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1

Many-body Wigner quantum systems  

SciTech Connect

We present examples of many-body Wigner quantum systems. The position and the momentum operators {bold R}{sub A} and {bold P}{sub A}, A=1,{hor_ellipsis},n+1, of the particles are noncanonical and are chosen so that the Heisenberg and the Hamiltonian equations are identical. The spectrum of the energy with respect to the center of mass is equidistant and has finite number of energy levels. The composite system is spread in a small volume around the center of mass and within it the geometry is noncommutative. The underlying statistics is an exclusion statistics. {copyright} {ital 1997 American Institute of Physics.}

Palev, T.D.; Stoilova, N.I. [International Centre for Theoretical Physics, 34100 Trieste (Italy)] [International Centre for Theoretical Physics, 34100 Trieste (Italy)

1997-05-01

2

Quantum scaling in many-body systems  

NASA Astrophysics Data System (ADS)

The theory of quantum critical phenomena is introduced to study some current many-body problems in condensed matter physics. Renormalization group concepts are applied to strongly correlated electronic materials which are close to a zero-temperature instability. These systems have enhanced effective masses and susceptibility. Scaling arguments yield the exponents which govern the critical behavior of these quantities in terms of the usual critical exponents associated with a zero-temperature phase transition. We show the existence of a new energy scale, related to the quantum nature of the many-body instability, which can be generally associated with the setting of Fermi-liquid behavior with decreasing temperature in three-dimensional strongly interacting electronic systems. The theory of quantum critical phenomena is used to investigate the Kondo lattice problem, which provides a model to describe heavy-fermion systems and to introduce a scaling theory of the Mott transition with special emphasis on charge fluctuation effects. However, this report is not a review on heavy fermions and Mott insulators. The microscopic theories of these systems are still controversial and present some of the most challenging and instigating problems in condensed matter physics. This state of affairs stimulated the author to review and extend the scaling approach. The scaling theory we develop provides a powerful tool, based on the notion of universality, to understand the physical properties of correlated systems beyond the mean-field level. This is illustrated by our treatment of the one-dimensional Hubbard model, where, although the Fermi-liquid fixed point does not survive the fluctuations, the scaling approach is still useful. Finally, we discuss briefly how disorder affect our results.

Continentino, Mucio A.

1994-04-01

3

Quantum theory of many-body systems  

Microsoft Academic Search

In this article a survey is given of the present status of the quantum theory of many-particle systems with special emphasis on the underlying principles. Very little is said about applications. A brief introduction to some models, which are of interest for an approximate or qualitative description of actual physical systems, is followed by a discussion of two important phenomena

N M Hugenholtz

1965-01-01

4

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

5

Many-body quantum mechanics as a symplectic dynamical system  

Microsoft Academic Search

An approach is formulated to the problem of obtaining approximate solutions to many-body quantum mechanics. The starting point is the representation of quantum mechanics as Hamiltonian mechanics on a symplectic manifold (phase space). It is shown that Dirac's variation of an action integral provides a natural mechanism for constraining the dynamics to symplectic submanifolds and gives rise to a hierarchy

D. J. Rowe; A. Ryman; G. Rosensteel

1980-01-01

6

Quench dynamics of isolated many-body quantum systems  

NASA Astrophysics Data System (ADS)

We study isolated quantum systems with two-body interactions after a quench. In these systems, the energy shell is a Gaussian of width ?, and it gives the maximum possible spreading of the energy distribution of the initial states. When the distribution achieves this shape, the fidelity decay can be Gaussian until saturation. This establishes a lower bound for the fidelity decay in realistic systems. An ultimate bound for systems with many-body interactions is also derived based on the analysis of full random matrices. We find excellent agreement between numerical and analytical results. We also provide the conditions under which the short-time dynamics of few-body observables is controlled by ?. The analyses are developed for systems, initial states, and observables accessible to experiments.

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

2014-04-01

7

Dissipation and dynamics in quantum many-body systems  

NASA Astrophysics Data System (ADS)

In this thesis, we simulate the time evolution of quantum many-body systems and use comparisons to experimental data in order to learn more about the properties of nuclear matter and understand better the dynamical processes in central nuclear collisions. We further advance the development of a nonequilibrium Green's function description of both central nuclear collisions and Bose-Einstein Condensates. First in the thesis, we determine the viscosity of nuclear matter by adjusting the in-medium nucleon-nucleon cross section (IMNNCS) in our BUU transport model until the simulation results match experimental data on nuclear stopping in central nuclear collisions at intermediate energies. Then we use that cross section to calculate the viscosity self-consistently. We also calculate the ratio of shear viscosity to entropy density to determine how close the system is to the proposed universal quantum lower limit. Next, we use the same BUU transport model to isolate the protons emitted early in a central nuclear collision at intermediate energy, as predicted in the model, using a filter on high transverse momentum, and we show the effect on the source function. We predict a recontraction of protons at late times in the central collision of 112Sn+112Sn at 50 MeV/nucleon that results in a resurgence of emission of protons and show how to use the transverse momentum filter and the source function to test this prediction in experiment. Next, we develop an early implementation of a more fully quantal transport model than the BUU equations, with our sights set on solving central nuclear collisions in 3D using nonequilibrium Green's functions. In our 1D, mean field, density matrix model, we demonstrate the initial state preparation and collision of 1D nuclear "slabs". With the aim of reducing the computational cost of the calculation, we show that we can neglect far off-diagonal elements in the density matrix without affecting the one-body observables. Further, we describe a method of recasting the density matrix in a rotated coordinate system, enabling us to not only ignore the irrelevant matrix elements in the time evolution, but also avoid computing them completely, reducing the computational cost. As an added benefit, we find that the rotation allows us to partially decouple the position and momentum discretization, permitting access to arbitrary regimes of kinetic energy without altering the resolution and range of the 1D box in position space. Finally, we exhibited the wide applicability of this density matrix approach by applying it to a system of 2000 ultracold 87Rb atoms in a Bose-Einstein condensate, as described by the Gross-Pitaevskii equation, successfully achieving a stable state in a harmonic oscillator trap.

Barker, Brent Wendolyn

8

Characterizing and quantifying frustration in quantum many-body systems.  

PubMed

We present a general scheme for the study of frustration in quantum systems. We introduce a universal measure of frustration for arbitrary quantum systems and we relate it to a class of entanglement monotones via an exact inequality. If all the (pure) ground states of a given Hamiltonian saturate the inequality, then the system is said to be inequality saturating. We introduce sufficient conditions for a quantum spin system to be inequality saturating and confirm them with extensive numerical tests. These conditions provide a generalization to the quantum domain of the Toulouse criteria for classical frustration-free systems. The models satisfying these conditions can be reasonably identified as geometrically unfrustrated and subject to frustration of purely quantum origin. Our results therefore establish a unified framework for studying the intertwining of geometric and quantum contributions to frustration. PMID:22243147

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

2011-12-23

9

Quantum control of infinite-dimensional many-body systems  

NASA Astrophysics Data System (ADS)

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

Bliss, Roger S.; Burgarth, Daniel

2014-03-01

10

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

11

Schrieffer-Wolff transformation for quantum many-body systems  

SciTech Connect

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

12

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

PubMed

Quantum simulators, in which well-controlled quantum systems are used to reproduce the dynamics of less understood ones, have the potential to explore physics inaccessible to modeling with classical computers. However, checking the results of such simulations also becomes classically intractable as system sizes increase. Here, we introduce and implement a coherent imaging spectroscopic technique, akin to magnetic resonance imaging, to validate a quantum simulation. We use this method to determine the energy levels and interaction strengths of a fully connected quantum many-body system. Additionally, we directly measure the critical energy gap near a quantum phase transition. We expect this general technique to become a verification tool for quantum simulators once experiments advance beyond proof-of-principle demonstrations and exceed the resources of conventional computers. PMID:25061207

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

2014-07-25

13

Self-consistent projection operator theory for quantum many-body systems  

NASA Astrophysics Data System (ADS)

We derive an exact equation of motion for the reduced density matrices of individual subsystems of quantum many-body systems of any lattice dimension and arbitrary system size. Our projection operator based theory yields a highly efficient analytical and numerical approach. Besides its practical use it provides an interpretation and systematic extension of mean-field approaches and an adaption of open quantum systems theory to settings where a dynamically evolving environment has to be taken into account. We show its high accuracy for two significant classes of complex quantum many-body dynamics, unitary evolutions of nonequilibrium states in closed and stationary states in driven-dissipative systems.

Degenfeld-Schonburg, Peter; Hartmann, Michael J.

2014-06-01

14

Simulation of Many-Body Fermi Systems on a Universal Quantum Computer  

Microsoft Academic Search

We provide fast algorithms for simulating many-body Fermi systems on a universal quantum computer. Both first and second quantized descriptions are considered, and the relative computational complexities are determined in each case. In order to accommodate fermions using a first quantized Hamiltonian, an efficient quantum algorithm for antisymmetrization is given. Finally, a simulation of the Hubbard model is discussed in

Daniel S. Abrams; Seth Lloyd

1997-01-01

15

Many-body quantum trajectories of non-Markovian open systems  

NASA Astrophysics Data System (ADS)

A long-standing open problem in the non-Markovian quantum state diffusion (QSD) approach to open quantum systems is to establish the non-Markovian QSD equations for multiple-qubit systems. In this paper, we settle this important question by explicitly constructing a set of exact time-local QSD equations for N-qubit systems. Our exact time-local (convolutionless) QSD equations have paved the way towards simulating quantum dynamics of many-body open systems interacting with a common bosonic environment. The applicability of this multiple-qubit stochastic equation is exemplified by numerically solving several quantum open many-body systems concerning quantum coherence dynamics and dynamical control.

Jing, Jun; Zhao, Xinyu; You, J. Q.; Strunz, Walter T.; Yu, Ting

2013-11-01

16

Renormalization algorithms for Quantum-Many Body Systems in two and higher dimensions  

Microsoft Academic Search

We describe quantum many--body systems in terms of projected entangled--pair states, which naturally extend matrix product states to two and more dimensions. We present an algorithm to determine correlation functions in an efficient way. We use this result to build powerful numerical simulation techniques to describe the ground state, finite temperature, and evolution of spin systems in two and higher

F. Verstraete; J. I. Cirac

2004-01-01

17

Quantum chaos in many-body systems: what can we learn from the Ce atom?  

NASA Astrophysics Data System (ADS)

Results of an extensive study of a real quantum chaotic many-body system - the Ce atom - are presented. We discuss the origins of the quantum chaotic behaviour of the system, analyse statistical and dynamical properties of the multi-particle chaotic eigenstates and consider matrix elements or transition amplitudes between them. We show that based on the universal properties of the chaotic eigenstates a statistical theory of finite few-particle systems with strong interaction can be developed. We also discuss such important physical effects as enhancement of weak perturbations in many-body quantum chaotic systems, distribution of single-particle occupation numbers and its deviations from the standard Fermi-Dirac shape, and ways of introducing statistical temperature-based description in such systems.

Flambaum, V. V.; Gribakina, A. A.; Gribakin, G. F.; Ponomarev, I. V.

1999-07-01

18

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

PubMed

The key to explaining and controlling a range of quantum phenomena is to study how information propagates around many-body systems. Quantum dynamics can be described by particle-like carriers of information that emerge in the collective behaviour of the underlying system, the so-called quasiparticles. These elementary excitations are predicted to distribute quantum information in a fashion determined by the system's interactions. Here we report quasiparticle dynamics observed in a quantum many-body system of trapped atomic ions. First, we observe the entanglement distributed by quasiparticles as they trace out light-cone-like wavefronts. Second, using the ability to tune the interaction range in our system, we observe information propagation in an experimental regime where the effective-light-cone picture does not apply. Our results will enable experimental studies of a range of quantum phenomena, including transport, thermalization, localization and entanglement growth, and represent a first step towards a new quantum-optic regime of engineered quasiparticles with tunable nonlinear interactions. PMID:25008526

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

2014-07-10

19

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

SciTech Connect

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

20

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

PubMed

We propose a real-space renormalization group method to explicitly decouple into independent components a many-body system that, as in the phenomenon of spin-charge separation, exhibits separation of degrees of freedom at low energies. Our approach produces a branching holographic description of such systems that opens the path to the efficient simulation of the most entangled phases of quantum matter, such as those whose ground state violates a boundary law for entanglement entropy. As in the coarse-graining transformation of Vidal [Phys. Rev. Lett. 99, 220405 (2007). PMID:24949747

Evenbly, G; Vidal, G

2014-06-01

21

Real-Space Decoupling Transformation for Quantum Many-Body Systems  

NASA Astrophysics Data System (ADS)

We propose a real-space renormalization group method to explicitly decouple into independent components a many-body system that, as in the phenomenon of spin-charge separation, exhibits separation of degrees of freedom at low energies. Our approach produces a branching holographic description of such systems that opens the path to the efficient simulation of the most entangled phases of quantum matter, such as those whose ground state violates a boundary law for entanglement entropy. As in the coarse-graining transformation of Vidal [Phys. Rev. Lett. 99, 220405 (2007)], the key ingredient of this decoupling transformation is the concept of entanglement renormalization, or removal of short-range entanglement. We demonstrate the feasibility of the approach, both analytically and numerically, by decoupling in real space the ground state of a critical quantum spin chain into two. Generalized notions of renormalization group flow and of scale invariance are also put forward.

Evenbly, G.; Vidal, G.

2014-06-01

22

Reduced Density Matrix and Entanglement Entropy of Permutationally Invariant Quantum Many-Body Systems  

NASA Astrophysics Data System (ADS)

In this paper we discuss the properties of the reduced density matrix of quantum many body systems with permutational symmetry and present basic quantification of the entanglement in terms of the von Neumann (VNE), Renyi and Tsallis entropies. In particular, we show, on the specific example of the spin 1/2 Heisenberg model, how the RDM acquires a block diagonal form with respect to the quantum number k fixing the polarization in the subsystem conservation of Sz and with respect to the irreducible representations of the Sn group. Analytical expression for the RDM elements and for the RDM spectrum are derived for states of arbitrary permutational symmetry and for arbitrary polarizations. The temperature dependence and scaling of the VNE across a finite temperature phase transition is discussed and the RDM moments and the Rényi and Tsallis entropies calculated both for symmetric ground states of the Heisenberg chain and for maximally mixed states.

Popkov, Vladislav; Salerno, Mario

2013-06-01

23

Reduced Density Matrix and Entanglement Entropy of Permutationally Invariant Quantum Many-Body Systems  

NASA Astrophysics Data System (ADS)

In this paper we discuss the properties of the reduced density matrix of quantum many body systems with permutational symmetry and present basic quantification of the entanglement in terms of the von Neumann (VNE), Renyi and Tsallis entropies. In particular, we show, on the specific example of the spin 1/2 Heisenberg model, how the RDM acquires a block diagonal form with respect to the quantum number k fixing the polarization in the subsystem conservation of Sz and with respect to the irreducible representations of the Sn group. Analytical expression for the RDM elements and for the RDM spectrum are derived for states of arbitrary permutational symmetry and for arbitrary polarizations. The temperature dependence and scaling of the VNE across a finite temperature phase transition is discussed and the RDM moments and the Rényi and Tsallis entropies calculated both for symmetric ground states of the Heisenberg chain and for maximally mixed states.

Popkov, Vladislav; Salerno, Mario

2012-11-01

24

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

25

Particle entanglement in continuum many-body systems via quantum Monte Carlo  

NASA Astrophysics Data System (ADS)

Entanglement of spatial bipartitions, used to explore lattice models in condensed matter physics, may be insufficient to fully describe itinerant quantum many-body systems in the continuum. We introduce a procedure to measure the Rényi entanglement entropies on a particle bipartition, with general applicability to continuum Hamiltonians via path integral Monte Carlo methods. Via direct simulations of interacting bosons in one spatial dimension, we confirm a logarithmic scaling of the single-particle entanglement entropy with the number of particles in the system. The coefficient of this logarithmic scaling increases with interaction strength, saturating to unity in the strongly interacting limit. Additionally, we show that the single-particle entanglement entropy is bounded by the condensate fraction, suggesting a practical route towards its measurement in future experiments.

Herdman, C. M.; Roy, P.-N.; Melko, R. G.; Del Maestro, A.

2014-04-01

26

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

SciTech Connect

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

Poulin, David [Departement de Physique, Universite de Sherbrooke, Sherbrooke, Quebec (Canada); Wocjan, Pawel [School of Electrical Engineering and Computer Science, University of Central Florida, Orlando, Florida (United States)

2009-04-03

27

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

PubMed

Preparing the ground state of a system of interacting classical particles is an NP-hard problem. Thus, there is in general no better algorithm to solve this problem than exhaustively going through all N configurations of the system to determine the one with lowest energy, requiring a running time proportional to N. A quantum computer, if it could be built, could solve this problem in time sqrt[N]. Here, we present a powerful extension of this result to the case of interacting quantum particles, demonstrating that a quantum computer can prepare the ground state of a quantum system as efficiently as it does for classical systems. PMID:19392338

Poulin, David; Wocjan, Pawel

2009-04-01

28

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

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

29

Exact solution of a 1D quantum many-body system with momentum-dependent interactions  

Microsoft Academic Search

We discuss a 1D quantum many-body model of distinguishable particles with local, momentum-dependent two-body interactions. We show that the restriction of this model to fermions corresponds to the non-relativistic limit of the massive Thirring model. This fermion model can be solved exactly by a mapping to the 1D boson gas with inverse coupling constant. We provide evidence that this mapping

Harald Grosse; Edwin Langmann; Cornelius Paufler

2004-01-01

30

Generalized local interactions in 1D: solutions of quantum many-body systems describing distinguishable particles  

Microsoft Academic Search

As is well known, there exists a four-parameter family of local interactions in 1D. We interpret these parameters as coupling constants of delta-type interactions which include different kinds of momentum-dependent terms, and determine all cases leading to many-body systems of distinguishable particles which are exactly solvable by the coordinate Bethe ansatz. We find two such families of systems, one with

Martin Hallnäs; Edwin Langmann; Cornelius Paufler

2005-01-01

31

The Quantum Mechanical Many-Body Problem.  

National Technical Information Service (NTIS)

A wide variety of quantum mechanical many-body problems were investigated. The two significant accomplishments of this research are as follows: The development of DCF (dynamical characteristic function) method for treating the statistical mechanics of qua...

A. E. Glassgold

1969-01-01

32

General many-body systems  

SciTech Connect

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

33

Coherent backscattering in Fock space: a signature of quantum many-body interference in interacting bosonic systems.  

PubMed

We predict a generic signature of quantum interference in many-body bosonic systems resulting in a coherent enhancement of the average return probability in Fock space. This enhancement is robust with respect to variations of external parameters even though it represents a dynamical manifestation of the delicate superposition principle in Fock space. It is a genuine quantum many-body effect that lies beyond the reach of any mean-field approach. Using a semiclassical approach based on interfering paths in Fock space, we calculate the magnitude of the backscattering peak and its dependence on gauge fields that break time-reversal invariance. We confirm our predictions by comparing them to exact quantum evolution probabilities in Bose-Hubbard models, and discuss their relevance in the context of many-body thermalization. PMID:24765925

Engl, Thomas; Dujardin, Julien; Argüelles, Arturo; Schlagheck, Peter; Richter, Klaus; Urbina, Juan Diego

2014-04-11

34

Quantum Information Processing with Quantum Zeno Many-Body Dynamics  

Microsoft Academic Search

We show how the quantum Zeno effect can be exploited to control quantum many-body dynamics for quantum information and computation purposes. In particular, we consider a one dimensional array of three level systems interacting via a nearest-neighbour interaction. By encoding the qubit on two levels and using simple projective frequent measurements yielding the quantum Zeno effect, we demonstrate how to

Alex Monras; Oriol Romero-Isart

2008-01-01

35

Entanglement in many-body systems  

Microsoft Academic Search

Recent interest in aspects common to quantum information and condensed matter has prompted a flurry of activity at the border of these disciplines that were far distant until a few years ago. Numerous interesting questions have been addressed so far. Here an important part of this field, the properties of the entanglement in many-body systems, are reviewed. The zero and

Luigi Amico; Rosario Fazio; Andreas Osterloh; Vlatko Vedral

2008-01-01

36

The Effects of Quantum Delocalization on the Structural and Thermodynamic Properties of Many-Body Systems  

NASA Astrophysics Data System (ADS)

The following dissertation is an account of my research in the Mandelshtam group at UC Irvine beginning in the Fall of 2006 and ending in the Summer of 2011. My general area of study falls within the realm of equilibrium quantum statistical mechanics, a discipline which attempts to relate molecular-scale properties to time averaged, macroscopic observables. The major tools used herein are the Variational Gaussian Wavepacket (VGW) approximation for quantum calculations, and Monte-Carlo methods, particularly parallel tempering, for global optimization and the prediction of equilibrium thermodynamic properties. Much of my work used these two methods to model both small and bulk systems at equilibrium where quantum effects are significant. All the systems considered are characterized by inter-molecular van der Waals forces, which are weak but significant electrostatic attractions between atoms and molecules and posses a 1/r6 dependence. The research herein begins at the microscopic level, starting with Lennard-Jones (LJ) clusters, then later shifts to the macroscopic for a study involving bulk para-hydrogen. For the LJ clusters the structural transitions induced by a changing deBoer parameter, ?, a measure of quantum delocalization of the constituent particles, are investigated over a range of cluster sizes, N. From the data a "phase" diagram as a function of ? and N is constructed, which depicts the structural motifs favored at different size and quantum parameter. Comparisons of the "quantum induced" structural transitions depicted in the latter are also made with temperature induced transitions and those caused by varying the range of the Morse potential. Following this, the structural properties of binary para-Hydrogen/ ortho-Deuterium clusters are investigated using the VGW approximation and Monte-Carlo methods within the GMIN framework. The latter uses the "Basin-Hopping" algorithm, which simplifies the potential energy landscape, and coupled with the VGW approximation, an efficient and viable method for predicting equilibrium quantum mechanical properties is demonstrated. In the next chapter my contribution to the numerical implementation of the Thermal Gaussian Molecular Dynamics (TGMD) method is discussed. Within TGMD, a mapping of a quantum system to a classical is performed by means of an effective Hamiltonian, H eff, which is computed within the VGW framework. Using the classical dynamical equations of motion with Heff, the properties of a quantum system can be modeled within a classical framework. After this, the bulk system of fluid para-Hydrogen is investigated using the VGW in the NPT ensemble in an attempt to derive the thermodynamic properties at the phase transition and construct the equation of state. The dissertation then concludes with a discussion on the adaptation of the VGW methodology to any molecular system.

Deckman, Jason

37

Efficient Simulation of One-Dimensional Quantum Many-Body Systems  

Microsoft Academic Search

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

Guifré Vidal

2004-01-01

38

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

39

Further Consequences of the Canonical sequence Method in Quantum Many-Body Systems  

NASA Astrophysics Data System (ADS)

A number of years ago, Horn and Weinstein (Phys. Rev. D30, 1256(1984)) introduced a novel nonperturbative method for calculating ground-state expectation values for Hamiltonian systems. Although close in spirit to standard variational schemes this ``t-expansion" introduces a fictional parameter t to the trial state exp(-hatHt/2) |?> wherein the limit tarrow ? yields convergence to the ground-state energy E0 for the expansion [ lim _tarrow ? frac< ? | hatH exp ( -hatHt) | ? > < ? | exp ( -hatHt) | ? > =E_0. ] Recently Samaj et al. (J. Phys. A30, 1471(1997)) have generalized the t-expansion technique and the related Connected Moments Expansion to a more general canonical sequence. They then apply this canonical series to the quantum Ising model. In the present work we have expounded upon the work of Samaj et al. and have applied this to a number of different many-particle Hamiltonian systems.

Fessatidis, Vassilios; Mancini, Jay D.; Murawski, Robert K.; Bowen, Samuel P.

2000-03-01

40

Thermal Gaussian molecular dynamics for quantum dynamics simulations of many-body systems: Application to liquid para-hydrogen  

NASA Astrophysics Data System (ADS)

A new method, here called thermal Gaussian molecular dynamics (TGMD), for simulating the dynamics of quantum many-body systems has recently been introduced [I. Georgescu and V. A. Mandelshtam, Phys. Rev. B 82, 094305 (2010)]. As in the centroid molecular dynamics (CMD), in TGMD the N-body quantum system is mapped to an N-body classical system. The associated both effective Hamiltonian and effective force are computed within the variational Gaussian wave-packet approximation. The TGMD is exact for the high-temperature limit, accurate for short times, and preserves the quantum canonical distribution. For a harmonic potential and any form of operator Â, it provides exact time correlation functions CAB(t) at least for the case of B?, a linear combination of the position, ?, and momentum, p?, operators. While conceptually similar to CMD and other quantum molecular dynamics approaches, the great advantage of TGMD is its computational efficiency. We introduce the many-body implementation and demonstrate it on the benchmark problem of calculating the velocity time auto-correlation function for liquid para-hydrogen, using a system of up to N = 2592 particles.

Georgescu, Ionu?; Deckman, Jason; Fredrickson, Laura J.; Mandelshtam, Vladimir A.

2011-05-01

41

Thermal Gaussian molecular dynamics for quantum dynamics simulations of many-body systems: application to liquid para-hydrogen.  

PubMed

A new method, here called thermal Gaussian molecular dynamics (TGMD), for simulating the dynamics of quantum many-body systems has recently been introduced [I. Georgescu and V. A. Mandelshtam, Phys. Rev. B 82, 094305 (2010)]. As in the centroid molecular dynamics (CMD), in TGMD the N-body quantum system is mapped to an N-body classical system. The associated both effective Hamiltonian and effective force are computed within the variational Gaussian wave-packet approximation. The TGMD is exact for the high-temperature limit, accurate for short times, and preserves the quantum canonical distribution. For a harmonic potential and any form of operator A?, it provides exact time correlation functions C(AB)(t) at least for the case of B, a linear combination of the position, x, and momentum, p, operators. While conceptually similar to CMD and other quantum molecular dynamics approaches, the great advantage of TGMD is its computational efficiency. We introduce the many-body implementation and demonstrate it on the benchmark problem of calculating the velocity time auto-correlation function for liquid para-hydrogen, using a system of up to N = 2592 particles. PMID:21548675

Georgescu, Ionut; Deckman, Jason; Fredrickson, Laura J; Mandelshtam, Vladimir A

2011-05-01

42

Tensor product expansions for correlation in quantum many-body systems  

NASA Astrophysics Data System (ADS)

We explore a class of computationally feasible approximations of the two-body density matrix as a finite sum of tensor products of single-particle operators. Physical symmetries then uniquely determine the two-body matrix in terms of the one-body matrix. Representing dynamical correlation alone as a single tensor product results in a theory that predicts near zero dynamical correlation in the homogeneous electron gas at moderate to high densities. But, representing both dynamical and statistical correlation effects together as a tensor product leads to the recently proposed ``natural orbital functional.'' We find that this latter theory has some asymptotic properties consistent with established many-body theory but is no more accurate than Hartree-Fock in describing the homogeneous electron gas for the range of densities typically found in the valence regions of solids.

Csányi, Gábor; Arias, T. A.

2000-03-01

43

Exact solutions of two complementary 1D quantum many-body systems on the half-line  

Microsoft Academic Search

We consider two particular 1D quantum many-body systems with local\\u000ainteractions related to the root system $C_N$. Both models describe identical\\u000aparticles moving on the half-line with non-trivial boundary conditions at the\\u000aorigin, and they are in many ways complementary to each other. We discuss the\\u000aBethe Ansatz solution for the first model where the interaction potentials are\\u000adelta-functions, and

Martin Hallnas; Edwin Langmann

2004-01-01

44

Quantum nonlocality. Detecting nonlocality in many-body quantum states.  

PubMed

Intensive studies of entanglement properties have proven essential for our understanding of quantum many-body systems. In contrast, much less is known about the role of quantum nonlocality in these systems because the available multipartite Bell inequalities involve correlations among many particles, which are difficult to access experimentally. We constructed multipartite Bell inequalities that involve only two-body correlations and show how they reveal the nonlocality in many-body systems relevant for nuclear and atomic physics. Our inequalities are violated by any number of parties and can be tested by measuring total spin components, opening the way to the experimental detection of many-body nonlocality, for instance with atomic ensembles. PMID:24926014

Tura, J; Augusiak, R; Sainz, A B; Vértesi, T; Lewenstein, M; Acín, A

2014-06-13

45

Complexity of controlling quantum many-body dynamics  

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

46

HOLOMORPHIC BUNDLES AND MANY-BODY SYSTEMS  

Microsoft Academic Search

IntroductionIntegrable many-body systems attract attention for the following reasons: they areimportant in condensed matter physics and they appear quite often in two dimensionalgauge theories as well as in conformal field theory. Recently they have been recognized infour dimensional gauge theories.Among these systems the following ones will be of special interest for us:1 . Spin generalization of Elliptic Calogero - Moser

Nikita Nekrasov

1995-01-01

47

Holomorphic bundles and many-body systems  

Microsoft Academic Search

We show that spin generalization of elliptic Calogero-Moser system, elliptic extension of Gaudin model and their cousins are the degenerations of Hitchin systems. Applications to the constructions of integrals of motion, angle-action variables and quantum systems are discussed. The constructions of classical systems are motivated by Conformal Field Theory, and their quantum counterparts can be thought of as being the

Nikita Nekrasov

1996-01-01

48

EDITORIAL: Focus on Quantum Information and Many-Body Theory  

NASA Astrophysics Data System (ADS)

Quantum many-body models describing natural systems or materials and physical systems assembled piece by piece in the laboratory for the purpose of realizing quantum information processing share an important feature: intricate correlations that originate from the coherent interaction between a large number of constituents. In recent years it has become manifest that the cross-fertilization between research devoted to quantum information science and to quantum many-body physics leads to new ideas, methods, tools, and insights in both fields. Issues of criticality, quantum phase transitions, quantum order and magnetism that play a role in one field find relations to the classical simulation of quantum systems, to error correction and fault tolerance thresholds, to channel capacities and to topological quantum computation, to name but a few. The structural similarities of typical problems in both fields and the potential for pooling of ideas then become manifest. Notably, methods and ideas from quantum information have provided fresh approaches to long-standing problems in strongly correlated systems in the condensed matter context, including both numerical methods and conceptual insights. Focus on quantum information and many-body theory Contents TENSOR NETWORKS Homogeneous multiscale entanglement renormalization ansatz tensor networks for quantum critical systems M Rizzi, S Montangero, P Silvi, V Giovannetti and Rosario Fazio Concatenated tensor network states R Hübener, V Nebendahl and W Dür Entanglement renormalization in free bosonic systems: real-space versus momentum-space renormalization group transforms G Evenbly and G Vidal Finite-size geometric entanglement from tensor network algorithms Qian-Qian Shi, Román Orús, John Ove Fjærestad and Huan-Qiang Zhou Characterizing symmetries in a projected entangled pair state D Pérez-García, M Sanz, C E González-Guillén, M M Wolf and J I Cirac Matrix product operator representations B Pirvu, V Murg, J I Cirac and F Verstraete SIMULATION AND DYNAMICS A quantum differentiation of k-SAT instances B Tamir and G Ortiz Classical Ising model test for quantum circuits Joseph Geraci and Daniel A Lidar Exact matrix product solutions in the Heisenberg picture of an open quantum spin chain S R Clark, J Prior, M J Hartmann, D Jaksch and M B Plenio Exact solution of Markovian master equations for quadratic Fermi systems: thermal baths, open XY spin chains and non-equilibrium phase transition Tomaž Prosen and Bojan Žunkovi? Quantum kinetic Ising models R Augusiak, F M Cucchietti, F Haake and M Lewenstein ENTANGLEMENT AND SPECTRAL PROPERTIES Ground states of unfrustrated spin Hamiltonians satisfy an area law Niel de Beaudrap, Tobias J Osborne and Jens Eisert Correlation density matrices for one-dimensional quantum chains based on the density matrix renormalization group W Münder, A Weichselbaum, A Holzner, Jan von Delft and C L Henley The invariant-comb approach and its relation to the balancedness of multipartite entangled states Andreas Osterloh and Jens Siewert Entanglement scaling of fractional quantum Hall states through geometric deformations Andreas M Läuchli, Emil J Bergholtz and Masudul Haque Entanglement versus gap for one-dimensional spin systems Daniel Gottesman and M B Hastings Entanglement spectra of critical and near-critical systems in one dimension F Pollmann and J E Moore Macroscopic bound entanglement in thermal graph states D Cavalcanti, L Aolita, A Ferraro, A García-Saez and A Acín Entanglement at the quantum phase transition in a harmonic lattice Elisabeth Rieper, Janet Anders and Vlatko Vedral Multipartite entanglement and frustration P Facchi, G Florio, U Marzolino, G Parisi and S Pascazio Entropic uncertainty relations—a survey Stephanie Wehner and Andreas Winter Entanglement in a spin system with inverse square statistical interaction D Giuliano, A Sindona, G Falcone, F Plastina and L Amico APPLICATIONS Time-dependent currents of one-dimensional bosons in an optical lattice J Schachenmayer, G Pupillo and A J Daley Implementing quantum gates using t

Eisert, Jens; Plenio, Martin B.

2010-02-01

49

Towards measuring Entanglement Entropies in Many Body Systems  

Microsoft Academic Search

We explore the relation between entanglement entropy of quantum many body systems and the distribution of corresponding, properly selected, observables. Such a relation is necessary to actually measure the entanglement entropy. We show that in general, the Shannon entropy of the probability distribution of certain symmetry observables gives a lower bound to the entropy. In some cases this bound is

Israel Klich; Gil Refael; Alessandro Silva

50

Continuity Equations for Many-Body Systems.  

National Technical Information Service (NTIS)

The four-divergence of a generalized current is related to the Green's function formulation of the many-body problem. The relations obtained take the form of continuity equations, with an extra source term corresponding to the creation or annihilation of ...

D. G. Pelka N. Rivier

1971-01-01

51

Quantum many-body dynamics in optomechanical arrays.  

PubMed

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. PMID:23992065

Ludwig, Max; Marquardt, Florian

2013-08-16

52

Derivation of the cubic non-linear Schrödinger equation from quantum dynamics of many-body systems  

Microsoft Academic Search

We prove rigorously that the one-particle density matrix of three dimensional interacting Bose systems with a short-scale\\u000a repulsive pair interaction converges to the solution of the cubic non-linear Schrdinger equation in a suitable scaling limit.\\u000a The result is extended to k-particle density matrices for all positive integer k.

László Erdos; Benjamin Schlein; Horng-Tzer Yau

2007-01-01

53

Many-body energy localization transition in periodically driven systems  

SciTech Connect

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

D’Alessio, Luca, E-mail: dalessio@buphy.bu.edu [Physics Department, Boston University, Boston, MA 02215 (United States) [Physics Department, Boston University, Boston, MA 02215 (United States); Kavli Institute for Theoretical Physics, University of California, Santa Barbara, CA 93106 (United States); Polkovnikov, Anatoli, E-mail: asp@bu.edu [Physics Department, Boston University, Boston, MA 02215 (United States)] [Physics Department, Boston University, Boston, MA 02215 (United States)

2013-06-15

54

Many-Body Effects in Quantum-Well Intersubband Transitions  

NASA Technical Reports Server (NTRS)

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

Li, Jian-Zhong; Ning, Cun-Zheng

2003-01-01

55

Integrable many-body systems and gauge theories  

Microsoft Academic Search

We review the study of the relation between integrable many-body systems and gauge theories. We show that the degrees of freedom\\u000a of integrable systems are related to the topological degrees of freedom of gauge theories. We also describe the relation between\\u000a families of integrable systems and N=2 supersymmetric gauge theories. We show that the degrees of freedom of many-body systems

A. S. Gorskii; A. Mironov

2000-01-01

56

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

NASA Astrophysics Data System (ADS)

Feynman path-integral quantum Monte Carlo (QMC) simulations and an analytic many-body approach are used to study the ground state properties of one-dimensional (1D) chains in the theoretical framework of model Hamiltonians of the Hubbard type. The QMC algorithm is employed to derive position-space quantities, while band structure properties are evaluated by combining QMC data with expressions derived in momentum (k) space. Bridging link between both representations is the quasi-chemical approximation (QCA). Electronic charge fluctuations <(?n2i)> and the fluctuations of the magnetic local moments <(?s2i)> are studied as a function of the on-site density and correlation strength, which is given by the ratio between two-electron interaction and kinetic hopping. Caused by the non-analytic behaviour of the chemical potential ? = ?E/? (with E denoting the electronic energy), strict 1D systems with an on-site density of 1·0 do not exhibit the properties of a conductor for any non-zero interaction beyond the mean-field approximation. The QMC simulations lead to straightforward access to the probabilities Pi(n) of finding n = 0, 1, 2 electrons at the ith lattice site. The Pi(n) elements allow to calculate the enhancement factors on the electron spin susceptibility ?, effective electronic mass m* and Knight shift ?. m* is enhanced by a bandwidth renormalization factor D-10, ? by an element ?K mapping the additional localization of the correlated electrons in the presence of an external magnetic field B and ? by the product D-10 ?K. Available experimental data are discussed in the light of the present theoretical findings.

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

57

Brillouin-Wigner Methods for Many-Body Systems  

Microsoft Academic Search

\\u000a The Brillouin–Wigner many-body problem in atomic and molecular physics and in quantum chemistry is described. The use of coupled\\u000a cluster expansions,\\u000a configuration interaction and perturbation series is considered both for the single-reference function case and for those\\u000a cases requiring the use of a multi-reference formalism.

Ivan Huba?; Stephen Wilson

58

Preparation of many-body states for quantum simulation  

SciTech Connect

While quantum computers are capable of simulating many quantum systems efficiently, the simulation algorithms must begin with the preparation of an appropriate initial state. We present a method for generating physically relevant quantum states on a lattice in real space. In particular, the present algorithm is able to prepare general pure and mixed many-particle states of any number of particles. It relies on a procedure for converting from a second-quantized state to its first-quantized counterpart. The algorithm is efficient in that it operates in time that is polynomial in all the essential descriptors of the system, the number of particles, the resolution of the lattice, and the inverse of the maximum final error. This scaling holds under the assumption that the wave function to be prepared is bounded or its indefinite integral is known and that the Fock operator of the system is efficiently simulatable.

Ward, Nicholas J.; Kassal, Ivan; Aspuru-Guzik, Alan [Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138 (United States)

2009-05-21

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

Phase transitions in fermionic systems with many-body interaction  

NASA Technical Reports Server (NTRS)

A linearized version of the Hartree-Fock method is used as a probe to investigate phase transitions in fermionic systems with many-body interactions. An application to a new exactly solvable model which includes two- and three-body forces is shown.

Bozzolo, G.; Plastino, A.; Ferrante, J.

1989-01-01

61

Nearest-neighbor distribution functions in many-body systems  

Microsoft Academic Search

The probability of finding a nearest neighbor at some given distance from a reference point in a many-body system of interacting particles is of importance in a host of problems in the physical as well as biological sciences. We develop a formalism to obtain two different types of nearest-neighbor probability density functions (void and particle probability densities) and closely related

S. Torquato; B. Lu; J. Rubinstein

1990-01-01

62

Self-Consistent Approximations in Many-Body Systems  

Microsoft Academic Search

This paper investigates the criteria for maintenance of the macroscopic conservation laws of number, momentum, and energy by approximate two-particle correlation functions in many-body systems. The methods of generating such approximations are the same as in a previous paper. However, the derivations of the conservation laws given here clarify both why the approximation method works and the connection between the

Gordon Baym

1962-01-01

63

Entanglement Theory and the Quantum Simulation of Many-Body Physics  

NASA Astrophysics Data System (ADS)

In this thesis we present new results relevant to two important problems in quantum information science: the development of a theory of entanglement and the exploration of the use of controlled quantum systems to the simulation of quantum many-body phenomena. In the first part we introduce a new approach to the study of entanglement by considering its manipulation under operations not capable of generating entanglement and show there is a total order for multipartite quantum states in this framework. We also present new results on hypothesis testing of correlated sources and give further evidence on the existence of NPPT bound entanglement. In the second part, we study the potential as well as the limitations of a quantum computer for calculating properties of many-body systems. First we analyse the usefulness of quantum computation to calculate additive approximations to partition functions and spectral densities of local Hamiltonians. We then show that the determination of ground state energies of local Hamiltonians with an inverse polynomial spectral gap is QCMA-hard. In the third and last part, we approach the problem of quantum simulating many-body systems from a more pragmatic point of view. We analyze the realization of paradigmatic condensed matter Hamiltonians in arrays of coupled microcavities, such as the Bose-Hubbard and the anisotropic Heisenberg models, and discuss the feasibility of an experimental realization with state-of-the-art current technology.

Brandao, Fernando G. S. L.

2008-10-01

64

Many-body dynamics of a Bose-Einstein condensate collapsing by quantum tunneling  

NASA Astrophysics Data System (ADS)

The dynamics of a Bose-Einstein condensate of atoms having attractive interactions is studied using quantum many-body simulations. The collapse of the condensate by quantum tunneling is numerically demonstrated, and the tunneling rate is calculated. The correlation properties of the quantum many-body state are investigated.

Saito, Hiroki

2014-02-01

65

Many-body quantum chaos: Recent developments and applications to nuclei  

NASA Astrophysics Data System (ADS)

In the last decade, there has been an increasing interest in the analysis of energy level spectra and wave functions of nuclei, particles, atoms and other quantum many-body systems by means of statistical methods and random matrix ensembles. The concept of quantum chaos plays a central role for understanding the universal properties of the energy spectrum of quantum systems. Since these properties concern the whole spectrum, statistical methods become an essential tool. Besides random matrix theory, new theoretical developments making use of information theory, time series analysis, and the merging of thermodynamics and the semiclassical approximation are emphasized. Applications of these methods to quantum systems, especially to atomic nuclei, are reviewed. We focus on recent developments like the study of “imperfect spectra” to estimate the degree of symmetry breaking or the fraction of missing levels, the existence of chaos remnants in nuclear masses, the onset of chaos in nuclei, and advances in the comprehension of the Hamiltonian structure in many-body systems. Finally, some applications of statistical spectroscopy methods generated by many-body chaos and two-body random matrix ensembles are described, with emphasis on Gamow-Teller strength sums and beta decay rates for stellar evolution and supernovae.

Gómez, J. M. G.; Kar, K.; Kota, V. K. B.; Molina, R. A.; Relaño, A.; Retamosa, J.

2011-03-01

66

(Super)conformal many-body quantum mechanics with extended supersymmetry  

Microsoft Academic Search

We study N=4 supersymmetric quantum-mechanical many-body systems with M bosonic and 4M fermionic degrees of freedom. We also investigate the further restrictions of conformal and superconformal invariance. In particular, we construct conformal N=4 extensions of the AM-1 Calogero models, which for generic values of the coupling constant are not SU(1,1|2) superconformal. This class of models is also extended to arbitrary

Niclas Wyllard

2000-01-01

67

Expansion of the Gibbs potential for quantum many-body systems: general formalism with applications to the spin glass and the weakly nonideal Bose gas.  

PubMed

For general quantum systems the power expansion of the Gibbs potential and consequently the power expansion of the self-energy is derived in terms of the interaction strength. Employing a generalization of the projector technique, a compact representation of the general terms of the expansion results. The general aspects of the approach are discussed with special emphasis on the effects characteristic for quantum systems. The expansion is systematic and leads directly to contributions beyond the mean field of all thermodynamic quantities. These features are explicitly demonstrated and illustrated for two nontrivial systems, the infinite-range quantum spin glass and the weakly interacting Bose gas. The Onsager terms of both systems are calculated, which represent the first beyond-mean-field contributions. For the spin glass Thouless-Anderson-Palmer-like equations are presented and discussed in the paramagnetic region. The investigation of the Bose gas leads to a beyond-mean-field thermodynamic description. At the Bose-Einstein condensation temperature complete agreement is found with the results presented recently by alternative techniques. PMID:16486238

Plefka, T

2006-01-01

68

Path integral Monte Carlo for dissipative many-body systems  

Microsoft Academic Search

We address the possibility of performing numerical Monte Carlo simulations for the thermodynamics of quantum dissipative systems. Dissipation is considered within the Caldeira-Leggett formulation, which describes the system in the path-integral formalism through the inclusion of an influence action that is bilocal and quadratic in the system's coordinates. At a first sight the usual direct approach of discretizing the path

Luca Capriotti; Alessandro Cuccoli; Andrea Fubini; Valerio Tognetti; Ruggero Vaia

2003-01-01

69

Many-body exciton states in self-assembled quantum dots coupled to a Fermi sea  

NASA Astrophysics Data System (ADS)

Using voltage dependent photoluminescence spectroscopy we have studied the coupling between QD states and the continuum of states of a Fermi sea of electrons in the close proximity of a self-assembled InAs quantum dot embedded in GaAs. This coupling gives rise to new optical transitions, manifesting the formation of many-body exciton states. The lines in the photoluminescence spectra can be well explained within the Anderson and Mahan exciton models. The presence of Mahan excitons originates from the Coulomb interaction between electrons in the Fermi sea and the hole(s) in the QD whereas a the second type of many-body exciton is due to a hybridized exciton originating from the tunnel interaction between the continuum of states in the Fermi sea and the localized state in the QD. Our study demonstrates the possibility to investigate a variety of many-body states in QDs coupled to a Fermi sea and opens the way to investigate optically the Kondo effect and related spin phenomena in these systems.

Koenraad, P. M.; Kleemans, N. A. J. M.; van Bree, J.; Govorov, A. O.; Hamhuis, G. J.; Notzel, R.; Silov, A. Yu.

2010-03-01

70

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

71

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

PubMed Central

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.

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

2012-01-01

72

Vibrational many-body methods for molecules and extended systems  

NASA Astrophysics Data System (ADS)

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

Keceli, Murat

73

Many-Body Effects and Lineshape of Intersubband Transitions in Semiconductor Quantum Wells  

NASA Technical Reports Server (NTRS)

Intersubband Transition (ISBT) infrared (IR) absorption and PL in InAs/AlSb were studied for narrow Quantum Wells (QWs). A large redshift was observed (7-10 meV) as temperature increased. A comprehensive many-body theory was developed for ISBTs including contributions of c-c and c-phonon scatterings. Many-body effects were studied systematically for ISBTs. Redshift and linewidth dependence on temperature, as well as spectral features were well explained by theory.

Ning, Cun-Zheng

2003-01-01

74

Quantum-circuit design for efficient simulations of many-body quantum dynamics  

NASA Astrophysics Data System (ADS)

We construct an efficient autonomous quantum-circuit design algorithm for creating efficient quantum circuits to simulate Hamiltonian many-body quantum dynamics for arbitrary input states. The resultant quantum circuits have optimal space complexity and employ a sequence of gates that is close to optimal with respect to time complexity. We also devise an algorithm that exploits commutativity to optimize the circuits for parallel execution. As examples, we show how our autonomous algorithm constructs circuits for simulating the dynamics of Kitaev's honeycomb model and the Bardeen-Cooper-Schrieffer model of superconductivity. Furthermore, we provide numerical evidence that the rigorously proven upper bounds for the simulation error here and in previous work may sometimes overestimate the error by orders of magnitude compared to the best achievable performance for some physics-inspired simulations.

Raeisi, Sadegh; Wiebe, Nathan; Sanders, Barry C.

2012-10-01

75

Strongdeco: Expansion of analytical, strongly correlated quantum states into a many-body basis  

NASA Astrophysics Data System (ADS)

We provide a Mathematica code for decomposing strongly correlated quantum states described by a first-quantized, analytical wave function into many-body Fock states. Within them, the single-particle occupations refer to the subset of Fock-Darwin functions with no nodes. Such states, commonly appearing in two-dimensional systems subjected to gauge fields, were first discussed in the context of quantum Hall physics and are nowadays very relevant in the field of ultracold quantum gases. As important examples, we explicitly apply our decomposition scheme to the prominent Laughlin and Pfaffian states. This allows for easily calculating the overlap between arbitrary states with these highly correlated test states, and thus provides a useful tool to classify correlated quantum systems. Furthermore, we can directly read off the angular momentum distribution of a state from its decomposition. Finally we make use of our code to calculate the normalization factors for Laughlin's famous quasi-particle/quasi-hole excitations, from which we gain insight into the intriguing fractional behavior of these excitations. Program summaryProgram title: Strongdeco Catalogue identifier: AELA_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AELA_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 5475 No. of bytes in distributed program, including test data, etc.: 31 071 Distribution format: tar.gz Programming language: Mathematica Computer: Any computer on which Mathematica can be installed Operating system: Linux, Windows, Mac Classification: 2.9 Nature of problem: Analysis of strongly correlated quantum states. Solution method: The program makes use of the tools developed in Mathematica to deal with multivariate polynomials to decompose analytical strongly correlated states of bosons and fermions into a standard many-body basis. Operations with polynomials, determinants and permanents are the basic tools. Running time: The distributed notebook takes a couple of minutes to run.

Juliá-Díaz, Bruno; Graß, Tobias

2012-03-01

76

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

Microsoft Academic Search

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

77

Quantum gases. Observation of many-body dynamics in long-range tunneling after a quantum quench.  

PubMed

Quantum tunneling is at the heart of many low-temperature phenomena. In strongly correlated lattice systems, tunneling is responsible for inducing effective interactions, and long-range tunneling substantially alters many-body properties in and out of equilibrium. We observe resonantly enhanced long-range quantum tunneling in one-dimensional Mott-insulating Hubbard chains that are suddenly quenched into a tilted configuration. Higher-order tunneling processes over up to five lattice sites are observed as resonances in the number of doubly occupied sites when the tilt per site is tuned to integer fractions of the Mott gap. This forms a basis for a controlled study of many-body dynamics driven by higher-order tunneling and demonstrates that when some degrees of freedom are frozen out, phenomena that are driven by small-amplitude tunneling terms can still be observed. PMID:24926015

Meinert, Florian; Mark, Manfred J; Kirilov, Emil; Lauber, Katharina; Weinmann, Philipp; Gröbner, Michael; Daley, Andrew J; Nägerl, Hanns-Christoph

2014-06-13

78

Ultrafast dynamics of many-body processes and fundamental quantum mechanical phenomena in semiconductors  

PubMed Central

The large dielectric constant and small effective mass in a semiconductor allows a description of its electronic states in terms of envelope wavefunctions whose energy, time, and length scales are mesoscopic, i.e., halfway between those of atomic and those of condensed matter systems. This property makes it possible to demonstrate and investigate many quantum mechanical, many-body, and quantum kinetic phenomena with tabletop experiments that would be nearly impossible in other systems. This, along with the ability to custom-design semiconductor nanostructures, makes semiconductors an ideal laboratory for experimental investigations. We present an overview of some of the most exciting results obtained in semiconductors in recent years using the technique of ultrafast nonlinear optical spectrocopy. These results show that Coulomb correlation plays a major role in semiconductors and makes them behave more like a strongly interacting system than like an atomic system. The results provide insights into the physics of strongly interacting systems that are relevant to other condensed matter systems, but not easily accessible in other materials.

Chemla, Daniel S.; Shah, Jagdeep

2000-01-01

79

Many-body exciton states in self-assembled quantum dots coupled to a Fermi sea  

NASA Astrophysics Data System (ADS)

Many-body interactions give rise to fascinating physics such as the X-ray Fermi-edge singularity in metals, the Kondo effect in the resistance of metals with magnetic impurities and the fractional quantum Hall effect. Here we report the observation of striking many-body effects in the optical spectra of a semiconductor quantum dot interacting with a degenerate electron gas. A semiconductor quantum dot is an artificial atom, the properties of which can be controlled by means of a tunnel coupling between a metallic contact and the quantum dot. Previous studies concern mostly the regime of weak tunnel coupling, whereas here we investigate the regime of strong coupling, which markedly modifies the optical spectra. In particular we observe two many-body exciton states: Mahan and hybrid excitons. These experimental results open the route towards the observation of a tunable Kondo effect in excited states of semiconductors and are of importance for the technological implementation of quantum dots in devices for quantum information processing.

Kleemans, N. A. J. M.; van Bree, J.; Govorov, A. O.; Keizer, J. G.; Hamhuis, G. J.; Nötzel, R.; Silov, A. Yu.; Koenraad, P. M.

2010-07-01

80

Many-Body Effect in Spin Dephasing in n-Type GaAs Quantum Wells  

NASA Astrophysics Data System (ADS)

By constructing and numerically solving the kinetic Bloch equations we perform a many-body study of the spin dephasing due to the D'yakonov-Perel' effect in n-type GaAs (100) quantum wells for high temperatures. In our study, we include the spin-conserving scattering such as the electron-phonon, the electron-nonmagnetic impurity as well as the electron-electron Coulomb scattering into consideration. The dephasing obtained from our theory contains both the single-particle and the many-body contributions with the latter originating from the inhomogeneous broadening introduced by the DP term [J. Supercond.: Incorp. Novel Magn. 14 (2001) 245 Eur. Phys. J. B 18 (2000) 373]. Our result agrees very well with the experimental data [Phys. Rev. B 62 (2000) 13034] of Malinowski et al. We further show that in the case we study, the spin dephasing is dominated by the many-body effect.

Weng, Ming-Qi; Wu, Ming-Wei

2005-03-01

81

Exact solvability of interacting many body lattice systems  

Microsoft Academic Search

We address the problem of exactly describing stochastic nonequilibrium systems that are widely used to model one-dimensional\\u000a transport, in biology, traffic flow and others. We review the matrix product states ansatz to interacting multiparticle systems\\u000a and its extension to a tridiagonal (generalized Onsager) algebra approach. The stationary probability distribution is expressed\\u000a as a matrix product state with respect to a

Boyka Aneva

2010-01-01

82

An efficient and accurate quantum lattice-gas model for the many-body Schrödinger wave equation  

Microsoft Academic Search

Presented is quantum lattice-gas model for simulating the time-dependent evolution of a many-body quantum mechanical system of particles governed by the non-relativistic Schrödinger wave equation with an external scalar potential. A variety of computational demonstrations are given where the numerical predictions are compared with exact analytical solutions. In all cases, the model results accurately agree with the analytical predictions and

Jeffrey Yepez; Bruce Boghosian

2002-01-01

83

Many-body optical gain in CdZnO/ZnMgO quantum well lasers  

NASA Astrophysics Data System (ADS)

The Many-body optical gain in CdZnO/MgZnO quantum well (QW) structures with spontaneous and piezoelectric polarizations are investigated by using the non-Markovian gain model with many-body effects. As the Cd composition increases, the sign change of the internal field is observed and the bottom of the potential well in the conduction band is shown to exist on the right side in the well. The CdZnO/MgZnO QW structure with high Cd composition is found to have smaller optical gain because the strain-induced piezoelectric polarization and the spontaneous polarization in the well increase with the inclusion of Cd.

Li, Mingkai; Won Kang, Tae; Joo Lee, Seung; Park, Seoung-Hwan; Ahn, Doyeol; Ihm, Gukhyung

2010-01-01

84

First-principles path-integral renormalization-group method for Coulombic many-body systems  

SciTech Connect

An approach for obtaining the ground state of Coulombic many-body systems is presented. This approach is based on the path-integral renormalization-group method with nonorthogonal Slater determinants, is free of the negative sign problem, and can handle higher dimensional systems with consideration of the correlation effect. Furthermore, it can be easily extended to the multicomponent quantum systems that contain more than two kinds of quantum particles. According to our results obtained with the present approach, it achieves the same accuracy as the variational Monte Carlo method with a few Slater determinants and enables us to study the entire ground state consisting of electrons and nuclei without the need to use the Born-Oppenheimer approximation.

Kojo, Masashi; Hirose, Kikuji [Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871 (Japan)

2009-10-15

85

Hybrid Quantum Magnetism in Circuit QED: From Spin-Photon Waves to Many-Body Spectroscopy  

NASA Astrophysics Data System (ADS)

We introduce a model of quantum magnetism induced by the nonperturbative exchange of microwave photons between distant superconducting qubits. By interconnecting qubits and cavities, we obtain a spin-boson lattice model that exhibits a quantum phase transition where both qubits and cavities spontaneously polarize. We present a many-body ansatz that captures this phenomenon all the way, from a the perturbative dispersive regime where photons can be traced out, to the nonperturbative ultrastrong coupling regime where photons must be treated on the same footing as qubits. Our ansatz also reproduces the low-energy excitations, which are described by hybridized spin-photon quasiparticles, and can be probed spectroscopically from transmission experiments in circuit QED, as shown by simulating a possible experiment by matrix-product-state methods.

Kurcz, Andreas; Bermudez, Alejandro; García-Ripoll, Juan José

2014-05-01

86

Hybrid Quantum Magnetism in Circuit QED: From Spin-Photon Waves to Many-Body Spectroscopy.  

PubMed

We introduce a model of quantum magnetism induced by the nonperturbative exchange of microwave photons between distant superconducting qubits. By interconnecting qubits and cavities, we obtain a spin-boson lattice model that exhibits a quantum phase transition where both qubits and cavities spontaneously polarize. We present a many-body ansatz that captures this phenomenon all the way, from a the perturbative dispersive regime where photons can be traced out, to the nonperturbative ultrastrong coupling regime where photons must be treated on the same footing as qubits. Our ansatz also reproduces the low-energy excitations, which are described by hybridized spin-photon quasiparticles, and can be probed spectroscopically from transmission experiments in circuit QED, as shown by simulating a possible experiment by matrix-product-state methods. PMID:24856680

Kurcz, Andreas; Bermudez, Alejandro; García-Ripoll, Juan José

2014-05-01

87

Single-particle and many-body analyses of a quasiperiodic integrable system after a quench  

NASA Astrophysics Data System (ADS)

In general, isolated integrable quantum systems have been found to relax to an apparent equilibrium state in which the expectation values of few-body observables are described by the generalized Gibbs ensemble. However, recent work has shown that relaxation to such a generalized statistical ensemble can be precluded by localization in a quasiperiodic lattice system. Here we undertake complementary single-particle and many-body analyses of noninteracting spinless fermions and hard-core bosons within the Aubry-André model to gain insight into this phenomenon. Our investigations span both the localized and delocalized regimes of the quasiperiodic system, as well as the critical point separating the two. Considering first the case of spinless fermions, we study the dynamics of the momentum distribution function and characterize the effects of real-space and momentum-space localization on the relevant single-particle wave functions and correlation functions. We show that although some observables do not relax in the delocalized and localized regimes, the observables that do relax in these regimes do so in a manner consistent with a recently proposed Gaussian equilibration scenario, whereas relaxation at the critical point has a more exotic character. We also construct various statistical ensembles from the many-body eigenstates of the fermionic and bosonic Hamiltonians and study the effect of localization on their properties.

He, Kai; Santos, Lea F.; Wright, Tod M.; Rigol, Marcos

2013-06-01

88

Collective many-body van der Waals interactions in molecular systems  

PubMed Central

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.

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

2012-01-01

89

Inclusion of finite-temperature effects in a nonlinear description of strongly interacting many-body systems  

Microsoft Academic Search

We consider a class of quantum many-body systems which are coupled by one- and two-body interactions. Following our earlier work on deriving nonlinear field equations of motion for such systems, we incorporate the effects of finite temperature through a semiclassical free energy functional. We first obtain implicit analytical formulas for the entropy density which lend themselves to simple asymptotic expansions.

J. A. Tuszy?ski; J. M. Dixon

2000-01-01

90

Hilbert-Glass Transition: New Universality of Temperature-Tuned Many-Body Dynamical Quantum Criticality  

NASA Astrophysics Data System (ADS)

We study a new class of unconventional critical phenomena that is characterized by singularities only in dynamical quantities and has no thermodynamic signatures. One example of such a transition is the recently proposed many-body localization-delocalization transition, in which transport coefficients vanish at a critical temperature with no singularities in thermodynamic observables. Describing this purely dynamical quantum criticality is technically challenging as understanding the finite-temperature dynamics necessarily requires averaging over a large number of matrix elements between many-body eigenstates. Here, we develop a real-space renormalization group method for excited states that allows us to overcome this challenge in a large class of models. We characterize a specific example: the 1 D disordered transverse-field Ising model with generic interactions. While thermodynamic phase transitions are generally forbidden in this model, using the real-space renormalization group method for excited states we find a finite-temperature dynamical transition between two localized phases. The transition is characterized by nonanalyticities in the low-frequency heat conductivity and in the long-time (dynamic) spin correlation function. The latter is a consequence of an up-down spin symmetry that results in the appearance of an Edwards-Anderson-like order parameter in one of the localized phases.

Pekker, David; Refael, Gil; Altman, Ehud; Demler, Eugene; Oganesyan, Vadim

2014-01-01

91

Many-body Effects in a Laterally Inhomogeneous Semiconductor Quantum Well  

NASA Technical Reports Server (NTRS)

Many body effects on conduction and diffusion of electrons and holes in a semiconductor quantum well are studied using a microscopic theory. The roles played by the screened Hartree-Fock (SHE) terms and the scattering terms are examined. It is found that the electron and hole conductivities depend only on the scattering terms, while the two-component electron-hole diffusion coefficients depend on both the SHE part and the scattering part. We show that, in the limit of the ambipolax diffusion approximation, however, the diffusion coefficients for carrier density and temperature are independent of electron-hole scattering. In particular, we found that the SHE terms lead to a reduction of density-diffusion coefficients and an increase in temperature-diffusion coefficients. Such a reduction or increase is explained in terms of a density-and temperature dependent energy landscape created by the bandgap renormalization.

Ning, Cun-Zheng; Li, Jian-Zhong; Biegel, Bryan A. (Technical Monitor)

2002-01-01

92

Renormalization of myoglobin-ligand binding energetics by quantum many-body effects.  

PubMed

We carry out a first-principles atomistic study of the electronic mechanisms of ligand binding and discrimination in the myoglobin protein. Electronic correlation effects are taken into account using one of the most advanced methods currently available, namely a linear-scaling density functional theory (DFT) approach wherein the treatment of localized iron 3d electrons is further refined using dynamical mean-field theory. This combination of methods explicitly accounts for dynamical and multireference quantum physics, such as valence and spin fluctuations, of the 3d electrons, while treating a significant proportion of the protein (more than 1,000 atoms) with DFT. The computed electronic structure of the myoglobin complexes and the nature of the Fe-O2 bonding are validated against experimental spectroscopic observables. We elucidate and solve a long-standing problem related to the quantum-mechanical description of the respiration process, namely that DFT calculations predict a strong imbalance between O2 and CO binding, favoring the latter to an unphysically large extent. We show that the explicit inclusion of the many-body effects induced by the Hund's coupling mechanism results in the correct prediction of similar binding energies for oxy- and carbonmonoxymyoglobin. PMID:24717844

Weber, Cédric; Cole, Daniel J; O'Regan, David D; Payne, Mike C

2014-04-22

93

Renormalization of myoglobin-ligand binding energetics by quantum many-body effects  

PubMed Central

We carry out a first-principles atomistic study of the electronic mechanisms of ligand binding and discrimination in the myoglobin protein. Electronic correlation effects are taken into account using one of the most advanced methods currently available, namely a linear-scaling density functional theory (DFT) approach wherein the treatment of localized iron 3d electrons is further refined using dynamical mean-field theory. This combination of methods explicitly accounts for dynamical and multireference quantum physics, such as valence and spin fluctuations, of the 3d electrons, while treating a significant proportion of the protein (more than 1,000 atoms) with DFT. The computed electronic structure of the myoglobin complexes and the nature of the Fe–O2 bonding are validated against experimental spectroscopic observables. We elucidate and solve a long-standing problem related to the quantum-mechanical description of the respiration process, namely that DFT calculations predict a strong imbalance between O2 and CO binding, favoring the latter to an unphysically large extent. We show that the explicit inclusion of the many-body effects induced by the Hund’s coupling mechanism results in the correct prediction of similar binding energies for oxy- and carbonmonoxymyoglobin.

Weber, Cedric; Cole, Daniel J.; O'Regan, David D.; Payne, Mike C.

2014-01-01

94

Quantum many-body effects on the electric and thermoelectric response of molecular heterojunctions  

NASA Astrophysics Data System (ADS)

A semi-empirical ?-electron Hamiltonian (extended Hubbard model) is used to model the electronic degrees of freedom most relevant for transport in a heterojunction consisting of a conjugated organic molecule coupled to two (or more) metallic electrodes. With an appropriate choice of parameters, the complete spectrum of electronic excitations of the molecule up to 8--10eV can be accurately described,^1 which is essential to accurately model transport far from equilibrium. The electric and thermoelectric response of the junction is calculated within a many-body theory of transport based on nonequilibrium Green's functions. For benzenedithiol-Au junctions, the parameters characterizing the lead-molecule coupling (tunneling width and chemical potential offset) are determined by comparison to linear-response measurements of conductance and thermopower. The nonlinear transport can then be predicted: the differential conductance as a function of gate and bias voltages exhibits clear signatures of charge quantization and resonant tunneling through excited states, with an irregular ``molecular diamond'' structure analogous to the regular Coulomb diamonds observed in quantum dot transport experiments. Several other small conjugated organic molecules are also investigated. ^1C. W. M. Castelton and W. Barford, J. Chem. Phys. 117, 3570 (2002).

Bergfield, Justin; Stafford, Charles

2009-03-01

95

Many Body Density Matrix Theory  

NASA Astrophysics Data System (ADS)

One fundamental limitation of quantum chemical methods is the accuracy of the approximate many-body theoretical framework. Accurate many-body formalisms for quantum chemical methods do exist, but these methods are computationally very expensive. Methods also exist that are much less computationally expensive such as Hatree-Fock, Density Functional and the Hybrid Functional theories, but at a reduced representation of the exact many-body ground state. This severely limits either the system size that can be addressed accurately, or the accuracy of the representation. What is needed is a method that represents the many-body ground states accurately, but with a low computational cost. Recently, a method for determining the response, to any order of the perturbation, within the density matrix formalism has been discovered. This method opens up the possibility of computing the variational many-body ground states to unprecedented accuracy within a simplified computational approach. We report on the theoretical development of this methodology, which we refer to as Many Body Density Matrix Theory. This theory has many significant advantages over existing methods. One, its computational cost is equivalent to Hartree-Fock or Density Functional theory. Two it is a variational upper bound to the exact many-body ground state energy. Three, like Hartree-Fock, it has no self-interaction. And four, it is size extensive.

Tymczak, C. J.

2011-03-01

96

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

NASA Astrophysics Data System (ADS)

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

Salerno, Mario; Popkov, Vladislav

2010-07-01

97

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

PubMed

Spectral properties of the reduced density matrix (RDM) of permutational invariant quantum many-body systems are investigated. The RDM block diagonalization which accounts for all symmetries of the Hamiltonian is achieved. The analytical expression of the RDM spectrum is provided for arbitrary parameters and rigorously proved in the thermodynamical limit. The existence of several sum rules and recurrence relations among RDM eigenvalues is also demonstrated and the distribution function of RDM eigenvalues (including degeneracies) characterized. In particular, we prove that the distribution function approaches a two-dimensional Gaussian in the limit of large subsystem sizes n>1. As a physical application we discuss the von Neumann entropy (VNE) of a block of size n for a system of hard-core bosons on a complete graph, as a function of n and of the temperature T. The occurrence of a crossover of VNE from purely logarithmic behavior at T=0 to a purely linear behavior in n for T?Tc, is demonstrated. PMID:20866600

Salerno, Mario; Popkov, Vladislav

2010-07-01

98

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

NASA Astrophysics Data System (ADS)

This work presents a new Microsoft Visual C# .NET code library, conceived as a general object oriented solution for chaos analysis of three-dimensional, relativistic many-body systems. In this context, we implemented the Lyapunov exponent and the “fragmentation level” (defined using the graph theory and the Shannon entropy). Inspired by existing studies on billiard nuclear models and clusters of galaxies, we tried to apply the virial theorem for a simplified many-body system composed by nucleons. A possible application of the “virial coefficient” to the stability analysis of chaotic systems is also discussed. Catalogue identifier: AEGH_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEGH_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 30?053 No. of bytes in distributed program, including test data, etc.: 801?258 Distribution format: tar.gz Programming language: Visual C# .NET 2005 Computer: PC Operating system: .Net Framework 2.0 running on MS Windows Has the code been vectorized or parallelized?: Each many-body system is simulated on a separate execution thread RAM: 128 Megabytes Classification: 6.2, 6.5 External routines: .Net Framework 2.0 Library Nature of problem: Chaos analysis of three-dimensional, relativistic many-body systems. Solution method: Second order Runge-Kutta algorithm for simulating relativistic many-body systems. Object oriented solution, easy to reuse, extend and customize, in any development environment which accepts .Net assemblies or COM components. Implementation of: Lyapunov exponent, “fragmentation level”, “average system radius”, “virial coefficient”, and energy conservation precision test. Additional comments: Easy copy/paste based deployment method. Running time: Quadratic complexity.

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

2010-08-01

99

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

NASA Astrophysics Data System (ADS)

The International EFES-IN2P3 conference on "Many body correlations from dilute to dense nuclear systems" was held at the Institut Henri Poincaré (IHP), Paris, France, from 15-18 February 2011, on the occasion of the retirement of our colleague Peter Schuck. Correlations play a decisive role in various many-body systems such as nuclear systems, condensed matter and quantum gases. Important examples include: pairing correlations (Cooper pairs) which give rise to nuclear superfluidity (analogous to superconductivity in condensed matter); particle-hole (RPA) correlations in the description of the ground state beyond mean-field theory; clusters; and ?-particle correlations in certain nuclei. Also, the nucleons themselves can be viewed as clusters of three quarks. During the past few years, researchers have started to study how the character of these correlations changes with the variation of the density. For instance, the Cooper pairs in dense matter can transform into a Bose-Einstein condensate (BEC) of true bound states at low density (this is the BCS-BEC crossover studied in ultracold Fermi gases). Similar effects play a role in neutron matter at low density, e.g., in the "neutron skin" of exotic nuclei. The ?-cluster correlation becomes particularly important at lower density, such as in the excited states of some nuclei (e.g., the ?-condensate-like structure in the Hoyle state of 12C) or in the formation of compact stars. In addition to nuclear physics, topics from astrophysics (neutron stars), condensed matter, and quantum gases were discussed in 48 talks and 19 posters, allowing the almost 90 participants from different communities to exchange their ideas, experiences and methods. The conference dinner took place at the Musée d'Orsay, and all the participants enjoyed the very pleasant atmosphere. One session of the conference was dedicated to the celebration of Peter's retirement. We would like to take this opportunity to wish Peter all the best and we hope that he will continue his scientific work full of creative and original ideas. We would like to thank all those who helped to make the conference a success: Nguyen van Giai, S Fujii, J Margueron, K Hagino, and Y Kanada-En'yo for their help with the organization; the advisory committee for suggesting invited speakers; V Frois for her administrative help; L Petizon for the website; and the director of IPN Orsay, F Azaiez, for his support. We are indebted to IHP for providing the lecture hall free of charge, and we acknowledge the financial support from JSPS through its EFES core-to-core program, from CNRS (IN2P3 and INP), and from LIA France-Japon. Last but not least, we are grateful to all of the participants for making the conference exciting and successful. Takaharu Otsuka, Michael Urban, Taiichi YamadaEditors of the proceedings

Otsuka, Takaharu; Urban, Michael; Yamada, Taiichi

2011-09-01

100

Coherent excitonic coupling in an asymmetric double InGaAs quantum well arises from many-body effects.  

PubMed

We study an asymmetric double InGaAs quantum well using optical two-dimensional coherent spectroscopy. The collection of zero-quantum, one-quantum, and two-quantum two-dimensional spectra provides a unique and comprehensive picture of the double well coherent optical response. Coherent and incoherent contributions to the coupling between the two quantum well excitons are clearly separated. An excellent agreement with density matrix calculations reveals that coherent interwell coupling originates from many-body interactions. PMID:24580472

Nardin, Gaël; Moody, Galan; Singh, Rohan; Autry, Travis M; Li, Hebin; Morier-Genoud, François; Cundiff, Steven T

2014-01-31

101

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. Program summaryProgram title: Chaos Many-Body Engine v02 Catalogue identifier: AEGH_v2_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEGH_v2_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 184 628 No. of bytes in distributed program, including test data, etc.: 7 905 425 Distribution format: tar.gz Programming language: Visual C#.NET 2005 Computer: PC Operating system: Net Framework 2.0 running on MS Windows Has the code been vectorized or parallelized?: Each many-body system is simulated on a separate execution thread. One processor used for each many-body system. RAM: 128 Megabytes Classification: 6.2, 6.5 Catalogue identifier of previous version: AEGH_v1_0 Journal reference of previous version: Comput. Phys. Comm. 181 (2010) 1464 External routines: Net Framework 2.0 Library Does the new version supersede the previous version?: Yes Nature of problem: Chaos analysis of three-dimensional, relativistic many-body systems with reactions. Solution method: Second order Runge-Kutta algorithm for simulating relativistic many-body systems with reactions. Object oriented solution, easy to reuse, extend and customize, in any development environment which accepts .Net assemblies or COM components. Treatment of two particles reactions and decays. For each particle, calculation of the time measured in the particle reference frame, according to the instantaneous velocity. Possibility to dynamically add particle properties (spin, isospin, etc.), and reactions/decays, using a specific XML input file. Basic support for Monte Carlo simulations. Implementation of: Lyapunov exponent, "fragmentation level", "average system radius", "virial coefficient", "clusterization map", and energy conservation precision test. As an example of use, we implemented a toy-model for nuclear relativistic collisions at 4.5 A GeV/c. Reasons for new version: Following our goal of applying chaos theory to nuclear relativistic collisions at 4.5 A GeV/c, we developed a reaction module integrated with the Chaos Many-Body Engine. Summary of revisions: In the previous version, inheriting the Particle class was the only possibility of implementing more particle properties (spin, isospin, and so on). In the new version, particle properties can be dynamically added using a dictionary object. The application was improved in order to calculate the time measured in the own reference frame of each particle. We developed a reaction module for treating the following processes: two particles reactions: a+b?c+d, decays: a?c+d, stimulated decays, more complicated schemas, implemented as various combinations of previous reactions. Following our goal of creating a flexible application, the reactions list, including the corresponding properties (cross sections, particles lifetime, etc.), could be supplied as parameter, using a specific XML configuration file. The simulation output files were modified for systems with reactions, assuring also the backward compatibility. We propose the "Clusterization Map" as a new investigation method of many-

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

2012-04-01

102

The quantified NTO analysis for the electronic excitations of molecular many-body systems  

NASA Astrophysics Data System (ADS)

We show that the origin of electronic transitions of molecular many-body systems can be investigated by a quantified natural transition orbitals (QNTO) analysis and the electronic excitations of the total system can be mapped onto a standard orbitals set of a reference system. We further illustrate QNTO on molecular systems by studying the origin of electronic transitions of DNA moiety, thymine and thymidine. This QNTO analysis also allows us to assess the performance of various functionals used in time-dependent density functional response theory.

Li, Jian-Hao; Chai, Jeng-Da; Guo, Guang-Yu; Hayashi, Michitoshi

2011-10-01

103

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

104

Force field development for actinyl ions via quantum mechanical calculations: an approach to account for many body solvation effects.  

PubMed

Advances in computational algorithms and methodologies make it possible to use highly accurate quantum mechanical calculations to develop force fields (pair-wise additive intermolecular potentials) for condensed phase simulations. Despite these advances, this approach faces numerous hurdles for the case of actinyl ions, AcO2(n+) (high-oxidation-state actinide dioxo cations), mainly due to the complex electronic structure resulting from an interplay of s, p, d, and f valence orbitals. Traditional methods use a pair of molecules (“dimer”) to generate a potential energy surface (PES) for force field parametrization based on the assumption that many body polarization effects are negligible. We show that this is a poor approximation for aqueous phase uranyl ions and present an alternative approach for the development of actinyl ion force fields that includes important many body solvation effects. Force fields are developed for the UO2(2+) ion with the SPC/Fw, TIP3P, TIP4P, and TIP5P water models and are validated by carrying out detailed molecular simulations on the uranyl aqua ion, one of the most characterized actinide systems. It is shown that the force fields faithfully reproduce available experimental structural data and hydration free energies. Failure to account for solvation effects when generating PES leads to overbinding between UO2(2+) and water, resulting in incorrect hydration free energies and coordination numbers. A detailed analysis of arrangement of water molecules in the first and second solvation shell of UO2(2+) is presented. The use of a simple functional form involving the sum of Lennard-Jones + Coulomb potentials makes the new force field compatible with a large number of available molecular simulation engines and common force fields. PMID:22857380

Rai, Neeraj; Tiwari, Surya P; Maginn, Edward J

2012-09-01

105

Derivation of the Euler equations from many-body quantum mechanics  

Microsoft Academic Search

The Heisenberg dynamics of the energy, momentum, and particle densities for fermions with short-range pair interactions is shown to converge to the compressible Euler equations in the hydrodynamic limit. The pressure function is given by the standard formula from quantum statistical mechanics with the two-body potential under consideration. Our derivation is based on a quantum version of the entropy method

Bruno Nachtergaele; Horng-Tzer Yau

2002-01-01

106

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

107

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

NASA Astrophysics Data System (ADS)

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

Krajewski, Florian R.; Müser, Martin H.

2005-07-01

108

Many-body Coulomb effects in room-temperature II--VI quantum well semiconductor lasers  

SciTech Connect

This letter investigates the gain medium properties in II--VI blue-green quantum well semiconductor lasers, including band structure and carrier interactions in the electron-hole plasma are found to be significantly more important than in infrared III--V lasers. In particular, the interband Coulombic enhancement of the optical transitions, together with a band gap renormalization result in an increase in gain and a reduction in the antiguiding or linewidth enhancement factor. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.

Chow, W.W. [Semiconductor Physics Department, Sandia National Laboratories, Albuquerque, New Mexico 87185-0601 (United States)] [Semiconductor Physics Department, Sandia National Laboratories, Albuquerque, New Mexico 87185-0601 (United States); Koch, S.W. [Department of Physics and Materials Sciences Center, Philipps University, 35032 Marburg (Germany)] [Department of Physics and Materials Sciences Center, Philipps University, 35032 Marburg (Germany)

1995-05-29

109

Efficient calculation of many-body induced electrostatics in molecular systems  

SciTech Connect

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

McLaughlin, Keith, E-mail: kmclaugh@mail.usf.edu; Cioce, Christian R.; Pham, Tony; Space, Brian [Department of Chemistry, University of South Florida, 4202 E. Fowler Ave., CHE205, Tampa, Florida 33620 (United States)] [Department of Chemistry, University of South Florida, 4202 E. Fowler Ave., CHE205, Tampa, Florida 33620 (United States); Belof, Jonathan L. [Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, California 94550 (United States)] [Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, California 94550 (United States)

2013-11-14

110

Centre-of-mass separation in quantum mechanics: Implications for the many-body treatment in quantum chemistry and solid state physics  

Microsoft Academic Search

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

111

Termination of rotational bands: disappearance of quantum many-body collectivity  

NASA Astrophysics Data System (ADS)

One of the most interesting features of nuclei is the process by which specific configurations, manifest as collective rotational bands at intermediate spin values, gradually lose their collectivity and terminate in a non-collective state at the maximum spin which can be built within the configuration. Recent advances in both experiment and theory allow the study of this nuclear structure feature in detail. The bands, which show such a continuous transition from high collectivity to a pure particle-hole (terminating) state, are generally called terminating bands or to underline their continuous character, smooth terminating bands. The best examples of such bands known at present are in the neutron-deficient A?110 mass region, where terminating configurations involving proton particle-hole excitations across the Z=50 gap can be observed over their entire spin range. The main features of band termination as a specific high-spin phenomenon inherent to finite many-fermion strongly interacting systems are overviewed, based mainly on the configuration-dependent cranked Nilsson-Strutinsky approach. The extensive experimental results on smooth terminating bands in the A?110 mass region, which have been addressed by these theoretical calculations, are presented along with the theoretical comparisons in a systematic way. In addition, specific features of band termination in other parts of the periodic chart and other possible theoretical approaches are briefly reviewed.

Afanasjev, A. V.; Fossan, D. B.; Lane, G. J.; Ragnarsson, I.

1999-12-01

112

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

113

Many body effect induced energy gap in an optically pumped graphene system  

NASA Astrophysics Data System (ADS)

We develop a simple way to investigate the energy gap induced by many body effect in optically pumped graphene at different carrier densities. The exchange self-energy and energy dispersions are obtained analytically at the long wave limit. An energy gap depending on the carrier density is observed at the Dirac point. The energy gap induced by many body effect lies in the microwave range which is in accordance with the experimental measurements. Our theoretical results indicate that the exchange interaction via Coulomb interaction can be a mechanism to create an energy gap in optically pumped graphene.

Wei, X. F.; Wang, W. Y.; Long, M. S.; Gong, Y. P.; Liu, L. W.

2014-03-01

114

Many body physics with light  

NASA Astrophysics Data System (ADS)

Systems of strongly interacting atoms and photons, which can be realized wiring up individual Cavity QED (CQED) systems into lattices, are perceived as a new platform for quantum simulation [1-3]. While sharing important properties with other systems of interacting quantum particles, the nature of light-matter interaction gives rise to unique features with no analogs in condensed matter or atomic physics setups. Such Lattice CQED systems operate on polaritonic quasi-particles that are hybrids of light and matter in a controllable proportion, combining long-range coherence of photons and strong interactions typically displayed by massive particles. In this talk, I will discuss our recent efforts [4-6] on the possibility of observing quantum many body physics and quantum phase transitions in Lattice CQED systems. Unavoidable photon loss coupled with the ease of feeding in additional photons through continuous external driving renders such lattices open quantum systems [5]. Another key aspect of many body physics with light that I will focus on is the particle number non-conserving nature of the fundamental light-matter interaction [6] and the question of what quantity, if not the chemical potential, can stabilize finite density quantum phases of correlated photons.[4pt] [1] M. J. Hartmann, F. G. Brandao, and M. B. Plenio, Laser and Photonics Reviews 2, 527 (2008).[0pt] [2] A. Tomadin and R. Fazio, JOSA B 27, A130 (2010).[0pt] [3] A. Houck, H. E. Tureci, and J. Koch, Nature Phys. 8, 292 (2012).[0pt] [4] S. Schmidt, D. Gerace, A. A. Houck, G. Blatter, and H. E. Tureci, Physical Review B 82, 100507 (2010).[0pt] [5] F. Nissen, S. Schmidt, M. Biondi, G. Blatter, H. E. Tureci, J. Keeling, Phys. Rev. Lett. 108, 233603 (2012).[0pt] [6] M. Schiro, M. Bordyuh, B. Oztop, H. E. Tureci, Phys. Rev. Lett. 109, 053601 (2012).

Tureci, Hakan E.

2013-03-01

115

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

PubMed

Electronic structure methods based on low-order "n-body" expansions are an increasingly popular means to defeat the highly nonlinear scaling of ab initio quantum chemistry calculations, taking advantage of the inherently distributable nature of the numerous subsystem calculations. Here, we examine how the finite precision of these subsystem calculations manifests in applications to large systems, in this case, a sequence of water clusters ranging in size up to [Formula: see text]. Using two different computer implementations of the n-body expansion, one fully integrated into a quantum chemistry program and the other written as a separate driver routine for the same program, we examine the reproducibility of total binding energies as a function of cluster size. The combinatorial nature of the n-body expansion amplifies subtle differences between the two implementations, especially for n ? 4, leading to total energies that differ by as much as several kcal/mol between two implementations of what is ostensibly the same method. This behavior can be understood based on a propagation-of-errors analysis applied to a closed-form expression for the n-body expansion, which is derived here for the first time. Discrepancies between the two implementations arise primarily from the Coulomb self-energy correction that is required when electrostatic embedding charges are implemented by means of an external driver program. For reliable results in large systems, our analysis suggests that script- or driver-based implementations should read binary output files from an electronic structure program, in full double precision, or better yet be fully integrated in a way that avoids the need to compute the aforementioned self-energy. Moreover, four-body and higher-order expansions may be too sensitive to numerical thresholds to be of practical use in large systems. PMID:25005278

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

2014-07-01

116

Waveguide QED: Many-body bound-state effects in coherent and Fock-state scattering from a two-level system  

Microsoft Academic Search

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

Huaixiu Zheng; Daniel J. Gauthier; Harold U. Baranger

2010-01-01

117

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

118

Many-body effects in electron spin resonance in 2D systems with Rashba spin-orbit interaction  

NASA Astrophysics Data System (ADS)

We report effects of electron–electron (e–e) interaction on electron spin resonance (ESR) in two-dimensional (2D) systems with Rashba spin–orbit interaction (SOI). Using the Hartree–Fock approximation, we demonstrate that Rashba SOI results in non-zero many-body corrections to the ESR energy. We discover that e–e interaction in 2D systems with SOI can not only enhance the ESR energy but also lead to the ESR energy reduction. The magnitude of this effect exhibits remarkable features in a wide range of parameters relevant to experiment: it is found to be rather sensitive to the sign of g-factor and the filling factor of Landau levels ?. We derive analytical expressions for many-body corrections to ESR energy and energy dispersion of spin wave excitations for the case of \

Krishtopenko, S. S.

2014-06-01

119

Many-body systems interacting via a two-body random ensemble. I. Angular momentum distribution in the ground states  

Microsoft Academic Search

In this paper we discuss in detail the P(I)'s, angular momentum I probabilities in the ground states, of many-body systems interacting via a two-body random ensemble (TBRE). In particular, we extensively apply an approach introduced in an earlier paper and compare the predicted P(I)'s with those obtained by diagonalizing a TBRE Hamiltonian. We begin with a few solvable cases, such

Y. M. Zhao; A. Arima; N. Yoshinaga

2002-01-01

120

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

121

a Solvable Model of Interacting Many Body Systems Exhibiting a Breakdown of the Boltzmann Equation  

NASA Astrophysics Data System (ADS)

In a particular exactly solvable model of an interacting system, the Boltzmann equation predicts a constant single particle density operator, whereas the exact solution gives a single particle density operator with a nontrivial time dependence. All of the time dependence of the single particle density operator is generated by the correlations.

McKellar, B. H. J.

2014-12-01

122

Relativistic nuclear many-body theory  

SciTech Connect

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

123

Excitonic analysis of many-body effects on the 1s-2p intraband transition in semiconductor systems  

NASA Astrophysics Data System (ADS)

We present a detailed study of many-body effects associated with the intraband 1s-2p transition in two- and three-dimensional photoexcited semiconductors. We employ a previously developed excitonic model to treat effects of exchange and phase space filling (PSF). In this work, we extend the model to include intraband transitions and static free-carrier screening. The exciton transition energies are renormalized by many-body interactions, and the excitonic dynamical equations provide simple expressions for the individual contributions of screening, PSF and exchange. The excitonic model correctly predicts the blue shift and bleaching of the 1s exciton resonance due to exchange and PSF. Free-carrier screening is found to enhance these effects by lowering the binding energy of the 1s exciton. In contrast, the effects of free-carrier screening on the 1s-2p transition energy are subtler. For a coherent exciton system, in the absence of free-carrier screening, exchange and PSF lead to a blue shift of the transition energy. However, screening decreases the 1s binding energy faster than the 2p binding energy, which in turn decreases the transition energy. Thus screening effects oppose exchange and PSF, and the overall magnitude and sign of the 1s-2p transition energy shift depends on the free-carrier density. Specifically, for low to moderate excitation densities, exchange and PSF can be dominated by screening, leading to a net redshift of the transition energy. The results for two- and three-dimensional systems are qualitatively similar, although the magnitude of the shift is much smaller in three dimensions.

Parks, Andrew M.; Dignam, Marc M.; Wang, Dawei

2013-05-01

124

Waveguide QED: Many-body bound-state effects in coherent and Fock-state scattering from a two-level system  

SciTech Connect

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

125

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

PubMed

Building on previous charge-optimized many-body (COMB) potentials for metallic ?-U and gaseous O2, we have developed a new potential for UO2, which also allows the simulation of U-UO2-O2 systems. The UO2 lattice parameter, elastic constants and formation energies of stoichiometric and non-stoichiometric intrinsic defects are well reproduced. Moreover, this is the first rigid-ion potential that produces the correct deviation of the Cauchy relation, as well as the first classical interatomic potential that is able to determine the defect energies of non-stoichiometric intrinsic point defects in UO2 with an appropriate reference state. The oxygen molecule interstitial in the ?-U structure is shown to decompose, with some U-O bonds approaching the natural bond length of perfect UO2. Finally, we demonstrate the capability of this COMB potential to simulate a complex system by performing a simulation of the ?-U + O2 ? UO2 phase transformation. We also identify a possible mechanism for uranium oxidation and the orientation of the resulting fluorite UO2 structure relative to the coordinate system of orthorhombic ?-U. PMID:24275484

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

2013-12-18

126

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

SciTech Connect

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

Georgescu, Ionu?, E-mail: ionutg@gmail.com; Mandelshtam, Vladimir A. [Chemistry Department, University of California, Irvine, California 92697 (United States)] [Chemistry Department, University of California, Irvine, California 92697 (United States); Jitomirskaya, Svetlana [Department of Mathematics, University of California, Irvine, California 92697 (United States)] [Department of Mathematics, University of California, Irvine, California 92697 (United States)

2013-11-28

127

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

PubMed

Given a quantum many-body system, the Self-Consistent Phonons (SCP) method provides an optimal harmonic approximation by minimizing the free energy. In particular, the SCP estimate for the vibrational ground state (zero temperature) appears to be surprisingly accurate. We explore the possibility of going beyond the SCP approximation by considering the system Hamiltonian evaluated in the harmonic eigenbasis of the SCP Hamiltonian. It appears that the SCP ground state is already uncoupled to all singly- and doubly-excited basis functions. So, in order to improve the SCP result at least triply-excited states must be included, which then reduces the error in the ground state estimate substantially. For a multidimensional system two numerical challenges arise, namely, evaluation of the potential energy matrix elements in the harmonic basis, and handling and diagonalizing the resulting Hamiltonian matrix, whose size grows rapidly with the dimensionality of the system. Using the example of water hexamer we demonstrate that such calculation is feasible, i.e., constructing and diagonalizing the Hamiltonian matrix in a triply-excited SCP basis, without any additional assumptions or approximations. Our results indicate particularly that the ground state energy differences between different isomers (e.g., cage and prism) of water hexamer are already quite accurate within the SCP approximation. PMID:24289341

Georgescu, Ionu?; Jitomirskaya, Svetlana; Mandelshtam, Vladimir A

2013-11-28

128

Efficient interacting many body similations using GPUs  

NASA Astrophysics Data System (ADS)

Graphics Processing Units (GPUs) provide an ideal tool to study interacting systems using classical machanics with huge speedups for example in molecular dynamics. The quantum-mechanical calculations of many-body systems require additional work, but are feasible using additional degrees of freedom to incorporate quantum-mechanical effects [1]. As an example of the method I show the self-consistent solution to the current transport in a magnetic field can be obtained from a microscopic model with thousands of Coulomb interacting electrons. This yields a microscopic model of the Hall effect [2]. For few electron systems I compare the electronic density evolution based on the GPU classical-quantum model to TD-DFT calculations and discuss prospects of GPUs for solving the Schrodinger equation for many-particles. [4pt] [1] Time dependent approach to transport and scattering in atomic and mesoscopic systems, T. Kramer AIP Conf. Proc., 1334, 142 (2011) [0pt] [2] Self-consistent calculation of electric potentials in Hall devices, T. Kramer, V. Krueckl, E. Heller, and R. Parrott Phys. Rev. B, 81, 205306 (2010)

Kramer, Tobias

2012-02-01

129

A REDUCTION OF THE MANY-BODY PROBLEM OF SOLID-STATE PHYSICS TO PARTIAL SYSTEMS FOR ELECTRONS AND LATTICE  

Microsoft Academic Search

The solid body was considered as a coupled system of electrons and ; nuclei with Coulomb interaction, and it was assumed that the smaller the ; probability for a distribution of the electron pulse, the more the electron ; pulses lie outside the Fermi sphere. With these assumptions, the eigenvalue ; equation of the total Hamilton operator can be reduced,

Sauermann

1962-01-01

130

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

SciTech Connect

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

Hernandez-Quiroz, Saul; Benet, Luis [Instituto de Ciencias Fisicas, Universidad Nacional Autonoma de Mexico (UNAM), 62210 Cuernavaca, Morelos, Mexico and Facultad de Ciencias, Universidad Autonoma del Estado de Morelos (UAEM), 62209 Cuernavaca, Morelos (Mexico); Instituto de Ciencias Fisicas, Universidad Nacional Autonoma de Mexico (UNAM), 62210 Cuernavaca, Morelos (Mexico)

2010-03-15

131

Local Energy-Density Functional Approach to Many-Body Nuclear Systems with S-Wave Pairing  

NASA Astrophysics Data System (ADS)

The ground-state properties of superfluid nuclear systems with 1S0 pairing are studied within a local energy-density functional (LEDF) approach. A new form of the LEDF is proposed with a volume part which fits the Friedman-Pandharipande and Wiringa-Fiks-Fabrocini equation of state at low and moderate densities and allows an extrapolation to higher densities which preserves causality. For inhomogeneous systems, a surface term is added, with two free parameters, which has a fractional form like a Padé approximant containing the square of the density gradient in both the numerator and denominator. In addition to the direct and exchange Coulomb interaction energy, an effective density-dependent Coulomb-nuclear correlation term is included with one more free parameter. A three-parameter fit to the masses and radii of about 100 spherical nuclei has shown that the latter term gives a contribution of the same order of magnitude as the Nolen-Schiffer anomaly in the Coulomb displacement energy. The root-mean-square deviations from experimental masses and radii with the proposed LEDF come out about a factor of two smaller than those obtained with the conventional functionals based on the Skyrme or finite-range Gogny force, or on relativistic mean-field theory. The generalized variational principle is formulated leading to the self-consistent Gor'kov equations which are sovled exactly, with physical boundary conditions both for the bound and scattering states. The method is used to calculate the differential observables such as odd-even mass differences and staggering in charge radii. With a zero-range density-dependent cutoff pairing interaction incorporating a density-gradient term, the evolution of these observables is reproduced reasonably well, including the kinks at magic neutron numbers and the sizes of the associated staggering. An extrapolation from the pairing properties of finite nuclei to pairing in infinite nuclear matter is discussed. A "reference" value of the pairing gap ?F? 3.3 MeV is found for subsaturated nuclear matter at about 0.65 of the equilibrium density. With the formulated LEDF approach, we study also the dilute limit in both the weak and strong coupling regimes. Within the sum rules approach it is shown that the density-dependent pairing may also induce sizeable staggering and kinks in the evolution of the mean energies of multipole excitations.

Fayans, S. A.; Zawischa, D.

132

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

133

Pseudopotential many-body Calculation of the spin structure of Excitons and Trions in InAs/GaAs self-assembled quantum dots  

NASA Astrophysics Data System (ADS)

Motivated by the potential of zero-dimensional quantum dots for spintronic device applications we present a calculation of the spin structure of quantum dots. Our calculational procedure involves two steps. (1) The construction of the single-particle Hamiltonian using empirical pseudopotentials and its diagonalization in a basis of strained bulk Bloch functions [1]. (2) Inclusion of many particle effects by calculating the direct and exchange Coulomb integrals using the fully atomistic single particle wavefunctions, and then solving the Configuration Interaction Hamiltonian in the subspace of electron-hole Slater determinants. Starting by presenting the effect of exchange splitting in a spherical InAs/GaAs dot we will then discuss the spin structure of the neutral exciton (ground and excited states) and the negative trion (consisting of two electrons and one hole) for a lens shaped InAs/GaAs self-assembled quantum dot. We will also present results for the excitonic finestructure and for the dipole transition elements for optical excitations. [1] L-W.Wang and A. Zunger, Phys. Rev. B 59, 15806 (1999).

Bester, Gabriel; Nair, Selvakumar; Zunger, Alex

2002-03-01

134

Many-body wave function in a dipole blockade configuration  

SciTech Connect

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

135

Probing many-body interactions in an optical lattice clock  

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

136

Many-body calculations of low-energy eigenstates in magnetic and periodic systems with self-healing diffusion Monte Carlo: Steps beyond the fixed phase  

NASA Astrophysics Data System (ADS)

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.

Reboredo, Fernando Agustín

2012-05-01

137

Many-Body van der Waals Effects in Advanced Materials  

NASA Astrophysics Data System (ADS)

Van der Waals (vdW) interactions are ubiquitous in molecules and condensed matter. These interactions are inherently quantum mechanical phenomena that arise from concerted correlations between many electrons within a given molecular system. Despite this fact, the vast majority of theoretical calculations include long-range vdW interactions based on a simple effective interatomic pairwise model. We introduce an efficient method that accurately describes the full long-range many-body vdW energy [1,2], and demonstrate that many-body contributions can significantly exceed the highly coveted ``chemical accuracy''. Cases studied include intermolecular binding energies, the conformational hierarchy of DNA structures [2], the geometry and stability of molecular crystals [1], and supramolecular host--guest complexes [3]. Our findings suggest that inclusion of the many-body vdW energy is essential for achieving chemical accuracy and therefore must be accounted for when studying advanced materials. [1] Tkatchenko, DiStasio, Car, Scheffler, PRL (2012), [2] DiStasio, von Lilienfeld, Tkatchenko, PNAS (2012), [3] Tkatchenko, Alfe, Kim, JCTC (2012).

Tkatchenko, Alexandre; von Lilienfeld, Anatole; Distasio, Robert A., Jr.

2013-03-01

138

QM\\/MM Approaches to the Electronic Spectra of Hydrogen-Bonding Systems with Connection to Many-Body Decomposition Schemes  

Microsoft Academic Search

A review on recent applications of the sequential quantum Mechanics\\/Molecular mechanics (QM\\/MM) methodology to the study of the electronic properties of hydrogen bond systems is presented. Results for the absorption spectra of water clusters and liquid water, ionization of liquid water and ammonia, charge transfer to solvent in halide aqueous solution, and solvatochromic shifts of small organic molecules in water

Ricardo A. Mata; B. J. Costa Cabral

2010-01-01

139

Magnetic field spectra and many-body correlations of spin 3/2 holes confined to GaAs quantum well  

NASA Astrophysics Data System (ADS)

We consider two dimensional spin 3/2 hole liquid in the presence of a perpendicular magnetic field. Single particle states of Luttinger Hamiltonian are calculated. For the semiclassical limit, the Hamiltonian is separated into the time-symmetric part treated exactly and time-antisymmetric part treated perturbatively. The angular momentum (spin) 3/2 states are characterized by the Landau level index and parity with respect to reflection about the growth direction. The single-particle spectrum exhibits level-crossings as magnetic field is varied, with or without Rashba and Dresselhaus interactions. The numerical calculations were performed for infinite barrier well, finite size barrier, well doped on one side, symmetrically doped well and parabolic well. Cyclotron mass was calculated and its dependence of the type of structure, magnetic field and symmetry of states is discussed and compared with experimental values. Landèeffective factor is defined and evaluated. Shubnikov-de Haas oscillations are calculated. Electron-electron interactions are accounted using (time-dependent) mean field theories. An interesting effect is a single-well non-homogeneous spin-texture state. Possible implications of shape of hole spectra for fractional quantum Hall states are explored.

Simion, George; Lyanda-Geller, Yuli

2012-02-01

140

Stochastic gene expression as a many-body problem  

PubMed Central

Gene expression has a stochastic component because of the single-molecule nature of the gene and the small number of copies of individual DNA-binding proteins in the cell. We show how the statistics of such systems can be mapped onto quantum many-body problems. The dynamics of a single gene switch resembles the spin-boson model of a two-site polaron or an electron transfer reaction. Networks of switches can be approximately described as quantum spin systems by using an appropriate variational principle. In this way, the concept of frustration for magnetic systems can be taken over into gene networks. The landscape of stable attractors depends on the degree and style of frustration, much as for neural networks. We show the number of attractors, which may represent cell types, is much smaller for appropriately designed weakly frustrated stochastic networks than for randomly connected networks.

Sasai, Masaki; Wolynes, Peter G.

2003-01-01

141

Introducing many-body physics using atomic spectroscopy  

NASA Astrophysics Data System (ADS)

Atoms constitute relatively simple many-body systems, making them suitable objects for developing an understanding of basic aspects of many-body physics. Photoabsorption spectroscopy is a prominent method to study the electronic structure of atoms and the inherent many-body interactions. In this article, the impact of many-body effects on well-known spectroscopic features, such as Rydberg series, Fano resonances, Cooper minima, and giant resonances, is studied and related many-body phenomena in other fields are outlined. To calculate photoabsorption cross sections, the time-dependent configuration interaction singles (TDCIS) model is employed. The conceptual clearness of TDCIS in combination with the compactness of atomic systems allows for a pedagogical introduction to many-body phenomena.

Krebs, Dietrich; Pabst, Stefan; Santra, Robin

2014-02-01

142

On the Neutrino Self Refraction Problem from a Many-Body Perspective  

SciTech Connect

We consider a dense neutrino gas as a many body system by taking into account both vacuum oscillations and self interactions of neutrinos. We show that the exact many body Hamiltonian which describes the flavor oscillations of such a dense neutrino gas has many constants of motion whose eigenvalues represent a set of good quantum numbers. However, if one adopts the random phase approximation as an effective one particle description, these operators are no longer conserved (i.e. they cease to represent good quantum numbers) although their expectation values are still conserved.

Pehlivan, Y. [Mimar Sinan Fine Arts University Besiktas, Istanbul 34349 (Turkey); National Astronomical Observatory of Japan 2-21-1 Osawa, Mitaka Tokyo, 181-8588 (Japan); Kajino, Toshitaka [National Astronomical Observatory of Japan 2-21-1 Osawa, Mitaka Tokyo, 181-8588 (Japan); Department of Astronomy, Graduate School of Science, University of Tokyo, Tokyo 113-0033 (Japan); Balantekin, A. B. [Department of Physics, University of Wisconsin, Madison, WI 53706 (United States); Yoshida, Takashi [Department of Astronomy, Graduate School of Science, University of Tokyo, Tokyo 113-0033 (Japan); Maruyama, Tomoyuki [College of Bioresource Sciences, Nihon University, Fujisawa 252-8510 (Japan)

2010-08-12

143

Many-body effects in semiconductor lasers  

SciTech Connect

A microscopic theory, that is based on the coupled Maxwell-semiconductor-Bloch equations, is used to investigate the effects of many-body Coulomb interactions in semiconductor laser devices. This paper describes two examples where the many-body effects play important roles. Experimental data supporting the theoretical results are presented.

Chow, W.W.

1995-03-01

144

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

145

Factorization in large-scale many-body calculations  

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

146

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

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

147

Many body population trapping in ultracold dipolar gases  

NASA Astrophysics Data System (ADS)

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

Dutta, Omjyoti; Lewenstein, Maciej; Zakrzewski, Jakub

2014-05-01

148

Dynamically induced frustration as a route to a quantum spin ice state in Tb2Ti2O7 via virtual crystal field excitations and quantum many-body effects.  

PubMed

The Tb2Ti2O7 pyrochlore magnetic material is attracting much attention for its spin liquid state, failing to develop long-range order down to 50 mK despite a Curie-Weiss temperature thetaCW approximately -14 K. In this Letter we reinvestigate the theoretical description of this material by considering a quantum model of independent tetrahedra to describe its low-temperature properties. The naturally tuned proximity of this system near a Néel to spin ice phase boundary allows for a resurgence of quantum fluctuation effects that lead to an important renormalization of its effective low-energy spin Hamiltonian. As a result, Tb2Ti2O7 is argued to be a quantum spin ice. We put forward an experimental test of this proposal using neutron scattering on a single crystal. PMID:17501378

Molavian, Hamid R; Gingras, Michel J P; Canals, Benjamin

2007-04-13

149

Relativistic effects in many-body systems of finite size, internal structure, and internal motions: I. “Self-acceleration” of astrophysical systems  

Microsoft Academic Search

It is proved that the post-Newtonian general relativistic center of rest mass of a bounded physical system composed of a number of bodies characterized by finite dimensions, arbitrary internal structure, and arbitrary internal motions cannot in general move uniformly, contrary to what was conventionally accepted up to now. Mathematical expressions are derived and discussed describing, in terms of the above

N. Spyrou

1979-01-01

150

Symmetry-protected many-body Aharonov-Bohm effect  

NASA Astrophysics Data System (ADS)

It is known as a purely quantum effect that a magnetic flux affects the real physics of a particle, such as the energy spectrum, even if the flux does not interfere with the particle's path—the Aharonov-Bohm effect. Here we examine an Aharonov-Bohm effect on a many-body wave function. Specifically, we study this many-body effect on the gapless edge states of a bulk gapped phase protected by a global symmetry (such as ZN)—the symmetry-protected topological (SPT) states. The many-body analog of spectral shifts, the twisted wave function, and the twisted boundary realization are identified in this SPT state. An explicit lattice construction of SPT edge states is derived, and a challenge of gauging its non-onsite symmetry is overcome. Agreement is found in the twisted spectrum between a numerical lattice calculation and a conformal field theory prediction.

Santos, Luiz H.; Wang, Juven

2014-05-01

151

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

NASA Astrophysics Data System (ADS)

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

Tkatchenko, Alexandre

2012-02-01

152

Many-Body Entanglement: a New Application of the Full Counting Statistics  

NASA Astrophysics Data System (ADS)

Entanglement entropy is a measure of quantum correlations between separate parts of a many-body system, which plays an important role in many areas of physics. Here we review recent work in which a relation between this quantity and the Full Counting Statistics description of electron transport was established for noninteracting fermion systems. Using this relation, which is of a completely general character, we discuss how the entanglement entropy can be directly measured by detecting current fluctuations in a driven quantum system such as quantum point contact.

Klich, Israel; Levitov, Leonid

2009-05-01

153

Standard-Basis Operator Method in the Green's-Function Technique of Many-Body Systems with an Application to Ferromagnetism.  

National Technical Information Service (NTIS)

The following topics are discussed: Interacting systems in solids; Standard-basis operator formalism; Advantage of using standard-basis operators; Application of new formalism to an ensemble of identical interacting ions in a crystal; Green's functions of...

P. Erdoes S. B. Haley

1971-01-01

154

Many-body core-valence partitioning  

Microsoft Academic Search

We discuss the physics related to partitioning core and valence electrons, a common approach taken so that one need deal only with valence electrons in subsequent work. We present an approach to core-valence partitioning which explicitly includes many-body correlations, unlike traditional single-body approaches (such as Hartree Fock or the local-density approximation). Effects of intracore and core-valence correlations are incorporated in

Eric Shirley; Richard Martin

1993-01-01

155

Dynamic calculation of rail vehicles: A concept for the application of the process of statistical linearization in the many body program system MEDYNA  

NASA Astrophysics Data System (ADS)

A substructure for the wheel sets is developed. The problem of relating the substructures to the general body system by the calculation of statistical linearized, generalized force vectors for various linear and nonlinear joining elements is solved. Nonlinear spring and damper connections, Coulomb translation friction dampers, and Coulomb rotation friction dampers are covered. Statistically linearized dynamic connecting elements are modelized. It is shown how the general differential equation system is to be constructed. The iteration process for the determination of the free linearization parameter is presented.

Renger, A.

156

Efficient Numerical Self-Consistent Mean-Field Approach for Fermionic Many-Body Systems by Polynomial Expansion on Spectral Density  

NASA Astrophysics Data System (ADS)

We propose an efficient numerical algorithm to solve Bogoliubov--de Gennes equations self-consistently for inhomogeneous superconducting systems with a reformulated polynomial expansion scheme. This proposed method is applied to typical issues such as a vortex under randomly distributed impurities and a normal conducting junction sandwiched between superconductors. With various technical remarks, we show that its efficiency becomes remarkable in large-scale parallel performance.

Nagai, Yuki; Ota, Yukihiro; Machida, Masahiko

2012-02-01

157

Many-body calculations of low energy eigenstates in magnetic and periodic systems with self healing diffusion Monte Carlo: steps beyond the fixed-phase  

SciTech Connect

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

158

Quantum Field Theory of Many-Body Systems: From the Origin of Sound to an Origin of Light and Electrons  

Microsoft Academic Search

Abstract For most of the last century, condensed matter physics has been dominated by band theory and Landau’s symmetry breaking theory. In the last twenty years, however, there has been an emer- gence of a new paradigm associated with fractionalization, emergent gauge bosons and fermions, topological order, string-net condensation, and long range entanglements. These new physical con- cepts are so

Xiao-Gang Wen; Matthew Fisher

2005-01-01

159

Many-body van der Waals interactions in molecules and condensed matter.  

PubMed

This work reviews the increasing evidence that many-body van der Waals (vdW) or dispersion interactions play a crucial role in the structure, stability and function of a wide variety of systems in biology, chemistry and physics. Starting with the exact expression for the electron correlation energy provided by the adiabatic connection fluctuation-dissipation theorem, we derive both pairwise and many-body interatomic methods for computing the long-range dispersion energy by considering a model system of coupled quantum harmonic oscillators within the random-phase approximation. By coupling this approach to density functional theory, the resulting many-body dispersion (MBD) method provides an accurate and efficient scheme for computing the frequency-dependent polarizability and many-body vdW energy in molecules and materials with a finite electronic gap. A select collection of applications are presented that ascertain the fundamental importance of these non-bonded interactions across the spectrum of intermolecular (the S22 and S66 benchmark databases), intramolecular (conformational energies of alanine tetrapeptide) and supramolecular (binding energy of the 'buckyball catcher') complexes, as well as molecular crystals (cohesive energies in oligoacenes). These applications demonstrate that electrodynamic response screening and beyond-pairwise many-body vdW interactions--both captured at the MBD level of theory--play a quantitative, and sometimes even qualitative, role in describing the properties considered herein. This work is then concluded with an in-depth discussion of the challenges that remain in the future development of reliable (accurate and efficient) methods for treating many-body vdW interactions in complex materials and provides a roadmap for navigating many of the research avenues that are yet to be explored. PMID:24805055

DiStasio, Robert A; Gobre, Vivekanand V; Tkatchenko, Alexandre

2014-05-28

160

Many-body van der Waals interactions in molecules and condensed matter  

NASA Astrophysics Data System (ADS)

This work reviews the increasing evidence that many-body van der Waals (vdW) or dispersion interactions play a crucial role in the structure, stability and function of a wide variety of systems in biology, chemistry and physics. Starting with the exact expression for the electron correlation energy provided by the adiabatic connection fluctuation–dissipation theorem, we derive both pairwise and many-body interatomic methods for computing the long-range dispersion energy by considering a model system of coupled quantum harmonic oscillators within the random-phase approximation. By coupling this approach to density functional theory, the resulting many-body dispersion (MBD) method provides an accurate and efficient scheme for computing the frequency-dependent polarizability and many-body vdW energy in molecules and materials with a finite electronic gap. A select collection of applications are presented that ascertain the fundamental importance of these non-bonded interactions across the spectrum of intermolecular (the S22 and S66 benchmark databases), intramolecular (conformational energies of alanine tetrapeptide) and supramolecular (binding energy of the ‘buckyball catcher’) complexes, as well as molecular crystals (cohesive energies in oligoacenes). These applications demonstrate that electrodynamic response screening and beyond-pairwise many-body vdW interactions—both captured at the MBD level of theory—play a quantitative, and sometimes even qualitative, role in describing the properties considered herein. This work is then concluded with an in-depth discussion of the challenges that remain in the future development of reliable (accurate and efficient) methods for treating many-body vdW interactions in complex materials and provides a roadmap for navigating many of the research avenues that are yet to be explored.

DiStasio, Robert A., Jr.; Gobre, Vivekanand V.; Tkatchenko, Alexandre

2014-05-01

161

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

162

Non-equilibrium many body dynamics  

SciTech Connect

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

163

The relativistic nuclear many-body problem  

Microsoft Academic Search

This volume presents sections which explore important aspects of relativistic baryons, nuclear models, relativistic Hartree descriptions of nuclei, quantum hadrodynamics, the dynamical quantum vacuum, charged mesons, relativistic pion dynamics, two-nucleon correlations, electroweak interactions with nuclei, and quantum chromodynamics. Appendixes cover notation and conventions, dimensional regularization, path-integral derivation of Feynman rules, and the Feynman rules in local gauge theories.

J. W. Negele; B. D. Serot; E. Vogt; J. D. Walecka

1986-01-01

164

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

165

Dynamically-Induced Frustration as a Route to a Quantum Spin Ice State in Tb2Ti2O7 via Virtual Crystal Field Excitations and Quantum Many-Body Effects  

Microsoft Academic Search

The Tb2Ti2O7 pyrochlore magnetic material is attracting much attention for its spin liquid state, failing to develop long range order down to 50 mK despite a Curie-Weiss temperatureCW ? ?14 K. In this paper we reinvestigate the theoretical description of this material by considering a quantum model of independent tetrahedra to describe its low temperature properties. The naturally- tuned proximity

Hamid R. Molavian; Michel J. P. Gingras; Benjamin Canals

166

Class of Highly Entangled Many-Body States that can be Efficiently Simulated  

NASA Astrophysics Data System (ADS)

We describe a quantum circuit that produces a highly entangled state of N qubits from which one can efficiently compute expectation values of local observables. This construction yields a variational ansatz for quantum many-body states that can be regarded as a generalization of the multiscale entanglement renormalization ansatz (MERA), which we refer to as the branching MERA. In a lattice system in D dimensions, the scaling of entanglement of a region of size LD in the branching MERA is not subject to restrictions such as a boundary law LD -1, but can be proportional to the size of the region, as we demonstrate numerically.

Evenbly, G.; Vidal, G.

2014-06-01

167

Dynamically Induced Frustration as a Route to a Quantum Spin Ice State in Tb_{2}Ti_{2}O_{7} via Virtual Crystal Field Excitations and Quantum Many-Body Effects  

Microsoft Academic Search

The Tb$_2$Ti$_2$O$_7$ pyrochlore magnetic material is attracting much\\u000aattention for its {\\\\em spin liquid} state, failing to develop long range order\\u000adown to 50 mK despite a Curie-Weiss temperature $\\\\theta_{\\\\rm CW} \\\\sim -14$ K.\\u000aIn this paper we reinvestigate the theoretical description of this material by\\u000aconsidering a quantum model of independent tetrahedra to describe its low\\u000atemperature properties. The

Hamid R. Molavian; Michel J. P. Gingras; Benjamin Canals

2007-01-01

168

Many-body effects in the cyclotron resonance of a magnetic dot  

NASA Astrophysics Data System (ADS)

Intraband cyclotron resonance (CR) transitions of a two-electron quantum dot containing a single magnetic ion is investigated for different Coulomb interaction strengths and different positions of the magnetic ion. In contrast to the usual parabolic quantum dots where CR is independent of the number of electrons, we found here that due to the presence of the magnetic ion Kohn’s theorem no longer holds and CR is different for systems with different number of electrons and different effective electron-electron Coulomb interaction strength. Many-body effects result in shifts in the transition energies and change the number of CR lines. The position of the magnetic ion inside the quantum dot affects the structure of the CR spectrum by changing the position and the number of crossings and anticrossings in the transition energies and oscillator strengths.

Nguyen, Nga T. T.; Peeters, F. M.

2009-09-01

169

Many-Body Coherent Destruction of Tunneling  

SciTech Connect

A new route to coherent destruction of tunneling is established by considering a monochromatic fast modulation of the self-interaction strength of a many-boson system. The modulation can be tuned such that only an arbitrarily, a priori prescribed number of particles are allowed to tunnel. The associated tunneling dynamics is sensitive to the odd or even nature of the number of bosons.

Gong Jiangbin [Department of Physics and Center for Computational Science and Engineering, National University of Singapore, Singapore 117542 (Singapore); NUS Graduate School for Integrative Sciences and Engineering, Singapore 117597 (Singapore); Morales-Molina, Luis [Department of Physics and Center for Computational Science and Engineering, National University of Singapore, Singapore 117542 (Singapore); Facultad de Fisica, Pontificia Universidad Catolica de Chile, Santiago 22 (Chile); Haenggi, Peter [Department of Physics and Center for Computational Science and Engineering, National University of Singapore, Singapore 117542 (Singapore); Theoretische Physik I, Institut fuer Physik, Universitaet Augsburg, D-86135 Augsburg (Germany)

2009-09-25

170

Many-body dynamics on a time-dependent basis  

NASA Astrophysics Data System (ADS)

We propose a method of solution of the many-body Schrödinger equation that involves an expansion of the wave function in terms of a finite, time-dependent basis of a relevant subspace. The equations of motion for the expansion coefficients generalize previous proposals of approximate dynamics. The method is illustrated in the case of an N-particle system with an SU(2) Hamiltonian, and it is shown that it improves the approximation that disregards off-diagonal elements of the dynamical matrices.

Hernández, E. S.; Jezek, D. M.

1988-11-01

171

Statistical Mechanics of the Cosmological Many-body Problem  

NASA Astrophysics Data System (ADS)

The statistical mechanical description of the cosmological many-body problem is reviewed in light of the recent advances [1, 2, 3]. This description makes it possible to take into account the extended nature of galaxies, include the effect of higher order contributions, allow a description for the two-component system of galaxies and possibly account for a fraction of the dark matter in the Universe, besides providing a more fundamental basis for the earlier results. The spatial galaxy distribution function is shown as a powerful statistic showing excellent agreement with observations and N-body simulation results.

Malik, Manzoor A.

2009-07-01

172

Interacting many-body simulations including contacts using graphics processing units (GPU)  

NASA Astrophysics Data System (ADS)

Already the solution of the interacting classical many-body problem is difficult to achieve, since the integration of the equations of motions couples all positions of the particles contained in the system. Transport calculations require to include the contacts within the simulation and to study the effect of interactions there. Classical and quantum-mechanical equations of motions can be related by the time-dependent variational principle for Coulombic interacting electrons in a magnetic field [1]. Interacting systems require to carefully consider the questions of self-consistency. The emergence of an mean-field potential out of a large (10000 electrons!) many-body calculation is shown in [2]. The calculation is only possible due to our usage of graphics processing units, which are ideal tools to study interacting systems. [4pt] [1] Two interacting electrons in a magnetic field: comparison of semiclassical, quantum, and variational solutions, T. Kramer, AIP in press (2010), arxiv:1009.6051 [0pt] [2] Self-consistent calculation of electric potentials in Hall devices, T. Kramer, V. Krueckl, E. Heller, and R. Parrott Phys. Rev. B, 81, 205306 (2010)

Kramer, Tobias

2011-03-01

173

Matrix elements of many-body operators and density correlations  

Microsoft Academic Search

The matrix element of a general many-body operator between two Slater determinants is calculated explicitly. For this, a split-and-pair method is introduced that provides a convenient expression of Wick's theorem and simplifies many-body calculations. The same method is used to determine the generating function of the matrix elements of many-body operators. The split-and-pair method allows also for the diagonalization of

Christian Brouder; Christian

2005-01-01

174

Generalizing the self-healing diffusion Monte Carlo approach to finite temperature: a path for the optimization of low-energy many-body basis expansions  

SciTech Connect

The self-healing diffusion Monte Carlo method for complex functions [F. A. Reboredo J. Chem. Phys. {\\bf 136}, 204101 (2012)] and some ideas of the correlation function Monte Carlo approach [D. M. Ceperley and B. Bernu, J. Chem. Phys. {\\bf 89}, 6316 (1988)] are blended to obtain a method for the calculation of thermodynamic properties of many-body systems at low temperatures. In order to allow the evolution in imaginary time to describe the density matrix, we remove the fixed-node restriction using complex antisymmetric trial wave functions. A statistical method is derived for the calculation of finite temperature properties of many-body systems near the ground state. In the process we also obtain a parallel algorithm that optimizes the many-body basis of a small subspace of the many-body Hilbert space. This small subspace is optimized to have maximum overlap with the one expanded by the lower energy eigenstates of a many-body Hamiltonian. We show in a model system that the Helmholtz free energy is minimized within this subspace as the iteration number increases. We show that the subspace expanded by the small basis systematically converges towards the subspace expanded by the lowest energy eigenstates. Possible applications of this method to calculate the thermodynamic properties of many-body systems near the ground state are discussed. The resulting basis can be also used to accelerate the calculation of the ground or excited states with Quantum Monte Carlo.

Kim, Jeongnim [ORNL] [ORNL; Reboredo, Fernando A [ORNL] [ORNL

2014-01-01

175

Atomic Properties Calculated by Many-Body Theory.  

National Technical Information Service (NTIS)

The use of many-body perturbation theory to calculate atomic properties is discussed. Results are given for correlation energies, hyperfine, constants, frequency-dependent polarizabilities, and London dispersion forces. (Author)

H. P. Kelly

1970-01-01

176

Many-Body Matter-Wave Dark Soliton  

NASA Astrophysics Data System (ADS)

The Gross-Pitaevskii equation—which describes interacting bosons in the mean-field approximation—possesses solitonic solutions in dimension one. For repulsively interacting particles, the stationary soliton is dark, i.e., is represented by a local density minimum. Many-body effects may lead to filling of the dark soliton. Using quasiexact many-body simulations, we show that, in single realizations, the soliton appears totally dark although the single particle density tends to be uniform.

Delande, Dominique; Sacha, Krzysztof

2014-01-01

177

Many-body matter-wave dark soliton.  

PubMed

The Gross-Pitaevskii equation--which describes interacting bosons in the mean-field approximation--possesses solitonic solutions in dimension one. For repulsively interacting particles, the stationary soliton is dark, i.e., is represented by a local density minimum. Many-body effects may lead to filling of the dark soliton. Using quasiexact many-body simulations, we show that, in single realizations, the soliton appears totally dark although the single particle density tends to be uniform. PMID:24580420

Delande, Dominique; Sacha, Krzysztof

2014-01-31

178

Communication: Random phase approximation renormalized many-body perturbation theory  

NASA Astrophysics Data System (ADS)

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

Bates, Jefferson E.; Furche, Filipp

2013-11-01

179

Communication: Random phase approximation renormalized many-body perturbation theory  

SciTech Connect

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

Bates, Jefferson E.; Furche, Filipp, E-mail: filipp.furche@uci.edu [Department of Chemistry, University of California, Irvine, 1102 Natural Sciences II, Irvine, California 92697-2025 (United States)] [Department of Chemistry, University of California, Irvine, 1102 Natural Sciences II, Irvine, California 92697-2025 (United States)

2013-11-07

180

Many-body Green functions of q-deformed oscillators  

NASA Astrophysics Data System (ADS)

Certain thermal (Matsubara) Green functions are obtained for a “free” system of quantum-deformed harmonic oscillators. It is shown that the form of the single-particle Matsubara function is changed, with an explicit dependence on s = 1n q appearing in a simple form and suggesting that quantum-deformed commutation rules intrinsically incorporate interactions even in the “free case”. A two-particle Matsubara function gives no evidence of a bound state energy shift.

Birman, Joseph L.

1992-07-01

181

GRAPE3: highly parallelized special-purpose computer for gravitational many-body simulations  

Microsoft Academic Search

The authors have developed a highly parallelized special-purpose computer GRAPE (GRAvity PipE)-3 for gravitational many-body simulations. It accelerates gravitational force calculations which are the most expensive part of the many-body simulations. The peak computing speed is equivalent to about 15 GFLOPS. The GRAPE-3 system consists of two identical boards connected to a host computer through a VME bus. Each board

S. K. Okumura; J. Makino; T. Ebisuzaki; T. Ito; T. Fukushige; D. Sugimoto; E. Hashimoto; K. Tomida; N. Miyakawa

1992-01-01

182

Stability in Microcanonical Many-Body Spin Glasses  

NASA Astrophysics Data System (ADS)

We generalize the de Almeida--Thouless line for the many-body Ising spin glass to the microcanonical ensemble and show that it coincides with the canonical one. This enables us to draw a complete microcanonical phase diagram of this model.

Bertalan, Zsolt; Takahashi, Kazutaka

2012-04-01

183

Enhancement models of momentum densities of annihilating electron-positron pairs: The many-body picture of natural geminals  

NASA Astrophysics Data System (ADS)

The correlated motion of a positron surrounded by electrons is a fundamental many-body problem. We approach this by modeling the momentum density of annihilating electron-positron pairs using the framework of reduced density matrices, natural orbitals, and natural geminals (electron-positron pair wave functions) of the quantum theory of many-particle systems. We find that an expression based on the natural geminals provides an exact, unique, and compact expression for the momentum density. The natural geminals can be used to define and to determine enhancement factors for enhancement models going beyond the independent-particle model for a better understanding of the results of positron annihilation experiments.

Makkonen, Ilja; Ervasti, Mikko M.; Siro, Topi; Harju, Ari

2014-01-01

184

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

PubMed

We show how an embedded many-body expansion (EMBE) can be used to calculate accurate ab initio energies of water clusters and ice structures using wavefunction-based methods. We use the EMBE described recently by Bygrave et al. [J. Chem. Phys. 137, 164102 (2012)], in which the terms in the expansion are obtained from calculations on monomers, dimers, etc., acted on by an approximate representation of the embedding field due to all other molecules in the system, this field being a sum of Coulomb and exchange-repulsion fields. Our strategy is to separate the total energy of the system into Hartree-Fock and correlation parts, using the EMBE only for the correlation energy, with the Hartree-Fock energy calculated using standard molecular quantum chemistry for clusters and plane-wave methods for crystals. Our tests on a range of different water clusters up to the 16-mer show that for the second-order Møller-Plesset (MP2) method the EMBE truncated at 2-body level reproduces to better than 0.1 mE(h)/monomer the correlation energy from standard methods. The use of EMBE for computing coupled-cluster energies of clusters is also discussed. For the ice structures Ih, II, and VIII, we find that MP2 energies near the complete basis-set limit reproduce very well the experimental values of the absolute and relative binding energies, but that the use of coupled-cluster methods for many-body correlation (non-additive dispersion) is essential for a full description. Possible future applications of the EMBE approach are suggested. PMID:24070273

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

2013-09-21

185

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

186

Quantum breathing dynamics of ultracold bosons in one-dimensional harmonic traps: Unraveling the pathway from few- to many-body systems  

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

187

Many-body approach to proton emission and spectroscopic factors  

NASA Astrophysics Data System (ADS)

A formal study of the proton emission process is presented. The decay width for the process is re-derived in a time-dependent formalism that makes use of the two-potential approach by Gurvitz and Kalbermann and places special emphasis on the proper treatment of many-body effects. We demonstrate that the many-body aspects of the problem are contained in an overall normalization factor for the decay width. While this result agrees with traditional approaches to proton emission, we find that the usual interpretation of the normalization as the square root of a spectroscopic factor is not necessarily correct. This result has important consequences for extracting spectroscopic factors from proton emission experiments. (This work was performed in part under the auspices of the U. S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48.)

Escher, Jutta; Al-Khalili, Jim; Barbieri, Carlo; Jennings, Byron; Sparenberg, Jean-Marc

2003-10-01

188

Many-body polarization effects and the membrane dipole potential.  

SciTech Connect

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

189

Strontium clusters: Many-body potential, energetics, and structural transitions  

NASA Astrophysics Data System (ADS)

A many-body potential for strontium clusters is developed with parameters fitted to the energy surface of strontium clusters containing up to ten atoms calculated within the density functional theory in the generalized gradient approximation. Structure and energetics of the most stable cluster isomers with up to 63 atoms are obtained with genetic algorithms. Additionally, the high resolution mass spectrum of strontium clusters up to Sr96 at finite temperature is provided. Several thermodynamic properties are studied under the many-body potential as a function of temperature. It is found that stability patterns, indicating how stable a cluster size is with respect to its neighboring sizes, change significantly with temperature. This behavior is due to structural transitions of the strontium clusters that occur at finite temperatures. A comparison with the experimental mass abundance indicates that only the structures above 400 K were observed experimentally. Very prominent magic numbers are predicted at 34 and 61.

Wang, Guan Ming; Blaisten-Barojas, Estela; Roitberg, A. E.; Martin, T. P.

2001-08-01

190

Combined coupled-cluster and many-body perturbation theories  

NASA Astrophysics Data System (ADS)

Various approximations combining coupled-cluster (CC) and many-body perturbation theories have been derived and implemented into the parallel execution programs that take into account the spin, spatial (real Abelian), and permutation symmetries and that are applicable to closed- and open-shell molecules. The implemented models range from the CCSD(T), CCSD[T], CCSD(2)T, CCSD(2)TQ, and CCSDT(2)Q methods to the completely renormalized (CR) CCSD(T) and CCSD[T] approaches, where CCSD (CCSDT) stands for the CC method with connected single and double (single, double, and triple) cluster operators, and subscripted or parenthesized 2, T, and Q indicate the perturbation order or the excitation ranks of the cluster operators included in the corrections. The derivation and computer implementation have been automated by the algebraic and symbolic manipulation program TENSOR CONTRACTION ENGINE (TCE). The TCE-synthesized subroutines generate the tensors with the highest excitation rank in a blockwise manner so that they need not be stored in their entirety, while enabling the efficient reuse of other precalculated intermediate tensors defined by prioritizing the memory optimization as well as operation minimization. Consequently, the overall storage requirements for the corrections due to connected triple and quadruple cluster operators scale as O(n4) and O(n6), respectively (n being a measure of the system size). For systems with modest multireference character of their wave functions, we found that the order of accuracy is CCSD

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

2004-12-01

191

Many-Body Effects on Bandgap Shrinkage, Effective Masses, and Alpha Factor  

NASA Technical Reports Server (NTRS)

Many-body Coulomb effects influence the operation of quantum-well (QW) laser diode (LD) strongly. In the present work, we study a two-band electron-hole plasma (EHP) within the Hatree-Fock approximation and the single plasmon pole approximation for static screening. Full inclusion of momentum dependence in the many-body effects is considered. An empirical expression for carrier density dependence of the bandgap renormalization (BGR) in an 8 nm GaAs/Al(0.3)G(4.7)As single QW will be given, which demonstrates a non-universal scaling behavior for quasi-two-dimension structures, due to size-dependent efficiency of screening. In addition, effective mass renormalization (EMR) due to momentum-dependent self-energy many-body correction, for both electrons and holes is studied and serves as another manifestation of the many-body effects. Finally, the effects on carrier density dependence of the alpha factor is evaluated to assess the sensitivity of the full inclusion of momentum dependence.

Li, Jian-Zhong; Ning, C. Z.; Woo, Alex C. (Technical Monitor)

2000-01-01

192

Numerical finite size scaling approach to many-body localization.  

PubMed

We develop a numerical technique to study Anderson localization in interacting electronic systems. The ground state of the disordered system is calculated with quantum Monte Carlo simulations while the localization properties are extracted from the "Thouless conductance" g, i.e., the curvature of the energy with respect to an Aharonov-Bohm flux. We apply our method to polarized electrons in a two-dimensional system of size L. We recover the well-known universal beta(g)=dlogg/dlogL one parameter scaling function without interaction. Upon switching on the interaction, we find that beta(g) is unchanged while the system flows toward the insulating limit. We conclude that polarized electrons in two dimensions stay in an insulating state in the presence of weak to moderate electron-electron correlations. PMID:18352582

Fleury, Geneviève; Waintal, Xavier

2008-02-22

193

Many-body-theory study of lithium photoionization  

NASA Technical Reports Server (NTRS)

A detailed theoretical calculation is carried out for the photoionization of lithium at low energies within the framework of Brueckner-Goldstone perturbational approach. In this calculation extensive use is made of the recently developed multiple-basis-set technique. Through this technique all second-order perturbation terms, plus a number of important classes of terms to infinite order, have been taken into account. Analysis of the results enables one to resolve the discrepancies between two previous works on this subject. The detailed calculation also serves as a test on the convergence of the many-body perturbation-expansion approach.

Chang, T. N.; Poe, R. T.

1975-01-01

194

Meson structure in a relativistic many-body approach  

PubMed

Results from an extensive relativistic many-body analysis utilizing a realistic effective QCD Hamiltonian are presented for the meson spectrum. A comparative numerical study of the BCS, Tamm-Dancoff (TDA), and RPA treatments provides new, significant insight into the condensate structure of the vacuum, the chiral symmetry governance of the pion, and the meson spin, orbital, and flavor mass splitting contributions. In contrast to a previous glueball application, substantial quantitative differences are computed between TDA and RPA for the light quark sector with the pion emerging as a Goldstone boson only in the RPA. PMID:11017454

Llanes-Estrada; Cotanch

2000-02-01

195

Quantum-information processing in disordered and complex quantum systems  

SciTech Connect

We study quantum information processing in complex disordered many body systems that can be implemented by using lattices of ultracold atomic gases and trapped ions. We demonstrate, first in the short range case, the generation of entanglement and the local realization of quantum gates in a disordered magnetic model describing a quantum spin glass. We show that in this case it is possible to achieve fidelities of quantum gates higher than in the classical case. Complex systems with long range interactions, such as ions chains or dipolar atomic gases, can be used to model neural network Hamiltonians. For such systems, where both long range interactions and disorder appear, it is possible to generate long range bipartite entanglement. We provide an efficient analytical method to calculate the time evolution of a given initial state, which in turn allows us to calculate its quantum correlations.

Sen, Aditi; Sen, Ujjwal [ICFO-Institut de Ciencies Fotoniques, Parc Mediterrani de la Tecnologia, E-08860 Castelldefels (Barcelona) (Spain); Institut fuer Theoretische Physik, Universitaet Hannover, D-30167 Hannover (Germany); Ahufinger, Veronica [ICREA and Grup d'Optica, Universitat Autonoma de Barcelona, E-08193 Bellaterra (Spain); Briegel, Hans J. [Institut fuer Quantenoptik und Quanteninformation, Oesterreichische Akademie der Wissenschaften, A-6020 Innsbruck (Austria); Institut fuer Theoretische Physik, Universitaet Innsbruck, Technikerstrasse 25, A-6020 Innsbruck (Austria); Sanpera, Anna [Institut fuer Theoretische Physik, Universitaet Hannover, D-30167 Hannover (Germany); ICREA and Grup de Fisica Teorica, Universitat Autonoma de Barcelona, E-08193 Bellaterra (Spain); Lewenstein, Maciej [Institut fuer Theoretische Physik, Universitaet Hannover, D-30167 Hannover (Germany); ICREA and ICFO-Institut de Ciencies Fotoniques, Parc Mediterrani de la Tecnologia, E-08860 Castelldefels (Barcelona) (Spain)

2006-12-15

196

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

197

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

198

First-principles energetics of water clusters and ice: A many-body analysis  

NASA Astrophysics Data System (ADS)

Standard forms of density-functional theory (DFT) have good predictive power for many materials, but are not yet fully satisfactory for cluster, solid, and liquid forms of water. Recent work has stressed the importance of DFT errors in describing dispersion, but we note that errors in other parts of the energy may also contribute. We obtain information about the nature of DFT errors by using a many-body separation of the total energy into its 1-body, 2-body, and beyond-2-body components to analyze the deficiencies of the popular PBE and BLYP approximations for the energetics of water clusters and ice structures. The errors of these approximations are computed by using accurate benchmark energies from the coupled-cluster technique of molecular quantum chemistry and from quantum Monte Carlo calculations. The systems studied are isomers of the water hexamer cluster, the crystal structures Ih, II, XV, and VIII of ice, and two clusters extracted from ice VIII. For the binding energies of these systems, we use the machine-learning technique of Gaussian Approximation Potentials to correct successively for 1-body and 2-body errors of the DFT approximations. We find that even after correction for these errors, substantial beyond-2-body errors remain. The characteristics of the 2-body and beyond-2-body errors of PBE are completely different from those of BLYP, but the errors of both approximations disfavor the close approach of non-hydrogen-bonded monomers. We note the possible relevance of our findings to the understanding of liquid water.

Gillan, M. J.; Alfè, D.; Bartók, A. P.; Csányi, G.

2013-12-01

199

Many-Body Hydrodynamic Interactions in Charge-Stabilized Suspensions  

NASA Astrophysics Data System (ADS)

In this joint experimental-theoretical work we study hydrodynamic interaction effects in dense suspensions of charged colloidal spheres. Using x-ray photon correlation spectroscopy we have determined the hydrodynamic function H(q), for a varying range of electrosteric repulsion. We show that H(q) can be quantitatively described by means of a novel Stokesian dynamics simulation method for charged Brownian spheres, and by a modification of a many-body theory developed originally by Beenakker and Mazur. Very importantly, we can explain the behavior of H(q) for strongly correlated particles without resorting to the controversial concept of hydrodynamic screening, as was attempted in earlier work by Riese [Phys. Rev. Lett. 85, 5460 (2000)]PRLTAO0031-900710.1103/PhysRevLett.85.5460.

Banchio, Adolfo J.; Gapinski, Jacek; Patkowski, Adam; Häußler, Wolfgang; Fluerasu, Andrei; Sacanna, Stefano; Holmqvist, Peter; Meier, Gerhard; Lettinga, M. Paul; Nägele, Gerhard

2006-04-01

200

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 {1 0 1¯ 0}<1 1 2¯ 0> slip and pyramidal {1 1 2¯ 2}<1 1 2¯ 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

201

Many-body Anderson localization in one-dimensional systems  

NASA Astrophysics Data System (ADS)

We show, using quasi-exact numerical simulations, that Anderson localization in a disordered one-dimensional potential survives in the presence of attractive interaction between particles. The localization length of the particles' center of mass—computed analytically for weak disorder—is in good agreement with the quasi-exact numerical observations using the time evolving block decimation algorithm. Our approach allows for simulation of the entire experiment including the final measurement of all atom positions.

Delande, Dominique; Sacha, Krzysztof; P?odzie?, Marcin; Avazbaev, Sanat K.; Zakrzewski, Jakub

2013-04-01

202

Approaching the complete-basis limit with a truncated many-body expansion  

NASA Astrophysics Data System (ADS)

High-accuracy electronic structure calculations with correlated wave functions demand the use of large basis sets and complete-basis extrapolation, but the accuracy of fragment-based quantum chemistry methods has most often been evaluated using double-? basis sets, with errors evaluated relative to a supersystem calculation using the same basis set. Here, we examine the convergence towards the basis-set limit of two- and three-body expansions of the energy, for water clusters and ion-water clusters, focusing on calculations at the level of second-order Møller-Plesset perturbation theory (MP2). Several different corrections for basis-set superposition error (BSSE), each consistent with a truncated many-body expansion, are examined as well. We present a careful analysis of how the interplay of errors (from all sources) influences the accuracy of the results. We conclude that fragment-based methods often benefit from error cancellation wherein BSSE offsets both incompleteness of the basis set as well as higher-order many-body effects that are neglected in a truncated many-body expansion. An n-body counterpoise correction facilitates smooth extrapolation to the MP2 basis-set limit, and at n = 3 affords accurate results while requiring calculations in subsystems no larger than trimers.

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

2013-12-01

203

Many-Body Effects in the Mesoscopic x-Ray Edge Problem  

NASA Astrophysics Data System (ADS)

Many-body phenomena, a key interest in the investigation ofbulk solid state systems, are studied here in the context of the x-ray edge problem for mesoscopic systems. We investigate the many-body effects associated with the sudden perturbation following the x-ray excition of a core electron into the conduction band. For small systems with dimensions at the nanoscale we find considerable deviations from the well-understood metallic case where Anderson orthogonality catastrophe and the Mahan-Nozières-DeDominicis response cause characteristic deviations of the photoabsorption cross section from the naive expectation. Whereas the K-edge is typically rounded in metallic systems, we find a slightly peaked K-edge in generic mesoscopic systems with chaotic-coherent electron dynamics. Thus the behavior of the photoabsorption cross section at threshold depends on the system size and is different for the metallic and the mesoscopic case.

Hentschel, M.; R"Oder, G.; Ullmo, D.

204

Many-body theory of positron-atom interactions  

SciTech Connect

A many-body theory approach is developed for the problem of positron-atom scattering and annihilation. Strong electron-positron correlations are included nonperturbatively through the calculation of the electron-positron vertex function. It corresponds to the sum of an infinite series of ladder diagrams, and describes the physical effect of virtual positronium formation. The vertex function is used to calculate the positron-atom correlation potential and nonlocal corrections to the electron-positron annihilation vertex. Numerically, we make use of B-spline basis sets, which ensures rapid convergence of the sums over intermediate states. We have also devised an extrapolation procedure that allows one to achieve convergence with respect to the number of intermediate-state orbital angular momenta included in the calculations. As a test, the present formalism is applied to positron scattering and annihilation on hydrogen, where it is exact. Our results agree with those of accurate variational calculations. We also examine in detail the properties of the large correlation corrections to the annihilation vertex.

Gribakin, G.F.; Ludlow, J. [Department of Applied Mathematics and Theoretical Physics, Queen's University, Belfast BT7 1NN, Northern Ireland (United Kingdom)

2004-09-01

205

Many-body theory of positron-atom interactions  

NASA Astrophysics Data System (ADS)

The interaction of low-energy positrons with atoms is characterised by strong electron-positron correlation effects. For example, they increase the positron annihilation rate in collisions with Xe atoms by three orders of magnitude! We have developed a many-body theory approach [1] which accounts for all major correlation effects, i.e, polarization of the atom by the positron, virtual positronium formation, and short-range enhancement of the electron-positron contact density. The first two give rise to strong positron-atom attraction. It affects positron elastic scattering and promotes positron-atom binding. The third effect determines positron-atom annihilation rates and spectra of annihilation gamma quanta [2]. Thus, a good quantitative understanding of positron-atom interactions has been achieved. This gives hope of understanding a much more difficult problem of positron annihilation with polyatomic molecules, where molecular vibrational degrees of freedom play an important role [3,4]. -3pt-12pt *G. F. Gribakin and J. Ludlow, Phys. Rev. A 70, 032720 (2004). *L. J. M. Dunlop and G. F. Gribakin, submitted to J. Phys. B (2005). *C. M. Surko, G. F. Gribakin and S. J. Buckman, J. Phys. B 38, R57 (2005). *G. F. Gribakin and P. M. W. Gill, Nucl. Instrum. and Methods B 221, 30 (2004).

Gribakin, Gleb

2006-05-01

206

Relativistic many-body Hamiltonian approach to mesons  

NASA Astrophysics Data System (ADS)

We represent QCD at the hadronic scale by means of an effective Hamiltonian, H, formulated in the Coulomb gauge. As in the Nambu-Jona-Lasinio model, chiral symmetry is explicitly broken, however our approach is renormalizable and also includes confinement through a linear potential with slope specified by lattice gauge theory. This interaction generates an infrared integrable singularity and we detail the computationally intensive procedure necessary for numerical solution. We focus upon applications for the u, d, s and c quark flavors and compute the mass spectrum for the pseudoscalar, scalar and vector mesons. We also perform a comparative study of alternative many-body techniques for approximately diagonalizing H: BCS for the vacuum ground state; TDA and RPA for the excited hadron states. The Dirac structure of the field theoretical Hamiltonian naturally generates spin-dependent interactions, including tensor, spin-orbit and hyperfine, and we clarify the degree of level splitting due to both spin and chiral symmetry effects. Significantly, we find that roughly two-thirds of the ?- ? mass difference is due to chiral symmetry and that only the RPA preserves chiral symmetry. We also document how hadronic mass scales are generated by chiral symmetry breaking in the model vacuum. In addition to the vacuum condensates, we compute meson decay constants and detail the Nambu-Goldstone realization of chiral symmetry by numerically verifying the Gell-Mann-Oakes-Renner relation.

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

2002-01-01

207

Many-Body Approach to Mesons, Hybrids and Glueballs  

NASA Astrophysics Data System (ADS)

We represent QCD at the hadronic scale by means of an effective Hamiltonian, H, formulated in the Coulomb gauge. As in the Nambu-Jona-Lasinio model, chiral symmetry is dynamically broken, however our approach is renormalizable and also includes confinement through a linear potential with slope specified by lattice gauge theory. We perform a comparative study of alternative many-body techniques for approximately diagonalizing H: BCS for the vacuum ground state; TDA and RPA for the excited hadron states. We adequately describe the experimental meson and lattice glueball spectra and perform the first relativistic, three quasiparticle calculation for hybrid mesons. In general agreement with alternative theoretical approaches, we predict the lightest hybrid states near but above 2 GeV, indicating the two recently observed JPC = 1-+ exotics at 1.4 and 1.6 GeV are of a different, perhaps four quark, structure. We also detail a new isospin dependent interaction from q/line{q} color octet annihilation (analogous to ortho positronium) which splits I = 0 and I = 1 states.

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

2002-02-01

208

Unified many-body approach to mesons, Glueballs and hybrids  

NASA Astrophysics Data System (ADS)

A unified quark and gluon description of mesons, glueballs and exotic hybrids is presented for a relativistic field theoretical Hamiltonian in the Coulomb gauge. The effective QCD Hamiltonian entails a linear confining interaction with slope predetermined by lattice theory and is approximately diagonalized using different many-body techniques: BCS for the vacuum ground state; TDA and RPA for the excited hadron spectrum. Chiral symmetry rigorously emerges and is spontaneously broken by the model BCS vacuum which contains dynamically generated constituent quark and gluon condensates described by respective gap equations. The observed low energy meson spectrum and the quenched lattice glueball measurements are reproduced along with a Regge trajectory consistent with the Pomeron. Using generalized vector meson dominance, glueball decays are predicted and a glueball photoproduction experimental signature is predicted. Finally, a variational relativistic three quasiparticle calculation for hybrid mesons is reported which concurs with alternative model predictions that the lightest hybrid states are near but above 2 GeV. This strongly indicates that the recently observed J PC = 1 -+ exotics at 1.4 and 1.6 GeV are more likely four quark states.

Cotanch, S. R.

209

Hadrons in a Relativistic Many-Body Approach  

NASA Astrophysics Data System (ADS)

Results from a relativistic, field theoretical QCD analysis are reported for the low lying meson, glueball and hybrid spectra. Alternative many-body techniques are utilized to approximately diagonalize an effective QCD Hamiltonian containing a linear confining interaction with slope (string tension) determined from lattice gauge calculations. The ground state vacuum properties (condensates and dressed/constituent masses) are calculated using the BCS approach with spontaneous dynamical chiral symmetry breaking and a non-linear (similar to the Dyson-Schwinger) gap equation. The excited meson states are then predicted using the Tamm-Dancoff (TDA) and random phase (RPA) approximations (analogous to the Bethe-Salpeter equation). With only one predetermined interaction parameter, the string tension, and standard u, d, s and c current quark masses, the low mass meson states in the different spin and flavor channels are reproduced. Significantly, new insight is obtained concerning the condensate structure of the vacuum, meson decay constants, spin/orbital and flavor mass splitting contributions and the chiral symmetry governance of the pion. Substantial TDA-RPA differences are found in the light quark sector with the pion emerging as a Goldstone boson only in the RPA. This comprehensive approach also encompasses the gluon sector and, with the same string tension parameter, reproduces the gluon condensate value from QCD sum rules and, most importantly, the quenched lattice glueball spectrum. Finally, the exotic 1-+ hybrid meson mass is calculated to be above 2 GeV and in rough agreement with lattice and flux tube model results. This suggests the recently observed 1-+ exotic states have an alternative, perhaps four quark, structure.

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

2001-11-01

210

Finite-Size Error in Many-Body Simulations with Long-Range Interactions  

Microsoft Academic Search

We discuss the origin of the finite size error of the energy in many-body\\u000asimulation of systems of charged particles and we propose a correction based on\\u000athe random phase approximation at long wave lengths. The correction comes from\\u000acontributions mainly determined by the organized collective oscillations of the\\u000ainteracting system. Finite size corrections, both on kinetic and potential\\u000aenergy,

Simone Chiesa; David M. Ceperley; Richard M. Martin; Markus Holzmann

2006-01-01

211

Finite-Size Error in Many-Body Simulations with Long-Range Interactions  

Microsoft Academic Search

We discuss the origin of the finite-size error of the energy in many-body simulation of systems of charged particles and we propose a correction based on the random-phase approximation at long wavelengths. The correction is determined mainly by the collective charge oscillations of the interacting system. Finite-size corrections, both on kinetic and potential energy, can be calculated within a single

Simone Chiesa; David M. Ceperley; Richard M. Martin; Markus Holzmann

2006-01-01

212

Calculation of Dilational and Uniaxial Shear Potentials of Ge by a State-Independent Many-Body Projection Technique  

NASA Astrophysics Data System (ADS)

Utilizing state-independent projection operators, we present a new optical conductivity formula for cyclotron transition in the system of electrons interacting anisotropically with phonons. The line-shape factor appearing in the conductivity tensor contains the many body effects for electrons and phonons. Applying this formula, we determine the two deformation potentials (dilation potential ?d and uniaxial shear potential ?u) of Ge in the quantum limit. By fitting the present theoretical values with the experimental data of Murase, Enjouji and Otsuka [J. Phys. Soc. Jpn. 29 (1970) 1248] and Kobori, Ohyama and Otsuka [J. Phys. Soc. Jpn. 59 (1990) 2141], we obtain ?u=17.0±0.6 eV and ?d=-10.88±0.47 eV.

Kang, Nam; Ryu, Jai; Choi, Sang

1998-07-01

213

Many-body renormalization of the minimal conductivity in graphene.  

PubMed

The conductance of ballistic graphene at the neutrality point is due to coherent electron tunneling between the leads, the so called pseudodiffusive regime. The conductance scales as a function of the sample dimensions in the same way as in a diffusive metal, despite the difference in the physical mechanisms involved. The electron-electron interaction modifies this regime, and plays a role similar to that of the environment in macroscopic quantum phenomena. We show that interactions can change substantially the transport properties. In the presence of nearby metallic layers, the conductance near the neutrality point can decrease with decreasing temperature, and reach values well below the quantum unit of conductance, as in an insulator. PMID:24702399

Guinea, F; Katsnelson, M I

2014-03-21

214

A many-body potential approach to modelling the thermomechanical properties of actinide oxides  

NASA Astrophysics Data System (ADS)

A many-body potential model for the description of actinide oxide systems, which is robust at high temperatures, is reported for the first time. The embedded atom method is used to describe many-body interactions ensuring good reproduction of a range of thermophysical properties (lattice parameter, bulk modulus, enthalpy and specific heat) between 300 and 3000 K for AmO2, CeO2, CmO2, NpO2, ThO2, PuO2 and UO2. Additionally, the model predicts a melting point for UO2 between 3000 and 3100 K, in close agreement with experiment. Oxygen-oxygen interactions are fixed across the actinide oxide series because it facilitates the modelling of oxide solid solutions. The new potential is also used to predict the energies of Schottky and Frenkel pair disorder processes.

Cooper, M. W. D.; Rushton, M. J. D.; Grimes, R. W.

2014-03-01

215

A many-body potential approach to modelling the thermomechanical properties of actinide oxides.  

PubMed

A many-body potential model for the description of actinide oxide systems, which is robust at high temperatures, is reported for the first time. The embedded atom method is used to describe many-body interactions ensuring good reproduction of a range of thermophysical properties (lattice parameter, bulk modulus, enthalpy and specific heat) between 300 and 3000 K for AmO2, CeO2, CmO2, NpO2, ThO2, PuO2 and UO2. Additionally, the model predicts a melting point for UO2 between 3000 and 3100 K, in close agreement with experiment. Oxygen-oxygen interactions are fixed across the actinide oxide series because it facilitates the modelling of oxide solid solutions. The new potential is also used to predict the energies of Schottky and Frenkel pair disorder processes. PMID:24553129

Cooper, M W D; Rushton, M J D; Grimes, R W

2014-03-12

216

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

217

Dielectric breakdown of Mott insulators and the many-body Schwinger mechanism studied with the generalized Bethe ansatz  

NASA Astrophysics Data System (ADS)

The dielectric breakdown may be regarded as a condensed matter realization of the Schwinger mechanism - creation of electron-positron pairs by electric fields - in which the threshold for breakdown is considerably reduced due to a quantum leakage of the wave function. In Mott insulators, a many-body counterpart of this phenomena is shown to take place, which is here studied with the quantum tunneling formalism due to Dykhne-Davis-Pechukas as applied to the one-dimensional Hubbard model. We implement this for the quantum tunneling rate with an analytic continuation of the Bethe-ansatz solution for excited states to a non-Hermitian case. This enables us to extend the many- body Landau-Zener picture to the thermodynamic limit, with a remarkable agreement with the time-dependent density matrix renormalization group result. (arXiv:0903.2707)

Oka, Takashi; Aoki, Hideo

2010-03-01

218

Stochastic evaluation of second-order many-body perturbation energies  

NASA Astrophysics Data System (ADS)

With the aid of the Laplace transform, the canonical expression of the second-order many-body perturbation correction to an electronic energy is converted into the sum of two 13-dimensional integrals, the 12-dimensional parts of which are evaluated by Monte Carlo integration. Weight functions are identified that are analytically normalizable, are finite and non-negative everywhere, and share the same singularities as the integrands. They thus generate appropriate distributions of four-electron walkers via the Metropolis algorithm, yielding correlation energies of small molecules within a few mEh of the correct values after 108 Monte Carlo steps. This algorithm does away with the integral transformation as the hotspot of the usual algorithms, has a far superior size dependence of cost, does not suffer from the sign problem of some quantum Monte Carlo methods, and potentially easily parallelizable and extensible to other more complex electron-correlation theories.

Willow, Soohaeng Yoo; Kim, Kwang S.; Hirata, So

2012-11-01

219

Possible experimental manifestations of the many-body localization  

NASA Astrophysics Data System (ADS)

Recently, it was predicted that if all one-electron states in a noninteracting disordered system are localized, the interaction between electrons in the absence of coupling to phonons leads to a finite-temperature metal-insulator transition. Here, we show that even in the presence of a weak coupling to phonons the transition manifests itself (i) in the nonlinear conduction, leading to a bistable I-V curve, and (ii) by a dramatic enhancement of the nonequilibrium current noise near the transition.

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

2007-08-01

220

Nonperturbative dynamical many-body theory of a Bose-Einstein condensate  

SciTech Connect

A dynamical many-body theory is presented which systematically extends beyond mean-field and perturbative quantum-field theoretical procedures. It allows us to study the dynamics of strongly interacting quantum-degenerate atomic gases. The nonperturbative approximation scheme is based on a systematic expansion of the two-particle irreducible effective action in powers of the inverse number of field components. This yields dynamic equations which contain direct scattering, memory, and 'off-shell' effects that are not captured by the Gross-Pitaevskii equation. This is relevant to account for the dynamics of, e.g., strongly interacting quantum gases atoms near a scattering resonance, or of one-dimensional Bose gases in the Tonks-Girardeau regime. We apply the theory to a homogeneous ultracold Bose gas in one spatial dimension. Considering the time evolution of an initial state far from equilibrium we show that it quickly evolves to a nonequilibrium quasistationary state and discuss the possibility to attribute an effective temperature to it. The approach to thermal equilibrium is found to be extremely slow.

Gasenzer, Thomas; Berges, Juergen; Schmidt, Michael G.; Seco, Marcos [Institut fuer Theoretische Physik, Universitaet Heidelberg, Philosophenweg 16, 69120 Heidelberg (Germany)

2005-12-15

221

The relativistic many body problem with an oscillator interaction  

NASA Technical Reports Server (NTRS)

We start with the total energy E for a system of three scalar relativistic particles that, because of Einstein's relation, will have square roots of functions of the momenta. By taking powers of this relation, we finally get a fourth degree polynomial in E(exp 2), where the square roots have disappeared, and which we can convert into a type of Schroedinger equation. To be in the center of mass frame we pass to Jocobi momenta and then replace them by creation and annihilation operators. We thus get an equation in terms of the generators of a U(2) group, which, in principle, we can solve in an elementary way. Finally, we rewrite our equation in a Poincare invariant form.

Moshinsky, Marcos

1995-01-01

222

Many-body interatomic U and Al-U potentials  

NASA Astrophysics Data System (ADS)

In the present work, an interatomic potential in the framework of the embedded atom method (EAM) is developed for the Al-U binary system. A methodology is detailed to fit the U potential, that reproduces the stability of the ? phase at low temperatures and the ? phase at high ones. The thermal stability of both phases, thermal expansion and vacancy driven self diffusion are studied. The Al-U potential is fit to first principles calculated formation energies of the experimentally observed intermetallic phases, Al2U (cubic C15), Al3U (cubic L12) and Al4U (orthorhombic D1b). As a first validation the potentials are tested against available experimental measurements.

Pascuet, M. I.; Bonny, G.; Fernández, J. R.

2012-05-01

223

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

224

Non-perturbative approaches to problems in strongly-correlated many-body physics  

NASA Astrophysics Data System (ADS)

The physics of strongly-correlated many-body systems pose formidable theoretical challenges. Methods based on perturbation theory break down due to the lack of a small parameter. This leads generically to the closure problem in a diagramatic expansion. In this thesis, we consider two such problems. The first involves the Mott insulator, a remarkable example of strong correlation effects among electrons leading to an insulating phase of what would otherwise be a metal. Of particular interest is the case when the ground state breaks neither the global rotational symmetry of the electronic spins nor the spatial symmetries of the lattice. Here the combination of strong coupling and quantum fluctuations leads to novel ground states with purely quantum mechanical origins. The second problem involves the statistics of dynamical systems. Although a set of nonlinear differential equations is deterministic and has a unique solution, it may be unstable to small triggering disturbances. Despite the unpredictability of individual trajectories, there may be reproducible and smoothly varying statistical properties. General methods to access directly statistical quantities are then necessary. In Part I of this thesis, we take the pragmatic view that the basic physics of spin liquids is contained in the one-band Hubbard model. For large on-site Coulomb repulsion, U ? infinity, we consider the Heisenberg limit at half-filling and include possible subleading exchange anisotropies of the Dzyaloshinskii-Moriya (DM) type. The work is motivated by two experimental realizations of layered spin-1/2 antiferromagnets. The first is Cs2CuCl4 where the spins reside on a spatially anisotropic triangular lattice. The second is ZnCu3(OH)6Cl2, called Herbertsmithite. Here, the spins reside on a spatially isotropic kagome lattice. Both are rare candidate materials in the search for spin liquid physics in two dimensions. To interpret experimentally measured quantities, we exactly diagonalize the Hamiltonian on small clusters. In addition, we utilize Gutzwiller-projected mean field theory to test whether various spin liquid states may be realized in nature. In Part II of this thesis, we apply the method of Hopf to low dimensional toy models of turbulence. A well-known example is the first-order system of three coupled nonlinear equations invented by Lorenz. The motivation was to find a simple model, amenable to fast numerical evaluation and capturing essential difficulties found in long-term weather prediction. In the hope of developing a statistical understanding of the Navier-Stokes equations, Hopf pioneered a functional integral method. The Hopf equations are in terms of a characteristic functional that determines the full time-independent problem and is equivalent to knowledge of the exact probability distribution. In our discussion, we focus on a simple chaotic dynamical system introduced by Orszag and McLaughlin and determine the exact Hopf characteristic functional.

Ma, Seungwook

225

Advances in quantum Monte Carlo for quantum critical systems  

NASA Astrophysics Data System (ADS)

During the past few years, there has been significant progress in efficient quantum Monte Carlo methods for certain classes of spin systems and other lattice many-body problems. Cluster updates have been developed that speed up the sampling by several orders of magnitude, and schemes to avoid the systematic errors of the traditionally used Trotter decomposition have been deviced. Thanks to these developments, quantum critical phenomena (for systems where there are no sign problems) can now be investigated to a level of accuracy approaching classical simulation studies. I will discuss an approach to quantum simulations which is particularly efficient for (unfrustrated) S=1/2 Heisenberg models; the stochastic series expansion (SSE) method incorporating a cluster update for sampling the power series expansion of exp(-? H) to all contributing orders [A. W. Sandvik, Phys. Rev. B 59 R14157 (1999)]. I will also discuss high-precision calculations using the SSE algorithm for the Heisenberg antiferromagnet on a bilayer. This model can be tuned through a quantum critical point by varying the ratio of the inter-plane (J_?) to in-plane interaction (J), and has been very useful for testing predictions for quantum critical behavior in two-dimensional antiferromagnets. I will discuss finite-size scaling of ground state data, as well as the finite-temperature quantum critical behavior.

Sandvik, Anders

2000-03-01

226

Quantum dynamics of finite atomic and molecular systems through density matrix methods  

Microsoft Academic Search

We develop a mixed quantum-classical formulation to describe the dynamics of few- and many-body atomic systems by applying a partial Wigner transform over the quantum Liouville equation of motion. In this approach, the density operator becomes a function in quasiclassical phase space, while remaining an operator over a subset of quantal variables. By taking appropriate limits and introducing an effective

Brian Thorndyke

2004-01-01

227

New Approach to N-Body Relativistic Quantum Mechanics  

Microsoft Academic Search

In this paper, we propose a new approach to the relativistic quantum mechanics for many-body, which is a self-consistent system constructed by juxtaposed but mutually coupled nonlinear Dirac's equations. The classical approximation of this approach provides the exact Newtonian dynamics for many-body, and the nonrelativistic approximation gives the complete Schrödinger equation for many-body.

Ying-Qiu Gu

2007-01-01

228

Accurate and Efficient Method for Many-Body van der Waals Interactions  

NASA Astrophysics Data System (ADS)

An efficient method is developed for the microscopic description of the frequency-dependent polarizability of finite-gap molecules and solids. This is achieved by combining the Tkatchenko-Scheffler van der Waals (vdW) method [Phys. Rev. Lett. 102, 073005 (2009)PRLTAO0031-900710.1103/PhysRevLett.102.073005] with the self-consistent screening equation of classical electrodynamics. This leads to a seamless description of polarization and depolarization for the polarizability tensor of molecules and solids. The screened long-range many-body vdW energy is obtained from the solution of the Schrödinger equation for a system of coupled oscillators. We show that the screening and the many-body vdW energy play a significant role even for rather small molecules, becoming crucial for an accurate treatment of conformational energies for biomolecules and binding of molecular crystals. The computational cost of the developed theory is negligible compared to the underlying electronic structure calculation.

Tkatchenko, Alexandre; DiStasio, Robert A., Jr.; Car, Roberto; Scheffler, Matthias

2012-06-01

229

Many-Body Localization in One Dimension as a Dynamical Renormalization Group Fixed Point  

NASA Astrophysics Data System (ADS)

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 log?log?t 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.

Vosk, Ronen; Altman, Ehud

2013-02-01

230

Periodic thermodynamics of isolated quantum systems.  

PubMed

The nature of the behavior of an isolated many-body quantum system periodically driven in time has been an open question since the beginning of quantum mechanics. After an initial transient period, such a system is known to synchronize with the driving; in contrast to the nondriven case, no fundamental principle has been proposed for constructing the resulting nonequilibrium state. Here, we analytically show that, for a class of integrable systems, the relevant ensemble is constructed by maximizing an appropriately defined entropy subject to constraints, which we explicitly identify. This result constitutes a generalization of the concepts of equilibrium statistical mechanics to a class of far-from-equilibrium systems, up to now mainly accessible using ad hoc methods. PMID:24785013

Lazarides, Achilleas; Das, Arnab; Moessner, Roderich

2014-04-18

231

Periodic Thermodynamics of Isolated Quantum Systems  

NASA Astrophysics Data System (ADS)

The nature of the behavior of an isolated many-body quantum system periodically driven in time has been an open question since the beginning of quantum mechanics. After an initial transient period, such a system is known to synchronize with the driving; in contrast to the nondriven case, no fundamental principle has been proposed for constructing the resulting nonequilibrium state. Here, we analytically show that, for a class of integrable systems, the relevant ensemble is constructed by maximizing an appropriately defined entropy subject to constraints, which we explicitly identify. This result constitutes a generalization of the concepts of equilibrium statistical mechanics to a class of far-from-equilibrium systems, up to now mainly accessible using ad hoc methods.

Lazarides, Achilleas; Das, Arnab; Moessner, Roderich

2014-04-01

232

Extension of many-body theory and approximate density functionals to fractional charges and fractional spins  

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

233

Extension of many-body theory and approximate density functionals to fractional charges and fractional spins.  

PubMed

The exact conditions for density functionals and density matrix functionals in terms of fractional charges and fractional spins are known, and their violation in commonly used functionals has been shown to be the root of many major failures in practical applications. However, approximate functionals are designed for physical systems with integer charges and spins, not in terms of the fractional variables. Here we develop a general framework for extending approximate density functionals and many-electron theory to fractional-charge and fractional-spin systems. Our development allows for the fractional extension of any approximate theory that is a functional of G(0), the one-electron Green's function of the non-interacting reference system. The extension to fractional charge and fractional spin systems is based on the ensemble average of the basic variable, G(0). We demonstrate the fractional extension for the following theories: (1) any explicit functional of the one-electron density, such as the local density approximation and generalized gradient approximations; (2) any explicit functional of the one-electron density matrix of the non-interacting reference system, such as the exact exchange functional (or Hartree-Fock theory) and hybrid functionals; (3) many-body perturbation theory; and (4) random-phase approximations. A general rule for such an extension has also been derived through scaling the orbitals and should be useful for functionals where the link to the Green's function is not obvious. The development thus enables the examination of approximate theories against known exact conditions on the fractional variables and the analysis of their failures in chemical and physical applications in terms of violations of exact conditions of the energy functionals. The present work should facilitate the calculation of chemical potentials and fundamental bandgaps with approximate functionals and many-electron theories through the energy derivatives with respect to the fractional charge. It should play an important role in developing accurate approximate density functionals and many-body theory. PMID:24050335

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

2013-09-14

234

Quantum Games and Programmable Quantum Systems  

Microsoft Academic Search

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

235

Many-body spectral moment sum rules for the Bose Hubbard model  

NASA Astrophysics Data System (ADS)

Exact results for many-body interacting systems are rare. Here we derive a series of exact results for the single-band Bose-Hubbard model. In particular, we derive spectral moment sum rules for the Green's functions of the Bose-Hubbard model. Unlike the fermionic sum rules, the bosonic ones depend on complicated expectation values of the bosons that go beyond just needing to know the local particle density. Nevertheless, they can be used to benchmark the quality of different numerical calculations of spectral functions. These sum rules hold with arbitrary values of the interaction strength and even into nonequilibrium situations, similar to what is seen for the fermionic case. We present some case studies comparing the exact moments to those found with other numerical techniques like the VCA approximation.

Freericks, James; Turkowski, Volodomyr; Krishnamurthy, Hulikal

2011-03-01

236

Electronic excitations of LiI within many-body perturbation theory  

NASA Astrophysics Data System (ADS)

We report the calculated quasiparticle band structure and optical absorption spectrum of LiI, using many-body perturbation theory. Density-functional theory within local density approximation is used to calculate the ground-state properties of the system. The quasiparticle band structure is evaluated within the GW approximation. Taking the electron-hole interaction into account, electron-hole pair states and optical excitations are derived from the solution of the Bethe-Salpeter equation for the electron-hole two-particle Green function. The band gap is estimated within the GW approximation as 6.3 eV, which is in good agreement with the experimental result of 6.4 eV. And the calculated optical spectrum is also in agreement with experimental data.

Gao, Yan-Min; Jiang, Yun-Feng; Wang, Neng-Ping

2014-08-01

237

A charge optimized many-body potential for titanium nitride (TiN).  

PubMed

This work presents a new empirical, variable charge potential for TiN systems in the charge-optimized many-body potential framework. The potential parameters were determined by fitting them to experimental data for the enthalpy of formation, lattice parameters, and elastic constants of rocksalt structured TiN. The potential does a good job of describing the fundamental physical properties (defect formation and surface energies) of TiN relative to the predictions of first-principles calculations. This potential is used in classical molecular dynamics simulations to examine the interface of fcc-Ti(0?0?1)/TiN(0?0?1) and to characterize the adsorption of oxygen atoms and molecules on the TiN(0?0?1) surface. The results indicate that the potential is well suited to model TiN thin films and to explore the chemistry associated with their oxidation. PMID:24903100

Cheng, Y-T; Liang, T; Martinez, J A; Phillpot, S R; Sinnott, S B

2014-07-01

238

A charge optimized many-body potential for titanium nitride (TiN)  

NASA Astrophysics Data System (ADS)

This work presents a new empirical, variable charge potential for TiN systems in the charge-optimized many-body potential framework. The potential parameters were determined by fitting them to experimental data for the enthalpy of formation, lattice parameters, and elastic constants of rocksalt structured TiN. The potential does a good job of describing the fundamental physical properties (defect formation and surface energies) of TiN relative to the predictions of first-principles calculations. This potential is used in classical molecular dynamics simulations to examine the interface of fcc-Ti(0?0?1)/TiN(0?0?1) and to characterize the adsorption of oxygen atoms and molecules on the TiN(0?0?1) surface. The results indicate that the potential is well suited to model TiN thin films and to explore the chemistry associated with their oxidation.

Cheng, Y.-T.; Liang, T.; Martinez, J. A.; Phillpot, S. R.; Sinnott, S. B.

2014-07-01

239

Half-metallic ferromagnets: From band structure to many-body effects  

NASA Astrophysics Data System (ADS)

A review of new developments in theoretical and experimental electronic-structure investigations of half-metallic ferromagnets (HMFs) is presented. Being semiconductors for one spin projection and metals for another, these substances are promising magnetic materials for applications in spintronics (i.e., spin-dependent electronics). Classification of HMFs by the peculiarities of their electronic structure and chemical bonding is discussed. The effects of electron-magnon interaction in HMFs and their manifestations in magnetic, spectral, thermodynamic, and transport properties are considered. Special attention is paid to the appearance of nonquasiparticle states in the energy gap, which provide an instructive example of essentially many-body features in the electronic structure. State-of-the-art electronic calculations for correlated d -systems are discussed, and results for specific HMFs (Heusler alloys, zinc-blende structure compounds, CrO2 , and Fe3O4 ) are reviewed.

Katsnelson, M. I.; Irkhin, V. Yu.; Chioncel, L.; Lichtenstein, A. I.; de Groot, R. A.

2008-04-01

240

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

241

Spectroscopic Fingerprinting of Small Molecules via Many-Body Perturbation Theory  

NASA Astrophysics Data System (ADS)

Quantitative understanding of the photophysics of small organic molecules is an important challenge and relevant to a range of energy conversion applications. Existing first-principles methods, such as time-dependent density functional theory, coupled cluster, and other quantum chemistry-based approaches can sometimes provide onset energies with good accuracy, but agreement at higher energies - a more complete spectral fingerprint - is frequently less adequate. Here we use DFT and many-body perturbation theory, within the GW approximation and the Bethe-Salpeter Equation approach, to compute the UV-Vis absorption spectra for a range of small molecules, comparing closely to room-temperature, solution-phase measurements of onsets and spectra. First-principles molecular dynamics is used to prepare snapshots of finite temperature conformations. The effects of continuum and explicit solvation models are considered. The importance of dynamic disorder, delocalized unoccupied states, and solvation are thoroughly discussed in the context of experiments. Support: DOE via the Molecular Foundry and Helios SERC, and NSF via NCN. Computational support provided by NERSC.

Doak, Peter; Darancet, Pierre; Neaton, Jeffrey

2012-02-01

242

The dimensionality reduction at surfaces as a playground for many-body and correlation effects  

NASA Astrophysics Data System (ADS)

Low-dimensional systems have always deserved attention due to the peculiarity of their physics, which is different from or even at odds with three-dimensional expectations. This is precisely the case for many-body effects, as electron-electron correlation or electron-phonon coupling are behind many intriguing problems in condensed matter physics. These interesting phenomena at low dimensions can be studied in one of the paradigms of two dimensionality—the surface of crystals. The maturity of today's surface science techniques allows us to perform thorough experimental studies that can be complemented by the current strength of state-of-the-art calculations. Surfaces are thus a natural two-dimensional playground for studying correlation and many-body effects, which is precisely the object of this special section. This special section presents a collection of eight invited articles, giving an overview of the current status of selected systems, promising techniques and theoretical approaches for studying many-body effects at surfaces and low-dimensional systems. The first article by Hofmann investigates electron-phonon coupling in quasi-free-standing graphene by decoupling graphene from two different substrates with different intercalating materials. The following article by Kirschner deals with the study of NiO films by electron pair emission, a technique particularly well-adapted for studying high electron correlation. Bovensiepen investigates electron-phonon coupling via the femtosecond time- and angle-resolved photoemission spectroscopy technique. The next article by Malterre analyses the phase diagram of alkalis on Si(111):B and studies the role of many-body physics. Biermann proposes an extended Hubbard model for the series of C, Si, Sn and Pb adatoms on Si(111) and obtains the inter-electronic interaction parameters by first principles. Continuing with the theoretical studies, Bechstedt analyses the influence of on-site electron correlation in insulating antiferromagnetic surfaces. Ortega reports on the gap of molecular layers on metal systems, where the metal-organic interaction affects the organic gap through correlation effects. Finally, Cazalilla presents a study of the phase diagram of one-dimensional atoms or molecules displaying a Kondo-exchange interaction with the substrate. Acknowledgments The editors are grateful to all the invited contributors to this special section of Journal of Physics: Condensed Matter. We also thank the IOP Publishing staff for handling the administrative matters and the refereeing process. Correlation and many-body effects at surfaces contents The dimensionality reduction at surfaces as a playground for many-body and correlation effectsA Tejeda, E G Michel and A Mascaraque Electron-phonon coupling in quasi-free-standing grapheneJens Christian Johannsen, Søren Ulstrup, Marco Bianchi, Richard Hatch, Dandan Guan, Federico Mazzola, Liv Hornekær, Felix Fromm, Christian Raidel, Thomas Seyller and Philip Hofmann Exploring highly correlated materials via electron pair emission: the case of NiO/Ag(100)F O Schumann, L Behnke, C H Li and J Kirschner Coherent excitations and electron-phonon coupling in Ba/EuFe2As2 compounds investigated by femtosecond time- and angle-resolved photoemission spectroscopyI Avigo, R Cortés, L Rettig, S Thirupathaiah, H S Jeevan, P Gegenwart, T Wolf, M Ligges, M Wolf, J Fink and U Bovensiepen Understanding the insulating nature of alkali-metal/Si(111):B interfacesY Fagot-Revurat, C Tournier-Colletta, L Chaput, A Tejeda, L Cardenas, B Kierren, D Malterre, P Le Fèvre, F Bertran and A Taleb-Ibrahimi What about U on surfaces? Extended Hubbard models for adatom systems from first principlesPhilipp Hansmann, Loïg Vaugier, Hong Jiang and Silke Biermann Influence of on-site Coulomb interaction U on properties of MnO(001)2 × 1 and NiO(001)2 × 1 surfacesA Schrön, M Granovskij and F Bechstedt On the organic energy gap problemF Flores, E Abad, J I Martínez, B Pieczyrak and J Ortega Easy-axis ferromagnetic chain on a metallic surfaceMiguel A Cazalilla

Tejeda, A.; Michel, E. G.; Mascaraque, A.

2013-03-01

243

Dielectric breakdown in a Mott insulator: Many-body Schwinger-Landau-Zener mechanism studied with a generalized Bethe ansatz  

NASA Astrophysics Data System (ADS)

The nonadiabatic quantum tunneling picture, which may be called the many-body Schwinger-Landau-Zener mechanism, for the dielectric breakdown of Mott insulators in strong electric fields is studied in the one-dimensional Hubbard model. The tunneling probability is calculated by a method due to Dykhne-Davis-Pechukas with an analytical continuation of the Bethe-ansatz solution for excited states to a non-Hermitian case. A remarkable agreement with the time-dependent density-matrix renormalization-group result is obtained.

Oka, Takashi; Aoki, Hideo

2010-01-01

244

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

Microsoft Academic Search

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

245

Synthetic quantum systems  

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

246

Many-body effects in a semiconductor microcavity laser: Experiment and theory  

SciTech Connect

Many-body effects are observed in the threshold properties of selectively oxidized vertical-cavity surface-emitting lasers. These microcavity lasers represent the state-of-the-art in low threshold semiconductor injection lasers.

Crawford, M.H.; Choquette, K.D.; Chow, W.W.; Schneider, R.P. Jr.

1996-07-01

247

Modelling the many-body dynamics of heavy ion collisions. Present status and future perspective.  

National Technical Information Service (NTIS)

Basic problems of the semiclassical microscopic modelling of strongly interacting systems are discussed within the framework of Quantum Molecular Dynamics (QMD). It is shown that the same predictions can be obtained with several - numerically completely d...

C. Hartnack R. K. Puri J. Aichelin J. Konopka S. A. Bass

1996-01-01

248

Relativistic many-body investigation of hyperfine interactions in excited S states of alkali metals: francium and potassium  

Microsoft Academic Search

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

249

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

250

Including many-body screening into self-consistent calculations: Tight-binding model studies with the Gutzwiller approximation  

NASA Astrophysics Data System (ADS)

We introduce a scheme to include many-body screening processes explicitly into a set of self-consistent equations for electronic-structure calculations using the Gutzwiller approximation. The method is illustrated by the application to a tight-binding model describing the strongly correlated ?-Ce system. With the inclusion of the 5d electrons into the local Gutzwiller projection subspace, the correct input Coulomb repulsion Uff between the 4f electrons for ?-Ce in the calculations can be pushed far beyond the usual screened value Uffscr and close to the bare atomic value Uffbare. This indicates that the d-f many-body screening is the dominant contribution to the screening of Uff in this system. The method provides a promising way toward the ab initio Gutzwiller density functional theory.

Yao, Y. X.; Wang, C. Z.; Ho, K. M.

2011-06-01

251

A charge optimized many-body (comb) potential for titanium and titania.  

PubMed

This work proposes an empirical, variable charge potential for Ti and TiO2 systems based on the charge-optimized many-body (COMB) potential framework. The parameters of the potential function are fit to the structural and mechanical properties of the Ti hcp phase, the TiO2 rutile phase, and the energetics of polymorphs of both Ti and TiO2. The relative stabilities of TiO2 rutile surfaces are predicted and compared to the results of density functional theory (DFT) and empirical potential calculations. The transferability of the developed potential is demonstrated by determining the adsorption energy of Cu clusters of various sizes on the rutile TiO2(1?1?0) surface using molecular dynamics simulations. The results indicate that the adsorption energy is dependent on the number of Cu-Cu bonds and Cu-O bonds formed at the Cu/TiO2 interface. The adsorption energies of Cu clusters on the reduced and oxidized TiO2(1?1?0) surfaces are also investigated, and the COMB potential predicts enhanced bonding between Cu clusters and the oxidized surface, which is consistent with both experimental observations and the results of DFT calculations for other transition metals (Au and Ag) on this oxidized surface. PMID:24943265

Cheng, Yu-Ting; Shan, Tzu-Ray; Liang, Tao; Behera, Rakesh K; Phillpot, Simon R; Sinnott, Susan B

2014-08-01

252

An Introductory Guide to GREEN’S Function Methods in Nuclear Many-Body Problems  

NASA Astrophysics Data System (ADS)

We present an elementary and fairly detailed review of several Green’s function methods for treating nuclear and other many-body systems. We first treat the single-particle Green’s function, by way of which some details concerning linked diagram expansion, rules for evaluating Green’s function diagrams and solution of the Dyson’s integral equation for Green’s function are exhibited. The particle-particle hole-hole (pphh) Green’s function is then considered, and a specific time-blocking technique is discussed. This technique enables us to have a one-frequency Dyson’s equation for the pphh and similarly for other Green’s functions, thus considerably facilitating their calculation. A third type of Green’s function considered is the particle-hole Green’s function. RPA and high order RPA are treated, along with examples for setting up particle-hole RPA equations. A general method for deriving a model-space Dyson’s equation for Green’s functions is discussed. We also discuss a method for determining the normalization of Green’s function transition amplitudes based on its vertex function. Some applications of Green’s function methods to nuclear structure and recent deep inelastic lepton-nucleus scattering are addressed.

Kuo, T. T. S.; Tzeng, Yiharn

253

The Role of Many-Body Dispersion Interactions in Molecular Crystals  

NASA Astrophysics Data System (ADS)

The structure, energetics, and electronic properties of molecular crystals are studied using density functional theory (DFT) with the recently developed many-body dispersion (MBD) method [Tkatchenko et al. Phys. Rev. Lett. 108, 236402 (2012)]. It is shown that accounting for the long-range electrostatic screening in extended systems is essential for obtaining the correct dielectric constants and ensuing optical properties of molecular crystals [Schatschneider et al., arXiv:1211.1683]. Furthermore, accounting for the non-additive many-center dispersion interactions is crucial for obtaining a highly accurate description of the energetics of molecular crystals. This includes lattice energies, sublimation enthalpies [Reilly et al., to be published], and relative stabilities of polymorphs [Marom et al. arXiv: 1210.5636] [4pt] In collaboration with Leslie Leiserowitz, Weizmann Institute of Science, Israel; Bohdan Schatschneider, The Pennsylvania State University, Fayette; Robert DiStasio, Princeton University; Anthony Reilly and Guo-Xu Zhang, Fritz Haber Institute of the Max Planck Society, Berlin; James Chelikowsky, The University of Texas at Austin; and Alexandre Tkatchenko, Fritz Haber Institute of the Max Planck Society, Berlin.

Marom, Noa

2013-03-01

254

PROGRAPE-1: A Programmable, Multi-Purpose Computer for Many-Body Simulations  

NASA Astrophysics Data System (ADS)

We have developed PROGRAPE-1 (PROgrammable GRAPE-1), a programmable multi-purpose computer for many-body simulations. The main difference between PROGRAPE-1 and ``traditional'' GRAPE systems is that the former uses FPGA (Field Programmable Gate Array) chips as the processing elements, while the latter relies on a hardwired pipeline processor specialized to gravitational interactions. Since the logic implemented in FPGA chips can be reconfigured, we can use PROGRAPE-1 to calculate not only gravitational interactions, but also other forms of interactions, such as the van der Waals force, hydro\\-dynamical interactions in the SPHr calculation, and so on. PROGRAPE-1 comprises two Altera EPF10K100 FPGA chips, each of which contains nominally 100000 gates. To evaluate the programmability and performance of PROGRAPE-1, we implemented a pipeline for gravitational interactions similar to that of GRAPE-3. One pipeline is fitted into a single FPGA chip, operated at 16 MHz clock. Thus, for gravitational interactions, PROGRAPE-1 provided a speed of 0.96 Gflops-equivalent. PROGRAPE will prove to be useful for a wide-range of particle-based simulations in which the calculation cost of interactions other than gravity is high, such as the evaluation of SPH interactions.

Hamada, Tsuyoshi; Fukushige, Toshiyuki; Kawai, Atsushi; Makino, Junichiro

2000-10-01

255

The solvation of Li + and Na + in acetonitrile from ab initio-derived many-body ion-solvent potentials  

NASA Astrophysics Data System (ADS)

Several Li +- and Na +-acetonitrile models were derived from ab initio calculations at the counterpoise-corrected MP2/TZV++(d,p) level for distorted ion-(MeCN) n clusters with n=1, 4 and 6. Two different many-body ion-acetonitrile models were constructed: an effective three-body potential for use with the six-site effective pair model of Böhm et al., and an effective polarizable many-body model. The polarizable acetonitrile model used in the latter model is a new empirical model which was also derived in the present paper. Mainly for comparative purposes, two ion-acetonitrile pair potentials were also constructed from the ab initio cluster calculations: one pure pair potential and one effective pair potential. Using all these potential models, MD simulations in the NPT ensemble were performed for the pure acetonitrile liquid and for Li +(MeCN) and Na +(MeCN) solutions with 1 ion in 512 solvent molecules and with a simulation time of at least 120 ps per system. Thermodynamic properties, solvation-shell structure and the self-diffusion coefficient of the ions and of the solvent molecules were calculated and compared between the different models and with experimental data, where available. The Li + ion is found to be four-coordinated when the new many-body potentials are used, in contrast to the six-coordinated structure obtained for the pure pair and effective pair potentials. The coordination number of Na + is close to six for all the models derived here, although the coordination number becomes slightly smaller with the many-body potentials. For both ions, the solvent molecules in the first shell point their nitrogen ends towards the cation, while in the second shell the opposite orientation is the most common.

Spångberg, Daniel; Hermansson, Kersti

2004-05-01

256

Artificial Atoms and Molecules: On Many Body Effects and Coherence in Semiconductor Quantum Dots.  

National Technical Information Service (NTIS)

The continuing miniaturization of solid state devices has raised the question how small transistors can be made without changing their properties. People interested in making increasingly more powerful computers will try to avoid these new properties, bec...

T. H. Oosterkamp

1999-01-01

257

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

258

Far-infrared studies in quantum Hall system of II-VI semiconductors at high magnetic fields  

NASA Astrophysics Data System (ADS)

The cyclotron resonance was studied in II-VI quantum Hall systems, CdTe/CdMgTe quantum well and CdMnTe/CdMgTe quantum well. The oscillation of the effective mass against the integer filling factor was observed clearly in CdTe/CdMgTe quantum well. The mass-split cyclotron resonance that originated in the many-body effect was confirmed in the temperature dependence of the transmission spectrum. In CdMnTe/CdMgTe quantum well, drastic narrowing of the resonant width was observed with increasing magnetic fields. This is the special feature in the quantum Hall system of diluted magnetic semiconductors.

Imanaka, Y.; Takamasu, T.; Kido, G.; Karczewski, G.; Wojtowicz, T.; Kossut, J.

2001-04-01

259

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

260

Molecular Applications of Coupled Cluster and Many-Body Perturbation Methods  

Microsoft Academic Search

A series of molecular applications of many-body perturbation theory (MBPT) and the coupled-cluster doubles (CCD) model are described. Even though these methods have been available for sometime, only recently have large scale, MBPT molecular calculations become available. In the case of CCD, the results presented here are among the first obtained from a general purpose ab initio program. The intention

Rodney J. Bartlett; George D. Purvis III

1980-01-01

261

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

SciTech Connect

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

262

Many-body theory for multipole polarizabilities and dispersion forces in helium-helium interactions  

Microsoft Academic Search

Linked cluster many-body perturbation theory has been developed for the calculation of the dynamic quadrupole polarizabilities of the helium atom in its ground state. The polarizabilities have been used to calculate the London dispersion force constants for He-He interactions. The results for the polarizabilities and the van der Waals constants compare very well with other standard values.

B. K. Rao

1984-01-01

263

Many-body theory for multipole polarizabilities and dispersion forces in helium-helium interactions  

NASA Astrophysics Data System (ADS)

Linked cluster many-body perturbation theory has been developed for the calculation of the dynamic quadrupole polarizabilities of the helium atom in its ground state. The polarizabilities have been used to calculate the London dispersion force constants for He-He interactions. The results for the polarizabilities and the van der Waals constants compare very well with other standard values.

Rao, B. K.

1984-06-01

264

Quantum identification system  

NASA Astrophysics Data System (ADS)

A secure quantum identification system combining a classical identification procedure and quantum key distribution is proposed. Each identification sequence is always used just once and sequences are ``refueled'' from a shared provably secret key transferred through the quantum channel. Two identification protocols are devised. The first protocol can be applied when legitimate users have an unjammable public channel at their disposal. The deception probability is derived for the case of a noisy quantum channel. The second protocol employs unconditionally secure authentication of information sent over the public channel, and thus can be applied even in the case when an adversary is allowed to modify public communications. An experimental realization of a quantum identification system is described.

Dušek, Miloslav; Haderka, Ond?ej; Hendrych, Martin; Myška, Robert

1999-07-01

265

Relativistic many-body investigation of hyperfine interactions in excited S states of alkali metals: Francium and potassium  

Microsoft Academic Search

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

266

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

PubMed

Weak H(2) 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(+)-4H(2). Attention has recently focused on this model chemistry to test the reliability of electronic structure methods for H(2) 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. PMID:22047226

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

2011-10-28

267

Many-body study of the photoisomerization of the minimal model of the retinal protonated Schiff base  

NASA Astrophysics Data System (ADS)

We investigate the optical properties of the tZt- penta-3,5- dieniminium cation, a simplified model for the protonated Schiff base of 11- cis retinal in rhodopsin, along the isomerization pathway by ab-initio calculations based on Many-Body Perturbation Theory using the GW method and the Bethe-Salpeter equation. Our calculations are carried out on a few significant CASSCF geometrical configurations of the isomerization minimal energy path taken from the literature. Our excitation energies are qualitatively in agreement with previous Quantum Monte Carlo and post-Hartree-Fock calculations. We also employ TDDFT based methods, and investigate the outcome of using different approximations and several exchange-correlation functionals.

Conte, Adriano Mosca; Guidoni, Leonardo; Del Sole, Rodolfo; Pulci, Olivia

2011-10-01

268

Hierarchy of multiple many-body interaction scales in high-temperature superconductors  

SciTech Connect

To date, angle-resolved photoemission spectroscopy has been successful in identifying energy scales of the many-body interactions in correlated materials, focused on binding energies of up to a few hundred meV below the Fermi energy. Here, at higher energy scale, we present improved experimental data from four families of high-T{sub c} superconductors over a wide doping range that reveal a hierarchy of many-body interaction scales focused on: the low energy anomaly ('kink') of 0.03-0.09eV, a high energy anomaly of 0.3-0.5eV, and an anomalous enhancement of the width of the LDA-based CuO{sub 2} band extending to energies of {approx} 2 eV. Besides their universal behavior over the families, we find that all of these three dispersion anomalies also show clear doping dependence over the doping range presented.

Hussain, Zahid; Meevasana, W.; Zhou, X.J.; Sahrakorpi, S.; Lee, W.S.; Yang, W.L.; Tanaka, K.; Mannella, N.; Yoshida, T.; Lu, D.H.; Chen, Y.L.; He, R.H.; Lin, Hsin; Komiya, S.; Ando, Y.; Zhou, F.; Ti, W.X.; Xiong, J.W.; Zhao, Z.X.; Sasagawa, T.; Kakeshita, T.; Fujita, K.; Uchida, S.; Eisaki, H.; Fujimori, A.; Hussain, Z.; Markiewicz, R.S.; Bansil, A.; Nagaosa, N.; Zaanen, J.; Devereaux, T.P.; Shen, Z.X.

2006-12-21

269

Tuning Many-Body Interactions in Graphene: The Effects of Doping on Excitons and Carrier Lifetimes  

NASA Astrophysics Data System (ADS)

The optical properties of graphene are strongly affected by electron-electron (e-e) and electron-hole (e-h) interactions. Here we tune these many-body interactions through varying the density of free charge carriers. Measurements from the infrared to the ultraviolet reveal significant changes in the optical conductivity of graphene for both electron and hole doping. The shift, broadening, and modification in shape of the saddle-point exciton resonance reflect strong screening of the many-body interactions by the carriers, as well as changes in quasiparticle lifetimes. Ab initio calculations by the GW Bethe-Salpeter equation method, which take into account the modification of both the repulsive e-e and the attractive e-h interactions, provide excellent agreement with experiment. Understanding the optical properties and high-energy carrier dynamics of graphene over a wide range of doping is crucial for both fundamental graphene physics and for emerging applications of graphene in photonics.

Mak, Kin Fai; da Jornada, Felipe H.; He, Keliang; Deslippe, Jack; Petrone, Nicholas; Hone, James; Shan, Jie; Louie, Steven G.; Heinz, Tony F.

2014-05-01

270

Optically Engineered Quantum States in Ultrafast and Ultracold Systems  

NASA Astrophysics Data System (ADS)

This short account summarizes our recent achievements in ultrafast coherent control of isolated molecules in the gas phase, and its ongoing applications to an ensemble of ultracold Rydberg atoms to explore quantum many-body dynamics.

Ohmori, Kenji

2014-03-01

271

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

Microsoft Academic Search

In this study, we have found a new random ordered phase in isotropic models\\u000awith many-body interactions. Spin correlations between neighboring planes are\\u000arigorously shown to form a long-range order, namely coplanar order, using a\\u000aunitary transformation, and the phase transition of this new order has been\\u000aanalyzed on the bases of the mean-field theory and correlation identities. In\\u000athe

Yoichiro Hashizume; Masuo Suzuki

2010-01-01

272

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

Microsoft Academic Search

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

Yoichiro Hashizume; Masuo Suzuki

2011-01-01

273

Relativistic many-body calculations of the hyperfine-structure intervals in caesium and francium atoms  

Microsoft Academic Search

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

274

Multiconfiguration Hartree-Fock method and many-body perturbation theory: A unified approach  

Microsoft Academic Search

The multiconfiguration Hartree-Fock theory and many-body perturbation theory are combined in a calculation of the correlation energy of the ground state of the neutral beryllium atom. For this purpose the two-component Be multiconfiguration Hartree-Fock wave function is treated as a reference state and perturbation theory is used to systematically improve upon the accuracy of this function. The correlation energy of

John C. Morrison; Charlotte Froese Fischer

1987-01-01

275

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

Microsoft Academic Search

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

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

1996-01-01

276

CLASSIC MANY BODY POTENTIAL FOR CONCENTRATED ALLOYS, AND THE INVERSION OF ORDER IN FE-CR  

SciTech Connect

Atomistic simulations of alloys at the classic--or empirical--level face the challenge to correctly model basic thermodynamic properties. In this work we propose a methodology to generalize many-body classic potentials to incorporate complex formation energy curves. Application to Fe-Cr allows us to correctly predict the order vs segregation tendency in this alloy, as observed experimentally and calculated with ab initio techniques, providing in this way a potential suitable for radiation damage studies.

Caro, A; Crowson, D A; Caro, M

2005-04-14

277

Zero-point energy differences and many-body dispersion forces  

Microsoft Academic Search

The fully retarded dispersion interaction potentials, including many-body interactions, among neutral molecules are found in a systematic way. The method used relates the total zero-point energy of all the electromagnetic modes with the spectral sum of a linear operator. The difference between the zero-point energies with and without the molecules present is given as a contour integral. From the value

E. A. Power; T. Thirunamachandran

1994-01-01

278

The molecular dynamics simulation of irradiation damage cascades in copper using a many-body potential  

Microsoft Academic Search

The evolution of irradiation damage cascades in a metal has been simulated by molecular dynamics, using a many-body potential. Over 100 cascades have been produced with random knock-on directions and primary knock-on atom (PKA) energies ranging from 60 to 2 keV. The cascade evolution has been followed for times typically up to about 10ps and in some cases up to

A. J. E. Foreman; W. J. Phythian; C. A. English

1992-01-01

279

On Quantum Integrable Systems  

SciTech Connect

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

Many-body effects on surface stress, surface energy and surface relaxation of fcc metals  

NASA Astrophysics Data System (ADS)

The results of an investigation aimed at isolating the role played by pair-wise and many-body contributions in determining the surface stress, surface energy and surface relaxation for clean, low-index fcc metal surfaces are presented. General expressions for surface stress and surface energy are developed for generic embedded atom method (EAM) potentials and are contrasted with results derived from central-force pair potentials. Calculations are presented for specific forms. We find that these pair-wise and many-body contributions usually act in opposition to each other. Pair potentials tend to produce compressive surface stress contributions and favor outward surface relaxations, while the many-body component produces tensile surface stress contributions and favors inward relaxations. We also bring to light certain relationships between surface and bulk thermodynamic properties within the framework of these models. It is shown how surface stress can be expressed in an approximate form involving terms proportional to the product of an elastic modulus and the neighbor spacing characteristic of the material, and constants of proportionality that depend only on surface orientation. This form provides a good fit to a set of first-principles results as well. Finally, we demonstrate how various surface properties display a strong correlation with the ratio of bulk-to-shear moduli, Beq/ Geq.

Trimble, T. M.; Cammarata, R. C.

2008-07-01

281

Many-body forces and stability of the alkaline-earth tetramers  

NASA Astrophysics Data System (ADS)

The comparative study of the interaction energy and its many-body decomposition for Be 4, Mg 4, and Ca 4 at the all-electron CCSD(T)/aug-cc-pVQZ level is performed. For study of dependence of the binding energy and the orbital population on the cluster size the corresponding dimers and trimers were also calculated at the same level of theory. In comparison with weakly bound dimers, the binding energy in trimers and, especially, in tetramers drastically increases; e.g., E b/ N in Be 3 is 7 times larger and in Be 4 is 18.4 times larger than in Be 2. This sharp increase is explained as a manifestation of many-body forces. As follows from the many-body decomposition, the tetramers, and trimers as well, are stabilized by the three-body forces, whereas the two- and four-body forces are repulsive. The attractive contribution to the three-body forces has a three-atom electron exchange origin. The latter benefits the promotion of ns-electrons to np-orbitals. The natural bond orbital (NBO) population analysis reveals a relatively large np-population in trimers and tetramers (in Be 4 it is equal to 2p 0.44). The population of the valence np-orbitals leads to the sp-hybridization providing the covalent bonding.

Díaz-Torrejón, C. C.; Kaplan, Ilya G.

2011-03-01

282

Full-potential KKR calculations for vacancies in Al : Screening effect and many-body interactions  

NASA Astrophysics Data System (ADS)

We give ab initio calculations for vacancies in Al . The calculations are based on the generalized-gradient approximation in the density-functional theory and employ the all-electron full-potential Korringa-Kohn-Rostoker Green’s function method for point defects, which guarantees the correct embedding of the cluster of point defects in an otherwise perfect crystal. First, we confirm the recent calculated results of Carling [Phys. Rev. Lett. 85, 3862 (2000)], i.e., repulsion of the first-nearest-neighbor (1NN) divacancy in Al , and elucidate quantitatively the micromechanism of repulsion. Using the calculated results for vacancy formation energies and divacancy binding energies in Na , Mg , Al , and Si of face-centered-cubic, we show that the single vacancy in nearly free-electron systems becomes very stable with increasing free-electron density, due to the screening effect, and that the formation of divacancy destroys the stable electron distribution around the single vacancy, resulting in a repulsion of two vacancies on 1NN sites, so that the 1NN divacancy is unstable. Second, we show that the cluster expansion converges rapidly for the binding energies of vacancy agglomerates in Al . The binding energy of 13 vacancies consisting of a central vacancy and its 12 nearest neighbors, is reproduced within the error of 0.002eV per vacancy, if many-body interaction energies up to the four-body terms are taken into account in the cluster expansion, being compared with the average error (>0.1eV) of the glue models which are very often used to provide interatomic potentials for computer simulations. For the cluster expansion of the binding energies of impurities, we get the same convergence as that obtained for vacancies. Thus, the present cluster-expansion approach for the binding energies of agglomerates of vacancies and impurities in Al may provide accurate data to construct the interaction-parameter model for computer simulations which are strongly requested to study the dynamical process in the initial stage of the formation of the so-called Guinier-Preston zones of low-concentrated Al -based alloys such as Al1-cXc ( X=Cu , Zn ; c<0.05 ).

Hoshino, T.; Asato, M.; Zeller, R.; Dederichs, P. H.

2004-09-01

283

Development of the many-body perturbation theory and calculations of atomic properties for optical clocks  

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

284

Renormalization of concurrence: The application of the quantum renormalization group to quantum-information systems  

SciTech Connect

We have combined the idea of renormalization group and quantum-information theory. We have shown how the entanglement or concurrence evolve as the size of the system becomes large, i.e., the finite size scaling is obtained. Moreover, we introduce how the renormalization-group approach can be implemented to obtain the quantum-information properties of a many-body system. We have obtained the concurrence as a measure of entanglement, its derivatives and their scaling behavior versus the size of system for the one-dimensional Ising model in transverse field. We have found that the derivative of concurrence between two blocks each containing half of the system size diverges at the critical point with the exponent, which is directly associated with the divergence of the correlation length.

Kargarian, M. [Physics Department, Sharif University of Technology, Tehran 11155-9161 (Iran, Islamic Republic of); Jafari, R. [Institute for Advanced Studies in Basic Sciences, Zanjan 45195-1159 (Iran, Islamic Republic of); Institute for Studies in Theoretical Physics and Mathematics, Tehran 19395-5531 (Iran, Islamic Republic of); Langari, A. [Physics Department, Sharif University of Technology, Tehran 11155-9161 (Iran, Islamic Republic of); Institute for Studies in Theoretical Physics and Mathematics, Tehran 19395-5531 (Iran, Islamic Republic of)

2007-12-15

285

Energy Gaps and Interaction Blockade in Confined Quantum Systems  

SciTech Connect

We investigate universal properties of strongly confined particles that turn out to be dramatically different from what is observed for electrons in atoms and molecules. For a large class of harmonically confined systems, such as small quantum dots and optically trapped atoms, many-body particle addition and removal energies, and energy gaps, are accurately obtained from single-particle eigenvalues. Transport blockade phenomena are related to the derivative discontinuity of the exchange-correlation functional. This implies that they occur very generally, with Coulomb blockade being a particular realization of a more general phenomenon. In particular, we predict a van der Waals blockade in cold atom gases in traps.

Capelle, K. [Departamento de Fisica e Informatica, Instituto de Fisica de Sao Carlos, Universidade de Sao Paulo, Caixa Postal 369, 13560-970 Sao Carlos, SP (Brazil); Mathematical Physics, LTH, Lund University, 22100 Lund (Sweden); Borgh, M.; Kaerkkaeinen, K.; Reimann, S. M. [Mathematical Physics, LTH, Lund University, 22100 Lund (Sweden)

2007-07-06

286

Density of States of Quantum Spin Systems from Isotropic Entanglement  

NASA Astrophysics Data System (ADS)

We propose a method that we call isotropic entanglement (IE), which predicts the eigenvalue distribution of quantum many body (spin) systems with generic interactions. We interpolate between two known approximations by matching fourth moments. Though such problems can be QMA-complete, our examples show that isotropic entanglement provides an accurate picture of the spectra well beyond what one expects from the first four moments alone. We further show that the interpolation is universal, i.e., independent of the choice of local terms.

Movassagh, Ramis; Edelman, Alan

2011-08-01

287

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

Microsoft Academic Search

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

288

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

SciTech Connect

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

289

On the atomic roughness of solid-vapor interfaces - Significance of many-body interactions  

NASA Astrophysics Data System (ADS)

Published experimental data on the atomic roughness of solid-vapor interfaces (SVIs) are compiled in a table and compared with the predictions of theoretical models based on the Bragg-Williams approximation (e.g., Jackson, 1958). Significant discrepancies are observed, and a new model employing site-dependent bond strengths based on many-body-interaction effects is developed and demonstrated. Predictions for Cu, Pb, and Zn are presented in extensive tables and graphs and characterized in detail: good agreement with experimental observations of anisotropic melting is obtained.

Chen, Jenn-Shing; Ming, Nai-Ben; Rosenberger, Franz

1986-02-01

290

Scheme of thinking quantum systems  

NASA Astrophysics Data System (ADS)

A general approach describing quantum decision procedures is developed. The approach can be applied to quantum information processing, quantum computing, creation of artificial quantum intelligence, as well as to analyzing decision processes of human decision makers. Our basic point is to consider an active quantum system possessing its own strategic state. Processing information by such a system is analogous to the cognitive processes associated to decision making by humans. The algebra of probability operators, associated with the possible options available to the decision maker, plays the role of the algebra of observables in quantum theory of measurements. A scheme is advanced for a practical realization of decision procedures by thinking quantum systems. Such thinking quantum systems can be realized by using spin lattices, systems of magnetic molecules, cold atoms trapped in optical lattices, ensembles of quantum dots, or multilevel atomic systems interacting with electromagnetic field.

Yukalov, V. I.; Sornette, D.

2009-10-01

291

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

292

Non-local propagation of correlations in quantum systems with long-range interactions.  

PubMed

The maximum speed with which information can propagate in a quantum many-body system directly affects how quickly disparate parts of the system can become correlated and how difficult the system will be to describe numerically. For systems with only short-range interactions, Lieb and Robinson derived a constant-velocity bound that limits correlations to within a linear effective 'light cone'. However, little is known about the propagation speed in systems with long-range interactions, because analytic solutions rarely exist and because the best long-range bound is too loose to accurately describe the relevant dynamical timescales for any known spin model. Here we apply a variable-range Ising spin chain Hamiltonian and a variable-range XY spin chain Hamiltonian to a far-from-equilibrium quantum many-body system and observe its time evolution. For several different interaction ranges, we determine the spatial and time-dependent correlations, extract the shape of the light cone and measure the velocity with which correlations propagate through the system. This work opens the possibility for studying a wide range of many-body dynamics in quantum systems that are otherwise intractable. PMID:25008525

Richerme, Philip; Gong, Zhe-Xuan; Lee, Aaron; Senko, Crystal; Smith, Jacob; Foss-Feig, Michael; Michalakis, Spyridon; Gorshkov, Alexey V; Monroe, Christopher

2014-07-10

293

An improved treatment of empirical dispersion and a many-body energy decomposition scheme for the explicit polarization plus symmetry-adapted perturbation theory (XSAPT) method  

NASA Astrophysics Data System (ADS)

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.

Lao, Ka Un; Herbert, John M.

2013-07-01

294

Informationally coherent quantum systems  

Microsoft Academic Search

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

295

The role of three-nucleon forces and many-body processes in nuclear pairing  

NASA Astrophysics Data System (ADS)

We present microscopic valence-shell calculations of pairing gaps in the calcium isotopes, focusing on the role of three-nucleon (3N) forces and many-body processes. In most cases, we find a reduction in pairing strength when the leading chiral 3N forces are included, compared to results with low-momentum two-nucleon (NN) interactions only. This is in agreement with a recent energy density functional study. At the NN level, calculations that include particle-particle and hole-hole ladder contributions lead to smaller pairing gaps compared with experiment. When particle-hole contributions as well as the normal-ordered one- and two-body parts of 3N forces are consistently included to third order, we find reasonable agreement with experimental three-point mass differences. This highlights the important role of 3N forces and many-body processes for pairing in nuclei. Finally, we relate pairing gaps to the evolution of nuclear structure in neutron-rich calcium isotopes and study the predictions for the 2+ excitation energies, in particular for 54Ca.

Holt, J. D.; Menéndez, J.; Schwenk, A.

2013-07-01

296

Scale-adaptive tensor algebra for local many-body methods of electronic structure theory  

SciTech Connect

While the formalism of multiresolution analysis (MRA), based on wavelets and adaptive integral representations of operators, is actively progressing in electronic structure theory (mostly on the independent-particle level and, recently, second-order perturbation theory), the concepts of multiresolution and adaptivity can also be utilized within the traditional formulation of correlated (many-particle) theory which is based on second quantization and the corresponding (generally nonorthogonal) tensor algebra. In this paper, we present a formalism called scale-adaptive tensor algebra (SATA) which exploits an adaptive representation of tensors of many-body operators via the local adjustment of the basis set quality. Given a series of locally supported fragment bases of a progressively lower quality, we formulate the explicit rules for tensor algebra operations dealing with adaptively resolved tensor operands. The formalism suggested is expected to enhance the applicability and reliability of local correlated many-body methods of electronic structure theory, especially those directly based on atomic orbitals (or any other localized basis functions).

Liakh, Dmitry I [ORNL] [ORNL

2014-01-01

297

Transitionless quantum driving in open quantum systems  

NASA Astrophysics Data System (ADS)

We extend the concept of superadiabatic dynamics, or transitionless quantum driving, to quantum open systems whose evolution is governed by a master equation in the Lindblad form. We provide the general framework needed to determine the control strategy required to achieve superadiabaticity. We apply our formalism to two examples consisting of a two-level system coupled to environments with time-dependent bath operators.

Vacanti, G.; Fazio, R.; Montangero, S.; Palma, G. M.; Paternostro, M.; Vedral, V.

2014-05-01

298

Stabilizing spin coherence through environmental entanglement in strongly dissipative quantum systems  

NASA Astrophysics Data System (ADS)

The key feature of a quantum spin coupled to a harmonic bath—a model dissipative quantum system—is competition between oscillator potential energy and spin tunneling rate. We show that these opposing tendencies cause environmental entanglement through superpositions of adiabatic and antiadiabatic oscillator states, which then stabilizes the spin coherence against strong dissipation. This insight motivates a fast-converging variational coherent-state expansion for the many-body ground state of the spin-boson model, which we substantiate via numerical quantum tomography.

Bera, Soumya; Florens, Serge; Baranger, Harold U.; Roch, Nicolas; Nazir, Ahsan; Chin, Alex W.

2014-03-01

299

Quantum generalized Toda system  

NASA Astrophysics Data System (ADS)

We construct a "spectral curve" for the generalized Toda system, which allows efficiently finding its quantization. In turn, the quantization is realized using the technique of the quantum characteristic polynomial for the Gaudin system and an appropriate Alder-Kostant-Symes reduction. We also discuss some relations of this result to the recent consideration of the Drinfeld Zastava space, the monopole space, and corresponding symmetries of the Borel Yangian.

Talalaev, D. V.

2012-05-01

300

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

301

Many-body treatment of white dwarf and neutron stars on the brane  

SciTech Connect

Brane-world models suggest modification of Newton's law of gravity on the 3-brane at submillimeter scales. The brane-world induced corrections are in higher powers of inverse distance and appear as additional terms with the Newtonian potential. The average interparticle distance in white dwarf and neutron stars is 10{sup -10} cms and 10{sup -13} cms, respectively, and therefore, the effect of submillimeter corrections needs to be investigated. We show, by carrying out simple many-body calculations, that the mass and mass-radius relationship of the white dwarf and neutron stars are not effected by submillimeter corrections. However, our analysis shows that the correction terms in the effective theory give rise to force akin to surface tension in normal liquids.

Azam, Mofazzal [Theoretical Physics Division, Bhabha Atomic Research Centre, Mumbai (India); Sami, M. [Inter-University Centre for Astronomy and Astrophysics, Pune (India)

2005-07-15

302

Charge-Transfer Excited States in Aqueous DNA: Insights from Many-Body Green's Function Theory  

NASA Astrophysics Data System (ADS)

Charge-transfer (CT) excited states play an important role in the excited-state dynamics of DNA in aqueous solution. However, there is still much controversy on their energies. By ab initio many-body Green's function theory, together with classical molecular dynamics simulations, we confirm the existence of CT states at the lower energy side of the optical absorption maximum in aqueous DNA as observed in experiments. We find that the hydration shell can exert strong effects (˜1 eV) on both the electronic structure and CT states of DNA molecules through dipole electric fields. In this case, the solvent cannot be simply regarded as a macroscopic screening medium as usual. The influence of base stacking and base pairing on the CT states is also discussed.

Yin, Huabing; Ma, Yuchen; Mu, Jinglin; Liu, Chengbu; Rohlfing, Michael

2014-06-01

303

Excitons in molecular crystals from first-principles many-body perturbation theory: Picene versus pentacene  

NASA Astrophysics Data System (ADS)

By solving the first-principles many-body Bethe-Salpeter equation, we compare the optical properties of two prototype and technological relevant organic molecular crystals: picene and pentacene. Albeit very similar for the structural and electronic properties, picene and pentacene show remarkable differences in their optical spectra. While for pentacene the absorption onset is due to a charge-transfer exciton, in picene it is related to a strongly localized Frenkel exciton. The detailed comparison between the two materials allows us to discuss, on general grounds, how the interplay between the electronic band dispersion and the exchange electron-hole interaction plays a fundamental role in setting the nature of the exciton. It represents a clear example of the relevance of the competition between localization and delocalization in the description of two-particle electronic correlation.

Cudazzo, Pierluigi; Gatti, Matteo; Rubio, Angel

2012-11-01

304

Many-body GW calculation of the oxygen vacancy in ZnO  

SciTech Connect

Density-functional theory (DFT) calculations of defect levels in semiconductors based on approximate functionals are subject to considerable uncertainties, in particular due to inaccurate band-gap energies. Testing previous correction methods by many-body GW calculations for the O vacancy in ZnO, we find that: (i) The GW quasiparticle shifts of the V{sub O} defect states increase the spitting between occupied and unoccupied states due to self-interaction correction, and do not reflect the conduction- versus valence-band character. (ii) The GW quasiparticle energies of charged defect states require important corrections for supercell finite-size effects. (iii) The GW results are robust with respect to the choice of the underlying DFT or hybrid-DFT functional, and the (2+/0) donor transition lies below midgap, close to our previous prediction employing rigid band-edge shifts.

Lany, Stephan; Zunger, Alex

2010-01-01

305

Ab-initio Calculations of Absorption Spectra of Semiconducting Nanowires Within Many Body Perturbation Theory  

SciTech Connect

We present a study of the optical absorption spectra of thin silicon nanowires using many-body perturbation theory. We solve the Bethe-Salpeter equation in the static approximation using a technique that avoids explicit calculation of empty electronic states, as well as storage and inversion of the dielectric matrix. We provide a detailed assessment of the numerical accuracy of this technique, when using plane wave basis sets and periodically repeated supercells. Our calculations show that establishing numerical error bars of computed spectra is critical, in order to draw meaningful comparisons with experiments and between results obtained within different algorithms. We also discuss the influence of surface structure on the absorption spectra of nanowires with {approx_equal}1-nm diameter. Finally, we compare our calculations with those obtained within time-dependent density functional theory and find substantial differences, more pronounced than in the case of Si nanoparticles with the same diameter.

Ping, Y.; Lu, D.; Rocca, D.; Galli, G.

2012-01-20

306

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

307

Ab Initio Many-Body Calculations Of Nucleon-Nucleus Scattering  

SciTech Connect

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

308

Many-Body Effects in Iron Pnictides and Chalcogenides: Nonlocal Versus Dynamic Origin of Effective Masses  

NASA Astrophysics Data System (ADS)

We apply the quasiparticle self-consistent GW approximation (QSGW) to some of the iron pnictide and chalcogenide superconductors. We compute Fermi surfaces and density of states, and find excellent agreement with experiment, substantially improving over standard band-structure methods. Analyzing the QSGW self-energy we discuss nonlocal and dynamic contributions to effective masses. We present evidence that the two contributions are mostly separable, since the quasiparticle weight is found to be essentially independent of momentum. The main effect of nonlocality is captured by the static but nonlocal QSGW effective potential. Moreover, these nonlocal self-energy corrections, absent in, e.g., dynamical mean field theory, can be relatively large. We show, on the other hand, that QSGW only partially accounts for dynamic renormalizations at low energies. These findings suggest that QSGW combined with dynamical mean field theory will capture most of the many-body physics in the iron pnictides and chalcogenides.

Tomczak, Jan M.; van Schilfgaarde, M.; Kotliar, G.

2012-12-01

309

Coupled-cluster many-body theory in a correlated basis  

NASA Astrophysics Data System (ADS)

The correlated-basis-functions method of Feenberg and the coupled-cluster formalism of Coester and Kümmel are joined to form a new ground-state many-body method combining the advantages of both older methods and avoiding their disadvantages. From the point of view of the correlated-basis-functions method, coupled-cluster theory is used to sum the perturbation series partially to arbitrary order. From the point of view of the coupled-cluster method, correlated basis functions are used to take out the repulsive core of the two-body interaction in order to allow more efficient truncation schemes. It is found that powerful renormalizations are possible. Explicit equations are given for the two-body subsystems embodying generalized Bethe-Goldstone and random-phase equations summing, in the correlated basis, ladder and ring diagrams to arbitrary order.

Krotscheck, E.; Kümmel, H.; Zabolitzky, J. G.

1980-09-01

310

Communication: Stochastic evaluation of explicitly correlated second-order many-body perturbation energy  

NASA Astrophysics Data System (ADS)

A stochastic algorithm is proposed that can compute the basis-set-incompleteness correction to the second-order many-body perturbation (MP2) energy of a polyatomic molecule. It evaluates the sum of two-, three-, and four-electron integrals over an explicit function of electron-electron distances by a Monte Carlo (MC) integration at an operation cost per MC step increasing only quadratically with size. The method can reproduce the corrections to the MP2/cc-pVTZ energies of H2O, CH4, and C6H6 within a few mEh after several million MC steps. It circumvents the resolution-of-the-identity approximation to the nonfactorable three-electron integrals usually necessary in the conventional explicitly correlated (R12 or F12) methods.

Willow, Soohaeng Yoo; Zhang, Jinmei; Valeev, Edward F.; Hirata, So

2014-01-01

311

Many-body effects in the electronic spectra of cubic boron nitride  

NASA Astrophysics Data System (ADS)

We present state of the art first-principles calculations of optical spectra and the loss function of bulk cubic boron nitride (c-BN) , starting from a density functional Kohn-Sham band structure. We investigate the influence of many-body effects beyond the random phase approximation (RPA) on the optical spectra through the inclusion of self-energy and excitonic effects by a GW calculation and the solution of the Bethe-Salpeter equation. For the loss function we only perform RPA calculations, since Bethe-Salpeter results are already available in the literature. We show to which extent, and in which kind of spectra, the description of many-body effects is important for a meaningful comparison with experiment, and when they can be neglected due to mutual cancellation. We also present results obtained within time-dependent density functional theory, both in the adiabatic local density approximation (TDLDA) and using a recently proposed long-range approximation for the exchange-correlation kernel. Our results show that the latter corrects a big part of the error with respect to RPA or TDLDA; however, the corrections are not sufficient to qualify the method for further quantitative predictions, in particular for the study of the optical gap. In fact, since experiments often quote a relatively low (around 6.4eV ) band gap, whereas the calculated optical absorption spectrum already in the random-phase approximation appears blueshifted by more than 2eV with respect to the available experimental curve, we study in particular the question of the optical gap in this material. It turns out that, although there is evidence for a weakly bound exciton in c-BN , the optical gap of pure monocrystalline cubic BN should be around 11eV , hence significantly bigger than has sometimes been quoted from experiments.

Satta, Guido; Cappellini, Giancarlo; Olevano, Valerio; Reining, Lucia

2004-11-01

312

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

313

Mechanisms of Zr surface corrosion determined via molecular dynamics simulations with charge-optimized many-body (COMB) potentials  

NASA Astrophysics Data System (ADS)

A charge-optimized many-body (COMB) potential is proposed for the zirconium-zirconium oxide-zirconium hydride system. This potential is developed to describe the energetics of the interactions of oxygen and hydrogen with zirconium metal. We perform classical molecular dynamics simulations showing the initial corrosion behavior of three low-index zirconium surfaces via the deposition of O2 and H2O molecules. The basal (0 0 0 1) surface shows greater resistance to oxygen diffusion than the prism (1 0 1bar 0) and (1 1 2bar 0) surfaces. We suggest ways in which the surface structure has a unique role in the experimentally observed enhanced corrosion of the prism surfaces.

Noordhoek, Mark J.; Liang, Tao; Chiang, Tsu-Wu; Sinnott, Susan B.; Phillpot, Simon R.

2014-09-01

314

Quantum Information Science Workshop (Proceedings)  

NSF Publications Database

Quantum Information Science (QIS) is an emerging field with the potential to cause revolutionary advances in fields of science and engineering involving computation, communication, precision measurement, and fundamental quantum science. A quantum computer could efficiently and accurately simulate the evolution of quantum many-body systems and quantum field theories that cannot be simulated on classical computers without making unjustified approximations. Entanglement can also be viewed as a ...

315

A new many-body theory for the superfluid Fermi gas in the molecular Bose-Einstein condensed state  

NASA Astrophysics Data System (ADS)

Recent experimental advances on ultracold atomic Fermi gases pose new challenges to condensed matter theory. It has been established that there is a continuous crossover from BCS to molecular Bose-Einstein condensation (BEC) as the attractive interaction is increased. The lowest order ground state wave function which describes this crossover was first introduced by D. M. Eagles and A. J. Leggett (EL). The present Thesis aims at formulating an improved many-body ground state wave function, which represents a modification of the Eagles-Leggett ground state to include 4-fermion, and all higher correlations. We show that this theory, importantly, contains the exactly determined 4-fermion scattering behavior at short distances and, meanwhile, reduces to composite-boson Bogoliubov physics at long distances, with the correct intermolecular interaction built in. Our approach can be viewed as a new diagrammatic methodology, based on a perturbation series in the many-body wave function as distinct from a perturbation series in the interparticle interactions. Some basic properties of this wave function are studied, and its parameters, as well as the system's equation of state, are computed beyond mean-field. Using the constraints imposed by collective mode and cloud size experiments near the unitary interaction regime, we determine the range of kFa where the new perturbation method is applicable, and the range where the positive frequency shifts in the breathing modes of a trapped atomic cloud, albeit small, may be observable. Here kF is the Fermi wave vector and a is the 2-fermion scattering length. Other observable implications of this theory are briefly discussed. We also discuss the possible implications of this theory in other physical systems, in particular high temperature superconductors.

Tan, Shina

316

Collective edge modes in fractional quantum Hall systems  

NASA Astrophysics Data System (ADS)

Over the past few years one of us (Murthy) in collaboration with Shankar has developed an extended Hamiltonian formalism capable of describing the ground-state and low-energy excitations in the fractional quantum Hall regime. The Hamiltonian, expressed in terms of composite fermion operators, incorporates all the nonperturbative features of the fractional Hall regime, so that conventional many-body approximations such as Hartree-Fock and time-dependent Hartree-Fock are applicable. We apply this formalism to develop a microscopic theory of the collective edge modes in fractional quantum Hall regime. We present the results for edge mode dispersions at principal filling factors ?=1/3 , 1/5 , and 2/5 for systems with unreconstructed edges. The primary advantage of the method is that one works in the thermodynamic limit right from the beginning, thus avoiding the finite-size effects which ultimately limit exact diagonalization studies.

Nguyen, Hoang K.; Joglekar, Yogesh N.; Murthy, Ganpathy

2004-07-01

317

Fidelity spectrum and phase transitions of quantum systems  

SciTech Connect

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

318

The scalable quantum computation based on quantum dot systems  

Microsoft Academic Search

We propose a scheme for realizing the scalable quantum computation based on nonidentical quantum dots trapped in a single-mode waveguide. In this system, the quantum dots simultaneously interact with a large detuned waveguide and classical light fields. During the process, neither the waveguide mode nor the quantum dots are excited, while the sub-system composed of any two quantum dots can

Jian-Qi Zhang; Ya-Fei Yu; Xun-Li Feng; Zhi-Ming Zhang

2011-01-01

319

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

320

Mapping between finite temperature classical and zero temperature quantum systems: Quantum critical jamming and quantum dynamical heterogeneities  

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

321

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

NASA Astrophysics Data System (ADS)

We studied theoretically the optical properties of C60 fullerene microcrystals as a function of hydrostatic pressure with first-principles many-body theories. Calculations of the electronic properties were done in the GW approximation. We computed electronic excited states in the crystal by diagonalizing the Bethe-Salpeter equation. Our results confirmed the existence of bound excitons in the crystal. Both the electronic gap and optical gap decrease continuously and nonlinearly as pressure of up to 6 GPa is applied. As a result, the absorption spectrum shows strong redshift. We also obtained 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 (C8H8) or other molecules with similar size to the interstitials of the microcrystal. For the moderate lattice distortions studied here, we 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 C60 as an active element in piezo-optical devices.

Tiago, Murilo L.; Reboredo, Fernando A.

2009-05-01

322

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

PubMed

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

323

Photoassociation in a Bose-Einstein condensate: Many-body treatments with realistic molecular potentials  

NASA Astrophysics Data System (ADS)

Photoassociation is a process creating an excited diatomic molecule from a pair of colliding cold atoms by use of a laser field. Photoassociation in a Bose-Einstein condensate is often well described by the standard Gross-Pitaevskii equation (GP) with a complex scattering length. However, for situations where the pair dynamics plays a significant role, one must go beyond this picture. We have considered two many-body models: one is based on the cumulant method [1] and the other is inspired by the pair wave function approach [2]. Both models are used with realistic molecular potentials, so that we can address the nonperturbative regimes. For continuous lasers of moderate intensities (References [1] T. K"ohler, T. Gasenzer and K. Burnett, Phys. Rev. A 67, 013601 (2003) [2] P. Naidon and F. Masnou-Seeuws, Phys. Rev. A 68, 033612 (2003)

Naidon, Pascal

2005-05-01

324

Approximations for many-body Green's functions: insights from the fundamental equations  

NASA Astrophysics Data System (ADS)

Several widely used methods for the calculation of band structures and photo emission spectra, such as the GW approximation, rely on many-body perturbation theory. They can be obtained by iterating a set of functional differential equations (DEs) relating the one-particle Green's function (GF) to its functional derivative with respect to an external perturbing potential. In this work, we apply a linear response expansion in order to obtain insights into various approximations for GF calculations. The expansion leads to an effective screening while keeping the effects of the interaction to all orders. In order to study various aspects of the resulting equations, we discretize them and retain only one point in space, spin and time for all variables. Within this one-point model we obtain an explicit solution for the GF, which allows us to explore the structure of the general family of solutions and to determine the specific solution that corresponds to the physical one. Moreover, we analyze the performances of established approaches like GW over the whole range of interaction strength, and we explore alternative approximations. Finally, we link certain approximations for the exact solution to the corresponding manipulations of the DE which produces them. This link is crucial in view of a generalization of our findings to the real (multidimensional functional) case where only the DE is known.

Lani, Giovanna; Romaniello, Pina; Reining, Lucia

2012-01-01

325

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

326

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

327

Many-body effects are essential in a physically motivated CO2 force field.  

PubMed

We develop a physically motivated many-body force field for CO(2), incorporating explicit three-body interactions parameterized on the basis of two- and three-body symmetry adapted perturbation theory (SAPT) calculations. The potential is parameterized consistently with, and builds upon, our successful SAPT-based two-body CO(2) model ("Schmidt, Yu, and McDaniel" (SYM) model) [K. Yu, J. G. McDaniel, and J. R. Schmidt, J. Phys Chem B 115, 10054 (2011)]. We demonstrate that three-body interactions are essential to achieve an accurate description of bulk properties, and that previous two-body models have therefore necessarily exploited large error cancellations to achieve satisfactory results. The resulting three-body model exhibits excellent second/third virial coefficients and bulk properties over the phase diagram, yielding a nearly empirical parameter-free model. We show that this explicit three-body model can be converted into a computationally efficient, density/temperature-dependent two-body model that reduces almost exactly to our prior SYM model in the high-density limit. PMID:22280763

Yu, Kuang; Schmidt, J R

2012-01-21

328

Many-body effects are essential in a physically motivated CO2 force field  

NASA Astrophysics Data System (ADS)

We develop a physically motivated many-body force field for CO2, incorporating explicit three-body interactions parameterized on the basis of two- and three-body symmetry adapted perturbation theory (SAPT) calculations. The potential is parameterized consistently with, and builds upon, our successful SAPT-based two-body CO2 model (``Schmidt, Yu, and McDaniel'' (SYM) model) [K. Yu, J. G. McDaniel, and J. R. Schmidt, J. Phys Chem B 115, 10054 (2011)]. We demonstrate that three-body interactions are essential to achieve an accurate description of bulk properties, and that previous two-body models have therefore necessarily exploited large error cancellations to achieve satisfactory results. The resulting three-body model exhibits excellent second/third virial coefficients and bulk properties over the phase diagram, yielding a nearly empirical parameter-free model. We show that this explicit three-body model can be converted into a computationally efficient, density/temperature-dependent two-body model that reduces almost exactly to our prior SYM model in the high-density limit.

Yu, Kuang; Schmidt, J. R.

2012-01-01

329

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

SciTech Connect

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

330

Zero-point energy differences and many-body dispersion forces  

NASA Astrophysics Data System (ADS)

The fully retarded dispersion interaction potentials, including many-body interactions, among neutral molecules are found in a systematic way. The method used relates the total zero-point energy of all the electromagnetic modes with the spectral sum of a linear operator. The difference between the zero-point energies with and without the molecules present is given as a contour integral. From the value of this integral it is possible to extract the N-body dispersion energy by locating those terms which depend on the product of the polarizabilities of those N molecules. The Casimir-Polder pairwise energy is the two-body result. General formulas are found, and the special cases for N=3 and 4 are discussed in detail. The nonretarded interaction potentials are found as the asymptotic limits for small intermolecular separations, and the London and the Axilrod-Teller results are the N=2 and N=3 special cases. The N=4 near-zone limit is presented in its explicit form. It is of interest to note that, for the one-body case, the energy shift given by this method is the nonrelativistic Lamb shift.

Power, E. A.; Thirunamachandran, T.

1994-11-01

331

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

Microsoft Academic Search

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

332

Improved lower bounds for uncertaintylike relationships in many-body systems  

NASA Astrophysics Data System (ADS)

We show that employing more stringent inequalities in the derivation of uncertaintylike relationships can improve their accuracy. In particular, Eq. (23) due to Romera et al. [Phys. Rev. A 59, 4064 (1999)] can be further improved using the Faris inequalities rather than using the Hölder inequalities.

Alexander Wang, Yan; Carter, Emily A.

1999-11-01

333

Equilibration of quantum chaotic systems.  

PubMed

The quantum ergordic theorem for a large class of quantum systems was proved by von Neumann [Z. Phys. 57, 30 (1929)] and again by Reimann [Phys. Rev. Lett. 101, 190403 (2008)] in a more practical and well-defined form. However, it is not clear whether the theorem applies to quantum chaotic systems. With a rigorous proof still elusive, we illustrate and verify this theorem for quantum chaotic systems with examples. Our numerical results show that a quantum chaotic system with an initial low-entropy state will dynamically relax to a high-entropy state and reach equilibrium. The quantum equilibrium state reached after dynamical relaxation bears a remarkable resemblance to the classical microcanonical ensemble. However, the fluctuations around equilibrium are distinct: The quantum fluctuations are exponential while the classical fluctuations are Gaussian. PMID:24483425

Zhuang, Quntao; Wu, Biao

2013-12-01

334

Many-body effects in heavy fermion compounds [sic]. Final technical report for period September 1984 - January 2001  

SciTech Connect

A theoretical investigation of many-body effects in Cerium and Uranium Heavy Fermion and Mixed Valent Compounds and their experimental manifestations in thermodynamic, transport, and spectroscopic properties is discussed in this report.

Riseborough, Peter S.

2002-05-01

335

Simulating Quantum Spin Models with Trapped Ytterbium Ions^1  

Microsoft Academic Search

Simulating large quantum many-body systems is practically impossible with classical computers, as it requires resources exponential in the system size. An array of cold trapped ions has recently been identified as a promising candidate for exploring many-body spin Hamiltonians. This is due to superb control of their quantum states and interactions, high-fidelity spin state detection of each and every ion,

M.-S. Chang; K. Kim; S. Korenblit; K. R. Islam; J. D. Sterk; A. Chew; R. Slusher; C. Monroe

2008-01-01

336

Many-Body Processes in Atomic and Molecular Physics. Progress Report, September 1, 1982-August 31, 1983.  

National Technical Information Service (NTIS)

Progress is reported in the following areas: (1) development of a powerful semiclassical many-mode Floquet theory for nonperturbative treatment of the multiphoton dynamics of a quantum system interacting with several monochromatic radiation fields, (2) de...

S. I. Chu

1983-01-01

337

Oxygen deficient centers in silica: optical properties within many-body perturbation theory.  

PubMed

The electronic and optical properties of neutral oxygen vacancies, also called oxygen deficient centers (ODC(I)s), have been investigated in pure and germanium doped silica (both amorphous and ?-quartz) through first-principles calculations. By means of density functional theory and many-body perturbation theory (GW approximation and the solution of the Bethe-Salpeter equation), we obtain the atomic and electronic structures as well as the optical absorption spectra of pure and Ge-doped silica in the presence of ODCs (SiODC(I)s and GeODC(I)s); our study allows us to interpret and explain the very nature of the optical features in experimental absorption spectra. The theoretical optical absorption signatures of these defects show excellent agreement with experiments for the SiODC(I)s, i.e. two absorption bands arise around 7.6 eV due to transitions between the defect levels. Our theoretical results also explain the experimental difficulty in measuring the GeODC(I) absorption band in Ge-doped silica, which was in fact tentatively assigned to a broad and very weak absorption signature, located between 7.5 and 8.5 eV. The influence of Ge-doping induced disorder on the nature of the defect-related optical transitions is discussed. We find that even if the atomic and electronic structures of SiODC(I) and GeODC(I) defects are relatively similar, the slight network distortion induced by the presence of the Ge atom, together with the increase in the Ge-Si bond asymmetry, completely changes the nature of the optical absorption edge. PMID:23877003

Richard, N; Martin-Samos, L; Girard, S; Ruini, A; Boukenter, A; Ouerdane, Y; Meunier, J-P

2013-08-21

338

New semiclassical approach for the spatial density of nuclear systems.  

National Technical Information Service (NTIS)

A new decomposition of the many-body Wigner function in the squeezed states basis set of the quantum phase space-associated to bound states-allows one to separate the spatial density of the many body system in a semiclassical part plus its quantum complem...

D. Galetti S. Pawel

1990-01-01

339

Controlling Atomic, Solid-State and Hybrid Systems for Quantum Information Processing  

NASA Astrophysics Data System (ADS)

Quantum information science involves the use of precise control over quantum systems to explore new technologies. However, as quantum systems are scaled up they require an ever deeper understanding of many-body physics to achieve the required degree of control. Current experiments are entering a regime which requires active control of a mesoscopic number of coupled quantum systems or quantum bits (qubits). This thesis describes several approaches to this goal and shows how mesoscopic quantum systems can be controlled and utilized for quantum information tasks. The first system we consider is the nuclear spin environment of GaAs double quantum dots containing two electrons. We show that the through appropriate control of dynamic nuclear polarization one can prepare the nuclear spin environment in three distinct collective quantum states which are useful for quantum information processing with electron spin qubits. We then investigate a hybrid system in which an optical lattice is formed in the near field scattering off an array of metallic nanoparticles by utilizing the plasmonic resonance of the nanoparticles. We show that such a system would realize new regimes of dense, ultra-cold quantum matter and can be used to create a quantum network of atoms and plasmons. Finally we investigate quantum nonlinear optical systems. We show that the intrinsic nonlinearity for plasmons in graphene can be large enough to make a quantum gate for single photons. We also consider two nonlinear optical systems based on ultracold gases of atoms. In one case, we demonstrate an all-optical single photon switch using cavity quantum electrodynamics (QED) and slow light. In the second case, we study few photon physics in strongly interacting Rydberg polariton systems, where we demonstrate the existence of two and three photon bound states and study their properties.

Gullans, Michael John

340

Quantum Communications Systems.  

National Technical Information Service (NTIS)

This project supported research activities for making quantum- enhanced communications and metrology practical. The strategy was to develop robust photonic quantum states and sensors serving as an archetype for loss- tolerant information acquisition beyon...

I. A. Walmsley

2012-01-01

341

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

342

Development of generalized potential-energy surfaces using many-body expansions, neural networks, and moiety energy approximations  

NASA Astrophysics Data System (ADS)

A general method for the development of potential-energy hypersurfaces is presented. The method combines a many-body expansion to represent the potential-energy surface with two-layer neural networks (NN) for each M-body term in the summations. The total number of NNs required is significantly reduced by employing a moiety energy approximation. An algorithm is presented that efficiently adjusts all the coupled NN parameters to the database for the surface. Application of the method to four different systems of increasing complexity shows that the fitting accuracy of the method is good to excellent. For some cases, it exceeds that available by other methods currently in literature. The method is illustrated by fitting large databases of ab initio energies for Sin (n=3,4,...,7) clusters obtained from density functional theory calculations and for vinyl bromide (C2H3Br) and all products for dissociation into six open reaction channels (12 if the reverse reactions are counted as separate open channels) that include C-H and C-Br bond scissions, three-center HBr dissociation, and three-center H2 dissociation. The vinyl bromide database comprises the ab initio energies of 71 969 configurations computed at MP4(SDQ) level with a 6-31G(d,p) basis set for the carbon and hydrogen atoms and Huzinaga's (4333/433/4) basis set augmented with split outer s and p orbitals (43321/4321/4) and a polarization f orbital with an exponent of 0.5 for the bromine atom. It is found that an expansion truncated after the three-body terms is sufficient to fit the Si5 system with a mean absolute testing set error of 5.693×10-4 eV. Expansions truncated after the four-body terms for Sin (n=3,4,5) and Sin (n=3,4,...,7) provide fits whose mean absolute testing set errors are 0.0056 and 0.0212 eV, respectively. For vinyl bromide, a many-body expansion truncated after the four-body terms provides fitting accuracy with mean absolute testing set errors that range between 0.0782 and 0.0808 eV. These errors correspond to mean percent errors that fall in the range 0.98%-1.01%. Our best result using the present method truncated after the four-body summation with 16 NNs yields a testing set error that is 20.3% higher than that obtained using a 15-dimensional (15-140-1) NN to fit the vinyl bromide database. This appears to be the price of the added simplicity of the many-body expansion procedure.

Malshe, M.; Narulkar, R.; Raff, L. M.; Hagan, M.; Bukkapatnam, S.; Agrawal, P. M.; Komanduri, R.

2009-05-01

343

Dissipative dynamics with the corrected propagator method. Numerical comparison between fully quantum and mixed quantum\\/classical simulations  

Microsoft Academic Search

The recently developed quantum-classical method has been applied to the study of dissipative dynamics in multidimensional systems. The method is designed to treat many-body systems consisting of a low dimensional quantum part coupled to a classical bath. Assuming the approximate zeroth order evolution rule, the corrections to the quantum propagator are defined in terms of the total Hamiltonian and the

David Gelman; Steven D. Schwartz

2010-01-01

344

Classical command of quantum systems.  

PubMed

Quantum computation and cryptography both involve scenarios in which a user interacts with an imperfectly modelled or 'untrusted' system. It is therefore of fundamental and practical interest to devise tests that reveal whether the system is behaving as instructed. In 1969, Clauser, Horne, Shimony and Holt proposed an experimental test that can be passed by a quantum-mechanical system but not by a system restricted to classical physics. Here we extend this test to enable the characterization of a large quantum system. We describe a scheme that can be used to determine the initial state and to classically command the system to evolve according to desired dynamics. The bipartite system is treated as two black boxes, with no assumptions about their inner workings except that they obey quantum physics. The scheme works even if the system is explicitly designed to undermine it; any misbehaviour is detected. Among its applications, our scheme makes it possible to test whether a claimed quantum computer is truly quantum. It also advances towards a goal of quantum cryptography: namely, the use of 'untrusted' devices to establish a shared random key, with security based on the validity of quantum physics. PMID:23619692

Reichardt, Ben W; Unger, Falk; Vazirani, Umesh

2013-04-25

345

Effective Constraints for Quantum Systems  

Microsoft Academic Search

An effective formalism for quantum constrained systems is presented which allows manageable derivations of solutions and observables, including a treatment of physical reality conditions without requiring full knowledge of the physical inner product. Instead of a state equation from a constraint operator, an infinite system of constraint functions on the quantum phase space of expectation values and moments of states

Martin Bojowald; Barbara Sandhöfer; Aureliano Skirzewski; Artur Tsobanjan

2009-01-01

346

Coulomb crystallization in classical and quantum systems  

NASA Astrophysics Data System (ADS)

Coulomb crystallization occurs in one-component plasmas when the average interaction energy exceeds the kinetic energy by about two orders of magnitude. A simple road to reach such strong coupling consists in using external confinement potentials the strength of which controls the density. This has been succsessfully realized with ions in traps and storage rings and also in dusty plasma. Recently a three-dimensional spherical confinement could be created [1] which allows to produce spherical dust crystals containing concentric shells. I will give an overview on our recent results for these ``Yukawa balls'' and compare them to experiments. The shell structure of these systems can be very well explained by using an isotropic statically screened pair interaction. Further, the thermodynamic properties of these systems, such as the radial density distribution are discussed based on an analytical theory [3]. I then will discuss Coulomb crystallization in trapped quantum systems, such as mesoscopic electron and electron hole plasmas in coupled layers [4,5]. These systems show a very rich correlation behavior, including liquid and solid like states and bound states (excitons, biexcitons) and their crystals. On the other hand, also collective quantum and spin effects are observed, including Bose-Einstein condensation and superfluidity of bound electron-hole pairs [4]. Finally, I consider Coulomb crystallization in two-component neutral plasmas in three dimensions. I discuss the necessary conditions for crystals of heavy charges to exist in the presence of a light component which typically is in the Fermi gas or liquid state. It can be shown that their exists a critical ratio of the masses of the species of the order of 80 [5] which is confirmed by Quantum Monte Carlo simulations [6]. Familiar examples are crystals of nuclei in the core of White dwarf stars, but the results also suggest the existence of other crystals, including proton or ?-particle crystals in dense matter and of hole crystals in semiconductors. [1] O. Arp, D. Block, A. Piel, and A. Melzer, Phys. Rev. Lett. 93, 165004 (2004). [2] M. Bonitz, D. Block, O. Arp, V. Golubnychiy, H. Baumgartner, P. Ludwig, A. Piel, and A. Filinov, Phys. Rev. Lett. 96, 075001 (2006). [3] C. Henning, H. Baumgartner, A. Piel, P. Ludwig, V. Golubnychiy, M. Bonitz, and D. Block, Phys. Rev. E 74, 056403 (2006) and Phys. Rev. E (2007). [4] A. Filinov, M. Bonitz, and Yu. Lozovik, Phys. Rev. Lett. 86, 3851 (2001). [5] M. Bonitz, V. Filinov, P. Levashov, V. Fortov, and H. Fehske, Phys. Rev. Lett. 95, 235006 (2005) and J. Phys. A: Math. Gen. 39, 4717 (2006). [6] Introduction to Computational Methods for Many-Body Systems, M. Bonitz and D. Semkat (eds.), Rinton Press, Princeton (2006)

Bonitz, Michael

2007-11-01

347

Including many-body screening into self-consistent calculations--tight-binding model studies with Gutzwiller approximation  

NASA Astrophysics Data System (ADS)

We introduce a scheme to include many-body screening process explicitly into self-consistent equations for electronic structure calculations by employing Gutzwiller approximation. The method is illustrated by applying to a tight-binding model of the strongly correlated ?-Ce. The critical Coulomb repulsion Uff^c between the 4f electrons for electronic phase transition can be greatly raised over the usual screened value by including the main onsite many-body screening 5d channels. The method provides a promising way towards parameter-free ab initio Gutzwiller density functional theory.

Yao, Yongxin

2011-03-01

348

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

SciTech Connect

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

349

Relativistic many-body investigation of hyperfine interactions in excited S states of alkali metals: Francium and potassium  

SciTech Connect

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)] [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)] [Technische Natuurkunde, Technische Universiteit Delft, 2628 CJ Delft (The Netherlands)

1997-07-01

350

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

SciTech Connect

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

351

Many-body theory of excitation dynamics in an ultracold Rydberg gas  

SciTech Connect

We develop a theoretical approach for the dynamics of Rydberg excitations in ultracold gases,with a realistically large number of atoms. We rely on the reduction of the single-atom Bloch equations to rate equations, which is possible under various experimentally relevant conditions. Here, we explicitly refer to a two-step excitation scheme. We discuss the conditions under which our approach is valid by comparing the results with the solution of the exact quantum master equation for two interacting atoms. Concerning the emergence of an excitation blockade in a Rydberg gas, our results are in qualitative agreement with experiment. Possible sources of quantitative discrepancy are carefully examined. Based on the two-step excitation scheme, we predict the occurrence of an antiblockade effect and propose possible ways to detect this excitation enhancement experimentally in an optical lattice, as well as in the gas phase.

Ates, C.; Pattard, T.; Rost, J. M. [Max Planck Institute for the Physics of Complex Systems, Noethnitzer Strasse 38, D-01187 Dresden (Germany); Pohl, T. [ITAMP, Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS14, Cambridge, Massachusetts 02138 (United States)

2007-07-15

352

Relativistic Path Integral as a Lattice-based Quantum Algorithm  

Microsoft Academic Search

We demonstrate the equivalence of two representations of many-body relativistic quantum mechanics: the quantum lattice-gas\\u000a method and the path integral method. The former serves as an efficient lattice-based quantum algorithm to simulate the space-time\\u000a dynamics of a system of Dirac particles.

Jeffrey Yepez

2005-01-01

353

Relativistic many-body results for the hyperfine structure of the ground state of the Ag I isoelectronic sequence  

SciTech Connect

Relativistic many-body results (in MHz) for the magnetic dipole coupling constants of {sup 107}Ag, {sup 111}Cd, {sup 115}In, {sup 119}Sn, and {sup 121}Sb are {minus}1682, 14 446, 21 349, {minus}48 407, and 39 637. Experimental results for Ag and Cd are {minus}1712.56 and {minus}14 700.

Beck, D.R.; Datta, D. (Department of Physics, Michigan Technological University, Houghton, Michigan 49931 (US))

1991-07-01

354

Cooperative Excitation and Many-Body Interactions in a Cold Rydberg Gas  

NASA Astrophysics Data System (ADS)

The dipole blockade of Rydberg excitations is a hallmark of the strong interactions between atoms in these high-lying quantum states [M. Saffman, T. G. Walker, and K. Mølmer, Rev. Mod. Phys. 82, 2313 (2010)RMPHAT0034-686110.1103/RevModPhys.82.2313; D. Comparat and P. Pillet, J. Opt. Soc. Am. B 27, A208 (2010)JOBPDE0740-322410.1364/JOSAB.27.00A208]. One of the consequences of the dipole blockade is the suppression of fluctuations in the counting statistics of Rydberg excitations, of which some evidence has been found in previous experiments. Here we present experimental results on the dynamics and the counting statistics of Rydberg excitations of ultracold rubidium atoms both on and off resonance, which exhibit sub- and super-Poissonian counting statistics, respectively. We compare our results with numerical simulations using a novel theoretical model based on Dicke states of Rydberg atoms including dipole-dipole interactions, finding good agreement between experiment and theory.

Viteau, Matthieu; Huillery, Paul; Bason, Mark G.; Malossi, Nicola; Ciampini, Donatella; Morsch, Oliver; Arimondo, Ennio; Comparat, Daniel; Pillet, Pierre

2012-08-01

355

Rydberg dressing: understanding of collective many-body effects and implications for experiments  

NASA Astrophysics Data System (ADS)

The strong interaction between Rydberg atoms can be used to control the strength and character of the interatomic interaction in ultracold gases by weakly dressing the atoms with a Rydberg state. Elaborate theoretical proposals for the realization of various complex phases and applications in quantum simulation exist. Also a simple model has been already developed that describes the basic idea of Rydberg dressing in a two-atom basis. However, an experimental realization has been elusive so far. We present a model describing the ground state of a Bose-Einstein condensate dressed with a Rydberg level based on the Rydberg blockade. This approach provides an intuitive understanding of the transition from pure two-body interaction to a regime of collective interactions. Furthermore it enables us to calculate the deformation of a three-dimensional sample under realistic experimental conditions in mean-field approximation. We compare full three-dimensional numerical calculations of the ground state to an analytic expression obtained within Thomas-Fermi approximation. Finally we discuss limitations and problems arising in an experimental realization of Rydberg dressing based on our experimental results and point out possible solutions for future approaches. Our work enables the reader to straight forwardly estimate the experimental feasibility of Rydberg dressing in realistic three-dimensional atomic samples.

Balewski, J. B.; Krupp, A. T.; Gaj, A.; Hofferberth, S.; Löw, R.; Pfau, T.

2014-06-01

356

Preconditioned Quantum Linear System Algorithm  

NASA Astrophysics Data System (ADS)

We describe a quantum algorithm that generalizes the quantum linear system algorithm [Harrow et al., Phys. Rev. Lett. 103, 150502 (2009)] to arbitrary problem specifications. We develop a state preparation routine that can initialize generic states, show how simple ancilla measurements can be used to calculate many quantities of interest, and integrate a quantum-compatible preconditioner that greatly expands the number of problems that can achieve exponential speedup over classical linear systems solvers. To demonstrate the algorithm’s applicability, we show how it can be used to compute the electromagnetic scattering cross section of an arbitrary target exponentially faster than the best classical algorithm.

Clader, B. D.; Jacobs, B. C.; Sprouse, C. R.

2013-06-01

357

On the many-body Van der Waals binding energy of a dense fluid  

Microsoft Academic Search

We consider a dense system of neutral atoms. When the atoms are represented by isotropic oscillators (Drude-Lorentz model) interacting with nonretarded dipole-dipole forces, the binding energy of the system is given exactly by a well-known expression which is written as a sum of two-bond, three-bond, etc., Van der Waals interactions. For a Bravais lattice this expression for the binding energy

B. R. A. Nijboer

1975-01-01

358

Electronic Structure and Properties of Ground State of Ozone Using Hartree-Fock Theory and Inclusion of Many-Body Effects  

NASA Astrophysics Data System (ADS)

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 will enable a quantitative understanding of the interaction of ozone with both ultraviolet light and other molecules of both natural and artificial origin like for instance nitrogen and its oxides, excited oxygen atom, halogens and fluorochlorohydrocarbons. In the present talk we will discuss our results for the ground state of ozone making comparisons with(Nigel J. Mason and S. K. Pathak, Contemp. Phys. 38), 289 (1997) experimental data and results of earlier theoretical investigations by other methods.

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

2001-03-01

359

Formulation of Quantum Statistical Mechanics Based on the Feynman Path Centroid Density IV. Algorithms for Centroid Molecular Dynamics.  

National Technical Information Service (NTIS)

Numerical algorithms are developed for the centroid molecular dynamics (centroid MD) method to calculate dynamical time correlation functions for general many-body quantum systems. Approaches based on the normal mode path integral molecular dynamics and s...

J. Cao G. A. Voth

1994-01-01

360

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

Microsoft Academic Search

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

Walter J. Freeman; Giuseppe Vitiello

2006-01-01

361

Many-body reduced fidelity susceptibility in Lipkin-Meshkov-Glick model  

NASA Astrophysics Data System (ADS)

We study the reduced fidelity susceptibility ?r for an M -body subsystem of an N -body Lipkin-Meshkov-Glick model with ?=M/N fixed. The reduced fidelity susceptibility can be viewed as the response of subsystem to a certain parameter. In noncritical region, the inner correlation of the system is weak, and ?r behaves similar with the global fidelity susceptibility ?g , the ratio ?=?r/?g depends on ? but not on N . However, at the critical point, the inner correlation tends to be divergent, and we find ?r approaches ?g with increasing the N . It is interesting to note that, ?=1 in the thermodynamic limit, which means the susceptibilities of the local and global system are the same. Finally, we make numerical computations, and they are in perfect agreement with the analytical predictions.

Ma, Jian; Wang, Xiaoguang; Gu, Shi-Jian

2009-08-01

362

Parallel molecular dynamics simulations for short-ranged many-body potentials  

Microsoft Academic Search

A new method is described that permits the efficient execution of parallel molecular dynamics simulations for irregular problems with several thousands of atoms on Single-Instruction Multiple-Data computers. The approach is based on a data-parallel atomic decomposition scheme and has overall time-complexity O(N) , where N is the size of the system. The method has been implemented on a MasPar MP-1

C. F. Cornwell; L. T. Wille

2000-01-01

363

A study of many-body phenomena in metal nanoclusters (Au, Cu) close to their transition to the nonmetallic state  

SciTech Connect

The results of a study of many-body phenomena in gold and copper nanoclusters are presented. The measured conductivity as a function of nanocluster height h was found to have a minimum at h {approx} 0.6 nm. Conductivity was local in character at nanocluster sizes l {<=} l{sub c} {approx} 2.5 nm. Changes in core hole screening and an anomalous increase in the Anderson singularity index {alpha} in gold and copper nanoclusters could be caused by changes in permittivity from metallic ({epsilon} {sup {yields}} {infinity}) to nonmetallic ({epsilon} {proportional_to} l{sup 2}). The many-body phenomenon characteristics observed in the X-ray photoelectron and tunnel spectra of gold and copper nanoclusters as the size of the nanoclusters changed led us to suggest changes in the band structure of the nanoclusters and, therefore, their possible transition from the metallic to nonmetallic state.

Borman, V. D.; Borisyuk, P. V.; Lebid'ko, V. V.; Pushkin, M. A.; Tronin, V. N.; Troyan, V. I. [Moscow Engineering Physics Institute (State University) (Russian Federation)], E-mail: Troyan@mephi.ru; Antonov, D. A.; Filatov, D. O. [Nizhni Novgorod State University (Russian Federation)

2006-02-15

364

Many-body dynamic localization of strongly correlated electrons in ac-driven Hubbard lattices.  

PubMed

In the framework of the Hubbard model, it is shown that approximate dynamic localization for strongly correlated electrons hopping on a one-dimensional lattice and driven by a high-frequency sinusoidal field can be realized provided that periodic ? phase slips are impressed into the sinusoidal field. A possible experimental demonstration of the proposed driving scheme is presented for a photonic model system of the two-particle Hubbard model, based on light transport in a square waveguide lattice with a sinusoidally curved optical axis. PMID:23032640

Longhi, S

2012-10-31

365

Effect of many-body interactions on the solid-liquid phase behavior of charge-stabilized colloidal suspensions  

Microsoft Academic Search

The solid-liquid phase diagram of charge-stabilized colloidal suspensions has been calculated using a technique that combines a continuous Poisson-Boltzmann description for the microscopic electrolyte ions with a molecular-dynamics simulation for the macroionic colloidal spheres. While correlations between the microions are neglected in this approach, many-body interactions between the colloids, mediated by the screening ionic fluid between them, are fully included.

J. Dobnikar; R. Rzehak; H. H. von Grünberg

2003-01-01

366

Exchange interaction in binuclear complexes with rare-earth and copper ions: A many-body model study  

Microsoft Academic Search

We have used a many-body model Hamiltonian to study the nature of the magnetic ground state of heterobinuclear complexes involving rare-earth and copper ions. We have taken into account all diagonal repulsions involving the rare-earth 4f and 5d orbitals and the copper 3d orbital. In addition, we have included direct exchange interaction, crystal field splitting of the rare-earth atomic levels

Indranil Rudra; C. Raghu; S. Ramasesha

2002-01-01

367

How do ovarian follicles interact? A many-body problem with unusual symmetry and symmetry-breaking properties  

NASA Astrophysics Data System (ADS)

The assumption that hormonal feedback regulates ovarian follicle growth is used to formulate a many-body problem in which interactions are spatially independent. This mechanism of interaction is shown to be sufficient to account for the regulation of ovulation number. A method is also developed to test if this assumption is consistent with the observed spatial distribution of follicles in the Rhesus monkey ovary.

Michael Lacker, H.; Percus, Allon

1991-06-01

368

Many-body processes in atomic and molecular physics. Progress report, September 1, 1982August 31, 1983  

Microsoft Academic Search

Progress is reported in the following areas: (1) development of a powerful semiclassical many-mode Floquet theory for nonperturbative treatment of the multiphoton dynamics of a quantum system interacting with several monochromatic radiation fields, (2) development of analytical quasi-level models for line shape analysis of intense field molecular multiphoton absorption spectra, (3) completion of a high-precision rotatonal predissociation lifetime determination of

1983-01-01

369

UNEDF: Advanced Scientific Computing Collaboration Transforms the Low-Energy Nuclear Many-Body Problem  

NASA Astrophysics Data System (ADS)

The demands of cutting-edge science are driving the need for larger and faster computing resources. With the rapidly growing scale of computing systems and the prospect of technologically disruptive architectures to meet these needs, scientists face the challenge of effectively using complex computational resources to advance scientific discovery. Multi-disciplinary collaborating networks of researchers with diverse scientific backgrounds are needed to address these complex challenges. The UNEDF SciDAC collaboration of nuclear theorists, applied mathematicians, and computer scientists is developing a comprehensive description of nuclei and their reactions that delivers maximum predictive power with quantified uncertainties. This paper describes UNEDF and identifies attributes that classify it as a successful computational collaboration. We illustrate significant milestones accomplished by UNEDF through integrative solutions using the most reliable theoretical approaches, most advanced algorithms, and leadership-class computational resources.

Nam, H.; Stoitsov, M.; Nazarewicz, W.; Bulgac, A.; Hagen, G.; Kortelainen, M.; Maris, P.; Pei, J. C.; Roche, K. J.; Schunck, N.; Thompson, I.; Vary, J. P.; Wild, S. M.

2012-12-01

370

Excited states of biological chromophores studied using many-body perturbation theory: Effects of resonant-antiresonant coupling and dynamical screening  

NASA Astrophysics Data System (ADS)

The excited states of model chromophores of the photoactive yellow protein and of rhodopsin are studied using ab initio many-body perturbation theory (within the GW approximation and Bethe-Salpeter equation). Calculations beyond the Tamm-Dancoff approximation, i.e., consideration of the resonant-antiresonant transition coupling, are needed for an accurate description of the lowest ???? excitations due to the large exchange interaction between the electron and hole localized in the low-dimension systems. The inclusion of dynamical effect in the electron-hole screening is important for an accurate description of the lowest n??? excitations.

Ma, Yuchen; Rohlfing, Michael; Molteni, Carla

2009-12-01

371

Applications of Feedback Control in Quantum Systems  

Microsoft Academic Search

We give an introduction to feedback control in quantum systems, as well as an overview of the variety of applications which have been explored to date. This introductory review is aimed primarily at control theorists unfamiliar with quantum mechanics, but should also be useful to quantum physicists interested in applications of feedback control. We explain how feedback in quantum systems

Kurt Jacobs

2006-01-01

372

Quantum Annealing and Quantum Fluctuation Effect in Frustrated Ising Systems  

NASA Astrophysics Data System (ADS)

Quantum annealing method has been widely attracted attention in statistical physics and information science since it is expected to be a powerful method to obtain the best solution of optimization problem as well as simulated annealing. The quantum annealing method was incubated in quantum statistical physics. This is an alternative method of the simulated annealing which is well-adopted for many optimization problems. In the simulated annealing, we obtain a solution of optimization problem by decreasing temperature (thermal fluctuation) gradually. In the quantum annealing, in contrast, we decrease quantum field (quantum fluctuation) gradually and obtain a solution. In this paper we review how to implement quantum annealing and show some quantum fluctuation effects in frustrated Ising spin systems.

Tanaka, Shu; Tamura, Ryo

2013-09-01

373

Communication: electronic band gaps of semiconducting zig-zag carbon nanotubes from many-body perturbation theory calculations.  

PubMed

Electronic band gaps for optically allowed transitions are calculated for a series of semiconducting single-walled zig-zag carbon nanotubes of increasing diameter within the many-body perturbation theory GW method. The dependence of the evaluated gaps with respect to tube diameters is then compared with those found from previous experimental data for optical gaps combined with theoretical estimations of exciton binding energies. We find that our GW gaps confirm the behavior inferred from experiment. The relationship between the electronic gap and the diameter extrapolated from the GW values is also in excellent agreement with a direct measurement recently performed through scanning tunneling spectroscopy. PMID:22583270

Umari, P; Petrenko, O; Taioli, S; De Souza, M M

2012-05-14

374

Quantum Monte Carlo calculation of entanglement Rényi entropies for generic quantum systems  

NASA Astrophysics Data System (ADS)

We present a general scheme for the calculation of the Rényi entropy of a subsystem in quantum many-body models that can be efficiently simulated via quantum Monte Carlo. When the simulation is performed at very low temperature, the above approach delivers the entanglement Rényi entropy of the subsystem, and it allows us to explore the crossover to the thermal Rényi entropy as the temperature is increased. We implement this scheme explicitly within the stochastic series expansion as well as within path-integral Monte Carlo, and apply it to quantum spin and quantum rotor models. In the case of quantum spins, we show that relevant models in two dimensions with reduced symmetry (XX model or hard-core bosons, transverse-field Ising model at the quantum critical point) exhibit an area law for the scaling of the entanglement entropy.

Humeniuk, Stephan; Roscilde, Tommaso

2012-12-01

375

Toward transferable interatomic van der Waals interactions without electrons: The role of multipole electrostatics and many-body dispersion.  

PubMed

We estimate polarizabilities of atoms in molecules without electron density, using a Voronoi tesselation approach instead of conventional density partitioning schemes. The resulting atomic dispersion coefficients are calculated, as well as many-body dispersion effects on intermolecular potential energies. We also estimate contributions from multipole electrostatics and compare them to dispersion. We assess the performance of the resulting intermolecular interaction model from dispersion and electrostatics for more than 1300 neutral and charged, small organic molecular dimers. Applications to water clusters, the benzene crystal, the anti-cancer drug ellipticine-intercalated between two Watson-Crick DNA base pairs, as well as six macro-molecular host-guest complexes highlight the potential of this method and help to identify points of future improvement. The mean absolute error made by the combination of static electrostatics with many-body dispersion reduces at larger distances, while it plateaus for two-body dispersion, in conflict with the common assumption that the simple 1/R(6) correction will yield proper dissociative tails. Overall, the method achieves an accuracy well within conventional molecular force fields while exhibiting a simple parametrization protocol. PMID:25053295

Bereau, Tristan; von Lilienfeld, O Anatole

2014-07-21

376

Up on the Jaynes-Cummings ladder of a quantum-dot/microcavity system.  

PubMed

In spite of their different natures, light and matter can be unified under the strong-coupling regime, yielding superpositions of the two, referred to as dressed states or polaritons. After initially being demonstrated in bulk semiconductors and atomic systems, strong-coupling phenomena have been recently realized in solid-state optical microcavities. Strong coupling is an essential ingredient in the physics spanning from many-body quantum coherence phenomena, such as Bose-Einstein condensation and superfluidity, to cavity quantum electrodynamics. Within cavity quantum electrodynamics, the Jaynes-Cummings model describes the interaction of a single fermionic two-level system with a single bosonic photon mode. For a photon number larger than one, known as quantum strong coupling, a significant anharmonicity is predicted for the ladder-like spectrum of dressed states. For optical transitions in semiconductor nanostructures, first signatures of the quantum strong coupling were recently reported. Here we use advanced coherent nonlinear spectroscopy to explore a strongly coupled exciton-cavity system. We measure and simulate its four-wave mixing response, granting direct access to the coherent dynamics of the first and second rungs of the Jaynes-Cummings ladder. The agreement of the rich experimental evidence with the predictions of the Jaynes-Cummings model is proof of the quantum strong-coupling regime in the investigated solid-state system. PMID:20208523

Kasprzak, J; Reitzenstein, S; Muljarov, E A; Kistner, C; Schneider, C; Strauss, M; Höfling, S; Forchel, A; Langbein, W

2010-04-01

377

Nonequilibrium quantum dissipation in spin-fermion systems  

NASA Astrophysics Data System (ADS)

Dissipative processes in nonequilibrium many-body systems are fundamentally different than their equilibrium counterparts. Such processes are of great importance for the understanding of relaxation in single-molecule devices. As a detailed case study, we investigate here a generic spin-fermion model, where a two-level system couples to two metallic leads with different chemical potentials. We present results for the spin relaxation rate in the nonadiabatic limit for an arbitrary coupling to the leads using both analytical and exact numerical methods. The nonequilibrium dynamics is reflected by an exponential relaxation at long times and via complex phase shifts, leading in some cases to an “antiorthogonality” effect. In the limit of strong system-lead coupling at zero temperature we demonstrate the onset of a Marcus-like Gaussian decay with voltage difference activation. This is analogous to the equilibrium spin-boson model, where at strong coupling and high temperatures, the spin excitation rate manifests temperature activated Gaussian behavior. We find that there is no simple linear relationship between the role of the temperature in the bosonic system and a voltage drop in a nonequilibrium electronic case. The two models also differ by the orthogonality-catastrophe factor existing in a fermionic system, which modifies the resulting line shapes. Implications for current characteristics are discussed. We demonstrate the violation of pairwise Coulomb gas behavior for strong coupling to the leads. The results presented in this paper form the basis of an exact, nonperturbative description of steady-state quantum dissipative systems.

Segal, Dvira; Reichman, David R.; Millis, Andrew J.

2007-11-01

378

Perturbative approach to Markovian open quantum systems.  

PubMed

The exact treatment of Markovian open quantum systems, when based on numerical diagonalization of the Liouville super-operator or averaging over quantum trajectories, is severely limited by Hilbert space size. Perturbation theory, standard in the investigation of closed quantum systems, has remained much less developed for open quantum systems where a direct application to the Lindblad master equation is desirable. We present such a perturbative treatment which will be useful for an analytical understanding of open quantum systems and for numerical calculation of system observables which would otherwise be impractical. PMID:24811607

Li, Andy C Y; Petruccione, F; Koch, Jens

2014-01-01

379

Perturbative approach to Markovian open quantum systems  

NASA Astrophysics Data System (ADS)

The exact treatment of Markovian open quantum systems, when based on numerical diagonalization of the Liouville super-operator or averaging over quantum trajectories, is severely limited by Hilbert space size. Perturbation theory, standard in the investigation of closed quantum systems, has remained much less developed for open quantum systems where a direct application to the Lindblad master equation is desirable. We present such a perturbative treatment which will be useful for an analytical understanding of open quantum systems and for numerical calculation of system observables which would otherwise be impractical.

Li, Andy C. Y.; Petruccione, F.; Koch, Jens

2014-05-01

380

Perturbative approach to Markovian open quantum systems  

PubMed Central

The exact treatment of Markovian open quantum systems, when based on numerical diagonalization of the Liouville super-operator or averaging over quantum trajectories, is severely limited by Hilbert space size. Perturbation theory, standard in the investigation of closed quantum systems, has remained much less developed for open quantum systems where a direct application to the Lindblad master equation is desirable. We present such a perturbative treatment which will be useful for an analytical understanding of open quantum systems and for numerical calculation of system observables which would otherwise be impractical.

Li, Andy C. Y.; Petruccione, F.; Koch, Jens

2014-01-01

381

Quasiparticle electronic structure and optical absorption of diamond nanoparticles from ab initio many-body perturbation theory  

NASA Astrophysics Data System (ADS)

The excited states of small-diameter diamond nanoparticles in the gas phase are studied using the GW method and Bethe-Salpeter equation (BSE) within the ab initio many-body perturbation theory. The calculated ionization potentials and optical gaps are in agreement with experimental results, with the average error about 0.2 eV. The electron affinity is negative and the lowest unoccupied molecular orbital is rather delocalized. Precise determination of the electron affinity requires one to take the off-diagonal matrix elements of the self-energy operator into account in the GW calculation. BSE calculations predict a large exciton binding energy which is an order of magnitude larger than that in the bulk diamond.

Yin, Huabing; Ma, Yuchen; Hao, Xiaotao; Mu, Jinglin; Liu, Chengbu; Yi, Zhijun

2014-06-01

382

Ab initio study of temporary anions of benzene and fluorobenzenes using the multipartitioning many-body perturbation theory.  

PubMed

We present an ab initio study of the lowest states of five temporary anions: C6H6(-), C6H5F(-), 1,4-C6H4F2(-), 1,2,3-C6H3F3(-), and 1,3,5-C6H3F3(-). Vertical positions and widths of anionic resonances have been calculated within the stabilization graph approach using the multipartitioning form of the many-body perturbation theory for state-selective effective Hamiltonians restricted to second order (MPPT-R). Good agreement with experimentally derived estimates justifies application of the MPPT-R method for theoretical investigation of haloaromatic temporary anion radicals. PMID:19810321

Izmaylov, Artur F; Shchegoleva, Lyudmila N; Scuseria, Gustavo E; Zaitsevskii, Andréi

2005-12-01

383

Quasiparticle electronic structure and optical absorption of diamond nanoparticles from ab initio many-body perturbation theory.  

PubMed

The excited states of small-diameter diamond nanoparticles in the gas phase are studied using the GW method and Bethe-Salpeter equation (BSE) within the ab initio many-body perturbation theory. The calculated ionization potentials and optical gaps are in agreement with experimental results, with the average error about 0.2 eV. The electron affinity is negative and the lowest unoccupied molecular orbital is rather delocalized. Precise determination of the electron affinity requires one to take the off-diagonal matrix elements of the self-energy operator into account in the GW calculation. BSE calculations predict a large exciton binding energy which is an order of magnitude larger than that in the bulk diamond. PMID:24908016

Yin, Huabing; Ma, Yuchen; Hao, Xiaotao; Mu, Jinglin; Liu, Chengbu; Yi, Zhijun

2014-06-01

384

General features of the relaxation dynamics of interacting quantum systems  

NASA Astrophysics Data System (ADS)

We study numerically and analytically isolated interacting quantum systems that are taken out of equilibrium instantaneously (quenched). The probability of finding the initial state in time, the so-called fidelity, decays fastest for systems described by full random matrices, where simultaneous many-body interactions are implied. In the realm of realistic systems with two-body interactions, the dynamics is slower and depends on the interplay between the initial state and the Hamiltonian characterizing the system. The fastest fidelity decay in this case is Gaussian and can persist until saturation. A simple general picture, in which the fidelity plays a central role, is also achieved for the short-time dynamics of few-body observables. It holds for initial states that are eigenstates of the observables. We also discuss the need to reassess analytical expressions that were previously proposed to describe the evolution of the Shannon entropy. Our analyses are mainly developed for initial states that can be prepared in experiments with cold atoms in optical lattices.

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

2014-06-01

385

Many-body processes in atomic and molecular physics. Progress report, September 1, 1982-August 31, 1983  

SciTech Connect

Progress is reported in the following areas: (1) development of a powerful semiclassical many-mode Floquet theory for nonperturbative treatment of the multiphoton dynamics of a quantum system interacting with several monochromatic radiation fields, (2) development of analytical quasi-level models for line shape analysis of intense field molecular multiphoton absorption spectra, (3) completion of a high-precision rotatonal predissociation lifetime determination of Ar-H/sub 2/ and Ar-HD van der Waals (vdW) molecules, using the complex-coordinate coupled-channel (CCCC) formalisms, and (4) development of the complex quasi-vibrational energy (QVE) and the inhomogeneous differential equation (IDE) approaches for calculating multiphoton dissociation (MPD) rates from highly excited vibrational states of diatomic molecules. (WHK)

Chu, S.I.

1983-04-01

386

Algorithms deducing thermodynamic and quantum critical properties of homogenous bulk systems from the data of trapped gases  

NASA Astrophysics Data System (ADS)

The goal of Quantum Simulation -- i.e. using cold atoms to simulate quantum many- body systems -- is to find out the properties of bulk homogeneous systems. Cold-gas experiments, however, are carried out in spatially inhomogeneous confining traps, which leads inevitably to different phases in the sample. This makes it difficult to deduce the properties of homogeneous phases with standard density imaging, which averages over different phases. Moreover, important properties like superfluid density are inaccessible by standard imaging techniques, and will remain inaccessible even when systems of interest are successfully simulated. Here, we present algorithms for mapping out a number of properties of homogeneous systems, including superfluid density. In addition, we present algorithms to determine the emergence and the details of quantum critical properties. Our schemes make explicit use of the inhomogeneity of the trap, turning the source of difficulty into a means of constructing solutions.

Ho, Tin-Lun

2010-03-01

387

Repeated interactions in open quantum systems  

NASA Astrophysics Data System (ADS)

Analyzing the dynamics of open quantum systems has a long history in mathematics and physics. Depending on the system at hand, basic physical phenomena that one would like to explain are, for example, convergence to equilibrium, the dynamics of quantum coherences (decoherence) and quantum correlations (entanglement), or the emergence of heat and particle fluxes in non-equilibrium situations. From the mathematical physics perspective, one of the main challenges is to derive the irreversible dynamics of the open system, starting from a unitary dynamics of the system and its environment. The repeated interactions systems considered in these notes are models of non-equilibrium quantum statistical mechanics. They are relevant in quantum optics, and more generally, serve as a relatively well treatable approximation of a more difficult quantum dynamics. In particular, the repeated interaction models allow to determine the large time (stationary) asymptotics of quantum systems out of equilibrium.

Bruneau, Laurent; Joye, Alain; Merkli, Marco

2014-07-01

388

Elucidating the role of many-body forces in liquid water. I. Simulations of water clusters on the VRT(ASP-W) potential surfaces  

NASA Astrophysics Data System (ADS)

We test two new potentials for water, fit to vibration-rotation tunneling (VRT) data by employing diffusion quantum Monte Carlo simulations to calculate the vibrational ground-state properties of water clusters. These potentials, VRT(ASP-W)II and VRT(ASP-W)III, are fits of the highly detailed ASP-W (anisotropic site potential with Woermer dispersion) ab initio potential to (D2O)2 microwave and far-infrared data, and along with the SAPT5s (five-site symmetry adapted perturbation theory) potentials, are the most accurate water dimer potential surfaces in the literature. The results from VRT(ASP-W)II and III are compared to those from the original ASP-W potential, the SAPT5s family of potentials, and several bulk water potentials. Only VRT(ASP-W)III and the spectroscopically ``tuned'' SAPT5st (with N-body induction included) accurately reproduce the vibrational ground-state structures of water clusters up to the hexamer. Finally, the importance of many-body induction and three-body dispersion are examined, and it is shown that the latter can have significant effects on water cluster properties despite its small magnitude.

Goldman, Nir; Saykally, R. J.

2004-03-01

389

Many-Body Problem with Quadratic and/or Inversely-Quadratic Potentials in One- and More-Dimensional Spaces: Some Retrospective Remarks  

NASA Astrophysics Data System (ADS)

In the context of an ambient space with an arbitrary number d of dimensions, the many-body problem consisting of an arbitrary number N of particles confined by a common, external harmonic potential (realizing a container with soft walls) and interacting among themselves and with the environment with arbitrary conservative repulsive forces scaling as the inverse cube of distances, displays a peculiar behaviour: its effective volume oscillates isochronously without damping. We recently discovered this remarkable phenomenon (valid in the context of both classical and quantum mechanics) and discussed its implications in the context of statistical mechanics and thermodynamics; but after publishing these findings we were informed that essentially analogous results had been previously obtained by Lyndell-Bell and Lyndell-Bell. In the present paper, motivated by the need we felt to acknowledge this fact, we also offer some retrospective remarks on the N -body problem with quadratic and/or inversely-quadratic potentials in one- and more-dimensional space.

Calogero, F.; Leyvraz, F.

2014-03-01

390

Multicomponent molecular orbital theory for electrons and nuclei including many-body effect with full configuration interaction treatment: isotope effects on hydrogen molecules  

Microsoft Academic Search

A multi-component molecular orbital (MC_MO) theory is developed for a combined quantum system of electrons and nuclei with the full configuration interaction (CI) scheme of Cartesian Gaussian-type functions. The technique of graphical unitary group approach (GUGA) is modified to obtain the CI matrix elements for many kinds of quantum particles efficiently. The optimum basis sets for quantum nuclei are proposed

Masanori Tachikawa

2002-01-01

391

Phase transitions and metastability in the distribution of the bipartite entanglement of a large quantum system  

SciTech Connect

We study the distribution of the Schmidt coefficients of the reduced density matrix of a quantum system in a pure state. By applying general methods of statistical mechanics, we introduce a fictitious temperature and a partition function and translate the problem in terms of the distribution of the eigenvalues of random matrices. We investigate the appearance of two phase transitions, one at a positive temperature, associated with very entangled states, and one at a negative temperature, signaling the appearance of a significant factorization in the many-body wave function. We also focus on the presence of metastable states (related to two-dimensional quantum gravity) and study the finite size corrections to the saddle point solution.

De Pasquale, A. [Dipartimento di Fisica, Universita di Bari, I-70126 Bari (Italy); INFN, Sezione di Bari, I-70126 Bari (Italy); MECENAS, Universita Federico II di Napoli, Via Mezzocannone 8, I-80134 Napoli (Italy); Facchi, P. [INFN, Sezione di Bari, I-70126 Bari (Italy); Dipartimento di Matematica, Universita di Bari, I-70125 Bari (Italy); Parisi, G. [Dipartimento di Fisica, Universita di Roma 'La Sapienza', Piazzale Aldo Moro 2, I-00185 Roma (Italy); Centre for Statistical Mechanics and Complexity (SMC), CNR-INFM, I-00185 Roma, Italy INFN Sezione di Roma, I-00185 Roma (Italy); Pascazio, S. [Dipartimento di Fisica, Universita di Bari, I-70126 Bari (Italy); INFN, Sezione di Bari, I-70126 Bari (Italy); Scardicchio, A. [Abdus Salam International Center for Theoretical Physics, Strada Costiera 11, I-34014 Trieste (Italy); INFN, Sezione di Trieste, I-34014 Trieste (Italy)

2010-05-15

392

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. Program summaryTitle of program: Feynman 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

393

Quantum discord in matrix product systems  

Microsoft Academic Search

We consider a class of quantum systems with spin-flip symmetry and derive the quantum correlation measured by the quantum discord (QD). As an illustration, we investigate the QD in a three-body interaction model and an XYZ interaction model, whose ground states can be expressed as matrix product states, and the QD is exactly soluble. We show that the QD behaves

Zhao-Yu Sun; Liang Li; Kai-Lun Yao; Gui-Huan Du; Ji-Wei Liu; Bo Luo; Neng Li; Hai-Na Li

2010-01-01

394

Quantum Monte Carlo Simulation of condensed van der Waals Systems  

NASA Astrophysics Data System (ADS)

Van der Waals forces are as ubiquitous as infamous. While post-Hartree-Fock methods enable accurate estimates of these forces in molecules and clusters, they remain elusive for dealing with many-electron condensed phase systems. We present Quantum Monte Carlo [1,2] results for condensed van der Waals systems. Interatomic many-body contributions to cohesive energies and bulk modulus will be discussed. Numerical evidence is presented for crystals of rare gas atoms, and compared to experiments and methods [3]. Sandia National Laboratories is a multiprogram laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. DoE's National Nuclear Security Administration under Contract No. DE-AC04-94AL85000.[4pt] [1] J. Kim, K. Esler, J. McMinis and D. Ceperley, SciDAC 2010, J. of Physics: Conference series, Chattanooga, Tennessee, July 11 2011 [0pt] [2] QMCPACK simulation suite, http://qmcpack.cmscc.org (unpublished)[0pt] [3] O. A. von Lillienfeld and A. Tkatchenko, J. Chem. Phys. 132 234109 (2010)

Benali, Anouar; Shulenburger, Luke; Romero, Nichols A.; Kim, Jeongnim; Anatole von Lilienfeld, O.

2012-02-01

395

Simulation of n-qubit quantum systems. V. Quantum measurements  

NASA Astrophysics Data System (ADS)

The FEYNMAN program has been developed during the last years to support case studies on the dynamics and entanglement of n-qubit quantum registers. Apart from basic transformations and (gate) operations, it currently supports a good number of separability criteria and entanglement measures, quantum channels as well as the parametrizations of various frequently applied objects in quantum information theory, such as (pure and mixed) quantum states, hermitian and unitary matrices or classical probability distributions. With the present update of the FEYNMAN program, we provide a simple access to (the simulation of) quantum measurements. This includes not only the widely-applied projective measurements upon the eigenspaces of some given operator but also single-qubit measurements in various pre- and user-defined bases as well as the support for two-qubit Bell measurements. In addition, we help perform generalized and POVM measurements. Knowing the importance of measurements for many quantum information protocols, e.g., one-way computing, we hope that this update makes the FEYNMAN code an attractive and versatile tool for both, research and education. New version program summaryProgram title: FEYNMAN Catalogue identifier: ADWE_v5_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/ADWE_v5_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 27 210 No. of bytes in distributed program, including test data, etc.: 1 960 471 Distribution format: tar.gz Programming language: Maple 12 Computer: Any computer with Maple software installed Operating system: Any system that supports Maple; the program has been tested under Microsoft Windows XP and Linux Classification: 4.15 Catalogue identifier of previous version: ADWE_v4_0 Journal reference of previous version: Comput. Phys. Commun. 179 (2008) 647 Does the new version supersede the previous version?: Yes Nature of problem: During the last decade, the field of quantum information science has largely contributed to our understanding of quantum mechanics, and has provided also new and efficient protocols that are used on quantum entanglement. To further analyze the amount and transfer of entanglement in n-qubit quantum protocols, symbolic and numerical simulations need to be handled efficiently. Solution method: Using the computer algebra system Maple, we developed a set of procedures in order to support the definition, manipulation and analysis of n-qubit quantum registers. These procedures also help to deal with (unitary) logic gates and (nonunitary) quantum operations and measurements that act upon the quantum registers. All commands are organized in a hierarchical order and can be used interactively in order to simulate and analyze the evolution of n-qubit quantum systems, both in ideal and noisy quantum circuits. Reasons for new version: Until the present, the FEYNMAN program supported the basic data structures and operations of n-qubit quantum registers [1], a good number of separability and entanglement measures [2], quantum operations (noisy channels) [3] as well as the parametrizations of various frequently applied objects, such as (pure and mixed) quantum states, hermitian and unitary matrices or classical probability distributions [4]. With the current extension, we here add all necessary features to simulate quantum measurements, including the projective measurements in various single-qubit and the two-qubit Bell basis, and POVM measurements. Together with the previously implemented functionality, this greatly enhances the possibilities of analyzing quantum information protocols in which measurements play a central role, e.g., one-way computation. Running time: Most commands require ?10 seconds of processor time on a Pentium 4 processor with ?2 GHz RAM or newer, if they work with quantum registers with five or less qubits. Moreover, about 5-20 MB of working memory is typically n

Radtke, T.; Fritzsche, S.

2010-02-01

396

Quantum probabilities and entanglement for multimode quantum systems  

NASA Astrophysics Data System (ADS)

Quantum probabilities are defined for several important physical cases characterizing measurements with multimode quantum systems. These are the probabilities for operationally testable measurements, for operationally uncertain measurements, and for entangled composite events. The role of the prospect and state entanglement is emphasized. Numerical modeling is presented for a two-mode Bose-condensed system of trapped atoms. The interference factor is calculated by invoking the channel-state duality.

Yukalov, V. I.; Yukalova, E. P.; Sornette, D.

2014-04-01

397

Tailoring structural and electronic properties of RuO2 nanotubes: a many-body approach and electronic transport.  

PubMed

The electrical conduction properties of ruthenium oxide nanocables are of high interest. These cables can be built as thin shells of RuO2 surrounding an inner solid nanowire of a dielectric insulating silica material. With this motivation we have investigated the structural, electronic and transport properties of RuO2 nanotubes using the density functional formalism, and applying many-body corrections to the electronic band structure. The structures obtained for the thinnest nanotubes are of the rutile type. The structures of nanotubes with larger diameters deviate from the rutile structure and have in common the formation of dimerized Ru-Ru rows along the axial direction. The cohesive energy shows an oscillating behavior as a function of the tube diameter. With the exception of the thinnest nanotubes, there is a correlation such that the electronic band structures of tubes with high cohesive energies show small gaps at the Fermi energy, whereas the less stable nanotubes exhibit metallic behavior, with bands crossing the Fermi surface. The electronic conductance of nanotubes of finite length connected to gold electrodes has been calculated using a Green-function formalism, and correlations have been established between the electronic band structure and the conductance at zero bias. PMID:23900202

Martínez, J I; Abad, E; Calle-Vallejo, F; Krowne, C M; Alonso, J A

2013-09-21

398

Supermolecular approach to many-body dispersion interactions in weak van der Waals complexes: He, Ne, and Ar trimers  

SciTech Connect

Using the diagrammatic many-body perturbation theory, various three-body dispersion terms that appear in the intermolecular Moller--Plesset perturbation theory (MPPT) are identified and classified with regard to the effects of intramonomer electron correlation on the dispersion term. Via the connection with the supermolecular MPPT, it is demonstrated how the leading dispersion nonadditivities arise within supermolecular calculations that employ MPPT or coupled cluster formalisms. The numerical calculations for He[sub 3], Ne[sub 3], and Ar[sub 3] in triangular geometries fully confirm theoretical predictions. The calculated values of dispersion nonadditivity clearly show that the coupled cluster theory with single, double, and noniterative triple excitations provides the proper framework for the efficient inclusion of the intramonomer correlation effects in dispersion nonadditivity. The convergence of the two-body and three-body terms is shown to be very similar if we compare the three-body terms of an order higher than the two-body terms. This pattern is used to provide the estimates of the total nonadditivities in the three trimers within a few percent accuracy.

Chalasinski, G. (Department of Chemistry, University of Warsaw, Pasteura 1, 02-093 Warszawa (Poland) Department of Chemistry and Biochemistry, Southern Illinois University, Carbondale, Illinois 62901 (United States) Department of Chemistry, Oakland University, Rochester, Michigan 48309 (United States)); Szczesniak, M.M. (Department of Chemistry, Oakland University, Rochester, Michigan 48309 (United States)); Kendall, R.A. (Molecular Science Software Group, Molecular Science Research Center, Environmental and Molecular Sciences Laboratory, Pacific Northwest Laboratory, Richland, Washington 99352 (United States))

1994-11-15

399

Bridging density-functional and many-body perturbation theory: Orbital-density dependence in electronic-structure functionals  

NASA Astrophysics Data System (ADS)

Energy functionals which depend explicitly on orbital densities, rather than on the total charge density, appear when applying self-interaction corrections to density-functional theory; this is, e.g., the case for Perdew-Zunger and Koopmans-compliant functionals. In these formulations the total energy is not invariant under unitary rotations of the orbitals, and local, orbital-dependent potentials emerge. We argue that this is not a shortcoming, and that instead these potentials can provide, in a functional form, a simplified quasiparticle approximation to the spectral potential, i.e., the local, frequency-dependent contraction of the many-body self-energy that is sufficient to describe exactly the spectral function. As such, orbital-density-dependent functionals have the flexibility to accurately describe both total energies and quasiparticle excitations in the electronic-structure problem. In addition, and at variance with the Kohn-Sham case, orbital-dependent potentials do not require nonanalytic derivative discontinuities. We present numerical solutions based on the frequency-dependent Sham-Schlüter equation to support this view, and examine some of the existing functionals in this perspective, highlighting the very close agreement between exact and approximate orbital-dependent potentials.

Ferretti, Andrea; Dabo, Ismaila; Cococcioni, Matteo; Marzari, Nicola

2014-05-01

400

A new many-body potential with the second-moment approximation of tight-binding scheme for Hafnium  

NASA Astrophysics Data System (ADS)

In this work, we develop a new many-body potential for alpha-hafnium (?-Hf) based on the second moment approximation of tight-binding (TB-SMA) theory by introducing an additional Heaviside step function into the potential model and a new analytical scheme of density function. All the parameters of the new potential have been systematically evaluated by fitting to ground-state properties including cohesive energy, lattice constants, elastic constants, vacancy formation energy, structure stability and equation of state. By using the present model, the melting point, melt heat, thermal expansion coefficient, point defects, and low-index surface energies of ?-Hf were calculated through molecular dynamics simulations. Comparing with experiment observations from others, it is shown that these properties can be reproduced reasonably by the present model, some results being more consistent to the experimental data than those by previous suggested models. This indicates that this work is sutiable in TB-SMA potential for hexagonal close packed metals.

Lin, DeYe; Wang, Yi; Shang, ShunLi; Lu, ZhaoPing; Liu, ZiKui; Hui, XiDong

2013-11-01

401

An efficient many-body potential for the interaction of transition and noble metal nano-objects with an environment  

NASA Astrophysics Data System (ADS)

We present a mean-field model for the description of transition or noble metal nano-objects interacting with an environment. It includes a potential given by the second-moment approximation to the tight-binding Hamiltonian for metal-metal interactions, and an additional many-body potential that depends on the local atomic coordination for the metal-environment interaction. The model does not refer to a specific type of chemical conditions, but rather provides trends as a function of a limited number of parameters. The capabilities of the model are highlighted by studying the relative stability of semi-infinite gold surfaces of various orientations and formation energies of a restricted set of single-faceted gold nanoparticles. It is shown that, with only two parameters and in a very efficient way, it is able to generate a great variety of stable structures and shapes, as the nature of the environment varies. It is thus expected to account for formation energies of nano-objects of various dimensionalities (surfaces, thin films, nano-rods, nano-wires, nanoparticles, nanoribbons, etc.) according to the environment.

Cortes-Huerto, Robinson; Goniakowski, Jacek; Noguera, Claudine

2013-06-01

402

Representation Systems, Orthoposets and Quantum Logic  

Microsoft Academic Search

We present a new approach of quantum logic and quantum systems description based on representation systems. This general algebraic formalism permits to represent systems from different points of view and reason about partial descriptions of it even though the descriptions are not available simultaneously (that is they can be associated to different points of view). We use a special form

Olivier Brunet

2004-01-01

403

Joint System Quantum Descriptions Arising from Local Quantumness  

NASA Astrophysics Data System (ADS)

Bipartite correlations generated by non-signalling physical systems that admit a finite-dimensional local quantum description cannot exceed the quantum limits, i.e., they can always be interpreted as distant measurements of a bipartite quantum state. Here we consider the effect of dropping the assumption of finite dimensionality. Remarkably, we find that the same result holds provided that we relax the tensor structure of space-like separated measurements to mere commutativity. We argue why an extension of this result to tensor representations seems unlikely.

Cooney, Tom; Junge, Marius; Navascués, Miguel; Pérez-García, David; Villanueva, Ignacio

2013-09-01

404

Electronic structure of dye-sensitized TiO2 clusters from many-body perturbation theory  

NASA Astrophysics Data System (ADS)

The development of new types of solar cells is driven by the need for clean and sustainable energy. In this respect dye-sensitized solar cells (DSC) are considered as a promising route for departing from the traditional solid state cells. The physical insight provided by computational modeling may help develop improved DSCs. To this end, it is important to obtain an accurate description of the electronic structure, including the fundamental gaps and level alignment at the dye-TiO2 interface. This requires a treatment beyond ground-state density functional theory (DFT). We present a many-body perturbation theory study, within the G0W0 approximation, of two of the crystalline phases of dye-sensitized TiO2 clusters, reported by Benedict and Coppens, [J. Am. Chem. Soc.JACSAT0002-786310.1021/ja909600w 132, 2938 (2010)]. We obtain geometries in good agreement with the experiment by using DFT with the Tkatchenko-Scheffler van der Waals correction. We demonstrate that even when DFT gives a good description of the valence spectrum and a qualitatively correct picture of the electronic structure of the dye-TiO2 interface, G0W0 calculations yield more valuable quantitative information regarding the fundamental gaps and level alignment. In addition, we systematically investigate the issues pertaining to G0W0 calculations, namely: (i) convergence with respect to the number of basis functions, (ii) dependence on the mean-field starting point, and (iii) the validity of the assumption that the DFT wave function is a good approximation to the quasiparticle wave function. We show how these issues are manifested for dye molecules and for dye-sensitized TiO2 clusters.

Marom, Noa; Moussa, Jonathan E.; Ren, Xinguo; Tkatchenko, Alexandre; Chelikowsky, James R.

2011-12-01

405

Quantum interference between independent reservoirs in open quantum systems  

NASA Astrophysics Data System (ADS)

When a quantum system interacts with multiple reservoirs, the environmental effects are usually treated in an additive manner. We show that this assumption breaks down for non-Markovian environments that have finite memory times. Specifically, we demonstrate that quantum interferences between independent environments can qualitatively modify the dynamics of the physical system. We illustrate this effect with a two-level system coupled to two structured photonic reservoirs, discuss its origin using a nonequilibrium diagrammatic technique, and show an example when the application of this interference can result in an improved dark state preparation in a ? system.

Chan, Ching-Kit; Lin, Guin-Dar; Yelin, Susanne F.; Lukin, Mikhail D.

2014-04-01

406

Graph approach to quantum systems  

NASA Astrophysics Data System (ADS)

Using a graph approach to quantum systems, we show that descriptions of 3-dim Kochen-Specker (KS) setups as well as descriptions of 3-dim spin systems by means of Greechie diagrams (a kind of lattice) that we find in the literature are wrong. Correct lattices generated by McKay-Megill-Pavicic (MMP) hypergraphs and Hilbert subspace equations are given. To enable future exhaustive generation of 3-dim KS setups by means of our recently found stripping technique, bipartite graph generation is used to provide us with lattices with equal numbers of elements and blocks (orthogonal triples of elements)-up to 41 of them. We obtain several new results on such lattices and hypergraphs, in particular, on properties such as superposition and orthoraguesian equations.

Pavi?i?, Mladen; McKay, Brendan D.; Megill, Norman D.; Fresl, Krešimir

2010-10-01

407

Many-body exchange-repulsion in polarizable molecular mechanics. I. Orbital-based approximations and applications to hydrated metal cation complexes.  

PubMed

We have quantified the extent of the nonadditivity of the short-range exchange-repulsion energy, E(exch-rep), in several polycoordinated complexes of alkali, alkaline-earth, transition, and metal cations. This was done by performing ab initio energy decomposition analyses of interaction energies in these complexes. The magnitude of E(exch-rep(n-body, n > 2)) was found to be strongly cation-dependent, ranging from close to zero for some alkali metal complexes to about 6 kcal/mol for the hexahydrated Zn(2+) complex. In all cases, the cation-water molecules, E(exch-rep(three-body)), has been found to be the dominant contribution to many-body exchange-repulsion effects, higher order terms being negligible. As the physical basis of this effect is discussed, a three-center exponential term was introduced in the SIBFA (Sum of Interactions Between Fragments Ab initio computed) polarizable molecular mechanics procedure to model such effects. The three-body correction is added to the two-center (two-body) overlap-like formulation of the short-range repulsion contribution, E(rep), which is grounded on simplified integrals obtained from localized molecular orbital theory. The present term is computed on using mostly precomputed two-body terms and, therefore, does not increase significantly the computational cost of the method. It was shown to match closely E(three-body) in a series of test cases bearing on the complexes of Ca(2+), Zn(2+), and Hg(2+). For example, its introduction enabled to restore the correct tetrahedral versus square planar preference found from quantum chemistry calculations on the tetrahydrate of Hg(2+) and [Hg(H(2)O)(4)](2+). PMID:21793002

Chaudret, Robin; Gresh, Nohad; Parisel, Olivier; Piquemal, Jean-Philip

2011-11-15

408

Quantum mechanics of open systems  

NASA Astrophysics Data System (ADS)

In quantum mechanics, there is a set of problems where the system of interest interacts with another system, usually called "environment". This interaction leads to the exchange of energy and information and makes the dynamics of the system of interest essentially non-unitary. Such problems often appeared in condensed matter physics and attracted much attention after recent advances in nanotechnology. As broadly posed as they are, these problems require a variety of different approaches. This thesis is an attempt to examine several of these approaches in applications to different condensed matter problems. The first problem concerns the so-called "Master equation" approach which is very popular in quantum optics. I show that analytic properties of environmental correlators lead to strong restrictions on the applicability of the approach to the strong-coupling regime of interest in condensed matter physics. In the second problem, I use path integrals to treat the localization of particles on attractive short-range potentials when the environment produces an effective viscous friction force. I find that friction changes drastically the localization properties and leads to much stronger localization in comparison to the non-dissipative case. This has implications for the motion of heavy particles in fermionic liquids and, as will be argued below, is also relevant to the problem of high-temperature superconductivity. Finally, the third problem deals with the interplay of geometric phases and energy dissipation which occurs in the motion of vortices in superconductors. It is shown that this interplay leads to interesting predictions for vortex tunneling in high-temperature superconductors which have been partially confirmed by experiments.

Melikidze, Akakii

409

Recent Progress in Quantum Simulation Using Superconducting Circuits  

NASA Astrophysics Data System (ADS)

Quantum systems are notoriously difficult to simulate with classical means. Recently, the idea of using another quantum system—which is experimentally more controllable—as a simulator for the original problem has gained significant momentum. Amongst the experimental platforms studied as quantum simulators, superconducting qubits are one of the most promising, due to relative straightforward scalability, easy design, and integration with standard electronics. Here I review the recent state-of-the art in the field and the prospects for simulating systems ranging from relativistic quantum fields to quantum many-body systems.

Paraoanu, G. S.

2014-06-01

410

Recent Progress in Quantum Simulation Using Superconducting Circuits  

NASA Astrophysics Data System (ADS)

Quantum systems are notoriously difficult to simulate with classical means. Recently, the idea of using another quantum system—which is experimentally more controllable—as a simulator for the original problem has gained significant momentum. Amongst the experimental platforms studied as quantum simulators, superconducting qubits are one of the most promising, due to relative straightforward scalability, easy design, and integration with standard electronics. Here I review the recent state-of-the art in the field and the prospects for simulating systems ranging from relativistic quantum fields to quantum many-body systems.

Paraoanu, G. S.

2014-04-01

411

Controlling the shannon entropy of quantum systems.  

PubMed

This paper proposes a new quantum control method which controls the Shannon entropy of quantum systems. For both discrete and continuous entropies, controller design methods are proposed based on probability density function control, which can drive the quantum state to any target state. To drive the entropy to any target at any prespecified time, another discretization method is proposed for the discrete entropy case, and the conditions under which the entropy can be increased or decreased are discussed. Simulations are done on both two- and three-dimensional quantum systems, where division and prediction are used to achieve more accurate tracking. PMID:23818819

Xing, Yifan; Wu, Jun

2013-01-01

412

Slightly anharmonic systems in quantum optics  

NASA Technical Reports Server (NTRS)

We consider an arbitrary atomic system (n-level atom or many such atoms) interacting with a strong resonant quantum field. The approximate evolution operator for a quantum field case can be produced from the atomic evolution operator in an external classical field by a 'quantization prescription', passing the operator arguments to Wigner D-functions. Many important phenomena arising from the quantum nature of the field can be described by such a way.

Klimov, Andrey B.; Chumakov, Sergey M.

1995-01-01

413

Hartman effect and dissipative quantum systems  

NASA Astrophysics Data System (ADS)

The dwell time for dissipative quantum system is shown to increase with barrier width. It clearly precludes Hartman effect for dissipative systems. Here calculation has been done for inverted parabolic potential barrier.

Bhattacharya, Samyadeb; Roy, Sisir

2013-05-01

414

Systematic reduction of sign errors in many-body problems: generalization of self-healing diffusion Monte Carlo to excited states  

SciTech Connect

A recently developed Self-Healing Diffusion Monte Carlo Algorithm [PRB {\\bf 79}, 195117 ] is extended to the calculation of excited states. The formalism is based on a excited-state fixed-node approximation and the mixed estimator of the excited-state probability density. The fixed-node ground state wave-functions of inequivalent nodal pockets are found simultaneously using a recursive approach. The decay of the wave-function into lower energy states is prevented using two methods: i) The projection of the improved trial-wave function into previously calculated eigenstates is removed. ii) The reference energy for each nodal pocket is adjusted in order to create a kink in the global fixed-node wave-function which, when locally smoothed out, increases the volume of the higher energy pockets at the expense of the lower energy ones until the energies of every pocket become equal. This reference energy method is designed to find nodal structures that are local minima for arbitrary fluctuations of the nodes within a given nodal topology. We demonstrate in a model system that the algorithm converges to many-body eigenstates in bosonic-like and fermionic cases.

Reboredo, Fernando A [ORNL

2009-01-01

415

Electronic and optical excitations in Agn clusters (n=1-8) : Comparison of density-functional and many-body theories  

NASA Astrophysics Data System (ADS)

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.; Idrobo, Juan C.; Ö?üt, Serdar; Jellinek, Julius; Chelikowsky, James R.

2009-04-01

416

An Introduction to Quantum Optomechanics  

NASA Astrophysics Data System (ADS)

We provide an introduction to the description of mechanical systems in the quantum regime, and provide a review of the various types of micro-scale and nano-scale optomechanical and electromechanical systems. The aim is to achieve quantum control of micromechanical and nanomechanical resonators using the electromagnetic field. Such control requires the demonstration of state preparation (in particular, cooling to the ground state), coherent control and quantum-limited measurement. These problems are discussed in turn. Some particular problems in force detection, metrology, nonlinear optomechanics and many-body optomechanics are also discussed.

Milburn, G.; Woolley, M.

2011-10-01

417

Quantum Simulation of Tunneling in Small Systems  

NASA Astrophysics Data System (ADS)

A number of quantum algorithms have been performed on small quantum computers; these include Shor's prime factorization algorithm, error correction, Grover's search algorithm and a number of analog and digital quantum simulations. Because of the number of gates and qubits necessary, however, digital quantum particle simulations remain untested. A contributing factor to the system size required is the number of ancillary qubits needed to implement matrix exponentials of the potential operator. Here, we show that a set of tunneling problems may be investigated with no ancillary qubits and a cost of one single-qubit operator per time step for the potential evolution, eliminating at least half of the quantum gates required for the algorithm and more than that in the general case. Such simulations are within reach of current quantum computer architectures.

Sornborger, Andrew T.

2012-08-01

418

Quantum Simulation of Tunneling in Small Systems  

PubMed Central

A number of quantum algorithms have been performed on small quantum computers; these include Shor's prime factorization algorithm, error correction, Grover's search algorithm and a number of analog and digital quantum simulations. Because of the number of gates and qubits necessary, however, digital quantum particle simulations remain untested. A contributing factor to the system size required is the number of ancillary qubits needed to implement matrix exponentials of the potential operator. Here, we show that a set of tunneling problems may be investigated with no ancillary qubits and a cost of one single-qubit operator per time step for the potential evolution, eliminating at least half of the quantum gates required for the algorithm and more than that in the general case. Such simulations are within reach of current quantum computer architectures.

Sornborger, Andrew T.

2012-01-01

419

Quantum Backaction Noise Cancellation for Linear Systems  

NASA Astrophysics Data System (ADS)

We show that it is always possible to convert a dissipationless linear sensor system under quantum nondemolition measurements into a backaction-evading one using the technique of quantum noise cancellation. This result generalizes our earlier work on optomechanical sensors [Tsang and Caves, Phys. Rev. Lett. 105, 123601 (2010)].

Tsang, Mankei

2011-10-01

420

Quantum contextuality in N-boson systems  

SciTech Connect

Quantum contextuality in systems of identical bosonic particles is explicitly exhibited via the maximum violation of a suitable inequality of Clauser-Horne-Shimony-Holt type. Unlike the approaches considered so far, which make use of single-particle observables, our analysis involves collective observables constructed using multiboson operators. An exemplifying scheme to test this violation with a quantum optical setup is also discussed.

Benatti, Fabio [Dipartimento di Fisica, Universita degli Studi di Trieste, I-34151 Trieste (Italy); Istituto Nazionale di Fisica Nucleare, Sezione di Trieste, I-34014 Trieste (Italy); Floreanini, Roberto [Istituto Nazionale di Fisica Nucleare, Sezione di Trieste, I-34014 Trieste (Italy); Genovese, Marco [INRIM, Strada delle Cacce 91, I-10135 Torino (Italy); Olivares, Stefano [Dipartimento di Fisica, Universita degli Studi di Trieste, I-34151 Trieste (Italy)

2011-09-15

421

QUANTUM SPIN SYSTEMS AT FINITE TEMPERATURE  

Microsoft Academic Search

We develop a novel approach to phase transitions in quantum spin models based on a relation to the corresponding classical spin systems. Explicitly, we show that whenever chessboard estimates can be used to prove a phase transition in the classical model, the corresponding quantum model will have a similar phase transition, provided the inverse temperature and the magnitude of the

MAREK BISKUP; LINCOLN CHAYES; SHANNON STARR

422

Emergent ``super-solitons'' following an interaction strength quantum quench across a Luttinger liquid-Mott insulating phase boundary  

Microsoft Academic Search

Rapid progress in cold atom experiments has motivated the study of non-equilibrium many-body dynamics following a sudden deformation of the system Hamiltonian (a ``quantum quench''). Here, we consider the dynamics of localized excitations produced via a quench across a quantum phase boundary separating critical Luttinger liquid and gapped Mott insulating states. Our initial liquid ground state is labeled by a

Matthew Foster; Emil Yuzbashyan

2010-01-01