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1

Antiadiabatic control of Many Body Quantum Systems

Classical control theory has played a major role in the development of\\u000apresent-day technologies. Likewise, recently developed quantum optimal control\\u000amethods can be applied to emerging quantum technologies, e.g. quantum\\u000ainformation processing -- until now, at the level of a few qubits. However,\\u000asuch methods encounter severe limits when applied to many-body quantum systems:\\u000adue to the complexity of simulating

Patrick Doria; Tommaso Calarco; Simone Montangero

2010-01-01

2

Seniority in quantum many-body systems

The use of the seniority quantum number in many-body systems is reviewed. A brief summary is given of its introduction by Racah in the context of atomic spectroscopy. Several extensions of Racah's original idea are discussed: seniority for identical nucleons in a single-j shell, its extension to the case of many, non-degenerate j shells and to systems with neutrons and protons. To illustrate its usefulness to this day, a recent application of seniority is presented in Bose-Einstein condensates of atoms with spin.

Van Isacker, P. [Grand Accelerateur National d'Ions Lourds, CEA/DSM-CNRS/IN2P3 BP 55027, F-14076 Caen Cedex 5 (France)

2010-12-23

3

Relativistic quantum dynamics of many-body systems.

National Technical Information Service (NTIS)

Relativistic quantum dynamics requires a unitary representation of the Poincare group on the Hilbert space of states. The Dynamics of many-body systems must satisfy cluster separability requirements. In this paper we formulate an abstract framework of fou...

F. Coester W. N. Polyzou

2000-01-01

4

Emergent thermodynamics in a quenched quantum many-body system.

We study the statistics of the work done, fluctuation relations, and irreversible entropy production in a quantum many-body system subject to the sudden quench of a control parameter. By treating the quench as a thermodynamic transformation we show that the emergence of irreversibility in the nonequilibrium dynamics of closed many-body quantum systems can be accurately characterized. We demonstrate our ideas by considering a transverse quantum Ising model that is taken out of equilibrium by an instantaneous change of the transverse field. PMID:23215064

Dorner, R; Goold, J; Cormick, C; Paternostro, M; Vedral, V

2012-10-18

5

Optimal correlations in many-body quantum systems.

Information and correlations in a quantum system are closely related through the process of measurement. We explore such relation in a many-body quantum setting, effectively bridging between quantum metrology and condensed matter physics. To this aim we adopt the information-theory view of correlations and study the amount of correlations after certain classes of positive-operator-valued measurements are locally performed. As many-body systems, we consider a one-dimensional array of interacting two-level systems (a spin chain) at zero temperature, where quantum effects are most pronounced. We demonstrate how the optimal strategy to extract the correlations depends on the quantum phase through a subtle interplay between local interactions and coherence. PMID:23004247

Amico, L; Rossini, D; Hamma, A; Korepin, V E

2012-06-15

6

On microstates counting in many body polymer quantum systems

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.

Chacon-Acosta, Guillermo; Morales-Tecotl, Hugo A. [Departamento de Fisica, Universidad Autonoma Metropolitana-Iztapalapa, Mexico D. F. 09340 (Mexico); Dagdug, Leonardo [Mathematical and Statistical Computing Laboratory, Division of Computational Bioscience, Center for Information Technology, National Institutes of Health, Bethesda, Maryland 20892 (United States); Departamento de Fisica, Universidad Autonoma Metropolitana-Iztapalapa, Mexico D. F. 09340 (Mexico)

2011-10-14

7

Toward engineered quantum many-body phonon systems

NASA Astrophysics Data System (ADS)

Arrays of coupled phonon cavities each including an impurity qubit in silicon are considered. We study experimentally feasible architectures that can exhibit quantum many-body phase transitions of phonons, e.g., Mott insulator and superfluid states, due to a strong phonon-phonon interaction (which is mediated by the impurity qubit-cavity phonon coupling). We investigate closed equilibrium systems as well as driven dissipative nonequilibrium systems at zero and nonzero temperatures. Our results indicate that quantum many-body phonon systems are achievable both in on-chip nanomechanical systems in silicon and distributed Bragg reflector phonon cavity heterostructures in silicon-germanium. Temperature and driving field are shown to play a critical role in achieving these phonon superfluid and insulator states, results that are also applicable to polariton systems. Experimental procedures to detect these states are also given. Cavity-phoniton systems enable strong phonon-phonon interactions as well as offering long wavelengths for forming extended quantum states; they may have some advantage in forming truly quantum many-body mechanical states as compared to other optomechanical systems.

Soykal, Ö. O.; Tahan, Charles

2013-10-01

8

Relativistic Quantum Dynamics of Many-Body Systems

NASA Astrophysics Data System (ADS)

Relativistic quantum dynamics requires a unitary representation of the Poincaré group on the Hilbert space of states. The Dynamics of many-body systems must satisfy cluster separability requirements. In this paper we formulate an abstract framework of four-dimensional Euclidean Green's functions that can be used to construct relativistic quantum dynamics of N-particle systems consistent with these requirements. This approach should be useful in bridging the gap between few-body dynamics based on phenomenological mass operators and on quantum field theory.

Coester, F.; Polyzou, W. N.

2001-09-01

9

Dynamic Stabilization of a Quantum Many-Body Spin System

NASA Astrophysics Data System (ADS)

We demonstrate dynamic stabilization of a strongly interacting quantum spin system realized in a spin-1 atomic Bose-Einstein condensate. The spinor Bose-Einstein condensate is initialized to an unstable fixed point of the spin-nematic phase space, where subsequent free evolution gives rise to squeezing and quantum spin mixing. To stabilize the system, periodic microwave pulses are applied that rotate the spin-nematic many-body fluctuations and limit their growth. The stability diagram for the range of pulse periods and phase shifts that stabilize the dynamics is measured and compares well with a stability analysis.

Hoang, T. M.; Gerving, C. S.; Land, B. J.; Anquez, M.; Hamley, C. D.; Chapman, M. S.

2013-08-01

10

A perturbative probabilistic approach to quantum many-body systems

NASA Astrophysics Data System (ADS)

In the probabilistic approach to quantum many-body systems, the ground-state energy is the solution of a nonlinear scalar equation written either as a cumulant expansion or as an expectation with respect to a probability distribution of the potential and hopping (amplitude and phase) values recorded during an infinitely lengthy evolution. We introduce a perturbative expansion of this probability distribution which conserves, at any order, a multinomial-like structure, typical of uncorrelated systems, but includes, order by order, the statistical correlations provided by the cumulant expansion. The proposed perturbative scheme is successfully tested in the case of pseudo-spin 1/2 hard-core boson Hubbard models also when affected by a phase problem due to an applied magnetic field.

Di Stefano, Andrea; Ostilli, Massimo; Presilla, Carlo

2013-04-01

11

Quantum phase transition in strongly correlated many-body system

NASA Astrophysics Data System (ADS)

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 in the Ising model, and then we say long range order (LRO) exists in the system. LRO plays a key role in determining the ordered-disorder transition. Thereby, we investigate two-dimensional 120° orbital-only model to present how to extract the information of LRO in a pedagogical manner, by applying the reflection positivity method introduced by Dyson, Lieb, and Simon. We rigorously establish the existence of an anti-ferromagnetic like transverse orbital long-range order in the so called two-dimensional 120° model at zero temperature. Next we consider possible pairings in the family of FeAs-based ReO1--xFxFeAs (Re=La, Nd, Ce, Pr, etc.) high-temperature superconductors. We build some identities based on a two-orbital model, and obtained some constraints on a few possible pairings. We also establish the sufficient conditions for the coexistence of two superconducting orders, and we propose the most favorable pairings around half filling according to physical consideration. In chapter 3, we present a quantum solvation process with solvent of fermion character based on the one-dimensional asymmetric t-J-Jz model. The model is experimental realizable in optical lattices and exhibits rich physics. In this work, we show that there exist two types of phase separations, one is driven by potential energy while the other by kinetic energy. In between, solvation process occurs. Analytically, we are able to obtain some rigorous results to understand the underlying physics. Numerically, we perform exact diagonalization and density matrix renormalization group calculations, accompanied by detailed finite size analysis. In chapter 4, we explore several characterizations of QPT points. As distinguished from the methods in condensed-matter physics, we give much attention to understand QPT from the quantum information (QI) point of view. The perspective makes a new bridge between these two fields. It no only can facilitate the understanding of condensed-matter physics, but also provide the prominent playground for the quantum information theory. They are fidelity susceptibility a

You, Wenlong

12

System of Coordinates for Quantum Many-Body Problems.

National Technical Information Service (NTIS)

An orthogonal transformation of the Jacobi coordinates is defined whih gives rise to a new set of coordinates, whose geometrical properties and the standard Racah algebra will prove to be useful to treat the many-body problem. In this sense an algorithm i...

M. C. K. Aguilera-Navarro V. C. Aguilera-Navarro

1982-01-01

13

Localization and Glassy Dynamics Of Many-Body Quantum Systems

When classical systems fail to explore their entire configurational space, intriguing macroscopic phenomena like aging and glass formation may emerge. Also closed quanto-mechanical systems may stop wandering freely around the whole Hilbert space, even if they are initially prepared into a macroscopically large combination of eigenstates. Here, we report numerical evidences that the dynamics of strongly interacting lattice bosons driven sufficiently far from equilibrium can be trapped into extremely long-lived inhomogeneous metastable states. The slowing down of incoherent density excitations above a threshold energy, much reminiscent of a dynamical arrest on the verge of a glass transition, is identified as the key feature of this phenomenon. We argue that the resulting long-lived inhomogeneities are responsible for the lack of thermalization observed in large systems. Such a rich phenomenology could be experimentally uncovered upon probing the out-of-equilibrium dynamics of conveniently prepared quantum states of trapped cold atoms which we hereby suggest.

Carleo, Giuseppe; Becca, Federico; Schiro, Marco; Fabrizio, Michele

2012-01-01

14

Numerical simulation of quantum many-body systems

Results for the single-particle density of states and the conductivity were obtained for both the attractive-and repulsive-U Hubbard models. At half-filling the densities of states for both models are identical, but the gap for the attractive case arises from the formation of charge-density-wave and superconducting correlations, while for the repulsive-U Hubbard model the gap is the Mott-Hubbard gap and arises from the antiferromagnetic, Coulomb, correlations. Hubbard chains were studied by use of a generalization of Handscomb's quantum Monte Carlo scheme. Monte Carlo calculations of the two-particle vertex of the 2D repulsive-U Hubbard model were carried out. Criteria for determining whether a system is insulating, metallic, or superconducting were investigated; it was found for lattice models (Hubbard, Holstein, etc.) that this is determined by the value of the current- function.

Scalapino, D.J.

1992-01-01

15

Numerical simulation of quantum many-body systems

Results for the single-particle density of states and the conductivity were obtained for both the attractive-and repulsive-U Hubbard models. At half-filling the densities of states for both models are identical, but the gap for the attractive case arises from the formation of charge-density-wave and superconducting correlations, while for the repulsive-U Hubbard model the gap is the Mott-Hubbard gap and arises from the antiferromagnetic, Coulomb, correlations. Hubbard chains were studied by use of a generalization of Handscomb`s quantum Monte Carlo scheme. Monte Carlo calculations of the two-particle vertex of the 2D repulsive-U Hubbard model were carried out. Criteria for determining whether a system is insulating, metallic, or superconducting were investigated; it was found for lattice models (Hubbard, Holstein, etc.) that this is determined by the value of the current- function.

Scalapino, D.J.

1992-12-31

16

Schrieffer-Wolff transformation for quantum many-body systems

The Schrieffer-Wolff (SW) method is a version of degenerate perturbation theory in which the low-energy effective Hamiltonian H{sub eff} is obtained from the exact Hamiltonian by a unitary transformation decoupling the low-energy and high-energy subspaces. We give a self-contained summary of the SW method with a focus on rigorous results. We begin with an exact definition of the SW transformation in terms of the so-called direct rotation between linear subspaces. From this we obtain elementary proofs of several important properties of H{sub eff} such as the linked cluster theorem. We then study the perturbative version of the SW transformation obtained from a Taylor series representation of the direct rotation. Our perturbative approach provides a systematic diagram technique for computing high-order corrections to H{sub eff}. We then specialize the SW method to quantum spin lattices with short-range interactions. We establish unitary equivalence between effective low-energy Hamiltonians obtained using two different versions of the SW method studied in the literature. Finally, we derive an upper bound on the precision up to which the ground state energy of the nth-order effective Hamiltonian approximates the exact ground state energy. - Highlights: > The Schrieffer-Wolff transformation is specialized to quantum spin lattices with short-range interactions. > We provide a diagram technique for computing high-order corrections to the effective low-energy Hamiltonian. > We derive a rigorous bound on the error up to which the nth-order effective low-energy dynamics approximates the exact dynamics.

Bravyi, Sergey, E-mail: sbravyi@us.ibm.com [IBM Watson Research Center, Yorktown Heights, NY 10598 (United States); DiVincenzo, David P., E-mail: d.divincenzo@fz-juelich.de [RWTH Aachen and Forschungszentrum Juelich (Germany); Loss, Daniel, E-mail: Daniel.Loss@unibas.ch [Department of Physics, University of Basel, Klingelbergstrasse 82, CH-4056 Basel (Switzerland)

2011-10-15

17

Localization and Glassy Dynamics Of Many-Body Quantum Systems

When classical systems fail to explore their entire configurational space, intriguing macroscopic phenomena like aging and glass formation may emerge. Also closed quanto-mechanical systems may stop wandering freely around the whole Hilbert space, even if they are initially prepared into a macroscopically large combination of eigenstates. Here, we report numerical evidences that the dynamics of strongly interacting lattice bosons driven

Giuseppe Carleo; Federico Becca; Marco Schiró; Michele Fabrizio

2011-01-01

18

A quantum many-body spin system in an optical lattice clock.

Strongly interacting quantum many-body systems arise in many areas of physics, but their complexity generally precludes exact solutions to their dynamics. We explored a strongly interacting two-level system formed by the clock states in (87)Sr as a laboratory for the study of quantum many-body effects. Our collective spin measurements reveal signatures of the development of many-body correlations during the dynamical evolution. We derived a many-body Hamiltonian that describes the experimental observation of atomic spin coherence decay, density-dependent frequency shifts, severely distorted lineshapes, and correlated spin noise. These investigations open the door to further explorations of quantum many-body effects and entanglement through use of highly coherent and precisely controlled optical lattice clocks. PMID:23929976

Martin, M J; Bishof, M; Swallows, M D; Zhang, X; Benko, C; von-Stecher, J; Gorshkov, A V; Rey, A M; Ye, Jun

2013-08-01

19

Classical simulation of quantum many-body systems with a tree tensor network

We show how to efficiently simulate a quantum many-body system with tree structure when its entanglement (Schmidt number) is small for any bipartite split along an edge of the tree. As an application, we show that any one-way quantum computation on a tree graph can be efficiently simulated with a classical computer.

Yaoyun Shi; L.-M. Duan; Guifre Vidal

2006-01-01

20

Classical simulation of quantum many-body systems with a tree tensor network

We show how to efficiently simulate a quantum many-body system with tree structure when its entanglement (Schmidt number) is small for any bipartite split along an edge of the tree. As an application, we show that any one-way quantum computation on a tree graph can be efficiently simulated with a classical computer.

Shi, Y.-Y. [Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, Michigan 48109 (United States); Duan, L.-M. [FOCUS Center and MCTP, Department of Physics, University of Michigan, Ann Arbor, Michigan 48109 (United States); Vidal, G. [School of Physical Sciences, The University of Queensland, Queensland 4072 (Australia)

2006-08-15

21

Dunkl Operator Formalism for Quantum Many-Body Problems Associated with Classical Root Systems

NASA Astrophysics Data System (ADS)

The integrable quantum many-body systems associated withthe classical root systems are formulated in terms of the(trigonometric) Dunkl operators.We define the Dunkl operators by use of the infinite-dimensionalrepresentation of the R and K matrices for the Yang-Baxterequation and the reflection equation.The eigenvalues of systems are also given.

Hikami, Kazuhiro

1996-02-01

22

Scaling approach to quantum non-equilibrium dynamics of many-body systems

NASA Astrophysics Data System (ADS)

Understanding the non-equilibrium quantum dynamics of many-body systems is one of the most challenging problems in modern theoretical physics. While numerous approximate and exact solutions exist for systems in equilibrium, examples of non-equilibrium dynamics of many-body systems that allow reliable theoretical analysis are few and far between. In this paper, we discuss a broad class of time-dependent interacting systems subject to external linear and parabolic potentials, for which the many-body Schrödinger equation can be solved using a scaling transformation. We demonstrate that scaling solutions exist for both local and non-local interactions, and derive appropriate self-consistency equations. We apply this approach to several specific experimentally relevant examples of interacting bosons in one and two dimensions. As an intriguing result, we find that weakly and strongly interacting Bose gases expanding from a parabolic trap can exhibit very similar dynamics.

Gritsev, Vladimir; Barmettler, Peter; Demler, Eugene

2010-11-01

23

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

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.

Stimming, H.-P.; Mauser, N. J. [Wolfgang Pauli Institute c/o Universitaet Wien, Nordbergstrasse 15, 1090 Vienna (Austria); Schmiedmayer, J. [Atominstitut, TU Wien, Stadionallee 2, 1020 Vienna (Austria); Mazets, I. E. [Wolfgang Pauli Institute c/o Universitaet Wien, Nordbergstrasse 15, 1090 Vienna (Austria); Atominstitut, TU Wien, Stadionallee 2, 1020 Vienna (Austria); Ioffe Physico-Technical Institute, 194021 St. Petersburg (Russian Federation)

2010-07-02

24

Efficient simulation of one-dimensional quantum many-body systems.

We present a numerical method to simulate the time evolution, according to a generic Hamiltonian made of local interactions, of quantum spin chains and systems alike. The efficiency of the scheme depends on the amount of entanglement involved in the simulated evolution. Numerical analysis indicates that this method can be used, for instance, to efficiently compute time-dependent properties of low-energy dynamics in sufficiently regular but otherwise arbitrary one-dimensional quantum many-body systems. As by-products, we describe two alternatives to the density matrix renormalization group method. PMID:15323740

Vidal, Guifré

2004-07-19

25

Local emergence of thermal correlations in an isolated quantum many-body system

NASA Astrophysics Data System (ADS)

Understanding the dynamics of isolated quantum many-body systems is a central open problem at the intersection between statistical physics and quantum physics. Despite important theoretical effort, no generic framework exists yet to understand when and how an isolated quantum system relaxes to a steady state. Regarding the question of how, it has been conjectured that equilibration must occur on a local scale in systems where correlations between distant points can establish only at a finite speed. Here, we provide the first experimental observation of this local equilibration hypothesis. In our experiment, we quench a one-dimensional Bose gas by coherently splitting it into two parts. By monitoring the phase coherence between the two parts we observe that the thermal correlations of a prethermalized state emerge locally in their final form and propagate through the system in a light-cone-like evolution. Our results underline the close link between the propagation of correlations and relaxation processes in quantum many-body systems.

Langen, T.; Geiger, R.; Kuhnert, M.; Rauer, B.; Schmiedmayer, J.

2013-10-01

26

Simulating local measurements on a quantum many-body system with stochastic matrix product states

We demonstrate how to simulate both discrete and continuous stochastic evolutions of a quantum many-body system subject to measurements using matrix product states. A particular, but generally applicable, measurement model is analyzed and a simple representation in terms of matrix product operators is found. The technique is exemplified by numerical simulations of the antiferromagnetic Heisenberg spin-chain model subject to various instances of the measurement model. In particular, we focus on local measurements with small support and nonlocal measurements, which induce long-range correlations.

Gammelmark, Soeren; Moelmer, Klaus [Lundbeck Foundation Theoretical Center for Quantum System Research, Department of Physics and Astronomy, University of Aarhus, DK-8000 Aarhus C (Denmark)

2010-01-15

27

Spin, angular momentum and spin-statistics for a relativistic quantum many-body system

NASA Astrophysics Data System (ADS)

The adaptation of Wigner’s induced representation for a relativistic quantum theory making possible the construction of wave packets and admitting covariant expectation values for the coordinate operator x? introduces a foliation on the Hilbert space of states. The spin-statistics relation for fermions and bosons implies the universality of the parametrization of orbits of the induced representation, implying that all particles within identical particle sets transform under the same SU(2) subgroup of the Lorentz group, and therefore their spins and angular momentum states can be computed using the usual Clebsch-Gordan coefficients associated with angular momentum. Important consequences, such as entanglement for subsystems at unequal times, covariant statistical correlations in many-body systems and the construction of relativistic boson and fermion statistical ensembles, as well as implications for the foliation of the Fock space and for quantum field theory are briefly discussed. This paper is dedicated to the memory of Constantin Piron.

Horwitz, Lawrence

2013-01-01

28

Simulating open quantum systems: from many-body interactions to stabilizer pumping

NASA Astrophysics Data System (ADS)

In a recent experiment, Barreiro et al (2011 Nature 470 486) demonstrated the fundamental building blocks of an open-system quantum simulator with trapped ions. Using up to five ions, dynamics were realized by sequences that combined single- and multi-qubit entangling gate operations with optical pumping. This enabled the implementation of both coherent many-body dynamics and dissipative processes by controlling the coupling of the system to an artificial, suitably tailored environment. This engineering was illustrated by the dissipative preparation of entangled two- and four-qubit states, the simulation of coherent four-body spin interactions and the quantum non-demolition measurement of a multi-qubit stabilizer operator. In this paper, we present the theoretical framework of this gate-based ('digital') simulation approach for open-system dynamics with trapped ions. In addition, we discuss how within this simulation approach, minimal instances of spin models of interest in the context of topological quantum computing and condensed matter physics can be realized in state-of-the-art linear ion-trap quantum computing architectures. We outline concrete simulation schemes for Kitaev's toric code Hamiltonian and a recently suggested color code model. The presented simulation protocols can be adapted to scalable and two-dimensional ion-trap architectures, which are currently under development.

Müller, M.; Hammerer, K.; Zhou, Y. L.; Roos, C. F.; Zoller, P.

2011-08-01

29

Size consistency of tensor network methods for quantum many-body systems

NASA Astrophysics Data System (ADS)

Recently developed tensor network methods demonstrate great potential for addressing the quantum many-body problem, by constructing variational spaces with polynomially, instead of exponentially, scaled parameters. Constructing such an efficient tensor network, and thus the variational space, is a subtle problem and the main obstacle of the method. We demonstrate the necessity of size consistency in tensor network methods for their success in addressing the quantum many-body problem. We further demonstrate that size consistency is independent of the entanglement criterion, thus providing a general and tight constraint to construct the tensor network method. We propose a general and easy rule to construct a size-consistent tensor network.

Wang, Zhen; Han, Yongjian; Guo, Guang-Can; He, Lixin

2013-09-01

30

Energy as an entanglement witness for quantum many-body systems

We investigate quantum many-body systems where all low-energy states are entangled. As a tool for quantifying such systems, we introduce the concept of the entanglement gap, which is the difference in energy between the ground-state energy and the minimum energy that a separable (unentangled) state may attain. If the energy of the system lies within the entanglement gap, the state of the system is guaranteed to be entangled. We find Hamiltonians that have the largest possible entanglement gap; for a system consisting of two interacting spin-1/2 subsystems, the Heisenberg antiferromagnet is one such example. We also introduce a related concept, the entanglement-gap temperature: the temperature below which the thermal state is certainly entangled, as witnessed by its energy. We give an example of a bipartite Hamiltonian with an arbitrarily high entanglement-gap temperature for fixed total energy range. For bipartite spin lattices we prove a theorem demonstrating that the entanglement gap necessarily decreases as the coordination number is increased. We investigate frustrated lattices and quantum phase transitions as physical phenomena that affect the entanglement gap.

Dowling, Mark R.; Doherty, Andrew C.; Bartlett, Stephen D. [School of Physical Sciences, University of Queensland, Queensland 4072 (Australia)

2004-12-01

31

The problem of how to visualize and sometimes solve a general many-body system is considered. The ideas are established in the context of very simple small systems, a Hubbard model and a coupled electron-phonon model, both on two lattice sites. These models are also solved to good approximation in the thermodynamic limit, although the Hubbard model is restricted to a small number of holes away from the Mott insulating state. Response functions are also considered. A fairly general many-body Hamiltonian is considered. It consists of an electron or other fermion kinetic energy and electron-electron interactions, which may be coupled to a bose field such as a phonon. The phonons themselves may be nonlinear (have self-interactions). The system may be strongly coupled. One may also add coupling to an external driving field, such as an ac electric field. The methods discussed are nonperturbative, and so differ from the standard methods of diagrammatic perturbation theory. A comparison is made with diagrammatic methods in the context of the random phase approximation. 6 refs., 12 figs.

Trugman, S.A.

1989-01-01

32

Simulation of the dynamics of many-body quantum spin systems using phase-space techniques

NASA Astrophysics Data System (ADS)

We reformulate the full quantum dynamics of spin systems using a phase-space representation based on SU(2) coherent states which generates an exact mapping of the dynamics of any spin system onto a set of stochastic differential equations. This representation is superior in practice to an earlier phase-space approach based on Schwinger bosons, with the numerical effort scaling only linearly with system size. By also implementing extrapolation techniques from quasiclassical equations to the full quantum limit, we are able to extend useful simulation times severalfold. This approach is applicable in any dimension including cases where frustration is present in the spin system. The method is demonstrated by simulating quenches in the transverse-field Ising model in one and two dimensions.

Ng, Ray; Sørensen, Erik S.; Deuar, Piotr

2013-10-01

33

Efficient and feasible state tomography of quantum many-body systems

NASA Astrophysics Data System (ADS)

We present a novel method for performing quantum state tomography for many-particle systems, which are particularly suitable for estimating the states in lattice systems such as of ultra-cold atoms in optical lattices. We show that the need to measure a tomographically complete set of observables can be overcome by letting the state evolve under some suitably chosen random circuits followed by the measurement of a single observable. We generalize known results about the approximation of unitary two-designs, i.e. certain classes of random unitary matrices, by random quantum circuits and connect our findings to the theory of quantum compressed sensing. We show that for ultra-cold atoms in optical lattices established experimental techniques such as optical super-lattices, laser speckles and time-of-flight measurements are sufficient to perform fully certified, assumption-free tomography. This is possible without the need to address single sites in any step of the procedure. Combining our approach with tensor network methods—in particular, the theory of matrix product states—we identify situations where the effort of reconstruction is even constant in the number of lattice sites, allowing, in principle, to perform tomography on large-scale systems readily available in present experiments.

Ohliger, M.; Nesme, V.; Eisert, J.

2013-01-01

34

Controlling the dynamics of an open many-body quantum system with localized dissipation.

We experimentally investigate the action of a localized dissipative potential on a macroscopic matter wave, which we implement by shining an electron beam on an atomic Bose-Einstein condensate (BEC). We measure the losses induced by the dissipative potential as a function of the dissipation strength observing a paradoxical behavior when the strength of the dissipation exceeds a critical limit: for an increase of the dissipation rate the number of atoms lost from the BEC becomes lower. We repeat the experiment for different parameters of the electron beam and we compare our results with a simple theoretical model, finding excellent agreement. By monitoring the dynamics induced by the dissipative defect we identify the mechanisms which are responsible for the observed paradoxical behavior. We finally demonstrate the link between our dissipative dynamics and the measurement of the density distribution of the BEC allowing for a generalized definition of the Zeno effect. Because of the high degree of control on every parameter, our system is a promising candidate for the engineering of fully governable open quantum systems. PMID:23373931

Barontini, G; Labouvie, R; Stubenrauch, F; Vogler, A; Guarrera, V; Ott, H

2013-01-15

35

Controlling the Dynamics of an Open Many-Body Quantum System with Localized Dissipation

NASA Astrophysics Data System (ADS)

We experimentally investigate the action of a localized dissipative potential on a macroscopic matter wave, which we implement by shining an electron beam on an atomic Bose-Einstein condensate (BEC). We measure the losses induced by the dissipative potential as a function of the dissipation strength observing a paradoxical behavior when the strength of the dissipation exceeds a critical limit: for an increase of the dissipation rate the number of atoms lost from the BEC becomes lower. We repeat the experiment for different parameters of the electron beam and we compare our results with a simple theoretical model, finding excellent agreement. By monitoring the dynamics induced by the dissipative defect we identify the mechanisms which are responsible for the observed paradoxical behavior. We finally demonstrate the link between our dissipative dynamics and the measurement of the density distribution of the BEC allowing for a generalized definition of the Zeno effect. Because of the high degree of control on every parameter, our system is a promising candidate for the engineering of fully governable open quantum systems.

Barontini, G.; Labouvie, R.; Stubenrauch, F.; Vogler, A.; Guarrera, V.; Ott, H.

2013-01-01

36

NASA Astrophysics Data System (ADS)

The property of quantum many-body systems under spatial reflection and the relevant physics of the renormalization group (RG) procedure are revealed. By virtue of the matrix product state (MPS) representation, various attributes for translational invariant systems associated with spatial reflection are manifested. We demonstrate subsequently a conservation rule of the conjugative relation for reflectional MPS pairs under RG transformations and illustrate further the property of the fixed points of RG flows. Finally, we show that a similar rule exists with respect to the target states in the density matrix renormalization group algorithm.

Cen, Li-Xiang; Wang, Z. D.

2008-05-01

37

Nuclear forces and the quantum many-body problem

1. Challenges for the nuclear many-body problem Intricate nuclear forces, which have yet to be completely determined, two different fermionic species (protons and neutrons) and the lack of an external force, generate a range and diversity of behaviours that make the nucleus a truly unique quantum many-body system. One major goal of the physics of nuclei is to develop a

B R Barrett; D J Dean; M Hjorth-Jensen; J P Vary

2005-01-01

38

EDITORIAL: Focus on Quantum Information and Many-Body Theory

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

Jens Eisert; Martin B. Plenio

2010-01-01

39

NASA Astrophysics Data System (ADS)

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 ?I and it evolves according to a different final Hamiltonian ?F. If the initial state has a chaotic structure with respect to ?F, i.e., if it fills the energy shell ergodically, thermalization is certain to occur. This happens when ?I is a full random matrix, because its states projected onto ?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 ?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.

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

2013-10-01

40

Many body effects in atomic systems

NASA Astrophysics Data System (ADS)

This thesis summarizes work on the theory of many-body effects in atomic systems. The modification of emission rates and spectra for a single impurity atom embedded in a many-body system is studied. In addition, the physics of two, cold atom systems is investigated. We first study the spontaneous decay of a source atom inside a dielectric. In a microscopic picture, the photon radiated by the source atom is scattered by the medium atoms. This scattered photon is absorbed by the source atom, which results in a modification of the atom's decay rate. The calculation is carried out to second order in the medium density and we find a result that differs from the one obtained in macroscopic calculations. Using the same microscopic model, we carry out a microscopic calculation for the recoil momentum acquired by a radiating atom in a medium. In our microscopic calculation, the average value of the photon momentum is modified by its scattering with the source atoms. This gives a modification to the recoil momentum of the source atom. The calculated correction agrees with the experimental observations. In the second part of the thesis, we study two, ultra-cold atomic systems. An exactly solvable model, a Tonks-Girardeau gas with a local potential, is explained first. Such a one dimensional quantum gas has been realized recently. The spectrum of the single particle density matrix is evaluated exactly. We find the "condensate density" as a function of the potential strength. We also propose to use time-of-flight imaging to detect experimental observables. The possibility of modulating the interaction strength in space using a Feshbach resonance in a degenerate Fermi gas is examined in the last part of the thesis. Using a periodic modulation, we find that the ground state of the system contains Cooper pairs with non-zero center-of-mass momenta. The resultant single particle spectrum is found to have an additional gap along particular directions. We propose experimental schemes to detect properties of both the ground state and the quasi-particle excitations.

Fu, Hao

41

The dynamics governed by a requantized collective Hamiltonian in the coupled Lipkin model are investigated in the time-dependent variational approach with a squeezed state. It is pointed out that there is a possibility of the parametric resonance mechanism which leads to amplifying the amplitude of quantum fluctuation around the collective mode in this model.

Yasuhiko Tsue; J. D. Providência; Atsushi Kuriyama; Masatoshi Yamamura

2006-01-01

42

Quantum many-body interactions in digital oxide superlattices.

Controlling the electronic properties of interfaces has enormous scientific and technological implications and has been recently extended from semiconductors to complex oxides that host emergent ground states not present in the parent materials. These oxide interfaces present a fundamentally new opportunity where, instead of conventional bandgap engineering, the electronic and magnetic properties can be optimized by engineering quantum many-body interactions. We use an integrated oxide molecular-beam epitaxy and angle-resolved photoemission spectroscopy system to synthesize and investigate the electronic structure of superlattices of the Mott insulator LaMnO(3) and the band insulator SrMnO(3). By digitally varying the separation between interfaces in (LaMnO(3))(2n)/(SrMnO(3))(n) superlattices with atomic-layer precision, we demonstrate that quantum many-body interactions are enhanced, driving the electronic states from a ferromagnetic polaronic metal to a pseudogapped insulating ground state. This work demonstrates how many-body interactions can be engineered at correlated oxide interfaces, an important prerequisite to exploiting such effects in novel electronics. PMID:22902897

Monkman, Eric J; Adamo, Carolina; Mundy, Julia A; Shai, Daniel E; Harter, John W; Shen, Dawei; Burganov, Bulat; Muller, David A; Schlom, Darrell G; Shen, Kyle M

2012-08-19

43

Estimation of many-body quantum Hamiltonians via compressive sensing

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.

Shabani, A.; Rabitz, H. [Department of Chemistry, Princeton University, Princeton, New Jersey 08544 (United States); Mohseni, M. [Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States); Lloyd, S. [Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States); Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States); Kosut, R. L. [SC Solutions, Sunnyvale, California 94085 (United States)

2011-07-15

44

Decoherence of many-body systems due to many-body interactions

We study a spin-gas model, where N{sub S} system qubits are interacting with N{sub B} bath qubits via many-body interactions. We consider multipartite Ising interactions and show how the effect of decoherence depends on the specific coupling between the system and its environment. For instance, we analyze the influence of decoherence induced by k-body interactions for different values of k. Moreover, we study how the effect of decoherence depends on the correlation between bath qubits that are coupled to different individual system qubits and compare Markovian with non-Markovian scenarios. We derive a useful canonical form of a completely positive map that describes a class of system environment interactions with a finite size of environment correlations. As examples we consider specific quantum many-body states and investigate their evolution under different decoherence models. As a complementary investigation, we study how the coupling to the environment can be employed to generate a desired multipartite state.

Carle, T.; Kraus, B. [Institute for Theoretical Physics, University of Innsbruck, Innsbruck (Austria); Briegel, H. J. [Institute for Theoretical Physics, University of Innsbruck, Innsbruck (Austria); Institute for Quantum Optics and Quantum Information, Austrian Academy of Science, Innsbruck (Austria)

2011-07-15

45

Scattering approach to quantum transport and many body effects

NASA Astrophysics Data System (ADS)

We review a series of works discussing how the scattering approach to quantum transport developed by Landauer and Buttiker for one body elastic scatterers can be extended to the case where electron-electron interactions act inside the scattering region and give rise to many body scattering. Firstly, we give an exact numerical result showing that at zero temperature a many body scatterer behaves as an effective one body scatterer, with an interaction dependent transmission. Secondly, we underline that this effective scatterer depends on the presence of external scatterers put in its vicinity. The implications of this non local scattering are illustrated studying the conductance of a quantum point contact where electrons interact with a scanning gate microscope. Thirdly, using the numerical renormalization group developed by Wilson for the Kondo problem, we study a double dot spinless model with an inter-dot interaction U and inter-dot hopping td, coupled to leads by hopping terms tc. We show that the quantum conductance as a function of td is given by a universal function, independently of the values of U and tc, if one measures td in units of a characteristic scale ?(U,tc). Mapping the double dot system without spin onto a single dot Anderson model with spin and magnetic field, we show that ?(U,tc) = 2TK, where TK is the Kondo temperature of the Anderson model.

Pichard, Jean-Louis; Freyn, Axel

2010-12-01

46

Thermalisation of a closed quantum system: From many-body dynamics to a Fokker-Planck equation

How a closed quantum system reaches a steady state in which observables assume time-independent expectation values is both an intriguing and fundamental question in physics. When such a steady state can be described by an equilibrium thermodynamic ensemble we speak of \\

C. Ates; J. P. Garrahan; I. Lesanovsky

2011-01-01

47

Quantum Many-Body Dynamics in Optomechanical Arrays

NASA Astrophysics Data System (ADS)

We study the nonlinear driven dissipative quantum dynamics of an array of optomechanical systems. At each site of such an array, a localized mechanical mode interacts with a laser-driven cavity mode via radiation pressure, and both photons and phonons can hop between neighboring sites. The competition between coherent interaction and dissipation gives rise to a rich phase diagram characterizing the optical and mechanical many-body states. For weak intercellular coupling, the mechanical motion at different sites is incoherent due to the influence of quantum noise. When increasing the coupling strength, however, we observe a transition towards a regime of phase-coherent mechanical oscillations. We employ a Gutzwiller ansatz as well as semiclassical Langevin equations on finite lattices, and we propose a realistic experimental implementation in optomechanical crystals.

Ludwig, Max; Marquardt, Florian

2013-08-01

48

Scattering approach to quantum transport and many body effects

We review a series of works discussing how the scattering approach to quantum transport developed by Landauer and Buttiker for one body elastic scatterers can be extended to the case where electron-electron interactions act inside the scattering region and give rise to many body scattering. Firstly, we give an exact numerical result showing that at zero temperature a many body scatterer behaves as an effective one body scatterer, with an interaction dependent transmission. Secondly, we underline that this effective scatterer depends on the presence of external scatterers put in its vicinity. The implications of this non local scattering are illustrated studying the conductance of a quantum point contact where electrons interact with a scanning gate microscope. Thirdly, using the numerical renormalization group developed by Wilson for the Kondo problem, we study a double dot spinless model with an inter-dot interaction U and inter-dot hopping t{sub d}, coupled to leads by hopping terms t{sub c}. We show that the quantum conductance as a function of t{sub d} is given by a universal function, independently of the values of U and t{sub c}, if one measures t{sub d} in units of a characteristic scale {tau}(U,t{sub c}). Mapping the double dot system without spin onto a single dot Anderson model with spin and magnetic field, we show that {tau}(U,t{sub c}) 2T{sub K}, where T{sub K} is the Kondo temperature of the Anderson model.

Pichard, Jean-Louis [Service de Physique de l'Etat Condense, (CNRS URA 2464), IRAMIS/SPEC, CEA Saclay, 91191 Gif sur Yvette cedex (France); Freyn, Axel [Service de Physique de l'Etat Condense, (CNRS URA 2464), IRAMIS/SPEC, CEA Saclay, 91191 Gif sur Yvette cedex (France); Institut Neel, 25 avenue des Martyrs, BP 166, 38042 Grenoble Cedex 9 (France)

2010-12-21

49

Quantum metrology -- optical atomic clocks and many-body physics.

NASA Astrophysics Data System (ADS)

Optical clocks based on atoms confined in optical lattices provide a unique opportunity for precise study and measurement of quantum many- body systems. The state-of-the-art optical lattice clock has reached an overall fractional frequency uncertainty of 1 x 10-16 [1]. One dominant contribution to this uncertainty is clock frequency shift arising from atomic collisions. Collisions between initially identical fermionic Sr atoms can occur when they are subject to slightly inhomogeneous optical excitations during the clock operation [2]. We have recently implemented a seemingly paradoxical solution to the collisionshift problem: with a strong atomic confinement in one-dimensional tube-shaped optical traps, we dramatically increase the atomic interactions. Instead of a naively expected increase of collisional frequency shifts, these shifts are increasingly suppressed [3]. The large atomic interaction strength creates an effective energy gap in the system such that inhomogeneous excitations can no longer drive fermions into a pseudo-spin antisymmetric state, and hence their collisions and the corresponding frequency shifts are suppressed. We demonstrate the effectiveness of this approach by reducing the density-related frequency shift to the level of 10-17, representing more than a factor of ten reduction from the previous record [1, 2]. In addition, we have observed well-resolved interaction sidebands separated from the main peak of the clock transition, giving a direct evidence for the removal of the interaction energy from the clock carrier transition. Control of atomic interactions at the level of 1 x 10-17 is a testimony to our understanding of a quantum many-body system and it removes an important obstacle for building an optical atomic clock based on such systems with high accuracy. [4pt] [1] A. D. Ludlow et al., Science 319, 1805 (2008). [0pt] [2] G. K. Campbell et al., Science 324, 360 (2009). [0pt] [3] M. D. Swallows et al., Science 331, 1043 (2011).

Ye, Jun

2011-10-01

50

Optimal Control Technique for Many-Body Quantum Dynamics

NASA Astrophysics Data System (ADS)

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.

Doria, Patrick; Calarco, Tommaso; Montangero, Simone

2011-05-01

51

Optimal control technique for many-body quantum dynamics.

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 et al., Phys. Rev. Lett. 92, 130403 (2004)]. Finally, we show that the optimal pulse is robust against atom number fluctuations. PMID:21668132

Doria, Patrick; Calarco, Tommaso; Montangero, Simone

2011-05-11

52

NASA Astrophysics Data System (ADS)

Contrary to common wisdom, not everything is clear and simple in the structure of many-electron atoms. Complexity in atoms is mainly a result of interelectron interaction that leads to rather unusual behaviour. Most transparently this is manifested in photo-ionization processes of many-electron atoms and some multi-atomic objects e.g. endohedrals. Particular attention will be given to the approach describing the interaction of photons with many-electron atoms in the frame of the many-body theory based on the Feynman diagrams technique. As a suitable one-electron approximation the Hartree - Fock (HF) approach will be presented. On its ground we will include the so-called electron correlation effects and discuss the frequently used Random Phase Approximation with Exchange - RPAE. Some results of recent calculations will be presented.

Amusia, M. Ya

2011-09-01

53

NASA Astrophysics Data System (ADS)

Recent cold atom researches are reaching out far beyond the realm that was conventionally viewed as atomic physics. Many long standing issues in other physics disciplines or in Gedanken-experiments are nowadays common targets of cold atom physicists. Two prominent examples will be discussed in this talk: BEC-BCS crossover and Efimov physics. Here, cold atoms are employed to emulate electrons in superconductors, and nucleons in nuclear reactions, respectively. The ability to emulate exotic or thought systems using cold atoms stems from the precisely determined, simple, and tunable interaction properties of cold atoms. New experimental tools have also been devised toward an ultimate goal: a complete control and a complete characterization of a few- or many-body quantum system. We are tantalizingly close to this major milestone, and will soon open new venues to explore new quantum phenomena that may (or may not!) exist in scientists' dreams.

Chin, Cheng

2011-06-01

54

In his Comment [see preceding Comment, Phys. Rev. A 82, 037601 (2010)] on the paper by Roux [Phys. Rev. A 79, 021608(R) (2009)], Rigol argued that the energy distribution after a quench is not related to standard statistical ensembles and cannot explain thermalization. The latter is proposed to stem from what he calls the eigenstate thermalization hypothesis and which boils down to the fact that simple observables are expected to be smooth functions of the energy. In this Reply, we show that there is no contradiction or confusion between the observations and discussions of Roux and the expected thermalization scenario discussed by Rigol. In addition, we emphasize a few other important aspects, in particular the definition of temperature and the equivalence of ensemble, which are much more difficult to show numerically even though we believe they are essential to the discussion of thermalization. These remarks could be of interest to people interested in the interpretation of the data obtained on finite-size systems.

Roux, Guillaume [Laboratoire de Physique Theorique et Modeles Statistiques, Universite Paris-Sud, CNRS, UMR8626, Orsay F-91405 (France)

2010-09-15

55

Computational nuclear quantum many-body problem: The UNEDF project

NASA Astrophysics Data System (ADS)

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.

Bogner, S.; Bulgac, A.; Carlson, J.; Engel, J.; Fann, G.; Furnstahl, R. J.; Gandolfi, S.; Hagen, G.; Horoi, M.; Johnson, C.; Kortelainen, M.; Lusk, E.; Maris, P.; Nam, H.; Navratil, P.; Nazarewicz, W.; Ng, E.; Nobre, G. P. A.; Ormand, E.; Papenbrock, T.; Pei, J.; Pieper, S. C.; Quaglioni, S.; Roche, K. J.; Sarich, J.; Schunck, N.; Sosonkina, M.; Terasaki, J.; Thompson, I.; Vary, J. P.; Wild, S. M.

2013-10-01

56

Many-body energy localization transition in periodically driven system

NASA Astrophysics Data System (ADS)

According to the second law of thermodynamics the total entropy and energy of a system is increased during almost any dynamical process. 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. 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 periodically driven ergodic systems in the thermodynamic limit. This phenomenon is reminiscent of many-body localization in energy space. We report numerical evidence based on exact diagonalization of small spin chains and theoretical arguments based on the Magnus expansion. Our findings are valid for both classical and quantum systems.

D'Alessio, Luca; Polkovnikov, Anatoli

2013-03-01

57

Experimental Characterization of Quantum Dynamics Through Many-Body Interactions

NASA Astrophysics Data System (ADS)

We report on the implementation of a quantum process tomography technique known as direct characterization of quantum dynamics applied on coherent and incoherent single-qubit processes in a system of trapped Ca+40 ions. Using quantum correlations with an ancilla qubit, direct characterization of quantum dynamics reduces substantially the number of experimental configurations required for a full quantum process tomography and all diagonal elements of the process matrix can be estimated with a single setting. With this technique, the system’s relaxation times T1 and T2 were measured with a single experimental configuration. We further show the first, complete characterization of single-qubit processes using a single generalized measurement realized through multibody correlations with three ancilla qubits.

Nigg, Daniel; Barreiro, Julio T.; Schindler, Philipp; Mohseni, Masoud; Monz, Thomas; Chwalla, Michael; Hennrich, Markus; Blatt, Rainer

2013-02-01

58

Many-body interactions with single-electron quantum dots for topological quantum computation

We show that a many-body system of single-electron quantum dots, whose orbital states are dressed by a global magnetic field, can be described by an effective Hamiltonian with an anisotropic XZ spin-spin interaction which is proportional to the Zeeman splitting. We show that these interaction potentials give rise to spin-dependent Hubbard models with tunable nearest neighbor two-body and three-body interactions. The two-body interactions can even be switched off via the external electric field, and hence the three-body interaction plays a dominant role. The derivation of these effective interaction potentials follows from a well-controlled and systematic expansion into many-body interaction terms. Models of this type have appeared in the recent discussion of exotic quantum phases, in particular in the context of topological quantum phases and quantum computing, and we show that quantum dots can be regarded as a realistic experimental route which provides the basic building blocks and techniques toward the study of these phenomena. The main application of this derived model is to develop topological quantum computation.

Xue Peng [Department of Physics, Southeast University, Nanjing 211189 (China)

2010-05-15

59

Lattice methods for strongly interacting many-body systems

NASA Astrophysics Data System (ADS)

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.

Drut, Joaquín E.; Nicholson, Amy N.

2013-04-01

60

Convexity and the quantum many-body problem

NASA Astrophysics Data System (ADS)

We recall some properties of convex functions and, in particular, of the sum of the largest eigenvalues of a Hermitian matrix. From these properties a new estimate of an arbitrary eigenvalue of a sum of Hermitian matrices is derived, which in turn is used to compute an approximate associated spectral projector. These estimates are applied for the first time to explain the generic spectral features of quantum systems. As an application of the formalism, we explain the preponderance of certain ground-state angular momenta as observed in the vibron model with random interactions. We show that the evolution of eigenstates can be predicted from the knowledge of a limited number of spectra and investigate the effect of a three-body interaction in the vibron model on eigenenergies and eigenvectors.

Chau Huu-Tai, P.; Van Isacker, P.

2013-05-01

61

Many-Body Theory for Multi-Agent Complex Systems

Multi-agent complex systems comprising populations of decision-making particles, have wide application across the biological, informational and social sciences. We uncover a formal analogy between these systems' time-averaged dynamics and conventional many-body theory in Physics. Their behavior is dominated by the formation of 'Crowd-Anticrowd' quasiparticles. For the specific example of the Minority Game, our formalism yields analytic expressions which are in

Neil F. Johnson; David M. D. Smith; Pak Ming Hui

2005-01-01

62

NASA Astrophysics Data System (ADS)

Approximate quantum pair radial correlation functions and thermodynamic quantities for Lennard-Jones systems can be computed with Monte Carlo simulation involving Feynman-Hibbs potentials. A convolution approach to produce the quantum pair radial function from the direct Monte Carlo structural results is presented by analysing its connection with the path-integral instantaneous and linear response pair radial functions. Several Lennard-Jones systems with substantial quantum behaviour: methane, argon, neon, deuterium and helium-4 (eighteen state points) are studied. For the sake of comparison, new path-integral simulations of helium-4 and improved path-integral results for methane are also reported. The effective potential results are in close agreement with experimental and exact path-integral data over a wide range of de Broglie wavelengths, densities and temperatures.

Sesé, Luis M.

63

Quantum Many-Body Theory and Mechanisms for Low Energy Nuclear Reaction Processes in Matter

Recently, a theoretical model of Bose-Einstein Condensation (BEC) mechanism has been developed to describe low-energy nuclear reaction in a quantum many-body system confined in a micro\\/nano scale trap. The BEC mechanism is applied to explain various anomalous results observed recently in experiments involved with low-energy nuclear reaction processes in matter and in acoustic cavitation. Experimental tests of the BEC mechanism

Y. E. Kim

2004-01-01

64

Quantum many-body theory and mechanisms for low energy nuclear reaction processes in matter

Recently, a theoretical model of Bose-Einstein Condensation (BEC) mechanism has been developed to describe low-energy nuclear reaction in a quantum many-body system confined in a micro\\/nano scale trap. The BEC mechanism is applied to explain various anomalous results observed recently in experiments involved with low-energy nuclear reaction processes in matter and in acoustic cavitation. Experimental tests of the BEC mechanism

Yeong E. Kim

2004-01-01

65

Many-Body Theory for Multi-Agent Complex Systems

Multi-agent complex systems comprising populations of decision-making\\u000aparticles, have wide application across the biological, informational and\\u000asocial sciences. We uncover a formal analogy between these systems'\\u000atime-averaged dynamics and conventional many-body theory in Physics. Their\\u000abehavior is dominated by the formation of 'Crowd-Anticrowd' quasiparticles. For\\u000athe specific example of the Minority Game, our formalism yields analytic\\u000aexpressions which are in

Neil F. Johnson; David M. D. Smith; Pak Ming Hui

2005-01-01

66

Lattice simulations for few- and many-body systems

NASA Astrophysics Data System (ADS)

We review the recent literature on lattice simulations for few- and many-body systems. We focus on methods that combine the framework of effective field theory with computational lattice methods. Lattice effective field theory is discussed for cold atoms as well as low-energy nucleons with and without pions. A number of different lattice formulations and computational algorithms are considered, and an effort is made to show common themes in studies of cold atoms and low-energy nuclear physics as well as common themes in work by different collaborations.

Lee, Dean

2009-07-01

67

Many-Body Green Function of Degenerate Systems

A rigorous nonperturbative adiabatic approximation of the evolution operator in the many-body physics of degenerate systems is derived. This approximation is used to solve the long-standing problem of the choice of the initial states of H{sub 0} leading to eigenstates of H{sub 0}+V for degenerate systems. These initial states are eigenstates of P{sub 0}VP{sub 0}, where P{sub 0} is the projection onto a degenerate eigenspace of H{sub 0}. This result is used to give the proper definition of the Green function, the statistical Green function and the nonequilibrium Green function of degenerate systems. The convergence of these Green functions is established.

Brouder, Christian [Institut de Mineralogie et de Physique des Milieux Condenses, CNRS UMR 7590, Universites Paris 6 et 7, IPGP, 140 rue de Lourmel, 75015 Paris (France); Panati, Gianluca [Dipartimento di Matematica, Universita di Roma La Sapienza, Roma (Italy); Stoltz, Gabriel [Universite Paris Est, CERMICS, Projet MICMAC ENPC-INRIA, 6 and 8 Avenue Pascal, 77455 Marne-la-Vallee Cedex 2 (France)

2009-12-04

68

NASA Astrophysics Data System (ADS)

We show a general approach for detecting genuine multipartite entanglement and partial inseparability in many-body systems by means of macroscopic observables (such as the energy) only. We show that the obtained criteria detect large areas of genuine multipartite entanglement and partial entanglement in typical mixed many-body states, which are not detected by other criteria. As genuine multipartite entanglement is a necessary property for several quantum information theoretic applications such as, e.g., secret sharing or certain kinds of quantum computation, our methods can be used to select or design appropriate condensed matter systems.

Gabriel, A.; Hiesmayr, B. C.

2013-02-01

69

Many-body dynamics of a Bose system with attractive interactions on a ring

We investigate the many-body dynamics of an effectively attractive one-dimensional Bose system confined in a toroidal trap. The mean-field theory predicts that a bright-soliton state will be formed when the interparticle interaction increases over a critical point. The study of quantum many-body dynamics in this paper reveals that there is a modulation instability in a finite Bose system correspondingly. We show that Shannon entropy becomes irregular near and above the critical point due to quantum correlations. We also study the dynamical behavior of the instability by exploring the momentum distribution and the fringe visibility, which can be verified experimentally by releasing the trap.

Li Weibin [Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071 (China); Graduate School, Chinese Academy of Sciences, Beijing 10080 (China); Department of Physics, Huazhong University of Science and Technology, Wuhan 430074 (China); Xie Xiaotao; Yang Xiaoxue [Department of Physics, Huazhong University of Science and Technology, Wuhan 430074 (China); Zhan Zhiming [School of Physics and Information Engineering, Jianghan University, Wuhan 430056 (China)

2005-10-15

70

GRAVITATIONAL PHASE TRANSITIONS IN THE COSMOLOGICAL MANY-BODY SYSTEM

Gravitational many-body clustering of particles (e.g., galaxies) in an expanding universe may be regarded as a form of phase transition. We calculate its properties here and find that it differs in several ways from usual laboratory phase transitions. The cosmological case is never complete since it takes longer to evolve dynamically on larger spatial scales. To examine this, we calculate the effects of higher order corrections on the thermodynamic properties and distribution functions (which are known to agree with observations). The additional higher order terms are subdominant and decrease as the number of particles in the system increases. We also propose an order parameter for this hierarchical phase transition and discuss its relation to the Yang-Lee theory of phase transitions. These results also help to quantify earlier ideas of 'continuous clustering'.

Saslaw, William C. [Astronomy Department, University of Virginia, Charlottesville, VA 22904 (United States); Ahmad, Farooq, E-mail: wcs@virginia.ed, E-mail: farphy@kashmiruniversity.ac.i [Institute of Astronomy, Madingley Road, Cambridge CB3 OHA (United Kingdom)

2010-09-10

71

Experimental quantum simulations of many-body physics with trapped ions.

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. PMID:22790343

Schneider, Ch; Porras, Diego; Schaetz, Tobias

2012-01-17

72

Long-distance entanglement in many-body atomic and optical systems

We discuss the phenomenon of long-distance entanglement (LDE) in the ground state of quantum spin models, its use in high-fidelity and robust quantum communication, and its realization in many-body systems of ultracold atoms in optical lattices and in arrays of coupled optical cavities. We investigate XX quantum spin models on one-dimensional lattices with open ends and different patterns of site-dependent

Salvatore M. Giampaolo; Fabrizio Illuminati

2010-01-01

73

Short-time-evolved wave functions for solving quantum many-body problems

NASA Astrophysics Data System (ADS)

The exact ground state of a strongly interacting quantum many-body system can be obtained by evolving a trial state with finite overlap with the ground state to infinite imaginary time. In many cases, since the convergence is exponential, the system converges essentially to the exact ground state in a relatively short time. Thus a short-time evolved wave function can be an excellent approximation to the exact ground state. Such a short-time-evolved wave function can be obtained by factorizing, or splitting, the evolution operator to high order. However, for the imaginary time Schrödinger equation, which contains an irreversible diffusion kernel, all coefficients, or time steps, must be positive. (Negative time steps would require evolving the diffusion process backward in time, which is impossible.) Heretofore, only second-order factorization schemes can have all positive coefficients, but without further iterations, these cannot be used to evolve the system long enough to be close to the exact ground state. In this work, we use a newly discovered fourth-order positive factorization scheme which requires knowing both the potential and its gradient. We show that the resulting fourth-order wave function alone, without further iterations, gives an excellent description of strongly interacting quantum systems such as liquid 4He, comparable to the best variational results in the literature. This suggests that such a fourth-order wave function can be used to study the ground state of diverse quantum many-body systems, including Bose-Einstein condensates and Fermi systems.

Ciftja, Orion; Chin, Siu A.

2003-10-01

74

A Relativistic Glauber Expansion for Many-Body System.

National Technical Information Service (NTIS)

According to the composite field theory, using the physical approximation essentially the same as Glauber's, and extending the generalized ladder summation method, the authors obtain an expression of the many-body amplitude of a high energy particle scatt...

Z. Xiquan H. Zuoxiu Z. Weiqin B. Chengguang

1979-01-01

75

Two-band Bose-Hubbard model for many-body resonant tunneling in the Wannier-Stark system

NASA Astrophysics Data System (ADS)

We study an experimentally realizable paradigm of complex many-body quantum systems, a two-band Wannier-Stark model, for which diffusion in Hilbert space as well as many-body Landau-Zener processes can be engineered. A crossover between regular and quantum chaotic spectra is found within the many-body avoided crossings at resonant tunneling conditions. The spectral properties are shown to determine the evolution of states across a cascade of Landau-Zener events. We apply the obtained spectral information to study the nonequilibrium dynamics of our many-body system in different parameter regimes.

Parra-Murillo, Carlos A.; Madroñero, Javier; Wimberger, Sandro

2013-09-01

76

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

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 ?-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

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

2012-08-06

77

Degeneracy of Many-Body Quantum States in an Optical Lattice under a Uniform Magnetic Field

We prove a theorem that shows the degeneracy of many-body states for particles in a periodic lattice and under a uniform magnetic field depends on the total particle number and the flux filling ratio. Noninteracting fermions and weakly interacting bosons are given as two examples. For the latter case, the phenomenon can also be physically understood in terms of destructive quantum interference of multiple symmetry-related tunneling paths between classical energy minima, which is reminiscent of the spin-parity effect discovered in magnetic molecular clusters. We also show that the quantum ground state of a mesoscopic number of bosons in this system is not a simple mean-field state but a fragmented state even for very weak interactions.

Zhang Jian; Jian Chaoming; Zhai Hui [Institute for Advanced Study, Tsinghua University, Beijing, 100084 (China); Ye Fei [College of Material Science and Optoelectronics Technology, Graduated University of Chinese Academy of Science, Beijing 100049 (China)

2010-10-08

78

Many-Body Quantum Theory in Condensed Matter Physics—An Introduction

This is undoubtedly an ambitious book. It aims to provide a wide ranging, yet self-contained and pedagogical introduction to techniques of quantum many-body theory in condensed matter physics, without losing mathematical `rigor' (which I hope means rigour), and with an eye on physical insight, motivation and application. The authors certainly bring plenty of experience to the task, the book having

D E Logan

2005-01-01

79

BOOK REVIEW: Many-Body Quantum Theory in Condensed Matter Physics---An Introduction

This is undoubtedly an ambitious book. It aims to provide a wide ranging, yet self-contained and pedagogical introduction to techniques of quantum many-body theory in condensed matter physics, without losing mathematical `rigor' (which I hope means rigour), and with an eye on physical insight, motivation and application. The authors certainly bring plenty of experience to the task, the book having

H. Bruus; K. Flensberg

2005-01-01

80

Magnetic Field Dependence of Many-Body Enhanced Electron Tunnelling Through a Quantum Dot

We consider many-body enhanced electron tunnelling through an InAs quantum dot in magnetic field applied perpendicular to the tunneling direction. Critical exponent of Fermi edge singularity in tunneling current is calculated as a function of magnetic field. We use lowest Landau level approximation for electrons in emitter and perform scattering matrix calculation in Born approximation. Results are compared with recent

Ivan A. Larkin; E. E. Vdovin; Yu. N. Khanin; M. Henini

2009-01-01

81

Algorithm for simulation of quantum many-body dynamics using dynamical coarse-graining

NASA Astrophysics Data System (ADS)

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 n3/2(lnn)-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 2×104 and 2×106 cold atoms in a double-well trap, described by the two-site Bose-Hubbard model.

Khasin, M.; Kosloff, R.

2010-04-01

82

Algorithm for simulation of quantum many-body dynamics using dynamical coarse-graining

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.

Khasin, M. [Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824 (United States); Fritz Haber Research Center for Molecular Dynamics, Hebrew University of Jerusalem, Jerusalem 91904 (Israel); Kosloff, R. [Fritz Haber Research Center for Molecular Dynamics, Hebrew University of Jerusalem, Jerusalem 91904 (Israel)

2010-04-15

83

Many-body force and mobility measurements in colloidal systems

NASA Astrophysics Data System (ADS)

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.

Merrill, Jason W.

84

Dynamical Phase Transitions and Instabilities in Open Atomic Many-Body Systems

We discuss an open driven-dissipative many-body system, in which the competition of unitary Hamiltonian and dissipative Liouvillian dynamics leads to a nonequilibrium phase transition. It shares features of a quantum phase transition in that it is interaction driven, and of a classical phase transition, in that the ordered phase is continuously connected to a thermal state. We characterize the phase diagram and the critical behavior at the phase transition approached as a function of time. We find a novel fluctuation induced dynamical instability, which occurs at long wavelength as a consequence of a subtle dissipative renormalization effect on the speed of sound.

Diehl, Sebastian; Micheli, Andrea; Zoller, Peter [Institute for Theoretical Physics, University of Innsbruck, Technikerstrasse 25, A-6020 Innsbruck (Austria); Institute for Quantum Optics and Quantum Information of the Austrian Academy of Sciences, A-6020 Innsbruck (Austria); Tomadin, Andrea [Institute for Quantum Optics and Quantum Information of the Austrian Academy of Sciences, A-6020 Innsbruck (Austria); NEST, Scuola Normale Superiore and Istituto Nanoscienze-CNR, Pisa (Italy); Fazio, Rosario [NEST, Scuola Normale Superiore and Istituto Nanoscienze-CNR, Pisa (Italy)

2010-07-02

85

Ground-state entanglement in a system with many-body interactions

Entanglement refers to the inability of many-body quantum mechanical systems to be separated into independent subsystems. This has been well investigated in systems consisting of two entangled subsystems. In larger systems, more complex types of entanglement exist. In a system consisting of three subsystems (e.g., qubits), it is possible that all three subsystems are entangled with each other in a way that cannot be reduced to bipartite entanglement, and it is known that two different, inequivalent forms of tripartite entanglement exist such as the GHZ and W states (GHZ denotes 'Greenberger-Horne-Zeilinger'). Here, we investigate a particularly interesting system with competing one-, two-, and three-body interactions. Its ground state can be a product state, a GHZ state, or a W state, depending on the type and strength of the spin-spin couplings. By varying an external control parameter, the system can be made to undergo quantum transitions between the various ground-state-entanglement phases. We implement the system in an NMR quantum simulator and use adiabatic evolution of the effective Hamiltonian to drive the system through the quantum transitions. In the experimental and numerical simulations, we check the suitability of different observables for making the quantum transitions visible and for characterizing the different phases.

Peng Xinhua [Hefei National Laboratory for Physical Sciences at Microscale and Department of Modern Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China); Fakultaet Physik, Technische Universitaet Dortmund, D-44221 Dortmund (Germany); Zhang Jingfu; Suter, Dieter [Fakultaet Physik, Technische Universitaet Dortmund, D-44221 Dortmund (Germany); Du Jiangfeng [Hefei National Laboratory for Physical Sciences at Microscale and Department of Modern Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China)

2010-04-15

86

NASA Astrophysics Data System (ADS)

The current worldwide effort to use cold atoms in optical lattices to simulate strongly correlated electron systems, referred to as Quantum Simulation, is a highly ambitious program in cold atom physics. Its success requires reaching temperatures far below nano Kelvin. Cooling to such low temperatures is the greatest challenge confronting this program. At the same time, to realize the full power of Quantum Simulation, one needs to find ways to deduce the equilibrium properties of homogenous systems from the data of trapped gases. In this talk, we shall discuss methods to achieve these goals.

Ho, Tin-Lun

2010-03-01

87

Simulation of Complete Many-Body Quantum Dynamics Using Controlled Quantum-Semiclassical Hybrids

A controlled hybridization between full quantum dynamics and semiclassical approaches (mean-field and truncated Wigner) is implemented for interacting many-boson systems. It is then demonstrated how simulating the resulting hybrid evolution equations allows one to obtain the full quantum dynamics for much longer times than is possible using an exact treatment directly. A collision of sodium BECs with 1.5x10{sup 5} atoms is simulated, in a regime that is difficult to describe semiclassically. The uncertainty of physical quantities depends on the statistics of the full quantum prediction. Cutoffs are minimized to a discretization of the Hamiltonian. The technique presented is quite general and extension to other systems is considered.

Deuar, P. [Laboratoire de Physique Theorique et Modeles Statistiques, Universite Paris-Sud, CNRS, 91405 Orsay (France)

2009-09-25

88

BOOK REVIEW: Many-Body Quantum Theory in Condensed Matter Physics—An Introduction

NASA Astrophysics Data System (ADS)

This is undoubtedly an ambitious book. It aims to provide a wide ranging, yet self-contained and pedagogical introduction to techniques of quantum many-body theory in condensed matter physics, without losing mathematical `rigor' (which I hope means rigour), and with an eye on physical insight, motivation and application. The authors certainly bring plenty of experience to the task, the book having grown out of their graduate lectures at the Niels Bohr Institute in Copenhagen over a five year period, with the feedback and refinement this presumably brings. The book is also of course ambitious in another sense, for it competes in the tight market of general graduate/advanced undergraduate texts on many-particle physics. Prospective punters will thus want reasons to prefer it to, or at least give it space beside, well established texts in the field. Subject-wise, the book is a good mix of the ancient and modern, the standard and less so. Obligatory chapters deal with the formal cornerstones of many-body theory, from second quantization, time-dependence in quantum mechanics and linear response theory, to Green's function and Feynman diagrams. Traditional topics are well covered, including two chapters on the electron gas, chapters on phonons and electron phonon coupling, and a concise account of superconductivity (confined, no doubt judiciously, to the conventional BCS case). Less mandatory, albeit conceptually vital, subjects are also aired. These include a chapter on Fermi liquid theory, from both semi-classical and microscopic perspectives, and a freestanding account of one-dimensional electron gases and Luttinger liquids which, given the enormity of the topic, is about as concise as it could be without sacrificing clarity. Quite naturally, the authors' own interests also influence the choice of material covered. A persistent theme, which brings a healthy topicality to the book, is the area of transport in mesoscopic systems or nanostructures. Two chapters, some fifty pages of the book, are devoted to electron transport in mesoscopic systems; the one on interacting systems is preceded by a brief account of equation of motion techniques a relative rarity in a general text, used here to provide background to subsequent discussion of the Coulomb blockade in quantum dots. So does it work, and will it find a niche beside other established, wide ranging texts? On the whole I think the answer has to be yes. To begin with, the book is well organised and user-friendly, which must surely appeal to students (and their mentors). The chapters are typically bite-sized and digestible. Each is accompanied by a summary/outlook, which in doing just that attempts to place the specific topic in a wider context, together with a set of problems that illustrate, and in many cases expand substantially on, the basic subject matter. A particularly healthy feature of the book is the extent to which the authors have sought where possible to include physical and/or material applications of basic theory, thereby enlivening old material and enhancing appreciation of the new. The first chapter on the electron gas, for example, introduces the reader to a range of material examples, including 2D heterostructures, carbon nanotubes and quantum dots. A chapter on the formalism of Green's functions takes time out to explain how the single-particle spectral function can be measured by tunnelling spectroscopy, while discussion of impurity scattering and conductivity is refreshed by consideration of weak localization in bulk and mesoscopic systems, and the phenomenon of universal conductance fluctuations. And so on: in a text that could readily descend to the purely formal, the authors have clearly taken seriously the task of incorporating relevant, topical applications of the underlying theory. In a book as wide ranging as this any reviewer is of course bound to perceive the occasional deficiency. I felt for example that some aspects of the discussion of conductance in quantum dots, notably the Coulomb blockade and the Kondo effect, were not quite up to scratch

Logan, D. E.

2005-02-01

89

Macroscopic quantum many-body tunneling of attractive Bose-Einstein condensate in anharmonic trap

NASA Astrophysics Data System (ADS)

We study the stability of attractive atomic Bose-Einstein condensate and the macroscopic quantum many-body tunneling (MQT) in the anharmonic trap. We utilize correlated two-body basis function which keeps all possible two-body correlations. The anharmonic parameter (?) is slowly tuned from harmonic to anharmonic. For each choice of ? the many-body equation is solved adiabatically. The use of the van der Waals interaction gives realistic picture which substantially differs from the mean-field results. For weak anharmonicity, we observe that the attractive condensate gains stability with larger number of bosons compared to that in the pure harmonic trap. The transition from resonances to bound states with weak anharmonicity also differs significantly from the earlier study of [N. Moiseyev, L.D. Carr, B.A. Malomed, Y.B. Band, J. Phys. B 37, L193 (2004)]. We also study the tunneling of the metastable condensate very close to the critical number Ncr of collapse and observe that near collapse the MQT is the dominant decay mechanism compared to the two-body and three-body loss rate. We also observe the power law behavior in MQT near the critical point. The results for pure harmonic trap are in agreement with mean-field results. However, we fail to retrieve the power law behavior in anharmonic trap although MQT is still the dominant decay mechanism.

Haldar, Sudip Kumar; Debnath, Pankaj Kumar; Chakrabarti, Barnali

2013-09-01

90

Collective many-body van der Waals interactions in molecular systems.

Van der Waals (vdW) interactions are ubiquitous in molecules and condensed matter, and play a crucial role in determining the structure, stability, and function for a wide variety of systems. The accurate prediction of these interactions from first principles is a substantial challenge because they are inherently quantum mechanical phenomena that arise from correlations between many electrons within a given molecular system. We introduce an efficient method that accurately describes the nonadditive many-body vdW energy contributions arising from interactions that cannot be modeled by an effective pairwise approach, and demonstrate that such contributions can significantly exceed the energy of thermal fluctuations--a critical accuracy threshold highly coveted during molecular simulations--in the prediction of several relevant properties. Cases studied include the binding affinity of ellipticine, a DNA-intercalating anticancer agent, the relative energetics between the A- and B-conformations of DNA, and the thermodynamic stability among competing paracetamol molecular crystal polymorphs. Our findings suggest that inclusion of the many-body vdW energy is essential for achieving chemical accuracy and therefore must be accounted for in molecular simulations. PMID:22923693

DiStasio, Robert A; von Lilienfeld, O Anatole; Tkatchenko, Alexandre

2012-08-24

91

A formal derivation of a generalized equation of a Wigner distribution function including all many-body effects and all scattering mechanisms is given. The result is given in integral operator form suitable for application to the numerical modeling of quantum tunneling and quantum interference solid state devices. In the absence of scattering and many-body effects, the result reduces to the “noninteracting-particle”

F. A. Buot

1990-01-01

92

Light clusters in nuclear matter: Excluded volume versus quantum many-body approaches

NASA Astrophysics Data System (ADS)

The formation of clusters in nuclear matter is investigated, which occurs, e.g., in low-energy heavy-ion collisions or core-collapse supernovae. In astrophysical applications, the excluded volume concept is commonly used for the description of light clusters. Here we compare a phenomenological excluded volume approach to two quantum many-body models, the quantum statistical model and the generalized relativistic mean-field model. All three models contain bound states of nuclei with mass number A?4. It is explored to which extent the complex medium effects can be mimicked by the simpler excluded volume model, regarding the chemical composition and thermodynamic variables. Furthermore, the role of heavy nuclei and excited states is investigated by use of the excluded volume model. At temperatures of a few MeV the excluded volume model gives a poor description of the medium effects on the light clusters, but there the composition is actually dominated by heavy nuclei. At larger temperatures there is a rather good agreement, whereas some smaller differences and model dependencies remain.

Hempel, Matthias; Schaffner-Bielich, Jürgen; Typel, Stefan; Röpke, Gerd

2011-11-01

93

Long-distance entanglement in many-body atomic and optical systems

NASA Astrophysics Data System (ADS)

We discuss the phenomenon of long-distance entanglement (LDE) in the ground state of quantum spin models, its use in high-fidelity and robust quantum communication, and its realization in many-body systems of ultracold atoms in optical lattices and in arrays of coupled optical cavities. We investigate XX quantum spin models on one-dimensional lattices with open ends and different patterns of site-dependent interaction couplings, singling out two general settings: patterns that allow for perfect LDE in the ground state of the system, namely such that the end-to-end entanglement remains finite in the thermodynamic limit, and patterns of quasi-long-distance entanglement (QLDE) in the ground state of the system, namely such that the end-to-end entanglement vanishes with a very slow power-law decay as the length of the spin chain is increased. We discuss physical realizations of these models in ensembles of ultracold bosonic atoms loaded in optical lattices. We show how, using either suitably engineered super-lattice structures or exploiting the presence of edge impurities in lattices with single periodicity, it is possible to realize models endowed with nonvanishing LDE or QLDE. We then study how to realize models that optimize the robustness of QLDE at finite temperature and in the presence of imperfections using suitably engineered arrays of coupled optical cavities. For both cases the numerical estimates of the end-to-end entanglement in the actual physical systems are thoroughly compared with the analytical results obtained for the spin model systems. We finally introduce LDE-based schemes of long-distance quantum teleportation in linear arrays of coupled cavities, and show that they allow for high-fidelity and high success rates even at moderately high temperatures.

Giampaolo, Salvatore M.; Illuminati, Fabrizio

2010-02-01

94

Charge-optimized many-body potential for the hafnium\\/hafnium oxide system

A dynamic-charge, many-body potential function is proposed for the hafnium\\/hafnium oxide system. It is based on an extended Tersoff potential for semiconductors and the charge-optimized many-body potential for silicon oxide. The materials fidelity of the proposed formalism is demonstrated for both hafnium metal and various hafnia polymorphs. In particular, the correct orders of the experimentally observed polymorphs of both the

Tzu-Ray Shan; Bryce D. Devine; Travis W. Kemper; Susan B. Sinnott; Simon R. Phillpot

2010-01-01

95

A many-body generalization of the Z2 topological invariant for the quantum spin Hall effect

We propose a many-body generalization of the Z2 topological invariant for the quantum spin Hall insulator, which does not rely on single-particle band structures. The invariant is derived as a topological obstruction that distinguishes topologically distinct many-body ground states on a torus. It is also expressed as a Wilson-loop of the SU(2) Berry gauge field, which is quantized due to

Sung-Sik Lee; Shinsei Ryu

2008-01-01

96

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

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.

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

1997-10-01

97

NASA Astrophysics Data System (ADS)

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.

Jones, Andrew P.; Crain, Jason; Sokhan, Vlad P.; Whitfield, Troy W.; Martyna, Glenn J.

2013-04-01

98

Spin-Reversed Quasiparticles in the Fractional Quantum Hall Effect - Many-Body Approach.

National Technical Information Service (NTIS)

The elementary excitations at 1/3 Landau-level filling have been studied in the many-body variational approach. In the absence of Zeeman energy, the lowest energy excitations involve spin-reversed quasiparticles. The proper excitation energies including t...

T. Chakraborty

1986-01-01

99

Charge-optimized many-body potential for the hafnium/hafnium oxide system

NASA Astrophysics Data System (ADS)

A dynamic-charge, many-body potential function is proposed for the hafnium/hafnium oxide system. It is based on an extended Tersoff potential for semiconductors and the charge-optimized many-body potential for silicon oxide. The materials fidelity of the proposed formalism is demonstrated for both hafnium metal and various hafnia polymorphs. In particular, the correct orders of the experimentally observed polymorphs of both the metal and the oxide are obtained. Satisfactory agreement is found for the structural and mechanical properties, defect energetics, and phase stability as compared to first-principles calculations and/or experimental values. The potential can be used in conjunction with the previously determined potentials for the Si and SiO2 system. This transferability is demonstrated by comparing the structure of a hafnia/silicon interface to that previously determined from electronic-structure calculations.

Shan, Tzu-Ray; Devine, Bryce D.; Kemper, Travis W.; Sinnott, Susan B.; Phillpot, Simon R.

2010-03-01

100

Charge optimized many-body potential for the Si\\/SiOâ system

A dynamic-charge, many-body potential for the Si\\/SiOâ system, based on an extended Tersoff potential for semiconductors, is proposed and implemented. The validity of the potential function is tested for both pure silicon and for five polymorphs of silica, for which good agreement is found between the calculated and experimental structural parameters and energies. The dynamic charge transfer intrinsic to the

Yu Jianguo; Susan B. Sinnott; Simon R. Phillpot

2007-01-01

101

Charge optimized many-body potential for the Si\\/SiO2 system

A dynamic-charge, many-body potential for the Si\\/SiO2 system, based on an extended Tersoff potential for semiconductors, is proposed and implemented. The validity of the potential function is tested for both pure silicon and for five polymorphs of silica, for which good agreement is found between the calculated and experimental structural parameters and energies. The dynamic charge transfer intrinsic to the

Jianguo Yu; Susan B. Sinnott; Simon R. Phillpot

2007-01-01

102

Nuclear quantum many-body dynamics. From collective vibrations to heavy-ion collisions

NASA Astrophysics Data System (ADS)

A summary of recent researches on nuclear dynamics with realistic microscopic quantum approaches is presented. The Balian-Vénéroni variational principle is used to derive the time-dependent Hartree-Fock (TDHF) equation describing the dynamics at the mean-field level, as well as an extension including small-amplitude quantum fluctuations which is equivalent to the time-dependent random-phase approximation (TDRPA). Such formalisms as well as their practical implementation in the nuclear physics framework with modern three-dimensional codes are discussed. Recent applications to nuclear dynamics, from collective vibrations to heavy-ion collisions are presented. Particular attention is devoted to the interplay between collective motions and internal degrees of freedom. For instance, the harmonic nature of collective vibrations is questioned. Nuclei are also known to exhibit superfluidity due to pairing residual interaction. Extensions of the theoretical approach to study such pairing vibrations are now available. Large amplitude collective motions are investigated in the framework of heavy-ion collisions leading, for instance, to the formation of a compound system. How fusion is affected by the internal structure of the collision partners, such as their deformation, is discussed. Other mechanisms in competition with fusion, and responsible for the formation of fragments which differ from the entrance channel (transfer reactions, deep-inelastic collisions, and quasi-fission) are investigated. Finally, studies of actinide collisions forming, during very short times of few zeptoseconds, the heaviest nuclear systems available on Earth, are presented.

Simenel, Cédric

2012-11-01

103

Many-body theory of carrier capture and relaxation in semiconductor quantum-dot lasers

For quantum dots on a wetting layer, the role of Coulomb scattering and carrier-phonon interaction for carrier capture and relaxation of carriers between the quantum-dot levels are studied theoretically

T. R. Nielsen; P. Gartner; F. Jahnke

2004-01-01

104

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

NASA Astrophysics Data System (ADS)

In this work we present a reaction module for "Chaos Many-Body Engine" (Grossu et al., 2010 [1]). Following our goal of creating a customizable, object oriented code library, the list of all possible reactions, including the corresponding properties (particle types, probability, cross section, particle lifetime, etc.), could be supplied as parameter, using a specific XML input file. Inspired by the Poincaré section, we propose also the "Clusterization Map", as a new intuitive analysis method of many-body systems. For exemplification, we implemented a numerical toy-model for nuclear relativistic collisions at 4.5 A?GeV/c (the SKM200 Collaboration). An encouraging agreement with experimental data was obtained for momentum, energy, rapidity, and angular ? distributions.

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

2012-04-01

105

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

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 and show that the lack of self-consistency may lead to physically wrong predictions. The convergence of the general MCHB(M) scheme with a growing number M is validated in a specific case of two bosons trapped in a symmetric double well.

Streltsov, Alexej I.; Alon, Ofir E.; Cederbaum, Lorenz S. [Theoretische Chemie, Universitaet Heidelberg, D-69120 Heidelberg (Germany)

2006-06-15

106

We show that in a semiconductor quantum wire the energy relaxation of the excited one-dimensional electron gas due to acoustic phonon emission is strongly enhanced at low temperatures by a subtle many-body effect arising from the broadening caused by the electron-acoustic-phonon interaction. This broadening opens up a ``virtual'' channel for energy transfer from the electrons to the low energy tail

J. R. Senna; S. Das Sarma

1993-01-01

107

Chaos in fermionic many-body systems and the metal-insulator transition

We show that finite Fermi systems governed by a mean field and a few-body interaction generically possess spectral fluctuations of the Wigner-Dyson type and are, thus, chaotic. Our argument is based on an analogy to the metal-insulator transition. We construct a sparse random-matrix scaffolding ensemble (ScE) that mimics this transition. Our claim then follows from the fact that the generic random-matrix ensemble modeling a fermionic interacting many-body system is much less sparse than ScE.

Papenbrock, T. [Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996 (United States); Physics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States); Pluhar, Z. [Institute of Particle and Nuclear Physics, Faculty of Mathematics and Physics, Charles University, CZ-18000 Praha 8 (Czech Republic); Tithof, J. [Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996 (United States); Weidenmueller, H. A. [Max-Planck-Institut fuer Kernphysik, DE-69029 Heidelberg (Germany)

2011-03-15

108

Chaos in Fermionic Many-Body Systems and the Metal Insulator Transition

We show that finite Fermi systems governed by a mean field and a few-body interaction generically possess spectral fluctuations of the Wigner-Dyson type and are thus chaotic. Our proof is based on an analogy to the metal-insulator transition. We construct a sparse random-matrix ensemble H^{cr} that mimicks that transition. Our claim then follows from the fact that the generic random-matrix ensemble modeling a fermionic interacting many-body is much less sparse than H^{cr}.

Papenbrock, Thomas F [ORNL; Pluhar, Z. [Charles University, Prague, Czech Republic; Tithof, J. [University of Tennessee, Knoxville (UTK); Weidenmueller, H. A. [Max-Planck Institut fur Kernphysik, Heidelberg, Germany

2011-01-01

109

Charge optimized many-body potential for the Si/SiO{sub 2} system

A dynamic-charge, many-body potential for the Si/SiO{sub 2} system, based on an extended Tersoff potential for semiconductors, is proposed and implemented. The validity of the potential function is tested for both pure silicon and for five polymorphs of silica, for which good agreement is found between the calculated and experimental structural parameters and energies. The dynamic charge transfer intrinsic to the potential function allows the interface properties to be captured automatically, as demonstrated for the silicon/{beta}-cristobalite interface.

Yu Jianguo; Sinnott, Susan B.; Phillpot, Simon R. [Department of Materials Science and Engineering, University of Florida, Gainesville, Florida 32611-6400 (United States)

2007-02-15

110

We investigate the effect of an applied magnetic field on resonant tunneling of electrons through the bound states of self-assembled InAs quantum dots (QDs) embedded within an (AlGa)As tunnel barrier. At low temperatures (no more than 2 K), a magnetic field B applied either parallel or perpendicular to the direction of current flow causes a significant enhancement of the tunnel

E. E. Vdovin; Yu. N. Khanin; O. Makarovsky; A. Patane; L. Eaves; M. Henini; C. J. Mellor; K. A. Benedict; R. Airey

2007-01-01

111

Long-Range Interacting Many-Body Systems with Alkaline-Earth-Metal Atoms

NASA Astrophysics Data System (ADS)

Alkaline-earth-metal atoms can exhibit long-range dipolar interactions, which are generated via the coherent exchange of photons on the P03-D13 transition of the triplet manifold. In the case of bosonic strontium, which we discuss here, this transition has a wavelength of 2.6?m and a dipole moment of 4.03 D, and there exists a magic wavelength permitting the creation of optical lattices that are identical for the states P03 and D13. This interaction enables the realization and study of mixtures of hard-core lattice bosons featuring long-range hopping, with tunable disorder and anisotropy. We derive the many-body master equation, investigate the dynamics of excitation transport, and analyze spectroscopic signatures stemming from coherent long-range interactions and collective dissipation. Our results show that lattice gases of alkaline-earth-metal atoms permit the creation of long-lived collective atomic states and constitute a simple and versatile platform for the exploration of many-body systems with long-range interactions. As such, they represent an alternative to current related efforts employing Rydberg gases, atoms with large magnetic moment, or polar molecules.

Olmos, B.; Yu, D.; Singh, Y.; Schreck, F.; Bongs, K.; Lesanovsky, I.

2013-04-01

112

NASA Astrophysics Data System (ADS)

We consider the 3D quantum many-body dynamics describing a dilute Bose gas with strong confinement in one direction. We study the corresponding Bogoliubov-Born-Green-Kirkwood-Yvon (BBGKY) hierarchy, which contains a diverging coefficient as the strength of the confining potential tends to ?. We find that this diverging coefficient is counterbalanced by the limiting structure of the density matrices and we establish the convergence of the BBGKY hierarchy. Moreover, we prove that the limit is fully described by a 2D cubic nonlinear Schrödinger equation (NLS) and we obtain the exact 3D to 2D coupling constant.

Chen, Xuwen; Holmer, Justin

2013-09-01

113

We address the question to what extent the centre-of-mass (COM) separation can change our view of the many-body problem in quantum chemistry and solid state physics. It was shown that the many-body treatment based on the electron-vibrational Hamiltonian is fundamentally inconsistent with the Born-Handy ansatz so that such a treatment can never respect the COM problem. Born-Oppenheimer (B-O) approximation reveals

Michal Svrcek

2010-01-01

114

Stefano Fantoni:. Feenberg Medalist 2007 Microscopic Many-Body Theory of Strongly Correlated Systems

NASA Astrophysics Data System (ADS)

The Eleventh Eugene Feenberg Medal is awarded to Stefano Fantoni in recognition of his leading role in the development and extensive application of correlated wave function approaches, including the advance of Fermi hypernetted chain theory, thereby providing an accurate, quantitative, microscopic description of strongly interacting quantum many-particle systems, especially for nuclear systems.

Polls, A.

2008-06-01

115

Efficient Evaluation of Partition Functions of Inhomogeneous Many-Body Spin Systems

We present a numerical method to evaluate partition functions and associated correlation functions of inhomogeneous 2D classical spin systems and 1D quantum spin systems. The method is scalable and has a controlled error. We illustrate the algorithm by calculating the finite-temperature properties of bosonic particles in 1D optical lattices, as realized in current experiments.

Murg, V.; Cirac, J.I. [Max-Planck-Institut fuer Quantenoptik, Hans-Kopfermann-Strasse 1, Garching, D-85748 (Germany); Verstraete, F. [Max-Planck-Institut fuer Quantenoptik, Hans-Kopfermann-Strasse 1, Garching, D-85748 (Germany); Institute for Quantum Information, Caltech, Pasadena, California (United States)

2005-07-29

116

High-accuracy calculations of term energies and wavelengths of resonance lines in Zn-like ions have been performed as benchmarks in the quest for accurate theoretical treatments of relativity, electron correlation, and quantum electrodynamic effects in multivalence-electron systems. Computed wavelengths of the 4s{sup 2} {sup 1}S{sub 0}-4s4p {sup 1}P{sub 1}{sup o} transitions are compared with the recent high-resolution wavelength measurements using electron-beam ion traps [E. Traebert, P. Beiersdorfer, and H. Chen, Phys. Rev. A 70, 032506 (2004)], a sensitive means of testing electronic structure theory that has revealed the inadequacies in treating multiple valence electrons in the extant relativistic many-body calculations.

Vilkas, Marius J.; Ishikawa, Yasuyuki [Department of Chemistry, University of Puerto Rico, P.O. Box 23346, San Juan, 00931-3346 (Puerto Rico)

2005-09-15

117

NASA Astrophysics Data System (ADS)

Intersubband semiconductor-Bloch equations are investigated by incorporating many-body Coulomb interaction, nonparabolicity, and coherence of resonant tunneling transport in a quantitative way based on the density matrix theory. The calculations demonstrate the importance of these parameters on optical properties, especially the optical gain spectrum, of terahertz (THz) quantum cascade lasers (QCLs). The results show that the lasing frequency at gain peak calculated by the proposed microscopic density matrix model is closer to the experimentally measured result, compared with that calculated by the existing macroscopic density matrix model. Specifically, both the many-body interaction and nonparabolicity effects red-shift the gain spectrum and reduce the gain peak. In addition, as the injection-coupling strength increases, the gain peak value is enhanced and the spectrum is slightly broadened, while an increase of the extraction-coupling strength reduces the gain peak value and broadens the gain spectrum. The dependence of optical gain of THz QCLs on device parameters such as external electrical bias, dephasing rate, doping density, and temperature is also systematically studied in details. This model provides a more comprehensive picture of the optical properties of THz QCLs from a microscopic point of view and potentially enables a more accurate and faster prediction and calculation of the device performance, e.g., gain spectra, current-voltage characteristics, optical output powers, and nonlinear amplitude-phase coupling.

Liu, Tao; Lee, Kenneth E.; Wang, Qi Jie

2012-12-01

118

The evolution of two dimensional interfaces in a Laplacian field is discussed. By mapping the growing region conformally onto the unit disk, the problem is converted to the dynamics of a many-body system. This problem is shown to be Hamiltonian. An extension of the many body approach to a continuous density is discussed. The Hamiltonian structure allows introduction of surface effects as an external field. These results are used to formulate a first-principles statistical theory for the morphology of the interface using statistical mechanics for the many-body system.

Blumenfeld, R.

1994-07-01

119

Exact BCS stochastic schemes for a time-dependent many-body fermionic system

NASA Astrophysics Data System (ADS)

A common approximate way to study the time evolution of a superfluid Fermi gas is to consider the mean-field time-dependent BCS equations. We show that, by inclusion of an appropriate fluctuating term in these mean-field equations, the exact quantum evolution of the Fermi gas is recovered, after an average over all possible realizations of the noise term: this leads to an exact quantum Monte Carlo technique for the real-time evolution of an interacting fermionic system. In practice, we derive the general conditions on the noise term, ensuring that the exact dynamics is reproduced, and we explore several explicit realizations of this noise term, trying to minimize the statistical spreading of the quantum Monte Carlo simulations. The convergence issue is discussed in detail, with upper bounds obtained on the statistical spreading, and the relation between the stochastic and the mean-field equations is analyzed. Finally, we apply the method to a simple two-site model, to exemplify that the simulations can display effects out of reach of the mean-field approximation.

Montina, A.; Castin, Yvan

2006-01-01

120

NASA Astrophysics Data System (ADS)

The (Berry-Aharonov-Anandan) geometric phase acquired during a cyclic quantum evolution of finite-dimensional quantum systems is studied. It is shown that a pure quantum state in a (2J+1)-dimensional Hilbert space (or, equivalently, of a spin-J system) can be mapped onto the partition function of a gas of independent Dirac strings moving on a sphere and subject to the Coulomb repulsion of 2J fixed test charges (the Majorana stars) characterizing the quantum state. The geometric phase may be viewed as the Aharonov-Bohm phase acquired by the Majorana stars as they move through the gas of Dirac strings. Expressions for the geometric connection and curvature, for the metric tensor, as well as for the multipole moments (dipole, quadrupole, etc.), are given in terms of the Majorana stars. Finally, the geometric formulation of the quantum dynamics is presented and its application to systems with exotic ordering such as spin nematics is outlined.

Bruno, Patrick

2012-06-01

121

The (Berry-Aharonov-Anandan) geometric phase acquired during a cyclic quantum evolution of finite-dimensional quantum systems is studied. It is shown that a pure quantum state in a (2J+1)-dimensional Hilbert space (or, equivalently, of a spin-J system) can be mapped onto the partition function of a gas of independent Dirac strings moving on a sphere and subject to the Coulomb repulsion of 2J fixed test charges (the Majorana stars) characterizing the quantum state. The geometric phase may be viewed as the Aharonov-Bohm phase acquired by the Majorana stars as they move through the gas of Dirac strings. Expressions for the geometric connection and curvature, for the metric tensor, as well as for the multipole moments (dipole, quadrupole, etc.), are given in terms of the Majorana stars. Finally, the geometric formulation of the quantum dynamics is presented and its application to systems with exotic ordering such as spin nematics is outlined. PMID:23004240

Bruno, Patrick

2012-06-11

122

NASA Astrophysics Data System (ADS)

The Fowler's expression for calculation of the reduced surface tension and surface energy has been used with Lennard-Jones (LJ) and two-body Hartree-Fock dispersion (HFD)-like potentials for neon and argon, respectively. The required radial distribution functions (RDFs) have been used from two recently determined expressions in the literature and a new equation proposed in this work. Quantum corrections for neon system have been considered using the Feynman-Hibbs (FH) and Wigner-Kirkwood (WK) approaches. To take many-body forces into account for argon system, the simple three-body potentials of Wang and Sadus (2006) [33] and Hauschild and Prausnitz (1993) [30] used with the HFD-like potential without requiring an expensive three-body calculation. The results show that the quantum and three-body effects improve the prediction of the surface tension of liquid neon and argon using the Fowler's expression.

Abbaspour, Mohsen

2012-01-01

123

Atomic Many-Body Theory Applied to Photoionization Processes in Complex Open-Shell Systems.

NASA Astrophysics Data System (ADS)

In this work, we examine the process of photoionization of complex open-shell atoms within the context of many -body perturbation theory (MBPT). A single-particle potential for excited states is introduced which is based on a potential defined by Qian et al.^{[ 1] } Analytic properties of this potential are derived using graphical techniques of angular momentum coupling. Values of the potential are tabulated for all s^{n}, p^{n }, and d^{n} initial state couplings. We have performed a photoionization cross section calculation of atomic tungsten for photon energies from threshold to 150 eV using the generalized resonance technique ^{[ 2]} over several LSJ couplings of the initial state. Although the formalism behind the generalized resonance technique has been discussed previously (ref. 2 of abstract), this work represents the first explicit use of this technique. Non -relativistic orbitals are used in the basis set, and relativistic corrections have been included. We consider excitations from the 4f, 5s, 5p, 5d, and 6s subshells. The effect of the strong 5p^{6}5d^{4} to 5p^{5}5d^5 and 4f^{14}5d^4to 4f ^{13}5d^5 transitions are included as resonant contributions to the 5d partial cross section. Specifically, we consider three LSJ couplings of the 5d subshell in the initial state. For the first case we consider the initial state to be 5d^4[^{5 }D_{J=0}]. In the second we place more emphasis on the J value by diagonalizing the initial state with respect to the spin-orbit Hamiltonian and the eigenstates 5d^4[^ {5}D, _sp{2}{3}P, _sp{4}{3}P, _sp {0}{1}S, _sp{4} {1}S] all coupled to J=0 . Thirdly, we remove the dependence of the initial state upon the J value by computing the cross sections for 5d^4[^{5}D _{j=0,1,2,3,4}], summing the results and weighting by (2J+1). Our results indicate that the 5d partial cross section dominates the total cross section below 100 eV. References. 1. Z. Qian, S. L. Carter, and H. P. Kelly, Phys. Rev. A, 33, 1751 (1986). 2. L. J. Garvin, A Study of Photoionization, including Resonance Structure and Spin-Orbit effects, in Atomic Manganese, Ph.D. Thesis, Univ. of Virginia (unpublished) (1983) pp. 128-45.

Boyle, James John

124

Introduction to the Statistical Physics of Integrable Many-body Systems

NASA Astrophysics Data System (ADS)

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.

Šamaj, Ladislav Å.; Bajnok, Zoltán

2013-05-01

125

A time-dependent multiconfigurational self-consistent field theory is presented to describe the many-body dynamics of a gas of identical bosonic atoms confined to an external trapping potential at zero temperature from first principles. A set of generalized evolution equations are developed, through the time-dependent variational principle, which account for the complete and self-consistent coupling between the expansion coefficients of each configuration and the underlying one-body wave functions within a restricted two state Fock space basis that includes the full effects of the condensate's mean field as well as atomic correlation. The resulting dynamical equations are a classical Hamiltonian system and, by construction, form a well-defined initial value problem. They are implemented in an efficient numerical algorithm. An example is presented, highlighting the generality of the theory, in which the ballistic expansion of a fragmented condensate ground state is compared to that of a macroscopic quantum superposition state, taken here to be a highly entangled number state, upon releasing the external trapping potential. Strikingly different many-body matter-wave dynamics emerge in each case, accentuating the role of both atomic correlation and mean-field effects in the two condensate states.

Masiello, David J.; Reinhardt, William P. [Department of Chemistry, University of Washington, Seattle, Washington 98195-1700 (United States)

2007-10-15

126

A 1D bosonic many-body system, related to the Bose–Einstein condensation in atomic traps and periodic optical lattices, is described by a coherent state path integral of the grand canonical partition function. Since the interaction is given by a contact potential, as commonly applied in atomic traps of BEC, the functional integral can be represented by spatial transfer matrices, ordered according

B. Mieck

2003-01-01

127

In order to study quantum many-body problems, we develop two matrix diagonalization codes, which solve only the ground state and all quantum states, respectively. The target model in both codes is the Hubbard model with confinement potential which describes an atomic Fermi gas loaded on an optical lattice and partly High-Tc cuprate superconductor. For the former code, we obtain 18.692TFlops

Susumu Yamada; Toshiyuki Imamura; Takuma Kano; Masahiko Machida

2006-01-01

128

ASYMPTOTIC COMPLETENESS OF SHORT-RANGE MANY-BODY SYSTEMS1

We announce a proof of asymptotic completeness for quan tum mechanical systems consisting of arbitrary numbers of particles in teracting via short-range forces (see conditions (A)-(D) below). A com plete proof is given in (SigSof 1). Previously, there were only partial results in this direction (see reviews and discussions in (Enss, RSIII, sigi). Consider an iV-body system in the physical

I. M. SIGAL; A. SOFFER

129

The Many-Body Physics of Some Quasi-One Magnetic Systems.

NASA Astrophysics Data System (ADS)

Available from UMI in association with The British Library. This thesis deals with original work on three crystalline magnetic systems, all of which possess one -dimensional equations of motion. The Heisenberg model, the most successful simple theory of insulating magnetic systems, and its phenomenology are introduced, with definitions of the quantities of interest and a discussion of the statics of the model. The important concepts in the treatment of the dynamics of magnetic systems are then described, and then the application of the coupled -mode formalism to this system is reviewed. The case of the Heisenberg model in one dimension, in which the coupled -mode theory fails conspicuously, is discussed, and a modified version of the theory is presented; this is shown to describe the dynamics of this system to a much better approximation at all temperatures, and in addition is exact in the low -temperature limit. Quasiperiodic order is the presence of long-range order in a system, despite the absence of any symmetry under translations. The distinction between this type of ordering and the cases of crystalline order and random disorder is discussed, and the important ideas in the study of such systems are introduced. The specific examples of two-dimensional Bloch electron states in a perpendicular magnetic field and of incommensurate spin phases in magnetic systems are reviewed, and then the most striking properties of quasiperiodically ordered systems are briefly summarised. The spectrum of Harper's equation, a quasiperiodic tight-binding equation which describes the wavefunctions of Bloch electrons in a magnetic field, is examined through the statistical distribution of the level spacings, normalised by the local density of states. It is shown that this distribution has a simple form in each regime of the system (that is, with localised, critical and extended eigenstates), in contrast to that of the unnormalised spacings, and these results are related to the concepts of level repulsion and spectral self-similarity. The theory of Ziman and Lindgard for a single-Q modulated spin phase of a magnet is introduced, and the cases of commensurate and incommensurate modulation are contrasted. A continued-fraction approach to the evaluation of the dynamic susceptibility is presented, and it is shown that this gives exact results for modulation wave vectors close to the commensurate values Q = 2 pimu/nu, thus providing values for the susceptibility for comparison with experimental results at any Q.

Megann, Alexis Peter

130

Single particle dynamics of many-body systems described by Vlasov-Fokker-Planck equations

NASA Astrophysics Data System (ADS)

Using Langevin equations we describe the random walk of single particles that belong to particle systems satisfying Vlasov-Fokker-Planck equations. In doing so, we show that Haissinski distributions of bunched particles in electron storage rings can be derived from a particle dynamics model.

Frank, T. D.

2003-12-01

131

Rigorous Bounds for the Pressure and Energy of Many-Body Systems.

National Technical Information Service (NTIS)

Bounds for the volume (or density) dependence of the energy and pressure of ordinary matter and other interacting particle systems are derived. Each bound consists of one term scaling as the potential energy and another scaling as the kinetic energy. (Aut...

P. Kleban R. D. Puff

1970-01-01

132

Parametrization of a reactive many-body potential for MoS systems

We present an interatomic potential for the Mo-S system based on the second-generation reactive empirical bond-order formalism. An analytic function is introduced to the bond-order term to capture the effect of the coordination number on the binding energy. The fitting scheme used for this potential is optimized by appropriate selection of the functions, training databases, initial guesses, and weights on

Tao Liang; Simon R. Phillpot; Susan B. Sinnott

2009-01-01

133

Anomalous decoherence and absence of thermalization in a photonic many-body system

The intention of this work is twofold: first, to present a most simple system capable of simulating the intrinsic bosonic Josephson effect with photons and, second, to study various outcomes deriving from inherent or external decoherence. A qubit induces an effective coupling between two externally pumped cavity modes. Without cavity losses and in the dispersive regime, intrinsic Josephson oscillations of photons between the two modes occurs. In this case, contrary to regular Markovian decoherence, the qubit purity shows a Gaussian decay and recurrence of its coherence. Due to intrinsic nonlinearities, both the Josephson oscillations as well as the qubit properties display a rich collapse-revival structure, where, however, the complexity of the qubit evolution is in some sense stronger. The qubit as a meter of the photon dynamics is considered, and it is shown that qubit dephasing, originating, for example, from nondemolition measurements, results in an exponential destruction of the oscillations which manifests the collectiveness of the Josephson effect. Nonselective qubit measurements, on the other hand, render a Zeno effect seen in a slowing down of the Josephson oscillations. Contrary to dephasing, cavity dissipation results in a Gaussian decay of the scaled Josephson oscillations. Finally, following Ponomarev et al. [Phys. Rev. Lett. 106, 010405 (2011)], we analyze aspects of thermalization. In particular, despite similarities with the generic model studied by Ponomarev et al., our system does not seem to thermalize.

Larson, Jonas [Department of Physics, Stockholm University, AlbaNova University Center, SE-10691 Stockholm (Sweden)

2011-05-15

134

Description of pairing correlation in many-body finite systems with density functional theory

Different steps leading to the new functional for pairing based on natural orbitals and occupancies proposed earlier [D. Lacroix and G. Hupin, Phys. Rev. B 82, 144509 (2010)] are carefully analyzed. Properties of quasiparticle states projected onto good particle numbers are first reviewed. These properties are used to (i) prove the existence of such a functional, (ii) provide an explicit functional through a 1/N expansion starting from the BCS approach, and (iii) give a compact form of the functional summing up all orders in the expansion. The functional is benchmarked in the case of the picket-fence pairing Hamiltonian where even and odd systems are studied, using the blocking technique, at various particle numbers and coupling strengths, with uniform and random single-particle level spacing. In all cases, very good agreement is found, with a deviation of <1% compared to the exact energy.

Hupin, Guillaume; Lacroix, Denis [Grand Accelerateur National d'Ions Lourds (GANIL), CEA/DSM-CNRS/IN2P3, Bvd Henri Becquerel, 14076 Caen (France)

2011-02-15

135

Parametrization of a reactive many-body potential for Mo-S systems

NASA Astrophysics Data System (ADS)

We present an interatomic potential for the Mo-S system based on the second-generation reactive empirical bond-order formalism. An analytic function is introduced to the bond-order term to capture the effect of the coordination number on the binding energy. The fitting scheme used for this potential is optimized by appropriate selection of the functions, training databases, initial guesses, and weights on each residual—the four factors that are involved in a weighted nonlinear least-squares fitting. The resulting potential is able to yield good agreement with the structure and energetics of Mo molecules, two-dimensional Mo structures, three-dimensional Mo crystals, small S molecules, and binary Mo-S crystal structures. We illustrate the capabilities of the new potential by presenting results of the simulation of friction between MoS2 layers. The results are consistent with our previous static potential surface calculations using density-functional theory.

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

2009-06-01

136

Many Body Physics: Unfinished Revolution

. The study of many body physics has provided a scientific playground of surprise and continuing revolution over the past half\\u000a century. The serendipitous discovery of new states and properties of matter, phenomena such as superfluidity, the Meissner,\\u000a the Kondo and the fractional quantum hall effect, have driven the development of new conceptual frameworks for our understanding\\u000a about collective behavior, the

Piers Coleman

2003-01-01

137

Relativistic nuclear many-body theory

Nonrelativistic models of nuclear systems have provided important insight into nuclear physics. In future experiments, nuclear systems will be examined under extreme conditions of density and temperature, and their response will be probed at momentum and energy transfers larger than the nucleon mass. It is therefore essential to develop reliable models that go beyond the traditional nonrelativistic many-body framework. General properties of physics, such as quantum mechanics, Lorentz covariance, and microscopic causality, motivate the use of quantum field theories to describe the interacting, relativistic, nuclear many-body system. Renormalizable models based on hadronic degrees of freedom (quantum hadrodynamics) are presented, and the assumptions underlying this framework are discussed. Some applications and successes of quantum hadrodynamics are described, with an emphasis on the new features arising from relativity. Examples include the nuclear equation of state, the shell model, nucleon-nucleus scattering, and the inclusion of zero-point vacuum corrections. Current issues and problems are also considered, such as the construction of improved approximations, the full role of the quantum vacuum, and the relationship between quantum hadrodynamics and quantum chromodynamics. We also speculate on future developments. 103 refs., 18 figs.

Serot, B.D. (Indiana Univ., Bloomington, IN (United States)); Walecka, J.D. (Southeastern Universities Research Association, Newport News, VA (United States). Continuous Electron Beam Accelerator Facility)

1991-09-11

138

We show that an exact solution of the generalized Langevin equation (GLE) for the autocorrelations of a many-body classical system can be given in an exponential functionality (EF) form. As a consequence, the power spectrum of the correlation has a Lorentzian functionality, i.e., is represented by an infinite sum of Lorentzian functions corresponding to the eigenmodes of the considered correlation. By means of the simple derivation of the GLE by M. H. Lee [Phys. Rev. B 26, 2547 (1982)], we also show that, in practical cases of interest to experimental spectroscopies, possible approximations of the EF are related to a reduction of the relevant dynamical variables via a restriction of the dimensions of the orthogonalized space onto which the dynamics of the system is projected. PMID:22463264

Barocchi, Fabrizio; Bafile, Ubaldo; Sampoli, Marco

2012-02-17

139

NASA Astrophysics Data System (ADS)

We derive a general linear-response many-body theory capable of computing excitation spectra of trapped interacting bosonic systems, e.g., depleted and fragmented Bose-Einstein condensates (BECs). To obtain the linear-response equations we linearize the multiconfigurational time-dependent Hartree for bosons (MCTDHB) method, which provides a self-consistent description of many-boson systems in terms of orbitals and a state vector (configurations), and is in principle numerically exact. The derived linear-response many-body theory, which we term LR-MCTDHB, is applicable to systems with interaction potentials of general form. For the special case of a ? interaction potential we show explicitly that the response matrix has a very appealing bilinear form, composed of separate blocks of submatrices originating from contributions of the orbitals, the state vector (configurations), and off-diagonal mixing terms. We further give expressions for the response weights and density response. We introduce the notion of the type of excitations, useful in the study of the physical properties of the equations. From the numerical implementation of the LR-MCTDHB equations and solution of the underlying eigenvalue problem, we obtain excitations beyond available theories of excitation spectra, such as the Bogoliubov–de Gennes (BdG) equations. The derived theory is first applied to study BECs in a one-dimensional harmonic potential. The LR-MCTDHB method contains the BdG excitations and, also, predicts a plethora of additional many-body excitations which are out of the realm of standard linear response. In particular, our theory describes the exact energy of the higher harmonic of the first (dipole) excitation not contained in the BdG theory. We next study a BEC in a very shallow one-dimensional double-well potential. We find with LR-MCTDHB low-lying excitations which are not accounted for by BdG, even though the BEC has only little fragmentation and, hence, the BdG theory is expected to be valid. The convergence of the LR-MCTDHB theory is assessed by systematically comparing the excitation spectra computed at several different levels of theory.

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

2013-08-01

140

NASA Astrophysics Data System (ADS)

Configuration-space matrix elements of N-body potentials arise naturally and ubiquitously in the Ritz-Galerkin solution of many-body quantum problems. For the common specialization of local, finite-range potentials, we develop the exact tensor hypercontraction method, which provides a quantized renormalization of the coordinate-space form of the N-body potential, allowing for a highly separable tensor factorization of the configuration-space matrix elements. This representation allows for substantial computational savings in chemical, atomic, and nuclear physics simulations, particularly with respect to difficult “exchangelike” contractions.

Parrish, Robert M.; Hohenstein, Edward G.; Schunck, Nicolas F.; Sherrill, C. David; Martínez, Todd J.

2013-09-01

141

Configuration-space matrix elements of N-body potentials arise naturally and ubiquitously in the Ritz-Galerkin solution of many-body quantum problems. For the common specialization of local, finite-range potentials, we develop the exact tensor hypercontraction method, which provides a quantized renormalization of the coordinate-space form of the N-body potential, allowing for a highly separable tensor factorization of the configuration-space matrix elements. This representation allows for substantial computational savings in chemical, atomic, and nuclear physics simulations, particularly with respect to difficult "exchangelike" contractions. PMID:24116775

Parrish, Robert M; Hohenstein, Edward G; Schunck, Nicolas F; Sherrill, C David; Martínez, Todd J

2013-09-27

142

Strong coupling between a two-level system (TLS) and bosonic modes produces dramatic quantum optics effects. We consider a one-dimensional continuum of bosons coupled to a single localized TLS, a system which may be realized in a variety of plasmonic, photonic, or electronic contexts. We present the exact many-body scattering eigenstate obtained by imposing open boundary conditions. Multiphoton bound states appear in the scattering of two or more photons due to the coupling between the photons and the TLS. Such bound states are shown to have a large effect on scattering of both Fock- and coherent-state wave packets, especially in the intermediate coupling-strength regime. We compare the statistics of the transmitted light with a coherent state having the same mean photon number: as the interaction strength increases, the one-photon probability is suppressed rapidly, and the two- and three-photon probabilities are greatly enhanced due to the many-body bound states. This results in non-Poissonian light.

Zheng Huaixiu; Baranger, Harold U. [Department of Physics, Duke University, P.O. Box 90305, Durham, North Carolina 27708 (United States); Center for Theoretical and Mathematical Sciences, Duke University, Durham, North Carolina 27708 (United States); Gauthier, Daniel J. [Department of Physics, Duke University, P.O. Box 90305, Durham, North Carolina 27708 (United States)

2010-12-15

143

We analyze the ground-state phase diagram of attractive lattice bosons, which are stabilized by a three-body onsite hardcore constraint. A salient feature of this model is an Ising-type transition from a conventional atomic superfluid to a dimer superfluid with vanishing atomic condensate. The study builds on an exact mapping of the constrained model to a theory of coupled bosons with polynomial interactions, proposed in a related paper [S. Diehl, M. Baranov, A. Daley, and P. Zoller, Phys. Rev. B 82, 064509 (2010).]. In this framework, we focus by analytical means on aspects of the phase diagram which are intimately connected to interactions, and are thus not accessible in a mean-field plus spin-wave approach. First, we determine shifts in the mean-field phase border, which are most pronounced in the low-density regime. Second, the investigation of the strong coupling limit reveals the existence of a 'continuous supersolid', which emerges as a consequence of enhanced symmetries in this regime. We discuss its experimental signatures. Third, we show that the Ising-type phase transition, driven first order via the competition of long-wavelength modes at generic fillings, terminates into a true Ising quantum critical point in the vicinity of half filling.

Diehl, S.; Daley, A. J.; Zoller, P. [Institute for Quantum Optics and Quantum Information, Austrian Academy of Sciences, A-6020 Innsbruck (Austria); Institute for Theoretical Physics, University of Innsbruck, A-6020 Innsbruck (Austria); Baranov, M. [Institute for Quantum Optics and Quantum Information, Austrian Academy of Sciences, A-6020 Innsbruck (Austria); Institute for Theoretical Physics, University of Innsbruck, A-6020 Innsbruck (Austria); RRC 'Kurchatov Institute', Kurchatov Square 1, 123182 Moscow (Russian Federation)

2010-08-01

144

NASA Astrophysics Data System (ADS)

Inter-cellular communication is essential for coordinated cell movement and spatio-temporal differentiation. Examples are collective behavior of unicellular organisms (such as Dictyostelium aggregation) and formation of structures in multi-cellular organisms (e.g. gastrulation in early embryos). Cells communicate with one another via short-range contact interactions and long-range interactions mediated by chemical signaling fields. In the examples given above the number of cells varies between hundreds to tens of thousands, and the cell population may have strong phenotypic heterogeneity. It is therefore important to develop a model framework which retains discrete cell identity, and allows a flexible description of cell-cell interactions. We present one such framework here, inspired by the many-body formulation of interacting systems, and constructed using approximations which are biologically plausible. We describe a perturbative analysis of chemotactic aggregation, which illustrates the importance of statistical correlations between cells. We also discuss the implementation of this framework as an optimized numerical algorithm, and show some early results on primitive streak formation in the chick embryo.

Newman, Timothy

2005-03-01

145

We have experimentally studied metal-insulator transitions in a two-dimensional electron system in Si-MOSFET's in a magnetic field and derived a phase diagram on anu (Landau level filling factor) vs. disorder (resistivity in the absence of magnetic field)plane. Structures of stabilized phase boundaries at nu=1 and nu=2 are discussed based on many-body enhancement of valley- and Zeeman-splitting, respectively.

Tohru Okamoto; Yoshinori shinohara; Shinji Kawaji; Atsuo Yagi

1995-01-01

146

Spin-orbit induced mixed-parity pairing in Sr2RuO4: a self-consistent quantum many-body analysis

NASA Astrophysics Data System (ADS)

The unusual superconducting state in Sr2RuO4 has long been viewed as being analogous to a superfluid state in liquid ^3He. Nevertheless, calculations based on a pure odd-parity state are presently unable to completely reconcile the properties of Sr2RuO4. Using a self-consistent quantum many-body scheme that employs realistic parameters, we are able to model several signature properties of the normal and superconducting states of Sr2RuO4 such as the weak temperature dependence of the spin susceptibility below Tc. However, we find that the dominant component of the model superconducting state is of even parity and closely related to superconducting state for the high-Tc cuprates although a smaller odd-parity component is induced by spin-orbit coupling. This mixed parity pairing state provides an alternative scenario for understanding the complex phenomena measured in Sr2RuO4.

Deisz, John; Kidd, Tim

2012-02-01

147

NASA Astrophysics Data System (ADS)

The unusual superconducting state in Sr2RuO4 has long been viewed as being analogous to a superfluid state in liquid He3. Nevertheless, calculations based on this odd-parity state are presently unable to completely reconcile the properties of Sr2RuO4. Using a self-consistent quantum many-body scheme that employs realistic parameters, we are able to model several signature properties of the normal and superconducting states of Sr2RuO4. We find that the dominant component of the model superconducting state is of even parity and closely related to superconducting state for the high-Tc cuprates although a smaller odd-parity component is induced by spin-orbit coupling. This mixed pairing state gives a more complete representation of the complex phenomena measured in Sr2RuO4.

Deisz, J. J.; Kidd, T. E.

2011-12-01

148

Overlap with the separable state is introduced in this article for the purpose of characterizing the overall correlation in many-body systems. This definition has clear geometric and physical meaning and moreover can be considered as the generalization of the concept of the Anderson orthogonality catastrophe. As an exemplification, it is used to mark the phase transition in the Dicke model for zero and finite temperatures, and the discussion shows that it can faithfully reflect the phase transition properties of this model whether for zero or finite temperature. Furthermore, the overlap for the ground state also indicates the appearance of multipartite entanglement in the Dicke model.

Cui, H. T. [School of Physics and Electrical Engineering, Anyang Normal University, Anyang 455000 (China)

2010-04-15

149

Gravitational Many-Body Problem

NASA Astrophysics Data System (ADS)

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.

Makino, J.

2008-04-01

150

Penn State: Consortium for Education in Many-Body Applications

NSDL National Science Digital Library

Funded by the National Science Foundation, the Consortium for Education in Many-Body Applications at Penn State University brings together scientists from a range of scientific and engineering disciplines to address "many-body" problems. These problems refer to "the complexities that arise when more than a few electrons or atoms or particles are involved." The solutions involve "the use of high performance and massively parallel computers coupled with improved algorithms." Drawing from seven academic departments (Aerospace Engineering, Chemistry, Chemical Engineering, Computer Science and Engineering, Materials Science and Engineering, Mathematics, and Physics) they offer courses, summer internships, seminars and tutorials, and conduct research projects. The Research section of the website provides summary articles on a variety of topics, including High-Performance and Parallel Computing; Advanced Visualization; and Quantum mechanics of many-body systems. Descriptions of courses and seminars as well as some of the PowerPoint presentations are also available online.

151

The many-body structure of high-lying excited states, including macroscopic quantum superpositions, of the gaseous double-well BEC is presented within the context of a multiconfigurational bosonic self-consistent field theory based upon underlying symmetry-broken one-body wave functions. To better understand our initial results, a model is constructed in the extreme Fock state limit, in which macroscopic quantum self-trapped and superposition states emerge

David J. Masiello; William P. Reinhardt

2006-01-01

152

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

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. PMID:24113334

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

2013-10-10

153

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

NASA Astrophysics Data System (ADS)

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.

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

2013-11-01

154

A time-dependent multiconfigurational self-consistent field theory is presented to describe the many-body dynamics of a gas of identical bosonic atoms confined to an external trapping potential at zero temperature from first principles. A set of generalized evolution equations are developed, through the time-dependent variational principle, which account for the complete and self-consistent coupling between the expansion coefficients of each configuration

David J. Masiello; William P. Reinhardt

2007-01-01

155

Two problems in many-body physics

NASA Astrophysics Data System (ADS)

In this dissertation, the applications of many-body physics in neutral bosons and electronic systems in transition metal oxides are discussed. In the first part of the thesis, I will introduce the concepts of Bose condensation, emphasize the significance of the order parameter in superfluids (macroscopic wave function), and its consequence such as the emergence of exotic vortex states under rotation. Dated back to the importance of the vortex dynamics in the properties of high Tc superconductors, people have introduced a dual vortex description to describe the dynamics of charged bosons in a magnetic field. Similarly, the dual description is adapted to the problems of neutral bosons under rotation. Based on that picture, vortices behave like charges in an effective magnetic field which has been known to demonstrate different quantum phases such as Wigner crystal phase, and fractional quantum Hall liquid phases depending on the relative fraction of the number of bosons and vortices. In this work, we would like to address the validity of the picture by low energy effective theory. We can identify the origin of the vortex masse and the parameter regimes in which the vortex dual description is appropriate. In the second part of the dissertation, density functional theory is used to describe the strongly correlated matters with local density approximation and local Hubbard U interaction(LDA+U). We are particularly interested in the interface states in the heterojunction systems of two different perovskite oxides. What we found is that the interface states can be engineered to appear in certain transitional metal oxide layers by controlling the number of positive and negative charged layers, leading to the formation of quantum wells in two dimension. This type of systems ignite the hope to search for broken symmetry states in the interface which can be tunable with chemical doping or electric field doping. Even room temperature superconducting state may or may not exist in the interface is still an intriguing issue.

Wang, Cheng-Ching

156

A time-dependent multiconfigurational self-consistent field theory is\\u000apresented to describe the many-body dynamics of a gas of identical bosonic\\u000aatoms confined to an external trapping potential at zero temperature from first\\u000aprinciples. A set of generalized evolution equations are developed, through the\\u000atime-dependent variational principle, which account for the complete and\\u000aself-consistent coupling between the expansion coefficients of each\\u000aconfiguration

David J. Masiello; William P. Reinhardt

2007-01-01

157

NASA Astrophysics Data System (ADS)

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.

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

2005-11-01

158

NASA Astrophysics Data System (ADS)

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.

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

1998-09-01

159

The many-body structure of high-lying excited states, including macroscopic\\u000aquantum superpositions, of the gaseous double-well BEC is presented within the\\u000acontext of a multiconfigurational bosonic self-consistent field theory based\\u000aupon underlying symmetry-broken one-body wave functions. To better understand\\u000aour initial results, a model is constructed in the extreme Fock state limit, in\\u000awhich macroscopic quantum self-trapped and superposition states emerge

David J. Masiello; William P. Reinhardt

2006-01-01

160

Many-body wave function in a dipole blockade configuration

We report the results of simulations of the many atom wave function when a cold gas is excited to highly excited states. We simulated the many body wave function by direct numerical solution of Schroedinger's equation. We investigated the fraction of atoms excited and the correlation of excited atoms in the gas for different types of excitation when the blockade region was small compared to the sample size. We also investigated the blockade effect when the blockade region is comparable to the sample size to determine the sensitivity of this system and constraints for quantum information.

Robicheaux, F.; Hernandez, J. V. [Department of Physics, Auburn University, Alabama 36849-5311 (United States)

2005-12-15

161

The self-healing diffusion Monte Carlo algorithm (SHDMC) [F. A. Reboredo, R. Q. Hood, and P. R. C. Kent, Phys. Rev. B 79, 195117 (2009); F. A. Reboredo, ibid. 80, 125110 (2009)] is extended to study the ground and excited states of magnetic and periodic systems. The method converges to exact eigenstates as the statistical data collected increase if the wave function is sufficiently flexible. It is shown that the dimensionality of the nodal surface is dependent on whether phase is a scalar function or not. A recursive optimization algorithm is derived from the time evolution of the mixed probability density, which is given by an ensemble of electronic configurations (walkers) with complex weight. This complex weight allows the phase of the fixed-node wave function to move away from the trial wave function phase. This novel approach is both a generalization of SHDMC and the fixed-phase approximation [G. Ortiz, D. M. Ceperley, and R. M. Martin, Phys Rev. Lett. 71, 2777 (1993)]. When used recursively it simultaneously improves the node and the phase. The algorithm is demonstrated to converge to nearly exact solutions of model systems with periodic boundary conditions or applied magnetic fields. The computational cost is proportional to the number of independent degrees of freedom of the phase. The method is applied to obtain low-energy excitations of Hamiltonians with magnetic field. Periodic boundary conditions are also considered optimizing wave functions with twisted boundary conditions which are included in a many-body Bloch phase. The potential applications of this new method to study periodic, magnetic, and complex Hamiltonians are discussed. PMID:22667534

Reboredo, Fernando Agustín

2012-05-28

162

A formalism for energy-dependent many-body perturbation theory (MBPT), previously indicated in our recent review articles [Lindgren et al., Phys. Rep. 389, 161 (2004); Can. J. Phys. 83, 183 (2005)], is developed in more detail. The formalism allows for an arbitrary mixture of energy-dependent (retarded) and energy-independent (instantaneous) interactions and hence for a merger of quantum-electrodynamics (QED) and standard (relativistic) MBPT. This combined many-body-QED procedure is particularly important for light elements, such as light heliumlike ions, where electron correlation is pronounced. It can also be quite significant in the medium-heavy mass range, as recently discussed by Fritzsche et al. [J. Phys. B 38, S707 (2005)], with the consequence that the effects might be significant also in analyzing the data of experiments with highly charged ions. A numerical procedure is described, and some preliminary results are given for heliumlike ions with a single retarded photon. This represent the first numerical evaluation of the combined many-body-QED effect on an atomic system. It is found that for heliumlike neon the effect of one retarded photon with correlation represents more than 99% of the nonradiative effects beyond energy-independent MBPT. The new procedure also allows for the inclusion of radiative effects (self-energy and vacuum polarization) in a more systematic fashion than has previously been possible.

Lindgren, Ingvar; Salomonson, Sten; Hedendahl, Daniel [Physics Department, Goeteborg University, Goeteborg (Sweden)

2006-06-15

163

NASA Astrophysics Data System (ADS)

A formalism for energy-dependent many-body perturbation theory (MBPT), previously indicated in our recent review articles [Lindgren , Phys. Rep. 389, 161 (2004); Can. J. Phys. 83, 183 (2005)], is developed in more detail. The formalism allows for an arbitrary mixture of energy-dependent (retarded) and energy-independent (instantaneous) interactions and hence for a merger of quantum-electrodynamics (QED) and standard (relativistic) MBPT. This combined many-body-QED procedure is particularly important for light elements, such as light heliumlike ions, where electron correlation is pronounced. It can also be quite significant in the medium-heavy mass range, as recently discussed by Fritzsche [J. Phys. B 38, S707 (2005)], with the consequence that the effects might be significant also in analyzing the data of experiments with highly charged ions. A numerical procedure is described, and some preliminary results are given for heliumlike ions with a single retarded photon. This represent the first numerical evaluation of the combined many-body-QED effect on an atomic system. It is found that for heliumlike neon the effect of one retarded photon with correlation represents more than 99% of the nonradiative effects beyond energy-independent MBPT. The new procedure also allows for the inclusion of radiative effects (self-energy and vacuum polarization) in a more systematic fashion than has previously been possible.

Lindgren, Ingvar; Salomonson, Sten; Hedendahl, Daniel

2006-06-01

164

Many-Body Models for Molecular Nanomagnets

NASA Astrophysics Data System (ADS)

We present a flexible and effective ab initio scheme to build many-body models for molecular nanomagnets, and to calculate magnetic exchange couplings and zero-field splittings. It is based on using localized Foster-Boys orbitals as a one-electron basis. We apply this scheme to three paradigmatic systems, the antiferromagnetic rings Cr8 and Cr7Ni, and the single-molecule magnet Fe4. In all cases we identify the essential magnetic interactions and find excellent agreement with experiments.

Chiesa, A.; Carretta, S.; Santini, P.; Amoretti, G.; Pavarini, E.

2013-04-01

165

Many-body coherent destruction of tunneling in photonic lattices

An optical realization of the phenomenon of many-body coherent destruction of tunneling, recently predicted for interacting many-boson systems by Gong, Molina, and Haenggi [Phys. Rev. Lett. 103, 133002 (2009)], is proposed for light transport in engineered waveguide arrays. The optical system enables a direct visualization in Fock space of the many-body tunneling control process.

Longhi, Stefano [Dipartimento di Fisica, Politecnico di Milano, Piazza L. da Vinci 32, I-20133 Milano (Italy)

2011-03-15

166

Area laws in a many-body localized state and its implications for topological order

NASA Astrophysics Data System (ADS)

The question whether Anderson insulators can persist to finite-strength interactions—a scenario dubbed many-body localization—has recently received a great deal of interest. The origin of such a many-body localized phase has been described as localization in Fock space, a picture we examine numerically. We then formulate a precise sense in which a single energy eigenstate of a Hamiltonian can be adiabatically connected to a state of a non-interacting Anderson insulator. We call such a state a many-body localized state and define a many-body localized phase as one in which almost all states are many-body localized states. We explore the possible consequences of this; the most striking is an area law for the entanglement entropy of almost all excited states in a many-body localized phase. We present the results of numerical calculations for a one-dimensional system of spinless fermions. Our results are consistent with an area law and, by implication, many-body localization for almost all states and almost all regions for weak enough interactions and strong disorder. However, there are rare regions and rare states with much larger entanglement entropies. Furthermore, we study the implications that many-body localization may have for topological phases and self-correcting quantum memories. We find that there are scenarios in which many-body localization can help to stabilize topological order at non-zero energy density, and we propose potentially useful criteria to confirm these scenarios.

Bauer, Bela; Nayak, Chetan

2013-09-01

167

NASA Astrophysics Data System (ADS)

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.

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

2013-09-01

168

Quantum circuits for strongly correlated quantum systems

NASA Astrophysics Data System (ADS)

We present an approach to gain detailed control on the quantum simulation of strongly correlated quantum many-body systems by constructing the explicit finite quantum circuits that diagonalize their dynamics. As a particularly simple instance, the full dynamics of a one-dimensional Quantum Ising model in a transverse field with four spins is shown to be reproduced using a quantum circuit of only six local gates. This opens up the possibility of experimentally producing strongly correlated states, their time evolution at zero time, and even thermal superpositions at zero temperature. Our method also allows one to uncover the exact circuits corresponding to models that exhibit topological order and to stabilizer states.

Verstraete, Frank; Cirac, J. Ignacio; Latorre, José I.

2009-03-01

169

Learning Many-Body Physics with Adelchi

NASA Astrophysics Data System (ADS)

We present an overview of the contributions that Adelchi Fabrocini gave to the field of many-body physics during the last thirty years. He has left us while he was still in full activity, and his work, which is certainly a reference for all of us, will motivate and guide the work of future research in many-body physics for a long time.

Benhar, O.; Co', G.; Polls, A.

2007-04-01

170

Probing many body effects in semiconductor nanostructures

NASA Astrophysics Data System (ADS)

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. Goldhaber-Gordon, Physical Review Letters 90, 133602 (2003).

Potok, Ron M.

171

An integrable many-body problem

NASA Astrophysics Data System (ADS)

Some years ago, Mikhailov and Sokolov identified as integrable the neat system of two evolution equations \\Udot=V2, \\Vdot=U2, where U ? U(t) and V ? V(t) are two N × N matrices, N is an arbitrarypositive integer, t (``time'') is the independent variable, and superimposed dots indicate the time derivatives. This entails, rather trivially, that the generic solution of the modified version of this model reading \\Udot=V2+i?U, \\Vdot=U2+i?V, with ? an arbitrary positive constant, is completely periodicwith period T = 2?/? (or possibly a period which is an integer multiple of T): ``isochrony.'' Another, less trivial, consequence of their finding is the observation that the solution of the many-body problem characterized by the Hamiltonian system of N Newtonian evolution equations, \\xumln=-a2xn5+g22?m=1,m?nN[(xn-xm)-3+xn+xm-3],n=1,...,N, where xn ? xn(t) are N scalar dependent variables and a, g are two arbitrary constants, is simply related to the evolution of the (appropriately rescaled) eigenvalues of a matrix simply related to an appropriate solution of the original Mikhailov-Sokolov integrablematrix evolution system, hence is itself integrable.

Calogero, F.

2011-10-01

172

Random matrices, symmetries, and many-body states

NASA Astrophysics Data System (ADS)

All nuclei with even numbers of protons and of neutrons have ground states with zero angular momentum. This is ascribed to the pairing force between nucleons, but simulations with random interactions suggest a much broader many-body phenomenon. I discuss how to project out random Hermitian matrices that have good quantum numbers and, computing the width of the Hamiltonian in subspaces, find ground states dominated by low quantum numbers, e.g. J = 0.

Johnson, Calvin

2011-10-01

173

Local Conservation Laws and the Structure of the Many-Body Localized States

NASA Astrophysics Data System (ADS)

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.

Serbyn, Maksym; Papi?, Z.; Abanin, Dmitry A.

2013-09-01

174

Probing many-body physics with an optical lattice clock

NASA Astrophysics Data System (ADS)

Advances in ultra-stable lasers now permit sub-Hz resolution of optical atomic transitions. At this level, interactions can dominate dynamics of the interrogated atoms, even for ultracold spin-polarized fermions. Density dependent frequency shifts of the ^1S0 to ^3P0 clock transition were first observed in ^87Sr [1]. Originally, this effect was attributed to s-wave interactions enabled by inhomogeneous excitations [2,3]. More recently, evidence for p-wave interactions was reported in ^171Yb [4]. Understanding interactions in theses systems is necessary to improve clock accuracy and stability. Moreover, such an understanding will enable optical lattice clock systems to serve as quantum simulators for open, driven, strongly-interacting quantum systems at the mesoscopic scale. We present a comprehensive evaluation and understanding of the interactions present in a ^87Sr optical lattice clock system under various conditions using a mean-field theory. The regime in which only a genuine many-body treatment can properly describe our system is within immediate experimental reach.[4pt] [1] G. Campbell et al., Science 324, 360 (2009). [2] A. M. Rey et al., PRL 103, 260402 (2009). [3] K. Gibble, PRL 103, 113202 (2009). [4] N. D. Lemke et al., PRL 107, 103902 (2011).

Bishof, Michael; Martin, Michael J.; Swallows, Matthew D.; Benko, Craig; von Stecher, Javier; Gorshkov, Alexey V.; Rey, Ana Maria; Ye, Jun

2012-06-01

175

Many-body dispersion forces of polarizable clusters and liquids

A system of atoms with embedded Drude dispersion oscillators interacting through dipole–dipole forces is simulated. Using path integrals it is shown that after the coordinates of the dispersion oscillators are integrated out, the atoms interact through many-body dispersion forces to all orders of the dipole–dipole interaction. Simulations are carried out on clusters to see if the presence of many-body forces

J. Cao; B. J. Berne

1992-01-01

176

Many-body interactions and nuclear structure

NASA Astrophysics Data System (ADS)

This paper presents several challenges to nuclear many-body theory and our understanding of the stability of nuclear matter. In order to achieve this, we present five different cases, starting with an idealized toy model. These cases expose problems that need to be understood in order to match recent advances in nuclear theory with current experimental programs in low-energy nuclear physics. In particular, we focus on our current understanding, or lack thereof, of many-body forces, and how they evolve as functions of the number of particles. We provide examples of discrepancies between theory and experiment and outline some selected perspectives for future research directions.

Hjorth-Jensen, M.; Dean, D. J.; Hagen, G.; Kvaal, S.

2010-06-01

177

Spectral properties of many-body Schrödinger operators with dilatation-analytic interactions

Quantum mechanicalN-body systems with dilatation analytic interactions are investigated. Absence of continuous singular part for the Hamiltonians is proved together with the existence of an absolutely continuous part having spectrum [?e, 8), where ?e is the lowest many body threshold of the system. In the complement of the set of thresholds the point spectrum is discrete; corresponding bound state wave-functions

E. Balslev; J. M. Combes

1971-01-01

178

The Bose gas: A subtle many-body problem

Now that the properties of the ground state of quantum-mechanical many-body\\u000asystems (bosons) at low density, $\\\\rho$, can be examined experimentally it is\\u000aappropriate to revisit some of the formulas deduced by many authors 4-5 decades\\u000aago. One of these is that the leading term in the energy\\/particle is $4\\\\pi a\\u000a\\\\rho$ where $a$ is the scattering length of the

Elliott H. Lieb

2000-01-01

179

The self-healing diffusion Monte Carlo algorithm (SHDMC) [Reboredo, Hood and Kent, Phys. Rev. B {\\bf 79}, 195117 (2009), Reboredo, {\\it ibid.} {\\bf 80}, 125110 (2009)] is extended to study the ground and excited states of magnetic and periodic systems. A recursive optimization algorithm is derived from the time evolution of the mixed probability density. The mixed probability density is given by an ensemble of electronic configurations (walkers) with complex weight. This complex weigh allows the amplitude of the fix-node wave function to move away from the trial wave function phase. This novel approach is both a generalization of SHDMC and the fixed-phase approximation [Ortiz, Ceperley and Martin Phys Rev. Lett. {\\bf 71}, 2777 (1993)]. When used recursively it improves simultaneously the node and phase. The algorithm is demonstrated to converge to the nearly exact solutions of model systems with periodic boundary conditions or applied magnetic fields. The method is also applied to obtain low energy excitations with magnetic field or periodic boundary conditions. The potential applications of this new method to study periodic, magnetic, and complex Hamiltonians are discussed.

Reboredo, Fernando A [ORNL

2012-01-01

180

Solving the many body pairing problem through Monte Carlo methods

NASA Astrophysics Data System (ADS)

Nuclear superconductivity is a central part of quantum many-body dynamics. In mesoscopic systems such as atomic nuclei, this phenomenon is influenced by shell effects, mean-field deformation, particle decay, and by other collective and chaotic components of nucleon motion. The ability to find an exact solution to these pairing correlations is of particular importance. In this presentation we develop and investigate the effectiveness of different methods of attacking the nucleon pairing problem in nuclei. In particular, we concentrate on the Monte Carlo approach. We review the configuration space Monte Carlo techniques, the Suzuki-Trotter breakup of the time evolution operator, and treatment of the pairing problem with non-constant matrix elements. The quasi-spin symmetry allows for a mapping of the pairing problem onto a problem of interacting spins which in turn can be solved using a Monte Carlo approach. The algorithms are investigated for convergence to the true ground state of model systems and calculated ground state energies are compared to those found by an exact diagonalization method. The possibility to include other non-pairing interaction components of the Hamiltonian is also investigated.

Lingle, Mark; Volya, Alexander

2012-03-01

181

Microscopic diagonal entropy and many-body dynamics

NASA Astrophysics Data System (ADS)

We define microscopic diagonal entropy to characterize many-body dynamics of systems far from equilibrium. For the systems prepared initially in thermal equilibrium, it increases with time and is related to the heat generated in the dynamics. We illustrate our results with numerical simulations of a toy-BCS model.

Barankov, Roman

2009-03-01

182

Unbounded growth of entanglement in models of many-body localization.

An important and incompletely answered question is whether a closed quantum system of many interacting particles can be localized by disorder. The time evolution of simple (unentangled) initial states is studied numerically for a system of interacting spinless fermions in one dimension described by the random-field XXZ Hamiltonian. Interactions induce a dramatic change in the propagation of entanglement and a smaller change in the propagation of particles. For even weak interactions, when the system is thought to be in a many-body localized phase, entanglement shows neither localized nor diffusive behavior but grows without limit in an infinite system: interactions act as a singular perturbation on the localized state with no interactions. The significance for proposed atomic experiments is that local measurements will show a large but nonthermal entropy in the many-body localized state. This entropy develops slowly (approximately logarithmically) over a diverging time scale as in glassy systems. PMID:23031128

Bardarson, Jens H; Pollmann, Frank; Moore, Joel E

2012-07-03

183

Non-equilibrium many body dynamics

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.

Creutz, M.; Gyulassy, M.

1997-09-22

184

Controlled many-body interactions in a frozen Rydberg gas

Previous resonant dipole-dipole energy-transfer experiments of cold Rydberg gases [Anderson et al., Phys. Rev. Lett. 80, 249 (1998); Mourachko et al., Phys. Rev. Lett. 80, 253 (1998)] have been interpreted as providing evidence of many-body, as opposed to purely binary, effects. Here we separate two-body and many-body interactions by introducing an additional Rydberg state, which does not participate directly in the energy-transfer process, but is strongly coupled to one of the final states. We observe broadening of the energy-transfer resonances due to this added Rydberg state, which clearly demonstrates the many-body nature of the dipole-dipole interactions in such a system.

Mourachko, I.; Li Wenhui; Gallagher, T.F. [Department of Physics, University of Virginia, Charlottesville, Virginia 22904 (United States)

2004-09-01

185

Recent Progress in Many-Body Theories: Proceedings of the 12th International Conference

NASA Astrophysics Data System (ADS)

Preface -- International advisory committee -- Feenberg medal session. Surface and superconductivity / L. P. Gor'kov. Spartak T. Belyaev - recipient of the Feenberg Medal / V. Zelevinsky. Many-body physics and spontaneous symmetry breaking / S. T. Belyaev -- Keynote speaker. The future lies ahead / P. W. Anderson -- Strongly correlated systems and phase transitions. Exact results for many-body problems using few-body methods / J. Cardy. Quantum matters: physics beyond Landau's paradigms / T. Senthil. Microscopic calculations of quantum phase transitions in frustrated magnetic lattices / R. F. Bishop & S. E. Krüger. Recent applications of the DMRG method / K. Hallberg. Functional renormalization group in the 2D Hubbard model / C. Honerkamp. Quantum phase transitions and event horizons: condensed matter analogies / G. Chapline. Spin-charge separation and topological phase transitions in Aharnov-Bohm rings of interacting electrons / B. Normand ... [et al.] -- Quantum fluids and solids. Two-particle-two-hole excitations in [symbol]He / E. Krotscheck, H. M. Böhm & K. Schörkhuber. Monolayer charged quantum films: a quantum simulation study / K. Wierschem & E. Manousakis. Can inconmensuration stabilize a superfluid phase of para-hydrogen? / M. Boninsegni. Analysis of the interatomic potential of the helium systems / S. Ujevic & S. A. Vitiello -- Nuclear physics and QCD. Quantum phase transitions in mesoscopic systems / F. Iachello. Nuclear-structure theory in the search for new fundamental physics / J. Engel. Matter at extreme density and its role in neutron stars and supernova / S. Reddy. New approaches to strong coupling lattice QCD / S. Chandrasekharan. Nuclear interactions from the renormalization group / A. Schwenk. Random interactions and ground state spin of finite Fermi systems / V. Zelevinsky & A. Volya -- Cold atoms and quantum information. Superfluid regimes in degenerate atomic fermi gases / G. V. Shlyapnikov. Bosons in optical lattices / S. L. Rolston. Generalized entanglement and quantum phase transitions / R. Somma ... [et al.]. Ground state of many-body lattice systems via a central limit theorem / C. Presilla & M. Ostilli. Effects of a single quantum spin on Josephson oscillations / M. Hru\\vska ... [et al.] -- Complex systems. Spin textures and random fields in dirty quantum hall ferromagnets / J. T. Chalker. Dissipative quantum disordered models / L. F. Cugliandolo. Possibly exact solution for the multicritical point of finite-dimensional spin glasses / H. Nishimori, K. Takeda & T. Sasamoto. From statistical physics methods to algorithms / D. Battaglia, M. Kola? & R. Zecchina.

Carlson, Joseph A.; Ortiz, Gerardo

2006-07-01

186

The importance of many-body effects in the theory of XAFS is reviewed. The dominant effects are inelastic losses: Extrinsic losses refer to inelastic losses in the propagation of the photoelectron and are treated using a complex, energy-dependent self-energy. The real part of the self-energy yields an important energy-dependent shift in the phase of the XAFS oscillations, while the imaginary part contributes to the mean-free-path. Intrinsic losses refer to losses associated with the creation of the core-hole. They give rise to shake-up/shake-off contributions to the absorption spectra. These losses may be calculated in terms of a corehole Green`s function. Interference between these processes leads to dynamical corrections, which are important at low energies.

Rehr, J.J.

1992-12-31

187

The importance of many-body effects in the theory of XAFS is reviewed. The dominant effects are inelastic losses: Extrinsic losses refer to inelastic losses in the propagation of the photoelectron and are treated using a complex, energy-dependent self-energy. The real part of the self-energy yields an important energy-dependent shift in the phase of the XAFS oscillations, while the imaginary part contributes to the mean-free-path. Intrinsic losses refer to losses associated with the creation of the core-hole. They give rise to shake-up/shake-off contributions to the absorption spectra. These losses may be calculated in terms of a corehole Green's function. Interference between these processes leads to dynamical corrections, which are important at low energies.

Rehr, J.J.

1992-01-01

188

Interaction energies of large clusters from many-body expansion.

In the canonical supermolecular approach, calculations of interaction energies for molecular clusters involve a calculation of the whole cluster, which becomes expensive as the cluster size increases. We propose a novel approach to this task by demonstrating that interaction energies of such clusters can be constructed from those of small subclusters with a much lower computational cost by applying progressively lower-level methods for subsequent terms in the many-body expansion. The efficiency of such "stratified approximation" many-body approach (SAMBA) is due to the rapid convergence of the many-body expansion for typical molecular clusters. The method has been applied to water clusters (H(2)O)(n), n = 6, 16, 24. For the hexamer, the best results that can be obtained with current computational resources in the canonical supermolecular method were reproduced to within about one tenth of the uncertainty of the canonical approach while using 24 times less computer time in the many-body expansion calculations. For (H(2)O)(24), SAMBA is particularly beneficial and we report interaction energies with accuracy that is currently impossible to obtain with the canonical supermolecular approach. Moreover, our results were computed using two orders of magnitude smaller computer resources than used in the previous best calculations for this system. We also show that the basis-set superposition errors should be removed in calculations for large clusters. PMID:22168675

Góra, Urszula; Podeszwa, Rafa?; Cencek, Wojciech; Szalewicz, Krzysztof

2011-12-14

189

Many body interactions in binary ionic solids

NASA Astrophysics Data System (ADS)

Recent developments in phonon models and microscopic theories of lattice mechanics have been reviewed, with particular emphasis on binary ionic solids. In doing so, we have traced the evolution of many body interactions from the electron-shell deformation and charge-transfer mechanisms and the approach of their incorporation in the framework of a dipolar model to describe the lattice static, dynamic, and anharmonic behaviours of these solids. The essential background and formalism of the sophisticated lattice dynamical models thus developed have been thoroughly treated in order to make them understandable and establish interrelationships between phonon and microscopic models and among themselves. An assessment of the relative merit of these models (e.g. breathing shell model, deformable shell model and three-body-force shell model) has been performed by making a critical comparison of theoretical results obtained from their comparative and unified lattice mechanical investigations with those measured from the experimental techniques and extensively surveyed in this article. Finally, we have outlined the future prospects and the scope of extension of various phonon models in view of the current trends in lattice dynamics and needs for a comprehensive study of the defect and anharmonic properties exhibited by the crystalline solids. Present address: Department of Physics, University of Edinburgh, Scotland, U.K. Now returned to Jabalpur, India.

Singh, R. K.

1982-05-01

190

Simulating typical entanglement with many-body Hamiltonian dynamics

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.

Nakata, Yoshifumi [Department of Physics, Graduate School of Science, University of Tokyo, Tokyo 113-0033 (Japan); Murao, Mio [Department of Physics, Graduate School of Science, University of Tokyo, Tokyo 113-0033 (Japan); Institute for Nano Quantum Information Electronics, University of Tokyo, Tokyo 153-8505 (Japan)

2011-11-15

191

Hybrid quantum systems of atoms and ions

NASA Astrophysics Data System (ADS)

In recent years, ultracold atoms have emerged as an exceptionally controllable experimental system to investigate fundamental physics, ranging from quantum information science to simulations of condensed matter models. Here we go one step further and explore how cold atoms can be combined with other quantum systems to create new quantum hybrids with tailored properties. Coupling atomic quantum many-body states to an independently controllable single-particle gives access to a wealth of novel physics and to completely new detection and manipulation techniques. We report on recent experiments in which we have for the first time deterministically placed a single ion into an atomic Bose Einstein condensate. A trapped ion, which currently constitutes the most pristine single particle quantum system, can be observed and manipulated at the single particle level. In this single-particle/many-body composite quantum system we show sympathetic cooling of the ion and observe chemical reactions of single particles in situ.

Zipkes, Christoph; Ratschbacher, Lothar; Palzer, Stefan; Sias, Carlo; Köhl, Michael

2011-01-01

192

First-principles many-body theory for ultra-cold atoms

Recent breakthroughs in the creation of ultra-cold atoms in the laboratory have ushered in unprecedented changes in physical science. These enormous changes in the coldest temperatures available in the laboratory mean that many novel experiments are possible. There is unprecedented control and simplicity in these novel systems, meaning that quantum many-body theory is now facing severe challenges in quantitatively understanding these new results. We discuss some of the new experiments and recently developed theoretical techniques required to predict the results obtained.

Drummond, Peter D.; Hu Hui; Liu Xiaji [ARC Centre of Excellence for Quantum-Atom Optics, Centre for Atom Optics and Ultrafast Spectroscopy, Swinburne University of Technology, Melbourne 3122 (Australia)

2010-06-15

193

First-principles many-body theory for ultra-cold atoms

NASA Astrophysics Data System (ADS)

Recent breakthroughs in the creation of ultra-cold atoms in the laboratory have ushered in unprecedented changes in physical science. These enormous changes in the coldest temperatures available in the laboratory mean that many novel experiments are possible. There is unprecedented control and simplicity in these novel systems, meaning that quantum many-body theory is now facing severe challenges in quantitatively understanding these new results. We discuss some of the new experiments and recently developed theoretical techniques required to predict the results obtained.

Drummond, Peter D.; Hu, Hui; Liu, Xia-Ji

2010-06-01

194

Many-body effects for critical Casimir forces

NASA Astrophysics Data System (ADS)

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%.

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

2013-02-01

195

Many-Body Forces in Nuclear Shell-Model.

National Technical Information Service (NTIS)

In the microscopic derivation of the effective Hamiltonian for the nuclear shell model many-body forces between the valence nucleons occur. These many-body forces can be discriminated in ''real'' many-body forces, which can be related to mesonic and inter...

P. K. Rath

1985-01-01

196

Many-body theory of electric and thermal transport in single-molecule heterojunctions

NASA Astrophysics Data System (ADS)

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.

Bergfield, Justin

2010-03-01

197

Cavity-Free Photon Blockade Induced by Many-Body Bound States

NASA Astrophysics Data System (ADS)

We show theoretically that a variety of strong quantum nonlinear phenomena occur in a completely open one-dimensional waveguide coupled to an N-type four-level system. This system could be realized, for example, in experiments using superconducting circuits. We focus on photon blockade, photon-induced tunneling, bunching or anti-bunching, and the creation of single-photon states, all in the absence of a cavity. Many-body bound states appear due to the strong photon-photon correlation mediated by the four-level system. These bound states cause photon blockade, generating a sub-Poissonian single-photon source [1]. Such a source is crucial for quantum cryptography and distributed quantum networking; our work thus supports the notion that open quantum systems can play a critical role in the manipulation of individual, mobile quanta, a key goal of quantum communication. [1] H. Zheng, D. J. Gauthier, and H. U. Baranger, Phys. Rev. Lett. in press (2011), arXiv:1107.0309.

Zheng, Huaixiu; Gauthier, Daniel; Baranger, Harold

2012-02-01

198

Improved variational many-body wave function in light nuclei

We propose and implement a simple method for improving the variational wave function of a many-body system. We have obtained a significant improvement in the binding energies, wave functions, and variance for the light nuclei {sup 3}H, {sup 4}He, and {sup 6}Li, using the fully realistic Argonne (AV{sub 18}) two-body and Urbana-IX (UIX) three-body interactions. The energy of {sup 4}He was improved by about 0.2 MeV and the {sup 6}Li binding energy was increased by {approx_equal}1.7 MeV compared to earlier variational Monte Carlo results. The latter result demonstrates the significant progress achieved by our method, and detailed analyses of the improved results are given. With central interactions the results are found to be in agreement with the 'exact' calculations. Our study shows that the relative error in the many-body wave functions, compared to two-body pair correlations, increases rapidly at least proportionally to the number of pairs in the system. However, this error does not increase indefinitely since the pair interactions saturate owing to convergence of cluster expansion.

Usmani, Q. N.; Anwar, K. [Institute of Engineering Mathematics, University Malaysia Perlis (Malaysia); Singh, A. [Department of Physics, School of Technology, Kalinga Institute of Industrial Technology, Bhubaneswar 751 024 (India); Rawitscher, G. [Department of Physics, University of Connecticut, Storrs, Connecticut 06269-3046 (United States)

2009-09-15

199

Vortices in quantum droplets: Analogies between boson and fermion systems

The main theme of this review is the many-body physics of vortices in quantum droplets of bosons or fermions in the limit of small particle numbers. Systems of interest include cold atoms in traps as well as electrons confined in quantum dots. When set to rotate, these in principle different quantum systems show remarkable analogies. The topics reviewed include the structure of the finite rotating many-body state, universality of vortex formation and localization of vortices in both bosonic and fermionic systems, and the emergence of particle-vortex composites in the quantum Hall regime. An overview of the computational many-body techniques sets focus on the configuration-interaction and density-functional methods. Studies of quantum droplets with one or several particle components, where vortices as well as coreless vortices may occur, are reviewed, and theoretical as well as experimental challenges are discussed.

Saarikoski, H.; Reimann, S. M.; Harju, A.; Manninen, M. [Mathematical Physics, LTH, Lund University, SE-22100 Lund (Sweden); Department of Applied Physics and Helsinki Institute of Physics, Aalto University, FI-02150 Espoo (Finland); Nanoscience Center, Department of Physics, University of Jyvaeskylae, FI-40014 Jyvaeskylae (Finland)

2010-07-15

200

The quantum N-electron structure problem is expressed as a classical N-body structure problem plus a quantum many-body problem with a reduced number of variables. This forms the foundation of a method for solving the electronic structure problem using k-electron distribution functions instead of many-electron wave functions. The method represents a unified approach to the entire hierarchy of generalized density-functional theories, beginning with standard density-functional theory (k=1) and pair density-functional theory (k=2) and culminating in an exact treatment of the entire N-electron system (k=N)

Ayers, Paul W. [Department of Chemistry, McMaster University, Hamilton, Ontario, L8S 4M1 (Canada)

2006-10-15

201

NASA Astrophysics Data System (ADS)

We study the real-time dynamics of a quantum Ising chain driven periodically by instantaneous quenches of the transverse field between +?0 and ?0 back and forth in equal intervals of time. Two interesting phenomena are reported and analyzed. (i) We observe dynamical many-body freezing (DMF), i.e., strongly nonmonotonic freezing of the response with respect to the driving parameters (pulse width and height) resulting from coherent suppression of dynamics of all quasiparticle modes. For certain combinations of the pulse height and the period, maximal freezing (DMF peaks) is observed, where a massive collapse of the entire Floquet spectrum occurs and the many-body system remains frozen extremely close to the initial state for all time. (ii) Second, away from the freezing peak, we observe the emergence of a distinct oscillation with a single nontrivial frequency, which can be much lower than the driving frequency. This remarkable slow oscillation involving many high-energy modes dominates the response in the limit of long observation time. We identify this slow oscillation as the unique survivor of destructive quantum interference between the many-body modes. The oscillation tends to decay algebraically with time to a constant value. All the key features are demonstrated analytically with numerical evaluations for specific results.

Bhattacharyya, Sirshendu; Das, Arnab; Dasgupta, Subinay

2012-08-01

202

NASA Astrophysics Data System (ADS)

Fragment-based quantum chemistry methods are a promising route towards massively parallel electronic structure calculations in large systems. Unfortunately, the literature on this topic consists of a bewildering array of different methods, with no clear guiding principles to choose amongst them. Here, we introduce a conceptual framework that unifies many of these ostensibly disparate approaches. The common framework is based upon an approximate supersystem energy formula for a collection of intersecting (i.e., overlapping) fragments. This formula generalizes the traditional many-body expansion to cases where the ``bodies'' (fragments) share some nuclei in common, and reduces to the traditional many-body expansion for non-overlapping fragments. We illustrate how numerous fragment-based methods fit within this framework. Preliminary applications to molecular and ionic clusters suggest that two-body methods in which dimers are constructed from intersecting fragments may be a route to achieve very high accuracy in fragment-based calculations.

Richard, Ryan M.; Herbert, John M.

2012-08-01

203

Many-body Landau-Zener transition in cold-atom double-well optical lattices

NASA Astrophysics Data System (ADS)

Ultracold atoms in optical lattices provide an ideal platform for exploring many-body physics of a large system arising from the coupling among a series of small identical systems whose few-body dynamics is exactly solvable. Using Landau-Zener (LZ) transition of bosonic atoms in double-well optical lattices as an experimentally realizable model, we investigate such few- to many-body routes by exploring the relation and difference between the small few-body (in one double well) and the large many-body (in double-well lattice) nonequilibrium dynamics of cold atoms in optical lattices. We find the many-body coupling between double wells greatly enhances the LZ transition probability. The many-body dynamics in the double-well lattice shares both similarity and difference from the few-body dynamics in one and two double wells. The sign of the on-site interaction plays a significant role in the many-body LZ transition. Various experimental signatures of the many-body LZ transition, including atom density, momentum distribution, and density-density correlation, are obtained.

Qian, Yinyin; Gong, Ming; Zhang, Chuanwei

2013-01-01

204

Groundstatable fermionic wavefunctions and their associated many-body Hamiltonians

In the vast majority of many-body problems, it is the kinetic energy part of the Hamiltonian that is best known microscopically, and it is the detailed form of the interactions between the particles, the potential energy term, that is harder to determine from first principles. An example is the case of high temperature superconductors: while a tight-binding model captures the kinetic term, it is not clear that there is superconductivity with only an onsite repulsion and, thus, that the problem is accurately described by the Hubbard model alone. Here we pose the question of whether, once the kinetic energy is fixed, a candidate ground state is groundstatable or not. The easiness to answer this question is strongly related to the presence or the absence of a sign problem in the system. When groundstatability is satisfied, it is simple to obtain the potential energy that will lead to such a ground state. As a concrete case study, we apply these ideas to different fermionic wavefunctions with superconductive or spin-density wave correlations and we also study the influence of Jastrow factors. The kinetic energy considered is a simple nearest neighbor hopping term.

Charrier, Daniel [Physics Department, Boston University, Boston, MA 02215 (United States); Laboratoire de Physique Theorique, IRSAMC, UPS and CNRS, Universite de Toulouse, F-31062 Toulouse (France)], E-mail: dcharrie@buphy.bu.edu; Chamon, Claudio [Physics Department, Boston University, Boston, MA 02215 (United States)

2010-01-15

205

Many-Body Interactions in Condensed-Matters

In commemoration of the 50 years anniversary of Fujita-Miyaszawa theory on the 3-body interaction among nucleons, we would like to review on the phenomena inherent to many-body interactions in condensed matters: (1) 3-body non-additive interaction among atoms which causes significant effect on the third order virial coefficient, (2) the many-body (ring) exchange in the solid helium 3 which plays important role, and (3) effective long range interaction induced by the elastic interaction in spin-crossover materials which causes a peculiar phase transition of the mean-field universality class.

MIYASHITA, Seiji [Department of Physics, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033 (Japan); CREST, JST, 4-1-8 Honcho Kawaguchi, Saitama, 332-0012 (Japan)

2008-04-29

206

NASA Astrophysics Data System (ADS)

Following a “bottom-up approach” in understanding many-particle effects and dynamics we provide a systematic ab initio study of the dependence of the breathing dynamics of ultracold bosons in a one-dimensional (1D) harmonic trap on the number of bosons ranging from few to many. To this end, we employ the multilayer multiconfiguration time-dependent Hartree method for bosons (ML-MCTDHB) which has been developed very recently [Krönke, Cao, Vendrell, and Schmelcher, New J. Phys.NJOPFM1367-263010.1088/1367-2630/15/6/063018 15, 063018 (2013)]. The beating behavior for two bosons is found numerically and consequently explained by an analytical approach. Drawing on this, we show how to compute the complete breathing mode spectrum in this case. We examine how the two-mode breathing behavior of two bosons evolves to the single-frequency behavior of the many-particle limit when adding more particles. In the limit of many particles, we numerically study the dependence of the breathing mode frequency on both the interaction strength as well as on the particle number. We provide an estimate for the parameter region where the mean-field description provides a valid approximation.

Schmitz, Rüdiger; Krönke, Sven; Cao, Lushuai; Schmelcher, Peter

2013-10-01

207

Energy benchmarks for water clusters and ice structures from an embedded many-body expansion

NASA Astrophysics Data System (ADS)

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 mEh/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.

Gillan, M. J.; Alfè, D.; Bygrave, P. J.; Taylor, C. R.; Manby, F. R.

2013-09-01

208

Many-body electronic structure calculations for Americium metal

Total energies and electronic spectral functions for Americium are calculated using novel dynamical mean field based spectral density functional approach. Pressure dependence as a function of volume and bulk modules for different phases of Am will be studied by this many body calculation and compared to the predictions of experiment. Volume dependent spectral functions will be extracted and discussed in

Sergej Savrasov; Gabriel Kotliar

2005-01-01

209

Tailoring many-body entanglement through local control

NASA Astrophysics Data System (ADS)

We construct optimal time-local control pulses based on a multipartite entanglement measure as target functional. The underlying control Hamiltonians are derived in a purely algebraic fashion, and the resulting pulses drive a composite quantum system rapidly into that highly entangled state which can be created most efficiently for a given interaction mechanism, and which bears entanglement that is robust against decoherence. Moreover, it is shown that the control scheme is insensitive to experimental imperfections in first order.

Lucas, Felix; Mintert, Florian; Buchleitner, Andreas

2013-09-01

210

Many-body effects in silicene, silicane, germanene and germanane.

Silicene, which is the silicon equivalent of carbon-based graphene and shares some of the unique properties with graphene, has been attracting more and more attention since its synthesis and represents a breakthrough in current silicon-based technology. In this work, many-body effects in silicene, silicane, germanene and germanane have been demonstrated based on the Green's function perturbation theory, i.e., GW + Bethe-Salpeter equation. Due to confinement, many-body effects play a pivotal role in quasi-particle excitations and optical absorption spectra, which leads to excitonic resonance (???* excitation) in silicene and germanene, and strongly bound excitons in silicane and germanane with considerable binding energies. PMID:23640017

Wei, Wei; Dai, Ying; Huang, Baibiao; Jacob, Timo

2013-05-02

211

Bilayer superfluidity of fermionic polar molecules: Many-body effects

We study the BCS superfluid transition in a single-component fermionic gas of dipolar particles loaded in a tight bilayer trap, with the electric dipole moments polarized perpendicular to the layers. Based on the detailed analysis of the interlayer scattering, we calculate the critical temperature of the interlayer superfluid pairing transition when the layer separation is both smaller (dilute regime) and on the order or larger (dense regime) than the mean interparticle separation in each layer. Our calculations go beyond the standard BCS approach and include the many-body contributions resulting in the mass renormalization, as well as additional contributions to the pairing interaction. We find that the many-body effects have a pronounced effect on the critical temperature and can either decrease (in the very dilute limit) or increase (in the dense and moderately dilute limits) the transition temperature as compared to the BCS approach.

Baranov, M. A. [Institute for Theoretical Physics, University of Innsbruck, A-6020 Innsbruck (Austria); Institute for Quantum Optics and Quantum Information of the Austrian Academy of Sciences, A-6020 Innsbruck (Austria); RRC 'Kurchatov Institute', Kurchatov Square 1, 123182 Moscow (Russian Federation); Micheli, A.; Ronen, S.; Zoller, P. [Institute for Theoretical Physics, University of Innsbruck, A-6020 Innsbruck (Austria); Institute for Quantum Optics and Quantum Information of the Austrian Academy of Sciences, A-6020 Innsbruck (Austria)

2011-04-15

212

Many-body interactions in quasi-freestanding graphene

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.

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

2011-06-03

213

Many-body polarization effects and the membrane dipole potential.

Molecular dynamics simulations of a lipid monolayer at a water-air interface are used to investigate the dipole potential that arises at the water-lipid interface. One simulation explicitly accounts for many-body polarization effects by using a model based on classical Drude oscillators. The dipole potential of the Drude model monolayer is 0.35V in excellent agreement with experimental estimates that range between 0.3 and 0.4V, whereas, a simulation using a nonpolarizable model significantly overestimates the potential with a calculated value of 0.8V. Induced polarization effects in the nonpolar region of the monolayer are found to buffer the residual positive lipid potential that results from competing polarization effects at the polar water/monolayer interface. These results, indicate the utility of the inclusion of many-body polarization effects in empirical force field models of lipids.

Harder, E.; MacKerell, A. D.; Roux, B. (Biosciences Division); (Univ. of Chicago); (Univ. of Maryland)

2009-01-01

214

Many-body interactions in quasi-freestanding graphene

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.

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

2011-01-01

215

Effective Operators from Exact Many-Body Renormalization

We construct effective two-body Hamiltonians and E2 operators for the p-shell by performing 16 ab initio no-core shell model (NCSM) calculations for A = 5 and A = 6 nuclei and explicitly projecting the many-body Hamiltonians and E2 operator onto the 0 space. We then separate the effective E2 operator into one-body and two-body contributions employing the two-body valence cluster

A. F. Lisetskiy; M. K. G. Kruse; B. R. Barrett; P. Navratil; I. Stetcu; J. P. Vary

2009-01-01

216

Effective operators from exact many-body renormalization

We construct effective two-body Hamiltonians and E2 operators for the p shell by performing 16ℏOmega ab initio no-core shell model (NCSM) calculations for A=5 and A=6 nuclei and explicitly projecting the many-body Hamiltonians and E2 operator onto the 0ℏOmega space. We then separate the effective E2 operator into one-body and two-body contributions employing the two-body valence cluster approximation. We analyze

A. F. Lisetskiy; M. K. G. Kruse; B. R. Barrett; P. Navratil; I. Stetcu; J. P. Vary

2009-01-01

217

Many-Body Electronic Structure of Curium metal

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

Antonina Toropova; Kristjan Haule; Gabriel Kotliar

2006-01-01

218

Aspects of non-abelian many-body physics

NASA Astrophysics Data System (ADS)

The general formulation of quantum statistical mechanics hints at interesting generalizations of the usual Bose/Fermi framework in two spatial dimensions. Anyon statistics, which is essentially a continuous interpolation between Bose and Fermi statistics, is relevant to the Fractional Quantum Hall Effect in two- dimensional (i.e., thin layer) condensed matter systems. In addition, the possibility of non-abelian statistics, in which the multi-particle wavefunction transforms as a representation of a non-abelian group under the exchange of indistinguishable particles, has been explored. Spontaneously broken non-abelian gauge theories in (2 + 1) dimensions often have stable topological defects, called non-abelian vortices, that experience non-abelian statistics. In addition, it has been suggested that degenerate quasihole multiplets in Quantum Hall systems also transform as non-abelian representations of the braid group under particle exchange. In this thesis, I explore the braiding properties of systems of two-cycle flux vortices in a residual S3 discrete gauge group. The individual vortices are uncharged, but multi-vortex states can have Cheshire charge. The uncharged sectors all have non-vanishing bosonic subspaces, as do the non- abelian charged trivial flux sectors. A kinetic Hamiltonian for vortices on a periodic lattice is constructed. There is a modification to the translational symmetry in the periodically identified direction for non-trivial Z2 charged sectors. The ground state energies for various three and four vortex sectors is numerically determined. Typically, the ground state is bosonic, with a gap separating it from a non-abelian subspace.

Bradford, Kent B.

219

Parallel implementation of many-body mean-field equations

NASA Astrophysics Data System (ADS)

We describe the numerical methods used to solve the system of stiff, nonlinear partial differential equations resulting from the Hartree-Fock description of many-particle quantum systems, as applied to the structure of the nucleus. The solutions are performed on a three-dimensional Cartesian lattice. Discretization is achieved through the lattice basis-spline collocation method, in which quantum-state vectors and coordinate-space operators are expressed in terms of basis-spline functions on a spatial lattice. All numerical procedures reduce to a series of matrix-vector multiplications and other elementary operations, which we perform on a number of different computing architectures, including the Intel Paragon and the Intel iPSC/860 hypercube. Parallelization is achieved through a combination of mechanisms employing the Gram-Schmidt procedure, broadcasts, global operations, and domain decomposition of state vectors. We discuss the approach to the problems of limited node memory and node-to-node communication overhead inherent in using distributed-memory, multiple-instruction, multiple-data stream parallel computers. An algorithm was developed to reduce the communication overhead by pipelining some of the message passing procedures.

Chinn, C. R.; Umar, A. S.; Vallières, M.; Strayer, M. R.

1994-12-01

220

Many-Body Mean-Field Equations: Parallel implementation

We describe the implementation of Hartree-Fock Many-Body Mean-Field Equations on a Parallel Intel iPSC/860 hypercube. We first discuss the Nuclear Mean-Field approach in physical terms. Then we describe our parallel implementation of this approach on the Intel iPSC/860 hypercube. We discuss and compare the advantages and disadvantages of the domain partition versus the Hilbert space partition for this problem. We conclude by discussing some timing experiments on various computing platforms.

Vallieres, M. [Drexel Univ., Philadelphia, PA (United States). Physics & Atmospheric Science; Umar, S.; Chinn, C. [Vanderbilt Univ., Nashville, TN (United States). Dept. of Physics & Astronomy; Strayer, M. [Oak Ridge National Lab., TN (United States). Physics Division

1993-12-31

221

Collective Many-Body Interaction in Rydberg Dressed Atoms

We present a method to control the shape and character of the interaction potential between cold atomic gases by weakly dressing the atomic ground state with a Rydberg level. For increasing particle densities, a crossover takes place from a two-particle interaction into a collective many-body interaction, where the dipole-dipole or van der Waals blockade phenomenon between the Rydberg levels plays a dominant role. We study the influence of these collective interaction potentials on a Bose-Einstein condensate and present the optimal parameters for its experimental detection.

Honer, Jens; Weimer, Hendrik; Buechler, Hans Peter [Institute for Theoretical Physics III, University of Stuttgart, Stuttgart (Germany); Pfau, Tilman [5. Physikalische Institut, University of Stuttgart, Stuttgart (Germany)

2010-10-15

222

Novel approach to effective interactions for many-body calculations

NASA Astrophysics Data System (ADS)

Even in the absence of exact solutions from QCD, effective field theories (EFT) provide a modern understanding of the nuclear forces at low energies. Based on a EFT which integrates out the pions as degrees of freedom (pionless theory), we present a new approach to the derivation of effective interactions suitable for many-body calculations by means of the no-core shell model. Such an approach can provide a consistent, order-by-order improvable method to obtain interactions tailored for the model spaces used in the many-body calculations, as well as the corresponding electromagnetic and weak operators. In this work, we concentrate on the description of two-body scattering observables in a restricted harmonic oscillator basis. I.S. and B.R.B. acknowledge partial support by NSF grant numbers PHY0070858 and PHY0244389. U.v.K. acknowledges partial support from DOE grant number DE-FG02-04ER41338 and from the Sloan Foundation.

Stetcu, Ionel; Barrett, Bruce R.; van Kolck, Ubirajara

2006-04-01

223

Many-body properties of quasi-one-dimensional boson gas across a narrow CIR

NASA Astrophysics Data System (ADS)

We study strong interaction effects in a one-dimensional (1D) boson gas across a narrow confinement-induced resonance (CIR). In contrast to the zero-range potential, the 1D two-body interaction in the narrow CIR can be written as a polynomial of derivative ?-function interaction on many-body level. Using the asymptotic Bethe ansatz, we find that the low-energy physics of this many-body problem is described by the Tomonaga-Luttinger liquid where the Luttinger parameters are essentially modified by an effective finite-range parameter v. This parameter drastically alters quantum criticality and universal thermodynamics of the gas. In particular, it drives the Tonks-Girardeau (TG) gas from non-mutual Fermi statistics to mutual statistics or to a more exclusive super-TG gas. This novel feature is further discussed in terms of the breathing mode which is experimentally measurable.

Qi, Ran; Guan, Xiwen

2013-02-01

224

Evolution of regulatory complexes: a many-body system

NASA Astrophysics Data System (ADS)

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.

Nouemohammad, Armita; Laessig, Michael

2013-03-01

225

Strong many-body effects in silicene-based structures

NASA Astrophysics Data System (ADS)

Silicene, which is the silicon equivalent of carbon-based graphene and shares some unique properties with graphene, has been attracting more and more attention since its successful synthesis. Using Green's function perturbation theory, many-body effects in silicene, hydrogenated silicene (silicane), fluorinated silicene (fluorosilicene), as well as armchair silicene nanoribbons (ASiNRs) are studied. Optical resonances in silicene have been aroused by excitonic effects: The ???* excitonic resonance at 1.23 eV is contributed by the characteristic dispersion of Dirac fermions, while the one at 3.75 eV is due to the ???* transition. Hydrogenation or fluorination of silicene removes the conductivity at the Dirac point and causes band-gap opening. In addition to the remarkable self-energy effects, optical absorption properties of silicane, fluorosilicene, and ASiNRs are dominated by strong excitonic effects with formation of bound excitons with considerable binding energies.

Wei, Wei; Jacob, Timo

2013-07-01

226

Relativistic many-body theory of atomic structures

NASA Astrophysics Data System (ADS)

The effect of relativity and electron correlations on atomic processes were studied. Current efforts include hyperfine structure (hfs) studies using the multiconfiguration Dirac-Fock (MCDF) techniques. Atomic hfs are known to be sensitive to relativity and electron correlations, and provide important tests of relativistic atomic many-body theories. Preliminary results on the hfs of the 4f(12) (3)H ground state of 68Fr(167) are shown and are in good agreement with experiment. The MCDF technique is an efficient and powerful method for atomic hfs studies. Further tests of this method are in progress. The absorption spectra for Xe-like ions in the region of 4d (FEMALE) nf, epsilonf transitions is being studied.

Cheng, K. T.

227

Effective Operators from Exact Many-Body Renormalization

We construct effective two-body Hamiltonians and E2 operators for the p-shell by performing 16{h_bar}{Omega} ab initio no-core shell model (NCSM) calculations for A = 5 and A = 6 nuclei and explicitly projecting the many-body Hamiltonians and E2 operator onto the 0{h_bar}{Omega} space. We then separate the effective E2 operator into one-body and two-body contributions employing the two-body valence cluster approximation. We analyze the convergence of proton and neutron valence one-body contributions with increasing model space size and explore the role of valence two-body contributions. We show that the constructed effective E2 operator can be parametrized in terms of one-body effective charges giving a good estimate of the NCSM result for heavier p-shell nuclei.

Lisetskiy, A F; Kruse, M G; Barrett, B R; Navratil, P; Stetcu, I; Vary, J P

2009-06-11

228

Effective operators from exact many-body renormalization

NASA Astrophysics Data System (ADS)

We construct effective two-body Hamiltonians and E2 operators for the p shell by performing 16?? ab initio no-core shell model (NCSM) calculations for A=5 and A=6 nuclei and explicitly projecting the many-body Hamiltonians and E2 operator onto the 0?? space. We then separate the effective E2 operator into one-body and two-body contributions employing the two-body valence cluster approximation. We analyze the convergence of proton and neutron valence one-body contributions with increasing model space size and explore the role of valence two-body contributions. We show that the constructed effective E2 operator can be parametrized in terms of one-body effective charges giving a good estimate of the NCSM result for heavier p-shell nuclei.

Lisetskiy, A. F.; Kruse, M. K. G.; Barrett, B. R.; Navratil, P.; Stetcu, I.; Vary, J. P.

2009-08-01

229

Model Calculations of Many Body Effects in EXAFS

NASA Astrophysics Data System (ADS)

Extrinsic and intrinsic excitations and their interference are calculated for an electron gas using a generalization of the GW approach and a plasmon pole dielectric function. These effects lead to an asymmetric quasiparticle peak and an energy dependent satellite in the spectral function. Interference between the extrinsic and intrinsic excitations leads to a reduction of the satellite and an enhancement of the main peak. These interference effects cause maximal cancellation of extrinsic and intrinsic losses at threshold and become negligible at high energies. The EXAFS is expressed as a convolution of the spectral function with the one-electron EXAFS expression. This yields a many-body amplitude reduction factor and a phase shift, in terms of a phasor summation, in addition to the usual mean free path. The theory yields results in good agreement with experiment for Cu K-edge EXAFS.

Campbell, L. W.; Hedin, L.; Rehr, J. J.; Bardyszewski, W.

2001-03-01

230

Charge-optimized many-body (COMB) potential for zirconium

NASA Astrophysics Data System (ADS)

An interatomic potential for zirconium is developed within the charge-optimized many-body (COMB) formalism. The potential correctly predicts the hexagonal close-packed (HCP) structure as the ground state with cohesive energy, lattice parameters, and elastic constants matching experiment well. The most stable interstitial position is the basal octahedral followed by basal split, in agreement with recent first principles calculations. Stacking fault energies within the prism and basal planes satisfactorily match first principles calculations. A tensile test using nanocrystalline zirconium exhibits both prismatic {101¯0}<112¯0> slip and pyramidal {112¯2}<112¯3¯> slip, showing the model is capable of reproducing the mechanical deformation modes observed in experiments.

Noordhoek, Mark J.; Liang, Tao; Lu, Zizhe; Shan, Tzu-Ray; Sinnott, Susan B.; Phillpot, Simon R.

2013-10-01

231

Transitionless quantum driving for spin systems.

We apply the method of transitionless quantum driving for time-dependent quantum systems to spin systems. For a given Hamiltonian, the driving Hamiltonian is constructed so that the adiabatic states of the original system obey the Schrödinger equation. For several typical systems such as the XY spin chain and the Lipkin-Meshkov-Glick model, the driving Hamiltonian is constructed explicitly. We discuss possible interesting situations when the driving Hamiltonian becomes time independent and when the driving Hamiltonian is equivalent to the original one. For many-body systems, a crucial problem occurs at the quantum phase transition point where the energy gap between the ground and first excited states becomes zero. We discuss how the defect can be circumvented in the present method. PMID:23848637

Takahashi, Kazutaka

2013-06-12

232

Many-body braiding phases in a rotating strongly correlated photon gas

NASA Astrophysics Data System (ADS)

We present a theoretical study of fractional quantum Hall physics in a rotating gas of strongly interacting photons in a single cavity with a large optical nonlinearity. Photons are injected into the cavity by a Laguerre-Gauss laser beam with a non-zero orbital angular momentum. The Laughlin-like few-photon eigenstates appear as sharp resonances in the transmission spectra. Using additional localized repulsive potentials, quasi-holes can be created in the photon gas and then braided around in space: an unambiguous signature of the many-body Berry phase under exchange of two quasi-holes is observed as a spectral shift of the corresponding transmission resonance.

Umucal?lar, R. O.; Carusotto, I.

2013-11-01

233

Band structure of polyethylene from many-body perturbation theory

NASA Astrophysics Data System (ADS)

The electronic structure of polyethylene is an important benchmark and the infinite chain limit for the electronic properties of many molecules, monolayers, and oligomers. Therefore, the band structure of the ideal, one-dimensional polyethylene chain has been extensively researched, from both the experimental and the theoretical viewpoints. Despite this extensive effort, to the best of our knowledge agreement between theoretical calculations and the electronic structure obtained from photoelectron spectroscopy could only be obtained using artificial shifting and ``stretching'' of the computed data. Here, we present a quantitative quasi-particle band-structure for polyethylene using many-body perturbation theory. The approach is employed within the G0W0 approximation, based on a starting point calculated within the generalized gradient approximation to density functional theory. We compare our calculated band-structure to angle resolved photoemission spectroscopy measurements for various long saturated carbohydrates, demonstrate a much improved agreement with experiment, and discuss remaining discrepancies and their possible origins within both theory and experiment.

Biller, Ariel; Sharifzadeh, Sahar; Segev, Lior; Ismail-Beigi, Sohrab; Neaton, Jeffrey B.; Kronik, Leeor

2013-03-01

234

Quantum electromechanical systems

Quantum electromechanical systems are nano-to-micrometer (micron) scale mechanical resonators coupled to electronic devices of comparable dimensions, such that the mechanical resonator behaves in a manifestly quantum manner. We review progress towards realising quantum electromechanical systems, beginning with the phononic quantum of thermal conductance for suspended dielectric wires. We then describe efforts to reach the quantum zero-point displacement uncertainty detection limit

Miles Blencowe

2004-01-01

235

Quantum Simulation for Open-System Dynamics

NASA Astrophysics Data System (ADS)

Simulations are essential for predicting and explaining properties of physical and mathematical systems yet so far have been restricted to classical and closed quantum systems [1,2]. Although forays have been made into open-system quantum simulation [3], the strict algorithmic aspect has not been explored yet is necessary to account fully for resource consumption to deliver bounded-error answers to computational questions. An open-system quantum simulator would encompass classical and closed-system simulation and also solve outstanding problems concerning, e.g. dynamical phase transitions in non-equilibrium systems, establishing long-range order via dissipation, verifying the simulatability of open-system dynamics on a quantum Turing machine. We construct an efficient autonomous algorithm for designing an efficient quantum circuit to simulate many-body open-system dynamics described by a local Hamiltonian plus decoherence due to separate baths for each particle. The execution time and number of gates for the quantum simulator both scale polynomially with the system size.[4pt] [1] S. Lloyd, Science 273, 1073 (1996).[0pt] [2] D. W. Berry et al, Comm. Math. Phys. 270, 359 (2007).[0pt] [3] M. Kliesch et al, Phys. Rev. Lett. 107, 120501 (2011).

Wang, Dong-Sheng; de Oliveira, Marcos Cesar; Berry, Dominic; Sanders, Barry

2013-03-01

236

Dimensional Continuation in Electronic Structure and Many-Body Problems.

NASA Astrophysics Data System (ADS)

This dissertation concerns the development and application of new techniques for electronic structure calculations motivated by dimensional scaling (analytic continuation in the spatial dimensionality D followed by finitizing scalings). One desirable feature of dimensional scaling as applied to electronic structure problems is that it gives rise to two distinct singular (and hence simplifying) limits, namely Dto 1 and Dto infty. A scaling procedure which is finitizing and uniform for 1<= D<=infty is presented. Dimensional limit results obtained with this scaling can be used to obtain quite accurate approximations to D=3 eigenvalues. The procedure is demonstrated for H_sp{2 }{+} and for H_2 in the Hartree approximation. For the latter problem both the Dto 1 and Dtoinfty solutions are obtained for the first time. Another advantage of the dimensional scaling approach is its usefulness for studying correlation effects. This is demonstrated for the model many-body problem of N mutually gravitating bosons. The exact and Hartree Dto infty solutions are derived (both in closed form), and combined with literature results for the exact and Hartree Dto 1 solutions (also both in closed form) to obtain approximate D=3 solutions. For comparison, the Hartree D=3 solution is also solved numerically. The dimensionally generalized hamiltonian used for this problem is obtained in a quite general form which should also be useful for other problems. A third benefit of dimensional scaling is that it provides conceptually simple models of electronic structure. The Dtoinfty limit yields classical structures which are useful but by themselves are at best qualitatively correct. A procedure for generating classical representations which incorporates finite-D effects is presented. Electronic structures obtained from these non -differential "subhamiltonians" are classical in character, and may be regarded as optimal classical representations of D=3 electronic structures. This approach also models the D=3 energies to within a few percent.

Tan, Agnes Lay-Choo

1992-01-01

237

Quantum Games and Programmable Quantum Systems

Attention to the very physical aspects of information characterizes the current research in quantum computation, quantum cryptography and quantum communication. In most of the cases quantum description of the system provides advantages over the classical approach. Game theory, the study of decision making in conflict situation has already been extended to the quantum domain. We would like to review the

Edward W. Piotrowski; Jan Sladkowski

2005-01-01

238

Dielectric many-body effects in arrays of charged cylindrical macromolecules

NASA Astrophysics Data System (ADS)

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.

Sinkovits, Daniel W.; Barros, Kipton; Dobnikar, Jure; Kandu&{Caron; C}, Matej; Naji, Ali; Podgornik, Rudolf; Luijten, Erik

2012-02-01

239

Two-dimensional electrons in a magnetic field. III. Many-body effects

A many-body theory is given to show that the magnetic properties of a two-dimensional electron system are dependent on the filling factor gamma-10 defined as the ratio of the ideal Fermi energy against the field energy. Explicit results are obtained for absolute zero and large values of this factor. The internal energy is evaluated explicitly in consideration of the ideal,

Y. Shiwa; A. Isihara

1983-01-01

240

Importance of many-body correlations in glass transition: an example from polydisperse hard spheres.

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. PMID:23556787

Leocmach, Mathieu; Russo, John; Tanaka, Hajime

2013-03-28

241

Importance of many-body correlations in glass transition: An example from polydisperse hard spheres

NASA Astrophysics Data System (ADS)

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.

Leocmach, Mathieu; Russo, John; Tanaka, Hajime

2013-03-01

242

Many-body spin interactions and the ground state of a dense Rydberg lattice gas.

We study a one-dimensional atomic lattice gas in which Rydberg atoms are excited by a laser and whose external dynamics is frozen. We identify a parameter regime in which the Hamiltonian is well approximated by a spin Hamiltonian with quasilocal many-body interactions which possesses an exact analytic ground state solution. This state is a superposition of all states of the system that are compatible with an interaction induced constraint weighted by a fugacity. We perform a detailed analysis of this state which exhibits a crossover between a paramagnetic phase with short-ranged correlations and a crystal. This study also leads us to a class of spin models with many-body interactions that permit an analytic ground state solution. PMID:21405236

Lesanovsky, Igor

2011-01-11

243

Recent advances in Many Body Dissipative Particles Dynamics simulations of liquid-vapor interfaces.

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. PMID:23361618

Ghoufi, Aziz; Emile, Janine; Malfreyt, Patrice

2013-01-31

244

Kohn-Sham density-functional theory and renormalization of many-body perturbation expansions

NASA Astrophysics Data System (ADS)

Numerous practical applications provide strong evidence that despite its simplicity and crude approximations, density-functional theory leads to a rather accurate description of ground state properties of various condensed matter systems. Although well documented numerically, to our knowledge a theoretical explanation of the accuracy of density-functional theory has not been given. This issue is clarified in this work by demonstrating that density-functional theory represents a particular renormalization procedure of a many-body perturbation expansion. In other words, it is shown that density-functional theory is a many-body perturbation theory whose convergence properties have been optimized. The realization of this fact brings new meaning into density-functional theory and explains the success of density-functional based calculations. For more information go to http://alchemy.ucsd.edu/marat/ .

Valiev, Marat

1998-03-01

245

Many-Body Spin Interactions and the Ground State of a Dense Rydberg Lattice Gas

NASA Astrophysics Data System (ADS)

We study a one-dimensional atomic lattice gas in which Rydberg atoms are excited by a laser and whose external dynamics is frozen. We identify a parameter regime in which the Hamiltonian is well approximated by a spin Hamiltonian with quasilocal many-body interactions which possesses an exact analytic ground state solution. This state is a superposition of all states of the system that are compatible with an interaction induced constraint weighted by a fugacity. We perform a detailed analysis of this state which exhibits a crossover between a paramagnetic phase with short-ranged correlations and a crystal. This study also leads us to a class of spin models with many-body interactions that permit an analytic ground state solution.

Lesanovsky, Igor

2011-01-01

246

Many-Body Spin Interactions and the Ground State of a Dense Rydberg Lattice Gas

We study a one-dimensional atomic lattice gas in which Rydberg atoms are excited by a laser and whose external dynamics is frozen. We identify a parameter regime in which the Hamiltonian is well approximated by a spin Hamiltonian with quasilocal many-body interactions which possesses an exact analytic ground state solution. This state is a superposition of all states of the system that are compatible with an interaction induced constraint weighted by a fugacity. We perform a detailed analysis of this state which exhibits a crossover between a paramagnetic phase with short-ranged correlations and a crystal. This study also leads us to a class of spin models with many-body interactions that permit an analytic ground state solution.

Lesanovsky, Igor [Midlands Ultracold Atom Research Centre (MUARC), School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD (United Kingdom)

2011-01-14

247

Exact and approximate many-body dynamics with stochastic one-body density matrix evolution

NASA Astrophysics Data System (ADS)

We show that the dynamics of interacting fermions can be exactly replaced by a quantum jump theory in the many-body density matrix space. In this theory, jumps occur between densities formed of pairs of Slater determinants, Dab=|?a>many-body density along the path, the presented theory is equivalent to a stochastic theory in one-body density matrix space, in which each density matrix evolves according to its own mean-field augmented by a one-body noise. Guided by the exact reformulation, a stochastic mean-field dynamics valid in the weak coupling approximation is proposed. This theory leads to an approximate treatment of two-body effects similar to the extended time-dependent Hartree-Fock scheme. In this stochastic mean-field dynamics, statistical mixing can be directly considered and jumps occur on a coarse-grained time scale. Accordingly, numerical effort is expected to be significantly reduced for applications.

Lacroix, Denis

2005-06-01

248

Many-body correlations of electrostatically trapped dipolar excitons

NASA Astrophysics Data System (ADS)

We study the photoluminescence (PL) of a two-dimensional liquid of oriented dipolar excitons in InxGa1-xAs coupled double quantum wells confined to a microtrap. Generating excitons outside the trap and transferring them at lattice temperatures down to T=240 mK into the trap we create cold quasiequilibrium bosonic ensembles of some 1000 excitons with thermal de Broglie wavelengths exceeding the excitonic separation. With decreasing temperature and increasing density n?5×1010(1)/(cm2) we find an increasingly asymmetric PL line shape with a sharpening blue edge and a broad red tail which we interpret to reflect correlated behavior mediated by dipolar interactions. From the PL intensity I(E) below the PL maximum at E0 we extract at T<5 K a distinct power law I(E)˜(E0-E)-|?| with -|?|?-0.8 in the range E0-E of 1.5-4 meV, comparable to the dipolar interaction energy.

Schinner, G. J.; Repp, J.; Schubert, E.; Rai, A. K.; Reuter, D.; Wieck, A. D.; Govorov, A. O.; Holleitner, A. W.; Kotthaus, J. P.

2013-05-01

249

The damping of the harmonic oscillator is studied in the framework of the\\u000aLindblad theory for open quantum systems. A generalization of the fundamental\\u000aconstraints on quantum mechanical diffusion coefficients which appear in the\\u000amaster equation for the damped quantum oscillator is presented; the\\u000aSchr\\\\\\

A. Isar; A. Sandulescu; H. Scutaru; E. Stefanescu; W. Scheid

2004-01-01

250

NASA Astrophysics Data System (ADS)

So far proposed quantum computers use fragile and environmentally sensitive natural quantum systems. Here we explore the new notion that synthetic quantum systems suitable for quantum computation may be fabricated from smart nanostructures using topological excitations of a stochastic neural-type network that can mimic natural quantum systems. These developments are a technological application of process physics which is an information theory of reality in which space and quantum phenomena are emergent, and so indicates the deep origins of quantum phenomena. Analogous complex stochastic dynamical systems have recently been proposed within neurobiology to deal with the emergent complexity of biosystems, particularly the biodynamics of higher brain function. The reasons for analogous discoveries in fundamental physics and neurobiology are discussed.

Cahill, Reginald T.

2002-10-01

251

Pair-excitation energetics of highly correlated many-body states

NASA Astrophysics Data System (ADS)

A microscopic approach is developed to determine the excitation energetics of highly correlated quasi-particles in optically excited semiconductors based entirely on a pair-correlation function input. For this purpose, the Wannier equation is generalized to compute the energy per excited electron-hole pair of a many-body state probed by a weak pair excitation. The scheme is verified for the degenerate Fermi gas and incoherent excitons. In a certain range of experimentally accessible parameters, a new stable quasi-particle state is predicted which consists of four to six electron-hole pairs forming a liquid droplet of fixed radius. The energetics and pair-correlation features of these ‘quantum droplets’ are analyzed.

Mootz, M.; Kira, M.; Koch, S. W.

2013-09-01

252

Possible experimental manifestations of the many-body localization

Recently, it was predicted that if all one-electron states in a\\u000anon-interacting disordered system are localized, the interaction between\\u000aelectrons in the absence of coupling to phonons leads to a finite-temperature\\u000ametal-insulator trnasition. Here we show that even in the presence of a weak\\u000acoupling to phonons the transition manifests itself (i) in the nonlinear\\u000aconduction, leading to a bistable

D. M. Basko; I. L. Aleiner; B. L. Altshuler

2007-01-01

253

Many-body approach for quartet condensation in strong coupling

The theory for condensation of higher fermionic clusters is developed. Fully self-consistent nonlinear equations for the quartet order parameter in strongly coupled fermionic systems are established and solved. The breakdown of the quasiparticle picture is pointed out. Derivation of numerically tractable approximation is described. The momentum projected factorization ansatz for the order parameter is employed. As a definite example, the condensation of alpha particles in nuclear matter is worked out.

Sogo, Takaaki; Roepke, Gerd; Schuck, Peter [Institut fuer Physik, Universitaet Rostock, D-18051 Rostock (Germany); Institut de Physique Nucleaire, CNRS, UMR 8608, Orsay F-91406 (France); Universite Paris-Sud, Orsay F-91505, France Laboratoire de Physique et Modelisation des Milieux Condenses, CNRS, and Universite Joseph Fourier, 25 Avenue des Martyrs, Boite Postale 166, F-38042 Grenoble Cedex 9 (France) and Groupe de Physique Theorique Institut de Physique Nucleaire, F-91406 Orsay Cedex (France)

2010-06-15

254

Liquid-gas phase transition in nuclear matter from realistic many-body approaches

NASA Astrophysics Data System (ADS)

The existence of a liquid-gas phase transition for hot nuclear systems at subsaturation densities is a well-established prediction of finite-temperature nuclear many-body theory. In this paper, we discuss for the first time the properties of such a phase transition for homogeneous nuclear matter within the self-consistent Green's function approach. We find a substantial decrease of the critical temperature with respect to the Brueckner-Hartree-Fock approximation. Even within the same approximation, the use of two different realistic nucleon-nucleon interactions gives rise to large differences in the properties of the critical point.

Rios, A.; Polls, A.; Ramos, A.; Müther, H.

2008-10-01

255

Relativistic many-body calculation of low-energy dielectronic resonances in Be-like carbon

NASA Astrophysics Data System (ADS)

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 , Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.81.313 81, 313 (1998)].

Derevianko, A.; Dzuba, V. A.; Kozlov, M. G.

2010-08-01

256

Halogen-halogen interaction in view of many-body approach

NASA Astrophysics Data System (ADS)

The many-body theory was applied in order to estimate the character of interaction in quadruple complex consisting of four bromomethane molecules. The tetrameric complex used as a model system was found in the crystal structure in which halogen bonds were stabilizing the solid state structure. Decomposition of interaction energy on two-, three- and four-body terms allowed to conclude that individual halogen bonds in tetramer rather does not cooperate forming the complex. The nonadditive contribution to interaction energy is negative, but of very small value in respect to total interaction energy (less than 0.01%), indicating very weak cooperativity of halogen bridges.

Dominikowska, Justyna; Palusiak, Marcin

2013-09-01

257

Many-body theory of electrical, thermal and optical response of molecular heterojunctions

NASA Astrophysics Data System (ADS)

In this work, we develop a many-body theory of electronic transport through single molecule junctions based on nonequilibrium Green's functions (NEGFs). The central quantity of this theory is the Coulomb self-energy matrix of the junction SigmaC. SigmaC is evaluated exactly in the sequential-tunneling limit, and the correction due to finite lead-molecule tunneling is evaluated using a conserving approximation based on diagrammatic perturbation theory on the Keldysh contour. In this way, tunneling processes are included to infinite order, meaning that any approximation utilized is a truncation in the physical processes considered rather than in the order of those processes. Our theory reproduces the key features of both the Coulomb blockade and coherent transport regimes simultaneously in a single unified theory. Nonperturbative effects of intramolecular correlations are included, which are necessary to accurately describe the highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gap, essential for a quantitative theory of transport. This work covers four major topics related to transport in single-molecule junctions. First, we use our many-body theory to calculate the nonlinear electrical response of the archetypal Au-1,4-benzenedithiol-Au junction and find irregularly shaped 'molecular diamonds' which have been experimentally observed in some larger molecules but which are inaccessible to existing theoretical approaches. Next, we extend our theory to include heat transport and develop an exact expression for the heat current in an interacting nanostructure. Using this result, we discover that quantum coherence can strongly enhance the thermoelectric response of a device, a result with a number of technological applications. We then develop the formalism to include multi-orbital lead-molecule contacts and multi-channel leads, both of which strongly affect the observable transport. Lastly, we include a dynamic screening correction to Sigma C and investigate the optoelectric response of several molecular junctions.

Bergfield, Justin Phillip

258

Quantum Monte Carlo for transition metal systems: Method developments and applications

Quantum Monte Carlo (QMC) is a powerful computational tool to study correlated systems of electrons, allowing us to explicitly treat many-body interactions with favorable scaling in the number of particles. It has been regarded as a benchmark tool for condensed matter systems containing elements from the first and second row of the periodic table. It holds particular promise for the

Lucas K. Wagner

2006-01-01

259

Quantum gases: Relaxation dynamics

NASA Astrophysics Data System (ADS)

The current understanding of the relaxation dynamics in quantum many-body systems is still incomplete, but an ultracold atom experiment brings new insights by confirming the local emergence and propagation of thermal correlations.

Cheneau, Marc

2013-10-01

260

Herman–Kluk allows analysis of quantum discrete breathers in higher dimensional systems

Discrete breathers (DBs) provide an important example of spatial localization of energy encountered in non-linear many-body systems. Studying the quantum equivalent of DBs has always been restricted to small or simple systems. We show that Herman–Kluk (HK), a well studied semi-classical method, can be used successfully to observe the dynamics of a quantum state for systems that are too large

Kirill Igumenshchev; Misha Ovchinnikov; Oleg V. Prezhdo

2012-01-01

261

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

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. PMID:23432299

Vosk, Ronen; Altman, Ehud

2013-02-07

262

Fidelity spectrum and phase transitions of quantum systems

NASA Astrophysics Data System (ADS)

Quantum fidelity between two density matrices F(?1,?2) is usually defined as the trace of the operator F=?1?2?1. We study the logarithmic spectrum of this operator, which we denote by the fidelity spectrum, in the cases of the XX spin chain in a magnetic field, a magnetic impurity inserted in a conventional superconductor, and a bulk superconductor at finite temperature. When the density matrices are equal, ?1=?2, the fidelity spectrum reduces to the entanglement spectrum. We find that the fidelity spectrum can be a useful tool in giving a detailed characterization of the different phases of many-body quantum systems.

Sacramento, P. D.; Paunkovi?, N.; Vieira, V. R.

2011-12-01

263

Quantum Knizhnik-Zamolodchikov equations and affine root systems

NASA Astrophysics Data System (ADS)

Quantum (difference) Knizhnik-Zamolodchikov equations [S1, FR] are generalized for the R-matrices from [Ch1] with the arguments in arbitrary root systems (and their formal counterparts). In particular, QKZ equations with certain boundary conditions are introducted. The self-consistency of the equations from [FR] and the cross-derivative integrability conditions for the r-matrix KZ equations from [Ch2] are obtained as corollaries. A difference counterpart of the quantum many-body problem connected with Macdonald's operators is defined as an application.

Cherednik, Ivan

1992-11-01

264

NASA Astrophysics Data System (ADS)

The Lippmann-Schwinger equation for the scattering of electrons by atoms and molecules is investigated from the perspective of Brillouin-Wigner perturbation theory. It is shown that the solution of the Lippmann-Schwinger can be obtained from many-body Brillouin-Wigner methods for bound-state problems. In particular, the equations of many-body Brillouin-Wigner coupled cluster theory for bound-state systems can be shown to lead directly to equations for the amplitudes for electron-molecule scattering processes.

Huba?, Ivan; Masarik, Jozef; Wilson, Stephen

2011-10-01

265

NASA Astrophysics Data System (ADS)

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 G0, 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, G0. 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 fractional charge. It should play an important role in developing accurate approximate density functionals and many-body theory.

Yang, Weitao; Mori-Sánchez, Paula; Cohen, Aron J.

2013-09-01

266

Loschmidt echo and the many-body orthogonality catastrophe in a qubit-coupled Luttinger liquid.

We investigate the many-body generalization of the orthogonality catastrophe by studying the generalized Loschmidt echo of Luttinger liquids (LLs) after a global change of interaction. It decays exponentially with system size and exhibits universal behavior: the steady state exponent after quenching back and forth n times between 2 LLs (bang-bang protocol) is 2n times bigger than that of the adiabatic overlap and depends only on the initial and final LL parameters. These are corroborated numerically by matrix-product state based methods of the XXZ Heisenberg model. An experimental setup consisting of a hybrid system containing cold atoms and a flux qubit coupled to a Feshbach resonance is proposed to measure the Loschmidt echo using rf spectroscopy or Ramsey interferometry. PMID:23931387

Dóra, Balázs; Pollmann, Frank; Fortágh, József; Zaránd, Gergely

2013-07-23

267

Loschmidt Echo and the Many-Body Orthogonality Catastrophe in a Qubit-Coupled Luttinger Liquid

NASA Astrophysics Data System (ADS)

We investigate the many-body generalization of the orthogonality catastrophe by studying the generalized Loschmidt echo of Luttinger liquids (LLs) after a global change of interaction. It decays exponentially with system size and exhibits universal behavior: the steady state exponent after quenching back and forth n times between 2 LLs (bang-bang protocol) is 2n times bigger than that of the adiabatic overlap and depends only on the initial and final LL parameters. These are corroborated numerically by matrix-product state based methods of the XXZ Heisenberg model. An experimental setup consisting of a hybrid system containing cold atoms and a flux qubit coupled to a Feshbach resonance is proposed to measure the Loschmidt echo using rf spectroscopy or Ramsey interferometry.

Dóra, Balázs; Pollmann, Frank; Fortágh, József; Zaránd, Gergely

2013-07-01

268

Periodic Steady Regime and Interference in a Periodically Driven Quantum System

NASA Astrophysics Data System (ADS)

We study the coherent dynamics of a quantum many-body system subject to a time-periodic driving. We argue that in many cases, destructive interference in time makes most of the quantum averages time periodic, after an initial transient. We discuss in detail the case of a quantum Ising chain periodically driven across the critical point, finding that, as a result of quantum coherence, the system never reaches an infinite temperature state. Floquet resonance effects are moreover observed in the frequency dependence of the various observables, which display a sequence of well-defined peaks or dips. Extensions to nonintegrable systems are discussed.

Russomanno, Angelo; Silva, Alessandro; Santoro, Giuseppe E.

2012-12-01

269

Periodic steady regime and interference in a periodically driven quantum system.

We study the coherent dynamics of a quantum many-body system subject to a time-periodic driving. We argue that in many cases, destructive interference in time makes most of the quantum averages time periodic, after an initial transient. We discuss in detail the case of a quantum Ising chain periodically driven across the critical point, finding that, as a result of quantum coherence, the system never reaches an infinite temperature state. Floquet resonance effects are moreover observed in the frequency dependence of the various observables, which display a sequence of well-defined peaks or dips. Extensions to nonintegrable systems are discussed. PMID:23368490

Russomanno, Angelo; Silva, Alessandro; Santoro, Giuseppe E

2012-12-17

270

Presented is a charge-optimized many-body potential (COMB) for metallic copper and copper oxide systems based on an extended Tersoff formalism coupled with variable charge electrostatics. To faithfully reproduce interactions between molecular oxygen and the metal surface, the potential includes atomic polarizabilities via both a point dipole model and dynamic partial charges, both of which are equilibrated through an extended Lagrangian

Bryce Devine; Tzu-Ray Shan; Yu-Ting Cheng; Alan J. H. McGaughey; Minyoung Lee; Simon R. Phillpot; Susan B. Sinnott

2011-01-01

271

Neutral and charged excitations in carbon fullerenes from first-principles many-body theories

We use first-principles many-body theories to investigate the low energy excitations of the carbon fullerenes C_20, C_24, C_50, C_60, C_70, and C_80. Properties are calculated via the GW-Bethe-Salpeter Equation (GW-BSE) and diffusion Quantum Monte Carlo (QMC) methods. At a lower level of theoretical complexity, we also calculate these properties using static and time-dependent density-functional theory. We critically compare these theories and assess their accuracy against available experimental data. The first ionization potentials are consistently well reproduced and are similar for all the fullerenes and methods studied. The electron affinities and first triplet excitation energies show substantial method and geometry dependence. Compared to available experiment, GW-BSE underestimates excitation energies by approximately 0.3 eV while QMC overestimates them by approximately 0.5 eV. We show the GW-BSE errors result primarily from a systematic overestimation of the electron affinities, while the QMC errors likely result from nodal error in both ground and excited state calculations.

Tiago, Murilo L [ORNL; Kent, Paul R [ORNL; Hood, Randolph Q. [Lawrence Livermore National Laboratory (LLNL); Reboredo, Fernando A [ORNL

2008-01-01

272

Irreducible Scalar Many-Body Casimir Energies: Theorems and Numerical Studies

NASA Astrophysics Data System (ADS)

We define irreducible N-body spectral functions and Casimir energies and consider a massless scalar quantum field interacting locally by positive potentials with classical objects. Irreducible N-body spectral functions in this case are shown to be conditional probabilities of random walks. The corresponding irreducible contributions to scalar many-body Casimir energies are finite and positive/negative for an odd/even number of objects. The force between any two finite objects separable by a plane is always attractive in this case. Analytical and numerical world-line results for the irreducible four-body Casimir energy of a scalar with Dirichlet boundary conditions on a tic-tac-toe pattern of lines are presented. Numerical results for the irreducible three-body Casimir energy of a massless scalar satisfying Dirichlet boundary conditions on three intersecting lines forming an isosceles triangle are also reported. In both cases the symmetric configuration (square and isosceles triangle) corresponds to the minimal irreducible contribution to the Casimir energy.

Schaden, Martin

2012-07-01

273

Many-body physics in the classical-field description of a degenerate Bose gas

The classical-field formalism has been widely applied in the calculation of normal correlation functions, and the characterization of condensation, in finite-temperature Bose gases. Here we discuss the extension of this method to the calculation of more general correlations, including the so-called anomalous correlations of the field, without recourse to symmetry-breaking assumptions. Our method is based on the introduction of U(1)-symmetric classical-field variables analogous to the modified quantum ladder operators of number-conserving approaches to the degenerate Bose gas, and allows us to rigorously quantify the anomalous and non-Gaussian character of the field fluctuations. We compare our results for anomalous correlation functions with the predictions of mean-field theories, and demonstrate that the nonlinear classical-field dynamics incorporate a full description of many-body processes which modify the effective mean-field potentials experienced by condensate and noncondensate atoms. We discuss the role of these processes in shaping the condensate mode, and thereby demonstrate the consistency of the Penrose-Onsager definition of the condensate orbital in the classical-field equilibrium. We consider the contribution of various noncondensate-field correlations to the overall suppression of density fluctuations and interactions in the field, and demonstrate the distinct roles of phase and density fluctuations in the transition of the field to the normal phase.

Wright, T. M.; Davis, M. J. [University of Queensland, School of Mathematics and Physics, ARC Centre of Excellence for Quantum-Atom Optics, Queensland 4072 (Australia); Proukakis, N. P. [School of Mathematics and Statistics, Newcastle University, Newcastle upon Tyne, NE1 7RU (United Kingdom); University of Queensland, School of Mathematics and Physics, ARC Centre of Excellence for Quantum-Atom Optics, Queensland 4072 (Australia)

2011-08-15

274

The effect of many-body forces on the elastic properties of simple oxides and olivine

The single crystal elastic moduli bear evidence of non-central or many-body forces in the simple oxides with transition-metal oxides being very distinctive from alkaline-earth oxides. These features which persist in more complicated structures such as olivine, suggest that noncentral or many-body forces are important in defining the physical properties of these compounds as well.

Donald J. Weidner; Geoffery D. Price

1988-01-01

275

The coupled-cluster approach to non-relativistic and relativistic many-body calculations

NASA Astrophysics Data System (ADS)

A review is given of the atomic many-body theory in the coupled-cluster approach or exponential-Ansatz formulation. Explicit equations and corresponding graphical representations are given in the pair-approximation, where the one- and two-body parts of the cluster (exponent) operator are considered. Also the effect of a small, additional perturbation is considered. The technique of evaluating diagrams by means of one- and two-particle functions, satisfying inhomogeneous differential equations, is reviewed. Illustrative numerical results are given for the electron correlation energy, electron binding energy, hyperfine separation and specific mass shift of simple atomic systems. The extension of the non-relativistic procedure to the relativistic regime is discussed by considering the effect of the exchange of one and two virtual, transverse photons between the electrons. In lowest order this leads to the "no-virtual-pair approximation".

Lindgren, Ingvar

1987-10-01

276

Probing Real-Space and Time-Resolved Correlation Functions with Many-Body Ramsey Interferometry

NASA Astrophysics Data System (ADS)

We propose to use Ramsey interferometry and single-site addressability, available in synthetic matter such as cold atoms or trapped ions, to measure real-space and time-resolved spin correlation functions. These correlation functions directly probe the excitations of the system, which makes it possible to characterize the underlying many-body states. Moreover, they contain valuable information about phase transitions where they exhibit scale invariance. We also discuss experimental imperfections and show that a spin-echo protocol can be used to cancel slow fluctuations in the magnetic field. We explicitly consider examples of the two-dimensional, antiferromagnetic Heisenberg model and the one-dimensional, long-range transverse field Ising model to illustrate the technique.

Knap, Michael; Kantian, Adrian; Giamarchi, Thierry; Bloch, Immanuel; Lukin, Mikhail D.; Demler, Eugene

2013-10-01

277

Rydberg tagging time-of-flight imaging: An improved apparatus for studying many-body processes

NASA Astrophysics Data System (ADS)

With Rydberg tagging time-of-flight imaging of cold atoms, we have achieved a velocity resolution of ˜2.5 cm/s. The apparatus and resolution have already allowed us to observe ultralong-range electric field-induced Cs2 molecules, and differentiate them from low-energy inelastic collisional processes. Addition of a Zeeman-slowed atomic beam and tapered amplifier system have given nearly two orders of magnitude increase in the number of atoms trapped in our MOT, making many-body processes, such as three-body recombination, much easier to detect. With the implementation of two crossed dipole trapping beams, the number density available in the trap has also increased by nearly two orders of magnitude. Data on nS1/2+6S1/2 Rydberg molecules and other ultracold collision processes will be presented.

Tallant, Jonathan; Booth, Donald; Schwettmann, Arne; Shaffer, James

2010-03-01

278

Probing real-space and time-resolved correlation functions with many-body ramsey interferometry.

We propose to use Ramsey interferometry and single-site addressability, available in synthetic matter such as cold atoms or trapped ions, to measure real-space and time-resolved spin correlation functions. These correlation functions directly probe the excitations of the system, which makes it possible to characterize the underlying many-body states. Moreover, they contain valuable information about phase transitions where they exhibit scale invariance. We also discuss experimental imperfections and show that a spin-echo protocol can be used to cancel slow fluctuations in the magnetic field. We explicitly consider examples of the two-dimensional, antiferromagnetic Heisenberg model and the one-dimensional, long-range transverse field Ising model to illustrate the technique. PMID:24138270

Knap, Michael; Kantian, Adrian; Giamarchi, Thierry; Bloch, Immanuel; Lukin, Mikhail D; Demler, Eugene

2013-10-04

279

Many quantum integrable systems are obtained using an accelerator physics technique known as Ermakov (or normalized variables) transformation. This technique was used to create classical nonlinear integrable lattices for accelerators and nonlinear integrable plasma traps. Now, all classical results are carried over to a nonrelativistic quantum case. In this paper we have described an extension of the Ermakov-like transformation to the Schroedinger and Pauli equations. It is shown that these newly found transformations create a vast variety of time dependent quantum equations that can be solved in analytic functions, or, at least, can be reduced to time-independent ones.

Danilov, Viatcheslav; /Oak Ridge; Nagaitsev, Sergei; /Fermilab

2011-11-01

280

A degenerate dynamical system is characterized by a symplectic structure whose rank is not constant throughout phase space. Its phase space is divided into causally disconnected, nonoverlapping regions in each of which the rank of the symplectic matrix is constant, and there are no classical orbits connecting two different regions. Here the question of whether this classical disconnectedness survives quantization is addressed. Our conclusion is that in irreducible degenerate systems-in which the degeneracy cannot be eliminated by redefining variables in the action-the disconnectedness is maintained in the quantum theory: there is no quantum tunnelling across degeneracy surfaces. This shows that the degeneracy surfaces are boundaries separating distinct physical systems, not only classically, but in the quantum realm as well. The relevance of this feature for gravitation and Chern-Simons theories in higher dimensions cannot be overstated.

Micheli, Fiorenza de [Centro de Estudios Cientificos, Arturo Prat 514, Valdivia (Chile); Instituto de Fisica, Pontificia Universidad Catolica de Valparaiso, Casilla 4059, Valparaiso (Chile); Zanelli, Jorge [Centro de Estudios Cientificos, Arturo Prat 514, Valdivia (Chile); Universidad Andres Bello, Av. Republica 440, Santiago (Chile)

2012-10-15

281

NASA Astrophysics Data System (ADS)

A degenerate dynamical system is characterized by a symplectic structure whose rank is not constant throughout phase space. Its phase space is divided into causally disconnected, nonoverlapping regions in each of which the rank of the symplectic matrix is constant, and there are no classical orbits connecting two different regions. Here the question of whether this classical disconnectedness survives quantization is addressed. Our conclusion is that in irreducible degenerate systems--in which the degeneracy cannot be eliminated by redefining variables in the action--the disconnectedness is maintained in the quantum theory: there is no quantum tunnelling across degeneracy surfaces. This shows that the degeneracy surfaces are boundaries separating distinct physical systems, not only classically, but in the quantum realm as well. The relevance of this feature for gravitation and Chern-Simons theories in higher dimensions cannot be overstated.

de Micheli, Fiorenza; Zanelli, Jorge

2012-10-01

282

Quantum Electromechanical Systems

NASA Astrophysics Data System (ADS)

Quantum electromechanical systems are nano-to-micron scale mechanical resonators coupled to electronic devices of comparable dimensions, such that the mechanical resonator behaves in a manifestly quantum manner. Dramatic progress towards realising such systems has been made with the recent demonstration of a GHz mechanical resonator [1], and demonstrated displacement detection close to the quantum limit based on the single electron transistor [2-4]. The latter system, comprising a single electron transistor and micron-scale mechanical resonator electrostatically-coupled to the transistor island, is predicted to exhibit surprisingly rich dynamical behavior [5]. The unprecedented displacement sensitivity of the SET transducer may also enable the observation of quantum 'jumps' in the motion of nanomechanical resonators at milliKelvin temperatures, due to the strain-mediated coupling between the flexing motion and tunneling defects of the resonator [6]. Such investigations are contributing towards a deeper understanding of the transition between quantum and classical dynamics. [1] X. Huang, C. Zorman, M. Mehregany, M. Roukes, Nature 421 (2003) 496; [2] M. Blencowe, M. Wybourne, Appl. Phys. Lett. 77 (2000) 3845; [3] R. Knobel, A. Cleland, Nature 424 (2003), 291; [4] M. LaHaye, O. Buu, B. Camarota, K. Schwab (unpublished); [5] A. Armour, M. Blencowe, Y. Zhang, cond-mat/0307528 (Phys. Rev. B to appear); [6] Y. Tanaka, M. Blencowe (unpublished).

Blencowe, Miles

2004-03-01

283

Time-Dependent, Many-Body Scattering Theory and Nuclear Reaction Applications.

National Technical Information Service (NTIS)

The channel component state form of the channel coupling array theory of many-body scattering is briefly reviewed. These states obey a non-hermitian matrix equation whose exact solution yields the Schroedinger eigenstates, eigenvalues and scattering ampli...

F. S. Levin

1977-01-01

284

To enhance the current understanding of mechanisms contributing to magnetic hyperfine interactions in excited states of atomic systems, in particular, alkali-metal atom systems, the hyperfine fields in the excited 5 2 S1\\/2 -8 2 S1\\/2 states of potassium and 8 2 S1\\/2 -1 2 2 S1\\/2 states of francium atoms have been studied using the relativistic linked-cluster many-body perturbation procedure.

Alfred Owusu; R. W. Dougherty; G. Gowri; T. P. Das; J. Andriessen

1997-01-01

285

New Random Ordered Phase in Isotropic Models with Many-Body Interactions

NASA Astrophysics Data System (ADS)

In this study, we have found a new random ordered phase in isotropic models with many-body interactions. Spin correlations between neighboring planes are rigorously shown to form a long-range order, namely coplanar spin-pair order, using a unitary transformation, and the phase transition of this new order has been analyzed on the bases of the mean-field theory and correlation identities. In the systems with regular 4-body interactions, the transition temperature Tc is obtained as Tc = (z-2)J/kB, and the field conjugate to this new order parameter is found to be H2. In contrast, the corresponding physical quantities in the systems with random 4-body interactions are given by T c=? {z-2}J/k B and H4, respectively. Scaling forms of order parameters for regular or random 4-body interactions are expressed by the same scaling functions in the systems with regular or random 2-body interactions, respectively. Furthermore, we have obtained the nonlinear susceptibilities in the regular and random systems, where the coefficient ?nl of H3 in the magnetization shows positive divergence in the regular model, while the coefficient ?7 of H7 in the magnetization shows negative divergence in the random model.

Hashizume, Yoichiro; Suzuki, Masuo

286

Informationally coherent quantum systems

An information-theoretic approach to correlated quantum systems is developed. The precise definitions of the informationally coherent N-component system are presented in terms of the state (observable) dependent index of correlation. The informational coherence of the N-particle GHZ system in an entangled pure state is analysed and it is found that the observable-dependent index of correlation is less than or equal

Ryszard Horodecki

1994-01-01

287

Models of PT symmetric quantum mechanics provide examples of biorthogonal quantum systems. The latter incorporate all the structure of PT symmetric models, and allow for generalizations, especially in situations where the PT construction of the dual space fails. The formalism is illustrated by a few exact results for models of the form H=(p+{nu}){sup 2}+{sigma}{sub k>0}{mu}{sub k} exp(ikx). In some nontrivial cases, equivalent Hermitian theories are obtained and shown to be very simple: They are just free (chiral) particles. Field theory extensions are briefly considered.

Curtright, Thomas; Mezincescu, Luca [Department of Physics, University of Miami, Coral Gables, Florida 33124 (United States) and School of Natural Sciences, Institute for Advanced Study, Princeton, New Jersey 08540 (United States); Department of Physics, University of Miami, Coral Gables, Florida 33124 (United States)

2007-09-15

288

Integrable quantum Stäckel systems

NASA Astrophysics Data System (ADS)

The Stäckel separability of a Hamiltonian system is well known to ensure existence of a complete set of Poisson commuting integrals of motion quadratic in the momenta. We consider a class of Stäckel separable systems where the entries of the Stäckel matrix are monomials in the separation variables. We show that the only systems in this class for which the integrals of motion arising from the Stäckel construction keep commuting after quantization are, up to natural equivalence transformations, the so-called Benenti systems. Moreover, it turns out that the latter are the only quantum separable systems in the class under study.

B?aszak, Maciej; Doma?ski, Ziemowit; Sergyeyev, Artur; Szablikowski, B?a?ej M.

2013-11-01

289

Quantum algorithm in quantum network systems

Recently, the quantum computer (QC) using the nano-devices have significantly attracted attention, because a large-scale extention of the qubits could be easily realized in the nano-devices. However, some problems for the realization of the QC with nano-devices arise from the short decoherence time and the interaction of qubits only between nearest-neighbor qubits. Therefore, we try to design the optimal quantum circuit of the quantum Fourier transform in various network system by means of the genetic algorithm (GA)

Sakamoto, I.; Yamaguchi, T.; Nagao, H.; Nishikawa, K. [Department of Computational Science, Faculty of Science, Kanazawa University, Kakuma, Kanazawa, 920-1192 (Japan)

2004-04-30

290

Localization-protected quantum order

NASA Astrophysics Data System (ADS)

Closed quantum systems with quenched randomness exhibit many-body localized regimes wherein they do not equilibrate, even though prepared with macroscopic amounts of energy above their ground states. We show that such localized systems can order, in that individual many-body eigenstates can break symmetries or display topological order in the infinite-volume limit. Indeed, isolated localized quantum systems can order even at energy densities where the corresponding thermally equilibrated system is disordered, i.e., localization protects order. In addition, localized systems can move between ordered and disordered localized phases via nonthermodynamic transitions in the properties of the many-body eigenstates. We give evidence that such transitions may proceed via localized critical points. We note that localization provides protection against decoherence that may allow experimental manipulation of macroscopic quantum states. We also identify a “spectral transition” involving a sharp change in the spectral statistics of the many-body Hamiltonian.

Huse, David A.; Nandkishore, Rahul; Oganesyan, Vadim; Pal, Arijeet; Sondhi, S. L.

2013-07-01

291

Many-body interaction analysis: algorithm development and application to large molecular clusters.

A completely automated algorithm for performing many-body interaction energy analysis of clusters (MBAC) [M. J. Elrodt and R. J. Saykally, Chem. Rev. 94, 1975 (1994); S. S. Xantheas, J. Chem. Phys. 104, 8821 (1996)] at restricted Hartree-Fock (RHF)/MA Plesset 2nd order perturbation theory (MP2)/density functional theory (DFT) level of theory is reported. Use of superior guess density matrices (DM's) for smaller fragments generated from DM of the parent system and elimination of energetically insignificant higher-body combinations, leads to a more efficient performance (speed-up up to 2) compared to the conventional procedure. MBAC approach has been tested out on several large-sized weakly bound molecular clusters such as (H(2)O)(n), n=8, 12, 16, 20 and hydrated clusters of amides and aldehydes. The MBAC results indicate that the amides interact more strongly with water than aldehydes in these clusters. It also reconfirms minimization of the basis set superposition error for large cluster on using superior quality basis set. In case of larger weakly bound clusters, the contributions higher than four body are found to be repulsive in nature and smaller in magnitude. The reason for this may be attributed to the increased random orientations of the interacting molecules separated from each other by large distances. PMID:15352794

Kulkarni, Anant D; Ganesh, V; Gadre, Shridhar R

2004-09-15

292

Third-order many-body perturbation theory calculations for low-lying states in beryllium

NASA Astrophysics Data System (ADS)

A detailed breakdown of many-body perturbation theory (MBPT) contributions through third order is presented for energies of the ten (2l ,l') states of beryllium. A total of 84 one-body and 578 two-body terms contribute to the third-order energy. Third-order MBPT calculations for monovalent atoms were carried out fifteen years ago by Blundell et al.[1] Second-order calculations for ions of the berylliumlike isoelectronic sequence were also reported six years later[2]. In that paper, only 4 one-body and 20 two-body terms contribute to the second-order energy of neutral Be. The agreement with experimental energies was at 5% level. Our study aims to present complete third-order MBPT formulas, and apply them to the simplest two-valence particles system beryllium to improve the agreement with experiment.^1 S.A. Blundell, W.R. Johnson and J. Sapirstein, Phys. Rev. A 42, 3751 (1990).^2 M.S. Safronova, W.R. Johnson and U.I. Safronova, Phys. Rev. A 53, 4036 (1996).

Ho, Hung-Cheuk

2005-05-01

293

A periodic small-cluster approach to many-body problems

Many-body problems can very seldom be solved exactly, and their study normally requires approximate methods. These approximations are of various kinds and accuracy, but usually they involve either a perturbation treatment, or a variational approach. The method employed also depends on whether the problem under study is a real or realistic system or a prototype, ideal model. The method proposed by the author and used with his collaborators in the solution of a variety of problems consists of taking explicit advantage of finite sampling, finite cluster duality. By a systematic, symmetric and wise choice of N points in reciprocal space, the problem can be reduced to that of a symmetric periodic cluster with N sites. If, in addition, N is small enough - as is the case in the normal handling of perturbation expansions - the problem can then be solved exactly, without recourse to perturbation methods. With the aid of group theory, only modest computer facilities are required. A similar approach has been taken by Callaway and his collatorators. 56 refs.

Falicov, L.M.

1987-08-01

294

Simulation Models with Many-Body Polarization Effects: Application to Vitreous Boron Oxide.

NASA Astrophysics Data System (ADS)

We present an application of a general "polarization model" to the structural chemistry of vitreous boron oxide. This model combines atomic pair interactions with a many-body potential to represent directed covalent bonds, hydrogen bonds and dielectric phenomena. Here we consider the application of the this model to the structure of boron oxide [B_2O_3]. This material is a trigonal network glass, with short-range structures consisting of BO3 triangles. The intermediate range order in B_2O3 is well established experimentally as the planar, six-membered boroxol ring, which exists at fraction f = 0.50 - 0.75 at temperatures near the glass transition. Computer simulations of this material have found limited amounts [less than 20%] of these structures. Using the polarization model, we find a fraction of boroxol rings, f = 0.45, which approaches relevant experimental levels. The rings become stabilized relative to non-ring structures as the temperature is lowered. The ultimate level of ring structures in the system depends on the temperature at which the network structure is formed. If a connected network consisting of a primarily non-ring structures is subsequently cooled to temperatures where ring formation is favored, the existing network does not rearrange to produce boroxol rings.

Chen, Yingzi; Maranas, Janna; Stillinger, Frank

2001-03-01

295

Applications of a Relativistic Quantum Field Theory to the Nuclear Many-Body Problem

NASA Astrophysics Data System (ADS)

A relativistic mean field model was investigated through three separate applications. In the first of these, the electric dipole sum rule was evaluated using a relativistic formulation and consistently determined single particle orbitals. The resulting predictions for the total integrated photon absorption cross section were in qualitative agreement with experiment. Such agreement was difficult to obtain with standard nonrelativistic techniques. In the second application, a relativistic schematic model for nuclear structure was developed. Although the model provided certain insights and suggested interesting areas for further investigation, due to the more complicated nature of the relativistic model it did not have the same power as previous nonrelativistic models for explaining the relationship between the energy shifts of certain excited states and the corresponding transition strengths. Finally, in the third application, numerical techniques for obtaining shell model orbitals for deformed nuclei in a relativistic mean field model were developed and applied to a variety of nuclei. In general, this procedure provides self consistently determined meson mean fields and single particle orbitals for use in other calculations. For the nuclei considered here, the results were in qualitative agreement with both previous nonrelativistic calculations and experiment.

Price, Charles Eldridge

296

Construction and analysis of a simplified many-body neutrino model

In dense neutrino systems, such as found in the early Universe, or near a supernova core, neutrino flavor evolution is affected by coherent neutrino-neutrino scattering. It has been recently suggested that many-particle quantum entanglement effects may play an essential role in these systems, potentially invalidating the traditional description in terms of a set of single-particle evolution equations. We model the neutrino system by a system of interacting spins, following an earlier work which showed that such a spin system can in some cases be solved exactly [A. Friedland and C. Lunardini, J. High Energy Phys. 10 (2003) 043.]. We extend this work by constructing an exact analytical solution to a more general spin system, including initial states with asymmetric spin distribution and, moreover, not necessarily aligned along the same axis. Our solution exhibits a rich set of behaviors, including coherent oscillations and dephasing and a transition from the classical to quantum regimes. We argue that the classical evolution of the spin system captures the entire coherent behavior of the neutrino system, while the quantum effects in the spin system capture some, but not all, of the neutrino incoherent evolution. By comparing the spin and neutrino systems, we find no evidence for the violation of the accepted one-body description, though the argument involves some subtleties not appreciated before. The analysis in this paper may apply to other two-state systems beyond the neutrino field.

Friedland, Alexander; McKellar, Bruce H.J.; Okuniewicz, Ivona [Theoretical Division, T-8, MS B285, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); School of Physics, Research Center for High Energy Physics, The University of Melbourne, Victoria 3010 (Australia)

2006-05-01

297

Intrinsic Properties of Quantum Systems

NASA Astrophysics Data System (ADS)

A new realist interpretation of quantum mechanics is introduced. Quantum systems are shown to have two kinds of properties: the usual ones described by values of quantum observables, which are called extrinsic, and those that can be attributed to individual quantum systems without violating standard quantum mechanics, which are called intrinsic. The intrinsic properties are classified into structural and conditional. A systematic and self-consistent account is given. Much more statements become meaningful than any version of Copenhagen interpretation would allow. A new approach to classical properties and measurement problem is suggested. A quantum definition of classical states is proposed.

Hájí?ek, P.; Tolar, J.

2009-05-01

298

Quantum dynamics and open quantum systems

NASA Astrophysics Data System (ADS)

The thesis deals with the quantum mechanical description of dynamical properties of open systems, and, in particular, with studying the temporal evolution of quantum systems interacting with their environments. In this thesis we apply a microscopic approach to study such systems thus explicitly considering the hamiltonian of the environment and its interaction with the quantum system under consideration. We also consider how the microscopic hamiltonians can be used in order to produce several logical operations as a result of the temporal dynamics of the systems governed by such hamiltonians. In the introductory chapter we start by discussing the physical motivation for studying open quantum systems and describe the most significant phenomena that result due to such interactions. We also briefly outline the experimental realizations in which the type of systems studied in the dissertation can arise. Then, in chapter 1, we consider a model of a quantum spin interacting with free electron gas. It is shown that this model can be mapped onto the spin-boson model with an Ohmic spectral function. The criterion for the localization of the spin is explicitly derived in terms of the parameters of the original fermionic model. In chapter 2, we study a general quantum system interacting with an environment modeled by the bosonic heat bath of the Caldeira and Leggett type. We argue that this model provides an appropriate description of adiabatic quantum decoherence, i.e. loss of entanglement on time scales short compared to those of thermal relaxation processes associated with energy exchange with the bath. Calculation of the elements of the reduced density matrix of the system is carried out exactly, and time-dependent decoherence is identified, similar to recent results for related models. Our key finding is that the decoherence process is controlled by the spectral properties of the interaction rather than by the system's hamiltonian. In chapter 3, a model of a quantum spin interacting with a spin environment is considered. The interaction is chosen to be such that the state of the environment is conserved. The reduced density matrix of the spin is calculated exactly for arbitrary coupling strength. The density matrix reaches its stationary state at t = /infty, which can be explicitly expressed in terms of elementary functions. It turns out that this state is quite different from the canonical distribution thus pointing out that the Markovian assumption is playing an essential role quantum mechanical description of a heat bath. Chapter 4 deals with quantum computing. We propose to design multi-spin quantum gates in which the input and output two-state systems (spins) are not necessarily identical. We outline the design criteria for such devices and then review recent results for single-unit Hamiltonians that accomplish the NOT and XOR functions. Chapter 5 is devoted to the problem of quantum copying. We consider a quantum evolution in which the basis states of I at time t are duplicated in at least two of the systems I, C, D, at time t + /Delta t. In essence, the restriction on the initial target states is exchanged for uncertainty as to which two of the three qubits retain copies of the initial source state. Finally, in chapter 6, we summarize and discuss the results obtained in the thesis and also describe directions for future research.

Mozyrsky, Dima

1999-02-01

299

Many-Body Treatment of the Collisional Frequency Shift in Fermionic Atoms

Recent experiments have measured collisional frequency shifts in polarized fermionic alkaline-earth atoms using {sup 1}S{sub 0}-{sup 3}P{sub 0} Rabi spectroscopy. Here, we provide a first-principles nonequilibrium theoretical description of the interaction frequency shifts starting from the microscopic many-body Hamiltonian. Our formalism describes the dependence of the frequency shift on excitation inhomogeneity, interactions, temperature, and many-body dynamics, provides a fundamental understanding of the effects of the measurement process, and explains the observed density shift data.

Rey, A. M.; Rubbo, C. [JILA, NIST, and Department of Physics, University of Colorado Boulder, Colorado 80309 (United States); Gorshkov, A. V. [Physics Department, Harvard University, Cambridge, Massachusetts 02138 (United States)

2009-12-31

300

Many-body rate limit on photoassociation of a Bose-Einstein condensate

We briefly report on zero-temperature photoassociation of a Bose-Einstein condensate, focusing on the many-body rate limit for atom-molecule conversion. An upgraded model that explicitly includes spontaneous radiative decay leads to an unanticipated shift in the position of the photoassociation resonance, which affects whether the rate (constant) maximizes or saturates, as well as the limiting value itself. A simple analytical model agrees with numerical experiments, but only for high density. Finally, an explicit comparison with the two-body unitary limit, set by the size of the condensate, finds that the many-body rate limit is generally more strict.

Mackie, Matt; Phou, Pierre [Department of Physics, Temple University, Philadelphia, Pennsylvania 19122 (United States)

2010-09-15

301

Angle-resolved photoelectron spectra of metal cluster anions within a many-body-theory approach

A consistent many-body theory based on the jellium model is applied for the description of angular resolved photoelectron spectra of metal clusters anions. The results of calculations demonstrate the dominant role of the many-body effects in the formation of angular distributions of photoelectrons emitted from sodium clusters and are in a good agreement with recent experimental data. The concrete comparison of theory and experiment has been performed for the photoionization of Na{sub 7}{sup -} and Na{sub 19}{sup -} anions being characterized by the entirely closed shells of delocalized electrons.

Solov'yov, Andrey V.; Polozkov, Roman G.; Ivanov, Vadim K. [Frankfurt Institute for Advanced Studies, Ruth-Moufang-Strasse 1, D-60438 Frankfurt am Main (Germany); St. Petersburg State Polytechnical University, Politekhnicheskaya 29, Saint-Petersburg RU-195251 (Russian Federation)

2010-02-15

302

Incorporating many-body effects into modeling of semiconductor lasers and amplifiers

Major many-body effects that are important for semiconductor laser modeling are summarized. The authors adopt a bottom-up approach to incorporate these many-body effects into a model for semiconductor lasers and amplifiers. The optical susceptibility function ({Chi}) computed from the semiconductor Bloch equations (SBEs) is approximated by a single Lorentzian, or a superposition of a few Lorentzians in the frequency domain. Their approach leads to a set of effective Bloch equations (EBEs). The authors compare this approach with the full microscopic SBEs for the case of pulse propagation. Good agreement between the two is obtained for pulse widths longer than tens of picoseconds.

Ning, C.Z.; Moloney, J.V.; Indik, R.A. [Univ. of Arizona, Tucson, AZ (United States)] [and others

1997-06-01

303

Relativistic multireference many-body perturbation theory calculations on Au64+ - Au69+ ions

Many-body perturbation theory (MBPT) calculations are an adequate tool for the description of the structure of highly charged multi-electron ions and for the analysis of their spectra. They demonstrate this by way of a re-investigation of n=3, {Delta}n=0 transitions in the EUV spectra of Na-, Mg-, Al-like, and Si-like ions of Au that have been obtained previously by heavy-ion accelerator based beam-foil spectroscopy. They discuss the evidence and propose several revisions on the basis of the multi-reference many-body perturbation theory calculations of Ne- through P-like ions of Au.

Vilkas, M J; Ishikawa, Y; Tr?bert, E

2006-03-31

304

Coarse-grained (CG) models often employ pair potentials that are parametrized to reproduce radial distribution functions (rdf's) determined for an atomistic model. This implies that the CG model must reproduce the corresponding atomistic mean forces. These mean forces include not only a direct contribution from the corresponding interaction but also correlated contributions from the surrounding environment. The many-body correlations that influence this second contribution present significant challenges for accurately reproducing atomistic distribution functions. This work presents a detailed investigation of these many-body correlations and their significance for determining CG potentials while using liquid heptane as a model system. We employ a transparent geometric framework for directly determining CG potentials that has been previously developed within the context of the multiscale coarse-graining and generalized Yvon-Born-Green methods. In this framework, a metric tensor quantifies the relevant many-body correlations and precisely decomposes atomistic mean forces into contributions from specific interactions, which then determine the CG force field. Numerical investigations reveal that this metric tensor reflects both the CG representation and also subtle correlations between molecular geometry and intermolecular packing, but can be largely interpreted in terms of generic considerations. Our calculations demonstrate that contributions from correlated interactions can significantly impact the pair mean force and, thus, also the CG force field. Finally, an eigenvector analysis investigates the importance of these interactions for reproducing atomistic distribution functions. PMID:22564079

Rudzinski, Joseph F; Noid, William G

2012-06-01

305

Nonlinear brain dynamics as macroscopic manifestation of underlying many-body field dynamics

NASA Astrophysics Data System (ADS)

Neural activity patterns related to behavior occur at many scales in time and space from the atomic and molecular to the whole brain. Patterns form through interactions in both directions, so that the impact of transmitter molecule release can be analyzed to larger scales through synapses, dendrites, neurons, populations and brain systems to behavior, and control of that release can be described step-wise through transforms to smaller scales. Here we explore the feasibility of interpreting neurophysiological data in the context of many-body physics by using tools that physicists have devised to analyze comparable hierarchies in other fields of science. We focus on a mesoscopic level that offers a multi-step pathway between the microscopic functions of neurons and the macroscopic functions of brain systems revealed by hemodynamic imaging. We use electroencephalographic (EEG) records collected from high-density electrode arrays fixed on the epidural surfaces of primary sensory and limbic areas in rabbits and cats trained to discriminate conditioned stimuli (CS) in the various modalities. High temporal resolution of EEG signals with the Hilbert transform gives evidence for diverse intermittent spatial patterns of amplitude (AM) and phase modulations (PM) of carrier waves that repeatedly re-synchronize in the beta and gamma ranges in very short time lags over very long distances. The dominant mechanism for neural interactions by axodendritic synaptic transmission should impose distance-dependent delays on the EEG oscillations owing to finite propagation velocities and sequential synaptic delays. It does not. EEGs show evidence for anomalous dispersion: neural populations have a low velocity range of information and energy transfers, and a high velocity range of the spread of phase transitions. This distinction labels the phenomenon but does not explain it. In this report we analyze these phenomena using concepts of energy dissipation, the maintenance by cortex of multiple ground states corresponding to AM patterns, and the exclusive selection by spontaneous breakdown of symmetry (SBS) of single states in sequential phase transitions.

Freeman, Walter J.; Vitiello, Giuseppe

2006-06-01

306

Quantum Dynamics with AN Ensemble of Hamiltonians

NASA Astrophysics Data System (ADS)

We review recent progress in the nonequilibrium dynamics of thermally isolated many-body quantum systems, evolving with an ensemble of Hamiltonians as opposed to deterministic evolution with a single time-dependent Hamiltonian. Such questions arise in (i) quantum dynamics of disordered systems, where different realizations of disorder give rise to an ensemble of real-time quantum evolutions, (ii) quantum evolution with noisy Hamiltonians (temporal disorder), which leads to stochastic Schrödinger equations, and, (iii) in the broader context of quantum optimal control, where one needs to analyze an ensemble of permissible protocols in order to find one that optimizes a given figure of merit. The theme of ensemble quantum evolution appears in several emerging new directions in noneqilibrium quantum dynamics of thermally isolated many-body systems, which include many-body localization, noise-driven systems, and shortcuts to adiabaticity.

Rahmani, Armin

2013-10-01

307

An accurate single-sheeted double many-body expansion potential energy surface is reported for the title system. A switching function formalism has been used to warrant the correct behavior at the H2(X1?g+)+N(2D) and NH?(X3?-)+H(2S) dissociation channels involving nitrogen in the ground N(4S) and first excited N(2D) states. The topographical features of the novel global potential energy surface are examined in detail, and found to be in good agreement with those calculated directly from the raw ab initio energies, as well as previous calculations available in the literature. The novel surface can be using to treat well the Renner-Teller degeneracy of the 12A? and 12A' states of NH?2. Such a work can both be recommended for dynamics studies of the N(2D)+H2 reaction and as building blocks for constructing the double many-body expansion potential energy surface of larger nitrogen/hydrogen-containing systems. In turn, a test theoretical study of the reaction N(2D)+H2(X1?g+)(?=0,j=0)?NH?(X3?-)+H(2S) has been carried out with the method of quantum wave packet on the new potential energy surface. Reaction probabilities, integral cross sections, and differential cross sections have been calculated. Threshold exists because of the energy barrier (68.5 meV) along the minimum energy path. On the curve of reaction probability for total angular momentum J?=?0, there are two sharp peaks just above threshold. The value of integral cross section increases quickly from zero to maximum with the increase of collision energy, and then stays stable with small oscillations. The differential cross section result shows that the reaction is a typical forward and backward scatter in agreement with experimental measurement result. PMID:23666848

Li, Yongqing; Yuan, Jiuchuang; Chen, Maodu; Ma, Fengcai; Sun, Mengtao

2013-05-10

308

An empirical many-body potential energy function constructed from pair-interactions

A new empirical potential energy function (PEF) is proposed, which is formed from pair-interactions only, and containes the many-body contributions. The PEF satisfies bulk cohesive energy and bulk stability condition. The PEF is parameterized for copper, silver, and gold elements in fcc crystal structure. The elastic constants C 11 and C 12 and the bulk modulus of the elements are

Ssakir Erkoç

1994-01-01

309

Evolution of Nuclear Many-Body Forces with the Similarity Renormalization Group

The first practical method to evolve many-body nuclear forces to softened form using the Similarity Renormalization Group (SRG) in a harmonic oscillator basis is demonstrated. When applied to 4He calculations, the two- and three-body oscillator matrix elements yield rapid convergence of the ground-state energy with a small net contribution of the induced four-body force.

Jurgenson, E D; Navratil, P; Furnstahl, R J

2009-05-01

310

Ab Initio Many-Body Calculations Of Nucleon-Nucleus Scattering

We develop a new ab initio many-body approach capable of describing simultaneously both bound and scattering states in light nuclei, by combining the resonating-group method with the use of realistic interactions, and a microscopic and consistent description of the nucleon clusters. This approach preserves translational symmetry and Pauli principle. We outline technical details and present phase shift results for neutron

S Quaglioni; P Navratil

2008-01-01

311

N=2 superconformal Newton-Hooke algebra and many-body mechanics

NASA Astrophysics Data System (ADS)

A representation of the conformal Newton-Hooke algebra on a phase space of n particles in arbitrary dimension which interact with one another via a generic conformal potential and experience a universal cosmological repulsion or attraction is constructed. The minimal N=2 superconformal extension of the Newton-Hooke algebra and its dynamical realization in many-body mechanics are studied.

Galajinsky, Anton

2009-10-01

312

Relaxation Dynamics and Pre-thermalization in an isolated Quantum System

NASA Astrophysics Data System (ADS)

Understanding non-equilibrium dynamics of many-body quantum systems is crucial for understanding many fundamental and applied physics problems ranging from decoherence and equilibration to the development of future quantum technologies such as quantum computers which are inherently non-equilibrium quantum systems. One of the biggest challenges is that there is no general approach to characterize the resulting quantum states. In this talk I will present how to use the full distribution functions of a quantum observable to study the relaxation dynamics in one-dimensional quantum systems and to characterize the underlying many body states. Interfering two 1 dimensional quantum gases allows to study how the coherence created between the two many body systems by the splitting process [1] slowly dies by coupling to the many internal degrees of freedom available [2]. To reveal the nature of the quantum states behind this de-coherence we analyze the interference of the two evolving quantum systems. The full distribution function of the shot to shot variations of the interference patterns [3,4], especially its higher moments, allows characterizing the underlying physical processes [5]. Two distinct regimes are clearly visible in the experiment: for short length scales the system is characterized by spin diffusion, for long length scales by spin decay [6]. After a rapid evolution the distributions approach a steady state which can be characterized by thermal distribution functions. Interestingly, its (effective) temperature is over five times lower than the kinetic temperature of the initial system. Our system, being a weakly-interacting Bosons in one dimension, is nearly integrable and the dynamics is constrained by constants of motion which leads to the establishment of a generalized Gibbs ensemble and pre-thermalization. We therefore interpret our observations as an illustration of the fast relaxation of a nearly integrable many-body system to a quasi-steady state through de-phasing. The observation of an effective temperature significant different from the expected kinetic temperature supports the observation of the generalized Gibbs state [6]. [4pt] [1] T. Schumm et al. Nature Physics, 1, 57 (2005).[0pt] [2] S. Hofferberth et al. Nature 449, 324 (2007).[0pt] [3] A. Polkovnikov, et al. Proc. Natl. Acad. Sci. 103, 6125 (2006); V. Gritsev, et al., Nature Phys. 2, 705 (2006); [0pt] [4] S. Hofferberth et al. Nature Physics 4, 489 (2008); [0pt] [5] T. Kitagawa, et al., Phys. Rev. Lett. 104, 255302 (2010); New Journal of Physcs, 13 073018 (2011)[0pt] [6] Gring et al., to be published

Schmiedmayer, Jörg

2012-02-01

313

Various approximations of combined coupled-cluster (CC) and many-body perturbation theories (MBPT) have been derived and implemented into parallel execution programs that take account of spin, spatial (real Abelian), and permutation symmetries within the spin-orbital formalisms for closed- and open-shell molecules. The models range from CCSD(T), CCSD[T], CCSD(2)T, CCSD(2)TQ, CCSDT(2)Q to the completely renormalized CCSD(T) and CCSD[T], where CCSD (CCSDT) is the CC with connected single and double (and triple) excitation operators and subscripted or parenthesized 2, T, and Q indicate the order of perturbation or the rank of connected excitation operators in the correction. The derivation and implementation have been semi-automated by the algebraic and symbolic manipulation program. The computer-synthesized subroutines generate the tensors with the highest rank in a block-wise manner so that they never need to be stored in their entirety, reusing the other pre-calculated intermediate tensors defined also prioritizing the memory optimization (subroutines for these are also computer synthesized). Consequently, the overall memory cost for the perturbation corrections of connected triple and quadruple excitation operators scales as O(n4) and O(n6), respectively (n is the number of orbitals). For systems with different multi-reference character in their wave functions, we found the order of accuracy is roughly CCSD < CR-CCSD(T) ? CCSD(2)T ? CCSD(T) < CCSD(2)TQ ? CCSDT < CCSDT(2)Q, whereas CR-CCSD(T) is effective for extreme cases of quasi-degeneracy (particularly for stretched single bonds) and the operation costs of CCSD(2)TQ and CCSDT(2)Q in the present implementations scale as rather steep O(n9). The perturbation correction part of the CCSD(T)/cc-pVDZ calculations for azulene exhibited a 45-fold speedup upon a 64-fold increase in the number of processors to 512 processors.

Hirata, So; Fan, Peng-Dong; Auer, Alexander A.; Nooijen, Marcel; Piecuch, Piotr

2004-12-22

314

Assessing weak hydrogen binding on Ca+ centers: An accurate many-body study with large basis sets

NASA Astrophysics Data System (ADS)

Weak H2 physisorption energies present a significant challenge to even the best correlated theoretical many-body methods. We use the phaseless auxiliary-field quantum Monte Carlo method to accurately predict the binding energy of Ca+- 4H2. Attention has recently focused on this model chemistry to test the reliability of electronic structure methods for H2 binding on dispersed alkaline earth metal centers. A modified Cholesky decomposition is implemented to realize the Hubbard-Stratonovich transformation efficiently with large Gaussian basis sets. We employ the largest correlation-consistent Gaussian type basis sets available, up to cc-pCV5Z for Ca, to accurately extrapolate to the complete basis limit. The calculated potential energy curve exhibits binding with a double-well structure.

Purwanto, Wirawan; Krakauer, Henry; Virgus, Yudistira; Zhang, Shiwei

2011-10-01

315

NASA Astrophysics Data System (ADS)

In order to study many-body effects in ZnO structures with reduced-dimensionality, electronic and optical absorption properties of ZnO monolayer and armchair ZnO nanoribbons (AZnONRs) are studied by means of Green's function perturbation theory using the GW+Bethe-Salpeter equation approach. In both ZnO monolayer and AZnONRs, as a consequence of enhanced quantum confinement, the quasi-particle corrections are significant and the optical absorption properties are dominated by strong excitonic effects with considerable binding energies (1-2 eV) assigned to the lowest-energy bound excitons. It reveals that inclusion of excitonic effects, which are neglected in calculations at single-particle approximation, is crucial to qualitatively and quantitatively describe the optical properties of such materials with reduced-dimensionality.

Wei, Wei; Dai, Ying; Huang, Baibiao; Jacob, Timo

2013-10-01

316

Many-body calculation of spin-orbit induced mixed-parity pairing in Sr2RuO4

NASA Astrophysics Data System (ADS)

The unusual superconducting state in Sr2RuO4 has long been viewed as being analogous to a superfluid state in liquid ^3He. Nevertheless, calculations based on this odd-parity state are presently unable to completely reconcile the properties of Sr2RuO4. Using a self-consistent quantum many-body scheme that employs realistic parameters, we are able to model several signature properties of the normal and superconducting states of Sr2RuO4. We find that the dominant component of the model superconducting state is of even parity and closely related to superconducting state for the high-Tc cuprates although a smaller odd-parity component is induced by spin-orbit coupling. This mixed pairing state gives a more complete representation of the complex phenomena measured in Sr2RuO4.

Deisz, John; Kidd, Tim

2011-11-01

317

NASA Astrophysics Data System (ADS)

A correlated many-body calculation is presented to characterize the Shannon information entropy of trapped interacting bosons. We reformulate the one-body Shannon information entropy in terms of the one-body probability density. The minimum limit of the entropy uncertainty relation is approached by making N very small in our numerical work. We examine the effect of correlations in the calculation of information entropy. Comparison with the mean-field result shows that the correlated basis function is indeed required to characterize the important features of the information entropies. We also accurately calculate the point of critical instability of an attractive BEC, which is in close agreement with the experimental value. Next, we calculate two-body entropies in position and momentum spaces and study quantum correlations in the attractive BEC.

Haldar, Sudip Kumar; Chakrabarti, Barnali; Das, Tapan Kumar; Biswas, Anindya

2013-09-01

318

In order to study many-body effects in ZnO structures with reduced-dimensionality, electronic and optical absorption properties of ZnO monolayer and armchair ZnO nanoribbons (AZnONRs) are studied by means of Green's function perturbation theory using the GW+Bethe-Salpeter equation approach. In both ZnO monolayer and AZnONRs, as a consequence of enhanced quantum confinement, the quasi-particle corrections are significant and the optical absorption properties are dominated by strong excitonic effects with considerable binding energies (1-2 eV) assigned to the lowest-energy bound excitons. It reveals that inclusion of excitonic effects, which are neglected in calculations at single-particle approximation, is crucial to qualitatively and quantitatively describe the optical properties of such materials with reduced-dimensionality. PMID:24116637

Wei, Wei; Dai, Ying; Huang, Baibiao; Jacob, Timo

2013-10-14

319

To enhance the current understanding of mechanisms contributing to magnetic hyperfine interactions in excited states of atomic systems, in particular, alkali-metal atom systems, the hyperfine fields in the excited 5 2S1\\/2-8 2S1\\/2 states of potassium and 8 2S1\\/2-12 2S1\\/2 states of francium atoms have been studied using the relativistic linked-cluster many-body perturbation procedure. The net theoretical values of the hyperfine

Alfred Owusu; R. W. Dougherty; G. Gowri; T. P. Das; J. Andriessen

1997-01-01

320

Computational issues of configuration interaction frameworks describing open quantum systems

NASA Astrophysics Data System (ADS)

Open quantum systems (OQS), extended in space (halo nuclei) or even unbound, differ from closed quantum systems (CQS), for which the methods of standard shell model (SM) [1] can be utilized in order to expand their wave function in a configuration interaction framework. Configuration interaction methods based on the use of Berggren bases [2], comprising bound, resonant and scattering states, which have the ability to generate the very long range asymptotic behavior of OQSs, are used instead for that matter. This demands the introduction of new computational techniques, including the optimization and discretization of the Berggren basis [3], the development of an algorithm to efficiently calculate their two-body matrix elements [4], and an overall optimization of memory storage absent from SM, where, for instance, all data related to proton and neutron spaces only can be precalculated and stored [1]. In order to diagonalize the very large induced matrices, the Density Matrix Renormalization Group (DMRG) method [5] extended to OQSs has been developed [6, 7]. A renormalization procedure which generates more and more correlated many-body basis states iteratively is used therein, so that the Hamiltonian matrix to diagonalize is very small compared to that occurring with a many-body basis of independent particles [6, 7]. Parallelization of presented methods will also be discussed.

Michel, Nicolas

2013-08-01

321

Ultracold quantum gases in optical lattices

Artificial crystals of light, consisting of hundreds of thousands of optical microtraps, are routinely created by interfering optical laser beams. These so-called optical lattices act as versatile potential landscapes to trap ultracold quantum gases of bosons and fermions. They form powerful model systems of quantum many-body systems in periodic potentials for probing nonlinear wave dynamics and strongly correlated quantum phases,

Immanuel Bloch

2005-01-01

322

NASA Astrophysics Data System (ADS)

Many electronic systems (e.g., the cuprate superconductors and heavy fermions) exhibit striking features in their dynamical response over a prominent range of experimental parameters. While there are some empirical suggestions of particular increasing length scales that accompany such transitions in some cases, this identification is not universal and in numerous instances no large correlation length is evident. To better understand, as a matter of principle, such behavior in quantum systems, we extend a known mapping (earlier studied in stochastic or supersymmetric quantum mechanics) between finite temperature classical Fokker-Planck systems and related quantum systems at zero temperature to include general nonequilibrium dynamics. Unlike Feynman mappings or stochastic quantization methods in field theories (as well as more recent holographic type dualities), the classical systems that we consider and their quantum duals reside in the same number of space-time dimensions. The upshot of our very broad and rigorous result is that a Wick rotation exactly relates (i) the dynamics in general finite temperature classical dissipative systems to (ii) zero temperature dynamics in the corresponding dual many-body quantum systems. Using this correspondence, we illustrate that, even in the absence of imposed disorder, many continuum quantum fluid systems (and possible lattice counterparts) may exhibit a zero-point “quantum dynamical heterogeneity” wherein the dynamics, at a given instant, is spatially nonuniform. While the static length scales accompanying this phenomenon do not seem to exhibit a clear divergence in standard correlation functions, the length scale of the dynamical heterogeneities can increase dramatically. We further study “quantum jamming” and illustrate how a hard-core bosonic system can undergo a zero temperature quantum critical metal-to-insulator-type transition with an extremely large effective dynamical exponent z>4 that is consistent with length scales that increase far more slowly than the relaxation time as a putative critical transition is approached. Similar results may hold for spin-liquid-type as well as interacting electronic systems. We suggest ways to analyze experimental data in order to adduce such phenomena. Our approach may be used to analyze other quenched quantum systems.

Nussinov, Zohar; Johnson, Patrick; Graf, Matthias J.; Balatsky, Alexander V.

2013-05-01

323

NASA Astrophysics Data System (ADS)

An efficient, monomer-based electronic structure method is introduced for computing non-covalent interactions in molecular and ionic clusters. It builds upon our ``explicit polarization" (XPol) with pairwise-additive symmetry-adapted perturbation theory (SAPT) using the Kohn-Sham (KS) version of SAPT, but replaces the problematic and expensive sum-over-states dispersion terms with empirical potentials. This modification reduces the scaling from {O}(N^5) to {O}(N^3) and also facilitates the use of Kohn-Sham density functional theory (KS-DFT) as a low-cost means to capture intramolecular electron correlation. Accurate binding energies are obtained for benchmark databases of dimer binding energies, and potential energy curves are also captured accurately, for a variety of challenging systems. As compared to traditional DFT-SAPT or SAPT(DFT) methods, it removes the limitation to dimers and extends SAPT-based methodology to many-body systems. For many-body systems such as water clusters and halide-water cluster anions, the new method is superior to established density-functional methods for non-covalent interactions. We suggest that using different asymptotic corrections for different monomers is necessary to get good binding energies in general, as DFT-SAPT or SAPT(DFT), especially for hydrogen-bonded complexes. We also introduce a decomposition scheme for the interaction energy that extends traditional SAPT energy decomposition analysis to systems containing more than two monomers, and we find that the various energy components (electrostatic, exchange, induction, and dispersion) are in very good agreement with high-level SAPT benchmarks for dimers. For (H_2O)_6, the many-body contribution to the interaction energy agrees well with that obtained from traditional Kitaura-Morokuma energy decomposition analysis.

Lao, Ka Un; Herbert, John M.

2013-06-01

324

Fine structure of Ca-, Sr-, Ba-, and Ra- from the many-body theory calculation

NASA Astrophysics Data System (ADS)

Atomic many-body theory methods are used to calculate the fine structure of negative ions formed by binding a p electron into an open shell, Ca-, Sr-, Ba-, and Ra-. This binding is due to a strong correlation potential acting between the electron and the neutral atom. Comparison with experimental data shows that the second order many-body perturbation theory calculation overestimates the correlation potential by 10% to 15%. Scaling factors are introduced in the correlation potential to reproduce experimental binding energies of the lower p1/2 components. This procedure yields fine-structure intervals in excellent agreement with experiment for Ca-, Sr-, and Ba-, and allows us to predict that in Ra- the p1/2 state is bound by 100 meV, and p3/2 is a resonance at 16 meV in the continuum.

Dzuba, V. A.; Gribakin, G. F.

1997-03-01

325

An universal algorithm of calculating terms of atomic many-body perturbation theory

NASA Astrophysics Data System (ADS)

An algorithm, based on numerical description of the terms of many-body perturbation theory (Goldstone diagrams), is presented. The algorithm allows the use of the same piece of computer code to evaluate any particular diagram in any specific order of the perturbation theory or to calculate similar terms in other areas of the many-body theory, like, e.g., terms in the coupled-cluster equations. The use of the algorithm is illustrated by calculating the second- and third-order correlation corrections to the removal energies of electrons from the ground state of sodium, copper and gallium and by calculating the hyperfine structure constants of sodium in the linearized single-double coupled cluster approximation.

Dzuba, V. A.

2009-03-01

326

Photodetachment of metal cluster negative ions within many-body theory

NASA Astrophysics Data System (ADS)

The photodetachment cross section and photoelectron angular distribution of metal cluster negative ions are studied theoretically within the consistent many-body theory. Using the Hartree-Fock approximation for the delocalized electrons and the jellium model for the ionic core as the initial approximations, the many-electron correlations are taken into account within the Random Phase Approximation with Exchange. Our calculations demonstrate the dominant role of the many-body effects in the formation of cross sections and angular distributions of photoelectrons emitted from sodium clusters and are in good agreement with the existing experimental data. The concrete comparison of the theory and experiment has been performed for the photoionization of Na7 -, Na19 -, Na57 anions with entirely closed shells of delocalized electrons.

Polozkov, R. G.; Ivanov, V. K.; Korol, A. V.; Solov'yov, A. V.

2012-11-01

327

Many-body interaction effects on the low-k structure of liquid Kr.

Neutron diffraction measurements and theoretical calculations of the structure factor S(k) of liquid Kr are extended to small k values (k<4 nm(-1)). The results show that many-body interaction contributions have an increasing effect on S(k) as k-->0, reaching at least 40% of the measured intensity. Both the phase diagram and the low-k structural data of dense Kr turn out to be closely reproduced by the hierarchical reference theory if additional many-body forces are taken into account by an augmented strength of the Axilrod-Teller triple-dipole potential. The experimental density derivative of S(k) is also used for a very sensitive test of the theories and interaction models considered here. PMID:11414942

Guarini, E; Magli, R; Tau, M; Barocchi, F; Casanova, G; Reatto, L

2001-04-11

328

Electronic and optical properties of cadmium fluoride: The role of many-body effects

NASA Astrophysics Data System (ADS)

Electronic excitations and optical spectra of CdF2 are calculated up to ultraviolet employing state-of-the-art techniques based on density functional theory and many-body perturbation theory. The GW scheme proposed by Hedin has been used for the electronic self-energy to calculate single-particle excitation properties as energy bands and densities of states. For optical properties many-body effects, treated within the Bethe-Salpeter equation framework, turn out to be crucial. A bound exciton located about 1 eV below the quasiparticle gap is predicted. Within the present scheme the optical absorption spectra and other optical functions show an excellent agreement with experimental data. Moreover, we tested different schemes to obtain the best agreement with experimental data. Among the several schemes, we suggest a self-consistent quasiparticle energy scheme.

Cappellini, Giancarlo; Furthmüller, Jürgen; Cadelano, Emiliano; Bechstedt, Friedhelm

2013-02-01

329

Finite quantal systems -- from semiconductor quantum dots to cold atoms in traps

Many-body systems that are set rotating may form vortices, characterized by rotating motion around a central cavity. This is familiar to us from every-day life: you can observe vortices while stirring your coffee, or watching a hurricane. In quantum physics, vortices are known to occur in superconducting films and rotating bosonic He-4 or fermionic He-3 liquids, and recently became a

Stephanie M. Reimann

2007-01-01

330

In view of the importance of ozone in environmental problems, it is necessary to understand its formation and depletion in the stratosphere and troposhere from a microscopic physical-chemical point of view. We have started a first-principle quantum mechanical study of its electronic structure and geometry for both ground and excited states using the Hartree-Fock-Roothaan method combined with many-body effects. This

M. M. Aryal; D. D. Paudyal; R. H. Scheicher; J. Jeong; Binod Dhakal; Sekhar Gurung; T. P. Das

2001-01-01

331

Fidelity spectrum and phase transitions of quantum systems

Quantum fidelity between two density matrices F({rho}{sub 1},{rho}{sub 2}) is usually defined as the trace of the operator F={radical}({radical}({rho}{sub 1}){rho}{sub 2}{radical}({rho}{sub 1})). We study the logarithmic spectrum of this operator, which we denote by the fidelity spectrum, in the cases of the XX spin chain in a magnetic field, a magnetic impurity inserted in a conventional superconductor, and a bulk superconductor at finite temperature. When the density matrices are equal, {rho}{sub 1}={rho}{sub 2}, the fidelity spectrum reduces to the entanglement spectrum. We find that the fidelity spectrum can be a useful tool in giving a detailed characterization of the different phases of many-body quantum systems.

Sacramento, P. D.; Vieira, V. R. [Departamento de Fisica and CFIF, Instituto Superior Tecnico, TU Lisbon, Avenida Rovisco Pais, P-1049-001 Lisboa (Portugal); Paunkovic, N. [SQIG-Instituto de Telecomunicacoes, IST, TU Lisbon, Avenida Rovisco Pais, P-1049-001 Lisboa (Portugal)

2011-12-15

332

Solving the Gross-Neveu model with relativistic many-body methods

The Gross-Neveu model provides a unique opportunity to apply relativistic many-body techniques (Dirac-Hartree approximation, RPA) in a context where all calculations can be done analytically and — in the largeN limit — yield the exact results. The physical fermion as well as multifermion (“baryon”) and fermion-antifermion (“meson”) bound states are discussed in this spirit, with special emphasis on the role

R. Pausch; M. Thies; V. L. Dolman

1991-01-01

333

An empirical many-body potential energy function constructed from pair-interactions

A new empirical potential energy function (PEF) is proposed, which is formed from pair-interactions only, and containes the many-body contributions. The PEF satisfies bulk cohesive energy and bulk stability condition. The PEF is parameterized for copper, silver, and gold elements in fcc crystal structure. The elastic constantsC11 andC12 and the bulk modulus of the elements are calculated, and the structural

?Sakir Erkoç

1994-01-01

334

Electronic excitations: density-functional versus many-body Green's-function approaches

Electronic excitations lie at the origin of most of the commonly measured spectra. However, the first-principles computation of excited states requires a larger effort than ground-state calculations, which can be very efficiently carried out within density-functional theory. On the other hand, two theoretical and computational tools have come to prominence for the description of electronic excitations. One of them, many-body

Giovanni Onida; Lucia Reining; Angel Rubio

2002-01-01

335

The hyperfine structure of caesium and francium levels has been calculated using the relativistic Hartree-Fock (RHF) method and with the correlations being taken into account by means of the many-body perturbation theory. The hyperfine interaction has been included in the Hartree-Fock equations. The effect of the finite size of the nucleus has been considered. For the s and p1\\/2 states,

V A Dzuba; V V Flambaum; O P Sushkov

1984-01-01

336

Probing many-body states of ultracold atoms via noise correlations

We propose to utilize density-density correlations in the image of an expanding gas cloud to probe complex many-body states of trapped ultracold atoms. In particular, we show how this technique can be used to detect superfluidity of fermionic gases and to study spin correlations of multicomponent atoms in optical lattices. The feasibility of the method is investigated by analysis of the relevant signal to noise ratio including experimental imperfections.

Altman, Ehud; Demler, Eugene; Lukin, Mikhail D. [Physics Department, Harvard University, Cambridge, Massachusetts 02138 (United States)

2004-07-01

337

Detecting many-body entanglement in noninteracting ultracold atomic Fermi gases

We explore the possibility of detecting many-body entanglement using time-of-flight (TOF) momentum correlations in ultracold atomic Fermi gases. In analogy to the vacuum correlations responsible for Bekenstein-Hawking black hole entropy, a partitioned atomic gas will exhibit particle-hole correlations responsible for entanglement entropy. The signature of these momentum correlations might be detected by a sensitive TOF-type experiment.

Levine, G. C.; Bantegui, M. J. [Department of Physics and Astronomy, Hofstra University, Hempstead, New York 11549 (United States); Friedman, B. A. [Department of Physics, Sam Houston State University, Huntsville, Texas 77341 (United States)

2011-01-15

338

Ab initio many-body calculations of nucleon scattering on He, Li, Be, ¹²C, and ¹O

We combine a recently developed ab initio many-body approach capable of describing simultaneously both bound and scattering states, the ab initio no-core shell model\\/resonating-group method (NCSM\\/RGM), with an importance-truncation scheme for the cluster eigenstate basis and demonstrate its applicability to nuclei with mass numbers as high as 17. By using soft similarity renormalization-group-evolved chiral nucleon-nucleon interactions, we first calculate nucleon-He

Petr Navratil; Sofia Quaglioni; Robert Roth

2010-01-01

339

Hyperfine Structure of Oxygen Calculated by Many-Body Theory. II

Many-body perturbation theory is used to calculate the contributions to the hyperfine structure of atomic oxygen from the orbital, spin-dipolar, and quadrupole interactions. The resulting values for

Hugh P. Kelly

1969-01-01

340

Ab initio many-body calculations of nucleon-nucleus scattering

We develop a new ab initio many-body approach capable of describing simultaneously both bound and scattering states in light nuclei, by combining the resonating-group method with the use of realistic interactions, and a microscopic and consistent description of the nucleon clusters. This approach preserves translational symmetry and the Pauli principle. We outline technical details and present phase-shift results for neutron

Sofia Quaglioni; Petr Navrátil

2009-01-01

341

Anisotropy of the many-body enhancements on the Fermi surface of Pd

A new Korringa-Kohn-Rostoker parametrization of the cyclotron effective masses in Pd based on the data reported in the preceding paper is described. The parametrization was used to derive the many-body-enhanced Fermi velocities of electrons in the high-symmetry planes on each of the four sheets of the Fermi surface, the enhanced density of states for each sheet, and the total enhanced

W. Joss; G. W. Crabtree

1984-01-01

342

Many-Body Enhancement Effects on the 2D ACAR in Chromium

The electron-positron many-body enhancement effect on the two-dimensional angular correlation distribution of positron annihilation radiation (2D ACAR) inchromium is phenomelogically investigated. The enhancement parameters are determined so as to obtain the best fit of the theoretical 2D ACAR to the experimental one. Two kinds of enhancement are considered. The first is a state-dependent one. In this scheme two enhancement factors

Makoto Matsumoto; Shinya Wakoh

1987-01-01

343

Many-body enhancement of the Pauli susceptibility of A_3C_60

The density of states N(0) of A_3C_60 at the Fermi level can be estimated from various types of experiments. The value deduced from the specific heat and NMR measurements is 5-6 and 7 states\\/(eV spin), respectively, whereas the estimate obtained form the measured susceptibility -- without taking into account many-body effects -- is 10-16 states\\/(eV spin). To understand this discrepancy,

Ferdi Aryasetiawan; Olle Gunnarsson; Erik Koch; Richard M. Martin

1997-01-01

344

Many-body effective mass enhancement in a two-dimensional electron liquid

Motivated by a large number of recent magnetotransport studies we have revisited the problem of the microscopic calculation of the quasiparticle effective mass in a paramagnetic two-dimensional (2D) electron liquid (EL). Our systematic study is based on a generalized $GW$ approximation which makes use of the many-body local fields and takes advantage of the results of the most recent QMC

R. Asgari; B. Davoudi; M. Polini; M. P. Tosi; G. F. Giuliani; G. Vignale

2004-01-01

345

Destruction of interference by many-body interactions in cold atomic Bose gases

We study the effects of many-body interactions on the interference in a Mach-Zehnder interferometer for matter waves of ultracold Bose atoms. After switching off an axial trapping potential, the thermal initial wave packet expands, and subsequently interference fringes may be observed in a circular one-dimensional trap. These are computed for axial harmonic or delta-function traps, and for interaction strengths from

Shu Chen; Reinhold Egger

2003-01-01

346

Determinism Beneath Composite Quantum Systems

NASA Astrophysics Data System (ADS)

This paper aims at the development of 't Hooft's quantization proposal to describe composite quantum mechanical systems. In particular, we show how 't Hooft's method can be utilized to obtain from two classical Bateman oscillators a composite quantum system corresponding to a quantum isotonic oscillator. For a suitable range of parameters, the composite system can be also interpreted as a particle in an effective magnetic field interacting through a spin-orbital interaction term. In the limit of a large separation from the interaction region we can identify the irreducible subsystems with two independent quantum oscillators.

Blasone, Massimo; Vitiello, Giuseppe; Jizba, Petr; Scardigli, Fabio

347

Local controllability of quantum systems

NASA Astrophysics Data System (ADS)

We give a criterion that is sufficient for controllability of multipartite quantum systems. We generalize the graph infection criterion to the quantum systems that cannot be described with the use of a graph theory. We introduce the notation of hypergraphs and reformulate the infection property in this setting. The introduced criterion has a topological nature and therefore it is not connected to any particular experimental realization of quantum information processing.

Pucha?a, Zbigniew

2013-01-01

348

Spectroscopic studies in open quantum systems

The Hamiltonian H of an open quantum system is non-Hermitian. Its complex eigenvalues E(R) are the poles of the S matrix and provide both the energies and widths of the states. We illustrate the interplay between Re(H) and Im(H) by means of the different interference phenomena between two neighboring resonance states. Level repulsion may occur along the real or imaginary axis (the latter is called resonance trapping). In any case, the eigenvalues of the two states avoid crossing in the complex plane. We then calculate the poles of the S matrix and the corresponding wave functions for a rectangular microwave resonator with a scatter as a function of the area of the resonator as well as of the degree of opening to a waveguide. The calculations are performed by using the method of exterior complex scaling. Re(H) and Im(H) cause changes in the structure of the wave functions which are permanent, as a rule. The resonance picture obtained from the microwave resonator shows all the characteristic features known from the study of many-body systems in spite of the absence of two-body forces. The effects arising from the interplay between resonance trapping and level repulsion along the real axis are not involved in the statistical theory (random matrix theory). PMID:11088480

Rotter; Persson; Pichugin; Seba

2000-07-01

349

Short-time dynamics of correlated quantum Coulomb systems

NASA Astrophysics Data System (ADS)

Strong correlations in dense Coulomb systems are attracting increasing interest in many fields ranging from dense astrophysical plasmas, dusty plasmas and semiconductors to metal clusters and ultracold trapped ions [1]. Examples are bound states in dense plasmas (atoms, molecules, clusters) and semiconductors (excitons, trions, biexcitons) and many-particle correlations such as Coulomb and Yukawa liquids and crystals. Of particular current interest is the response of these systems to short excitations generated e.g. by femtosecond laser pulses and giving rise to ultrafast relaxation processes and build up of binary correlations. The proper theoretical tool are non-Markovian quantum kinetic equations [1,2] which can be derived from Nonequilibrium Green's Functions (NEGF) and are now successfully solved numerically for dense plasmas and semiconductors [3], correlated electrons [4] and other many-body systems with moderate correlations [5]. This method is well suited to compute the nonlinear response to strong fields selfconsistently including many-body effects [6]. Finally, we discuss recent extensions of the NEGF-computations to the dynamics of strongly correlated Coulomb systems, such as single atoms and molecules [7] and electron and exciton Wigner crystals in quantum dots [8,9]. [1] H. Haug and A.-P. Jauho, Quantum Kinetics in Transport and Optics of Semiconductors, Springer 1996; M. Bonitz Quantum Kinetic Theory, Teubner, Stuttgart/Leipzig 1998; [2] Progress in Nonequilibrium Green's Functions III, M. Bonitz and A. Filinov (Eds.), J. Phys. Conf. Ser. vol. 35 (2006); [3] M. Bonitz et al. Journal of Physics: Condensed Matter 8, 6057 (1996); R. Binder, H.S. K"ohler, and M. Bonitz, Phys. Rev. B 55, 5110 (1997); [4] N.H. Kwong, and M. Bonitz, Phys. Rev. Lett. 84, 1768 (2000); [5] Introduction to Computational Methods for Many-Body Systems, M. Bonitz and D. Semkat (eds.), Rinton Press, Princeton (2006); [6] H. Haberland, M. Bonitz, and D. Kremp, Phys. Rev. E 64, 026405 (2001); [7] N.E. Dahlen, A. Stan and R. van Leeuwen, p. 324 in Ref. 2.; [8] A. Filinov, M. Bonitz, and Yu. Lozovik, Phys. Rev. Lett. 86, 3851 (2001); [9] K. Balzer, N.E. Dahlen, R. van Leeuwen, and M. Bonitz, to be published

Bonitz, Michael

2007-03-01

350

NASA Astrophysics Data System (ADS)

We investigate the role of quantum mechanical effects in the central stability concept of evolutionary game theory, i.e., an evolutionarily stable strategy (ESS). Using two and three-player symmetric quantum games we show how the presence of quantum phenomenon of entanglement can be crucial to decide the course of evolutionary dynamics in a population of interacting individuals.

Iqbal, A.; Toor, A. H.

2002-03-01

351

NASA Astrophysics Data System (ADS)

The relativistic many-body perturbation theory (MBPT) calculations for matrix elements of divalent atoms and ions is extended to third-order. The one-particle and two-particle contributions are carefully examined and a complete angular reduction of the third-order amplitudes is carried out. Example calculations are performed on beryllium and magnesium isoelectronic sequences. Oscillator strengths, transition probabilities, and lifetimes are calculated for selected ions. Significant improvement in comparison with second-order MBPT results is observed. The relativistic all-order method is introduced for high-precision calculations of atomic properties in monovalent systems, where all single, double, and partial triple excitations of the Dirac-Hartree-Fock wave function are included to all orders of perturbation theory. Energies, reduced electric-dipole matrix elements and lifetimes are calculated and compared with available experiments for the low-lying excited np and nd states in Sr+, Ba+ and Ra+ atoms. Electric-quadrupole moments of the metastable nd3/2 and nd 5/2 states of Ca+, Sr+, and Ba+ are evaluated for the optical clock development applications. Third-order MBPT is used to evaluate the contributions from high partial waves and Breit interaction, and a semi-empirical scaling procedure is carried out to evaluate the remaining omitted correlation corrections. An extensive study of the uncertainties establishes the accuracy of our recommended values as 0.5 - 1% depending on the particular ion. Extra attention is paid to the 5 s-4d5/2 clock transition in 88 Sr+. The scalar polarizabilities of the 5s and 4d5/2 states and the tensor polarizability of the 4d5/2 state are calculated through the summation of individual possible dipole transition contributions. A complete analysis on the uncertainties of the static polarizabilities. The black-body radiation (BBR) shift is evaluated to be 0.250(9) Hz at room temperature, T = 300 K. The dynamic correction to the electric-dipole contribution and the multipolar corrections due to M1 and E2 transitions were estimated and found to be small at the present level of accuracy. CI + all-order method is used for the calculations of the atomic properties in the divalent systems. This method combines the all-order approach currently used in precision calculations of monovalent system with the configuration-interaction (CI) approach that is applicable for many-electron systems. Energies are calculated in different orders of approximations for several low-lying excited states in the divalent systems from Mg to Hg. The results are compared with experiments. The static and frequency-dependent polarizabilities are evaluated for the lowest nsns 1S0 and nsnp 3P0 states in Sr, Zn, Cd, and Hg atoms. Magic wavelengths are found for the 1 S0 -3 P 0 transitions in those systems by matching the ac Stark shifts of the upper and lower states. The preliminary magic wavelength for the Sr system is in 0.03% agreement with the recent high-precision experiment performed by Brusch et al. [PRL, 96, 103003(2006)]. Other preliminary calculations are performed for the electric-dipole transition matrix elements in Sr, Zn, Cd, and Hg atoms. Transition rates of the ns 2 1S0-nsnp 1P1 resonant line and the ns 2 1S0-nsnp 3P1 intercombination line are evaluated for these systems. Major contributions to the scattering rates are evaluated for the cases where atoms are trapped at their magic wavelengths with a shallow potential depth.

Jiang, Dansha

352

Separability of Multipartite Quantum Systems

NASA Astrophysics Data System (ADS)

A necessary condition for separability of multipartite quantum systems is given. It is shown that for 2 × 2 × \\ctdot × 2 × quantum systems the condition of separability is equivalent to the criterion of positive partial transposition. We also define an entanglement measurement based on this separability condition which can be considered as a kind of generalization of negativity.

Li, Ming; Jing, Wang

2012-02-01

353

Ultrafast (but many-body) relaxation in a low-density electron glass.

We present a study of the relaxation dynamics of the photoexcited conductivity of the impurity states in the low-density electronic glass, phosphorous-doped silicon Si:P. Using subband gap optical pump-terahertz probe spectroscopy we find strongly temperature- and fluence-dependent glassy power-law relaxation occurring over subnanosecond time scales. Such behavior is in contrast to the much longer time scales found in higher electron density glassy systems. We also find evidence for both multiparticle relaxation mechanisms and/or coupling to electronic collective modes and a low temperature quantum relaxational regime. PMID:20868121

Thorsmølle, V K; Armitage, N P

2010-08-19

354

Quantum Harmonic Oscillator Systems with Disorder

NASA Astrophysics Data System (ADS)

We study many-body properties of quantum harmonic oscillator lattices with disorder. A sufficient condition for dynamical localization, expressed as a zero-velocity Lieb-Robinson bound, is formulated in terms of the decay of the eigenfunction correlators for an effective one-particle Hamiltonian. We show how state-of-the-art techniques for proving Anderson localization can be used to prove that these properties hold in a number of standard models. We also derive bounds on the static and dynamic correlation functions at both zero and positive temperature in terms of one-particle eigenfunction correlators. In particular, we show that static correlations decay exponentially fast if the corresponding effective one-particle Hamiltonian exhibits localization at low energies, regardless of whether there is a gap in the spectrum above the ground state or not. Our results apply to finite as well as to infinite oscillator systems. The eigenfunction correlators that appear are more general than those previously studied in the literature. In particular, we must allow for functions of the Hamiltonian that have a singularity at the bottom of the spectrum. We prove exponential bounds for such correlators for some of the standard models.

Nachtergaele, Bruno; Sims, Robert; Stolz, Günter

2012-12-01

355

Lie-algebraic Approach to Dynamics of Closed Quantum Systems and Quantum-to-Classical Correspondence

NASA Astrophysics Data System (ADS)

I will briefly review our recent work on a Lie-algebraic approach to various non-equilibrium quantum-mechanical problems, which has been motivated by continuous experimental advances in the field of cold atoms. First, I will discuss non-equilibrium driven dynamics of a generic closed quantum system. It will be emphasized that mathematically a non-equilibrium Hamiltonian represents a trajectory in a Lie algebra, while the evolution operator is a trajectory in a Lie group generated by the underlying algebra via exponentiation. This turns out to be a constructive statement that establishes, in particular, the fact that classical and quantum unitary evolutions are two sides of the same coin determined uniquely by the same dynamic generators in the group. An equation for these generators - dubbed dual Schr"odinger-Bloch equation - will be derived and analyzed for a few of specific examples. This non-linear equation allows one to construct new exact non-linear solutions to quantum-dynamical systems. An experimentally-relevant example of a family of exact solutions to the many-body Landau-Zener problem will be presented. One practical application of the latter result includes dynamical means to optimize molecular production rate following a quench across the Feshbach resonance.

Galitski, Victor

2012-02-01

356

We recently introduced a low-cost quantum chemistry method for computing intermolecular interactions, combining a monomer-based self-consistent field calculation (the "explicit polarization" method, XPol) with pairwise-additive symmetry adapted perturbation theory (SAPT). The method uses Kohn-Sham (KS) orbitals in the SAPT formalism but replaces the SAPT dispersion and exchange-dispersion terms with empirical potentials ("+D"), and we called this method XPol+SAPT(KS)+D. Here, we report a second-generation version of this approach, XPol+SAPT(KS)+D2 or XSAPT(KS)+D2 for short, in which we have modified the form of the empirical atom-atom dispersion potentials. Accurate binding energies are obtained for benchmark databases of dimer binding energies, and potential energy curves are captured accurately for a variety of challenging systems. We suggest that using different asymptotic corrections for different monomers is necessary to get good binding energies in general, especially for hydrogen-bonded complexes. As compared to our original "+D" formulation, the second-generation "+D2" method accurately reproduces not only total binding energies but also the various components of the interaction energy, and on this basis we introduce an energy decomposition scheme that extends traditional SAPT energy decomposition to systems containing more than two monomers. For (H2O)6, the many-body contribution to the interaction energy agrees well with that obtained from traditional Kitaura-Morokuma energy decomposition analysis in a large basis set. PMID:23883010

Lao, Ka Un; Herbert, John M

2013-07-21

357

Non-hermitian approach to decaying ultracold bosonic systems

NASA Astrophysics Data System (ADS)

A paradigm model of modern atom optics is studied, strongly interacting ultracold bosons in an optical lattice. This many-body system can be artificially opened in a controlled manner by modern experimental techniques. We present results based on a non-hermitian effective Hamiltonian whose quantum spectrum is analyzed. The direct access to the spectrum of the metastable many-body system allows us to easily identify relatively stable quantum states, corresponding to previously predicted solitonic many-body structures.

Wimberger, Sandro; Parra-Murillo, Carlos A.; Kordas, Georgios

2013-06-01

358

Many-body and model-potential calculations of low-energy photoionization parameters for francium

The photoionization cross section $\\\\sigma$, spin-polarization parameters $P$\\u000aand $Q$, and the angular-distribution asymmetry parameter $\\\\beta$ are\\u000acalculated for the $7s$ state of francium for photon energies below 10 eV. Two\\u000adistinct calculations are presented, one based on many-body perturbation theory\\u000aand another based on the model potential method. Although predictions of the\\u000atwo calculations are similar, the detailed energy

A. Derevianko; W. R. Johnson; H. R. Sadeghpour

2000-01-01

359

Self-consistent RPA based on a many-body vacuum

Self-Consistent RPA is extended in a way so that it is compatible with a variational ansatz for the ground-state wave function as a fermionic many-body vacuum. Employing the usual equation-of-motion technique, we arrive at extended RPA equations of the Self-Consistent RPA structure. In principle the Pauli principle is, therefore, fully respected. However, the correlation functions entering the RPA matrix can only be obtained from a systematic expansion in powers of some combinations of RPA amplitudes. We demonstrate for a model case that this expansion may converge rapidly.

Jemaie, M., E-mail: jemai@ipno.in2p3.fr [Universite de Tunis El-Manar, Departement de Physique, Faculte des Sciences de Tunis (Tunisia); Schuck, P., E-mail: schuck@ipno.in2p3.fr [Universite Paris-Sud, CNRS-IN2P3 15, Institut de Physique Nucleaire d'Orsay (France)

2011-08-15

360

Many-body electronic structure and Kondo properties of cobalt-porphyrin molecules.

We use a unique combination of first principles many-body methods and the numerical renormalization-group technique to study the Kondo regime of cobalt-porphyrin compounds adsorbed on a Cu(111) surface. We find the Kondo temperature to be highly sensitive to both molecule charging and distance to the surface, which can explain the variations observed in recent scanning tunneling spectroscopy measurements. We discuss the importance of manybody effects in the molecular electronic structure controlling this phenomenon and suggest scenarios where enhanced temperatures can be achieved in experiments.

Reboredo, Fernando A [ORNL; Tiago, Murilo L [ORNL; Dagotto, Elbio R [ORNL; Dias Da Silva, Luis G [ORNL; Ulloa, Sergio E [Ohio University, Athens

2009-01-01

361

No-go theorem in many-body dissipative particle dynamics.

Many body dissipative particle dynamics (MDPD) is a particle-based simulation method in which the interaction potential is a sum of self energies depending on locally sampled density variables. This functional form gives rise to density-dependent pairwise forces; however, not all such force laws are derivable from a potential, and the integrability condition for this to be the case provides a strong constraint. A strategy to assess the implications of this constraint is illustrated here by the derivation of a useful no-go theorem for multicomponent MDPD. PMID:23679556

Warren, Patrick B

2013-04-19

362

Decoherence in infinite quantum systems

We review and discuss a notion of decoherence formulated in the algebraic framework of quantum physics. Besides presenting some sufficient conditions for the appearance of decoherence in the case of Markovian time evolutions we provide an overview over possible decoherence scenarios. The framework for decoherence we establish is sufficiently general to accommodate quantum systems with infinitely many degrees of freedom.

Blanchard, Philippe; Hellmich, Mario [Faculty of Physics, University of Bielefeld, Universitaetsstr. 25, 33615 Bielefeld (Germany); Bundesamt fuer Strahlenschutz (Federal Office for Radiation Protection), Willy-Brandt-Strasse 5, 38226 Salzgitter (Germany)

2012-09-01

363

Electronic and Optical Properties of Brookite TiO2 Including Many-Body Effects

NASA Astrophysics Data System (ADS)

Of the three naturally-occurring polymorphs of TiO2, brookite has been the least studied. With a more complex unit cell than rutile or anatase, it is harder to simulate and synthesize. However, the need to understand brookite has become compelling due to improvements in its synthesis and enhanced photocatalytic activity observed in experiment. Here, we characterize the electronic and optical properties of brookite using density functional theory (DFT) and many-body perturbation theory. The many-body effects, which have been neglected in previous computational works, are necessary to accurately reproduce the band energies and to account for excitonic effects. An initial band structure is calculated using Kohn-Sham DFT with Ti semicore states treated explicitly. We determine the electronic band structure using G0W0 self-energy corrections and compute optical spectra using time-dependent DFT and Bethe-Salpeter. In addition to quasiparticle peaks, other neutral excitations such as plasmons are identified. We compare properties of brookite with those of rutile and anatase to assess the influence of the bulk structure, and discuss discrepancies between theoretical and experimental results.

Hung, Linda; Sottile, Francesco

2012-02-01

364

Quantum dissipation in unbounded systems.

In recent years trajectory based methodologies have become increasingly popular for evaluating the time evolution of quantum systems. A revival of the de Broglie--Bohm interpretation of quantum mechanics has spawned several such techniques for examining quantum dynamics from a hydrodynamic perspective. Using techniques similar to those found in computational fluid dynamics one can construct the wave function of a quantum system at any time from the trajectories of a discrete ensemble of hydrodynamic fluid elements (Bohm particles) which evolve according to nonclassical equations of motion. Until very recently these schemes have been limited to conservative systems. In this paper, we present our methodology for including the effects of a thermal environment into the hydrodynamic formulation of quantum dynamics. We derive hydrodynamic equations of motion from the Caldeira-Leggett master equation for the reduced density matrix and give a brief overview of our computational scheme that incorporates an adaptive Lagrangian mesh. Our applications focus upon the dissipative dynamics of open unbounded quantum systems. Using both the Wigner phase space representation and the linear entropy, we probe the breakdown of the Markov approximation of the bath dynamics at low temperatures. We suggest a criteria for rationalizing the validity of the Markov approximation in open unbound systems and discuss decoherence, energy relaxation, and quantum/classical correspondence in the context of the Bohmian paths. PMID:11863623

Maddox, Jeremy B; Bittner, Eric R

2002-01-25

365

Quantum Phase Transitions in Random Spin Systems

We report a systematic numerical study of quantum critical phenomena in random spin systems. At zero temperature, quantum phase transitions in these systems are caused by the interplay of quantum fluctuations and ordering interactions with built-in quenched randomness. As demonstrated in the one dimensional case, random quantum spin systems show unusual critical behavior as compared to classical systems. In this

Muyu Guo

1995-01-01

366

Modified many-body wave function for BCS-BEC crossover in Fermi gases

We present a many-body formalism for BCS-BEC crossover, which represents a modification of the Bardeen-Cooper-Schrieffer-Leggett ground state to include four-fermion and higher correlations. In the Bose-Einstein condensate regime, we show how our approach contains the four-fermion behavior of Petrov et al. and associated scattering length a{sub dd} at short distances and, second, reduces to composite-boson Bogoliubov physics at long distances. It reproduces the Lee-Yang term, whose numerical value is also fixed by a{sub dd}. We have also examined the next term beyond the Lee-Yang correction in a phenomenological fashion, building on cloud size data and collective mode experiments, although one has to view this phenomenological analysis with some caution since experiments are in a state of flux and are performed close to unitarity.

Tan, Shina; Levin, K. [James Franck Institute and Department of Physics, University of Chicago, Chicago, Illinois 60637 (United States)

2006-10-15

367

Electronic structure of assembled graphene nanoribbons: Substrate and many-body effects

NASA Astrophysics Data System (ADS)

Experimentally measured electronic band gaps of atomically sharp straight and chevronlike armchair graphene nanoribbons (GNRs) adsorbed on a gold substrate are smaller than theoretically predicted quasiparticle band gaps of their free-standing counterparts [Linden , Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.108.216801 108, 216801 (2012)]. The influence of the substrate on electronic properties of both straight and chevronlike GNRs is here investigated including many-body effects beyond semilocal density-functional theory. The predicted small electron transfer from a straight or chevronlike GNR to the gold surface is found to lead to a surface polarization at the GNR-metal interface responsible for a significant reduction of the quasiparticle band gap of the GNR. This reduction is quantified using a semiclassical image charge model. By considering both quasiparticle and surface polarization corrections, we obtain theoretical band gaps that are consistent with experimental ones for gold-supported GNRs.

Liang, Liangbo; Meunier, Vincent

2012-11-01

368

Ab initio many-body calculation of the Be7(p,?)B8 radiative capture

NASA Astrophysics Data System (ADS)

We apply the ab initio no-core shell model/resonating group method (NCSM/RGM) approach to calculate the cross section of the Be7(p,?)B8 radiative capture. This reaction is important for understanding the solar neutrino flux. Starting from a selected similarity-transformed chiral nucleon-nucleon interaction that accurately describes two-nucleon data, we performed many-body calculations that simultaneously predict both the normalization and the shape of the S-factor. We study the dependence on the number of 7Be eigenstates included in the coupled-channel equations and on the size of the harmonic oscillator basis used for the expansion of the eigenstates and of the localized parts of the integration kernels. Our S-factor result at zero energy is on the lower side of, but consistent with, the latest evaluation.

Navrátil, Petr; Roth, Robert; Quaglioni, Sofia

2011-10-01

369

Ab Initio Many-Body Calculations Of Nucleon-Nucleus Scattering

We develop a new ab initio many-body approach capable of describing simultaneously both bound and scattering states in light nuclei, by combining the resonating-group method with the use of realistic interactions, and a microscopic and consistent description of the nucleon clusters. This approach preserves translational symmetry and Pauli principle. We outline technical details and present phase shift results for neutron scattering on {sup 3}H, {sup 4}He and {sup 10}Be and proton scattering on {sup 3,4}He, using realistic nucleon-nucleon (NN) potentials. Our A = 4 scattering results are compared to earlier ab initio calculations. We find that the CD-Bonn NN potential in particular provides an excellent description of nucleon-{sup 4}He S-wave phase shifts. We demonstrate that a proper treatment of the coupling to the n-{sup 10}Be continuum is successful in explaining the parity-inverted ground state in {sup 11}Be.

Quaglioni, S; Navratil, P

2008-12-17

370

Generalized density functional theory for effective potentials in many-body electronic structure

NASA Astrophysics Data System (ADS)

We demonstrate the existence of different density functionals that retain selected properties of the many-body ground state in the non-interacting density functional solution. We focus on diffusion Monte Carlo applications that require trial wave functions with Fermion optimal nodes. The theory can be extended and used to understand current practices in several electronic structure methods [GW-BSE,CI,EPM] within a generalized density functional framework. The theory justifies and stimulates the search of optimal empirical density functionals and effective potentials but also cautions on the limits of their applicability. The theoretical concepts are tested against a near-analytic model that can be solved to numerical precision. Research performed at the Materials Science and Technology Division and the Center of Nanophase Material Sciences at Oak Ridge National Laboratory sponsored the Division of Materials Sciences and the Division of Scientific User Facilities U.S. Department of Energy.

Reboredo, F. A.; Kent, P. R. C.

2008-03-01

371

Further improvement in the variational many-body wave functions for light nuclei

NASA Astrophysics Data System (ADS)

An improved variational ansatz is proposed and implemented for variational many-body wave functions for light nuclei with nucleons interacting through Argonne (AV18) and Urbana IX (UIX) three-nucleon interactions. The new ansatz is based upon variationally distinguishing between the various components of the two-body Jastrow and operatorial correlations, which are operated upon by three-body and spin-orbit correlations. We obtain noticeable improvement in the quality of the wave function and lowering of the energies compared to earlier results. The new energies are -8.38(1), -28.07(1), and -29.90(1) MeV for 3H, 4He, and 6Li, respectively. Though, the present improved ansatz still fails to stabilize the 6Li nucleus against a breakup into an ? particle and a deuteron by 390 KeV; nonetheless, it is an improvement over previous studies.

Usmani, Q. N.; Anwar, K.; Abdullah, Nooraihan

2012-09-01

372

Many-body selective destruction of tunneling in a bosonic junction

NASA Astrophysics Data System (ADS)

A scheme for selective coherent destruction of tunneling (CDT) of strongly interacting bosons in a symmetric double-well potential, in which an arbitrarily and a priori prescribed number of bosons are allowed to tunnel from one well to the other one is theoretically proposed. As compared to the many-body CDT scheme recently proposed by Gong, Molina, and Hänggi [Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.103.133002 103, 133002 (2009)] and based on a fast modulation of the self-interaction strength, the method suggested in this work exploits the traditional method of fast modulation of the energy level unbalance between the two wells by an external ac force.

Longhi, Stefano

2012-10-01

373

The crucial component needed to understand molecular reactions is the potential energy surfaces (PES) that serve to describe the attractions among the atoms and molecules. However, such information is not easy to obtain. In many cases, the most direct approach to obtaining accurate potential surfaces for molecules, and detailed information about their excited states, vibrational spectra, and a wealth of other quantities, is high level ab initio solutions of the Schrodinger equation. However, more so than in most other areas, the ability to provide reliable quantum mechanical results for increasingly large molecules depends critically on improved method development. Whereas supercomputers can enable us to make much larger computations with old methods, the simultaneous development of new methods can increase computational capability by further orders of magnitude. In this regard, many-body perturbation theory (MBPT) and its infinite-order extensions termed coupled-cluster (CC) methods offer a number of attractive features that the more traditional configuration interaction approaches lack. Under AFOSR support, we have established these CC/MBPT theories as being among the most accurate available, and have developed very efficient and generally applicable computer programs to perform CC/MBPT calculations. Also, we have employed these methods for the first time in large-scale ab initio calculations of potential energy surfaces. The successes of our original work in this effort have been substantial (see previous AFOSR reports).

Bartlett, R.J.

1992-01-21

374

Macroscopic quantum effects in Josephson systems

Macroscopic quantum effects in Josephson systems have attracted great interest in the scientific community both for the physics involved and in view of applications. We present data on macroscopic quantum tunneling on Josephson junctions. Actually the most fascinating topic is the observation of macroscopic quantum coherence in rf-SQUID. This effect also has implications for quantum computing, because a quantum two-state

Valentina Corato; Emanuela Esposito; Carmine Granata; Antonia Monaco; Berardo Ruggiero; Maurizio Russo; Leo Stodolsky; Paolo Silvestrini

2001-01-01

375

Stabilizing Feedback Controls for Quantum Systems

No quantum measurement can give full information on the state of a quantum system; hence any quantum feedback control problem is necessarily one with partial observations and can generally be converted into a completely observed control problem for an appropriate quantum filter as in classical stochastic control theory. Here we study the properties of controlled quantum filtering equations as classical

Mazyar Mirrahimi; Ramon van Handel

2007-01-01

376

A hybrid quantum system of ultracold atoms and trapped ions

NASA Astrophysics Data System (ADS)

In the last decades, trapped ions and ultracold atoms have emerged as exceptionally controllable experimental systems to investigate fundamental physics, ranging from quantum information science to simulations of condensed matter models. Even though they share some common grounds in experimental techniques, such as laser cooling, ion trapping and atom trapping have developed very much independently, and only little cross-pollination has been seen. In our experiment we study how cold atoms can be combined with single trapped ions to create a new hybrid quantum system with tailored properties. We have deterministically placed a single ion into an atomic Bose Einstein condensate and demonstrated independent control over the two components within the hybrid system. We have studied the fundamental interaction processes and observed sympathetic cooling of the single ion by the condensate. Additionally, we have characterized elastic and inelastic atom- ion collisions and measured the energy-dependent reaction rate constants. Our experiment paves the way for coupling atomic quantum many-body states to an independently controllable single-particle, giving access to a wealth of novel physics and to completely new detection and manipulation techniques.

Sias, Carlo; Ratschbacher, Lothar; Zipkes, Christoph; Koehl, Michael

2011-06-01

377

Quantum Physical Symbol Systems

Today's theories of computing and machine learning developed within a nineteenth-century mechanistic mindset. Although digital computers would be impossible without quantum physics, their physical and logical architecture is based on the view of a computer as an automaton executing pre-programmed sequences of operations exactly as instructed. Recent innovations in representations and algorithms suggest that a shift in viewpoint may be

Kathryn Blackmond Laskey

2006-01-01

378

Electron correlation: the many-body problem at the heart of chemistry.

The physical interactions among electrons and nuclei, responsible for the chemistry of atoms and molecules, is well described by quantum mechanics and chemistry is therefore fully described by the solutions of the Schrödinger equation. In all but the simplest systems we must be content with approximate solutions, the principal difficulty being the treatment of the correlation between the motions of the many electrons, arising from their mutual repulsion. This article aims to provide a clear understanding of the physical concept of electron correlation and the modern methods used for its approximation. Using helium as a simple case study and beginning with an uncorrelated orbital picture of electronic motion, we first introduce Fermi correlation, arising from the symmetry requirements of the exact wave function, and then consider the Coulomb correlation arising from the mutual Coulomb repulsion between the electrons. Finally, we briefly discuss the general treatment of electron correlation in modern electronic-structure theory, focussing on the Hartree-Fock and coupled-cluster methods and addressing static and dynamical Coulomb correlation. PMID:17269126

Tew, David P; Klopper, Wim; Helgaker, Trygve

2007-06-01

379

Method for calculating elastic scattering between two composite many-body systems at high energies

An integral formula is derived for calculating the complete expansion of the Glauber amplitude of multiple scattering between two composite particles under the cluster structure, when the density function is of the form of the double Gaussian type.

Zhong, H.X. [Department of Physics, Xiamen University, Xiamen 361005, Fujian (China)

1995-05-01

380

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

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

Ingvar Lindgren; Stig Lundqvist

1980-01-01

381

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

We study fundamental morphological descriptors of disordered media (e.g., heterogeneous materials, liquids, and amorphous solids): thechord-lengthdistributionfunctionp(z) and the free-pathdistributionfunctionp(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,

Binglin Lu; S. Torquato

1993-01-01

382

Conditional pair distributions in many-body systems: Exact results for Poisson ensembles

NASA Astrophysics Data System (ADS)

We introduce a conditional pair distribution function (CPDF) which characterizes the probability density of finding an object (e.g., a particle in a fluid) to within a certain distance of each other, with each of these two having a nearest neighbor to a fixed but otherwise arbitrary distance. This function describes special four-body configurations, but also contains contributions due to the so-called mutual nearest neighbor (two-body) and shared neighbor (three-body) configurations. The CPDF is introduced to improve a Helmholtz free energy method based on space partitions. We derive exact expressions of the CPDF and various associated quantities for randomly distributed, noninteracting points at Euclidean spaces of one, two, and three dimensions. Results may be of interest in many diverse scientific fields, from fluid physics to social and biological sciences.

Rohrmann, René D.; Zurbriggen, Ernesto

2012-05-01

383

Excited states of many-body systems in the fermion dynamical symmetry model with random interactions

NASA Astrophysics Data System (ADS)

In this Brief Report we investigate excited yrast states under random interactions in the framework of the fermion dynamical symmetry model, for the ensemble with spin-0 ground states. Interesting correlations are seen between R6 and R4 (where RI?EI1+/E21+) by using the Mallmann plot, for cases with both SP(6) symmetry and SO(8) symmetry.

Fu, G. J.; Zhao, Y. M.; Ping, J. L.; Arima, A.

2013-09-01

384

Path Integrals and Degrees of Freedom in Many-Body Systems and Relativistic Field Theories

The identification of physical degrees of freedom is sometimes obscured in the path-integral formalism, and this makes it difficult to impose some constraints or to do some approximations. I review a number of cases where the difficulty is overcome by deriving the path integral from the operator form of the partition function after such identification has been made.

Palumbo, F. [INFN, Laboratori Nazionali di Frascati (Italy)

2005-05-01

385

Up-down quark mass difference effect in nuclear many-body systems

A charge-symmetry-breaking nucleon-nucleon force due to the up-down quark mass difference is evaluated in the quark cluster model. It is applied to the shell-model calculation for the isovector mass shifts of isospin multiplets in 1{ital s}0{ital d}-shell nuclei. We find that the contribution of the quark mass difference effect explains the systematic behavior of experiment. This contribution is large and may explain the Okamoto-Nolen-Schiffer anomaly, alternatively to the meson-mixing contribution, which is recently predicted to be reduced by the large off-shell correction. {copyright} {ital 1996 The American Physical Society.}

Nakamura, S.; Muto, K.; Oka, M.; Takeuchi, S.; Oda, T. [Institute for Nuclear Study, University of Tokyo, Tokyo 188 (Japan)]|[Department of Physics, Tokyo Institute of Technology, Tokyo 152 (Japan)]|[Department of Public Health and Environmental Science, Tokyo Medical and Dental University, Tokyo 113 (Japan)

1996-02-01

386

Bistability in a nonequilibrium quantum system with electron-phonon interactions

NASA Astrophysics Data System (ADS)

The existence of more than one steady state in a many-body quantum system driven out of equilibrium has been a matter of debate, both in the context of simple impurity models and in the case of inelastic tunneling channels. In this paper, we combine a reduced density matrix formalism with the multilayer multiconfiguration time-dependent Hartree method to address this problem. This allows us to obtain a converged numerical solution of the nonequilibrium dynamics. Considering a generic model for quantum transport through a quantum dot with electron-phonon interaction, we prove that a unique steady state exists regardless of the initial electronic preparation of the quantum dot, consistent with the converged numerical results. However, a bistability can be observed for different initial phonon preparations. The effects of the phonon frequency and strength of the electron-phonon couplings on the nonequilibrium dynamics and on the emergence of bistability is discussed.

Wilner, Eli Y.; Wang, Haobin; Cohen, Guy; Thoss, Michael; Rabani, Eran

2013-07-01

387

Many-body aspects of the parameterization of the hyperfine and other atomic interactions

NASA Astrophysics Data System (ADS)

The idea of the parametrization of atomic interactions, such as the hyperfine interaction, the spin-orbit interaction and the isotopic field shift, is reviewed from the point of view of atomic many-body theory. The close analogy between Goldstone perturbation diagrams and the angular-momentum diagrams of Jucys et al. is used extensively in the analysis. In the non-relativistic limit, when only electrostatic perturbations are considered, it is verified that the hyperfine interaction can be exactly described by the effective one-body operator, introduced by Harvey, provided LS-dependent parameters are used. When relativity is considered, it is shown that the consideration of effective one-body effects leads to the theory of Sandars and Beck, with LS-independent parameters, while the remaining effects can be represented by LS-dependent one-body operators of higher tensor ranks. When the same idea is applied to the spin-orbit interaction and to the isotope shift, it is shown that these two interactions can be represented by the same effective operators. This implies that the J dependence of the field shift should show certain similarity with the fine structure, as observed experimentally and, in particular, that this shift should follow the Landé interval rule close to LS coupling. The approach developed here of introducing tensor operators of higher tensor ranks to represent the relativistic effects is compared with the more conventional approach of using standard operators and intermediate-coupling wave functions.

Olsson, T.; Lindgren, I.

1987-06-01

388

The embedded many-body expansion for energetics of molecular crystals

NASA Astrophysics Data System (ADS)

Reliable prediction of molecular crystal energetics is a vital goal for computational chemistry. Here we show that accurate results can be obtained from a monomer-based many-body expansion truncated at the two-body level, with the monomer and dimer calculations suitably embedded in a model of the crystalline environment. By including the two dominant effects--electrostatics and exchange-repulsion--we are able to capture the important nonadditive terms in the energy, and approach very closely results from full periodic second-order Møller-Plesset calculations. The advantage of the current scheme is that extension to coupled-cluster and explicitly correlated F12 methods is completely straightforward. We demonstrate the approach through calculations on carbon dioxide, hydrogen fluoride, and ice XIh and XIc. In accord with previous studies, we find these two ice polymorphs to be very close in energy, with our periodic coupled-cluster single double triple-F12 calculation giving the hexagonal structure more stable by around 0.3 kJ mol-1.

Bygrave, P. J.; Allan, N. L.; Manby, F. R.

2012-10-01

389

Ab initio many-body calculations of nucleon scattering on ^16O

NASA Astrophysics Data System (ADS)

We develop a new ab initio many-body approachootnotetextS. Quaglioni and P. Navratil, arXiv:0804.1560. capable of describing simultaneously both bound and scattering states in light nuclei, by combining the resonating-group methodootnotetextY. C. Tang et al., Phys. Rep. 47, 167 (1978); K. Langanke and H. Friedrich, Advances in Nuclear Physics, Plenum, New York, 1987. with the ab initio no-core shell model (NCSM).ootnotetextP. Navratil, J. P. Vary, and B. R. Barrett, Phys. Rev. Lett. 84, 5728 (2000); Phys. Rev. C 62, 054311 (2000). In this way, we complement a microscopic-cluster technique with the use of realistic interactions, and a microscopic and consistent description of the nucleon clusters, while preserving Pauli principle and translational symmetry. We will present results for low-energy nucleon scattering on ^16O and for A=17 bound states obtained using realistic nucleon-nucleon potentials. The ^16O wave functions are calculated within the importance-truncated NCSMootnotetextR. Roth and P. Navratil, Phys. Rev. Lett. 99, 092501 (2007). that allows the use of model spaces up to 18? and ultimately enables to reach convergence of phase-shifts and other observables. Prepared by LLNL under Contract DE-AC52-07NA27344. Support from the U.S. DOE/SC/NP (Work Proposal No. SCW0498), and from the U. S. Department of Energy Grant DE-FC02-07ER41457 is acknowledged.

Navratil, Petr; Quaglioni, Sofia; Roth, Robert

2008-10-01

390

Third-order relativistic many-body perturbation theory (MBPT) is applied to obtain energies of ions with two valence electrons in the no virtual-pair approximation (NVPA). A total of 302 third-order Goldstone diagrams are organized into 12 one-body and 23 two-body terms. Only third-order two-body terms and diagrams are presented in this paper, owing to the fact that the one-body terms are identical to the previously studied third-order terms in monovalent ions. Dominant classes of diagrams are identified. The model potential is the Dirac-Hartree-Fock potential V{sup N-2}, and B-spline basis functions in a cavity of finite radius are employed in the numerical calculations. The Breit interaction is taken into account through the second order of perturbation theory, and the lowest-order Lamb shift is also evaluated. Sample calculations are performed for berylliumlike ions with Z=4-7, and for the magnesiumlike ion P IV. The third-order excitation energies are in excellent agreement with measurement with an accuracy at 0.2% level for the cases considered. Comparisons are made with second-order MBPT results, and with other calculations. The third-order energy correction is shown to be significant, improving the previous second-order calculations by an order of magnitude.

Ho, H. C.; Johnson, W. R.; Blundell, S. A.; Safronova, M. S. [Department of Physics, University of Notre Dame, Notre Dame, Indiana 46556 (United States); Departement de Recherche Fondamentale sur la Matiere Condensee, CEA-Grenoble/DSM 17 rue des Martyrs, F-38054 Grenoble Cedex 9 (France); Department of Physics, University of Delaware, Newark, Delaware 19716 (United States)

2006-08-15

391

Ramsey interferometry with atoms and molecules: Two-body versus many-body phenomena

We discuss the frequency and visibility of atom-molecule Ramsey fringes observed in recent experiments by Claussen et al. [Phys. Rev. A 67, 060701 (2003)]. In these experiments a {sup 85}Rb Bose-Einstein condensate was exposed to a sequence of magnetic field pulses on the high-field side of the 155 G Feshbach resonance. The observed oscillation frequencies largely agree with the theoretically predicted magnetic field dependence of the binding energy of the highest excited diatomic vibrational state, except for a small region very close to the singularity of the scattering length. Our analytic treatment of the experiment, as well as our dynamical simulations, follow the magnitude of the measured oscillation frequencies as well as the visibilities of the Ramsey fringes. We show that significant deviations from a purely binary dynamics, with an associated binding frequency, occur when the spatial extent of the molecular wave function becomes comparable with the mean distance between the atoms in the dilute gas. The experiments thus clearly identify the conditions under which diatomic molecules may be identified as a separate entity of the gas or, conversely, when the concept of binary physics in a many-body environment is bound to break down.

Goral, Krzysztof [Clarendon Laboratory, Department of Physics, University of Oxford, Parks Road, Oxford OX1 3PU (United Kingdom); Center for Theoretical Physics, Polish Academy of Sciences, Aleja Lotnikow 32/46, 02-668 Warsaw (Poland); Koehler, Thorsten; Burnett, Keith [Clarendon Laboratory, Department of Physics, University of Oxford, Parks Road, Oxford OX1 3PU (United Kingdom)

2005-02-01

392

Many-body effects in the formation of multiply charged ions in a strong laser field

Some of the many-body effects in the formation of multiply charged ions in a laser field have been taken into account: inelastic tunneling, collective tunneling, and magnetic moment projection relaxation of the atomic core. Strong fields with an intensity exceeding 10{sup 17} W cm{sup -2} are considered when the magnetic component of the laser field acts on the free motion of a photoelectron; therefore, the formation of multiply charged ions through rescattering becomes unlikely. Numerical calculations have been performed for Ar{sup 9+} Horizontal-Ellipsis Ar{sup 13+}, Kr{sup 19+} Horizontal-Ellipsis Kr{sup 23+}, Rb{sup 10+}, and Rb{sup 11+} ions. A significant contribution of collective tunneling, which was not observed in weaker fields investigated previously, has been revealed. Allowance for collective tunneling is shown to reduce the intensity leading to saturation by more than 10%. In this case, the yield of multiply charged Rb ions changes by an order of magnitude, while the yield of multiply charged Ar and Kr ions changes by more than a factor of 2. Comparison with experimental data on the formation of argon ions under the action of a linearly polarized laser pulse is made.

Zon, B. A., E-mail: zon@niif.vsu.ru; Kornev, A. S., E-mail: a-kornev@yandex.ru; Tulenko, E. B., E-mail: tulenko@mail.ru [Voronezh State University (Russian Federation)

2010-01-15

393

Wave-function formalisms in the channel coupling array theory of many-body scattering

Wave-function formalisms corresponding to different channel coupling array transition operators of many-body scattering theory are derived and discussed. The Kouri-Levin transition operators are seen to be in typical Lippmann-Schwinger form and allow for the introduction of wave-function components in a particularly straightforward way. The Baer-Kouri transition operators are not in the Lippmann-Schwinger form and an alternate procedure is used to derive their corresponding wave-function components. In the three-body case, the Kouri-Levin operators T/sub j/k obtained from the Faddeev-Lovelace choice of channel coupling array are seen to lead to precisely the Faddeev wave-function components. The Baer-Kouri operators are shown to lead to wave-function components obeying inhomogeneous equations. These inhomogeneous equations are used to give an alternate explanation of the nonunitary amplitudes obtained in recent calculations based on approximate forms of the Baer-Kouri operators.

Levin, F.S.

1980-06-01

394

Many-body central force potentials and properties of grain boundaries in NiAl

Empirical many-body central force potentials of the Finnis-Sinclair type have been constructed for B2 NiAl by fitting a number of equilibrium properties of this alloy and reproducing the asymmetric behavior of constitutional point defects in off-stoichiometric NiAl. At the same time these potentials ensure the structural and mechanical stability of the B2 lattice and reproduce quite adequately the equilibrium properties of Ni{sub 3}Al. Using these potentials, grain boundaries in NiAl have been studied by computer simulation. It was found that in stoichiometric NiAl alloy boundaries with a surplus of aluminium have appreciably lower cohesive strength than the stoichiometric boundaries or boundaries with a surplus of nickel. From the structural point of view, boundaries with a surplus of aluminium possess the largest expansions and large holes usually occur in the boundary regions. On the other hand, the largest expansions and large holes usually occur in the boundary regions. On the other hand, boundaries with the stoichiometric configuration or with a surplus of nickel have more compact structures. The interaction of the antisite defects and vacancies with grain boundaries was also studied and segregation of nickel and aluminium in off-stoichiometric alloys discussed with the help of these results.

Yan, M.; Chen, S.P. [Los Alamos National Lab., NM (United States). Theoretical Div.; Vitek, V. [Univ. of Pennsylvania, Philadelphia, PA (United States). Dept. of Materials Science and Engineering

1996-11-01

395

Relativistic Many-Body Calculations of n=2 States for the Beryllium Isoelectronic Sequence

NASA Astrophysics Data System (ADS)

Energies of the ten (2l2l') states of ions of the beryllium isoelectronic sequence are determined to second-order in relativistic many-body perturbation theory. Both the second-order Coulomb interaction and the second-order Breit-Coulomb interaction are included. Corrections for the frequency-dependent Breit interaction are taken in account in lowest order only. The effect of the Lamb shift is also estimated and included. Comparisons with other calculations and with experiment are made. Our theoretical results for the 2s-2p_3/2 transitions in U^88+ and Th^86+ (4501.60 eV and 4069.02 eV, resp.) differ only by 0.12 eV for U^88+ and 0.55 eV for Th^86+ from experimental data obtained at the SUPER-EBIT in LLNL.(P. Beiersdorfer, D. Knapp, R.E. Marrs, S.R. Elliot and M.H. Chen, Phys. Rev. Lett. 71), 3939 (1993); P. Beiersdorfer, A. Osterheld, S.R. Elliot, M.H. Chen, D. Knapp, and K. Reed, Phys. Rev. A52, 2693 (1995). Excellent agreement with experimental results for the splitting of ^3 P terms is found.

Safronova, M. S.; Johnson, W. R.; Safronova, U. I.

1996-05-01

396

The excitation energies of ns, np, nd, and nf (n{<=}6) states in neutral lithium are evaluated within the framework of relativistic many-body theory. First-, second-, third-, and all-order Coulomb energies and first- and second-order Breit corrections to energies are calculated. All-order calculations of reduced matrix elements, oscillator strengths, transition rates, and lifetimes are given for levels up to n=4. Electric-dipole (2s-np), electric-quadrupole (2s-nd), and electric-octupole (2s-nf), matrix elements are evaluated to obtain the corresponding ground-state multipole polarizabilities using the sum-over-states approach. Scalar and tensor polarizabilities for the 2p{sub 1/2} and 2p{sub 3/2} states are also calculated. Magnetic-dipole hyperfine constants A are determined for low-lying levels up to n=4. The quadratic Stark shift for the (F=2 M=0){r_reversible}(F=1 M=0) ground-state hyperfine transition is found to be -0.0582 Hz/(kV/cm){sup 2}, in slight disagreement with the experimental value -0.061{+-}0.002 Hz/(kV/cm){sup 2}. Matrix elements used in evaluating polarizabilities, hyperfine constants, and the quadratic Stark shift are obtained using the all-order method.

Johnson, W. R.; Safronova, U. I.; Derevianko, A.; Safronova, M. S. [Department of Physics, University of Notre Dame, Notre Dame, Indiana 46556 (United States); Physics Department, University of Nevada, Reno, Nevada 89557 (United States); Physics Department, University of Nevada, Reno, Nevada 89557 (United States); Department of Physics and Astronomy, 217 Sharp Lab, University of Delaware, Newark, Delaware 19716 (United States)

2008-02-15

397

Controlling the gap of fullerene microcrystals by applying pressure: Role of many-body effects

We characterize the optical properties of C_60 fullerene microcrystals as a function of hydrostatic pressure. Calculations were done using first-principles many-body theories based on evaluating electronic energy levels in the GW approximation. We compute electronic excited states in the crystal by diagonalizing the Bethe-Salpeter equation (BSE). Our results confirm the existence of bound excitons in the crystal. Both the electronic gap and optical gap decrease continuously and non-linearly as pressure of up to 6 GPa is applied. As a result, the absorption spectrum shows strong redshift. We also observe that "negative" pressure shows the opposite behavior: the gaps increase and the optical spectrum shifts toward the blue end of the spectrum. Negative pressure can be realized by adding cubane (C_8H_8) or other molecules with similar size to the interstitials of the microcrystal. For the moderate lattice distortions studied here, we have found that the optical properties of fullerene microcrystals with intercalated cubane are similar to the ones of an expanded undoped microcrystal. Based on these findings, we propose doped C_60 as active element in piezo-optical devices.

Tiago, Murilo L [ORNL; Reboredo, Fernando A [ORNL

2009-01-01

398

Ab initio many-body calculations of light nuclei neutron and proton scattering

NASA Astrophysics Data System (ADS)

One of the greatest challenges of nuclear physics today is the development of a quantitative microscopic theory of low-energy reactions on light nuclei. At the same time, technical progress on the theoretical front is urgent to match the major experimental advances in the study of exotic nuclei at the radioactive beam facilities. We build a new ab initio many-body approachootnotetextS. Quaglioni and P. Navratil, arXiv:0804.1560. capable of describing simultaneously both bound and scattering states in light nuclei, by combining the resonating-group methodootnotetextY. C. Tang et al., Phys. Rep. 47, 167 (1978); K. Langanke and H. Friedrich, Advances in Nuclear Physics, chapter 4., Plenum, New York, 1987. with the ab initio no-core shell model.ootnotetextP. Navratil, J. P. Vary, and B. R. Barrett, Phys. Rev. Lett. 84, 5728 (2000); Phys. Rev. C 62, 054311 (2000).. In this way, we complement a microscopic-cluster technique with the use of realistic interactions, and a microscopic and consistent description of the nucleon clusters, while preserving Pauli principle and translational symmetry. I will present results for neutron and proton scattering on light nuclei, including n- and p-^4He phase shifts, and low-lying states of one-neutron halo p-shell nuclei, obtained using realistic nucleon-nucleon potentials. In particular, I will address the parity inversion of the ^11Be ground state.

Quaglioni, Sofia

2008-10-01

399

Second-order many-body perturbation expansions of vibrational Dyson self-energies.

Second-order many-body perturbation theories for anharmonic vibrational frequencies and zero-point energies of molecules are formulated, implemented, and tested. They solve the vibrational Dyson equation self-consistently by taking into account the frequency dependence of the Dyson self-energy in the diagonal approximation, which is expanded in a diagrammatic perturbation series up to second order. Three reference wave functions, all of which are diagrammatically size consistent, are considered: the harmonic approximation and diagrammatic vibrational self-consistent field (XVSCF) methods with and without the first-order Dyson geometry correction, i.e., XVSCF[n] and XVSCF(n), where n refers to the truncation rank of the Taylor-series potential energy surface. The corresponding second-order perturbation theories, XVH2(n), XVMP2[n], and XVMP2(n), are shown to be rigorously diagrammatically size consistent for both total energies and transition frequencies, yield accurate results (typically within a few cm(-1) at n = 4 for water and formaldehyde) for both quantities even in the presence of Fermi resonance, and have access to fundamentals, overtones, and combinations as well as their relative intensities as residues of the vibrational Green's functions. They are implemented into simple algorithms that require only force constants and frequencies of the reference methods (with no basis sets, quadrature, or matrix diagonalization at any stage of the calculation). The rules for enumerating and algebraically interpreting energy and self-energy diagrams are elucidated in detail. PMID:23883014

Hermes, Matthew R; Hirata, So

2013-07-21

400

Second-order many-body perturbation expansions of vibrational Dyson self-energies

NASA Astrophysics Data System (ADS)

Second-order many-body perturbation theories for anharmonic vibrational frequencies and zero-point energies of molecules are formulated, implemented, and tested. They solve the vibrational Dyson equation self-consistently by taking into account the frequency dependence of the Dyson self-energy in the diagonal approximation, which is expanded in a diagrammatic perturbation series up to second order. Three reference wave functions, all of which are diagrammatically size consistent, are considered: the harmonic approximation and diagrammatic vibrational self-consistent field (XVSCF) methods with and without the first-order Dyson geometry correction, i.e., XVSCF[n] and XVSCF(n), where n refers to the truncation rank of the Taylor-series potential energy surface. The corresponding second-order perturbation theories, XVH2(n), XVMP2[n], and XVMP2(n), are shown to be rigorously diagrammatically size consistent for both total energies and transition frequencies, yield accurate results (typically within a few cm-1 at n = 4 for water and formaldehyde) for both quantities even in the presence of Fermi resonance, and have access to fundamentals, overtones, and combinations as well as their relative intensities as residues of the vibrational Green's functions. They are implemented into simple algorithms that require only force constants and frequencies of the reference methods (with no basis sets, quadrature, or matrix diagonalization at any stage of the calculation). The rules for enumerating and algebraically interpreting energy and self-energy diagrams are elucidated in detail.

Hermes, Matthew R.; Hirata, So

2013-07-01

401

Second-order many-body perturbation study of solid hydrogen fluoride.

A linear-scaling, local-basis, electron-correlation method based on a truncated many-body expansion of energies has been applied to crystalline hydrogen fluoride in three dimensions. The energies, equilibrium atomic positions, lattice constants, and dipole moments of the two structures (polar and nonpolar) have been determined, taking account of one- and two-body Coulomb (electrostatic), exchange, and correlation interactions exactly and three-body and higher-order Coulomb interactions approximately within certain truncation radii. The longer-range two-body Coulomb interactions are also included to an infinite distance by computing the Madelung constant. The second-order Møller-Plesset perturbation method has been used in conjunction with the aug-cc-pVDZ and aug-cc-pVTZ basis sets for correlation. Counterpoise corrections of the basis-set superposition errors have also been made. Predicted relative energies show that the nonpolar arrangement is considerably more stable than the polar one, establishing the precise three-dimensional structure of this crystal and finally resolving the controversy. The computed lattice constants of the nonpolar configuration agree with the observed to within 0.3 A. PMID:20593764

Sode, Olaseni; Hirata, So

2010-08-26

402

Locally preferred structures and many-body static correlations in viscous liquids

NASA Astrophysics Data System (ADS)

The influence of static correlations beyond the pair level on the dynamics of selected model glass formers is investigated. The pair structure, angular distribution functions, and statistics of Voronoi polyhedra of two well-known Lennard-Jones mixtures as well as of the corresponding Weeks-Chandler-Andersen variants, in which the attractive part of the potential is truncated, are compared. By means of the Voronoi construction, the atomic arrangements corresponding to the locally preferred structures of the models are identified. It is found that the growth of domains formed by interconnected locally preferred structures signals the onset of the slow-dynamics regime and allows the rationalization of the different dynamic behaviors of the models. At low temperature, the spatial extension of the structurally correlated domains, evaluated at fixed relaxation time, increases with the fragility of the models and is systematically reduced by truncating the attractions. In view of these results, proper inclusion of many-body static correlations in theories of the glass transition appears crucial for the description of the dynamics of fragile glass formers.

Coslovich, Daniele

2011-05-01

403

Quantum Entanglement and Quantum Discord in Gaussian Open Systems

In the framework of the theory of open systems based on completely positive quantum dynamical semigroups, we give a description of the continuous-variable quantum entanglement and quantum discord for a system consisting of two noninteracting modes embedded in a thermal environment. Entanglement and discord are used to quantify the quantum correlations of the system. For all values of the temperature of the thermal reservoir, an initial separable Gaussian state remains separable for all times. In the case of an entangled initial Gaussian state, entanglement suppression (entanglement sudden death) takes place for non-zero temperatures of the environment. Only for a zero temperature of the thermal bath the initial entangled state remains entangled for finite times. We analyze the time evolution of the Gaussian quantum discord, which is a measure of all quantum correlations in the bipartite state, including entanglement, and show that quantum discord decays asymptotically in time under the effect of the thermal bath.

Isar, Aurelian [National Institute of Physics and Nuclear Engineering, Bucharest-Magurele, P.O. Box MG-6 (Romania)

2011-10-03

404

Linear response as a singular limit for a periodically driven closed quantum system

NASA Astrophysics Data System (ADS)

We address the issue of the validity of linear response theory for a closed quantum system subject to a periodic external driving. Linear response theory (LRT) predicts energy absorption at frequencies of the external driving where the imaginary part of the appropriate response function is different from zero. Here we show that, for a fairly general nonlinear many-body system on a lattice subject to an extensive perturbation, this approximation should be expected to be valid only up to a time t* depending on the strength of the driving, beyond which the true coherent Schrödinger evolution departs from the linear response prediction and the system stops absorbing energy from the driving. We exemplify this phenomenon in detail with the example of a quantum Ising chain subject to a time-periodic modulation of the transverse field, by comparing an exact Floquet analysis with the standard results of LRT. In this context, we also show that if the perturbation is just local, the system is expected in the thermodynamic limit to keep absorbing energy, and LRT works at all times. We finally argue more generally the validity of the scenario presented for closed quantum many-body lattice systems with a bound on the energy-per-site spectrum, discussing the experimental relevance of our findings in the context of cold atoms in optical lattices and ultra-fast spectroscopy experiments.

Russomanno, Angelo; Silva, Alessandro; Santoro, Giuseppe E.

2013-09-01

405

Quantum Dynamics in Biological Systems

NASA Astrophysics Data System (ADS)

In the first part of this dissertation, recent efforts to understand quantum mechanical effects in biological systems are discussed. Especially, long-lived quantum coherences observed during the electronic energy transfer process in the Fenna-Matthews-Olson complex at physiological condition are studied extensively using theories of open quantum systems. In addition to the usual master equation based approaches, the effect of the protein structure is investigated in atomistic detail through the combined application of quantum chemistry and molecular dynamics simulations. To evaluate the thermalized reduced density matrix, a path-integral Monte Carlo method with a novel importance sampling approach is developed for excitons coupled to an arbitrary phonon bath at a finite temperature. In the second part of the thesis, simulations of molecular systems and applications to vibrational spectra are discussed. First, the quantum dynamics of a molecule is simulated by combining semiclassical initial value representation and density funcitonal theory with analytic derivatives. A computationally-tractable approximation to the sum-of-states formalism of Raman spectra is subsequently discussed.

Shim, Sangwoo

406

Second-generation charge-optimized many-body potential for Si\\/SiO2 and amorphous silica

A second-generation dynamic charge transfer, many-body potential function is proposed for crystalline and amorphous silica, and for silicon. The potential is based on the first-generation charge-optimized many-body (COMB) potential for these materials. The materials fidelity of the proposed formalism is demonstrated for several crystalline silica polymorphs and amorphous silica. The correct order of most of the experimentally observed polymorphs of

Tzu-Ray Shan; Bryce D. Devine; Jeffrey M. Hawkins; Aravind Asthagiri; Simon R. Phillpot; Susan B. Sinnott

2010-01-01

407

Motivated by a number of recent experimental studies we have revisited the problem of the microscopic calculation of the quasiparticle self-energy and many-body effective mass enhancement in an unpolarized two-dimensional electron liquid. Our systematic study is based on the many-body local field theory and takes advantage of the results of the most recent diffusion Monte Carlo calculations of the static

R. Asgari; B. Davoudi; M. Polini; Gabriele F. Giuliani; M. P. Tosi; G. Vignale

2005-01-01

408

The electrostatically embedded many-body expansion (EE-MB), previously applied to the total electronic energy, is here applied only to the electronic correlation energy (CE), combined with a Hartree-Fock calculation on the entire system. The separate treatment of the Hartree-Fock and correlation energies provides an efficient way to approximate correlation energy for extended systems. We illustrate this here by calculating accurate Møller-Plesset

Erin E. Dahlke; Donald G. Truhlar

2007-01-01

409

Detecting quantum and classical correlations using quantum dot system

NASA Astrophysics Data System (ADS)

We investigate the thermal classical and quantum correlations in an isolated quantum dot system (QDS) including the effects of different parameters. The thermal density operator is generated by simplifying the Hamiltonian of the quantum dot to the nature Hamiltonian by integrating and finding the unitary matrix. We find that the quantum discord (QD) is more resistant against temperature effect and might be finite even for higher temperatures in the asymptotic limit. Furthermore, we show that there is an optimal value of temperature such that the different kinds of correlations are maximal. Our results show that QDS is a useful resource and may open new perspectives in different quantum information tasks.

Berrada, K.

2013-12-01

410

Second-order many-body perturbation study of solid hydrogen fluoride under pressure.

A linear-scaling, embedded-fragment, second-order many-body perturbation (MP2) method with basis sets up to aug-cc-pVTZ is applied to the antiparallel structure of solid hydrogen fluoride and deuterium fluoride under 0-20 GPa of ambient pressure. The optimized structures, including the lattice parameters and molar volume, and phonon dispersion as well as phonon density of states (DOS), are determined as a function of pressure. The basis-set superposition errors are removed by the counterpoise correction. The structural parameters at 0 GPa calculated by MP2 agree accurately with the observed, making the predicted values at higher pressures a useful pilot for future experiments. The corresponding values obtained by the Hartree-Fock method have large, systematic errors. The MP2/aug-cc-pVDZ frequencies of the infrared- and Raman-active vibrations of the three-dimensional solids are in good agreement with the observed and also justify previous vibrational analyses based on one-dimensional chain models; the non-coincidence of the infrared and Raman mode pairs can be explained as factor-group (Davydov) splitting. The exceptions are one pair of modes in the librational region, for which band assignments based on a one-dimensional chain model need to be revised, as well as the five pseudo-translational modes that exist only in a three-dimensional treatment. The observed pressure dependence of Raman bands in the stretching region, which red-shift with pressure, is accounted for by theory only qualitatively, while that in the pseudo-translational region is reproduced with quantitative accuracy. The present calculation proves to be limited in explaining the complex pressure dependence of the librational modes. The hydrogen-amplitude-weighted phonon DOS at 0 GPa is much less structured than the DOS obtained from one-dimensional models and may be more realistic in view of the also broad, structureless observed inelastic neutron scattering spectra. All major observed peaks can be straightforwardly assigned to the calculated peaks in the DOS. With increasing pressure, MP2 predicts further broadening of bands and breach of the demarcation between the pseudo-translational and librational bands. PMID:22456828

Sode, Olaseni; Hirata, So

2012-03-28

411

NASA Astrophysics Data System (ADS)

1. Quantum mechanics and its interpretation; 2. Hamilton-Jacobi theory; 3. Elements of the quantum theory of motion; 4. Simple applications; 5. Interference and tunnelling; 6. The classical limit; 7. Many-body systems; 8. Theory of experiments; 9. Spin 1/2: The Pauli theory; 10. Spin 1/2: The rigid rotator; 11. The Einstein-Podolsky-Rosen experiment and nonlocality; 12. Relativistic quantum theory; References; Index.

Holland, Peter R.

1995-01-01

412

FAST TRACK COMMUNICATION: Diabatic electronic states from many-body perturbation theory

We apply the so-called diabatization method by Baer (1975 Chem. Phys. Lett. 35 112) to describe photo-excited electronic states. The diabatization is a unitary transformation which, applied to the adiabatic eigenstates of the quantum Hamiltonian, allows for treating the non-adiabatic effects correctly. These effects are all those which appear in the Born-Oppenheimer approximation as the areas of avoided crossings in

Marcin S. Kaczmarski; Michael Rohlfing

2010-01-01

413

Quantum memory assisted probing of dynamical spin correlations.

We propose a method to probe time-dependent correlations of nontrivial observables in many-body ultracold lattice gases. The scheme uses a quantum nondemolition matter-light interface, first to map the observable of interest on the many-body system into the light and then to store coherently such information into an external system acting as a quantum memory. Correlations of the observable at two (or more) instances of time are retrieved with a single final measurement that includes the readout of the quantum memory. Such a method brings to reach the study of dynamics of many-body systems in and out of equilibrium by means of quantum memories in the field of quantum simulators. PMID:22401082

Romero-Isart, O; Rizzi, M; Muschik, C A; Polzik, E S; Lewenstein, M; Sanpera, A

2012-02-10

414

We analyze the electronic and optical excitations in silver clusters Agn, n=1 8 using density-functional and many-body theories within an ab initio pseudopotential framework. Vertical ionization potentials and electron affinities are calculated within the so-called SCF and GW approximations. Results are compared with experimental data. For molecular orbitals of predominantly sp character, the GW results are found to be in good agreement with experiment. For orbitals of mainly d character, good agreement with experiment can be achieved only via the use of semicore pseudopotentials, due to strong correlations among 4s, 4p, and 4d electrons. Optical excitations are computed within the time-dependent local-density approximation TDLDA and by solving the Bethe-Salpeter equation BSE for electrons and holes. For most clusters, the TDLDA spectra are in reasonable agreement with experimental data. The optical excitations computed with the BSE method, on the other hand, are generally in poor agreement with experiment, especially as size increases. This finding is explained in terms of the nonlocality of the BSE kernel and correlations involving 4d electrons. We also discuss the roles played by self-consistency, vertex corrections, and satellite structures in the GW results of these confined systems with d valence electrons.

Tiago, Murilo L [ORNL; Idrobo Tapia, Juan C [ORNL; Ogut, Serdar [University of Illinois, Chicago; Jellinek, Julius [Argonne National Laboratory (ANL); Chelikowsky, James [University of Texas, Austin

2009-01-01

415

Classical and quantum correlative capacities of quantum systems

How strongly can one system be correlated with another? In the classical world, this basic question concerning correlative capacity has a very satisfying answer: The ''effective size'' of the marginal system, as quantified by the Shannon entropy, sets a tight upper bound to the correlations, as quantified by the mutual information. Although in the quantum world bipartite correlations, like their classical counterparts, are also well quantified by mutual information, the similarity ends here: The correlations in a bipartite quantum system can be twice as large as the marginal entropy. In the paradigm of quantum discord, the correlations are split into classical and quantum components, and it was conjectured that both the classical and quantum correlations are (like the classical mutual information) bounded above by each subsystem's entropy. In this work, by exploiting the interplay between entanglement of formation, mutual information, and quantum discord, we disprove that conjecture. We further indicate a scheme to restore harmony between quantum and classical correlative capacities. The results illustrate dramatically the asymmetric nature of quantum discord and highlight some subtle and unusual features of quantum correlations.

Li Nan; Luo Shunlong [Academy of Mathematics and Systems Science, Chinese Academy of Sciences, 100190 Beijing (China)

2011-10-15

416

A relativistic R-matrix close-coupling method is developed and implemented based on effective many-body Hamiltonians for accurate representation of the target and collisional states in multielectron ions. The effective Hamiltonian in relativistic multireference many-body perturbation theory accurately accounts for short-range many-body interactions unaccounted for in the extant nonrelativistic and Breit-Pauli R-matrix methods. The method is successfully applied to the near-threshold electron impact excitation of the 3s{sup 2} {sup 1}S{yields}3s3p {sup 3}P transition in Mg-like argon (Ar{sup 6+}) ion where the observed disagreement between the experimental absolute total cross sections and those predicted by using the Breit-Pauli R-matrix method reveals an inadequacy of the R-matrix methods based on the configuration-interaction representation of the basis states.

Vilkas, Marius J.; Ishikawa, Yasuyuki [Department of Chemistry, University of Puerto Rico, P.O. Box 23346 San Juan, Puerto Rico 00931-3346 (United States)

2007-06-15

417

NASA Astrophysics Data System (ADS)

We present a unified framework for equilibrium and nonequilibrium many-body perturbation theory. The most general nonequilibrium many-body theory valid for general initial states is based on a time-contour originally introduced by Konstantinov and Perel'. The various other well-known formalisms of Keldysh, Matsubara and the zero-temperature formalism are then derived as special cases that arise under different assumptions. We further present a single simple proof of Wick's theorem that is at the same time valid in all these flavors of many-body theory. It arises simply as a solution of the equations of the Martin-Schwinger hierarchy for the noninteracting many-particle Green's function with appropriate boundary conditions. We further discuss a generalized Wick theorem for general initial states on the Keldysh contour and derive how the formalisms based on the Keldysh and Konstantinov-Perel'-contours are related for the case of general initial states.

van Leeuwen, Robert; Stefanucci, Gianluca

2013-03-01

418

Feedback control of linear quantum optical systems

This paper studies feedback quantum control of a class of linear quantum optical systems by means of squeezing and phase modulation. A new quadrature representation of such systems is introduced, which includes explicitly phase modulation of light fields involved. Some fundamental relations are derived in terms of the new quadrature representation. The coherent quantum LQG control studied in (17) is

Hu Zhang; Guofeng Zhang; Daoyi Dong; Bo Huang; H. W. J. Lee

2011-01-01

419

Many-body processes in atomic and molecular physics. Progress report

A proposal is presented for theoretical efforts towards the following projects: (1) carry out rotational predissociation lifetime calculations of several van der Waals molecules for which accurate potential energy surfaces were obtained recently by van der Waals molecular spectroscopic methods; (2) development and extension of the complex coordinate - coupled channel formalism to vibrational predissociation studies; (3) Floquet theory study of the quantum dynamics of multiphoton excitation of vibrational-rotational states of small molecules by laser light; (4) development and extension of the method of complex quasi-vibrational energy formalism to the study of intense field multiphoton dissociation of diatomic molecules and to photodissociation process in the presence of shape resonances; (5) investigation of the external field effects in multiphoton excitation and dissociation of small molecules. Depending on time and resources, several other projects may also be pursued. A detailed discussion covering these proposed projects is presented.

Chu, S.I.

1981-01-01

420

To enhance the current understanding of mechanisms contributing to magnetic hyperfine interactions in excited states of atomic systems, in particular, alkali-metal atom systems, the hyperfine fields in the excited 5{sup 2}S{sub 1/2}{endash}8{sup 2}S{sub 1/2} states of potassium and 8{sup 2}S{sub 1/2}{endash}12{sup 2}S{sub 1/2} states of francium atoms have been studied using the relativistic linked-cluster many-body perturbation procedure. The net theoretical values of the hyperfine fields for the excited states studied are in excellent agreement with available experimental data for both atoms. There is a significant decrease in importance of the correlation contribution in going from the ground state to the excited states, the correlation contributions as ratios of the direct contribution decreasing rapidly as one moves to the higher excited states. However, the contribution from the exchange core polarization (ECP) effect is nearly a constant fraction of the direct effect for all the excited states considered. Physical explanations are offered for the observed trends in the contributions from the different mechanisms. A comparison is made of the different contributing effects to the hyperfine fields in potassium and francium to those in the related system, rubidium, studied earlier. Extrapolating from our results to the highly excited states of alkali-metal atoms, referred to as the Rydberg states, it is concluded that in addition to the direct contribution from the excited valence electron to the hyperfine fields, a significant contribution is expected from the ECP effect arising from the influence of exchange interactions between electrons in the valence and core states. {copyright} {ital 1997} {ital The American Physical Society}

Owusu, A.; Dougherty, R.W.; Gowri, G.; Das, T.P. [Department of Physics, State University of New York at Albany, Albany, New York, 12222 (United States); Andriessen, J. [Technische Natuurkunde, Technische Universiteit Delft, 2628 CJ Delft (The Netherlands)

1997-07-01

421

Many-Body Decomposition of the Binding Energies for OH•(H2O)2 and OH•(H2O)3 Complexes

We use ab initio electronic structure methods to calculate the many-body decomposition of the binding energies of the OH?(H2O)n (n=2,3) complexes. We employ MP2 and CCSD(T) levels of theory with aug-cc-pVDZ and aug-cc-pVTZ basis sets and analyze the significance of the non-pairwise interactions between OH radical and the surrounding water molecules. We also evaluate the accuracy of our newly developed potential function, the modified Thole-type model (mTTM), for predicting the many-body terms in these complexes. Our analysis of the many-body contributions to the OH?(H2O)n binding energies clearly shows that they are just as important in the OH interactions with water as they are for interactions in pure water systems. This work was supported by the Division of Chemical Sciences, Office of Basic Energy Sciences of the U.S. Department of Energy (DOE) and was performed in part using the Molecular Science Computing Facility in the William R. Wiley Environmental Molecular Sciences Laboratory (EMSL) at the Pacific Northwest National Laboratory. The EMSL is funded by the DOE Office of Biological and Environmental Research. Battelle operates Pacific Northwest National Laboratory for DOE. The authors thank Sotiris Xantheas, Jun Li, Tzvetelin Iordanov, and Jun Cui for helpful discussions and assistance.

Du, Shiyu; Francisco, Joseph S.; Schenter, Gregory K.; Garrett, Bruce C.

2008-02-27

422

Critical Stability in Quantum Systems

In the frame of non-relativistic quantum mechanics we discuss the systems of N particles, whose energy is close to that of the dissociation threshold. We show that in systems, where a long-range repulsion acts between the dissociation fragments, there is a super-size blocking, i.e. the halo structures in these systems do not appear. We discuss the connection between bound states at the threshold and spreading and derive the conditions on pair potentials, which guarantee the super-size blocking. Under minor assumptions we prove that negative atomic ions have a bound state at the threshold when the charge of the nucleus is critical.

Gridnev, Dmitry K. [Kassel University, Institut fuer Theoretische Physik, 34132 Kassel (Germany)

2008-04-03

423

Folding simulations on peptides and proteins using empirical force fields have demonstrated the sensitivity of the results to details of the backbone potential. A recently revised version of the additive CHARMM protein force field, which includes optimization of the backbone CMAP potential to achieve good balance between different types of secondary structure, correcting the ?-helical bias present in the former CHARMM22/CMAP energy function, is shown to result in improved cooperativity for the helix-coil transition. This is due to retention of the empirical corrections introduced in the original CMAP to reproduce folded protein structures—corrections that capture many-body effects missing from an energy surface fitted to gas phase calculations on dipeptides. The experimental temperature dependence of helix formation in (AAQAA)3 and parameters for helix nucleation and elongation are in much better agreement with experiment than those obtained with other recent force fields. In contrast, CMAP parameters derived by fitting to a vacuum quantum mechanical surface for the alanine dipeptide do not reproduce the enhanced cooperativity, showing that the empirical backbone corrections, and not some other feature of the force field, are responsible. We also find that the cooperativity of ?-hairpin formation is much improved relative to other force fields we have studied. Comparison with (?,?) distributions from the Protein Data Bank further justifies the inclusion of many-body effects in the CMAP. These results suggest that the revised energy function will be suitable for both simulations of unfolded or intrinsically disordered proteins and for investigating protein-folding mechanisms.

Best, Robert B.; Mittal, Jeetain; Feig, Michael; MacKerell, Alexander D.

2012-01-01

424

Supersymmetric biorthogonal quantum systems

We discuss supersymmetric biorthogonal systems, with emphasis given to the periodic solutions that occur at spectral singularities of PT symmetric models. For these periodic solutions, the dual functions are associated polynomials that obey inhomogeneous equations. We construct in detail some explicit examples for the supersymmetric pairs of potentials V{sub {+-}}(z)=-U(z){sup 2}{+-}z(d/dz)U(z) where U(z){identical_to}{sigma}{sub k>0}{upsilon}{sub k}z{sup k}. In particular, we consider the cases generated by U(z)=z and z/(1-z). We also briefly consider the effects of magnetic vector potentials on the partition functions of these systems.

Curtright, Thomas; Mezincescu, Luca; Schuster, David [Department of Physics, University of Miami, Coral Gables, Florida 33124 (United States) and School of Natural Sciences, Institute for Advanced Study, Princeton, New Jersey 08540 (United States); Department of Physics, University of Miami, Coral Gables, Florida 33124 (United States)

2007-09-15

425

Path integral calculation of free energies: Quantum effects on the melting temperature of neon

The path integral formulation has been combined with several methods to determine free energies of quantum many-body systems, such as adiabatic switching and reversible scaling. These techniques are alternatives to the standard thermodynamic integration method. A quantum Einstein crystal is used as a model to demonstrate the accuracy and reliability of these free energy methods in quantum simulations. Our main

R. Ramírez; C. P. Herrero; A. Antonelli; E. R. Hernández

2008-01-01

426

Simulation of n-qubit quantum systems. III. Quantum operations

NASA Astrophysics Data System (ADS)

During the last decade, several quantum information protocols, such as quantum key distribution, teleportation or quantum computation, have attracted a lot of interest. Despite the recent success and research efforts in quantum information processing, however, we are just at the beginning of understanding the role of entanglement and the behavior of quantum systems in noisy environments, i.e. for nonideal implementations. Therefore, in order to facilitate the investigation of entanglement and decoherence in n-qubit quantum registers, here we present a revised version of the FEYNMAN program for working with quantum operations and their associated (Jamio?kowski) dual states. Based on the implementation of several popular decoherence models, we provide tools especially for the quantitative analysis of quantum operations. Apart from the implementation of different noise models, the current program extension may help investigate the fragility of many quantum states, one of the main obstacles in realizing quantum information protocols today. Catalogue identifier: ADWE_v3_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/ADWE_v3_0 Program obtainable from: CPC Program Library, Queen's University of Belfast, N. Ireland Licensing provisions: None Operating systems: Any system that supports MAPLE; tested under Microsoft Windows XP, SuSe Linux 10 Program language used:MAPLE 10 Typical time and memory requirements: Most commands that act upon quantum registers with five or less qubits take ?10 seconds of processor time (on a Pentium 4 processor with ?2 GHz or equivalent) and 5 20 MB of memory. Especially when working with symbolic expressions, however, the memory and time requirements critically depend on the number of qubits in the quantum registers, owing to the exponential dimension growth of the associated Hilbert space. For example, complex (symbolic) noise models (with several Kraus operators) for multi-qubit systems often result in very large symbolic expressions that dramatically slow down the evaluation of measures or other quantities. In these cases, MAPLE's assume facility sometimes helps to reduce the complexity of symbolic expressions, but often only numerical evaluation is possible. Since the complexity of the FEYNMAN commands is very different, no general scaling law for the CPU time and memory usage can be given. No. of bytes in distributed program including test data, etc.: 799?265 No. of lines in distributed program including test data, etc.: 18?589 Distribution format: tar.gz Reasons for new version: While the previous program versions were designed mainly to create and manipulate the state of quantum registers, the present extension aims to support quantum operations as the essential ingredient for studying the effects of noisy environments. Does this version supersede the previous version: Yes Nature of the physical problem: Today, entanglement is identified as the essential resource in virtually all aspects of quantum information theory. In most practical implementations of quantum information protocols, however, decoherence typically limits the lifetime of entanglement. It is therefore necessary and highly desirable to understand the evolution of entanglement in noisy environments. Method of solution: Using the computer algebra system MAPLE, we have developed a set of procedures that support the definition and manipulation of n-qubit quantum registers as well as (unitary) logic gates and (nonunitary) quantum operations that act on the quantum registers. The provided hierarchy of commands can be used interactively in order to simulate and analyze the evolution of n-qubit quantum systems in ideal and nonideal quantum circuits.

Radtke, T.; Fritzsche, S.

2007-05-01

427

Global quantum discord in multipartite systems

We propose a global measure for quantum correlations in multipartite systems, which is obtained by suitably recasting the quantum discord in terms of relative entropy and local von Neumann measurements. The measure is symmetric with respect to subsystem exchange and is shown to be nonnegative for an arbitrary state. As an illustration, we consider tripartite correlations in the Werner-GHZ (Greenberger-Horne-Zeilinger) state and multipartite correlations at quantum criticality. In particular, in contrast with the pairwise quantum discord, we show that the global quantum discord is able to characterize the infinite-order quantum phase transition in the Ashkin-Teller spin chain.

Rulli, C. C.; Sarandy, M. S. [Instituto de Fisica, Universidade Federal Fluminense, Av. Gal. Milton Tavares de Souza s/n, Gragoata, 24210-346 Niteroi, RJ (Brazil)

2011-10-15

428

Quantum correlations in two-mode Gaussian open quantum systems

NASA Astrophysics Data System (ADS)

In the framework of the theory of open systems based on completely positive quantum dynamical semigroups, we give a description of continuous variable quantum entanglement and quantum discord for a system consisting of two non-interacting non-resonant bosonic modes embedded in a thermal environment. We study the time evolution of logarithmic negativity, which characterizes the degree of entanglement, and show that in the case of an entangled initial squeezed thermal state, entanglement suppression takes place for all temperatures of the environment, including zero temperature. We analyze the time evolution of the Gaussian quantum discord, which is a measure of all quantum correlations in the bipartite state, including entanglement, and show that discord decays asymptotically in time under the effect of the thermal bath. We describe also the time evolution of classical correlations.

Isar, Aurelian

2013-06-01

429

A first-principles relativistic many-body treatment is carried out for the hyperfine constant in europium atom. This investigation has allowed us to sort out for the first time all the contributing physical mechanisms, core polarization, correlation, relativistic modifications of these, and the purely relativistic Casimir and breakdown of LS coupling effects. It is found that all these competing contributions have to

J. Andriessen; K. Raghunathan; S. N. Ray; T. P. Das

1977-01-01

430

Measures of macroscopicity for quantum spin systems

NASA Astrophysics Data System (ADS)

We investigate the notion of ‘macroscopicity’ in the case of quantum spin systems and provide two main results. Firstly, we motivate the quantum Fisher information as a measure of the macroscopicity of quantum states. Secondly, we make a comparison with the existing literature on this topic. We report on a hierarchy among the measures and we conclude that one should carefully distinguish between ‘macroscopic quantum states’ and ‘macroscopic superpositions’, which is a strict subclass of the former.

Fröwis, Florian; Dür, Wolfgang

2012-09-01

431

Path integrals in configuration space in weakly relativistic many-body theory

The functional method of quantizing weakly relativistic theories is considered. It is shown that in the general case of systems with Lagrangian nonquadratic in the velocities the Green's function can be represented in the form of the regular part of a path integral in the configuration space. On this basis, a functional formulation of equilibrium statistical mechanics that does not require a Hamiltonian description of the system is developed. The results are used to determine the free energy of a system of charged particles described by the Darwin Lagrangian.

Blazhievskii, L.F.

1986-09-01

432

Classical equations for quantum systems

The origin of the phenomenological deterministic laws that approximately govern the quasiclassical domain of familiar experience is considered in the context of the quantum mechanics of closed systems such as the universe as a whole. A formulation of quantum mechanics is used that predicts probabilities for the individual members of a set of alternative coarse-grained histories that [ital decohere], which means that there is negligible quantum interference between the individual histories in the set. We investigate the requirements for coarse grainings to yield decoherent sets of histories that are quasiclassical, i.e., such that the individual histories obey, with high probability, effective classical equations of motion interrupted continually by small fluctuations and occasionally by large ones. We discuss these requirements generally but study them specifically for coarse grainings of the type that follows a distinguished subset of a complete set of variables while ignoring the rest. More coarse graining is needed to achieve decoherence than would be suggested by naive arguments based on the uncertainty principle. Even coarser graining is required in the distinguished variables for them to have the necessary inertia to approach classical predictability in the presence of the noise consisting of the fluctuations that typical mechanisms of decoherence produce. We describe the derivation of phenomenological equations of motion explicitly for a particular class of models.

Gell-Mann, M. (Theoretical Astrophysics Group (T-6), Los Alamos National Laboratory, Los Alamos, New Mexico 87545) (United States) (Santa Fe Institute, 1660 Old Pecos Trail, Santa Fe, New Mexico 87501); Hartle, J.B. (Department of Physics, University of California enSanta Barbara, Santa Barbara, (California) 93106)

1993-04-15