the relevant systems are in the nanometer scale and nuclear spin baths are quantum objects which require a quantum description. Recently, quantum pictures have been established to understand the decoherence and quantum many-body theories have been developed to quantitatively describe this phenomenon. Anomalous quantum effects have been predicted and some have been experimentally confirmed. A systematically truncated cluster-correlation expansion theory has been developed to account for the many-body correlations in nanoscale nuclear spin baths that are built up during electron spin decoherence. The theory has successfully predicted and explained a number of experimental results in a wide range of physical systems. In this review, we will cover this recent progress. The limitations of the present quantum many-body theories and possible directions for future development will also be discussed.

  8. Applications of Tensor Network Algorithms in Quantum Many-Body Physics

    NASA Astrophysics Data System (ADS)

    West, Colin G.

    The classical simulation of many-body quantum systems is an essential tool in understanding many fundamental aspects of condensed matter physics. But a major obstacle arises from the number of degrees of freedom involved in describing such systems, which is exponential in the system size. Recently, however, a class of numerical techniques based on structures called "tensor networks" has emerged, which allows many "typical" quantum states (such as the ground states of gapped, local Hamiltonians) to be represented much more efficiently. In this work we extend and apply these techniques to consider several central topics in quantum many-body physics. After reviewing the relevant background material from the field of tensor networks and tensor network states, we demonstrate a method for computing high order moments and cumulants of operators with respect to such states, including the so-called "Binder cumulant," a powerful tool for detecting phase transitions. Next, we employ tensor network algorithms to characterize the ground state phase diagram of a quantum spin model, including both symmetry-breaking phases and symmetry protected topological order, and find a signicant variety of phases and phase transitions. Finally, we consider the entanglement properties of quantum states exhibiting many-body localization, using a combination of exact diagonalization and tensor network techniques.

  9. The Many-Body Correlation of Bose-Fermi Mixture in the Ring Trap

    NASA Astrophysics Data System (ADS)

    Shibato, Ryosuke; Nishimura, Takushi

    2012-02-01

    Since the realization of Bose-Einstein Condensation in alkali atoms in 1995, studies on cold atomic gases have greatly advanced. The cold atoms are precisely controlled by electromagnetism and optics, and flexible to design quantum systems. In 2001, A. G"orlitz's group has realized the Bose-Einstein condensates in the quasi-one-dimensional system [1]. One have now obtained the ideal system to study the one-dimensional many-body physics experimentally. The purpose of our study is to clarify the effect of quantum many-body correlation beyond the mean-field approximation. To accomplish this purpose, we first prepare the bosons and fermions in the ring trap [2]. We prepare the initial state in the trap with the small distortion and obtained that both kinds of particles tend to be localized. After taking off this distortion, we solved the time-dependent Schr"odinger equation. We derived the energy spectrum, density profile, and studied pair-correlation effect. Our results predict that the many-body correlation emerges, which has never been observed experimentally up to now. [4pt] [1] A. G"orlitz et al., Phys. Rev. Lett. 87, 130402 (2001)[0pt] [2] O. Morizot et al., Phys. Rev. A. 74, 023617 (2006)

  10. Local reversibility and entanglement structure of many-body ground states

    NASA Astrophysics Data System (ADS)

    Kuwahara, Tomotaka; Arad, Itai; Amico, Luigi; Vedral, Vlatko

    2017-03-01

    The low-temperature physics of quantum many-body systems is largely governed by the structure of their ground states. Minimizing the energy of local interactions, ground states often reflect strong properties of locality such as the area law for entanglement entropy and the exponential decay of correlations between spatially separated observables. Here, we present a novel characterization of quantum states, which we call ‘local reversibility’. It characterizes the type of operations that are needed to reverse the action of a general disturbance on the state. We prove that unique ground states of gapped local Hamiltonian are locally reversible. This way, we identify new universal features of many-body ground states, which cannot be derived from the aforementioned properties. We use local reversibility to distinguish between states enjoying microscopic and macroscopic quantum phenomena. To demonstrate the potential of our approach, we prove specific properties of ground states, which are relevant both to critical and non-critical theories.

  11. Dynamics of many-body localization in a translation-invariant quantum glass model

    NASA Astrophysics Data System (ADS)

    van Horssen, Merlijn; Levi, Emanuele; Garrahan, Juan P.

    2015-09-01

    We study the real-time dynamics of a translationally invariant quantum spin chain, based on the East kinetically constrained glass model, in search for evidence of many-body localization in the absence of disorder. Numerical simulations indicate a change, controlled by a coupling parameter, from a regime of fast relaxation-corresponding to thermalization-to a regime of very slow relaxation. This slowly relaxing regime is characterized by dynamical features usually associated with nonergodicity and many-body localization (MBL): memory of initial conditions, logarithmic growth of entanglement entropy, and nonexponential decay of time correlators. We show that slow relaxation is a consequence of sensitivity to spatial fluctuations in the initial state. While numerical results and physical considerations indicate that relaxation time scales grow markedly with size, our finite size results are consistent both with an MBL transition, expected to only occur in disordered systems, and with a pronounced quasi-MBL crossover.

  12. Many-body interferometry of a Rydberg-dressed spin lattice

    NASA Astrophysics Data System (ADS)

    Zeiher, Johannes; van Bijnen, Rick; Schauß, Peter; Hild, Sebastian; Choi, Jae-Yoon; Pohl, Thomas; Bloch, Immanuel; Gross, Christian

    2016-12-01

    Ultracold atoms in optical lattices are ideal to study fundamentally new quantum many-body systems including frustrated or topological magnetic phases and supersolids. However, the necessary control of strong long-range interactions between distant ground state atoms has remained a long-standing goal. Optical dressing of ground state atoms via off-resonant laser coupling to Rydberg states is one way to tailor such interactions. Here we report the realization of coherent Rydberg dressing to implement a two-dimensional synthetic spin lattice. Our single-atom-resolved interferometric measurements of the many-body dynamics enable the microscopic probing of the interactions and reveal their highly tunable range and anisotropy. Our work marks the first step towards the use of laser-controlled Rydberg interactions for the study of exotic quantum magnets in optical lattices.

  13. Quantum simulators by design: Many-body physics in reconfigurable arrays of tunnel-coupled traps

    NASA Astrophysics Data System (ADS)

    Sturm, M. R.; Schlosser, M.; Walser, R.; Birkl, G.

    2017-06-01

    We present a platform for the bottom-up construction of itinerant many-body systems: ultracold atoms transferred from a Bose-Einstein condensate into freely configurable arrays of microlens generated focused-beam dipole traps. This complements traditional optical lattices and provides a different access to the field of two-dimensional quantum simulators. The ultimate control of topology, well depth, atom number, and interaction strength is matched by sufficient tunneling. We characterize the required light fields, derive the Bose-Hubbard parameters for several alkali-metal species, and investigate the loading procedures and heating mechanisms. To demonstrate the potential of this approach, we analyze coupled annular Josephson contacts exhibiting many-body resonances.

  14. Solving the quantum many-body problem with artificial neural networks.

    PubMed

    Carleo, Giuseppe; Troyer, Matthias

    2017-02-10

    The challenge posed by the many-body problem in quantum physics originates from the difficulty of describing the nontrivial correlations encoded in the exponential complexity of the many-body wave function. Here we demonstrate that systematic machine learning of the wave function can reduce this complexity to a tractable computational form for some notable cases of physical interest. We introduce a variational representation of quantum states based on artificial neural networks with a variable number of hidden neurons. A reinforcement-learning scheme we demonstrate is capable of both finding the ground state and describing the unitary time evolution of complex interacting quantum systems. Our approach achieves high accuracy in describing prototypical interacting spins models in one and two dimensions.

  15. Rotation of Quantum Impurities in the Presence of a Many-Body Environment

    NASA Astrophysics Data System (ADS)

    Schmidt, Richard; Lemeshko, Mikhail

    2015-05-01

    We develop a microscopic theory describing a quantum impurity whose rotational degree of freedom is coupled to a many-particle bath. We approach the problem by introducing the concept of an "angulon"—a quantum rotor dressed by a quantum field—and reveal its quasiparticle properties using a combination of variational and diagrammatic techniques. Our theory predicts renormalization of the impurity rotational structure, such as that observed in experiments with molecules in superfluid helium droplets, in terms of a rotational Lamb shift induced by the many-particle environment. Furthermore, we discover a rich many-body-induced fine structure, emerging in rotational spectra due to a redistribution of angular momentum within the quantum many-body system.

  16. Solving the quantum many-body problem with artificial neural networks

    NASA Astrophysics Data System (ADS)

    Carleo, Giuseppe; Troyer, Matthias

    2017-02-01

    The challenge posed by the many-body problem in quantum physics originates from the difficulty of describing the nontrivial correlations encoded in the exponential complexity of the many-body wave function. Here we demonstrate that systematic machine learning of the wave function can reduce this complexity to a tractable computational form for some notable cases of physical interest. We introduce a variational representation of quantum states based on artificial neural networks with a variable number of hidden neurons. A reinforcement-learning scheme we demonstrate is capable of both finding the ground state and describing the unitary time evolution of complex interacting quantum systems. Our approach achieves high accuracy in describing prototypical interacting spins models in one and two dimensions.

  17. Encoding the structure of many-body localization with matrix product operators

    NASA Astrophysics Data System (ADS)

    Pekker, David; Clark, Bryan K.

    2015-03-01

    Anderson insulators are non-interacting disordered systems which have localized single particle eigenstates. The interacting analogue of Anderson insulators are the Many-Body Localized (MBL) phases. The natural language for representing the spectrum of the Anderson insulator is that of product states over the single-particle modes. We show that product states over Matrix Product Operators of small bond dimension is the corresponding natural language for describing the MBL phases. In this language all of the many-body eigenstates are encode by Matrix Product States (i.e. DMRG wave function) consisting of only two sets of low bond-dimension matrices per site: the Gi matrix corresponding to the local ground state on site i and the Ei matrix corresponding to the local excited state. All 2 n eigenstates can be generated from all possible combinations of these matrices.

  18. Flow equation approach to one-body and many-body localization

    NASA Astrophysics Data System (ADS)

    Quito, Victor; Bhattacharjee, Paraj; Pekker, David; Refael, Gil

    2014-03-01

    We study one-body and many-body localization using the flow equation technique applied to spin-1/2 Hamiltonians. This technique, first introduced by Wegner, allows us to exact diagonalize interacting systems by solving a set of first-order differential equations for coupling constants. Besides, by the flow of individual operators we also compute physical properties, such as correlation and localization lengths, by looking at the flow of probability distributions of couplings in the Hilbert space. As a first example, we analyze the one-body localization problem written in terms of spins, the disordered XY model with a random transverse field. We compare the results obtained in the flow equation approach with the diagonalization in the fermionic language. For the many-body problem, we investigate the physical properties of the disordered XXZ Hamiltonian with a random transverse field in the z-direction.

  19. How should we understand non-equilibrium many-body steady states?

    NASA Astrophysics Data System (ADS)

    Maghrebi, Mohammad; Gorshkov, Alexey

    : Many-body systems with both coherent dynamics and dissipation constitute a rich class of models which are nevertheless much less explored than their dissipationless counterparts. The advent of numerous experimental platforms that simulate such dynamics poses an immediate challenge to systematically understand and classify these models. In particular, nontrivial many-body states emerge as steady states under non-equilibrium dynamics. In this talk, I use a field-theoretic approach based on the Keldysh formalism to study nonequilibrium phases and phase transitions in such models. I show that an effective temperature generically emerges as a result of dissipation, and the universal behavior including the dynamics near the steady state is described by a thermodynamic universality class. In the end, I will also discuss possibilities that go beyond the paradigm of an effective thermodynamic behavior.

  20. Many-body localization transition in random quantum spin chains with long-range interactions

    NASA Astrophysics Data System (ADS)

    Moure, N.; Haas, S.; Kettemann, S.

    2015-07-01

    While there are well-established methods to study delocalization transitions of single particles in random systems, it remains a challenging problem how to characterize many-body delocalization transitions. Here, we use a generalized real-space renormalization group technique to study the anisotropic Heisenberg model with long-range interactions, decaying with a power α, which are generated by placing spins at random positions along the chain. This method permits a large-scale finite-size scaling analysis. We examine the full distribution function of the excitation energy gap from the ground state and observe a crossover with decreasing α. At αc the full distribution coincides with a critical function. Thereby, we find strong evidence for the existence of a many-body localization transition in disordered antiferromagnetic spin chains with long-range interactions.

  1. Recent advances in Many Body Dissipative Particles Dynamics simulations of liquid-vapor interfaces.

    PubMed

    Ghoufi, Aziz; Emile, Janine; Malfreyt, Patrice

    2013-01-01

    Many Body Dissipative Particles Dynamics (MDPD) simulation is a novel promising mesoscopic method to model the liquid-vapor interfaces. Based upon works of Paganobarraga and Frenkel (J. Chem. Phys. 15, 5015 (2001)) and Trofimov (J. Chem. Phys. 117, 9383 (2002)) and of Warren (Phys. Rev. E 68, 066702 (2003)) this method has been critically reviewed during this last decade. We propose here to give an overview of the Many Body Dissipative Particles Dynamic simulation within the framework of the liquid-vapor interfaces. We recall the theoretical background of MDPD and we present some recent results of systems of interest such as water liquid-vapor interfaces and salt effect on water surface tension. Additionally we discuss the ability of MDPD to capture the mechanisms at the mesoscopic scale through the formation of micelles and the coalescence of a nanodroplet water on water surface.

  2. A many-body potential approach to modelling the thermomechanical properties of actinide oxides.

    PubMed

    Cooper, M W D; Rushton, M J D; Grimes, R W

    2014-03-12

    A many-body potential model for the description of actinide oxide systems, which is robust at high temperatures, is reported for the first time. The embedded atom method is used to describe many-body interactions ensuring good reproduction of a range of thermophysical properties (lattice parameter, bulk modulus, enthalpy and specific heat) between 300 and 3000 K for AmO2, CeO2, CmO2, NpO2, ThO2, PuO2 and UO2. Additionally, the model predicts a melting point for UO2 between 3000 and 3100 K, in close agreement with experiment. Oxygen-oxygen interactions are fixed across the actinide oxide series because it facilitates the modelling of oxide solid solutions. The new potential is also used to predict the energies of Schottky and Frenkel pair disorder processes.

  3. On the simulation of indistinguishable fermions in the many-body Wigner formalism

    NASA Astrophysics Data System (ADS)

    Sellier, J. M.; Dimov, I.

    2015-01-01

    The simulation of quantum systems consisting of interacting, indistinguishable fermions is an incredible mathematical problem which poses formidable numerical challenges. Many sophisticated methods addressing this problem are available which are based on the many-body Schrödinger formalism. Recently a Monte Carlo technique for the resolution of the many-body Wigner equation has been introduced and successfully applied to the simulation of distinguishable, spinless particles. This numerical approach presents several advantages over other methods. Indeed, it is based on an intuitive formalism in which quantum systems are described in terms of a quasi-distribution function, and highly scalable due to its Monte Carlo nature. In this work, we extend the many-body Wigner Monte Carlo method to the simulation of indistinguishable fermions. To this end, we first show how fermions are incorporated into the Wigner formalism. Then we demonstrate that the Pauli exclusion principle is intrinsic to the formalism. As a matter of fact, a numerical simulation of two strongly interacting fermions (electrons) is performed which clearly shows the appearance of a Fermi (or exchange-correlation) hole in the phase-space, a clear signature of the presence of the Pauli principle. To conclude, we simulate 4, 8 and 16 non-interacting fermions, isolated in a closed box, and show that, as the number of fermions increases, we gradually recover the Fermi-Dirac statistics, a clear proof of the reliability of our proposed method for the treatment of indistinguishable particles.

  4. Early Breakdown of Area-Law Entanglement at the Many-Body Delocalization Transition

    NASA Astrophysics Data System (ADS)

    Devakul, Trithep; Singh, Rajiv R. P.

    2015-10-01

    We introduce the numerical linked cluster expansion as a controlled numerical tool for the study of the many-body localization transition in a disordered system with continuous nonperturbative disorder. Our approach works directly in the thermodynamic limit, in any spatial dimension, and does not rely on any finite size scaling procedure. We study the onset of many-body delocalization through the breakdown of area-law entanglement in a generic many-body eigenstate. By looking for initial signs of an instability of the localized phase, we obtain a value for the critical disorder, which we believe should be a lower bound for the true value, that is higher than current best estimates from finite size studies. This implies that most current methods tend to overestimate the extent of the localized phase due to finite size effects making the localized phase appear stable at small length scales. We also study the mobility edge in these systems as a function of energy density, and we find that our conclusion is the same at all examined energies.

  5. Particle-hole symmetry, many-body localization, and topological edge modes

    NASA Astrophysics Data System (ADS)

    Vasseur, Romain; Friedman, Aaron J.; Parameswaran, S. A.; Potter, Andrew C.

    We study the excited states of interacting fermions in one dimension with particle-hole symmetric disorder (equivalently, random-bond XXZ chains) using a combination of renormalization group methods and exact diagonalization. Absent interactions, the entire many-body spectrum exhibits infinite-randomness quantum critical behavior with highly degenerate excited states. We show that though interactions are an irrelevant perturbation in the ground state, they drastically affect the structure of excited states: even arbitrarily weak interactions split the degeneracies in favor of thermalization (weak disorder) or spontaneously broken particle-hole symmetry, driving the system into a many-body localized spin glass phase (strong disorder). In both cases, the quantum critical properties of the non-interacting model are destroyed, either by thermal decoherence or spontaneous symmetry breaking. This system then has the interesting and counterintuitive property that edges of the many-body spectrum are less localized than the center of the spectrum. We argue that our results rule out the existence of certain excited state symmetry-protected topological orders. Supported by the Gordon and Betty Moore Foundation's EPiQS Initiative (Grant GBMF4307 (ACP), the Quantum Materials Program at LBNL (RV), NSF Grant DMR-1455366 and UCOP Research Catalyst Award No. CA-15-327861 (SAP).

  6. On the simulation of indistinguishable fermions in the many-body Wigner formalism

    SciTech Connect

    Sellier, J.M. Dimov, I.

    2015-01-01

    The simulation of quantum systems consisting of interacting, indistinguishable fermions is an incredible mathematical problem which poses formidable numerical challenges. Many sophisticated methods addressing this problem are available which are based on the many-body Schrödinger formalism. Recently a Monte Carlo technique for the resolution of the many-body Wigner equation has been introduced and successfully applied to the simulation of distinguishable, spinless particles. This numerical approach presents several advantages over other methods. Indeed, it is based on an intuitive formalism in which quantum systems are described in terms of a quasi-distribution function, and highly scalable due to its Monte Carlo nature. In this work, we extend the many-body Wigner Monte Carlo method to the simulation of indistinguishable fermions. To this end, we first show how fermions are incorporated into the Wigner formalism. Then we demonstrate that the Pauli exclusion principle is intrinsic to the formalism. As a matter of fact, a numerical simulation of two strongly interacting fermions (electrons) is performed which clearly shows the appearance of a Fermi (or exchange–correlation) hole in the phase-space, a clear signature of the presence of the Pauli principle. To conclude, we simulate 4, 8 and 16 non-interacting fermions, isolated in a closed box, and show that, as the number of fermions increases, we gradually recover the Fermi–Dirac statistics, a clear proof of the reliability of our proposed method for the treatment of indistinguishable particles.

  7. Many-body theory of electric and thermal transport in single-molecule heterojunctions

    NASA Astrophysics Data System (ADS)

    Bergfield, Justin

    2010-03-01

    Electron transport in single-molecule junctions (SMJ) is a key example of a strongly-correlated system far from equilibrium, with myriad potential applications in nanotechnology. When macroscopic leads are attached to a single molecule, a SMJ is formed, transforming the ``few-body'' molecular problem into a true ``many-body'' problem. Until recently, a theory of transport that properly accounts for both the particle and wave character of the electron has been lacking, so that the Coulomb blockade and coherent transport regimes were considered ``complementary.'' We have developed a nonequilibrium many-body theoryfootnotetextJ. P. Bergfield and C. A. Stafford, Phys. Rev. B 79, 245125 (2009). that reproduces the key features of both the Coulomb blockade and coherent transport regimes simultaneously. Our approach is based on nonequilibrium Green's functions, enabling physically motivated approximations that sum terms to all orders. The junction Green's functions are calculated exactly in the sequential-tunneling limit, and the corrections to the electron self-energy due to finite tunneling width are included via Dyson-Keldysh equations. In this talk, I will present a brief overview of our many-body theory of SMJ and discuss the simulated linear and nonlinear response of a benzenedithiol-gold junction. I will also outline our derivation of an exact expression for the heat current in an interacting nanostructure, highlighting our predictionfootnotetextJ. P. Bergfield and C. A. Stafford, Nano Letters 9, 3072 (2009). of a dramatic quantum-induced enhancement of thermoelectric effects in the vicinity of a transmission node. Finally, I will provide several striking examples where the predictions of our many-body theory differ drastically from those of mean-field (density functional) theory.

  8. Developing Novel Frameworks for Many-Body Ensembles

    DTIC Science & Technology

    2016-03-17

    namely we seek to predict whether inhomogeneities appear and to develop a description of inhomogeneity formation that is valid across particle and...Research Triangle Park, NC 27709-2211 Markov model, particle ensembles, mesoscale structure REPORT DOCUMENTATION PAGE 11. SPONSOR/MONITOR’S REPORT...valid across particle and system scales. These systems can be tricky to analyze as mesoscale structures can lead to highly nonlinear macroscopic

  9. An Efficient and Accurate Quantum Lattice-Gas Model for the Many-Body Schroedinger Wave Equation

    DTIC Science & Technology

    2002-01-01

    CONTRACT NUMBER AN EFFICIENT AND ACCURATE QUANTUM LATTICE-GAS MODEL FOR THE MANY-BODY SCHROEDINGER WAVE EQUATION 5b. GRANT NUMBER SC. PROGRAM ELEMENT...for simulating the time-dependent evolution of a many-body jiiantum mechanical system of particles governed by the non-relativistic Schroedinger " wave...the numerical dispersion of the simulated wave packets is compared with the analytical solutions. 15. SUBJECT TERM: Schroedinger wave equation

  10. Many-body critical Casimir interactions in colloidal suspensions.

    PubMed

    Hobrecht, Hendrik; Hucht, Alfred

    2015-10-01

    We study the fluctuation-induced Casimir interactions in colloidal suspensions, especially between colloids immersed in a binary liquid close to its critical demixing point. To simulate these systems, we present a highly efficient cluster Monte Carlo algorithm based on geometric symmetries of the Hamiltonian. Utilizing the principle of universality, the medium is represented by an Ising system while the colloids are areas of spins with fixed orientation. Our results for the Casimir interaction potential between two particles at the critical point in two dimensions perfectly agree with the exact predictions. However, we find that in finite systems the behavior strongly depends on whether the Z(2) symmetry of the system is broken by the particles. We present Monte Carlo results for the three-body Casimir interaction potential and take a close look onto the case of one particle in the vicinity of two adjacent particles, which can be calculated from the two-particle interaction by a conformal mapping. These results emphasize the failure of the common decomposition approach for many-particle critical Casimir interactions.

  11. Nonstationary Time Series Analysis of Many-Body Dynamics

    DTIC Science & Technology

    1992-05-01

    statistical mechanics in condensed matter systems [2. A simulation is essentially a numerical experiment, however, and considerable data reduction of the...equilibrium, statistical mechanics provides the appropriate formal foundation [3], and the data reduction accompanying molecular dynamics simulations...involves calculating thermodynamic or statistical mechanical quantities, such as temperature, pressure, density, pair correlation functions, time

  12. Optimal dynamical control of many-body entanglement.

    PubMed

    Platzer, Felix; Mintert, Florian; Buchleitner, Andreas

    2010-07-09

    We construct time-dependent optimal control pulses based on a multipartite entanglement measure as the target functional. The control Hamiltonian is given purely algebraically and drives a composite quantum system rapidly into a highly entangled state that is robust against decoherence.

  13. Charge-dependent many-body exchange and dispersion interactions in combined QM/MM simulations

    NASA Astrophysics Data System (ADS)

    Kuechler, Erich R.; Giese, Timothy J.; York, Darrin M.

    2015-12-01

    Accurate modeling of the molecular environment is critical in condensed phase simulations of chemical reactions. Conventional quantum mechanical/molecular mechanical (QM/MM) simulations traditionally model non-electrostatic non-bonded interactions through an empirical Lennard-Jones (LJ) potential which, in violation of intuitive chemical principles, is bereft of any explicit coupling to an atom's local electronic structure. This oversight results in a model whereby short-ranged exchange-repulsion and long-ranged dispersion interactions are invariant to changes in the local atomic charge, leading to accuracy limitations for chemical reactions where significant atomic charge transfer can occur along the reaction coordinate. The present work presents a variational, charge-dependent exchange-repulsion and dispersion model, referred to as the charge-dependent exchange and dispersion (QXD) model, for hybrid QM/MM simulations. Analytic expressions for the energy and gradients are provided, as well as a description of the integration of the model into existing QM/MM frameworks, allowing QXD to replace traditional LJ interactions in simulations of reactive condensed phase systems. After initial validation against QM data, the method is demonstrated by capturing the solvation free energies of a series of small, chlorine-containing compounds that have varying charge on the chlorine atom. The model is further tested on the SN2 attack of a chloride anion on methylchloride. Results suggest that the QXD model, unlike the traditional LJ model, is able to simultaneously obtain accurate solvation free energies for a range of compounds while at the same time closely reproducing the experimental reaction free energy barrier. The QXD interaction model allows explicit coupling of atomic charge with many-body exchange and dispersion interactions that are related to atomic size and provides a more accurate and robust representation of non-electrostatic non-bonded QM/MM interactions.

  14. Charge-dependent many-body exchange and dispersion interactions in combined QM/MM simulations

    SciTech Connect

    Kuechler, Erich R.; Giese, Timothy J.; York, Darrin M.

    2015-12-21

    Accurate modeling of the molecular environment is critical in condensed phase simulations of chemical reactions. Conventional quantum mechanical/molecular mechanical (QM/MM) simulations traditionally model non-electrostatic non-bonded interactions through an empirical Lennard-Jones (LJ) potential which, in violation of intuitive chemical principles, is bereft of any explicit coupling to an atom’s local electronic structure. This oversight results in a model whereby short-ranged exchange-repulsion and long-ranged dispersion interactions are invariant to changes in the local atomic charge, leading to accuracy limitations for chemical reactions where significant atomic charge transfer can occur along the reaction coordinate. The present work presents a variational, charge-dependent exchange-repulsion and dispersion model, referred to as the charge-dependent exchange and dispersion (QXD) model, for hybrid QM/MM simulations. Analytic expressions for the energy and gradients are provided, as well as a description of the integration of the model into existing QM/MM frameworks, allowing QXD to replace traditional LJ interactions in simulations of reactive condensed phase systems. After initial validation against QM data, the method is demonstrated by capturing the solvation free energies of a series of small, chlorine-containing compounds that have varying charge on the chlorine atom. The model is further tested on the S{sub N}2 attack of a chloride anion on methylchloride. Results suggest that the QXD model, unlike the traditional LJ model, is able to simultaneously obtain accurate solvation free energies for a range of compounds while at the same time closely reproducing the experimental reaction free energy barrier. The QXD interaction model allows explicit coupling of atomic charge with many-body exchange and dispersion interactions that are related to atomic size and provides a more accurate and robust representation of non-electrostatic non-bonded QM

  15. Optimal free descriptions of many-body theories

    NASA Astrophysics Data System (ADS)

    Turner, Christopher J.; Meichanetzidis, Konstantinos; Papić, Zlatko; Pachos, Jiannis K.

    2017-04-01

    Interacting bosons or fermions give rise to some of the most fascinating phases of matter, including high-temperature superconductivity, the fractional quantum Hall effect, quantum spin liquids and Mott insulators. Although these systems are promising for technological applications, they also present conceptual challenges, as they require approaches beyond mean-field and perturbation theory. Here we develop a general framework for identifying the free theory that is closest to a given interacting model in terms of their ground-state correlations. Moreover, we quantify the distance between them using the entanglement spectrum. When this interaction distance is small, the optimal free theory provides an effective description of the low-energy physics of the interacting model. Our construction of the optimal free model is non-perturbative in nature; thus, it offers a theoretical framework for investigating strongly correlated systems.

  16. Communication: stochastic evaluation of explicitly correlated second-order many-body perturbation energy.

    PubMed

    Willow, Soohaeng Yoo; Zhang, Jinmei; Valeev, Edward F; Hirata, So

    2014-01-21

    A stochastic algorithm is proposed that can compute the basis-set-incompleteness correction to the second-order many-body perturbation (MP2) energy of a polyatomic molecule. It evaluates the sum of two-, three-, and four-electron integrals over an explicit function of electron-electron distances by a Monte Carlo (MC) integration at an operation cost per MC step increasing only quadratically with size. The method can reproduce the corrections to the MP2/cc-pVTZ energies of H2O, CH4, and C6H6 within a few mEh after several million MC steps. It circumvents the resolution-of-the-identity approximation to the nonfactorable three-electron integrals usually necessary in the conventional explicitly correlated (R12 or F12) methods.

  17. Efficient quantum transport in disordered interacting many-body networks.

    PubMed

    Ortega, Adrian; Stegmann, Thomas; Benet, Luis

    2016-10-01

    The coherent transport of n fermions in disordered networks of l single-particle states connected by k-body interactions is studied. These networks are modeled by embedded Gaussian random matrix ensemble (EGE). The conductance bandwidth and the ensemble-averaged total current attain their maximal values if the system is highly filled n∼l-1 and k∼n/2. For the cases k=1 and k=n the bandwidth is minimal. We show that for all parameters the transport is enhanced significantly whenever centrosymmetric embedded Gaussian ensemble (csEGE) are considered. In this case the transmission shows numerous resonances of perfect transport. Analyzing the transmission by spectral decomposition, we find that centrosymmetry induces strong correlations and enhances the extrema of the distributions. This suppresses destructive interference effects in the system and thus causes backscattering-free transmission resonances that enhance the overall transport. The distribution of the total current for the csEGE has a very large dominating peak for n=l-1, close to the highest observed currents.

  18. Efficient quantum transport in disordered interacting many-body networks

    NASA Astrophysics Data System (ADS)

    Ortega, Adrian; Stegmann, Thomas; Benet, Luis

    2016-10-01

    The coherent transport of n fermions in disordered networks of l single-particle states connected by k -body interactions is studied. These networks are modeled by embedded Gaussian random matrix ensemble (EGE). The conductance bandwidth and the ensemble-averaged total current attain their maximal values if the system is highly filled n ˜l -1 and k ˜n /2 . For the cases k =1 and k =n the bandwidth is minimal. We show that for all parameters the transport is enhanced significantly whenever centrosymmetric embedded Gaussian ensemble (csEGE) are considered. In this case the transmission shows numerous resonances of perfect transport. Analyzing the transmission by spectral decomposition, we find that centrosymmetry induces strong correlations and enhances the extrema of the distributions. This suppresses destructive interference effects in the system and thus causes backscattering-free transmission resonances that enhance the overall transport. The distribution of the total current for the csEGE has a very large dominating peak for n =l -1 , close to the highest observed currents.

  19. Tunable many-body effects in triple quantum dots

    NASA Astrophysics Data System (ADS)

    Kim, Jihan; Melnikov, Dmitriy V.; Leburton, Jean-Pierre

    2009-07-01

    Exchange energies and charge densities for a few electrons in electrically tunable triangular and collinear triple quantum dot (TQD) systems are investigated by using the variational Monte Carlo method in the presence of magnetic fields. For N=2 electrons we observe a discontinuity in the J derivative with detuning voltage (dJ/dVT) in triangular triple QDs at B=0T as crossing of the eigenenergy levels leads to abrupt spatial symmetry change in the singlet and the triplet densities (density rotation) and relocalization. For B≠0T , the angular momentum provided to the electrons quenches this effect. The density rotation is absent in the collinear TQD for all magnetic fields as the lowest excited state remains the px state and as such, no change in symmetry is possible. By varying the triangular TQD configuration, we show the discontinuity in dJ/dVT persists for the top angle comprised between ˜20° and ˜70° . For three electrons in the symmetric triangular TQD, the monotonicity of the quadruplet-doublet energy difference from B=0 to 4 T remains intact for decoupled QDs but not for coupled QDs. Finally, addition energy for the triangular TQD system is computed for up to N=3 electrons.

  20. Prediction of quantum many-body chaos in the protactinium atom

    NASA Astrophysics Data System (ADS)

    Viatkina, A. V.; Kozlov, M. G.; Flambaum, V. V.

    2017-02-01

    The energy-level spectrum of the protactinium atom (Pa, Z =91 ) is simulated with a configuration interaction calculation. Levels belonging to the separate manifolds of a given total angular momentum and parity Jπ exhibit distinct properties of many-body quantum chaos. Moreover, an extremely strong enhancement of small perturbations takes place. As an example, effective three-electron interaction is investigated and found to play a significant role in the system. Chaotic properties of the eigenstates allow one to develop a statistical theory and predict probabilities of different processes in chaotic systems.

  1. Many-body effects on adiabatic passage through Feshbach resonances

    SciTech Connect

    Tikhonenkov, I.; Pazy, E.; Band, Y. B.; Vardi, A.; Fleischhauer, M.

    2006-04-15

    We theoretically study the dynamics of an adiabatic sweep through a Feshbach resonance, thereby converting a degenerate quantum gas of fermionic atoms into a degenerate quantum gas of bosonic dimers. Our analysis relies on a zero temperature mean-field theory which accurately accounts for initial molecular quantum fluctuations, triggering the association process. The structure of the resulting semiclassical phase space is investigated, highlighting the dynamical instability of the system towards association, for sufficiently small detuning from resonance. It is shown that this instability significantly modifies the finite-rate efficiency of the sweep, transforming the single-pair exponential Landau-Zener behavior of the remnant fraction of atoms {gamma} on sweep rate {alpha}, into a power-law dependence as the number of atoms increases. The obtained nonadiabaticity is determined from the interplay of characteristic time scales for the motion of adiabatic eigenstates and for fast periodic motion around them. Critical slowing-down of these precessions near the instability leads to the power-law dependence. A linear power law {gamma}{proportional_to}{alpha} is obtained when the initial molecular fraction is smaller than the 1/N quantum fluctuations, and a cubic-root power law {gamma}{proportional_to}{alpha}{sup 1/3} is attained when it is larger. Our mean-field analysis is confirmed by exact calculations, using Fock-space expansions. Finally, we fit experimental low temperature Feshbach sweep data with a power-law dependence. While the agreement with the experimental data is well within experimental error bars, similar accuracy can be obtained with an exponential fit, making additional data highly desirable.

  2. Many-body localization and thermalization: Insights from the entanglement spectrum

    NASA Astrophysics Data System (ADS)

    Geraedts, Scott D.; Nandkishore, Rahul; Regnault, Nicolas

    2016-05-01

    We study the entanglement spectrum in the many-body localizing and thermalizing phases of one- and two-dimensional Hamiltonian systems and periodically driven "Floquet" systems. We focus on the level statistics of the entanglement spectrum as obtained through numerical diagonalization, finding structure beyond that revealed by more limited measures such as entanglement entropy. In the thermalizing phase the entanglement spectrum obeys level statistics governed by an appropriate random matrix ensemble. For Hamiltonian systems this can be viewed as evidence in favor of a strong version of the eigenstate thermalization hypothesis (ETH). Similar results are also obtained for Floquet systems, where they constitute a result "beyond ETH" and show that the corrections to ETH governing the Floquet entanglement spectrum have statistical properties governed by a random matrix ensemble. The particular random matrix ensemble governing the Floquet entanglement spectrum depends on the symmetries of the Floquet drive and therefore can depend on the choice of origin of time. In the many-body localized phase the entanglement spectrum is also found to show level repulsion, following a semi-Poisson distribution (in contrast to the energy spectrum, which follows a Poisson distribution). This semi-Poisson distribution is found to come mainly from states at high entanglement energies. The observed level repulsion occurs only for interacting localized phases. We also demonstrate that equivalent results can be obtained by calculating with a single typical eigenstate or by averaging over a microcanonical energy window, a surprising result in the localized phase. This discovery of new structure in the pattern of entanglement of localized and thermalizing phases may open up new lines of attack on many-body localization, thermalization, and the localization transition.

  3. Quantum many-body simulation using monolayer exciton-polaritons in coupled-cavities.

    PubMed

    Wang, Hai-Xiao; Zhan, Alan; Xu, Yadong; Chen, Huanyang; You, Wen-Long; Majumdar, Arka; Jiang, JianHua

    2017-08-30

    Quantum simulation is a promising approach to understand complex strongly correlated many-body systems using relatively simple and tractable systems. Photon-based quantum simulators have great advantages due to the possibility of direct measurements of multi-particle correlations and ease of simulating non-equilibrium physics. However, interparticle interaction in existing photonic systems is often too weak limiting the potential of quantum simulation. Here we propose an approach to enhance the interparticle interaction using exciton-polaritons in MoS$_2$ monolayer quantum-dots embedded in 2D photonic crystal microcavities. Realistic calculation yields optimal repulsive interaction in the range of $1$-$10$~meV --- more than an order of magnitude greater than the state-of-art value. Such strong repulsive interaction is found to emerge neither in the photon-blockade regime for small quantum dot nor in the polariton-blockade regime for large quantum dot, but in the crossover between the two regimes with a moderate quantum-dot radius around 20~nm. The optimal repulsive interaction is found to be largest in MoS$_2$ among commonly used optoelectronic materials. Quantum simulation of strongly correlated many-body systems in a finite chain of coupled cavities and its experimental signature are studied via exact diagonalization of the many-body Hamiltonian. A method to simulate 1D superlattices for interacting exciton-polariton gases in serially coupled cavities is also proposed. Realistic considerations on experimental realizations reveal advantages of transition metal dichalcogenide monolayer quantum-dots over conventional semiconductor quantum-emitters. © 2017 IOP Publishing Ltd.

  4. Real-Time Quantum Dynamics Reveals Complex, Many-Body Interactions in Solvated Nanodroplets.

    PubMed

    Oviedo, M Belén; Wong, Bryan M

    2016-04-12

    Electronic excitations in the liquid phase are surprisingly rich and considerably more complex than either gas-phase or solid-state systems. While the majority of physical and biological processes take place in solvent, our understanding of nonequilibrium excited-state processes in these condensed phase environments remains far from complete. A central and long-standing issue in these solvated environments is the assessment of many-body interactions, particularly when the entire system is out of equilibrium and many quantum states participate in the overall process. Here we present a microscopic picture of solute-solvent electron dynamics and solvatochromic effects, which we uncover using a new real-time quantum dynamics approach for extremely large solvated nanodroplets. In particular, we find that a complex interplay of quantum interactions underlies our observations of solute-solvent effects, and simple macroscopic solvatochromic shifts can even be qualitatively different at the microscopic molecular level in these systems. By treating both the solvent and the solute on the same footing at a quantum-mechanical level, we demonstrate that the electron dynamics in these systems are surprisingly complex, and the emergence of many-body interactions underlies the dynamics in these solvated systems.

  5. Machine learning for many-body physics: The case of the Anderson impurity model

    SciTech Connect

    Arsenault, Louis-François; Lopez-Bezanilla, Alejandro; von Lilienfeld, O. Anatole; Millis, Andrew J.

    2014-10-31

    We applied machine learning methods in order to find the Green's function of the Anderson impurity model, a basic model system of quantum many-body condensed-matter physics. Furthermore, different methods of parametrizing the Green's function are investigated; a representation in terms of Legendre polynomials is found to be superior due to its limited number of coefficients and its applicability to state of the art methods of solution. The dependence of the errors on the size of the training set is determined. Our results indicate that a machine learning approach to dynamical mean-field theory may be feasible.

  6. Relativistic many-body calculation of low-energy dielectronic resonances in Be-like carbon

    SciTech Connect

    Derevianko, A.; Dzuba, V. A.; Kozlov, M. G.

    2010-08-15

    We apply the relativistic configuration-interaction method coupled with the many-body perturbation theory (CI+MBPT) to describe low-energy dielectronic recombination. We combine the CI+MBPT approach with the complex rotation method (CRM) and compute the dielectronic recombination spectrum for Li-like carbon, which recombines into Be-like carbon. We demonstrate the utility and evaluate the accuracy of this newly developed CI+MBPT+CRM approach by comparing our results with the results of the previous high-precision study of the Ciii system [Mannervik et al., Phys. Rev. Lett. 81, 313 (1998)].

  7. Machine learning for many-body physics: The case of the Anderson impurity model

    NASA Astrophysics Data System (ADS)

    Arsenault, Louis-François; Lopez-Bezanilla, Alejandro; von Lilienfeld, O. Anatole; Millis, Andrew J.

    2014-10-01

    Machine learning methods are applied to finding the Green's function of the Anderson impurity model, a basic model system of quantum many-body condensed-matter physics. Different methods of parametrizing the Green's function are investigated; a representation in terms of Legendre polynomials is found to be superior due to its limited number of coefficients and its applicability to state of the art methods of solution. The dependence of the errors on the size of the training set is determined. The results indicate that a machine learning approach to dynamical mean-field theory may be feasible.

  8. Many-body self-localization in a translation-invariant Hamiltonian

    NASA Astrophysics Data System (ADS)

    Mondaini, Rubem; Cai, Zi

    2017-07-01

    We study the statistical and dynamical aspects of a translation-invariant Hamiltonian, without quench disorder, as an example of the manifestation of the phenomenon of many-body localization. This is characterized by the breakdown of thermalization and by information preservation of initial preparations at long times. To realize this, we use quasiperiodic long-range interactions, which are now achievable in high-finesse cavity experiments, to find evidence suggestive of a divergent time-scale in which charge inhomogeneities in the initial state survive asymptotically. This is reminiscent of a glassy behavior, which appears in the ground state of this system, being also present at infinite temperatures.

  9. Scale-adaptive tensor algebra for local many-body methods of electronic structure theory

    SciTech Connect

    Liakh, Dmitry I

    2014-01-01

    While the formalism of multiresolution analysis (MRA), based on wavelets and adaptive integral representations of operators, is actively progressing in electronic structure theory (mostly on the independent-particle level and, recently, second-order perturbation theory), the concepts of multiresolution and adaptivity can also be utilized within the traditional formulation of correlated (many-particle) theory which is based on second quantization and the corresponding (generally nonorthogonal) tensor algebra. In this paper, we present a formalism called scale-adaptive tensor algebra (SATA) which exploits an adaptive representation of tensors of many-body operators via the local adjustment of the basis set quality. Given a series of locally supported fragment bases of a progressively lower quality, we formulate the explicit rules for tensor algebra operations dealing with adaptively resolved tensor operands. The formalism suggested is expected to enhance the applicability and reliability of local correlated many-body methods of electronic structure theory, especially those directly based on atomic orbitals (or any other localized basis functions).

  10. The many-body Wigner Monte Carlo method for time-dependent ab-initio quantum simulations

    SciTech Connect

    Sellier, J.M. Dimov, I.

    2014-09-15

    The aim of ab-initio approaches is the simulation of many-body quantum systems from the first principles of quantum mechanics. These methods are traditionally based on the many-body Schrödinger equation which represents an incredible mathematical challenge. In this paper, we introduce the many-body Wigner Monte Carlo method in the context of distinguishable particles and in the absence of spin-dependent effects. Despite these restrictions, the method has several advantages. First of all, the Wigner formalism is intuitive, as it is based on the concept of a quasi-distribution function. Secondly, the Monte Carlo numerical approach allows scalability on parallel machines that is practically unachievable by means of other techniques based on finite difference or finite element methods. Finally, this method allows time-dependent ab-initio simulations of strongly correlated quantum systems. In order to validate our many-body Wigner Monte Carlo method, as a case study we simulate a relatively simple system consisting of two particles in several different situations. We first start from two non-interacting free Gaussian wave packets. We, then, proceed with the inclusion of an external potential barrier, and we conclude by simulating two entangled (i.e. correlated) particles. The results show how, in the case of negligible spin-dependent effects, the many-body Wigner Monte Carlo method provides an efficient and reliable tool to study the time-dependent evolution of quantum systems composed of distinguishable particles.

  11. A many-body field theory approach to stochastic models in population biology.

    PubMed

    Dodd, Peter J; Ferguson, Neil M

    2009-09-01

    Many models used in theoretical ecology, or mathematical epidemiology are stochastic, and may also be spatially-explicit. Techniques from quantum field theory have been used before in reaction-diffusion systems, principally to investigate their critical behavior. Here we argue that they make many calculations easier and are a possible starting point for new approximations. We review the many-body field formalism for Markov processes and illustrate how to apply it to a 'Brownian bug' population model, and to an epidemic model. We show how the master equation and the moment hierarchy can both be written in particularly compact forms. The introduction of functional methods allows the systematic computation of the effective action, which gives the dynamics of mean quantities. We obtain the 1-loop approximation to the effective action for general (space-) translation invariant systems, and thus approximations to the non-equilibrium dynamics of the mean fields. The master equations for spatial stochastic systems normally take a neater form in the many-body field formalism. One can write down the dynamics for generating functional of physically-relevant moments, equivalent to the whole moment hierarchy. The 1-loop dynamics of the mean fields are the same as those of a particular moment-closure.

  12. Optimal control of many-body quantum dynamics: Chaos and complexity

    NASA Astrophysics Data System (ADS)

    Poggi, P. M.; Wisniacki, D. A.

    2016-09-01

    Achieving full control of the time-evolution of a many-body quantum system is currently a major goal in physics. In this work we investigate the different ways in which the controllability of a quantum system can be influenced by its complexity, or even its chaotic properties. By using optimal control theory, we are able to derive the control fields necessary to drive various physical processes in a spin chain. Then, we study the spectral properties of such fields and how they relate to different aspects of the system complexity. We find that the spectral bandwidth of the fields is, quite generally, independent of the system dimension. Conversely, the spectral complexity of such fields does increase with the number of particles. Nevertheless, we find that the regular or chaotic nature of the system does not affect significantly its controllability.

  13. Optical conductivity study of screening of many-body effects in graphene interfaces

    NASA Astrophysics Data System (ADS)

    Gogoi, Pranjal Kumar; Santoso, Iman; Saha, Surajit; Wang, Sihao; Castro Neto, Antonio H.; Loh, Kian Ping; Venkatesan, T.; Rusydi, Andrivo

    2012-09-01

    Theoretical studies have shown that electron-electron (e-e) and electron-hole (e-h) interactions play important roles in many observed quantum properties of graphene making this an ideal system to study many-body effects. In this report we show that spectroscopic ellipsometry can enable us to measure this interactions quantitatively. We present spectroscopic data in two extreme systems of graphene on quartz (GOQ), an insulator, and graphene on copper (GOC), a metal which show that for GOQ, both e-e and e-h interactions dominate while for GOC e-h interactions are screened. The data further enables the estimation of the strength of the many-body interaction through the effective fine-structure constant, α*g. The α*g for GOQ indicates a strong correlation with an almost energy-independent value of about 1.37. In contrast, the α*g value of GOC is photon energy dependent and is almost two orders of magnitude lower at low energies indicating very weak correlation.

  14. On the possibility of many-body localization in a doped Mott insulator

    NASA Astrophysics Data System (ADS)

    He, Rong-Qiang; Weng, Zheng-Yu

    2016-10-01

    Many-body localization (MBL) is currently a hot issue of interacting systems, in which quantum mechanics overcomes thermalization of statistical mechanics. Like Anderson localization of non-interacting electrons, disorders are usually crucial in engineering the quantum interference in MBL. For translation invariant systems, however, the breakdown of eigenstate thermalization hypothesis due to a pure many-body quantum effect is still unclear. Here we demonstrate a possible MBL phenomenon without disorder, which emerges in a lightly doped Hubbard model with very strong interaction. By means of density matrix renormalization group numerical calculation on a two-leg ladder, we show that whereas a single hole can induce a very heavy Nagaoka polaron, two or more holes will form bound pair/droplets which are all localized excitations with flat bands at low energy densities. Consequently, MBL eigenstates of finite energy density can be constructed as composed of these localized droplets spatially separated. We further identify the underlying mechanism for this MBL as due to a novel ‘Berry phase’ of the doped Mott insulator, and show that by turning off this Berry phase either by increasing the anisotropy of the model or by hand, an eigenstate transition from the MBL to a conventional quasiparticle phase can be realized.

  15. On the possibility of many-body localization in a doped Mott insulator

    PubMed Central

    He, Rong-Qiang; Weng, Zheng-Yu

    2016-01-01

    Many-body localization (MBL) is currently a hot issue of interacting systems, in which quantum mechanics overcomes thermalization of statistical mechanics. Like Anderson localization of non-interacting electrons, disorders are usually crucial in engineering the quantum interference in MBL. For translation invariant systems, however, the breakdown of eigenstate thermalization hypothesis due to a pure many-body quantum effect is still unclear. Here we demonstrate a possible MBL phenomenon without disorder, which emerges in a lightly doped Hubbard model with very strong interaction. By means of density matrix renormalization group numerical calculation on a two-leg ladder, we show that whereas a single hole can induce a very heavy Nagaoka polaron, two or more holes will form bound pair/droplets which are all localized excitations with flat bands at low energy densities. Consequently, MBL eigenstates of finite energy density can be constructed as composed of these localized droplets spatially separated. We further identify the underlying mechanism for this MBL as due to a novel ‘Berry phase’ of the doped Mott insulator, and show that by turning off this Berry phase either by increasing the anisotropy of the model or by hand, an eigenstate transition from the MBL to a conventional quasiparticle phase can be realized. PMID:27752064

  16. Many-body interactions and correlations in coarse-grained descriptions of polymer solutions

    NASA Astrophysics Data System (ADS)

    Bolhuis, P. G.; Louis, A. A.; Hansen, J. P.

    2001-08-01

    We calculate the two-, three-, four-, and five-body (state-independent) effective potentials between the centers of mass (c.m.'s) of self-avoiding walk polymers by Monte Carlo simulations. For full overlap, these coarse-grained n-body interactions oscillate in sign as (-1)n, and decrease in absolute magnitude with increasing n. We find semiquantitative agreement with a scaling theory, and use this to discuss how the coarse-grained free energy converges when expanded to arbitrary order in the many-body potentials. We also derive effective density dependent two-body potentials that exactly reproduce the pair-correlations between the c.m. of the self avoiding walk polymers. The density dependence of these pair potentials can be largely understood from the effects of the density independent three-body potential. Triplet correlations between the c.m. of the polymers are surprisingly well, but not exactly, described by our coarse-grained effective pair potential picture. In fact, we demonstrate that a pair potential cannot simultaneously reproduce the two- and three-body correlations in a system with many-body interactions. However, the deviations that do occur in our system are very small, and can be explained by the direct influence of three-body potentials.

  17. Scaling Theory of Entanglement at the Many-Body Localization Transition

    NASA Astrophysics Data System (ADS)

    Dumitrescu, Philipp T.; Vasseur, Romain; Potter, Andrew C.

    2017-09-01

    We study the universal properties of eigenstate entanglement entropy across the transition between many-body localized (MBL) and thermal phases. We develop an improved real space renormalization group approach that enables numerical simulation of large system sizes and systematic extrapolation to the infinite system size limit. For systems smaller than the correlation length, the average entanglement follows a subthermal volume law, whose coefficient is a universal scaling function. The full distribution of entanglement follows a universal scaling form, and exhibits a bimodal structure that produces universal subleading power-law corrections to the leading volume law. For systems larger than the correlation length, the short interval entanglement exhibits a discontinuous jump at the transition from fully thermal volume law on the thermal side, to pure area law on the MBL side.

  18. Many-body localization in a quantum simulator with programmable random disorder

    NASA Astrophysics Data System (ADS)

    Smith, J.; Lee, A.; Richerme, P.; Neyenhuis, B.; Hess, P. W.; Hauke, P.; Heyl, M.; Huse, D. A.; Monroe, C.

    2016-10-01

    When a system thermalizes it loses all memory of its initial conditions. Even within a closed quantum system, subsystems usually thermalize using the rest of the system as a heat bath. Exceptions to quantum thermalization have been observed, but typically require inherent symmetries or noninteracting particles in the presence of static disorder. However, for strong interactions and high excitation energy there are cases, known as many-body localization (MBL), where disordered quantum systems can fail to thermalize. We experimentally generate MBL states by applying an Ising Hamiltonian with long-range interactions and programmable random disorder to ten spins initialized far from equilibrium. Using experimental and numerical methods we observe the essential signatures of MBL: initial-state memory retention, Poissonian distributed energy level spacings, and evidence of long-time entanglement growth. Our platform can be scaled to more spins, where a detailed modelling of MBL becomes impossible.

  19. Extended slow dynamical regime close to the many-body localization transition

    NASA Astrophysics Data System (ADS)

    Luitz, David J.; Laflorencie, Nicolas; Alet, Fabien

    2016-02-01

    Many-body localization is characterized by a slow logarithmic growth of the entanglement entropy after a global quantum quench while the local memory of an initial density imbalance remains at infinite time. We investigate how much the proximity of a many-body localized phase can influence the dynamics in the delocalized ergodic regime where thermalization is expected. Using an exact Krylov space technique, the out-of-equilibrium dynamics of the random-field Heisenberg chain is studied up to L =28 sites, starting from an initially unentangled high-energy product state. Within most of the delocalized phase, we find a sub-ballistic entanglement growth S (t ) ∝t1 /z with a disorder-dependent exponent z ≥1 , in contrast with the pure ballistic growth z =1 of clean systems. At the same time, anomalous relaxation is also observed for the spin imbalance I (t ) ∝t-ζ with a continuously varying disorder-dependent exponent ζ , vanishing at the transition. This provides a clear experimental signature for detecting this nonconventional regime.

  20. Aromatic molecules on low-index coinage metal surfaces: Many-body dispersion effects

    NASA Astrophysics Data System (ADS)

    Jiang, Yingda; Yang, Sha; Li, Shuang; Liu, Wei

    2016-12-01

    Understanding the binding mechanism for aromatic molecules on transition-metal surfaces in atomic scale is a major challenge in designing functional interfaces for to (opto)electronic devices. Here, we employ the state-of-the-art many-body dispersion (MBD) approach, coupled with density functional theory methods, to study the interactions of benzene with low-index coinage metal surfaces. The many-body effects contribute mostly to the (111) surface, and leastly to the (110) surface. This corresponds to the same sequence of planar atomic density of face-centered-cubic lattices, i.e., (111) > (100) > (110). The binding energy for benzene/Au(110) is even stronger than that for benzene/Ag(110), due to a larger broadening of molecular orbitals in the former case. On the other hand, our calculations show almost identical binding energies for benzene on Ag(111) and Au(111), which contradicts the classic d-band center theory that could well predict the trend in chemisorption energies for various small molecules on a number of metal surfaces. Our results provide important insight into the benchmark adsorption systems with opener surfaces, which could help in designing more complex functional interfaces.

  1. Differential Many-Body Cooperativity in Electronic Spectra of Oligonuclear Transition-Metal Complexes.

    PubMed

    Chmela, Jiří; Harding, Michael E; Matioszek, Dimitri; Anson, Christopher E; Breher, Frank; Klopper, Wim

    2016-01-04

    In computational chemistry, non-additive and cooperative effects can be defined in terms of a (differential) many-body expansion of the energy or any other physical property of the molecular system of interest. One-body terms describe energies or properties of the subsystems, two-body terms describe non-additive but pairwise contributions and three-body as well as higher-order terms can be interpreted as a measure for cooperativity. In the present article, this concept is applied to the analysis of ultraviolet/visible (UV/Vis) spectra of homotrinuclear transition-metal complexes by means of a many-body expansion of the change in the spectrum induced by replacing each of the three transition-metal ions by another transition-metal ion to yield a different homotrinuclear transition-metal complex. Computed spectra for the triangulo-complexes [M3 {Si(mt(Me) )3}2] (M=Pd/Pt, mt(Me) =methimazole) and tritopic triphenylene-based N-heterocyclic carbene Rh/Ir complexes illustrate the concept, showing large and small differential three-body cooperativity, respectively. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  2. Aromatic molecules on low-index coinage metal surfaces: Many-body dispersion effects

    PubMed Central

    Jiang, Yingda; Yang, Sha; Li, Shuang; Liu, Wei

    2016-01-01

    Understanding the binding mechanism for aromatic molecules on transition-metal surfaces in atomic scale is a major challenge in designing functional interfaces for to (opto)electronic devices. Here, we employ the state-of-the-art many-body dispersion (MBD) approach, coupled with density functional theory methods, to study the interactions of benzene with low-index coinage metal surfaces. The many-body effects contribute mostly to the (111) surface, and leastly to the (110) surface. This corresponds to the same sequence of planar atomic density of face-centered-cubic lattices, i.e., (111) > (100) > (110). The binding energy for benzene/Au(110) is even stronger than that for benzene/Ag(110), due to a larger broadening of molecular orbitals in the former case. On the other hand, our calculations show almost identical binding energies for benzene on Ag(111) and Au(111), which contradicts the classic d-band center theory that could well predict the trend in chemisorption energies for various small molecules on a number of metal surfaces. Our results provide important insight into the benchmark adsorption systems with opener surfaces, which could help in designing more complex functional interfaces. PMID:28004793

  3. Hong-Ou-Mandel Interference with Atomic Many-Body States

    NASA Astrophysics Data System (ADS)

    Islam, Rajibul; Lukin, Alexander; Ma, Ruichao; Preiss, Philipp; Rispoli, Matthew; Tai, M. Eric; Greiner, Markus

    2015-05-01

    Hong-Ou-Mandel (HOM) interference experiments are a powerful probe for the indistinguishability and underlying quantum statistics of particles. In the classic HOM experiment, a pair of identical photons incident on different input ports of a beamsplitter exits via the same output port. Using the precise control and readout afforded by our quantum gas microscope, we present an implementation of this classic experiment using massive bosons in a doublewell optical potential. Identical states are prepared on each site of the doublewell and by lowering the tunnel coupling between the sites for specific times, we drive a beam splitter operation between the sites. For single-atom Fock input states, we have realized a high fidelity beamsplitter operation and observed an HOM interference contrast of >90%. By generalizing to more complex initial states on the input ports, we have been able to establish HOM experiment protocols as a robust approach towards studying the indistinguishability of many-body states as well as probe interaction-induced effects. These techniques open a path towards the measurement of purity in a quantum system and entanglement entropy in many-body states.

  4. Many-body expansion of the Fock matrix in the fragment molecular orbital method.

    PubMed

    Fedorov, Dmitri G; Kitaura, Kazuo

    2017-09-14

    A many-body expansion of the Fock matrix in the fragment molecular orbital method is derived up to three-body terms for restricted Hartree-Fock and density functional theory in the atomic orbital basis and compared to the expansion in the basis of fragment molecular orbitals (MOs). The physical nature of many-body corrections is revealed in terms of charge transfer terms. An improvement of the fragment MO expansion is proposed by adding exchange to the embedding. The accuracy of all developed methods is demonstrated in comparison to unfragmented results for polyalanines, a water cluster, Trp-cage (PDB: 1L2Y) and crambin (PDB: 1CRN) proteins, a zeolite cluster, a Si nano-wire, and a boron nitride ribbon. The physical nature of metallicity is discussed, and it is shown what kinds of metallic systems can be treated by fragment-based methods. The density of states is calculated for a fully closed and a partially open nano-ring of boron nitride with a diameter of 105 nm.

  5. Many-Body Effects on the Thermodynamics of Fluids, Mixtures, and Nanoconfined Fluids.

    PubMed

    Desgranges, Caroline; Delhommelle, Jerome

    2015-11-10

    Using expanded Wang-Landau simulations, we show that taking into account the many-body interactions results in sharp changes in the grand-canonical partition functions of single-component systems, binary mixtures, and nanoconfined fluids. The many-body contribution, modeled with a 3-body Axilrod-Teller-Muto term, results in shifts toward higher chemical potentials of the phase transitions from low-density phases to high-density phases and accounts for deviations of more than, e.g., 20% of the value of the partition function for a single-component liquid. Using the statistical mechanics formalism, we analyze how this contribution has a strong impact on some properties (e.g., pressure, coexisting densities, and enthalpy) and a moderate impact on others (e.g., Gibbs or Helmholtz free energies). We also characterize the effect of the 3-body terms on adsorption isotherms and adsorption thermodynamic properties, thereby providing a full picture of the effect of the 3-body contribution on the thermodynamics of nanoconfined fluids.

  6. Many-body expansion of the Fock matrix in the fragment molecular orbital method

    NASA Astrophysics Data System (ADS)

    Fedorov, Dmitri G.; Kitaura, Kazuo

    2017-09-01

    A many-body expansion of the Fock matrix in the fragment molecular orbital method is derived up to three-body terms for restricted Hartree-Fock and density functional theory in the atomic orbital basis and compared to the expansion in the basis of fragment molecular orbitals (MOs). The physical nature of many-body corrections is revealed in terms of charge transfer terms. An improvement of the fragment MO expansion is proposed by adding exchange to the embedding. The accuracy of all developed methods is demonstrated in comparison to unfragmented results for polyalanines, a water cluster, Trp-cage (PDB: 1L2Y) and crambin (PDB: 1CRN) proteins, a zeolite cluster, a Si nano-wire, and a boron nitride ribbon. The physical nature of metallicity is discussed, and it is shown what kinds of metallic systems can be treated by fragment-based methods. The density of states is calculated for a fully closed and a partially open nano-ring of boron nitride with a diameter of 105 nm.

  7. Electro-optic and Many-body Effects on Optical Absorption of Twisted Bilayer Graphene

    NASA Astrophysics Data System (ADS)

    Lee, Kan-Heng; Huang, Lujie; Kim, Cheol-Joo; Park, Jiwoong

    2015-03-01

    In twisted bilayer graphene (tBLG), the interlayer rotation angle between the two graphene layers induces additional angle-dependent van Hove singularities (vHSs) in its band structure where the two Dirac cones from each layer intersect. These vHSs introduce extra angle-dependent absorption peaks in the optical absorption spectra of tBLG. Here, we experimentally investigate the effects of the overall doping and the interlayer potential on these interlayer absorption features at various angles. We independently tune the doping concentration of each layer with a newly-developed, optically transparent, dual-gate transistor geometry to perform simultaneous optical and electrical measurements. Our data show strong electro-optic phenomena in the optical absorption of tBLG: the peak energy and width of the interlayer resonance feature sensitively depends on the overall doping and interlayer potential. We explain our observation using a simple band picture as well as many-body effects. Our study provides a powerful experimental platform for studying more complicated structures such as rotated tri- and multi-layer graphene systems in the future. Moreover, the understanding of electro-optic and many-body effects in these materials opens up a way for novel electrochromic devices.

  8. Designing exotic many-body states of atomic spin and motion in photonic crystals.

    PubMed

    Manzoni, Marco T; Mathey, Ludwig; Chang, Darrick E

    2017-03-08

    Cold atoms coupled to photonic crystals constitute an exciting platform for exploring quantum many-body physics. For example, such systems offer the potential to realize strong photon-mediated forces between atoms, which depend on the atomic internal (spin) states, and where both the motional and spin degrees of freedom can exhibit long coherence times. An intriguing question then is whether exotic phases could arise, wherein crystalline or other spatial patterns and spin correlations are fundamentally tied together, an effect that is atypical in condensed matter systems. Here, we analyse one realistic model Hamiltonian in detail. We show that this previously unexplored system exhibits a rich phase diagram of emergent orders, including spatially dimerized spin-entangled pairs, a fluid of composite particles comprised of joint spin-phonon excitations, phonon-induced Néel ordering, and a fractional magnetization plateau associated with trimer formation.

  9. Accessing Rydberg-dressed interactions using many-body Ramsey dynamics

    NASA Astrophysics Data System (ADS)

    Mukherjee, Rick; Killian, Thomas C.; Hazzard, Kaden R. A.

    2016-11-01

    We demonstrate that Ramsey spectroscopy can be used to observe Rydberg-dressed interactions in a many-body system well within experimentally measured lifetimes, in contrast to previous research, which either focused on interactions near Förster resonances or on few-atom systems. We build a spin-1/2 from one level that is Rydberg-dressed and another that is not. These levels may be hyperfine or long-lived electronic states. An Ising spin model governs the Ramsey dynamics, which we demonstrate can be used to characterize the Rydberg-dressed interactions. Furthermore, the dynamics can differ significantly from that observed in other spin systems. As one example, spin echo can increase the rate at which coherence decays. The results also apply to bare (undressed) Rydberg states as a special case, for which we quantitatively reproduce recent ultrafast experiments without fitting.

  10. Effect of long-range hopping and interactions on entanglement dynamics and many-body localization

    NASA Astrophysics Data System (ADS)

    Singh, Rajeev; Moessner, Roderich; Roy, Dibyendu

    2017-03-01

    We numerically investigate the dynamics of entanglement in a chain of spinless fermions with nonrandom but long-range hopping and interactions, and with random on-site energies. For moderate disorder in the absence of interactions, the chain hosts delocalized states at the top of the band which undergo a delocalization-localization transition with increasing disorder. We find an interesting regime in this noninteracting disordered chain where the long-time entanglement entropy scales as S (t )˜lnt and the saturated entanglement entropy scales with system size L as S (L ,t →∞ )˜lnL . We further study the interplay of long-range hopping and interactions on the growth of entanglement and the many-body localization (MBL) transition in this system. We develop an analogy to higher-dimensional short-range systems to compare and contrast such behavior with the physics of MBL in a higher dimension.

  11. Designing exotic many-body states of atomic spin and motion in photonic crystals

    PubMed Central

    Manzoni, Marco T.; Mathey, Ludwig; Chang, Darrick E.

    2017-01-01

    Cold atoms coupled to photonic crystals constitute an exciting platform for exploring quantum many-body physics. For example, such systems offer the potential to realize strong photon-mediated forces between atoms, which depend on the atomic internal (spin) states, and where both the motional and spin degrees of freedom can exhibit long coherence times. An intriguing question then is whether exotic phases could arise, wherein crystalline or other spatial patterns and spin correlations are fundamentally tied together, an effect that is atypical in condensed matter systems. Here, we analyse one realistic model Hamiltonian in detail. We show that this previously unexplored system exhibits a rich phase diagram of emergent orders, including spatially dimerized spin-entangled pairs, a fluid of composite particles comprised of joint spin-phonon excitations, phonon-induced Néel ordering, and a fractional magnetization plateau associated with trimer formation. PMID:28272466

  12. Many-body Tunneling and Nonequilibrium Dynamics of Doublons in Strongly Correlated Quantum Dots.

    PubMed

    Hou, WenJie; Wang, YuanDong; Wei, JianHua; Zhu, ZhenGang; Yan, YiJing

    2017-05-30

    Quantum tunneling dominates coherent transport at low temperatures in many systems of great interest. In this work we report a many-body tunneling (MBT), by nonperturbatively solving the Anderson multi-impurity model, and identify it a fundamental tunneling process on top of the well-acknowledged sequential tunneling and cotunneling. We show that the MBT involves the dynamics of doublons in strongly correlated systems. Proportional to the numbers of dynamical doublons, the MBT can dominate the off-resonant transport in the strongly correlated regime. A T (3/2)-dependence of the MBT current on temperature is uncovered and can be identified as a fingerprint of the MBT in experiments. We also prove that the MBT can support the coherent long-range tunneling of doublons, which is well consistent with recent experiments on ultracold atoms. As a fundamental physical process, the MBT is expected to play important roles in general quantum systems.

  13. Digital quantum simulation of many-body non-Markovian dynamics

    NASA Astrophysics Data System (ADS)

    Sweke, R.; Sanz, M.; Sinayskiy, I.; Petruccione, F.; Solano, E.

    2016-08-01

    We present an algorithmic method for the digital quantum simulation of many-body locally indivisible non-Markovian open quantum systems. It consists of two parts: first, a Suzuki-Lie-Trotter decomposition of the global system propagator into the product of subsystem propagators, which may not be quantum channels, and second, an algorithmic procedure for the implementation of the subsystem propagators through unitary operations and measurements on a dilated space. By providing rigorous error bounds for the relevant Suzuki-Lie-Trotter decomposition, we are able to analyze the efficiency of the method, and connect it with an appropriate measure of the local indivisibility of the system. In light of our analysis, the proposed method is expected to be experimentally achievable for a variety of interesting cases.

  14. Designing exotic many-body states of atomic spin and motion in photonic crystals

    NASA Astrophysics Data System (ADS)

    Manzoni, Marco T.; Mathey, Ludwig; Chang, Darrick E.

    2017-03-01

    Cold atoms coupled to photonic crystals constitute an exciting platform for exploring quantum many-body physics. For example, such systems offer the potential to realize strong photon-mediated forces between atoms, which depend on the atomic internal (spin) states, and where both the motional and spin degrees of freedom can exhibit long coherence times. An intriguing question then is whether exotic phases could arise, wherein crystalline or other spatial patterns and spin correlations are fundamentally tied together, an effect that is atypical in condensed matter systems. Here, we analyse one realistic model Hamiltonian in detail. We show that this previously unexplored system exhibits a rich phase diagram of emergent orders, including spatially dimerized spin-entangled pairs, a fluid of composite particles comprised of joint spin-phonon excitations, phonon-induced Néel ordering, and a fractional magnetization plateau associated with trimer formation.

  15. Fidelity of the diagonal ensemble signals the many-body localization transition

    NASA Astrophysics Data System (ADS)

    Hu, Taotao; Xue, Kang; Li, Xiaodan; Zhang, Yan; Ren, Hang

    2016-11-01

    In this work, we use exact matrix diagonalization to explore the many-body localization (MBL) transition in a random-field Heisenberg chain. We demonstrate that the fidelity and fidelity susceptibility can be utilized to characterize the interaction-driven many-body localization transition in this closed spin system which is in agreement with previous analytical and numerical results [S. Garnerone, N. T. Jacobson, S. Haas, and P. Zanardi, Phys. Rev. Lett. 102, 057205 (2009), 10.1103/PhysRevLett.102.057205; P. Zanardi and N. Paunkovic, Phys. Rev. E 74, 031123 (2006), 10.1103/PhysRevE.74.031123]. In particular, instead of ground-state fidelity, we test the fidelity between two diagonal ensembles related by a small parameter perturbation δ h , it is special that here the parameter perturbation δ hi for each site are random variables like hi. It shows that fidelity of the diagonal ensemble develop a pronounced drop at the transition. We utilize fidelity to estimate the critical disorder strength hc for different system size, we get hc∈ [2.5,3.9] and get a power-law decay with an exponent of roughly -1.49 (2 ) for system size N , and can extrapolate hcinf of the infinite system is about 2.07 which all agree with a recent work by Huse and Pal, in which the MBL transition in the same model was predicted to be hc [2,4]. We also estimate the scaling of maximum of averaged fidelity susceptibility as a function of system size N , it shows a power law increase with an exponent of about 5.05(1).

  16. Extension of many-body theory and approximate density functionals to fractional charges and fractional spins.

    PubMed

    Yang, Weitao; Mori-Sánchez, Paula; Cohen, Aron J

    2013-09-14

    The exact conditions for density functionals and density matrix functionals in terms of fractional charges and fractional spins are known, and their violation in commonly used functionals has been shown to be the root of many major failures in practical applications. However, approximate functionals are designed for physical systems with integer charges and spins, not in terms of the fractional variables. Here we develop a general framework for extending approximate density functionals and many-electron theory to fractional-charge and fractional-spin systems. Our development allows for the fractional extension of any approximate theory that is a functional of G(0), the one-electron Green's function of the non-interacting reference system. The extension to fractional charge and fractional spin systems is based on the ensemble average of the basic variable, G(0). We demonstrate the fractional extension for the following theories: (1) any explicit functional of the one-electron density, such as the local density approximation and generalized gradient approximations; (2) any explicit functional of the one-electron density matrix of the non-interacting reference system, such as the exact exchange functional (or Hartree-Fock theory) and hybrid functionals; (3) many-body perturbation theory; and (4) random-phase approximations. A general rule for such an extension has also been derived through scaling the orbitals and should be useful for functionals where the link to the Green's function is not obvious. The development thus enables the examination of approximate theories against known exact conditions on the fractional variables and the analysis of their failures in chemical and physical applications in terms of violations of exact conditions of the energy functionals. The present work should facilitate the calculation of chemical potentials and fundamental bandgaps with approximate functionals and many-electron theories through the energy derivatives with respect to the

  17. Fidelity of the diagonal ensemble signals the many-body localization transition.

    PubMed

    Hu, Taotao; Xue, Kang; Li, Xiaodan; Zhang, Yan; Ren, Hang

    2016-11-01

    In this work, we use exact matrix diagonalization to explore the many-body localization (MBL) transition in a random-field Heisenberg chain. We demonstrate that the fidelity and fidelity susceptibility can be utilized to characterize the interaction-driven many-body localization transition in this closed spin system which is in agreement with previous analytical and numerical results [S. Garnerone, N. T. Jacobson, S. Haas, and P. Zanardi, Phys. Rev. Lett. 102, 057205 (2009)PRLTAO0031-900710.1103/PhysRevLett.102.057205; P. Zanardi and N. Paunkovic, Phys. Rev. E 74, 031123 (2006)PLEEE81539-375510.1103/PhysRevE.74.031123]. In particular, instead of ground-state fidelity, we test the fidelity between two diagonal ensembles related by a small parameter perturbation δh, it is special that here the parameter perturbation δh_{i} for each site are random variables like h_{i}. It shows that fidelity of the diagonal ensemble develop a pronounced drop at the transition. We utilize fidelity to estimate the critical disorder strength h_{c} for different system size, we get h_{c}∈ [2.5,3.9] and get a power-law decay with an exponent of roughly -1.49(2) for system size N, and can extrapolate h_{c}^{inf} of the infinite system is about 2.07 which all agree with a recent work by Huse and Pal, in which the MBL transition in the same model was predicted to be hc [2,4]. We also estimate the scaling of maximum of averaged fidelity susceptibility as a function of system size N, it shows a power law increase with an exponent of about 5.05(1).

  18. Many-body quantum electrodynamics networks: Non-equilibrium condensed matter physics with light

    NASA Astrophysics Data System (ADS)

    Le Hur, Karyn; Henriet, Loïc; Petrescu, Alexandru; Plekhanov, Kirill; Roux, Guillaume; Schiró, Marco

    2016-10-01

    We review recent developments regarding the quantum dynamics and many-body physics with light, in superconducting circuits and Josephson analogues, by analogy with atomic physics. We start with quantum impurity models addressing dissipative and driven systems. Both theorists and experimentalists are making efforts towards the characterization of these non-equilibrium quantum systems. We show how Josephson junction systems can implement the equivalent of the Kondo effect with microwave photons. The Kondo effect can be characterized by a renormalized light frequency and a peak in the Rayleigh elastic transmission of a photon. We also address the physics of hybrid systems comprising mesoscopic quantum dot devices coupled with an electromagnetic resonator. Then, we discuss extensions to Quantum Electrodynamics (QED) Networks allowing one to engineer the Jaynes-Cummings lattice and Rabi lattice models through the presence of superconducting qubits in the cavities. This opens the door to novel many-body physics with light out of equilibrium, in relation with the Mott-superfluid transition observed with ultra-cold atoms in optical lattices. Then, we summarize recent theoretical predictions for realizing topological phases with light. Synthetic gauge fields and spin-orbit couplings have been successfully implemented in quantum materials and with ultra-cold atoms in optical lattices - using time-dependent Floquet perturbations periodic in time, for example - as well as in photonic lattice systems. Finally, we discuss the Josephson effect related to Bose-Hubbard models in ladder and two-dimensional geometries, producing phase coherence and Meissner currents. The Bose-Hubbard model is related to the Jaynes-Cummings lattice model in the large detuning limit between light and matter (the superconducting qubits). In the presence of synthetic gauge fields, we show that Meissner currents subsist in an insulating Mott phase.

  19. Periodically driven interacting electrons in one dimension: Many-body Floquet approach

    NASA Astrophysics Data System (ADS)

    Puviani, M.; Manghi, F.

    2016-10-01

    We propose a method to study the time evolution of correlated electrons driven by a harmonic perturbation. Combining Floquet formalism to include the time-dependent field and cluster perturbation theory to solve the many-body problem in the presence of short-range correlations, we treat the electron double dressing, by photons and by e -e interactions, on the same footing. We apply the method to an extended Hubbard chain at half occupation, and we show that in the regime of small field frequency and for given values of field strength, the zero-mode Floquet band is no longer gapped and the system recovers a metallic state. Our results are indicative of an omnipresent mechanism for insulator-to-metal transitions in one-dimensional systems.

  20. The path integral picture of quantum systems

    NASA Astrophysics Data System (ADS)

    Ceperley, David

    2011-03-01

    The imaginary time path integral ``formalism'' was introduced in 1953 by Feynman to understand the superfluid transition in liquid helium. The equilibrium properties of quantum many body systems is isomorphic to the classical statistical mechanics of cross-linking polymer-like objects. With the Markov Chain Monte Carlo method, invented by Metropolis et al., also in 1953, a potential way of calculating properties of correlated quantum systems was in place. But calculations for many-body quantum systems did not become routine until computers and algorithms had become sufficiently powerful three decades later. Once such simulations could happen, it was realized that simulations provided a deeper insight into boson superfluids, in particular the relation of bose condensation to the polymer end-to-end distance, and the superfluid density to the polymer ``winding number.'' Some recent developments and applications to supersolids, and helium droplets will be given. Finally, limitations of the methodology e.g. to fermion systems are discussed.

  1. The Asakura Oosawa model in the protein limit: the role of many-body interactions

    NASA Astrophysics Data System (ADS)

    Moncho-Jordá, A.; Louis, A. A.; Bolhuis, P. G.; Roth, R.

    2003-12-01

    We study the Asakura-Oosawa model in the 'protein limit', where the penetrable sphere radius RAO is much greater than the hard sphere radius Rc. The phase behaviour and structure calculated with a full many-body treatment show important qualitative differences when compared to a description based on pair potentials alone. The overall effect of the many-body interactions is repulsive.

  2. Field-Theoretical Approach to Many-Body Perturbation Theory: Combining MBPT and QED

    SciTech Connect

    Lindgren, Ingvar; Salomonson, Sten; Hedendahl, Daniel

    2007-12-26

    Many-Body Perturbation Theory (MBPT) is today highly developed. The electron correlation of atomic and molecular systems can be evaluated to essentially all orders of perturbation theory--also relativistically (RMBPT)--by means of techniques of Coupled-Cluster type. When high accuracy is needed, effects beyond RMBPT will enter, i.e., effects of retarded Breit interaction and of radiative effects (Lamb shift), effects normally referred to as QED effects. These effects can be evaluated by means of special techniques, like S-matrix formulation, which cannot simultaneously treat electron correlation. It would for many applications be desirable to have access to a numerical technique, where effects of electron correlation and of QED could be treated on the same footing. Such a technique is presently being developed and gradually implemented at our laboratory. Some numerical results will be given.

  3. Engineering many-body dynamics with quantum light potentials and measurements

    NASA Astrophysics Data System (ADS)

    Elliott, T. J.; Mekhov, I. B.

    2016-07-01

    Interactions between many-body atomic systems in optical lattices and light in cavities induce long-range and correlated atomic dynamics beyond the standard Bose-Hubbard model, due to the global nature of the light modes. We characterize these processes, and show that uniting such phenomena with dynamical constraints enforced by the backaction resultant from strong light measurement leads to a synergy that enables the atomic dynamics to be tailored, based on the particular optical geometry, exploiting the additional structure imparted by the quantum light field. This leads to a range of tunable effects such as long-range density-density interactions, perfectly correlated atomic tunneling, superexchange, and effective pair processes. We further show that this provides a framework for enhancing quantum simulations to include such long-range and correlated processes, including reservoir models and dynamical global gauge fields.

  4. Many-body localization in a long range XXZ model with random-field

    NASA Astrophysics Data System (ADS)

    Li, Bo

    2016-12-01

    Many-body localization (MBL) in a long range interaction XXZ model with random field are investigated. Using the exact diagonal method, the MBL phase diagram with different tuning parameters and interaction range is obtained. It is found that the phase diagram of finite size results supplies strong evidence to confirm that the threshold interaction exponent α = 2. The tuning parameter Δ can efficiently change the MBL edge in high energy density stats, thus the system can be controlled to transfer from thermal phase to MBL phase by changing Δ. The energy level statistics data are consistent with result of the MBL phase diagram. However energy level statistics data cannot detect the thermal phase correctly in extreme long range case.

  5. Approaching many-body localization from disordered Luttinger liquids via the functional renormalization group

    NASA Astrophysics Data System (ADS)

    Karrasch, C.; Moore, J. E.

    2015-09-01

    We study the interplay of interactions and disorder in a one-dimensional fermion lattice coupled adiabatically to infinite reservoirs. We employ both the functional renormalization group (FRG) as well as matrix product state techniques, which serve as an accurate benchmark for small systems. Using the FRG, we compute the length- and temperature-dependence of the conductance averaged over 104 samples for lattices as large as 105 sites. We identify regimes in which non-Ohmic power law behavior can be observed and demonstrate that the corresponding exponents can be understood by adapting earlier predictions obtained perturbatively for disordered Luttinger liquids. In the presence of both disorder and isolated impurities, the conductance has a universal single-parameter scaling form. This lays the groundwork for an application of the functional renormalization group to the realm of many-body localization.

  6. Electronic excitations of bulk LiCl from many-body perturbation theory.

    PubMed

    Jiang, Yun-Feng; Wang, Neng-Ping; Rohlfing, Michael

    2013-12-07

    We present the quasiparticle band structure and the optical excitation spectrum of bulk LiCl, using many-body perturbation theory. Density-functional theory is used to calculate the ground-state geometry of the system. The quasiparticle band structure is calculated within the GW approximation. Taking the electron-hole interaction into consideration, electron-hole pair states and optical excitations are obtained by solving the Bethe-Salpeter equation for the electron-hole two-particle Green function. The calculated band gap is 9.5 eV, which is in good agreement with the experimental result of 9.4 eV. And the calculated optical absorption spectrum, which contains an exciton peak at 8.8 eV and a resonant-exciton peak at 9.8 eV, is also in good agreement with experimental data.

  7. Electronic excitations of LiI within many-body perturbation theory

    NASA Astrophysics Data System (ADS)

    Gao, Yan-Min; Jiang, Yun-Feng; Wang, Neng-Ping

    2014-08-01

    We report the calculated quasiparticle band structure and optical absorption spectrum of LiI, using many-body perturbation theory. Density-functional theory within local density approximation is used to calculate the ground-state properties of the system. The quasiparticle band structure is evaluated within the GW approximation. Taking the electron-hole interaction into account, electron-hole pair states and optical excitations are derived from the solution of the Bethe-Salpeter equation for the electron-hole two-particle Green function. The band gap is estimated within the GW approximation as 6.3 eV, which is in good agreement with the experimental result of 6.4 eV. And the calculated optical spectrum is also in agreement with experimental data.

  8. Electronic excitations of bulk LiCl from many-body perturbation theory

    SciTech Connect

    Jiang, Yun-Feng; Wang, Neng-Ping; Rohlfing, Michael

    2013-12-07

    We present the quasiparticle band structure and the optical excitation spectrum of bulk LiCl, using many-body perturbation theory. Density-functional theory is used to calculate the ground-state geometry of the system. The quasiparticle band structure is calculated within the GW approximation. Taking the electron-hole interaction into consideration, electron-hole pair states and optical excitations are obtained by solving the Bethe-Salpeter equation for the electron-hole two-particle Green function. The calculated band gap is 9.5 eV, which is in good agreement with the experimental result of 9.4 eV. And the calculated optical absorption spectrum, which contains an exciton peak at 8.8 eV and a resonant-exciton peak at 9.8 eV, is also in good agreement with experimental data.

  9. The many-body localized phase of the quantum random energy model

    NASA Astrophysics Data System (ADS)

    Baldwin, C. L.; Laumann, C. R.; Pal, A.; Scardicchio, A.

    2016-01-01

    The random energy model (REM) provides a solvable mean-field description of the equilibrium spin-glass transition. Its quantum sibling (the QREM), obtained by adding a transverse field to the REM, has similar properties and shows a spin-glass phase for sufficiently small transverse field and temperature. In a recent work, some of us have shown that the QREM further exhibits a many-body localization-delocalization (MBLD) transition when viewed as a closed quantum system, evolving according to the quantum dynamics. This phase encloses the familiar equilibrium spin-glass phase. In this paper, we study in detail the MBLD transition within the forward-scattering approximation and replica techniques. The predictions for the transition line are in good agreement with the exact diagonalization numerics. We also observe that the structure of the eigenstates at the MBLD critical point changes continuously with the energy density, raising the possibility of a family of critical theories for the MBLD transition.

  10. Screened test-charge - electron interaction including many-body effects in two and three dimensions

    NASA Astrophysics Data System (ADS)

    Gold, A.; Ghazali, A.

    1997-05-01

    Bound states of a negatively charged test particle and an electron are studied by incorporating many-body effects (exchange and correlation) in the screening function of an interacting electron gas via the local-field correction. Using a variational method and a matrix-diagonalization method we determine the energies and the wave functions of the ground state and the excited states as functions of the electron density for three-dimensional and two-dimensional systems. For high electron density no bound states are found. Below a critical density the number and the energy of the bound states increase with decreasing electron density. We also present results for bound-state energies of a positively charged test particle with an electron, and compare them with results obtained within the random-phase approximation where the local-field correction is ignored.

  11. How Many-Body Correlations and α Clustering Shape He6

    DOE PAGES

    Romero-Redondo, Carolina; Quaglioni, Sofia; Navrátil, Petr; ...

    2016-11-23

    The Borromean 6He nucleus is an exotic system characterized by two halo neutrons orbiting around a compact 4He (or α) core, in which the binary subsystems are unbound. The simultaneous reproduction of its small binding energy and extended matter and point-proton radii has been a challenge for ab initio theoretical calculations based on traditional bound-state methods. Using soft nucleon-nucleon interactions based on chiral effective field theory potentials, we show that supplementing the model space with 4He + n + n cluster degrees of freedom largely solves this issue. Lastly, we analyze the role played by α clustering and many-body correlations,more » and study the dependence of the energy spectrum on the resolution scale of the interaction.« less

  12. How Many-Body Correlations and α Clustering Shape 6He

    NASA Astrophysics Data System (ADS)

    Romero-Redondo, Carolina; Quaglioni, Sofia; Navrátil, Petr; Hupin, Guillaume

    2016-11-01

    The Borromean 6He nucleus is an exotic system characterized by two halo neutrons orbiting around a compact 4He (or α ) core, in which the binary subsystems are unbound. The simultaneous reproduction of its small binding energy and extended matter and point-proton radii has been a challenge for ab initio theoretical calculations based on traditional bound-state methods. Using soft nucleon-nucleon interactions based on chiral effective field theory potentials, we show that supplementing the model space with 4He +n +n cluster degrees of freedom largely solves this issue. We analyze the role played by α clustering and many-body correlations, and study the dependence of the energy spectrum on the resolution scale of the interaction.

  13. Many-body ab initio study of antiferromagnetic {Cr7M } molecular rings

    NASA Astrophysics Data System (ADS)

    Chiesa, A.; Carretta, S.; Santini, P.; Amoretti, G.; Pavarini, E.

    2016-12-01

    Antiferromagnetic molecular rings are widely studied both for fundamental quantum-mechanical issues and for technological applications, particularly in the field of quantum information processing. Here we present a detailed first-principles study of two families—purple and green—of {Cr7M } antiferromagnetic rings, where M is a divalent transition metal ion (M =Ni2 + , Mn2 +, and Zn2 +). We employ a recently developed flexible and efficient scheme to build ab initio system-specific Hubbard models. From such many-body models we systematically derive the low-energy effective spin Hamiltonian for the rings. Our approach allows us to calculate isotropic as well as anisotropic terms of the spin Hamiltonian, without any a priori assumption on its form. For each compound we calculate magnetic exchange couplings, zero-field splitting tensors, and gyromagnetic tensors, finding good agreement with experimental results.

  14. Many-body effects in the van der Waals-Casimir interaction between graphene layers

    NASA Astrophysics Data System (ADS)

    Sarabadani, Jalal; Naji, Ali; Asgari, Reza; Podgornik, Rudolf

    2011-10-01

    Van der Waals-Casimir dispersion interactions between two apposed graphene layers, a graphene layer and a substrate, and in a multilamellar graphene system are analyzed within the framework of the Lifshitz theory. This formulation hinges on a known form of the dielectric response function of an undoped or doped graphene sheet, assumed to be of a random-phase-approximation form. In the geometry of two apposed layers, the separation dependence of the van der Waals-Casimir interaction for both types of graphene sheets is determined and critically compared with some well-known limiting cases. In a multilamellar array, the many-body effects are quantified and shown to increase the magnitude of the van der Waals-Casimir interactions.

  15. Many body effects study of electronic & optical properties of silicene-graphene hybrid

    NASA Astrophysics Data System (ADS)

    Drissi, L. B.; Ramadan, F. Z.

    2015-04-01

    Using first principles many-body calculations method, we study electronic and optical properties of 2D silicene-graphene hybrid. Based on phonon-spectrum calculations, we show the absence of soft modes indicating the stability of the system. We also calculate the band gap in both the absence and the presence of quasiparticle corrections. The analysis of optical absorption spectra and the correlation in real space between the excited electron-hole states reveals that the excitonic effects in silicene-graphene hybrid are significant and leads to strong bound excitons. The first active exciton is characterized by a binding energy of 0.81 eV, an effective mass 0.41m0 and a Bohr radius of 2.78 Å. The results of this work make silicene-graphene hybrid a promising candidate for optoelectronic applications.

  16. Many-body localization phase transition: A simplified strong-randomness approximate renormalization group

    NASA Astrophysics Data System (ADS)

    Zhang, Liangsheng; Zhao, Bo; Devakul, Trithep; Huse, David A.

    2016-06-01

    We present a simplified strong-randomness renormalization group (RG) that captures some aspects of the many-body localization (MBL) phase transition in generic disordered one-dimensional systems. This RG can be formulated analytically and is mathematically equivalent to a domain coarsening model that has been previously solved. The critical fixed-point distribution and critical exponents (that satisfy the Chayes inequality) are thus obtained analytically or to numerical precision. This reproduces some, but not all, of the qualitative features of the MBL phase transition that are indicated by previous numerical work and approximate RG studies: our RG might serve as a "zeroth-order" approximation for future RG studies. One interesting feature that we highlight is that the rare Griffiths regions are fractal. For thermal Griffiths regions within the MBL phase, this feature might be qualitatively correctly captured by our RG. If this is correct beyond our approximations, then these Griffiths effects are stronger than has been previously assumed.

  17. Half-metallic ferromagnets: From band structure to many-body effects

    NASA Astrophysics Data System (ADS)

    Katsnelson, M. I.; Irkhin, V. Yu.; Chioncel, L.; Lichtenstein, A. I.; de Groot, R. A.

    2008-04-01

    A review of new developments in theoretical and experimental electronic-structure investigations of half-metallic ferromagnets (HMFs) is presented. Being semiconductors for one spin projection and metals for another, these substances are promising magnetic materials for applications in spintronics (i.e., spin-dependent electronics). Classification of HMFs by the peculiarities of their electronic structure and chemical bonding is discussed. The effects of electron-magnon interaction in HMFs and their manifestations in magnetic, spectral, thermodynamic, and transport properties are considered. Special attention is paid to the appearance of nonquasiparticle states in the energy gap, which provide an instructive example of essentially many-body features in the electronic structure. State-of-the-art electronic calculations for correlated d -systems are discussed, and results for specific HMFs (Heusler alloys, zinc-blende structure compounds, CrO2 , and Fe3O4 ) are reviewed.

  18. Electronic structure of strongly correlated materials: from one-particle to many-body theory

    NASA Astrophysics Data System (ADS)

    Nilsson, F.; Aryasetiawan, F.

    2017-03-01

    One of the great challenges of modern condensed matter theory is to develop reliable and practical methods for describing the electronic structure of strongly correlated materials fully from first principles. It has been known for a long time that the widely used Kohn–Sham density functional theory within the local density approximation (LDA) often fails for these systems. This paper describes the theoretical development of including electron correlations beyond the LDA with emphasis on ab initio methods, starting from the highly successful LDA+U and the many-body Green’s function-based GW method to the state-of-the-art combination of dynamical mean-field theory and GW. Apart from reviewing the development so far we also present some previously unpublished results.

  19. Influence of Fock exchange in combined many-body perturbation and dynamical mean field theory

    NASA Astrophysics Data System (ADS)

    Ayral, Thomas; Biermann, Silke; Werner, Philipp; Boehnke, Lewin

    2017-06-01

    In electronic systems with long-range Coulomb interaction, the nonlocal Fock-exchange term has a band-widening effect. While this effect is included in combined many-body perturbation theory and dynamical mean field theory (DMFT) schemes, it is not taken into account in standard extended DMFT (EDMFT) calculations. Here, we include this instantaneous term in both approaches and investigate its effect on the phase diagram and dynamically screened interaction. We show that the largest deviations between previously presented EDMFT and G W +EDMFT results originate from the nonlocal Fock term, and that the quantitative differences are especially large in the strong-coupling limit. Furthermore, we show that the charge-ordering phase diagram obtained in G W +EDMFT methods for moderate interaction values is very similar to the one predicted by dual-boson methods that include the fermion-boson or four-point vertex.

  20. New perspectives in the ultrafast spectroscopy of many-body excitations in correlated materials

    NASA Astrophysics Data System (ADS)

    Giannetti, C.

    2016-03-01

    Ultrafast spectroscopies constitute a fundamental tool to investigate the dynamics of non-equilibrium many-body states in correlated materials. Two-pulses (pump-probe) experiments have shed new light on the interplay between high-energy electronic excitations and the emerging low-energy properties, such as superconductivity and charge order, in many interesting materials. Here we will review some recent results on copper oxides and we will propose the use of high-resolution multi-dimensional techniques to investigate the decoherence processes of optical excitations in these systems. This novel piece of information is expected to open a new route toward the understanding of the fundamental interactions that lead to the exotic electronic and magnetic properties of correlated materials.

  1. Many-Body Dynamics of Dipolar Molecules in an Optical Lattice

    NASA Astrophysics Data System (ADS)

    Hazzard, Kaden R. A.; Gadway, Bryce; Foss-Feig, Michael; Yan, Bo; Moses, Steven A.; Covey, Jacob P.; Yao, Norman Y.; Lukin, Mikhail D.; Ye, Jun; Jin, Deborah S.; Rey, Ana Maria

    2014-11-01

    We use Ramsey spectroscopy to experimentally probe the quantum dynamics of disordered dipolar-interacting ultracold molecules in a partially filled optical lattice, and we compare the results to theory. We report the capability to control the dipolar interaction strength. We find excellent agreement between our measurements of the spin dynamics and theoretical calculations with no fitting parameters, including the dynamics' dependence on molecule number and on the dipolar interaction strength. This agreement verifies the microscopic model expected to govern the dynamics of dipolar molecules, even in this strongly correlated beyond-mean-field regime, and represents the first step towards using this system to explore many-body dynamics in regimes that are inaccessible to current theoretical techniques.

  2. Many-body dynamics of dipolar molecules in an optical lattice.

    PubMed

    Hazzard, Kaden R A; Gadway, Bryce; Foss-Feig, Michael; Yan, Bo; Moses, Steven A; Covey, Jacob P; Yao, Norman Y; Lukin, Mikhail D; Ye, Jun; Jin, Deborah S; Rey, Ana Maria

    2014-11-07

    We use Ramsey spectroscopy to experimentally probe the quantum dynamics of disordered dipolar-interacting ultracold molecules in a partially filled optical lattice, and we compare the results to theory. We report the capability to control the dipolar interaction strength. We find excellent agreement between our measurements of the spin dynamics and theoretical calculations with no fitting parameters, including the dynamics' dependence on molecule number and on the dipolar interaction strength. This agreement verifies the microscopic model expected to govern the dynamics of dipolar molecules, even in this strongly correlated beyond-mean-field regime, and represents the first step towards using this system to explore many-body dynamics in regimes that are inaccessible to current theoretical techniques.

  3. Energy benchmarks for water clusters and ice structures from an embedded many-body expansion.

    PubMed

    Gillan, M J; Alfè, D; Bygrave, P J; Taylor, C R; Manby, F R

    2013-09-21

    We show how an embedded many-body expansion (EMBE) can be used to calculate accurate ab initio energies of water clusters and ice structures using wavefunction-based methods. We use the EMBE described recently by Bygrave et al. [J. Chem. Phys. 137, 164102 (2012)], in which the terms in the expansion are obtained from calculations on monomers, dimers, etc., acted on by an approximate representation of the embedding field due to all other molecules in the system, this field being a sum of Coulomb and exchange-repulsion fields. Our strategy is to separate the total energy of the system into Hartree-Fock and correlation parts, using the EMBE only for the correlation energy, with the Hartree-Fock energy calculated using standard molecular quantum chemistry for clusters and plane-wave methods for crystals. Our tests on a range of different water clusters up to the 16-mer show that for the second-order Møller-Plesset (MP2) method the EMBE truncated at 2-body level reproduces to better than 0.1 mE(h)/monomer the correlation energy from standard methods. The use of EMBE for computing coupled-cluster energies of clusters is also discussed. For the ice structures Ih, II, and VIII, we find that MP2 energies near the complete basis-set limit reproduce very well the experimental values of the absolute and relative binding energies, but that the use of coupled-cluster methods for many-body correlation (non-additive dispersion) is essential for a full description. Possible future applications of the EMBE approach are suggested.

  4. Accurate localized resolution of identity approach for linear-scaling hybrid density functionals and for many-body perturbation theory

    NASA Astrophysics Data System (ADS)

    Ihrig, Arvid Conrad; Wieferink, Jürgen; Zhang, Igor Ying; Ropo, Matti; Ren, Xinguo; Rinke, Patrick; Scheffler, Matthias; Blum, Volker

    2015-09-01

    A key component in calculations of exchange and correlation energies is the Coulomb operator, which requires the evaluation of two-electron integrals. For localized basis sets, these four-center integrals are most efficiently evaluated with the resolution of identity (RI) technique, which expands basis-function products in an auxiliary basis. In this work we show the practical applicability of a localized RI-variant (‘RI-LVL’), which expands products of basis functions only in the subset of those auxiliary basis functions which are located at the same atoms as the basis functions. We demonstrate the accuracy of RI-LVL for Hartree-Fock calculations, for the PBE0 hybrid density functional, as well as for RPA and MP2 perturbation theory. Molecular test sets used include the S22 set of weakly interacting molecules, the G3 test set, as well as the G2-1 and BH76 test sets, and heavy elements including titanium dioxide, copper and gold clusters. Our RI-LVL implementation paves the way for linear-scaling RI-based hybrid functional calculations for large systems and for all-electron many-body perturbation theory with significantly reduced computational and memory cost.

  5. The dimensionality reduction at surfaces as a playground for many-body and correlation effects

    NASA Astrophysics Data System (ADS)

    Tejeda, A.; Michel, E. G.; Mascaraque, A.

    2013-03-01

    Low-dimensional systems have always deserved attention due to the peculiarity of their physics, which is different from or even at odds with three-dimensional expectations. This is precisely the case for many-body effects, as electron-electron correlation or electron-phonon coupling are behind many intriguing problems in condensed matter physics. These interesting phenomena at low dimensions can be studied in one of the paradigms of two dimensionality—the surface of crystals. The maturity of today's surface science techniques allows us to perform thorough experimental studies that can be complemented by the current strength of state-of-the-art calculations. Surfaces are thus a natural two-dimensional playground for studying correlation and many-body effects, which is precisely the object of this special section. This special section presents a collection of eight invited articles, giving an overview of the current status of selected systems, promising techniques and theoretical approaches for studying many-body effects at surfaces and low-dimensional systems. The first article by Hofmann investigates electron-phonon coupling in quasi-free-standing graphene by decoupling graphene from two different substrates with different intercalating materials. The following article by Kirschner deals with the study of NiO films by electron pair emission, a technique particularly well-adapted for studying high electron correlation. Bovensiepen investigates electron-phonon coupling via the femtosecond time- and angle-resolved photoemission spectroscopy technique. The next article by Malterre analyses the phase diagram of alkalis on Si(111):B and studies the role of many-body physics. Biermann proposes an extended Hubbard model for the series of C, Si, Sn and Pb adatoms on Si(111) and obtains the inter-electronic interaction parameters by first principles. Continuing with the theoretical studies, Bechstedt analyses the influence of on-site electron correlation in insulating

  6. Many-Body Localization and Quantum Nonergodicity in a Model with a Single-Particle Mobility Edge.

    PubMed

    Li, Xiaopeng; Ganeshan, Sriram; Pixley, J H; Das Sarma, S

    2015-10-30

    We investigate many-body localization in the presence of a single-particle mobility edge. By considering an interacting deterministic model with an incommensurate potential in one dimension we find that the single-particle mobility edge in the noninteracting system leads to a many-body mobility edge in the corresponding interacting system for certain parameter regimes. Using exact diagonalization, we probe the mobility edge via energy resolved entanglement entropy (EE) and study the energy resolved applicability (or failure) of the eigenstate thermalization hypothesis (ETH). Our numerical results indicate that the transition separating area and volume law scaling of the EE does not coincide with the nonthermal to thermal transition. Consequently, there exists an extended nonergodic phase for an intermediate energy window where the many-body eigenstates violate the ETH while manifesting volume law EE scaling. We also establish that the model possesses an infinite temperature many-body localization transition despite the existence of a single-particle mobility edge. We propose a practical scheme to test our predictions in atomic optical lattice experiments which can directly probe the effects of the mobility edge.

  7. Ultrafast dynamics of many-body processes and fundamental quantum mechanical phenomena in semiconductors

    PubMed Central

    Chemla, Daniel S.; Shah, Jagdeep

    2000-01-01

    The large dielectric constant and small effective mass in a semiconductor allows a description of its electronic states in terms of envelope wavefunctions whose energy, time, and length scales are mesoscopic, i.e., halfway between those of atomic and those of condensed matter systems. This property makes it possible to demonstrate and investigate many quantum mechanical, many-body, and quantum kinetic phenomena with tabletop experiments that would be nearly impossible in other systems. This, along with the ability to custom-design semiconductor nanostructures, makes semiconductors an ideal laboratory for experimental investigations. We present an overview of some of the most exciting results obtained in semiconductors in recent years using the technique of ultrafast nonlinear optical spectrocopy. These results show that Coulomb correlation plays a major role in semiconductors and makes them behave more like a strongly interacting system than like an atomic system. The results provide insights into the physics of strongly interacting systems that are relevant to other condensed matter systems, but not easily accessible in other materials. PMID:10716981

  8. Quantum Simulation with Circuit-QED Lattices: from Elementary Building Blocks to Many-Body Theory

    NASA Astrophysics Data System (ADS)

    Zhu, Guanyu

    Recent experimental and theoretical progress in superconducting circuits and circuit QED (quantum electrodynamics) has helped to develop high-precision techniques to control, manipulate, and detect individual mesoscopic quantum systems. A promising direction is hence to scale up from individual building blocks to form larger-scale quantum many-body systems. Although realizing a scalable fault-tolerant quantum computer still faces major barriers of decoherence and quantum error correction, it is feasible to realize scalable quantum simulators with state-of-the-art technology. From the technological point of view, this could serve as an intermediate stage towards the final goal of a large-scale quantum computer, and could help accumulating experience with the control of quantum systems with a large number of degrees of freedom. From the physical point of view, this opens up a new regime where condensed matter systems can be simulated and studied, here in the context of strongly correlated photons and two-level systems. In this thesis, we mainly focus on two aspects of circuit-QED based quantum simulation. First, we discuss the elementary building blocks of the quantum simulator, in particular a fluxonium circuit coupled to a superconducting resonator. We show the interesting properties of the fluxonium circuit as a qubit, including the unusual structure of its charge matrix elements. We also employ perturbation theory to derive the effective Hamiltonian of the coupled system in the dispersive regime, where qubit and the photon frequencies are detuned. The observables predicted with our theory, including dispersive shifts and Kerr nonlinearity, are compared with data from experiments, such as homodyne transmission and two-tone spectroscopy. These studies also relate to the problem of detection in a circuit-QED quantum simulator. Second, we study many-body physics of circuit-QED lattices, serving as quantum simulators. In particular, we focus on two different

  9. Experimental quantum simulations of many-body physics with trapped ions.

    PubMed

    Schneider, Ch; Porras, Diego; Schaetz, Tobias

    2012-02-01

    Direct experimental access to some of the most intriguing quantum phenomena is not granted due to the lack of precise control of the relevant parameters in their naturally intricate environment. Their simulation on conventional computers is impossible, since quantum behaviour arising with superposition states or entanglement is not efficiently translatable into the classical language. However, one could gain deeper insight into complex quantum dynamics by experimentally simulating the quantum behaviour of interest in another quantum system, where the relevant parameters and interactions can be controlled and robust effects detected sufficiently well. Systems of trapped ions provide unique control of both the internal (electronic) and external (motional) degrees of freedom. The mutual Coulomb interaction between the ions allows for large interaction strengths at comparatively large mutual ion distances enabling individual control and readout. Systems of trapped ions therefore exhibit a prominent system in several physical disciplines, for example, quantum information processing or metrology. Here, we will give an overview of different trapping techniques of ions as well as implementations for coherent manipulation of their quantum states and discuss the related theoretical basics. We then report on the experimental and theoretical progress in simulating quantum many-body physics with trapped ions and present current approaches for scaling up to more ions and more-dimensional systems.

  10. Algorithm for simulation of quantum many-body dynamics using dynamical coarse-graining

    SciTech Connect

    Khasin, M.; Kosloff, R.

    2010-04-15

    An algorithm for simulation of quantum many-body dynamics having su(2) spectrum-generating algebra is developed. The algorithm is based on the idea of dynamical coarse-graining. The original unitary dynamics of the target observables--the elements of the spectrum-generating algebra--is simulated by a surrogate open-system dynamics, which can be interpreted as weak measurement of the target observables, performed on the evolving system. The open-system state can be represented by a mixture of pure states, localized in the phase space. The localization reduces the scaling of the computational resources with the Hilbert-space dimension n by factor n{sup 3/2}(ln n){sup -1} compared to conventional sparse-matrix methods. The guidelines for the choice of parameters for the simulation are presented and the scaling of the computational resources with the Hilbert-space dimension of the system is estimated. The algorithm is applied to the simulation of the dynamics of systems of 2x10{sup 4} and 2x10{sup 6} cold atoms in a double-well trap, described by the two-site Bose-Hubbard model.

  11. Many-body entropies, correlations, and emergence of statistical relaxation in interaction quench dynamics of ultracold bosons

    NASA Astrophysics Data System (ADS)

    Lode, Axel U. J.; Chakrabarti, Barnali; Kota, Venkata K. B.

    2015-09-01

    We study the quantum many-body dynamics and the entropy production triggered by an interaction quench in a system of N =10 interacting identical bosons in an external one-dimensional harmonic trap. The multiconfigurational time-dependent Hartree method for bosons (MCTDHB) is used for solving the time-dependent Schrödinger equation at a high level of accuracy. We consider many-body entropy measures such as the Shannon information entropy, number of principal components, and occupation entropy that are computed from the time-dependent many-body basis set used in MCTDHB. These measures quantify relevant physical features such as irregular or chaotic dynamics, statistical relaxation, and thermalization. We monitor the entropy measures as a function of time and assess how they depend on the interaction strength. For larger interaction strength, the many-body information and occupation entropies approach the value predicted for the Gaussian orthogonal ensemble of random matrices. This implies statistical relaxation. The basis states of MCTDHB are explicitly time-dependent and optimized by the variational principle in a way that minimizes the number of significantly contributing ones. It is therefore a nontrivial fact that statistical relaxation prevails in MCTDHB computations. Moreover, we demonstrate a fundamental connection between the production of entropy, the buildup of correlations and loss of coherence in the system. Our findings imply that mean-field approaches such as the time-dependent Gross-Pitaevskii equation cannot capture statistical relaxation and thermalization because they neglect correlations. Since the coherence and correlations are experimentally accessible, their present connection to many-body entropies can be scrutinized to detect statistical relaxation. In this work we use the recent recursive software implementation of the MCTDHB (R-MCTDHB).

  12. Many-body dissipative particle dynamics modeling of fluid flow in fine-grained nanoporous shales

    NASA Astrophysics Data System (ADS)

    Xia, Yidong; Goral, Jan; Huang, Hai; Miskovic, Ilija; Meakin, Paul; Deo, Milind

    2017-05-01

    A many-body dissipative particle dynamics model, namely, MDPD, is applied for simulation of pore-scale, multi-component, multi-phase fluid flows in fine-grained, nanoporous shales. Since this model is able to simultaneously capture the discrete features of fluid molecules in nanometer size pores and continuum fluid dynamics in larger pores, and is relatively easy to parameterize, it has been recognized as being particularly suitable for simulating complex fluid flow in multi-length-scale nanopore networks of shales. A remarkable feature of this work is the integration of a high-resolution FIB-SEM (focused ion beam scanning electron microscopy) digital imaging technique to the MDPD model for providing 3D voxel data that contain the invaluable geometrical and compositional information of shale samples. This is the first time that FIB-SEM is seamlessly linked to a Lagrangian model like MDPD for fluid flow simulation, which offers a robust approach to bridging gaps between the molecular- and continuum-scales, since the relevant spatial and temporal scales are too big for molecular dynamics, and too small for computational fluid dynamics with known constitutive models. Simulations ranging from a number of benchmark problems to a forced two-fluid flow in a Woodford shale sample are presented. Results indicate that this model can be used to deliver reasonable simulations for multi-component, multi-phase fluid flows in arbitrarily complex pore networks in shales.

  13. A driven similarity renormalization group approach to quantum many-body problems.

    PubMed

    Evangelista, Francesco A

    2014-08-07

    Applications of the similarity renormalization group (SRG) approach [F. Wegner, Ann. Phys. 506, 77 (1994) and S. D. Głazek and K. G. Wilson, Phys. Rev. D 49, 4214 (1994)] to the formulation of useful many-body theories of electron correlation are considered. In addition to presenting a production-level implementation of the SRG based on a single-reference formalism, a novel integral version of the SRG is reported, in which the flow of the Hamiltonian is driven by a source operator. It is shown that this driven SRG (DSRG) produces a Hamiltonian flow that is analogous to that of the SRG. Compared to the SRG, which requires propagating a set of ordinary differential equations, the DSRG is computationally advantageous since it consists of a set of polynomial equations. The equilibrium distances, harmonic vibrational frequencies, and vibrational anharmonicities of a series of diatomic molecules computed with the SRG and DSRG approximated with one- and two-body normal ordered operators are in good agreement with benchmark values from coupled cluster with singles, doubles, and perturbative triples. Particularly surprising results are found when the SRG and DSRG methods are applied to C2 and F2. In the former case, both methods fail to converge, while in the latter case an unbound potential energy curve is obtained. A modified commutator approximation is shown to correct these problems in the case of the DSRG method.

  14. A driven similarity renormalization group approach to quantum many-body problems

    SciTech Connect

    Evangelista, Francesco A.

    2014-08-07

    Applications of the similarity renormalization group (SRG) approach [F. Wegner, Ann. Phys. 506, 77 (1994) and S. D. Głazek and K. G. Wilson, Phys. Rev. D 49, 4214 (1994)] to the formulation of useful many-body theories of electron correlation are considered. In addition to presenting a production-level implementation of the SRG based on a single-reference formalism, a novel integral version of the SRG is reported, in which the flow of the Hamiltonian is driven by a source operator. It is shown that this driven SRG (DSRG) produces a Hamiltonian flow that is analogous to that of the SRG. Compared to the SRG, which requires propagating a set of ordinary differential equations, the DSRG is computationally advantageous since it consists of a set of polynomial equations. The equilibrium distances, harmonic vibrational frequencies, and vibrational anharmonicities of a series of diatomic molecules computed with the SRG and DSRG approximated with one- and two-body normal ordered operators are in good agreement with benchmark values from coupled cluster with singles, doubles, and perturbative triples. Particularly surprising results are found when the SRG and DSRG methods are applied to C{sub 2} and F{sub 2}. In the former case, both methods fail to converge, while in the latter case an unbound potential energy curve is obtained. A modified commutator approximation is shown to correct these problems in the case of the DSRG method.

  15. Many-body forces and electron correlation in small metal clusters

    NASA Astrophysics Data System (ADS)

    Kaplan, Ilya G.; Hernández-Cobos, Jorge; Ortega-Blake, Iván; Novaro, Octavio

    1996-04-01

    The many-body decomposition of the interaction energy for BeN and LiN (N=2 to 4) clusters is calculated in two approximations: the self-consistent-field method and the Mo/ller-Plesset perturbation theory up to the fourth order. This allows us to estimate the electron-correlation contributions to the many-body forces. The explicit expressions for these contributions in the perturbation theory formalism are obtained. We present a comparative analysis of the role of electron correlations in the BeN and LiN cluster formations and in the many-body interactions in these clusters. As follows from our results, the contribution of electron correlation to many-body interactions is essential for both the BeN and LiN clusters, especially for the latter ones, where nonadditivities are surprisingly large.

  16. Solving the Quantum Many-Body Problem via Correlations Measured with a Momentum Microscope

    NASA Astrophysics Data System (ADS)

    Hodgman, S. S.; Khakimov, R. I.; Lewis-Swan, R. J.; Truscott, A. G.; Kheruntsyan, K. V.

    2017-06-01

    In quantum many-body theory, all physical observables are described in terms of correlation functions between particle creation or annihilation operators. Measurement of such correlation functions can therefore be regarded as an operational solution to the quantum many-body problem. Here, we demonstrate this paradigm by measuring multiparticle momentum correlations up to third order between ultracold helium atoms in an s -wave scattering halo of colliding Bose-Einstein condensates, using a quantum many-body momentum microscope. Our measurements allow us to extract a key building block of all higher-order correlations in this system—the pairing field amplitude. In addition, we demonstrate a record violation of the classical Cauchy-Schwarz inequality for correlated atom pairs and triples. Measuring multiparticle momentum correlations could provide new insights into effects such as unconventional superconductivity and many-body localization.

  17. Rotation of quantum impurities in the presence of a many-body environment

    NASA Astrophysics Data System (ADS)

    Lemeshko, Mikhail; Schmidt, Richard

    2015-05-01

    Pioneered by the seminal works of Wigner and Racah, the quantum theory of angular momentum evolved into a powerful machinery, commonly used to classify the states of isolated quantum systems and perturbations to their structure due to electromagnetic or crystalline fields. In ``realistic'' experiments, however, quantum systems are almost inevitably coupled to a many-particle environment and a field of elementary excitations associated with it, which is capable of fundamentally altering the physics of the system. We present the first systematic treatment of quantum rotation coupled to a many-particle environment. By using a series of canonical transformations on a generic microscopic Hamiltonian, we single out the conserved quantities of the problem. Using a variational ansatz accounting for an infinite number of many-body excitations, we characterize the spectrum of angular momentum eigenstates and identify the regions of instability, accompanied by emission of angular Cerenkov radiation. The developed technique can be applied to a wide range of systems described by the angular momentum algebra, from Rydberg atoms immersed into BEC's, to cold molecules solvated in helium droplets, to ultracold molecular ions.

  18. Many-body localization phase in a spin-driven chiral multiferroic chain

    NASA Astrophysics Data System (ADS)

    Stagraczyński, S.; Chotorlishvili, L.; Schüler, M.; Mierzejewski, M.; Berakdar, J.

    2017-08-01

    Many-body localization (MBL) is an emergent phase in correlated quantum systems with promising applications, particularly in quantum information. Here, we unveil the existence and analyze this phase in a chiral multiferroic model system. Conventionally, MBL occurrence is traced via level statistics by implementing a standard finite-size scaling procedure. Here, we present an approach based on the full distribution of the ratio of adjacent energy spacings. We find a strong broadening of the histograms of counts of these level spacings directly at the transition point from MBL to the ergodic phase. The broadening signals reliably the transition point without relying on an averaging procedure. The fast convergence of the histograms even for relatively small systems allows monitoring the MBL dynamics with much less computational effort. Numerical results are presented for a chiral spin chain with a dynamical Dzyaloshinskii-Moriya interaction, an established model to describe the spin excitations in a single-phase spin-driven multiferroic system. The multiferroic MBL phase is uncovered and it is shown how to steer it via electric fields.

  19. Many-Body Effects and Lineshape of Intersubband Transitions in Semiconductor Quantum Wells

    NASA Technical Reports Server (NTRS)

    Ning, Cun-Zheng

    2003-01-01

    Intersubband Transition (ISBT) infrared (IR) absorption and PL in InAs/AlSb were studied for narrow Quantum Wells (QWs). A large redshift was observed (7-10 meV) as temperature increased. A comprehensive many-body theory was developed for ISBTs including contributions of c-c and c-phonon scatterings. Many-body effects were studied systematically for ISBTs. Redshift and linewidth dependence on temperature, as well as spectral features were well explained by theory.

  20. Diagonalization and Many-Body Localization for a Disordered Quantum Spin Chain.

    PubMed

    Imbrie, John Z

    2016-07-08

    We consider a weakly interacting quantum spin chain with random local interactions. We prove that many-body localization follows from a physically reasonable assumption that limits the extent of level attraction in the statistics of eigenvalues. In a Kolmogorov-Arnold-Moser-style construction, a sequence of local unitary transformations is used to diagonalize the Hamiltonian by deforming the initial tensor-product basis into a complete set of exact many-body eigenfunctions.