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1

Theoretical studies of quantum dynamics  

Microsoft Academic Search

Quantum mechanical methods have been developed for the study of dynamical processes in polyatomic systems and condensed matter. First, we developed an exact scheme for wavefunction propagation with a few degrees of freedom based on time-dependent discrete variable representations (TD-DVR) of the evolution operator. The TD-DVR evolves under appropriate reference Hamiltonians and leads to an efficient scheme for studying intramolecular

Eunji Sim

1997-01-01

2

Quantum information dynamics  

Microsoft Academic Search

Presented is a study of quantum entanglement from the perspective of the theory of quantum information dynamics. We consider pairwise entanglement and present an analytical development using joint ladder operators, the sum of two single-particle fermionic ladder operators. This approach allows us to write down analytical representations of quantum algorithms and to explore quantum entanglement as it is manifested in

Jeffrey Yepez

2010-01-01

3

Computer studies of multiple-quantum spin dynamics  

SciTech Connect

The excitation and detection of multiple-quantum (MQ) transitions in Fourier transform NMR spectroscopy is an interesting problem in the quantum mechanical dynamics of spin systems as well as an important new technique for investigation of molecular structure. In particular, multiple-quantum spectroscopy can be used to simplify overly complex spectra or to separate the various interactions between a nucleus and its environment. The emphasis of this work is on computer simulation of spin-system evolution to better relate theory and experiment.

Murdoch, J.B.

1982-11-01

4

Quantum information dynamics  

NASA Astrophysics Data System (ADS)

Presented is a study of quantum entanglement from the perspective of the theory of quantum information dynamics. We consider pairwise entanglement and present an analytical development using joint ladder operators, the sum of two single-particle fermionic ladder operators. This approach allows us to write down analytical representations of quantum algorithms and to explore quantum entanglement as it is manifested in a system of qubits. We present a topological representation of quantum logic that views entangled qubit spacetime histories (or qubit world lines) as a generalized braid, referred to as a super-braid. The crossing of world lines may be either classical or quantum mechanical in nature, and in the latter case most conveniently expressed with our analytical expressions for entangling quantum gates. At a quantum mechanical crossing, independent world lines can become entangled. We present quantum skein relations that allow complicated superbraids to be recursively reduced to alternate classical histories. If the superbraid is closed, then one can decompose the resulting superlink into an entangled superposition of classical links. Also, one can compute a superlink invariant, for example the Jones polynomial for the square root of a knot. We present measurement-based quantum computing based on our joint number operators. We take expectation values of the joint number operators to determine kinetic-level variables describing the quantum information dynamics in the qubit system at the mesoscopic scale. We explore the issue of reversibility in quantum maps at this scale using a quantum Boltzmann equation. We then present an example of quantum information processing using a qubit system comprised of nuclear spins. We also discuss quantum propositions cast in terms of joint number operators. We review the well known dynamical equations governing superfluidity, with a focus on self-consistent dynamics supporting quantum vortices in a Bose-Einstein condensate (BEC). Furthermore, we review the mutual vortex-vortex interaction and the consequent Kelvin wave instability. We derive an effective equation of motion for a Fermi condensate that is the basis of our qubit representation of superfluidity. We then present our quantum lattice gas representation of a superfluid. We explore aspects of our model with two qubits per point, referred to as a Q2 model, particularly its usefulness for carrying out practical quantum fluid simulations. We find that it is perhaps the simplest yet most comprehensive model of superfluid dynamics. As a prime application of Q2, we explore the power-law regions in the energy spectrum of a condensate in the low-temperature limit. We achieved the largest quantum simulations to date of a BEC and, for the first time, Kolmogorov scaling in superfluids, a flow regime heretofore only obtainably by classical turbulence models. Finally, we address the subject of turbulence regarding information conservation on the small scales (both mesoscopic and microscopic) underlying the flow dynamics on the large hydrodynamic (macroscopic) scale. We present a hydrodynamic-level momentum equation, in the form of a Navier-Stokes equation, as the basis for the energy spectrum of quantum turbulence at large scales. Quantum turbulence, in particular the representation of fluid eddies in terms of a coherent structure of polarized quantum vortices, offers a unique window into the heretofore intractable subject of energy cascades.

Yepez, Jeffrey

5

Quantum molecular dynamics study of electron transport in an external field  

SciTech Connect

A quantum molecular dynamics method is proposed to study the transport of a quantum particle interacting with a classical system at finite temp- eratures in the presence of an applied electric field. Using this method the mobility of an excess electron in dense helium gas is calculated at 77 k. (AIP)

Kalia, R.K.; Vashishta, P.; de Leeuw, S.W.

1989-06-01

6

Quantum dynamics study for D{sub 2} + OH reaction  

SciTech Connect

A PA5D (potential averaged 5D) TD (time-dependent) quantum wave-packet calculation is reported for the reaction D{sub 2} + OH {yields} D + DOH on the Schatz-Elgersma potential energy surface. The dynamics calculation is carried out on a workstation with a modest memory, which is made possible by using a normalized angular quadrature scheme to minimize the requirement for computer memory during wave-packet propagation. Reaction probabilities, cross sections, and rate constants are presented for the title reaction, and the comparison of the present result with those of the isotopic reactions, H{sub 2} + OH and HD + OH, is given. Consistent with its isotopic reactions, the rotational orientation of D{sub 2} has a stronger effect than that of OH and, in particular, the D{sub 2} (j=1) reactant produces the largest reaction probability, which is attributed to a general steric effect. The comparison of all three isotopic reactions shows that the reactivity (reaction probability and cross section) of the HH(D) + OH system is in the order of P{sub H(2)} > P{sub HD} > P{sub D(2)}. This trend is in good agreement with reduced dimensionality calculations. 27 refs., 8 figs., 4 tabs.

Zhang, Y.; Zhang, D.; Li, W.; Zhang, Q. [Shandong Teacher`s Univ., Jinan (China); Wang, D.; Zhang, D.H.; Zhang, J.Z.H. [New York Univ., NY (United States)

1995-11-16

7

Quantum gases: Relaxation dynamics  

NASA Astrophysics Data System (ADS)

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

Cheneau, Marc

2013-10-01

8

Regular quantum dynamics  

NASA Astrophysics Data System (ADS)

The ill-posed problem of quantizing space-time is replaced by a more determined and well-posed problem of regularizing quantum dynamics. The problem is then to eliminate the Heisenberg singularity from quantum mechanics as economically as possible. The concepts of regular and singular groups are explained and the Heisenberg singularity defined. This singularity infests not only the theory of space-time, but also the Bose-Einstein statistics and the theory of the gauge fields and interactions. It is responsible for most of the infinities of present quantum field theory. The key new conceptual step is to turn attention from observables to "dynamicals", the observable-valued-functions of time which actually enters into the Heisenberg dynamical equations. The dynamicals have separate algebras from the algebra and Lie algebra of the observables. This reconception allows for the possibility of clock-system entanglement that is missing from the usual singular dynamics, and implied by the concept of quantum space-time. The dynamical Lie algebra and the resulting Lie group are regularized for an example system, the time-dependent isotropic harmonic oscillator of arbitrary finite dimension. The result is a quantize space-time, but also momentum-energy and every other dynamical variable in the theory. This method is readily extended to general dynamic quantum systems.

Baugh, James Emory

9

Quantum molecular dynamics study on light to-heat absorption mechanism: two metallic atom system  

Microsoft Academic Search

For understanding the fundamental mechanism of light absorption to be converted to the thermal energy, the atomic motions of matters are studied with the quantum molecular dynamics method. As a fundamental atomic system, two metallic atoms are considered to be irradiated with light changing the frequency and intensity. Under infra-red light irradiation, increase in the kinetic energy and atomic dissociation

Masahiko Shibahara; Susumu Kotake

1997-01-01

10

Quantum dynamical effects in liquid water: A semiclassical study on the diffusion and the infrared absorption spectrum  

Microsoft Academic Search

The important role of liquid water in many areas of science from chemistry, physics, biology, geology to climate research, etc., has motivated numerous theoretical studies of its structure and dynamics. The significance of quantum effects on the properties of water, however, has not yet been fully resolved. In this paper we focus on quantum dynamical effects in liquid water based

Jian Liu; William H. Miller; Francesco Paesani; Wei Zhang; David A. Case

2009-01-01

11

Time-domain ab initio studies of excitation dynamics in semiconductor quantum dots  

NASA Astrophysics Data System (ADS)

Solar energy applications require understanding of dynamical response of novel materials on nanometer scale. Our state-of-the-art non-adiabatic molecular dynamics techniques, implemented within time-dependent density functional theory, allow us to model such response at the atomistic level and in real time. The talk will focus on single and multiple exciton generation, relaxation, annihilation and dephasing in semiconductor quantum dots.[4pt] References:[0pt] [1] O. V. Prezhdo, "Multiple excitons and electron-phonon bottleneck in semiconductor quantum dots: Insights from ab initio studies", Chem. Phys. Lett. -- Frontier Article, 460, 1 (2008) [0pt] [2] O. V. Prezhdo "Photoinduced dynamics in semiconductor quantum-dots: insights from time-domain ab initio studies", Acc. Chem. Res., 42, 2005 (2009) [0pt] [3] A. B. Madrid, H.-D. Kim, O. V. Prezhdo, "Phonon-induced dephasing of excitons in silicon quantum dots: multiple exciton generation, fission and luminescence", ACS-Nano, 3, 2487 (2009) [0pt] [4] C. M. Isborn, O. V. Prezhdo, "Quantum dot charging quenches multiple exciton generation: first-principles calculations on small PbSe clusters", J. Phys. Chem. C, 113, 12617 (2009) [0pt] [5] S. V. Kilina, D. S. Kilin, O. V. Prezhdo, "Breaking the phonon bottleneck in PbSe and CdSe quantum dots: time-domain density functional theory of charge carrier relaxation", ACS-Nano, 3, 93 (2009). [0pt] [6] S. A. Fischer, A. B. Madrid, C. M. Isborn, O. V. Prezhdo, "Multiple exciton generation in small Si clusters: A high-level, ab initio study", J. Phys. Chem. Lett., 1, 232 (2010).

Prezhdo, Oleg

2011-03-01

12

Response of solid Ne upon photoexcitation of a NO impurity: a quantum dynamics study.  

PubMed

The ultrafast geometrical rearrangement dynamics of NO doped cryogenic Ne matrices after femtosecond laser pulse excitation is studied using a quantum dynamical approach based on a multi-dimensional shell model, with the shell radii being the dynamical variables. The Ne-NO interaction being only weakly anisotropic allows the model to account for the main dynamical features of the rare gas solid. Employing quantum wave packet propagation within the time dependent Hartree approximation, both, the static deformation of the solid due to the impurity and the dynamical response after femtosecond excitation, are analysed. The photoinduced dynamics of the surrounding rare gas atoms is found to be a complex high-dimensional process. The approach allows to consider realistic time-dependent femtosecond pulses and the effect of the pulse duration is clearly shown. Finally, using the pulse parameters of previous experiments, pump-probe signals are calculated and found to be in good agreement with experimental results, allowing for a clear analysis of the ultrafast mechanism of the energy transfer into the solid. PMID:22047249

Uranga-Piña, Ll; Meier, C; Rubayo-Soneira, J

2011-10-28

13

Dynamics of Quantum Vortices  

Microsoft Academic Search

Quantized vortices exist in systems ranging from low-T magnets, to superfluids and superconductors; however, their dynamics remain controversial. Even the existence of a force acting transverse to the motion (like a Lorentz force) relative to thermal quasiparticles has been widely debated. Quite remarkably, it remains unresolved just what forces act on a quantum vortex. From an influence functional calculation, we

Lara Thompson; Philip Stamp

2008-01-01

14

Quantum dynamics and open quantum systems  

NASA Astrophysics Data System (ADS)

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

Mozyrsky, Dima

1999-02-01

15

a Study of Quantum Electron Dynamics in Periodic Superlattices Under Electric Fields.  

NASA Astrophysics Data System (ADS)

This thesis examines the quantum dynamics of electrons in periodic semiconductor superlattices in the presence of electric fields, especially uniform static fields. Chapter 1 is an introduction to this vast and active field of research, with an analysis and suggested solutions to the fundamental theoretical difficulties. Chapter 2 is a detailed historical review of relevant theories, and Chapter 3 is a historical review of experiments. Chapter 4 is devoted to the time-independent quantum mechanical study of the electric-field-induced changes in the transmission properties of ballistic electrons, using the transfer matrix method. In Chapter 5, a new time-dependent quantum mechanical model free from the fundamental theoretical difficulties is introduced, with its validity tested at various limiting cases. A simplified method for calculating field-free bands of various potential models is designed. In Chapter 6, the general features of "Shifting Periodicity", a distinctive feature of this new model, is discussed, and a "Bloch-Floquet Theorem" is rigorously proven. Numerical evidences for the existence of Wannier-Stark-Ladders are presented, and the conditions for its experimental observability is also discussed. In Chapter 7, an analytical solution is found for Bloch Oscillations and Wannier-Stark-Ladders at low electric fields. In Chapter 8, a new quantum mechanical interpretation for Bloch Oscillations and Wannier-Stark -Ladders is derived from the analytical result. The extension of this work to the cases of time-dependent electric fields is also discussed.

Yuan, Daiqing

16

Quantum Dynamics in Biological Systems  

NASA Astrophysics Data System (ADS)

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

Shim, Sangwoo

17

Structure-function studies of DNA damage using AB INITIO quantum mechanics and molecular dynamics simulation  

SciTech Connect

Studies of ring-saturated pyrimidine base lesions are used to illustrate an integrated modeling approach that combines quantum-chemical calculations with molecular dynamics simulation. Electronic-structure calculations on the lesions in Isolation reveal strong conformational preferences due to interactions between equatorial substituents to the pyrimidine ring. Large distortions of DNA should result when these interactions force the methyl group of thymine to assume an axial orientation, as is the case for thymine glycol but not for dihydrothymine. Molecular dynamics simulations of the dodecamer d(CGCGAATTCGCG){sub 2} with and without a ring-saturated thymine lesion at position T7 support this conclusion. Implications of these studies for recognition of thymine lesions by endonuclease III are also discussed.

Miller, J.; Miaskiewicz, K. [Pacific Northwest Lab., Richland, WA (United States); Osman, R. [Mount Sinai School of Medicine, New York, NY (United States). Dept. of Physiology and Biophysics

1993-12-01

18

Quantum control of dynamics  

SciTech Connect

Coherent Control provides a quantum interference based method for controlling molecular dynamics. This theory is reviewed and applications to a variety of processes including photodissociation, and asymmetric synthesis, are discussed. Control scenarios and computations on the control of IBr, H{sub 2}O, DOH and Na{sub 2} photodissociation reactions are discussed. We show that a wide range of yield control is possible under suitable laboratory conditions. Recent experiments on the control photocurrent directionality in semiconductors and of the Na{sub 2} photodissociation to yield Na atoms in different excited states are shown to confirm the theory.

Shapiro, Moshe; Brumer, Paul [Chemical Physics Department, Weizmann Institute of Science, Rehovot, Israel 76100 (Israel); Chemical Physics Theory Group Department of Chemistry, University of Toronto, Toronto, M5S 1A1 (Canada)

1997-01-15

19

Electronic-structure and quantum dynamical study of the photochromism of the aromatic Schiff base salicylideneaniline  

SciTech Connect

The ultrafast proton transfer dynamics of salicylideneaniline has been theoretically analyzed in the ground and first singlet excited electronic states using density functional theory (DFT) and time-dependent DFT calculations, which predict a ({pi},{pi}*) barrierless excited state intramolecular proton transfer (ESIPT). In addition to this, the photochemistry of salicylideneaniline is experimentally known to present fast depopulation processes of the photoexcited species before and after the proton transfer reaction. Such processes are explained by means of conical intersections between the ground and first singlet ({pi},{pi}*) excited electronic states. The electronic energies obtained by the time-dependent density functional theory formalism have been fitted to a monodimensional potential energy surface in order to perform quantum dynamics study of the processes. Our results show that the proton transfer and deactivation of the photoexcited species before the ESIPT processes are completed within 49.6 and 37.7 fs, respectively, which is in remarkable good agreement with experiments.

Ortiz-Sanchez, Juan Manuel; Gelabert, Ricard; Moreno, Miquel; Lluch, Jose M. [Departament de Quimica, Universitat Autonoma de Barcelona, 08193 Bellaterra, Barcelona (Spain)

2008-12-07

20

Quantum Computation of Fluid Dynamics.  

National Technical Information Service (NTIS)

Presented is a quantum lattice gas for Navier-Stokes fluid dynamics simulation. The quantum lattice-gas transport equation at the microscopic scale is presented as a generalization of the classical lattice-gas transport equation. A special type of quantum...

J. Yepez

1998-01-01

21

Non-Born-Oppenheimer dynamics of the photoionized Zundel cation: A quantum wavepacket and surface-hopping study  

NASA Astrophysics Data System (ADS)

The ultrafast fragmentation of the Zundel cation H+(H2O)2 after photoionization is studied by quantum-dynamics with the multiconfiguration time-dependent Hartree method and with surface-hopping approaches. A picture emerges in which the correlated motion of the electron hole and the shared proton leads to localization of the two positively charged entities at opposite sides of the Zundel dication in less than 10 fs followed by Coulomb explosion. Electronic non-adiabatic effects play a crucial role in the fragmentation dynamics. The photoionization spectrum of the cluster between 20 and 24 eV is calculated quantum-dynamically and its features explained. Two- and three-body fragmentation channels accessible by outer-valence ionization are also calculated and the branching ratios as a function of ionization energy are discussed. A good agreement between the quantum-dynamical treatment and surface-hopping is obtained for observables for which both methods are applied.

Li, Zheng; Madjet, Mohamed El-Amine; Vendrell, Oriol

2013-03-01

22

Solvent nuclear quantum effects in electron transfer reactions. II. Molecular dynamics study on methanol solution  

Microsoft Academic Search

Solvent nuclear quantum effects in outer-sphere electron transfer (ET) reactions in methanol solution are examined via a molecular dynamics simulation analysis. The energy gap law of the quantum mechanical ET rate constant is decomposed into contributions from solvent intramolecular vibrations and other low-frequency intermolecular (collective) modes. It is shown that the high-frequency stretching and bending vibrations from the hydroxyl part

Koji Ando

2001-01-01

23

Relativistic quantum dynamical group for hadrons  

SciTech Connect

Motivated by previous work on relativistic quantum dynamics expressed in algebraic terms, we introduce a fully relativistic generalization of the Hooke group. The mathematical properties, relation to other proposed quantum dynamical groups, and the unitary ray representations of this group are studied. Hadrons are viewed as de Sitter type microuniverses, where the quantum dynamics is then determined by the relativistic Hooke group. Wave equations are studied, a mass formula is derived, the emergence of a Regge type formula is deduced, and correspondence with other extended hadron models is noted.

Roman, P.; Haavisto, J.

1981-02-01

24

Quantum dynamics in the partial Wigner picture  

NASA Astrophysics Data System (ADS)

Recently we have shown how the partial Wigner representation of quantum mechanics can be used to study hybrid quantum models where a system with a finite number of energy levels is coupled to linear or nonlinear oscillators (Beck and Sergi 2013 Phys. Lett. A 377 1047). The purpose of this work is to provide a detailed derivation of the partially Wigner-transformed quantum equations of motion for nonlinear oscillator subsystems under the action of general polynomial potentials. Such equations can be written in terms of a propagator, which can then be expanded in a power series. The linear terms of the series describe quantum-classical dynamics while the nonlinear terms provide the corrections needed to restore the fully quantum character of the evolution. In the case of polynomial potentials and position dependent couplings, the number of nonlinear terms is finite and the corrections can be calculated explicitly. In this work we show how to implement numerically the above scheme where, in principle, no assumption about the strength of the coupling must be taken. We illustrate the formalism by studying a two-level system interacting with an asymmetric quartic oscillator. We integrate the quantum dynamics of the total system and provide a comparison with the case of the quantum-classical dynamics of the quartic oscillator. The approach presented here is expected to be effective for studying hybrid quantum circuits in quantum information theory and for witnessing the quantum-to-classical transition in nano-oscillators coupled to pseudo-spins.

Beck, Geoffrey M.; Sergi, Alessandro

2013-10-01

25

Molecular dynamics with quantum fluctuations  

SciTech Connect

A quantum dynamics approach, called Gaussian molecular dynamics, is introduced. As in the centroid molecular dynamics, the N-body quantum system is mapped to an N-body classical system with an effective Hamiltonian arising within the variational Gaussian wave-packet approximation. The approach is exact for the harmonic oscillator and for the high-temperature limit, accurate in the short-time limit and is computationally very efficient.

Georgescu, Ionut; Mandelshtam, Vladimir A. [Chemistry Department, University of California at Irvine, Irvine, California 92697 (United States)

2010-09-01

26

Reactive resonances in the F + CHD3 reaction--a quantum dynamics study.  

PubMed

We present quantum dynamical investigations into the F + CHD(3) reaction. In our reduced dimensionality study we treat the two most important degrees of freedom, which describe the bond making and bond breaking explicitly, while treating the remaining spectator modes adiabatically. Cumulative as well as final state resolved reaction probabilities and cross sections are calculated for the two isotopic channels F + CHD(3) ? FH + CD(3) and F + CHD(3) ? FD + CHD(2). Our theoretical results are compared to the experimental findings of Liu and co-workers [Zhou et al., Mol. Phys., 2010, 108, 957]. Potential resonance states in the low collision energy regime are analyzed in detail employing Smith's lifetime matrix and bound state calculations. PMID:21264397

von Horsten, H Frank; Clary, David C

2011-01-24

27

Molecular modeling study of dihydrofolate reductase inhibitors. Molecular dynamics simulations, quantum mechanical calculations, and experimental corroboration.  

PubMed

A molecular modeling study on dihydrofolate reductase (DHFR) inhibitors was carried out. By combining molecular dynamics simulations with semiempirical (PM6), ab initio, and density functional theory (DFT) calculations, a simple and generally applicable procedure to evaluate the binding energies of DHFR inhibitors interacting with the human enzyme is reported here, providing a clear picture of the binding interactions of these ligands from both structural and energetic viewpoints. A reduced model for the binding pocket was used. This approach allows us to perform more accurate quantum mechanical calculations as well as to obtain a detailed electronic analysis using the quantum theory of atoms in molecules (QTAIM) technique. Thus, molecular aspects of the binding interactions between inhibitors and the DHFR are discussed in detail. A significant correlation between binding energies obtained from DFT calculations and experimental IC?? values was obtained, predicting with an acceptable qualitative accuracy the potential inhibitor effect of nonsynthesized compounds. Such correlation was experimentally corroborated synthesizing and testing two new inhibitors reported in this paper. PMID:23834278

Tosso, Rodrigo D; Andujar, Sebastian A; Gutierrez, Lucas; Angelina, Emilio; Rodríguez, Ricaurte; Nogueras, Manuel; Baldoni, Héctor; Suvire, Fernando D; Cobo, Justo; Enriz, Ricardo D

2013-07-24

28

Quantum dynamics in dual spaces  

NASA Astrophysics Data System (ADS)

Quantum mechanics gives us information about spectra of dynamical variables and transition rates including scattering cross sections. They can be exhibited as spectral information in analytically continued spaces and their duals. Quantum mechanics formulated in these generalized spaces is used to study scattering and time evolution. It is shown that the usual asymptotic condition is inadequate to deal with scattering of composite or unstable particles. Scattering theory needs amendment when the interacting system is not isospectral with the free Hamiltonian, and the amendment is formulated. Perturbation theory in generalized spaces is developed and used to study the deletion and augmentation of the spectrum of the Hamiltonian. A complete set of algebraically independent constants for an interacting system is obtained. The question of the breaking of time symmetry is discussed.

Sudarshan, E. C. G.

29

Quantum dynamics in dual spaces  

SciTech Connect

Quantum mechanics gives us information about spectra of dynamical variables and transition rates including scattering cross sections. They can be exhibited as spectral information in analytically continued spaces and their duals. Quantum mechanics formulated in these generalized spaces is used to study scattering and time evolution. It is shown that the usual asymptotic condition is inadequate to deal with scattering of composite or unstable particles. Scattering theory needs amendment when the interacting system is not isospectral with the free Hamiltonian, and the amendment is formulated. Perturbation theory in generalized spaces is developed and used to study the deletion and augmentation of the spectrum of the Hamiltonian. A complete set of algebraically independent constants for an interacting system is obtained. The question of the breaking of time symmetry is discussed.

Sudarshan, E.C.G.

1993-12-31

30

Quantum critical point at finite doping in the 2D Hubbard model: a dynamical cluster quantum Monte Carlo study.  

PubMed

We explore the Matsubara quasiparticle fraction and the pseudogap of the two-dimensional Hubbard model with the dynamical cluster quantum Monte Carlo method. The character of the quasiparticle fraction changes from non-Fermi-liquid, to marginal Fermi liquid, to Fermi liquid as a function of doping, indicating the presence of a quantum critical point separating non-Fermi-liquid from Fermi-liquid character. Marginal Fermi-liquid character is found at low temperatures at a very narrow range of doping where the single-particle density of states is also symmetric. At higher doping the character of the quasiparticle fraction is seen to cross over from Fermi liquid to marginal Fermi liquid as the temperature increases. PMID:19519050

Vidhyadhiraja, N S; Macridin, A; Sen, C; Jarrell, M; Ma, Michael

2009-05-21

31

Energy dependent dynamics of the O(1D) + HCl reaction: a quantum, quasiclassical and statistical study.  

PubMed

The dynamics of the reaction O((1)D) + HCl ? ClO + H, OH + Cl has been investigated in detail by means of a time-dependent wave packet (TDWP) method in comparison with quasiclassical trajectory (QCT) and statistical approaches on the ground potential energy surface by Martínez et al. [Phys. Chem. Chem. Phys., 2000, 2, 589]. Fully coupled quantum mechanical (QM) reaction probabilities for high values of the total angular momentum (J? 50) are reported for the first time. At the low collision energy regime (E(c)? 0.4 eV) the TDWP probabilities are well reproduced by the QCT and statistical results for the ClO forming product channel, but for the OH + Cl arrangement, only QCT probabilities are found to agree with the QM values. The good accordance found between the rigorous statistical models and the dynamical QM and QCT calculations for the O + HCl ? ClO + H process underpins the assumption that the reaction pathway leading to ClO is predominantly governed by a complex-forming mechanism. In addition, to further test the statistical character of this reaction channel, the laboratory angular distribution and time-of-flight spectra obtained in a crossed molecular beam study by Balucani et al. [Chem. Phys. Lett. 1991, 180, 34] at a collision energy as high as 0.53 eV have been simulated using the state resolved differential cross section obtained with the statistical approaches yielding a satisfactory agreement with the experimental results. For the other channel, O + HCl ? OH + Cl, noticeable differences between the statistical results and those found with the QCT calculation suggest that the dynamics of the reaction are controlled by a direct mechanism. The comparison between the QCT and QM-TDWP results in the whole range of collision energies lends credence to the QCT description of the dynamics of this reaction. PMID:21431209

Bargueño, P; Jambrina, P G; Alvariño, J M; Menéndez, M; Verdasco, E; Hankel, M; Smith, S C; Aoiz, F J; González-Lezana, T

2011-03-23

32

Inhibition of mixing in chaotic quantum dynamics  

SciTech Connect

We study the quantum chaotic dynamics of an initially well-localized wave packet in a cosine potential perturbed by an external time-dependent force. For our choice of initial condition and with [h bar] small but finite, we find that the wvae packet behaves classically (meaning that the quantum behavior is indistinguishable from that of the analogous classical system) as long as the motion is confined to the interior of the remnant separatrix of the cosine potential. Once the classical motion becomes unbounded, however, we find that quantum interference effects dominate. This interference leads to a long-lived accumulation of quantum ampliutde on top of the cosine barrier. This pinning of the amplitude on the barrier is a dynamic mechanism for the quantum inhibition of classical mixing.

Helmkamp, B.S.; Browne, D.A. (Department of Physics and Astronomy, Louisiana State University, Baton Rouge, Louisiana 70803-4001 (United States))

1995-03-01

33

Quantum molecular dynamics study of light-to-heat absorption mechanism in atomic systems  

Microsoft Academic Search

The quantum molecular dynamics method is applied to understand the fundamental mechanism of light-to-heat conversion in atomic systems under light irradiation. The light energy governs the time history of kinetic energy of the atomic system under light irradiation. Under infra-red light irradiation, the atomic fragments made by light irradiation have translational velocities parallel to the direction of light fluctuation. Under

S. Kotake

1998-01-01

34

Ab initio quantum dynamical study of the multi-state nonadiabatic photodissociation of pyrrole  

NASA Astrophysics Data System (ADS)

There has been a substantial amount of theoretical investigations on the photodynamics of pyrrole, often relying on surface hopping techniques or, if fully quantal, confining the study to the lowest two or three singlet states. In this study we extend ab initio based quantum dynamical investigations to cover simultaneously the lowest five singlet states, two ? - ?* and two ? - ?* excited states. The underlying potential energy surfaces are obtained from large-scale MRCI ab initio computations. These are used to extract linear and quadratic vibronic coupling constants employing the corresponding coupling models. For the N-H stretching mode Q24 an anharmonic treatment is necessary and also adopted. The results reveal a sub-picosecond internal conversion from the S4 (? - ?*) state, corresponding to the strongly dipole-allowed transition, to the S1 and S2 (? - ?*) states and, hence, to the ground state of pyrrole. The significance of the various vibrational modes and coupling terms is assessed. Results are also presented for the dissociation probabilities on the three lowest electronic states.

Faraji, S.; Vazdar, M.; Reddy, V. Sivaranjana; Eckert-Maksic, M.; Lischka, H.; Köppel, H.

2011-10-01

35

Quantum nature of the big bang: Improved dynamics  

Microsoft Academic Search

An improved Hamiltonian constraint operator is introduced in loop quantum cosmology. Quantum dynamics of the spatially flat, isotropic model with a massless scalar field is then studied in detail using analytical and numerical methods. The scalar field continues to serve as ``emergent time'', the big bang is again replaced by a quantum bounce, and quantum evolution remains deterministic across the

Abhay Ashtekar; Tomasz Pawlowski; Parampreet Singh

2006-01-01

36

Computer Visualization of Many-Particle Quantum Dynamics  

SciTech Connect

In this paper I show the importance of computer visualization in researching of many-particle quantum dynamics. Such a visualization becomes an indispensable illustrative tool for understanding the behavior of dynamic swarm-based quantum systems. It is also an important component of the corresponding simulation framework, and can simplify the studies of underlying algorithms for multi-particle quantum systems.

Ozhigov, A. Y. [Moscow State Institute of Electronics and Mathematics (Russian Federation)

2009-03-10

37

Reaction Dynamics and Mechanism of the Cl + HD(v = 1) Reaction: A Quantum Mechanical Study.  

PubMed

Time-independent quantum mechanical calculations have been performed in order to characterize the dynamics and stereodynamics of Cl + HD reactive collisions. Calculations have been carried out at two different total energy values and for various initial states using the adiabatic potential energy surface by Bian and Werner [J. Chem. Phys. 2000, 112, 220]. Special attention has been paid to the reaction with HD(v = 1) for which integral and differential cross-sections have been calculated and the effect of vibrational vs translational energy on the reactivity has been examined. In addition, the reactant polarization parameters and polarization-dependent differential cross-sections have been determined. From these results, the spatial preferences of the reaction and the extent of the control of the cross sections achievable through a suitable preparation of the reactants have been also studied. The directional requirements are tighter for the HCl channel than for the DCl one. Formation of the products takes place preferentially when the rotational angular momentum of the HD molecule is perpendicular to the reactants approach direction. Cross-sections and polarization moments computed from the scattering calculations have been compared with experimental results by Kandel et al. [J. Chem. Phys. 2000, 112, 670] for the reaction with HD(v = 1) produced by stimulated Raman pumping. The agreement so obtained is good, and it improves the accordance found in previous calculations with other methodologies and potential energy surfaces. PMID:23477493

González-Sánchez, L; Aldegunde, J; Jambrina, P G; Aoiz, F J

2013-03-27

38

Potential energy surface and quantum dynamics study of rovibrational states for HO(3) (X (2)A'').  

PubMed

An analytic potential energy surface has been constructed by fitting to about 28 thousand energy points for the electronic ground-state (X (2)A'') of HO(3). The energy points are calculated using a hybrid density functional HCTH and a large basis set aug-cc-pVTZ, i.e., a HCTH/aug-cc-pVTZ density functional theory (DFT) method. The DFT calculations show that the trans-HO(3) isomer is the global minimum with a potential well depth of 9.94 kcal mol(-1) with respect to the OH + O(2) asymptote. The equilibrium geometry of the cis-HO(3) conformer is located 1.08 kcal mol(-1) above that of the trans-HO(3) one with an isomerization barrier of 2.41 kcal mol(-1) from trans- to cis-HO(3). By using this surface, a rigorous quantum dynamics (QD) study has been carried out for computing the rovibrational energy levels of HO(3). The calculated results determine a dissociation energy of 6.15 kcal mol(-1), which is in excellent agreement with the experimental value of Lester et al. [J. Phys. Chem. A, 2007, 111, 4727.]. PMID:18688380

Braams, Bastiaan J; Yu, Hua-Gen

2008-04-08

39

Fractional-time quantum dynamics  

NASA Astrophysics Data System (ADS)

Application of the fractional calculus to quantum processes is presented. In particular, the quantum dynamics is considered in the framework of the fractional time Schrödinger equation (SE), which differs from the standard SE by the fractional time derivative: ?/?t???/?t? . It is shown that for ?=1/2 the fractional SE is isospectral to a comb model. An analytical expression for the Green’s functions of the systems are obtained. The semiclassical limit is discussed.

Iomin, Alexander

2009-08-01

40

The molecular dissociation of formaldehyde at medium photoexcitation energies: A quantum chemistry and direct quantum dynamics study  

SciTech Connect

The mechanisms of radiationless decay involved in the photodissociation of formaldehyde into H{sub 2} and CO have been investigated using complete active space self-consistent field (CASSCF) calculations and direct dynamics variational multiconfiguration Gaussian (DD-vMCG) quantum dynamics in the S{sub 1}, T{sub 1}, and S{sub 0} states. A commonly accepted scheme involves Fermi Golden Rule internal conversion from S{sub 1} followed by dissociation of vibrationally hot H{sub 2}CO in S{sub 0}. We recently proposed a novel mechanism [M. Araujo et al., J. Phys. Chem. A 112, 7489 (2008)] whereby internal conversion and dissociation take place in concert through a seam of conical intersection between S{sub 1} and S{sub 0} after the system has passed through an S{sub 1} transition barrier. The relevance of this mechanism depends on the efficiency of tunneling in S{sub 1}. At lower energy, an alternative scheme to internal conversion involves intersystem crossing via T{sub 1} to regenerate the reactant before the S{sub 0} barrier to dissociation. We propose here a previously unidentified mechanism leading directly to H{sub 2} and CO products via T{sub 1}. This channel opens at medium energies, near or above the T{sub 1} barrier to dissociation and still lower than the S{sub 1} barrier, thus making T{sub 1} a possible shortcut to molecular dissociation.

Araujo, Marta; Magalhaes, Alexandre L. [REQUIMTE, Faculdade de Ciencias, Universidade do Porto, Rua do Campo Alegre, 687, 4169-007 Porto (Portugal); Lasorne, Benjamin [Institut Charles Gerhardt (UMR 5253), CNRS, Universite Montpellier 2, CC 1501, Place Eugene Bataillon, 34095 Montpellier (France); Department of Chemistry, Imperial College London, London SW7 2AZ (United Kingdom); Worth, Graham A. [School of Chemistry, University of Birmingham, Edgbaston, Birmingham B15 2TT (United Kingdom); Bearpark, Michael J.; Robb, Michael A. [Department of Chemistry, Imperial College London, London SW7 2AZ (United Kingdom)

2009-10-14

41

Accurate polyatomic quantum dynamics studies of combustion reactions. Final progress report, July 1, 1994--June 30, 1998  

SciTech Connect

This program is designed to develop accurate yet practical computational methods, primarily based on time-dependent quantum mechanics, for studying the dynamics of polyatomic reactions beyond the atom-diatom systems. Efficient computational methodologies are developed and the applications of these methods to practical chemical reactions relevant to combustion processes are carried out. The program emphasizes the practical aspects of accurate quantum dynamics calculations in order to understand, explain and predict the dynamical properties of important combustion reactions. The aim of this research is to help provide not only qualitative dynamics information but also quantitative prediction of reaction dynamics of combustion reactions at the microscopic level. Through accurate theoretical calculations, the authors wish to be able to quantitatively predict reaction cross sections and rate constants of relatively small gas-phase reactions from first principles that are of direct interest to combustion. The long-term goal of this research is to develop practical computational methods that are capable of quantitatively predicting dynamics of more complex polyatomic gas-phase reactions that are of interest to combustion.

Zhang, J.Z.H.

1998-12-31

42

Quantum control of the dynamics of a semiconductor quantum well  

Microsoft Academic Search

We study the potential for control of the electron dynamics in a symmetric double quantum well, in the two-subband approximation, that is coupled by a strong, pulsed electric field, taking into account the effects of electron-electron interactions. For the system dynamics we use the effective nonlinear Bloch equations. Conditions for complete inversion are presented for hyberbolic secant, Gaussian and sin-squared

E. Paspalakis; M. Tsaousidou; A. Kanaki; A. F. Terzis

2007-01-01

43

Quantum model for the price dynamics  

NASA Astrophysics Data System (ADS)

We apply methods of quantum mechanics to mathematical modelling of price dynamics in a financial market. We propose to describe behavioral financial factors (e.g., expectations of traders) by using the pilot wave (Bohmian) model of quantum mechanics. Our model is a quantum-like model of the financial market, cf. with works of W. Segal, I.E. Segal, E. Haven. In this paper we study the problem of smoothness of price-trajectories in the Bohmian financial model. We show that even the smooth evolution of the financial pilot wave [psi](t,x) (representing expectations of traders) can induce jumps of prices of shares.

Choustova, Olga

2008-10-01

44

Nonperturbative quantum dynamical decoupling  

NASA Astrophysics Data System (ADS)

Current dynamical control based on the bang-bang control mechanism involving various types of pulse sequences is essentially a perturbative theory. This paper presents a nonperturbative dynamical control approach based on the exact stochastic Schrödinger equation. We report our findings on the pulse parameter regions in which the effective dynamical control can be exercised. The onset of the effective control zones reflects the nonperturbative feature of our approach. The nonperturbative methods offer possible new implementations when several different parameter regions are available.

Jing, Jun; Wu, Lian-Ao; You, J. Q.; Yu, Ting

2013-08-01

45

Quantum Dynamics of Insertion Reactions  

Microsoft Academic Search

We describe quantum-dynamical calculations of insertion reactions involving metastable C, N and O atoms with hydrogen molecules. We use a time independent hyperspherical body-frame formalism. Reaction probabilities, rovibrational distributions, integral and differential cross sections and product translational energy distributions have been computed and compared with recent experimental data.

Pascal Honvault; Jean-Michel Launay

46

Quantum dynamics with Bohmian trajectories.  

PubMed

We describe the advantages and disadvantages of numerical methods when Bohmian trajectory grids are used for numerical simulations of quantum dynamics. We focus on the crucial noncrossing property of Bohmian trajectories, which, numerically, must be given careful attention. Failure to do so causes instabilities or leads to false simulations. PMID:17629251

Deckert, D-A; Dürr, D; Pickl, P

2007-07-13

47

Femtosecond pump-probe reflectivity study of InGaAs/GaAs quantum dots carrier dynamics  

NASA Astrophysics Data System (ADS)

Ultrafast carrier dynamics have been studied on a single layer of self-assembled In0.4Ga0.6As/GaAs quantum dots (QDs) using femtosecond degenerate pump-probe differential reflectivity. The measurements were done with an 800 nm, 28 fs Ti-sapphire oscillator. The growth process of QDs consists of two steps, low temperature growth and high temperature annealing. Specifically, the InGaAs QD structures are fabricated on n-type GaAs(001) using molecular beam epitaxy (MBE). The In0.4Ga0.6As layer is deposited at 390-400 ^oC followed by QDs self assembly at 450-540 ^oC. Finally, these QDs are caped with a 10 nm or 100 nm layer of GaAs. Measured width and height of these QDs are typically 33 nm and 6 nm respectively. Dots annealed at higher temperature have larger base area (width and length) and reduced height as compared to those annealed at lower temperature. We have developed a rate equation model to describe the carrier dynamics and fit the reflectivity data. Dynamics depends on the size of the quantum dots: larger QDs have faster dynamics as compared to smaller dots. Additionally, dynamics are slower at higher excitation levels.

Chauhan, K. N.; Riffe, D. M.

2010-10-01

48

Dynamics of Avalanche Quantum Dot Infrared Photodetectors  

NASA Astrophysics Data System (ADS)

Time and frequency response of an avalanche quantum dot infrared photodetector (A-QDIP) operating at long infrared (IR) wavelengths is calculated and the effect of its structure on the dynamic behavior is studied. For this purpose, the rate equations of different regions are numerically solved considering the boundary conditions. Results show that detector with long multiplication region has a slower time response. Also frequency analysis predicts a 3-dB bandwidth above 100 GHz for a device with multiplication length of 200 nm. Gain bandwidth product (GBP) is calculated and a value of about 1000 GHz is obtained. Effect of charge layer doping on dynamic response of detector is also studied and results show that increase in doping improves the GBP while the bandwidth is reduced. We also study the effect of quantum dots of absorption region on frequency response of device and results show that longer electron relaxation time into quantum dot decreases the bandwidth of detector.

Zavvari, Mahdi; Ahmadi, Vahid

2012-12-01

49

Universal nonequilibrium quantum dynamics in imaginary time  

NASA Astrophysics Data System (ADS)

We propose a method to study dynamical response of a quantum system by evolving it with an imaginary-time-dependent Hamiltonian. The leading nonadiabatic response of the system driven to a quantum-critical point is universal and characterized by the same exponents in real and imaginary time. For a linear quench protocol, the fidelity susceptibility and the geometric tensor naturally emerge in the response functions. Beyond linear response, we extend the finite-size scaling theory of quantum phase transitions to nonequilibrium setups. This allows, e.g., for studies of quantum phase transitions in systems of fixed finite size by monitoring expectation values as a function of the quench velocity. Nonequilibrium imaginary-time dynamics is also amenable to quantum Monte Carlo (QMC) simulations, with a scheme that we introduce here and apply to quenches of the transverse-field Ising model to quantum-critical points in one and two dimensions. The QMC method is generic and can be applied to a wide range of models and nonequilibrium setups.

de Grandi, C.; Polkovnikov, A.; Sandvik, A. W.

2011-12-01

50

A mixed quantum-classical molecular dynamics study of vibrational relaxation of a molecule in solution  

NASA Astrophysics Data System (ADS)

An application of mixed quantum-classical molecular dynamics to vibrational relaxation of the solute molecule in the solution has been investigated. In the present paper, we demonstrate that mean field approximation, rather than surface hopping approximation, works satisfactorily well for the vibrational relaxation of, at least, the CN- ion in the aqueous solution, where the potential surface of the solvent water depends little on the vibrational quantum state of the solute. The calculated relaxation time is in good correspondence to those obtained from other two different methods based upon the same potential model, i.e., Fermi's Golden Rule with classical force autocorrelation function and path integral influence functional theory in its classical bath limit. The present method gives some interesting findings for the relaxation. For example, the energy relaxation time may be longer than the population relaxation time. With respect to the coupling to the solvent, water molecules in the first hydration shell make a leading contribution to the relaxation of the solute.

Terashima, Takeshi; Shiga, Motoyuki; Okazaki, Susumu

2001-04-01

51

Dynamics of the carbon nuclei in C{sub 60} studied by Feynman path-integral quantum Monte Carlo simulations  

SciTech Connect

The dynamics of the carbon nuclei in the C{sub 60} molecule have been studied by the Feynman path-integral (PI) quantum Monte Carlo (QMC) simulations and within a harmonic oscillator approximation. The following finite-temperature properties have been calculated: kinetic, potential, and total energy, radial and angular distribution functions (rdf, adf) as well as parameters describing the degree of atomic de/localization. The possible influence of quantum fluctuations on microscopic electronic structure properties of superconducting fullerides is briefly mentioned. PI simulations as well as simple analytical results show that the spatial uncertainty of the C atoms in C{sub 60} is comparable to the difference between the lengths of the short and long CC bonds in the icosahedral molecule. Reliable agreement between PI-derived rdf and the experimental curve based on neutron diffraction data is observed. 50 refs., 8 figs.

Boehm, M.C. [Fritz-Haber-Institut der Max-Planck-Gesellschaft, Berlin (Germany); Ramirez, R. [Instituto de Ciencia de Materiales, Madrid (Spain)

1995-08-17

52

Femtosecond two-photon photoassociation of hot magnesium atoms: A quantum dynamical study using thermal random phase wavefunctions.  

PubMed

Two-photon photoassociation of hot magnesium atoms by femtosecond laser pulses, creating electronically excited magnesium dimer molecules, is studied from first principles, combining ab initio quantum chemistry and molecular quantum dynamics. This theoretical framework allows for rationalizing the generation of molecular rovibrational coherence from thermally hot atoms [L. Rybak, S. Amaran, L. Levin, M. Tomza, R. Moszynski, R. Kosloff, C. P. Koch, and Z. Amitay, Phys. Rev. Lett. 107, 273001 (2011)]. Random phase thermal wavefunctions are employed to model the thermal ensemble of hot colliding atoms. Comparing two different choices of basis functions, random phase wavefunctions built from eigenstates are found to have the fastest convergence for the photoassociation yield. The interaction of the colliding atoms with a femtosecond laser pulse is modeled non-perturbatively to account for strong-field effects. PMID:24182021

Amaran, Saieswari; Kosloff, Ronnie; Tomza, Micha?; Skomorowski, Wojciech; Paw?owski, Filip; Moszynski, Robert; Rybak, Leonid; Levin, Liat; Amitay, Zohar; Berglund, J Martin; Reich, Daniel M; Koch, Christiane P

2013-10-28

53

Error avoiding quantum codes and dynamical stabilization of Grover's algorithm  

NASA Astrophysics Data System (ADS)

Dynamical stabilization properties of error avoiding quantum codes are investigated beyond the perturbative regime. As an example Grover's search algorithm and its behaviour under a particular class of coherent errors are studied. Numerical examples which demonstrate that error avoiding quantum codes may be capable of stabilizing quantum algorithms well beyond the regime for which they were designed originally are presented.

Mussinger, Michael; Delgado, Aldo; Alber, Gernot

2000-09-01

54

Pulsed Electrical Spin Injection into InGaAs Quantum Dots: Studies of the Electroluminescence Polarization Dynamics  

SciTech Connect

We present time-resolved studies of the spin polarization dynamics during and after initialization through pulsed electrical spin injection into InGaAs quantum dots embedded in a p-i-n-type spin-injection light-emitting diode. Experiments are performed with pulse widths in the nanosecond range and a time-resolved single photon counting setup is used to detect the subsequent electroluminescence. We find evidence that the achieved spin polarization shows an unexpected temporal behavior, attributed mainly to many-carrier and non-equilibrium effects in the device.

Asshoff, P.; Loeffler, W.; Fluegge, H.; Zimmer, J.; Mueller, J.; Westenfelder, B.; Hu, D. Z.; Schaadt, D. M.; Kalt, H.; Hetterich, M. [Institut fuer Angewandte Physik and DFG Center for Functional Nanostructures (CFN), Universitaet Karlsruhe, 76131 Karlsruhe (Germany)

2010-01-04

55

Controlling quantum dynamics phenomena  

NASA Astrophysics Data System (ADS)

Since the initial development of lasers in the 1960's, a longstanding dream has been to utilize these special intense radiation (light) sources to redirect the outcome of chemical reactions. In the ensuing years, much effort has gone into attempts at making this dream a reality. Emerging recent successful experiments derive from a confluence of ultrafast laser technology, control theory concepts, and suitable pattern recognition algorithms all drawn together to form adaptive machines. The adaptive machines are being used to manipulate chemical bonds, as well as a broad variety of other atomic and molecular dynamics phenomenon. These advances rest on the ability to delicately shape laser pulses so that they act as a special type of photonic reagents.

Rabitz, Herschel

2008-03-01

56

High fidelity quantum gates via dynamical decoupling.  

PubMed

Realizing the theoretical promise of quantum computers will require overcoming decoherence. Here we demonstrate numerically that high fidelity quantum gates are possible within a framework of quantum dynamical decoupling. Orders of magnitude improvement in the fidelities of a universal set of quantum gates, relative to unprotected evolution, is achieved over a broad range of system-environment coupling strengths, using recursively constructed (concatenated) dynamical decoupling pulse sequences. PMID:21231440

West, Jacob R; Lidar, Daniel A; Fong, Bryan H; Gyure, Mark F

2010-12-02

57

Classical and quantum discrete dynamical systems  

NASA Astrophysics Data System (ADS)

We study deterministic and quantum dynamics from a constructive "finite" point of view, since the introduction of the continuum or other actual infinities in physics poses severe conceptual and technical difficulties, and while all of these concepts are not really needed in physics, which is in fact an empirical science. Particular attention is paid to the symmetry properties of discrete systems. For a consistent description of the symmetries of dynamical systems at different time instants and the symmetries of various parts of such systems, we introduce discrete analogs of gauge connections. These gauge structures are particularly important to describe the quantum behavior. The symmetries govern the fundamental properties of the behavior of dynamical systems. In particular, we can show that the moving soliton-like structures are inevitable in a deterministic (classical) dynamical system, whose symmetry group breaks the set of states into a finite number of orbits of the group. We demonstrate that the quantum behavior is a natural consequence of symmetries of dynamical systems. This behavior is a result of the fundamental inability to trace the identity of indistinguish-able objects during their evolution. Information is only available on invariant statements and values related with such objects. Using general mathematical arguments, any quantum dynamics can be shown to reduce to a sequence of permutations. The quantum interferences occur in the invariant subspaces of permutation representations of the symmetry groups of dynamical systems. The observables can be expressed in terms of permutation invariants. We also show that in order to describe quantum phenomena it is sufficient to use cyclotomic fields—the minimal extensions of natural numbers suitable for quantum mechanics, instead of a non-constructive number system—the field of complex numbers. The finite groups of symmetries play the central role in this review. In physics there is an additional reason for such groups to be of interest. Numerous experiments and observations in particle physics point to the importance of finite groups of relatively low orders in a number of fundamental processes. The origin of these groups has no explanation within presently recognized theories, such as the Standard Model.

Kornyak, V. V.

2013-01-01

58

Quantum dynamics as a physical resource  

SciTech Connect

How useful is a quantum dynamical operation for quantum information processing? Motivated by this question, we investigate several strength measures quantifying the resources intrinsic to a quantum operation. We develop a general theory of such strength measures, based on axiomatic considerations independent of state-based resources. The power of this theory is demonstrated with applications to quantum communication complexity, quantum computational complexity, and entanglement generation by unitary operations.

Nielsen, Michael A.; Dawson, Christopher M.; Dodd, Jennifer L.; Gilchrist, Alexei; Mortimer, Duncan; Osborne, Tobias J.; Bremner, Michael J.; Hines, Andrew [Centre for Quantum Computer Technology and Department of Physics, University of Queensland, Brisbane 4072 (Australia); Harrow, Aram W. [MIT Physics, 77 Massachusetts Avenue, Cambridge Massachusetts 02139 (United States)

2003-05-01

59

Quantum Dynamics of Polariton Condensates  

NASA Astrophysics Data System (ADS)

We illustrate the rich and fundamental physics that is accessible with the semiconductor implementation of the quantum superposition of light and matter: exciton-polaritons. The short lifetime of polaritons makes them an out-of-equilibrium system. Their dynamic is an important ingredient in their behaviour and properties. Their peculiar dispersion also allows a rich engineering of various processes, tuning the system from light- to matter-like. Finally, the exciton-exciton interaction turns them into a non-linear system. The interplay of all these factors makes polaritons one of today's most versatile and fruitful research arena, both theoretically and experimentally. In this chapter we give a rather general picture of these specificities that we isolate in various dimensionalities (0, 1, and 2D). One of the most intensively researched area in the semiconductor implementation of the polariton physics is related to Bose-Einstein condensation. We solve exactly a configuration of relaxation from the Rayleigh circle into the ground state in the framework of quantum Boltzmann master equations and show how coherence builds up spontaneously in the system, by copying in a single quantum state statistical features characteristic of the macroscopic system. In this way, we extend to higher order correlations the historical reasoning of Einstein, who predicted the phenomenon by arguments on the mean populations. We show how lifetime and pumping allow a simpler treatment by reducing the required number of states, for which we present a full quantum treatment. We contrast this condensate build-up with the 0D case where the reduced complexity allows an exact numerical treatment. The coherence build-up in this cavity QED limit manifests as lasing with a sharp line in the cavity mode that produces a variation of the Mollow triplet in the exciton emission, as the cavity effectively replaces the laser in the conventional resonance fluorescence scenario. We show how lasing also arises in this case as a condensation of polaritons, and can be substituted in the case of vanishing intensities by a coherent field formed when strong coupling is optimum. This zero-dimensional limit also provides an exact picture of the transition from the quantum to the classical regime, a universal process of unsuspected complexity. Finally, we illustrate the recent development of polariton quantum hydrodynamics with propagation of coherent wave packets. The short lifetime allows a continuous observation of this dynamics in real space, a picture completed with the observation of their emission spectra in energy-momentum space. The peculiar polariton dispersion is the source of interesting behaviours even when described by the most fundamental and simplest equation of quantum physics: the Schrödinger equation.

Laussy, Fabrice P.

60

Radiation from quantum weakly dynamical horizons in loop quantum gravity.  

PubMed

We provide a statistical mechanical analysis of quantum horizons near equilibrium in the grand canonical ensemble. By matching the description of the nonequilibrium phase in terms of weakly dynamical horizons with a local statistical framework, we implement loop quantum gravity dynamics near the boundary. The resulting radiation process provides a quantum gravity description of the horizon evaporation. For large black holes, the spectrum we derive presents a discrete structure which could be potentially observable. PMID:23031096

Pranzetti, Daniele

2012-07-02

61

Non-Markovian dynamics of quantum discord  

SciTech Connect

We evaluate the quantum discord dynamics of two qubits in independent and common non-Markovian environments. We compare the dynamics of entanglement with that of quantum discord. For independent reservoirs the quantum discord vanishes only at discrete instants whereas the entanglement can disappear during a finite time interval. For a common reservoir, quantum discord and entanglement can behave very differently with sudden birth of the former but not of the latter. Furthermore, in this case the quantum discord dynamics presents sudden changes in the derivative of its time evolution which is evidenced by the presence of kinks in its behavior at discrete instants of time.

Fanchini, F. F.; Caldeira, A. O. [Instituto de Fisica Gleb Wataghin, Universidade Estadual de Campinas, Post Office Box 6165, 13083-970, Campinas, SP (Brazil); Werlang, T. [Departamento de Fisica, Universidade Federal de Sao Carlos, Post Office Box 676, 13565-905, Sao Carlos, SP (Brazil); Brasil, C. A.; Arruda, L. G. E. [Instituto de Fisica de Sao Carlos, Universidade de Sao Paulo, Post Office Box 369, 13560-970, Sao Carlos, SP (Brazil)

2010-05-15

62

Non-Markovian dynamics and entanglement in quantum Brownian motion  

Microsoft Academic Search

Dynamical aspects of quantum Brownian motion in a low temperature environment are investigated. We give a systematic calculation\\u000a of quantum entanglement among two Brownian oscillators without invoking Born–Markov approximation widely used for the study\\u000a of open systems. Our approach is suitable to probe short time dynamics at cold temperatures where many experiments on quantum\\u000a information processing are performed.

K. Shiokawa

2009-01-01

63

Equations of state and transport properties of warm dense beryllium: a quantum molecular dynamics study.  

PubMed

We have calculated the equations of state, the viscosity and self-diffusion coefficients, and electronic transport coefficients of beryllium in the warm dense regime for densities from 4.0 to 6.0 g/cm(3) and temperatures from 1.0 to 10.0 eV by using quantum molecular dynamics simulations. The principal Hugoniot curve is in agreement with underground nuclear explosive and high-power laser experimental results up to ~20 Mbar. The calculated viscosity and self-diffusion coefficients are compared with the one-component plasma model, using effective charges given by the average-atom model. The Stokes-Einstein relationship, which connects viscosity and self-diffusion coefficients, is found to hold fairly well in the strong coupling regime. The Lorenz number, which is the ratio between thermal and electrical conductivities, is computed via Kubo-Greenwood formula and compared to the well-known Wiedemann-Franz law in the warm dense region. PMID:23679528

Wang, Cong; Long, Yao; Tian, Ming-Feng; He, Xian-Tu; Zhang, Ping

2013-04-12

64

Quantum nature of the big bang: Improved dynamics  

SciTech Connect

An improved Hamiltonian constraint operator is introduced in loop quantum cosmology. Quantum dynamics of the spatially flat, isotropic model with a massless scalar field is then studied in detail using analytical and numerical methods. The scalar field continues to serve as ''emergent time'', the big bang is again replaced by a quantum bounce, and quantum evolution remains deterministic across the deep Planck regime. However, while with the Hamiltonian constraint used so far in loop quantum cosmology the quantum bounce can occur even at low matter densities, with the new Hamiltonian constraint it occurs only at a Planck-scale density. Thus, the new quantum dynamics retains the attractive features of current evolutions in loop quantum cosmology but, at the same time, cures their main weakness.

Ashtekar, Abhay [Institute for Gravitational Physics and Geometry, Physics Department, Penn State, University Park, Pennsylvania 16802 (United States); Institute for Theoretical Physics, University of Utrecht, Princetonplein5, 3584 CC Utrecht (Netherlands); Isaac Newton Institute for Mathematical Sciences, 20 Clarkson Road, Cambridge CB3 0EH (United Kingdom); Pawlowski, Tomasz; Singh, Parampreet [Institute for Gravitational Physics and Geometry, Physics Department, Penn State, University Park, Pennsylvania 16802 (United States)

2006-10-15

65

Quantum dynamics of a single vortex.  

PubMed

Vortices occur naturally in a wide range of gases and fluids, from macroscopic to microscopic scales. In Bose-Einstein condensates of dilute atomic gases, superfluid helium and superconductors, the existence of vortices is a consequence of the quantum nature of the system. Quantized vortices of supercurrent are generated by magnetic flux penetrating the material, and play a key role in determining the material properties and the performance of superconductor-based devices. At high temperatures the dynamics of such vortices are essentially classical, while at low temperatures previous experiments have suggested collective quantum dynamics. However, the question of whether vortex tunnelling occurs at low temperatures has been addressed only for large collections of vortices. Here we study the quantum dynamics of an individual vortex in a superconducting Josephson junction. By measuring the statistics of the vortex escape from a controllable pinning potential, we demonstrate the existence of quantized levels of the vortex energy within the trapping potential well and quantum tunnelling of the vortex through the pinning barrier. PMID:12968173

Wallraff, A; Lukashenko, A; Lisenfeld, J; Kemp, A; Fistul, M V; Koval, Y; Ustinov, A V

2003-09-11

66

Review on System-Spin Environment Dynamics of Quantum Discord  

NASA Astrophysics Data System (ADS)

Recent work has relatively comprehensively studied the quantum discord, which is supposed to account for all the nonclassical correlations present in a bipartite state (including entanglement), and provide computational speedup and quantum enhancement even in separable states. Firstly, we introduce several different indicators of nonclassical correlations, including their definitions and interpretations, mathematical properties, and the relationship between them. Secondly, we review two major topics of quantum discord. One is the remarkable behavior at quantum phase transitions. The pairwise quantum discord for nearest neighbors as well as distant spin pairs can perfectly signal the critical behavior of many physical models, even at finite temperatures. The other is quantum discord dynamics in open systems, especially for "system-spin environment" models. Quantum discord is more robust than entanglement against external perturbations. It can be created, greatly amplified or protected under certain conditions, and presents promising applications in quantum technologies such as quantum computers.

Liu, Ben-Qiong; Shao, Bin; Li, Jun-Gang; Zou, Jian

2013-01-01

67

Dynamic diffusion as approximation of quantum behavior  

Microsoft Academic Search

The approximation of quantum unitary dynamics of a particle by a swarm of point wise classical samples of this particle is proposed. Quantum mechanism of speedup rests on the creation and annihilation of absolutely rigid bons, which join samples in dot wise symplexes so that the density of swarm approximate the quantum probability. This mechanism does not require differentiation of

Yuri Ozhigov

2010-01-01

68

Nosè Hoover dynamics in quantum phase space  

NASA Astrophysics Data System (ADS)

Thermal fluctuations in time-dependent quantum processes are treated by a constant-temperature generalization of Wigner's formulation of quantum mechanics in phase space. To this end, quantum Nosè-Hoover dynamics is defined by generalizing the Moyal bracket. Computational applications of the formalism, together with further theoretical developments, are discussed.

Sergi, Alessandro; Petruccione, Francesco

2008-09-01

69

Surface induced molecular dynamics of thin lipid films confined to submicron cavities: A 1H multiple-quantum NMR study  

NASA Astrophysics Data System (ADS)

The dynamics and molecular order of thin lipid (lecithin) films confined to 200, 100 and 20 nm cylindrical pores with varying surface coverage, were investigated by 1H multiple-quantum NMR. The results show that the molecular dynamics in the surface controlled layers are less hindered compared to those in the bulk. Dynamic heterogeneity among terminal CH3 groups is evident. Enhanced dynamic freedom is observed for films with area per molecule, ~ 128 A2. The results are discussed in terms of changes in the lipid molecular organization with respect to surface concentration, its plausible motional modes and dynamic heterogeneity.

Jagadeesh, B.; Prabhakar, A.; Demco, D. E.; Buda, A.; Blumich, B.

2005-03-01

70

Storing quantum dynamics in quantum states: a stochastic programmable gate.  

PubMed

We show how to encode quantum dynamics in the state of a quantum system, in such a way that the system can be used to stochastically perform, at a later time, the stored transformation on some other quantum system. The probability of failure decreases exponentially with the number of qubits that store the transformation. We discuss optimality of this scheme, whose applications include viability of a (stochastic) programmable quantum gate and the teleportation of quantum transformations using entanglement and unidirectional classical communication. PMID:11801173

Vidal, G; Masanes, L; Cirac, J I

2002-01-11

71

Simulational studies of epitaxial semiconductor superlattices: Quantum dynamical phenomena in ac and dc electric fields  

SciTech Connect

Using high-accuracy numerical methods the author investigates the dynamics of independent electrons in both ideal and realistic superlattices subject to arbitrary ac and/or dc electric fields. For a variety of superlattice potentials, optically excited initial wave packets, and combinations of ac and dc electric fields, he numerically solves the time-dependent Schroedinger equation. In the case of ideal periodic superlattice potentials, he investigates a long list of dynamical phenomena involving multiple miniband transitions and time-dependent electric fields. These include acceleration effects associated with interminiband transitions in strong fields, Zener resonances between minibands, dynamic localization with ac fields, increased single-miniband transport with an auxiliary resonant ac field, and enhanced or suppressed interminiband probability exchange using an auxiliary ac field. For all of the cases studied, the resulting time-dependent wave function is analyzed by projecting the data onto convenient orthonormal bases. This allows a detailed comparison with approximately analytic treatments. In an effort to explain the rapid decay of experimentally measured Bloch oscillation (BO) signals the author incorporates a one-dimensional representation of interface roughness (IR) into their superlattice potential. He shows that as a result of IR, the electron dynamics can be characterized in terms of many discrete, incommensurate frequencies near the Block frequency. Chapters 2, 3, 4 and 5 have been removed from this report and will be processed separately.

Reynolds, J.

1997-10-08

72

An Eight-Degree-of-Freedom, Quantum Dynamics Study of the Isotopic Effect on the Reaction: HD+C?H  

SciTech Connect

An eight dimensional time-dependent quantum dynamics calculation is reported to study the isotopic reaction, HD+C?H, on a new modified potential energy surface(PES). Initial-state-selected reaction probability, integral cross section and rate constants are presented in this isotopic reaction study. This study shows that vibrational excitations of HD enhance the reactivity, whereas vibrational excitations of C?H only have a small effect on the reactivity. Furthermore, the bending excitations of C?H, comparing to the ground state reaction probability, hinder the reactivity. This is consistent with calculation on the reaction of H?+C?H. The comparison of these two reactions also shows the isotopic effect in the initial-state-selected reaction probability, integral cross section and rate constants. The rate constant comparison shows that the HD +C?H reaction has a smaller reactivity than the H? + C?H reaction.

Wang, Dunyou; Huo, Winifred M.

2008-08-28

73

Carrier Dynamics in Colloidal Graphene Quantum Dots  

Microsoft Academic Search

We describe carrier dynamics for single and multiple excitons in colloidal graphene quantum dots (GQDs). Strong confinement and corresponding size-tunable electronic structure make GQDs potentially useful sensitizers in photovoltaic devices. We have studied the optical response of GQDs consisting of 132 and 168 sp^2 hybridized carbon atoms dissolved in toluene with HOMO-LUMO transitions of 1.4-1.6 eV. From measurements of ultrafast

Cheng Sun; Xin Yan; Liang-Shi Li; John A. McGuire

2011-01-01

74

Quantum Dynamics of Helium Clusters.  

National Technical Information Service (NTIS)

Our study of helium clusters was motivated by the desire to understand the scaling of the unusual properties of bulk 4He, a quantum liquid, in finite size systems as one goes from the macroscopic regime to the regime of molecular dimensions. This is fully...

K. B. Whaley

1993-01-01

75

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

76

Entropic Fluctuations of Quantum Dynamical Semigroups  

NASA Astrophysics Data System (ADS)

We study a class of finite dimensional quantum dynamical semigroups {e^{t{L}}}_{t?0} whose generators {L} are sums of Lindbladians satisfying the detailed balance condition. Such semigroups arise in the weak coupling (van Hove) limit of Hamiltonian dynamical systems describing open quantum systems out of equilibrium. We prove a general entropic fluctuation theorem for this class of semigroups by relating the cumulant generating function of entropy transport to the spectrum of a family of deformations of the generator {{L}}. We show that, besides the celebrated Evans-Searles symmetry, this cumulant generating function also satisfies the translation symmetry recently discovered by Andrieux et al., and that in the linear regime near equilibrium these two symmetries yield Kubo's and Onsager's linear response relations.

Jakši?, V.; Pillet, C.-A.; Westrich, M.

2013-08-01

77

Quantum dynamics studies of gas-surface reactions and use of complex absorbing potentials in wave-packet calculations  

NASA Astrophysics Data System (ADS)

In this thesis, quantum dynamics studies are conducted on gas-surface reactions and complex absorbing potentials. Through a three-dimensional model, dissociation probabilities for O2 on both (110) and (100) surfaces of copper are calculated for ground state as well as rovibrationally excited oxygen molecules. Specifically, the reason for the difference in calculated dissociation probabilities of oxygen on two surfaces is explained. Then the thermal effect of the surface on the dissociation probability is studied by a one dimensional fluctuating barrier. It is observed that the quantum mechanical tunneling probability exhibits a maximum as a function of the oscillating frequency between the low and the high frequency limits. The physical origin and process underlying this resonantlike phenomenon are proposed. In the second part of this thesis, the complex absorbing potential (CAP) is introduced and studied. Exact numerical calculation shows that use of optimized CAP significantly improves the efficiency of wavefunction absorption over that of negative imaginary potential (NIP) in scattering applications. The CAP is optimized by an efficient time-dependent propagation approach. Application to the prototype inelastic scattering of He + H2 demonstrates the accuracy and efficiency of the channel-dependent CAP for extracting state-to-state scattering information.

Ge, Jiuyuan

1999-11-01

78

Dynamical Decoupling of Open Quantum Systems  

SciTech Connect

We propose a novel dynamical method for beating decoherence and dissipation in open quantum systems. We demonstrate the possibility of filtering out the effects of unwanted (not necessarily known) system-environment interactions and show that the noise-suppression procedure can be combined with the capability of retaining control over the effective dynamical evolution of the open quantum system. Implications for quantum information processing are discussed. {copyright} {ital 1999} {ital The American Physical Society}

Viola, L.; Lloyd, S. [d`Arbeloff Laboratory for Information Systems and Technology, Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States); Knill, E. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

1999-03-01

79

Monitoring entanglement evolution and collective quantum dynamics  

Microsoft Academic Search

We generalize a recently developed scheme for monitoring coherent quantum dynamics with good time resolution and low backaction [Reuther , Phys. Rev. Lett.PRLTAO0031-900710.1103\\/PhysRevLett.102.033602 102, 033602 (2009)] to the case of more complex quantum dynamics of one or several qubits. The underlying idea is to measure with lock-in techniques the response of the quantum system to a high-frequency ac field. We

Georg M. Reuther; David Zueco; Peter Hänggi; Sigmund Kohler

2011-01-01

80

Photoelectron spectroscopy of chlorine dioxide and its negative ion: A quantum dynamical study  

NASA Astrophysics Data System (ADS)

The photoelectron spectra of ClO2 and its negative ion are investigated theoretically by a time-dependent wave-packet method. The near equilibrium MRCI potential energy surfaces of Peterson and Werner [J. Chem. Phys. 99, 302 (1993)] are employed in the nuclear dynamical simulations. The theoretical findings are in good agreement with the experimental results. In the experimental recording, excitations along the symmetric stretching and bending vibrational modes of ClO2 were observed. The excitation along the asymmetric stretching vibrational mode is absent in the experimental results. Considering these observations, and utilizing the available electronic structure results, we in our dynamical study focused on the C2v nuclear arrangements of the system. The relevant intial wave function to describe the photoelectron transition is prepared in both ways by the Hamiltonian matrix diagonalization using the ab initio potential energy surface of the ground electronic state, as well as in terms of the dimensionless normal coordinates of the electronic ground state of ClO2. The stick vibronic spectra are calculated by solving the time-independent Schrödinger equation employing a basis set expansion approach and the Lanczos algorithm. The resulting vibrational eigenvalues are compared with the experimental results and are discussed. The inclusion of the asymmetric stretching vibration and the possible role of the nonadiabatic couplings in the nuclear dynamics are also emphasized.

Mahapatra, Susanta; Krishnan, Gireesh M.

2001-10-01

81

Quantum Speed Limits in Open System Dynamics  

NASA Astrophysics Data System (ADS)

Bounds to the speed of evolution of a quantum system are of fundamental interest in quantum metrology, quantum chemical dynamics, and quantum computation. We derive a time-energy uncertainty relation for open quantum systems undergoing a general, completely positive, and trace preserving evolution which provides a bound to the quantum speed limit. When the evolution is of the Lindblad form, the bound is analogous to the Mandelstam-Tamm relation which applies in the unitary case, with the role of the Hamiltonian being played by the adjoint of the generator of the dynamical semigroup. The utility of the new bound is exemplified in different scenarios, ranging from the estimation of the passage time to the determination of precision limits for quantum metrology in the presence of dephasing noise.

del Campo, A.; Egusquiza, I. L.; Plenio, M. B.; Huelga, S. F.

2013-02-01

82

Quantum speed limits in open system dynamics.  

PubMed

Bounds to the speed of evolution of a quantum system are of fundamental interest in quantum metrology, quantum chemical dynamics, and quantum computation. We derive a time-energy uncertainty relation for open quantum systems undergoing a general, completely positive, and trace preserving evolution which provides a bound to the quantum speed limit. When the evolution is of the Lindblad form, the bound is analogous to the Mandelstam-Tamm relation which applies in the unitary case, with the role of the Hamiltonian being played by the adjoint of the generator of the dynamical semigroup. The utility of the new bound is exemplified in different scenarios, ranging from the estimation of the passage time to the determination of precision limits for quantum metrology in the presence of dephasing noise. PMID:23414008

del Campo, A; Egusquiza, I L; Plenio, M B; Huelga, S F

2013-01-30

83

Hamiltonian quantum dynamics with separability constraints  

SciTech Connect

Schroedinger equation on a Hilbert space H, represents a linear Hamiltonian dynamical system on the space of quantum pure states, the projective Hilbert space PH. Separable states of a bipartite quantum system form a special submanifold of PH. We analyze the Hamiltonian dynamics that corresponds to the quantum system constrained on the manifold of separable states, using as an important example the system of two interacting qubits. The constraints introduce nonlinearities which render the dynamics nontrivial. We show that the qualitative properties of the constrained dynamics clearly manifest the symmetry of the qubits system. In particular, if the quantum Hamilton's operator has not enough symmetry, the constrained dynamics is nonintegrable, and displays the typical features of a Hamiltonian dynamical system with mixed phase space. Possible physical realizations of the separability constraints are discussed.

Buric, Nikola [Institute of Physics, P.O. Box 57, 11001 Belgrade (Serbia)], E-mail: buric@phy.bg.ac.yu

2008-01-15

84

Quantum control of charge carrier dynamics in layered semiconductor heterostructures  

Microsoft Academic Search

This dissertation presents theoretical studies of charge carrier dynamics in layered semiconductor heterostructures. Carrier dynamics are investigated by solving the Schrodinger equation numerically on a grid. Control methods are used to discover laser pulses that actively manipulate and control dynamics in quantum well systems. Results indicate that a wide array of possible target objectives can be achieved successfully using simple,

Kevin Lee Shuford

2003-01-01

85

A Quantum Lattice-Gas Model for Computational Fluid Dynamics  

Microsoft Academic Search

Quantum-computing ideas are applied to the practical and ubiquitous problem of fluid dynamics simulation. Hence, this paper addresses two separate areas of physics: quantum mechanics and fluid dynamics (or specially, the computational simulation of fluid dynamics). The quantum algorithm is called a quantum lattice gas. An analytical treatment of the microscopic quantum lattice-gas system is carried out to predict its

Jerey Yepez

1999-01-01

86

Engineering strontium binding affinity in an EF-hand motif: a quantum chemical and molecular dynamics study.  

PubMed

Proteins with the ability to specifically bind strontium would potentially be of great use in the field of nuclear waste management. Unfortunately, no such peptides or proteins are known -- indeed, it is uncertain whether they exist under natural conditions due to low environmental concentrations of strontium. To investigate the possibility of devising such molecules, one of us (CV), in a previous experimental study, proposed starting from an EF-hand motif of the protein calmodulin and mutating some residues to change the motif's specificity for calcium into one for strontium. In this paper, which represents a theoretical complement to the experimental work, we analyzed small-molecule crystallographic structures and performed quantum chemical calculations to identify possible mutations. We then constructed seven mutant sequences of the EF-hand motif and analyzed their dynamical and binding behaviors using molecular dynamics simulations and free-energy calculations (using the MM/PBSA method). As a result of these analyzes we were able to isolate some characteristics that could lead to mutant peptides with enhanced strontium affinity. PMID:15473703

Rinaldo, D; Vita, C; Field, M J

2004-12-01

87

Poisoning of hydrogen dissociation at Pd (100) by adsorbed sulfur studied by ab-initio quantum dynamics and ab-initio molecular dynamics  

Microsoft Academic Search

We report calculations of the dissociative adsorption of H2 at Pd (100) covered with 1\\/4 monolayer of sulfur using quantum dynamics as well as molecular dynamics and taking all six degrees of freedom of the two H atoms fully into account. The ab-initio potential-energy surface (PES) is found to be very strongly corrugated. In particular, we discuss the influence of

Axel Gross; Ching-Ming Wei; Matthias Scheffler

1998-01-01

88

Quantum Dynamics of Tunneling between Superconductors  

Microsoft Academic Search

A functional-integral formulation is used to treat the quantum dynamics of a microscopic model of a Josephson junction, including the dissipative effects of quasiparticle tunneling. The calculation is carried to a point where it makes contact with, and therefore substantiates, recent work by Caldeira and Leggett in which the system is treated by analogy with the quantum Brownian motion of

Vinay Ambegaokar; Ulrich Eckern; Gerd Schön

1982-01-01

89

Quantum Kinetic Heisenberg Models: A Unique Dynamics.  

National Technical Information Service (NTIS)

We suggest that the dynamics Glauber embodied in his kinetic Ising model can be introduced similarly and in an apparently unique way, into the quantum statistical mechanics of the quantum-integrable models like the Heisenberg, sine-Gordon and Massive Thir...

J. Timonen D. J. Pilling R. K. Bullough

1986-01-01

90

Lattice thermal conductivity reduction in Bi2Te3 quantum wires with smooth and rough surfaces: A molecular dynamics study  

Microsoft Academic Search

Using molecular dynamics simulations, we have predicted the thermal conductivity of Bi2Te3 nanowires with diameters ranging from 3 to 30 nm with both smooth and rough surfaces. It is found that when the nanowire diameter decreases to the molecular scale (below 10 nm, or the so-called ``quantum wire''), the thermal conductivity shows significant reduction as compared to bulk value. On

Bo Qiu; Lin Sun; Xiulin Ruan

2011-01-01

91

Few-body quantum dynamics of high-Z ions studied at the future relativistic high-energy storage ring  

NASA Astrophysics Data System (ADS)

At the FAIR facility for antiprotons and ion research, the high-energy storage ring will provide highly charged heavy ions with Z all the way to Z = 92 for beam energies ranging from 200 A MeV up to energies of approximately 5 A GeV. This opens up a wealth of opportunities for in-ring atomic physics experiments on few-body quantum dynamics ranging from, for example, the correlated dynamics of various e+-e- pair creation processes to quasi-photoionization of inner shells of the highest-Z ions.

Hagmann, S.; Stöhlker, Th; Litvinov, Yu; Kozhuharov, C.; Hillenbrand, P.-M.; Spillmann, U.; Shabaev, V.; Stiebing, K.; Lestinsky, M.; Surzhykov, A.; Voitkiv, A.; Franzke, B.; Fischer, D.; Schneider, D.; Jakubassa, D.; Artiomov, A.; DeFilippo, E.; Ma, X.; Dörner, R.; Rothard, H.

2013-09-01

92

Approche geometrique de la limite semi-classique par les etats coherents et mecanique quantique sur le tore. (Geometry-based approach to studying the semi-classical limit in quantum dynamics by the coherent states and quantum mechanics on the torus).  

National Technical Information Service (NTIS)

This thesis deals with problems linked to the study of the semi-classical limit in quantum dynamics. The first part presents a geometrical formulation which is tantamount to the time dependent variational principle. The classical dynamics is considered as...

F. Faure

1993-01-01

93

Carrier Dynamics in Colloidal Graphene Quantum Dots  

NASA Astrophysics Data System (ADS)

We describe carrier dynamics for single and multiple excitons in colloidal graphene quantum dots (GQDs). Strong confinement and corresponding size-tunable electronic structure make GQDs potentially useful sensitizers in photovoltaic devices. We have studied the optical response of GQDs consisting of 132 and 168 sp^2 hybridized carbon atoms dissolved in toluene with HOMO-LUMO transitions of 1.4-1.6 eV. From measurements of ultrafast (˜100 fs) transient absorption over nanosecond timescales, we extract the single-photon absorption cross-section and observe carrier-induced Stark shifts of the order of 0.1 eV indicating strong carrier-carrier interactions, as expected for the relatively weak screening of a two-dimensional nanostructure. Multiexcitons are observed to decay nonradiatively on ˜1 to 20 ps timescales, while single excitons display dynamics on multiple timescales due to carrier cooling, singlet-to-triplet intersystem crossing, and, on nanosecond to microsecond timescales, radiative recombination.

Sun, Cheng; Yan, Xin; Li, Liang-Shi; McGuire, John A.

2011-03-01

94

Real Time Nonequilibrium Dynamics of Quantum Plasmas  

NASA Astrophysics Data System (ADS)

We implement the dynamical renormalization group (DRG) using the hard thermal loop (HTL) approximation for the real-time nonequilibrium dynamics in hot plasmas. The focus is on the study of the relaxation of gauge and fermionic mean fields and on the quantum kinetics of the photon and fermion distribution functions. As a concrete physical prediction, we find that for a QGP of temperature T~200 MeV and lifetime 10<=t<= 50 fm/c there is a new contribution to the hard (k~T) photon production form off-shell bremsstrahlung (q-->q? and $\\bar{q}\\to \\bar{q}\\gamma$) at just O(?) that grows logarithmically in time and is comparable to the known on-shell Compton scattering and pair annihilation at O(??s).

de Vega, H. J.

95

Quantum dynamics study of fulvene double bond photoisomerization: the role of intramolecular vibrational energy redistribution and excitation energy.  

PubMed

The double bond photoisomerization of fulvene has been studied with quantum dynamics calculations using the multi-configuration time-dependent Hartree method. Fulvene is a test case to develop optical control strategies based on the knowledge of the excited state decay mechanism. The decay takes place on a time scale of several hundred femtoseconds, and the potential energy surface is centered around a conical intersection seam between the ground and excited state. The competition between unreactive decay and photoisomerization depends on the region of the seam accessed during the decay. The dynamics are carried out on a four-dimensional model surface, parametrized from complete active space self-consistent field calculations, that captures the main features of the seam (energy and locus of the seam and associated branching space vectors). Wave packet propagations initiated by single laser pulses of 5-25 fs duration and 1.85-4 eV excitation energy show the principal characteristics of the first 150 fs of the photodynamics. Initially, the excitation energy is transferred to a bond stretching mode that leads the wave packet to the seam, inducing the regeneration of the reactant. The photoisomerization starts after the vibrational energy has flowed from the bond stretching to the torsional mode. In our propagations, intramolecular energy redistribution (IVR) is accelerated for higher excess energies along the bond stretch mode. Thus, the competition between unreactive decay and isomerization depends on the rate of IVR between the bond stretch and torsion coordinates, which in turn depends on the excitation energy. These results set the ground for the development of future optical control strategies. PMID:21992301

Blancafort, Lluís; Gatti, Fabien; Meyer, Hans-Dieter

2011-10-01

96

On the adequacy of the Redfield equation and related approaches to the study of quantum dynamics in electronic energy transfer  

NASA Astrophysics Data System (ADS)

The observation of long-lived electronic coherence in photosynthetic excitation energy transfer (EET) by Engel et al. [Nature (London) 446, 782 (2007)] raises questions about the role of the protein environment in protecting this coherence and the significance of the quantum coherence in light harvesting efficiency. In this paper we explore the applicability of the Redfield equation in its full form, in the secular approximation and with neglect of the imaginary part of the relaxation terms for the study of these phenomena. We find that none of the methods can give a reliable picture of the role of the environment in photosynthetic EET. In particular the popular secular approximation (or the corresponding Lindblad equation) produces anomalous behavior in the incoherent transfer region leading to overestimation of the contribution of environment-assisted transfer. The full Redfield expression on the other hand produces environment-independent dynamics in the large reorganization energy region. A companion paper presents an improved approach, which corrects these deficiencies [A. Ishizaki and G. R. Fleming, J. Chem. Phys. 130, 234111 (2009)].

Ishizaki, Akihito; Fleming, Graham R.

2009-06-01

97

Speciation of the curium(III) ion in aqueous solution: a combined study by quantum chemistry and molecular dynamics simulation.  

PubMed

The structures of aquo complexes of the curium(III) ion have been systematically studied using quantum chemical and molecular dynamics (MD) methods. The first hydration shell of the Cm3+ ion has been calculated using density functional theory (DFT), with and without inclusion of the conductor-like polarizable continuum medium (CPCM) model of solvation. The calculated results indicate that the primary hydration number of Cm3+ is nine, with a Cm-O bond distance of 2.47-2.48 A. The calculated bond distances and the hydration number are in excellent agreement with available experimental data. The inclusion of a complete second hydration shell of Cm3+ has been investigated using both DFT and MD methods. The presence of the second hydration shell has significant effects on the primary coordination sphere, suggesting that the explicit inclusion of second-shell effects is important for understanding the nature of the first shell. The calculated results indicate that 21 water molecules can be coordinated in the second hydration shell of the Cm3+ ion. MD simulations within the hydrated-ion model suggest that the second-shell water molecules exchange with the bulk solvent with a lifetime of 161 ps. PMID:16813391

Yang, Tianxiao; Bursten, Bruce E

2006-07-10

98

Quantum dynamics study of the F + CH4 ? HF + CH3 reaction on an ab initio potential energy surface.  

PubMed

A quantum reactive dynamics, four degree-of-freedom, time-dependent wavepacket method is applied to study the F + CH4 ? HF + CH3 reaction using a slightly modified version of the ab initio potential energy surface of Czakó et al. [ J. Chem. Phys. 2009 , 130 , 084301 ]. A common resonance peak is found on all initial state-selected reaction probabilities close to the reaction threshold. The resonance also survives the averaging of partial waves and shows up in the integral cross section just after the threshold energy, in agreement with experiment. This early- barrier polyatomic reaction is more enhanced by the translational motion than the vibrational motion for energies below 0.38 eV; however, the reverse is true for energies higher than 0.38 eV. The vibrational excitation of the CH stretching mode enhances the reactivity, whereas the excitation of the umbrella mode of CH4 hinders the reactivity. The calculated thermal rate constants are in good agreement with one direct experimental measurement. PMID:23617790

Wang, Dunyou; Czakó, Gábor

2013-05-08

99

Universal non-equilibrium quantum dynamics in imaginary time  

NASA Astrophysics Data System (ADS)

We propose a method to study the dynamical response of a quantum systems by evolving it with an imaginary-time dependent Hamiltonian. The leading non-adiabatic response of the system driven to a quantum-critical point is universal and characterized by the same exponents in real and imaginary time. For a linear quench protocol, the fidelity susceptibility and the geometric tensor naturally emerge in the response functions. Beyond linear response we extend the finite-size scaling theory of quantum phase transitions to non-equilibrium setups. Imaginary-time dynamics is also amenable to quantum Monte Carlo simulations, which we apply here to quenches of the transverse-field Ising model to quantum critical points in one and two dimensions.

de Grandi, Claudia; Polkovnikov, Anatoli; Sandvik, Anders

2012-02-01

100

EDITORIAL: Quantum control theory for coherence and information dynamics Quantum control theory for coherence and information dynamics  

Microsoft Academic Search

Precisely characterizing and controlling the dynamics of realistic open quantum systems has emerged in recent years as a key challenge across contemporary quantum sciences and technologies, with implications ranging from physics, chemistry and applied mathematics to quantum information processing (QIP) and quantum engineering. Quantum control theory aims to provide both a general dynamical-system framework and a constructive toolbox to meet

Lorenza Viola; David Tannor

2011-01-01

101

Pattern dynamics and spatiotemporal chaos in the quantum Zakharov equations  

SciTech Connect

The dynamical behavior of the nonlinear interaction of quantum Langmuir waves (QLWs) and quantum ion-acoustic waves (QIAWs) is studied in the one-dimensional quantum Zakharov equations. Numerical simulations of coupled QLWs and QIAWs reveal that many coherent solitary patterns can be excited and saturated via the modulational instability of unstable harmonic modes excited by a modulation wave number of monoenergetic QLWs. The evolution of such solitary patterns may undergo the states of spatially partial coherence (SPC), coexistence of temporal chaos and spatiotemporal chaos (STC), as well as STC. The SPC state is essentially due to ion-acoustic wave emission and due to quantum diffraction, while the STC is caused by the combined effects of SPC and quantum diffraction, as well as by collisions and fusions among patterns in stochastic motion. The energy in the system is strongly redistributed, which may switch on the onset of weak turbulence in dense quantum plasmas.

Misra, A. P.; Shukla, P. K. [Department of Mathematics, Visva-Bharati University, Santiniketan 731 235 (India); Institut fuer Theoretische Physik IV and Centre for Plasma Science and Astrophysics, Fakultaet fuer Physik and Astronomie, Ruhr-Universitaet Bochum, D-44780 Bochum (Germany)

2009-05-15

102

Quantum charge transport and conformational dynamics of macromolecules.  

PubMed

We study the dynamics of quantum excitations inside macromolecules which can undergo conformational transitions. In the first part of the paper, we use the path integral formalism to rigorously derive a set of coupled equations of motion which simultaneously describe the molecular and quantum transport dynamics, and obey the fluctuation/dissipation relationship. We also introduce an algorithm which yields the most probable molecular and quantum transport pathways in rare, thermally activated reactions. In the second part of the paper, we apply this formalism to simulate the propagation of a quantum charge during the collapse of a polymer from an initial stretched conformation to a final globular state. We find that the charge dynamics is quenched when the chain reaches a molten globule state. Using random matrix theory we show that this transition is due to an increase of quantum localization driven by dynamical disorder. We argue that collapsing conducting polymers may represent a physical realization of quantum small-world networks with dynamical rewiring probability. PMID:22697534

Boninsegna, L; Faccioli, P

2012-06-01

103

Higher-order kinetic expansion of quantum dissipative dynamics: mapping quantum networks to kinetic networks.  

PubMed

We apply a new formalism to derive the higher-order quantum kinetic expansion (QKE) for studying dissipative dynamics in a general quantum network coupled with an arbitrary thermal bath. The dynamics of system population is described by a time-convoluted kinetic equation, where the time-nonlocal rate kernel is systematically expanded of the order of off-diagonal elements of the system Hamiltonian. In the second order, the rate kernel recovers the expression of the noninteracting-blip approximation method. The higher-order corrections in the rate kernel account for the effects of the multi-site quantum coherence and the bath relaxation. In a quantum harmonic bath, the rate kernels of different orders are analytically derived. As demonstrated by four examples, the higher-order QKE can reliably predict quantum dissipative dynamics, comparing well with the hierarchic equation approach. More importantly, the higher-order rate kernels can distinguish and quantify distinct nontrivial quantum coherent effects, such as long-range energy transfer from quantum tunneling and quantum interference arising from the phase accumulation of interactions. PMID:23901955

Wu, Jianlan; Cao, Jianshu

2013-07-28

104

Quantum dynamics in classical thermal baths  

NASA Astrophysics Data System (ADS)

A particular type of open quantum system dynamics is achieved by embedding a quantum system in a classical thermal bath. Such a bath can be represented in terms of the non-Hamiltonian evolution of few variables by means of the so-called Nosè-Hoover Power thermostat. The classical dynamics of the thermostat is integrated by means of time-reversible measure-preserving algorithms. In this work we show that the Nosè-Hoover Power thermostat, when applied to the dissipative evolution of a quantum spin, provides numerical results which agree with those obtained using Nosè-Hoover chains. However, since a fewer number of variables are needed to achieve the correct sampling of the canonical distribution at equilibrium, the Nosè-Hoover Power thermostat promises to be better suited for the simulation of low dimensional open quantum system on discrete grids.

Dlamini, Nkosinathi; Sergi, Alessandro

2013-11-01

105

Quantum fluctuations in beam dynamics.  

SciTech Connect

Quantum effects could become important for particle and photon beams used in high-luminosity and high brightness applications in the current and next generation accelerators and radiation sources. This paper is a review of some of these effects.

Kim, K.-J.

1998-06-04

106

Fractal dynamics in chaotic quantum transport  

NASA Astrophysics Data System (ADS)

Despite several experiments on chaotic quantum transport, corresponding ab initio quantum simulations have been out of reach so far. Here we carry out quantum transport calculations in real space and real time for a two-dimensional stadium cavity that shows chaotic dynamics. Applying a large set of magnetic fields yields a complete picture of the magnetoconductance that indicates fractal scaling on intermediate time scales. Two methods that originate from different fields of physics are used to analyze the scaling exponent and the fractal dimension. They lead to consistent results that, in turn, qualitatively agree with the previous experimental data.

Rasanen, Esa; Kotimaki, Ville; Hennig, Holger; Heller, Eric

2013-03-01

107

Quantum thermal transport from classical molecular dynamics.  

PubMed

Using a generalized Langevin equation of motion, quantum thermal transport is obtained from classical molecular dynamics. This is possible because the heat baths are represented by random noises obeying quantum Bose-Einstein statistics. The numerical method gives asymptotically exact results in both the low-temperature ballistic transport regime and the high-temperature strongly nonlinear classical regime. The method is a quasiclassical approximation to the quantum transport problem. A one-dimensional quartic on-site model is used to demonstrate the crossover from ballistic to diffusive thermal transport. PMID:17995230

Wang, Jian-Sheng

2007-10-15

108

Quantum theory of dynamic nuclear polarization in quantum dots  

NASA Astrophysics Data System (ADS)

Nuclear spins play a major role in the dynamics of spin qubits in III-V semiconductor quantum dots. Although the hyperfine interaction between nuclear and electron (or hole) spins is typically viewed as the leading source of decoherence in these qubits, understanding how to experimentally control the nuclear spin polarization can not only ameliorate this problem, but in fact turn the nuclear spins into a valuable resource for quantum computing. Beyond extending decoherence times, control of this polarization can enable universal quantum computation as shown in singlet-triplet qubits and, in addition, offers the possibility of repurposing the nuclear spins into a robust quantum memory. In [1], we took a first step toward taking advantage of this resource by developing a general, fully quantum theory of non-unitary electron-nuclear spin dynamics with a periodic train of delta-function pulses as the external control driving the electron spin. Here, we extend this approach to other types of controls and further expand on the predictions and physical insights that emerge from the theory. [1] Edwin Barnes and Sophia E. Economou, Phys. Rev. Lett. 107, 047601 (2011)

Economou, Sophia; Barnes, Edwin

2013-03-01

109

Quantum Simulation for Open-System Dynamics  

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

110

Dynamics of the Anderson model for dilute magnetic alloys: A quantum Monte Carlo and maximum entropy study  

SciTech Connect

In this article we describe the results of a new method for calculating the dynamical properties of the Anderson model. QMC generates data about the Matsubara Green's functions in imaginary time. To obtain dynamical properties, one must analytically continue these data to real time. This is an extremely ill-posed inverse problem similar to the inversion of a Laplace transform from incomplete and noisy data. Our method is a general one, applicable to the calculation of dynamical properties from a wide variety of quantum simulations. We use Bayesian methods of statistical inference to determine the dynamical properties based on both the QMC data and any prior information we may have such as sum rules, symmetry, high frequency limits, etc. This provides a natural means of combining perturbation theory and numerical simulations in order to understand dynamical many-body problems. Specifically we use the well-established maximum entropy (ME) method for image reconstruction. We obtain the spectral density and transport coefficients over the entire range of model parameters accessible by QMC, with data having much larger statistical error than required by other proposed analytic continuation methods.

Silver, R.N.; Gubernatis, J.E.; Sivia, D.S. (Los Alamos National Lab., NM (USA)); Jarrell, M. (Ohio State Univ., Columbus, OH (USA). Dept. of Physics)

1990-01-01

111

Quantum kinetics of dynamical decoupling  

NASA Astrophysics Data System (ADS)

In an ideal world, coherent control could be made perfect by running infinitely fast sequences of infinitely short pulses. In practice, in each system there are obvious spectral limitations. There is also a large-time limit set by decoherence due to environment coupling. Altogether, this makes pulse shape and sequence design an extremely complicated optimization problem. A systematic way to approach this problem is to consider a cumulant expansion of the evolution operator, treating the strong control fields exactly. The cumulants give the expansion of the effective Hamiltonian in powers of the system Hamiltonian. The locality of the cumulant expansion ensures that the classification by sequence order remains meaningful even for large systems. The corresponding calculation can be done efficiently by constructing a time-dependent perturbation theory expansion on small clusters [1]. Intuitively, refocusing should also remain effective in the presence of low-frequency environment, as long as the parameters of the system Hamiltonian are varying slowly compared to the refocusing period ?. A systematic study of this effect will be presented, based on the Floquet analysis of the non-Markovian quantum kinetic (master) equation for the open multi-qubit system in the presence of continuous refocusing fields exact up to 2nd order in the cumulant expansion [2]. [1] P. Sengupta and L. P. Pryadko, Phys. Rev. Lett. 95, 037202 (2005). [2] L. P. Pryadko and P. Sengupta, quant-ph/0510001 (2005).

Pryadko, Leonid P.; Sengupta, Pinaki

2006-03-01

112

Real time quantum dynamics in the Heisenberg picture  

SciTech Connect

In order to understand dynamics in the Heisenberg picture, a study is made of ordinary single particle quantum mechanics where the methods used can be compared with solving the Schroedinger equation numerically. The methods are generalized to field theory. Both analytic and numerical strategies are developed for solving the Heisenberg equations on a time lattice. The time development of an initial gaussian wave function is considered in various potentials in order to study both quantum tunnelling phenomena and the quantum roll. 9 refs., 1 fig. (LEW)

Cooper, F.

1986-01-01

113

Geometric origin of dynamically induced freezing of quantum evolution  

SciTech Connect

The phenomenon of dynamical, field-induced freezing of quantum evolution is discussed. It occurs when a time-dependent state is dynamically driven in such a way that the evolution of the corresponding wave function is effectively localized within a small region in the projective Hilbert space. As a consequence, the dynamics of the system is frozen and the expectation values of all physical observables hardly change with time. Necessary and sufficient conditions for inducing dynamical freezing are inferred from a general analysis of the geometry of quantum evolution. The relevance of the dynamical freezing for a sustainable in time, dynamical control is discussed and exemplified by a study of the coherent control of the kicked rotor motion.

Matos-Abiague, A.; Berakdar, J. [Max-Planck Institut fuer Mikrostrukturphysik, Weinberg 2, 06120 Halle (Germany)

2006-02-15

114

Relativistic versus nonrelativistic quantum molecular dynamics  

NASA Astrophysics Data System (ADS)

One of the most successful models to describe heavy ion reactions on the microscopic level is the Quantum Molecular Dynamics (QMD). At relativistic energies a covariant generalization of this model, the Relativistic Quantum Molecular Dynamics (RQMD), is available. We compare results concerning the time evolution of the phase space and particle production obtained by both methods at the intermediate energy range looking for relativistic effects in heavy ion collisions at these energies. now at I.N.F.N., Via Docecaneso 33, 16146 Genova, Italy

Lehmann, E.; Puri, R. K.; Faessler, A.; Maruyama, T.; Li, G. Q.; Ohtsuka, N.; Huang, S. W.; Khoa, D. T.; Matin, M. A.

115

Communications: Evaluation of the nondiabaticity of quantum molecular dynamics with the dephasing representation of quantum fidelity  

NASA Astrophysics Data System (ADS)

We propose an approximate method for evaluating the importance of non-Born-Oppenheimer effects on the quantum dynamics of nuclei. The method uses a generalization of the dephasing representation (DR) of quantum fidelity to several diabatic potential energy surfaces and its computational cost is the cost of dynamics of a classical phase space distribution. It can be implemented easily into any molecular dynamics program and also can utilize on-the-fly ab initio electronic structure information. We test the methodology on three model problems introduced by Tully and on the photodissociation of NaI. The results show that for dynamics close to the diabatic limit, the decay of fidelity due to nondiabatic effects is described accurately by the DR. In this regime, unlike the mixed quantum-classical methods such as surface hopping or Ehrenfest dynamics, the DR can capture more subtle quantum effects than the population transfer between potential energy surfaces. Hence we propose using the DR to estimate the dynamical importance of diabatic, spin-orbit, or other couplings between potential energy surfaces. The acquired information can help reduce the complexity of a studied system without affecting the accuracy of the quantum simulation.

Zimmermann, Tomáš; Vaní?ek, Ji?í

2010-06-01

116

Combining dynamical decoupling with fault-tolerant quantum computation  

SciTech Connect

We study how dynamical decoupling (DD) pulse sequences can improve the reliability of quantum computers. We prove upper bounds on the accuracy of DD-protected quantum gates and derive sufficient conditions for DD-protected gates to outperform unprotected gates. Under suitable conditions, fault-tolerant quantum circuits constructed from DD-protected gates can tolerate stronger noise and have a lower overhead cost than fault-tolerant circuits constructed from unprotected gates. Our accuracy estimates depend on the dynamics of the bath that couples to the quantum computer and can be expressed either in terms of the operator norm of the bath's Hamiltonian or in terms of the power spectrum of bath correlations; we explain in particular how the performance of recursively generated concatenated pulse sequences can be analyzed from either viewpoint. Our results apply to Hamiltonian noise models with limited spatial correlations.

Ng, Hui Khoon; Preskill, John [Institute for Quantum Information, California Institute of Technology, Pasadena, California 91125 (United States); Lidar, Daniel A. [Departments of Electrical Engineering, Chemistry, and Physics, and Center for Quantum Information Science and Technology, University of Southern California, Los Angeles, California 90089 (United States)

2011-07-15

117

Langevin Formulation of Quantum Dynamics.  

National Technical Information Service (NTIS)

We first show that nonrelativistic quantum mechanics formulated at imaginary-(h/2 (pi)) can formally be viewed as the Fokker-Planck description of a frictionless brownian motion, which occurs (in general) in an absorbing medium. We next offer a new formul...

M. Roncadelli

1989-01-01

118

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 studyquantum 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

119

Quantum memory assisted probing of dynamical spin correlations.  

PubMed

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

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

2012-02-10

120

Dynamics of a pulsed continuous-variable quantum memory  

NASA Astrophysics Data System (ADS)

We study the transfer dynamics of nonclassical fluctuations of light to the ground-state collective spin components of an atomic ensemble during a pulsed quantum memory sequence, and evaluate the relevant physical quantities to be measured in order to characterize such a quantum memory. We show in particular that the fluctuations stored into the atoms are emitted in temporal modes which are always different from those of the readout pulse, but which can nevertheless be retrieved efficiently using a suitable temporal mode-matching technique. We give a simple toy model—a cavity with variable transmission—that accounts for the behavior of the atomic quantum memory.

Dantan, A.; Cviklinski, J.; Pinard, M.; Grangier, Ph.

2006-03-01

121

Quantum number projection at finite temperature via thermofield dynamics  

NASA Astrophysics Data System (ADS)

Applying thermofield dynamics, we reformulate the exact quantum number projection in the finite-temperature Hartree-Fock-Bogoliubov theory. Explicit formulas are derived for the simultaneous projection of particle number and angular momentum, in parallel to the zero-temperature case. We also propose a practical method for the variation-after-projection calculation, by approximating entropy consistently with the Peierls inequality. Using quantum number projection in finite-temperature mean-field theory will be useful for studying the effects of quantum fluctuations associated with the conservation laws on thermal properties of nuclei.

Tanabe, K.; Nakada, H.

2005-02-01

122

Fractal dynamics in chaotic quantum transport  

NASA Astrophysics Data System (ADS)

Despite several experiments on chaotic quantum transport in two-dimensional systems such as semiconductor quantum dots, corresponding quantum simulations within a real-space model have been out of reach so far. Here we carry out quantum transport calculations in real space and real time for a two-dimensional stadium cavity that shows chaotic dynamics. By applying a large set of magnetic fields we obtain a complete picture of magnetoconductance that indicates fractal scaling. In the calculations of the fractality we use detrended fluctuation analysis—a widely used method in time-series analysis—and show its usefulness in the interpretation of the conductance curves. Comparison with a standard method to extract the fractal dimension leads to consistent results that in turn qualitatively agree with the previous experimental data.

Kotimäki, V.; Räsänen, E.; Hennig, H.; Heller, E. J.

2013-08-01

123

Dynamics of a complex quantum magnet.  

SciTech Connect

We have computed the low energy quantum states and low frequency dynamical susceptibility of complex quantum spin systems in the limit of strong interactions, obtaining exact results for system sizes enormously larger than accessible previously. The ground state is a complex superposition of a substantial fraction of all the classical ground states, and yet the dynamical susceptibility exhibits sharp resonances reminiscent of the behavior of single spins. These results show that strongly interacting quantum systems can organize to generate coherent excitations and shed light on recent experiments demonstrating that coherent excitations are present in a disordered spin liquid. The dependence of the energy spectra on system size differs qualitatively from that of the energy spectra of random undirected bipartite graphs with similar statistics, implying that strong interactions are giving rise to these unusual spectral properties.

Landry, James W.; Coppersmith, S. N. (University of Wisconsin, Madison, WI)

2003-01-01

124

Quantum signatures in the stabilization dynamics  

NASA Astrophysics Data System (ADS)

We investigate the phase-space dynamics of a hydrogenic atom in a very intense, high-frequency laser field, by comparing the time-dependent quantum Wigner functions with the corresponding classical distributions calculated using the Monte Carlo method. In both cases we model the atom by a one-dimensional soft-core potential in order to simplify the calculation. We demonstrate the importance of nonclassical interferences in the Wigner function and show how negative parts of it observed at the peak of the pulse are associated with the formation of a coherent superposition of dressed ``Kramers-Henneberger'' (KH) eigenstates. These signatures of the quantum dynamics are eliminated towards the end of the pulse when the coherence between the KH eigenstates degrades so that the classical and the quantum mechanical phase-space distributions come into agreement.

Watson, J. B.; Keitel, C. H.; Knight, P. L.; Burnett, K.

1995-11-01

125

Quantum Dynamical R Matrices and QuantumFrobenius Group  

Microsoft Academic Search

:  We propose an algebraic scheme for quantizing the rational Ruijsenaars-Schneider model in the R-matrix formalism. We introduce a special parametrization of the cotangent bundle over . In new variables the standard symplectic structure is described by a classical (Frobenius) r-matrix and by a new dynamical -matrix. Quantizing both of them we find the quantum L-operator algebra and construct its particular

G. E. Arutyunov; S. A. Frolov

1998-01-01

126

Quantum Metrology: Dynamics versus Entanglement  

Microsoft Academic Search

A parameter whose coupling to a quantum probe of n constituents includes all two-body interactions between the constituents can be measured with an uncertainty that scales as 1\\/n3\\/2, even when the constituents are initially unentangled. We devise a protocol that achieves the 1\\/n3\\/2 scaling without generating any entanglement among the constituents, and we suggest that the protocol might be implemented

Sergio Boixo; Animesh Datta; Matthew J. Davis; Steven T. Flammia; Anil Shaji; Carlton M. Caves

2008-01-01

127

Theoretical study of quantum molecular reaction dynamics and of the effects of intense laser radiation on a diatomic molecule  

SciTech Connect

Within the very broad field of molecular dynamics, we have concentrated on two simple yet important systems. The systems are simple enough so that they are adequately described with a single Born-Oppenheimer potential energy surface and that the dynamics can be calculated accurately. They are important because they give insight into solving more complicated systems. First we discuss H + H/sub 2/ reactive scattering. We present an exact formalism for atom-diatom reactive scattering which avoids the problem of finding a coordinate system appropriate for both reactants and products. We present computational results for collinear H + H/sub 2/ reactive scattering which agree very well with previous calculations. We also present a coupled channel distorted wave Born approximation for atom-diatom reactive scattering which we show is a first order approximation to our exact formalism. We present coupled channel DWBA results for three dimensional H + H/sub 2/ reactive scattering. The second system is an isolated HF molecule in an intense laser field. Using classical trajectories and quantum dynamics, we look at energy absorbed and transition probabilities as a function of the laser pulse time and also averaged over the pulse time. Calculations are performed for both rotating and nonrotating HF. We examine one and two photon absorption about the fundamental frequency, multiphoton absorption, and overtone absorption. 127 references, 31 figures, 12 tables.

Dardi, P.S.

1984-11-01

128

Quantum-Chemical and Molecular Dynamics Study of M(+)[TOTO](-) (M = Li, Na, K) Ionic Liquids.  

PubMed

Quantum-chemical calculations and classical molecular dynamics simulations with the Optimized Potentials for Liquid Simulations-All Atom (OPLS-AA) force field are presented for ionic liquids based on 2,5,8,11-tetraoxatridecan-13-oate anion (TOTO) and alkali cations (Li, Na, K). Complexation energies decrease with increasing cation radius from Li to K. Cation interactions with carboxylate oxygen atoms are preferred over complexation to ether oxygens. Cross-linking occurs in the structure of the liquid because of interactions of multiple metal ions with carboxylate oxygen atoms from multiple TOTO anions. Anticorrelated motion of ions of the same charge is an important factor decreasing conductivity of the liquid. Results of modeling agree with available experimental data for Na-TOTO. PMID:24066658

Eilmes, Andrzej; Kubisiak, Piotr

2013-10-07

129

Path integral molecular dynamic study of nuclear quantum effect on small chloride water clusters of Cl?(H2O)1–4  

NASA Astrophysics Data System (ADS)

The nuclear quantum effect, which plays important roles on ionic hydrogen bonded structures of Cl?(H2O)n (n = 1–4) clusters, was explored by carrying out path integral molecular dynamic simulations. An outer shell coordinate rl(Cl⋯O) is selected to display the rearrangement of single and multi hydration shell cluster structures. By incorporating the nuclear quantum effect, it is shown that the probability for single shell structures is decreased while the probability for multi shell structures is increased. On the other hand, the correlations between changing of bonded H? atom to Cl? (defined as ?) and other cluster vibration coordinates are studied. We have found that ? strongly correlates with proton transfer motion while it has little correlation with ion–water stretching motion. Contrary to ?(H–O–H?) coordinate, the correlations between ? and other coordinates are decreased by inclusion of nuclear quantum effect. The results indicate that the water–water hydrogen bond interactions are encouraged by quantum simulations.

Wang, Qi; Suzuki, Kimichi; Nagashima, Umpei; Tachikawa, Masanori; Yan, Shiwei

2013-06-01

130

Quantum dynamics and macroscopic quantum tunnelling of two weakly coupled condensates  

NASA Astrophysics Data System (ADS)

We study the quantum dynamics of a Bose–Josephson junction made up of two coupled Bose–Einstein condensates. We analyse different dynamical branches of Josephson oscillations within an ‘effective potential’ approach. At a critical coupling strength, a transition takes place between the dynamical branches of Josephson oscillations, which is also manifested in the energy spectrum, and pairs of (quasi)-degenerate excited states appear above the critical coupling strength. This phenomenon can be understood in terms of change in shape of the ‘effective potential’. Possible novel quantum phenomena like decay of metastable ‘?-oscillation’ by ‘macroscopic quantum tunnelling’ (MQT) and MQT between the ‘self-trapped’ states with equal and opposite number imbalance become evident from the simple picture of ‘effective potential’.

Kerkdyk, René John; Sinha, S.

2013-09-01

131

Role of controllability in optimizing quantum dynamics  

NASA Astrophysics Data System (ADS)

This paper reveals an important role that controllability plays in the complexity of optimizing quantum control dynamics. We show that the loss of controllability generally leads to multiple locally suboptimal controls when gate fidelity in a quantum control system is maximized, which does not happen if the system is controllable. Such local suboptimal controls may attract an optimization algorithm into a local trap when a global optimal solution is sought, even if the target gate can be perfectly realized. This conclusion results from an analysis of the critical topology of the corresponding quantum control landscape, which refers to the gate fidelity objective as a functional of the control fields. For uncontrollable systems, due to SU(2) and SU(3) dynamical symmetries, the control landscape corresponding to an implementable target gate is proven to possess multiple locally optimal critical points, and its ruggedness can be further increased if the target gate is not realizable. These results imply that the optimization of quantum dynamics can be seriously impeded when operating with local search algorithms under these conditions, and thus full controllability is demanded.

Wu, Re-Bing; Hsieh, Michael A.; Rabitz, Herschel

2011-06-01

132

Role of controllability in optimizing quantum dynamics  

SciTech Connect

This paper reveals an important role that controllability plays in the complexity of optimizing quantum control dynamics. We show that the loss of controllability generally leads to multiple locally suboptimal controls when gate fidelity in a quantum control system is maximized, which does not happen if the system is controllable. Such local suboptimal controls may attract an optimization algorithm into a local trap when a global optimal solution is sought, even if the target gate can be perfectly realized. This conclusion results from an analysis of the critical topology of the corresponding quantum control landscape, which refers to the gate fidelity objective as a functional of the control fields. For uncontrollable systems, due to SU(2) and SU(3) dynamical symmetries, the control landscape corresponding to an implementable target gate is proven to possess multiple locally optimal critical points, and its ruggedness can be further increased if the target gate is not realizable. These results imply that the optimization of quantum dynamics can be seriously impeded when operating with local search algorithms under these conditions, and thus full controllability is demanded.

Wu Rebing; Hsieh, Michael A.; Rabitz, Herschel [Department of Automation, Tsinghua University, Beijing, 100084, China and Center for Quantum Information Science and Technology, TNList, Beijing, 100084 (China); Department of Chemistry and Center for Quantum Information Science and Technology, University of Southern California, Los Angeles, California 90025 (United States); Department of Chemistry, Princeton University, Princeton, New Jersey 08544 (United States)

2011-06-15

133

Lévy flights and nonlocal quantum dynamics  

NASA Astrophysics Data System (ADS)

We develop a fully fledged theory of quantum dynamical patterns of behavior that are nonlocally induced. To this end we generalize the standard Laplacian-based framework of the Schrödinger picture quantum evolution to that employing nonlocal (pseudodifferential) operators. Special attention is paid to the Salpeter (here, m >= 0) quasirelativistic equation and the evolution of various wave packets, in particular to their radial expansion in 3D. Foldy's synthesis of ``covariant particle equations'' is extended to encompass free Maxwell theory, which however is devoid of any ``particle'' content. Links with the photon wave mechanics are explored.

Garbaczewski, Piotr; Stephanovich, Vladimir

2013-07-01

134

Dynamical renormalization group approach to relaxation in quantum field theory  

NASA Astrophysics Data System (ADS)

The real time evolution and relaxation of expectation values of quantum fields and of quantum states are computed as initial value problems by implementing the dynamical renormalization group (DRG). Linear response is invoked to set up the renormalized initial value problem to study the dynamics of the expectation value of quantum fields. The perturbative solution of the equations of motion for the field expectation values of quantum fields as well as the evolution of quantum states features secular terms, namely terms that grow in time and invalidate the perturbative expansion for late times. The DRG provides a consistent framework to resum these secular terms and yields a uniform asymptotic expansion at long times. Several relevant cases are studied in detail, including those of threshold infrared divergences which appear in gauge theories at finite temperature and lead to anomalous relaxation. In these cases the DRG is shown to provide a resummation akin to Bloch-Nordsieck but directly in real time and that goes beyond the scope of Bloch-Nordsieck and Dyson resummations. The nature of the resummation program is discussed in several examples. The DRG provides a framework that is consistent, systematic, and easy to implement to study the non-equilibrium relaxational dynamics directly in real time that does not rely on the concept of quasiparticle widths.

Boyanovsky, D.; de Vega, H. J.

2003-10-01

135

Dynamical localization of double quantum dots with two levels  

Microsoft Academic Search

We study the dynamics of a two-level double quantum dot system under the action of ac electric field, in which two electrons are confined. The results show that, although these electrons always transit between different energy levels, they can be localized in one dot with appropriate parameters. The localization can be significantly influenced by the external parameters, which provides an

Zhe Jiang; Duan Suqing; Xian-Geng Zhao

2005-01-01

136

Quantum Scaling Laws in the Onset of Dynamical Delocalization  

SciTech Connect

We study the destruction of dynamical localization experimentally observed in an atomic realization of the kicked rotor by a deterministic Hamiltonian perturbation, with a temporal periodicity incommensurate with the principal driving. We show that the destruction is gradual, with well-defined scaling laws for the various classical and quantum parameters, in sharp contrast to predictions based on the analogy with Anderson localization.

Chabe, Julien; Lignier, Hans; Cavalcante, Hugo; Szriftgiser, Pascal; Garreau, Jean Claude [Laboratoire de Physique des Lasers, Atomes et Molecules, Universite des Sciences et Technologies de Lille, Centre d'Etudes et Recherches Lasers et Applications, F-59655 Villeneuve d'Ascq Cedex (France); Delande, Dominique [Laboratoire Kastler-Brossel, Case 74, UPMC, 4 Place Jussieu, F-75252 Paris Cedex 05 (France)

2006-12-31

137

Perturbative quantum dynamics: variants of the Dirac method  

Microsoft Academic Search

A detailed comparative study of the structure and workability of various rearranged versions of the Dirac method of variation of constants for perturbative treatment of quantum dynamics is presented. The variants include a modified strategy proposed recently and also a new rearrangement of this form; both of these contain lambda dependent phase factors associated with the amplitudes which are determined

K. Bhattacharyya; D. Mukherjee

1986-01-01

138

Information geometry, dynamics and discrete quantum mechanics  

NASA Astrophysics Data System (ADS)

We consider a system with a discrete configuration space. We show that the geometrical structures associated with such a system provide the tools necessary for a reconstruction of discrete quantum mechanics once dynamics is brought into the picture. We do this in three steps. Our starting point is information geometry, the natural geometry of the space of probability distributions. Dynamics requires additional structure. To evolve the Pk, we introduce coordinates Sk canonically conjugate to the Pk and a symplectic structure. We then seek to extend the metric structure of information geometry, to define a geometry over the full space of the Pk and Sk. Consistency between the metric tensor and the symplectic form forces us to introduce a Kähler geometry. The construction has notable features. A complex structure is obtained in a natural way. The canonical coordinates of the ?k = PkeiSk Kähler space are precisely the wave functions of quantum mechanics. The full group of unitary transformations is obtained. Finally, one may associate a Hilbert space with the Kähler space, which leads to the standard version of quantum theory. We also show that the metric that we derive here using purely geometrical arguments is precisely the one that leads to Wootters' expression for the statistical distance for quantum systems.

Reginatto, Marcel; Hall, Michael J. W.

2013-08-01

139

Non-Abelian phases from quantum Zeno dynamics  

NASA Astrophysics Data System (ADS)

A connection is established between the non-Abelian phases obtained via adiabatic driving and those acquired via quantum Zeno dynamics induced by repeated projective measurements. In comparison to the adiabatic case, the Zeno dynamics is shown to be more flexible in tuning the system evolution, which paves the way for the implementation of unitary quantum gates and applications in quantum control.

Burgarth, Daniel; Facchi, Paolo; Giovannetti, Vittorio; Nakazato, Hiromichi; Pascazio, Saverio; Yuasa, Kazuya

2013-10-01

140

Dirac particle in a box, and relativistic quantum Zeno dynamics  

Microsoft Academic Search

After developing a complete set of eigenfunctions for a Dirac particle restricted to a box, the quantum Zeno dynamics of a relativistic system is considered. The evolution of a continuously observed quantum mechanical system is governed by the theorem put forth by Misra and Sudarshan. One of the conditions for quantum Zeno dynamics to be manifest is that the Hamiltonian

Govind Menon; Sergey Belyi

2004-01-01

141

Anti-de Sitter universe dynamics in loop quantum cosmology  

SciTech Connect

A model for a flat isotropic universe with a negative cosmological constant {lambda} and a massless scalar field as sole matter content is studied within the framework of loop quantum cosmology. By application of the methods introduced for the model with {lambda}=0, the physical Hilbert space and the set of Dirac observables are constructed. As in that case, the scalar field plays here the role of an emergent time. The properties of the system are found to be similar to those of the k=1 Friedmann-Robertson-Walker (FRW) model: for small energy densities, the quantum dynamics reproduces the classical one, whereas, due to modifications at near-Planckian densities, the big bang and big crunch singularities are replaced by a quantum bounce connecting deterministically the large semiclassical epochs. Thus in loop quantum cosmology the evolution is qualitatively cyclic.

Bentivegna, Eloisa [Institute for Gravitational Physics and Geometry, Physics Department, Penn State, University Park, PA 16802 (United States); Center for Gravitational Wave Physics, Physics Department, Penn State, University Park, PA 16802 (United States); Pawlowski, Tomasz [Instituto de Estructura de la Materia, Consejo Superior de Investigaciones Cientificas (CSIC), Serrano 121, 28006 Madrid (Spain); Institute for Gravitational Physics and Geometry, Physics Department, Penn State, University Park, PA 16802 (United States)

2008-06-15

142

Dynamic optical response of an excitonic quantum dot studied by solving the self-consistent Maxwell-Schrödinger equations nonperturbatively  

NASA Astrophysics Data System (ADS)

The optical excitation of a quantum dot in real-world working conditions is studied by self-consistent solution of the time-dependent Schrödinger equation coupled to the Maxwell equations by the finite-difference time domain method, resulting in a polarization modification which is the basis for the enhanced light-matter interaction in many nanoscale devices. The commonly used perturbational analysis approach is compared to the results and found to be an acceptable approximation even for intense femtosecond pulse excitations where using the perturbative approach is risky. This allows device designers and simulators to confidently use the simpler and faster perturbative results in their work.

Hellström, S.; Fu, Y.

2010-12-01

143

From Entropic Dynamics to Quantum Theory  

SciTech Connect

Non-relativistic quantum theory is derived from information codified into an appropriate statistical model. The basic assumption is that there is an irreducible uncertainty in the location of particles so that the configuration space is a statistical manifold. The dynamics then follows from a principle of inference, the method of Maximum Entropy. The concept of time is introduced as a convenient way to keep track of change. The resulting theory resembles both Nelson's stochastic mechanics and general relativity. The statistical manifold is a dynamical entity: its geometry determines the evolution of the probability distribution which, in its turn, reacts back and determines the evolution of the geometry. There is a new quantum version of the equivalence principle: 'osmotic' mass equals inertial mass. Mass and the phase of the wave function are explained as features of purely statistical origin.

Caticha, Ariel [Department of Physics, University at Albany-SUNY, Albany, NY 12222 (United States)

2009-12-08

144

Quantum-classical dynamics of wave fields  

NASA Astrophysics Data System (ADS)

An approach to the quantum-classical mechanics of phase space dependent operators, which has been proposed recently, is remodeled as a formalism for wave fields. Such wave fields obey a system of coupled nonlinear equations that can be written by means of a suitable non-Hamiltonian bracket. As an example, the theory is applied to the relaxation dynamics of the spin-boson model. In the adiabatic limit, a good agreement with calculations performed by the operator approach is obtained. Moreover, the theory proposed in this paper can take nonadiabatic effects into account without resorting to surface-hopping approximations. Hence, the results obtained follow qualitatively those of previous surface-hopping calculations and increase by a factor of (at least) 2, the time length over which nonadiabatic dynamics can be propagated with small statistical errors. Moreover, it is worth to note that the dynamics of quantum-classical wave fields proposed here is a straightforward non-Hamiltonian generalization of the formalism for nonlinear quantum mechanics that Weinberg introduced recently.

Sergi, Alessandro

2007-02-01

145

Dynamic electron tunneling through the quantum dot under conditions of Coulomb blockade  

SciTech Connect

The dynamics of electron tunneling through the quantum dot under the conditions of the Coulomb blockade is studied. The time-dependent Schroedinger equation is solved numerically, and the dynamics of the quantum multielectron wave packet in the system consisting of the quantum dot connected with two ohmic contacts is studied. The dependences of transparency on the average energy of the wave packet are constructed. The obtained dependences are compared with the solutions of the corresponding steady-state problem.

Kashin, S. M., E-mail: smkashin@gmail.com; Satanin, A. M., E-mail: sarkady@mail.ru [Nizhni Novgorod State University, Nizhni Novgorod Research Physicotechnical Institute (Russian Federation)

2010-11-15

146

Quantum Processes and Dynamic Networks in Physical and Biological Systems.  

NASA Astrophysics Data System (ADS)

Quantum theory since its earliest formulations in the Copenhagen Interpretation has been difficult to integrate with general relativity and with classical Newtonian physics. There has been traditionally a regard for quantum phenomena as being a limiting case for a natural order that is fundamentally classical except for microscopic extrema where quantum mechanics must be applied, more as a mathematical reconciliation rather than as a description and explanation. Macroscopic sciences including the study of biological neural networks, cellular energy transports and the broad field of non-linear and chaotic systems point to a quantum dimension extending across all scales of measurement and encompassing all of Nature as a fundamentally quantum universe. Theory and observation lead to a number of hypotheses all of which point to dynamic, evolving networks of fundamental or elementary processes as the underlying logico-physical structure (manifestation) in Nature and a strongly quantized dimension to macroscalar processes such as are found in biological, ecological and social systems. The fundamental thesis advanced and presented herein is that quantum phenomena may be the direct consequence of a universe built not from objects and substance but from interacting, interdependent processes collectively operating as sets and networks, giving rise to systems that on microcosmic or macroscopic scales function wholistically and organically, exhibiting non-locality and other non -classical phenomena. The argument is made that such effects as non-locality are not aberrations or departures from the norm but ordinary consequences of the process-network dynamics of Nature. Quantum processes are taken to be the fundamental action-events within Nature; rather than being the exception quantum theory is the rule. The argument is also presented that the study of quantum physics could benefit from the study of selective higher-scale complex systems, such as neural processes in the brain, by virtue of mathematical and computational models that may be transferred from the macroscopic domain to the microscopic. A consequence of this multi-faceted thesis is that there may be mature analytical tools and techniques that have heretofore not been adequately recognized for their value to quantum physics. These may include adaptations of neural networks, cellular automata, chaotic attractors, and parallel processing systems. Conceptual and practical architectures are presented for the development of software and hardware environments to employ massively parallel computing for the modeling of large populations of dynamic processes.

Dudziak, Martin Joseph

147

Dynamically triangulating Lorentzian quantum gravity  

NASA Astrophysics Data System (ADS)

Fruitful ideas on how to quantize gravity are few and far between. In this paper, we give a complete description of a recently introduced non-perturbative gravitational path integral whose continuum limit has already been investigated extensively in /d<4, with promising results. It is based on a simplicial regularization of Lorentzian spacetimes and, most importantly, possesses a well-defined, non-perturbative Wick rotation. We present a detailed analysis of the geometric and mathematical properties of the discretized model in /d=3,4. This includes a derivation of Lorentzian simplicial manifold constraints, the gravitational actions and their Wick rotation. We define a transfer matrix for the system and show that it leads to a well-defined self-adjoint Hamiltonian. In view of numerical simulations, we also suggest sets of Lorentzian Monte Carlo moves. We demonstrate that certain pathological phases found previously in Euclidean models of dynamical triangulations cannot be realized in the Lorentzian case.

Ambjørn, J.; Jurkiewicz, J.; Loll, R.

2001-09-01

148

Quantum effects in unimolecular reaction dynamics  

SciTech Connect

This work is primarily concerned with the development of models for the quantum dynamics of unimolecular isomerization and photodissociation reactions. We apply the rigorous quantum methodology of a Discrete Variable Representation (DVR) with Absorbing Boundary Conditions (ABC) to these models in an attempt to explain some very surprising results from a series of experiments on vibrationally excited ketene. Within the framework of these models, we are able to identify the experimental signatures of tunneling and dynamical resonances in the energy dependence of the rate of ketene isomerization. Additionally, we investigate the step-like features in the energy dependence of the rate of dissociation of triplet ketene to form {sup 3}B{sub 1} CH{sub 2} + {sup 1}{sigma}{sup +} CO that have been observed experimentally. These calculations provide a link between ab initio calculations of the potential energy surfaces and the experimentally observed dynamics on these surfaces. Additionally, we develop an approximate model for the partitioning of energy in the products of photodissociation reactions of large molecules with appreciable barriers to recombination. In simple bond cleavage reactions like CH{sub 3}COCl {yields} CH{sub 3}CO + Cl, the model does considerably better than other impulsive and statistical models in predicting the energy distribution in the products. We also investigate ways of correcting classical mechanics to include the important quantum mechanical aspects of zero-point energy. The method we investigate is found to introduce a number of undesirable dynamical artifacts including a reduction in the above-threshold rates for simple reactions, and a strong mixing of the chaotic and regular energy domains for some model problems. We conclude by discussing some of the directions for future research in the field of theoretical chemical dynamics.

Gezelter, J.D.

1995-12-01

149

Exact Quantum Dynamics of a Bosonic Josephson Junction  

SciTech Connect

The quantum dynamics of a one-dimensional bosonic Josephson junction is studied by solving the time-dependent many-boson Schroedinger equation numerically exactly. Already for weak interparticle interactions and on short time scales, the commonly employed mean-field and many-body methods are found to deviate substantially from the exact dynamics. The system exhibits rich many-body dynamics such as enhanced tunneling and a novel equilibration phenomenon of the junction depending on the interaction, which is attributed to a quick loss of coherence.

Sakmann, Kaspar; Streltsov, Alexej I.; Alon, Ofir E.; Cederbaum, Lorenz S. [Theoretische Chemie, Physikalisch-Chemisches Institut, Universitaet Heidelberg, Im Neuenheimer Feld 229, D-69120 Heidelberg (Germany)

2009-11-27

150

Quantum dynamical framework for Brownian heat engines.  

PubMed

We present a self-contained formalism modeled after the Brownian motion of a quantum harmonic oscillator for describing the performance of microscopic Brownian heat engines such as Carnot, Stirling, and Otto engines. Our theory, besides reproducing the standard thermodynamics results in the steady state, enables us to study the role dissipation plays in determining the efficiency of Brownian heat engines under actual laboratory conditions. In particular, we analyze in detail the dynamics associated with decoupling a system in equilibrium with one bath and recoupling it to another bath and obtain exact analytical results, which are shown to have significant ramifications on the efficiencies of engines involving such a step. We also develop a simple yet powerful technique for computing corrections to the steady state results arising from finite operation time and use it to arrive at the thermodynamic complementarity relations for various operating conditions and also to compute the efficiencies of the three engines cited above at maximum power. Some of the methods and exactly solvable models presented here are interesting in their own right and could find useful applications in other contexts as well. PMID:23944437

Agarwal, G S; Chaturvedi, S

2013-07-23

151

Oscillatory Dynamics and Non-Markovian Memory in Dissipative Quantum Systems  

NASA Astrophysics Data System (ADS)

The nonequilibrium dynamics of a small quantum system coupled to a dissipative environment is studied. We show that (i) the oscillatory dynamics close to a coherent-to-incoherent transition is significantly different from the one of the classical damped harmonic oscillator and that (ii) non-Markovian memory plays a prominent role in the time evolution after a quantum quench.

Kennes, D. M.; Kashuba, O.; Pletyukhov, M.; Schoeller, H.; Meden, V.

2013-03-01

152

The SU(2) Semi Quantum Systems Dynamics and Thermodynamics  

NASA Astrophysics Data System (ADS)

The dynamical description of a semi quantum nonlinear systems whose classical limit is not chaotic is still an open question. These systems are characterized by mixing a classical system with a quantum-mechanical one. As some of them lead to an irregular dynamics, the name "semi quantum chaos" arises. In this contribution we study two different Hamiltonians through the Maximum Entropy Principle Approach (MEP). Taking advantage of the MEP formalism, it can be clearly established that the Hamiltonians belonging to the SU(2) Lie algebra have common properties and a common treatment can be developed for them. These Hamiltonians resemble a quantum spin system coupled to a classical cavity. In the present contribution, we show that all of them share the generalized uncertainty principle as an invariant of the motion and other invariants as well. Two different classical potentials V(q) have been studied. Their specific heat are evaluated in terms of the extensive (mean values) and the intensive (Lagrange multipliers) variables. The main result of the present contribution is to show that the specific heat of these systems can be fixed independently of the temperature by setting only the initial conditions on the extensive or intensive variables, as well as the value of the quantum-classical coupling parameter. It could be possible to infer that this result can be extended to generalized forms for the V(q) classical potential.

Sarris, C. M.; Proto, A. N.

2011-03-01

153

The SU(2) Semi Quantum Systems Dynamics and Thermodynamics  

NASA Astrophysics Data System (ADS)

The dynamical description of a semi quantum nonlinear systems whose classical limit is not chaotic is still an open question. These systems are characterized by mixing a classical system with a quantum-mechanical one. As some of them lead to an irregular dynamics, the name "semi quantum chaos" arises. In this contribution we study two different Hamiltonians through the Maximum Entropy Principle Approach (MEP). Taking advantage of the MEP formalism, it can be clearly established that the Hamiltonians belonging to the SU(2) Lie algebra have common properties and a common treatment can be developed for them. These Hamiltonians resemble a quantum spin system coupled to a classical cavity. In the present contribution, we show that all of them share the generalized uncertainty principle as an invariant of the motion and other invariants as well. Two different classical potentials V(q) have been studied. Their specific heat are evaluated in terms of the extensive (mean values) and the intensive (Lagrange multipliers) variables. The main result of the present contribution is to show that the specific heat of these systems can be fixed independently of the temperature by setting only the initial conditions on the extensive or intensive variables, as well as the value of the quantum-classical coupling parameter. It could be possible to infer that this result can be extended to generalized forms for the V(q) classical potential.

Sarris, C. M.; Proto, A. N.

154

Nature computes: information processing in quantum dynamical systems.  

PubMed

Nature intrinsically computes. It has been suggested that the entire universe is a computer, in particular, a quantum computer. To corroborate this idea we require tools to quantify the information processing. Here we review a theoretical framework for quantifying information processing in a quantum dynamical system. So-called intrinsic quantum computation combines tools from dynamical systems theory, information theory, quantum mechanics, and computation theory. We will review how far the framework has been developed and what some of the main open questions are. On the basis of this framework we discuss upper and lower bounds for intrinsic information storage in a quantum dynamical system. PMID:20887080

Wiesner, Karoline

2010-09-01

155

23Na multiple quantum filtered NMR characterisation of Na+ binding and dynamics in animal cells: a comparative study and effect of Na+/Li + competition.  

PubMed

Double quantum and triple quantum filtered (23)Na nuclear magnetic resonance techniques were used to characterise in detail the isotropic and anisotropic binding and dynamics of intra- and extracellular Na(+) in different cellular systems, in the absence and presence of Li(+). The kinetics of Li(+) influx by different cell types was evaluated. At steady state, astrocytes accumulated more Li(+) than red blood cells (RBCs), while a higher intracellular Li(+) concentration was found in chromaffin than in SH-SY5Y cells. Anisotropic and isotropic motions were detected for extracellular Na(+) in all cellular systems studied. Isotropic intracellular Na(+) motions were observed in all types of cells, while anisotropic Na(+) motions in the intracellular compartment were only detected in RBCs. (23)Na triple quantum signal efficiency for intracellular Na(+) was SH-SY5Y > chromaffin > RBCs, while the reverse order was observed for the extracellular ions. (23)Na double quantum signal efficiency for intracellular Na(+) was non-zero only in RBCs, and for extracellular Na(+) the order RBCs > chromaffin > SH-SY5Y cells was observed. Li(+) loading generally decreased intracellular Na(+) isotropic movements in the cells, except for astrocytes incubated with a low Li(+) concentration and increased anisotropic intracellular Na(+) movements in RBCs. Li(+) effects on the extracellular signals were more complex, reflecting Li(+)/Na(+) competition for isotropic and anisotropic binding sites at the extracellular surface of cell membranes and also at the surface of the gel used for cell immobilisation. These results are relevant and contribute to the interpretation of the in vivo pharmacokinetics and sites of Li(+) action. PMID:23563802

Fonseca, Carla P; Fonseca, Luís L; Montezinho, Liliana P; Alves, Paula M; Santos, Helena; Castro, M Margarida C A; Geraldes, Carlos F G C

2013-04-06

156

Wigner dynamics of quantum semi-relativistic oscillator  

NASA Astrophysics Data System (ADS)

The integral Wigner-Liouville equation describing time evolution of the semi-relativistic quantum 1D harmonic oscillator have been exactly solved by combination of the Monte Carlo procedure and molecular dynamics methods. The strong influence of the relativistic effects on the time evolution of the momentum, velocity and coordinate Wigner distribution functions and the average values of quantum operators have been studied. Unexpected 'protuberances' in time evolution of the distribution functions were observed. Relativistic proper time dilation for oscillator have been calculated.

Larkin, A. S.; Filinov, V. S.

2013-07-01

157

Dynamical correlation functions and the quantum Rabi model  

NASA Astrophysics Data System (ADS)

We study the quantum Rabi model within the framework of the analytical solution developed in Phys. Rev. Lett.0031-900710.1103/PhysRevLett.107.100401 107, 100401 (2011). In particular, through time-dependent correlation functions, we give a quantitative criterion for classifying two regions of the quantum Rabi model, involving the Jaynes-Cummings, the ultrastrong-coupling, and the deep strong-coupling regimes. In addition, we find a stationary qubit-field entangled basis that governs the whole dynamics as the coupling strength overcomes the mode frequency.

Wolf, F. A.; Vallone, F.; Romero, G.; Kollar, M.; Solano, E.; Braak, D.

2013-02-01

158

Automated synthesis of dynamically corrected quantum gates  

NASA Astrophysics Data System (ADS)

Dynamically corrected gates are extended to non-Markovian open quantum systems where limitations on the available controls and/or the presence of control noise make existing analytical approaches unfeasible. A computational framework for the synthesis of dynamically corrected gates is formalized that allows sensitivity against non-Markovian decoherence and control errors to be perturbatively minimized via numerical search, resulting in robust gate implementations. Explicit sequences for achieving universal high-fidelity control in a singlet-triplet spin qubit subject to realistic system and control constraint are provided, which simultaneously cancel to the leading order the dephasing due to non-Markovian nuclear-bath dynamics and voltage noise affecting the control fields. Substantially improved gate fidelities are predicted for current laboratory devices.

Khodjasteh, Kaveh; Bluhm, Hendrik; Viola, Lorenza

2012-10-01

159

Signatures of discrete breathers in coherent state quantum dynamics.  

PubMed

In classical mechanics, discrete breathers (DBs) - a spatial time-periodic localization of energy - are predicted in a large variety of nonlinear systems. Motivated by a conceptual bridging of the DB phenomena in classical and quantum mechanical representations, we study their signatures in the dynamics of a quantum equivalent of a classical mechanical point in phase space - a coherent state. In contrast to the classical point that exhibits either delocalized or localized motion, the coherent state shows signatures of both localized and delocalized behavior. The transition from normal to local modes have different characteristics in quantum and classical perspectives. Here, we get an insight into the connection between classical and quantum perspectives by analyzing the decomposition of the coherent state into system's eigenstates, and analyzing the spacial distribution of the wave-function density within these eigenstates. We find that the delocalized and localized eigenvalue components of the coherent state are separated by a mixed region, where both kinds of behavior can be observed. Further analysis leads to the following observations. Considered as a function of coupling, energy eigenstates go through avoided crossings between tunneling and non-tunneling modes. The dominance of tunneling modes in the high nonlinearity region is compromised by the appearance of new types of modes - high order tunneling modes - that are similar to the tunneling modes but have attributes of non-tunneling modes. Certain types of excitations preferentially excite higher order tunneling modes, allowing one to study their properties. Since auto-correlation functions decrease quickly in highly nonlinear systems, short-time dynamics are sufficient for modeling quantum DBs. This work provides a foundation for implementing modern semi-classical methods to model quantum DBs, bridging classical and quantum mechanical signatures of DBs, and understanding spectroscopic experiments that involve a coherent state. PMID:23406095

Igumenshchev, Kirill; Ovchinnikov, Misha; Maniadis, Panagiotis; Prezhdo, Oleg

2013-02-01

160

Quantum corrections to inflaton and curvaton dynamics  

NASA Astrophysics Data System (ADS)

We compute the fully renormalized one-loop effective action for two interacting and self-interacting scalar fields in FRW space-time. We then derive and solve the quantum corrected equations of motion both for fields that dominate the energy density (such as an inflaton) and fields that do not (such as a subdominant curvaton). In particular, we introduce quantum corrected Friedmann equations that determine the evolution of the scale factor. We find that in general, gravitational corrections are negligible for the field dynamics. For the curvaton-type fields this leaves only the effect of the flat-space Coleman-Weinberg-type effective potential, and we find that these can be significant. For the inflaton case, both the corrections to the potential and the Friedmann equations can lead to behaviour very different from the classical evolution. Even to the point that inflation, although present at tree level, can be absent at one-loop order.

Markkanen, Tommi; Tranberg, Anders

2012-11-01

161

Optical Nonlinearities and Ultrafast Carrier Dynamics in Semiconductor Quantum Dots  

SciTech Connect

Low-dimensional semiconductors have attracted great interest due to the potential for tailoring their linear and nonlinear optical properties over a wide-range. Semiconductor nanocrystals (NC's) represent a class of quasi-zero-dimensional objects or quantum dots. Due to quantum cordhement and a large surface-to-volume ratio, the linear and nonlinear optical properties, and the carrier dynamics in NC's are significantly different horn those in bulk materials. napping at surface states can lead to a fast depopulation of quantized states, accompanied by charge separation and generation of local fields which significantly modifies the nonlinear optical response in NC's. 3D carrier confinement also has a drastic effect on the energy relaxation dynamics. In strongly confined NC's, the energy-level spacing can greatly exceed typical phonon energies. This has been expected to significantly inhibit phonon-related mechanisms for energy losses, an effect referred to as a phonon bottleneck. It has been suggested recently that the phonon bottleneck in 3D-confined systems can be removed due to enhanced role of Auger-type interactions. In this paper we report femtosecond (fs) studies of ultrafast optical nonlinearities, and energy relaxation and trap ping dynamics in three types of quantum-dot systems: semiconductor NC/glass composites made by high temperature precipitation, ion-implanted NC's, and colloidal NC'S. Comparison of ultrafast data for different samples allows us to separate effects being intrinsic to quantum dots from those related to lattice imperfections and interface properties.

Klimov, V.; McBranch, D.; Schwarz, C.

1998-08-10

162

Quantum tunneling and chaotic dynamics  

Microsoft Academic Search

We investigate the effect of the structure of a mixed (regular and chaotic) phase-space on the process of tunneling. This is done by studying the way in which classical transport in phase-space affects the energy splitting of quasidoublets of the spectrum of the laplacian on an annular domain bounded by two non-concentric circles. The tunneling is increased as the transport

O. Bohigas; D. Boosé; R. Egydio de Carvalho; V. Marvulle

1993-01-01

163

Structural and dynamical properties and vibrational spectra of bisulfate ion in water: a study by Ab initio quantum mechanical charge field molecular dynamics.  

PubMed

The ab initio quantum mechanical charge field molecular dynamics (QMCF MD) formalism was applied to simulate the bisulfate ion, HSO4-, in aqueous solution. The averaged geometry of bisulfate ion supports the separation of six normal modes of the O*-SO3 unit with C3v symmetry from three modes of the OH group in the evaluation of vibrational spectra obtained from the velocity autocorrelation functions (VACFs) with subsequent normal coordinate analyses. The calculated frequencies are in good agreement with the observations in Raman and IR experiments. The difference of the averaged coordination number obtained for the whole molecule (8.0) and the summation over coordinating sites (10.9) indicates some water molecules to be located in the overlapping volumes of individual hydration spheres. The averaged number of hydrogen bonds (H-bonds) during the simulation period (5.8) indicates that some water molecules are situated in the molecular hydration shell with an unsuitable orientation to form a hydrogen bond with the ion. The mean residence time in the surroundings of the bisulfate ion classify it generally as a weak structure-making ion, but the analysis of the individual sites reveals a more complex behavior of them, in particular a strong interaction with a water molecule at the hydrogen site. PMID:20707370

Vchirawongkwin, Viwat; Kritayakornupong, Chinapong; Rode, Bernd M

2010-09-01

164

Coupled Dynamics of a Nanomechanical Resonator and Superconducting Quantum Circuits  

NASA Astrophysics Data System (ADS)

The coupled dynamics of a nanomechanical resonator and superconducting quantum circuits are studied in three experiments, in the context of studying the quantum limit for force detection and quantum physics of macroscopic objects. In the first experiment, the dispersive mechanical resonance shift from the interaction with a Cooper-pair box qubit is studied. The measured coupling strength is large enough to satisfy one of the conditions required to perform many of the proposed quantum nanomechanical measurements. The resonance shift also probes the microwave-driven response of the qubit, showing Rabi oscillation and Landau-Zener tunneling, proving the coherent dynamics of the qubit. Second, the parametric excitation of nanomechanical motion is studied via experiments with a driven qubit. Degenerate parametric amplification and oscillation are demonstrated, with a new observation of nonlinear dissipation. The squeezing of the back-action noise from the detection amplifier is also observed, up to 4dB. It is the first demonstration using a qubit as an auxiliary system to modify the nanomechanical dynamics, showing a possible route for generation of nanomechanical quantum states. Finally, back-action cooling of nanomechanical motion has been investigated, which is implemented by capacitively coupling a high-Q coplanar waveguide microwave resonator to a nanomechanical resonator. The thermal state with 7.5 mechanical quanta on average is reached, a result that is ultimately limited due to increased bath heating with microwave power. The heating is consistent with a model based on two-level systems resonantly coupled to the nanomechanical mode. This additional heating suggests future efforts to improve coupling and for reducing two-level system density in materials employed to reach the motional ground state via back-action cooling.

Suh, Junho

165

Quantum Bayesianism: A study  

Microsoft Academic Search

The Bayesian approach to quantum mechanics of Caves, Fuchs and Schack is presented. Its conjunction of realism about physics along with anti-realism about much of the structure of quantum theory is elaborated; and the position defended from common objections: that it is solipsist; that it is too instrumentalist; that it cannot deal with Wigner's friend scenarios. Three more substantive problems

Christopher Gordon Timpson

2008-01-01

166

Quantum and classical molecular dynamics simulations of liquid methane  

NASA Astrophysics Data System (ADS)

We present a comparative study of classical and ab-initio molecular dynamics (MD) simulations of methane in the liquid state. The atom wise radial distribution function (RDF) of liquid methane for both classical and ab initio simulations is calculated. It is observed that the peaks of RDF are lowered and broadened when quantum effects are considered. Also, the peaks are shifted towards the slightly lower values of intermolecular distance r. The diffusion coefficient from the slope of Mean Square Displacement (MSD) and the partial density of states has also been calculated for Quantum MD. The bond angles of the final configuration obtained after running the simulations show more fluctuations in classical MD as compared to quantum MD simulations.

Pathania, Y.; Ahluwalia, P. K.

2013-02-01

167

Dynamical Causal Modeling from a Quantum Dynamical Perspective  

NASA Astrophysics Data System (ADS)

Recent research suggests that any set of first order linear vector ODEs can be converted to a set of specific vector ODEs adhering to what we have called ``Quantum Harmonical Form (QHF)''. QHF has been developed using a virtual quantum multi harmonic oscillator system where mass and force constants are considered to be time variant and the Hamiltonian is defined as a conic structure over positions and momenta to conserve the Hermiticity. As described in previous works, the conversion to QHF requires the matrix coefficient of the first set of ODEs to be a normal matrix. In this paper, this limitation is circumvented using a space extension approach expanding the potential applicability of this method. Overall, conversion to QHF allows the investigation of a set of ODEs using mathematical tools available to the investigation of the physical concepts underlying quantum harmonic oscillators. The utility of QHF in the context of dynamical systems and dynamical causal modeling in behavioral and cognitive neuroscience is briefly discussed.

Demiralp, Emre; Demiralp, Metin

2010-09-01

168

Quantum dynamics of a plane pendulum  

SciTech Connect

A semianalytical approach to the quantum dynamics of a plane pendulum is developed, based on Mathieu functions which appear as stationary wave functions. The time-dependent Schroedinger equation is solved for pendular analogs of coherent and squeezed states of a harmonic oscillator, induced by instantaneous changes of the periodic potential energy function. Coherent pendular states are discussed between the harmonic limit for small displacements and the inverted pendulum limit, while squeezed pendular states are shown to interpolate between vibrational and free rotational motion. In the latter case, full and fractional revivals as well as spatiotemporal structures in the time evolution of the probability densities (quantum carpets) are quantitatively analyzed. Corresponding expressions for the mean orientation are derived in terms of Mathieu functions in time. For periodic double well potentials, different revival schemes, and different quantum carpets are found for the even and odd initial states forming the ground tunneling doublet. Time evolution of the mean alignment allows the separation of states with different parity. Implications for external (rotational) and internal (torsional) motion of molecules induced by intense laser fields are discussed.

Leibscher, Monika [Institut fuer Chemie und Biochemie, Freie Universitaet Berlin, Takustr. 3, D-14195 Berlin (Germany); Schmidt, Burkhard [Institut fuer Mathematik, Freie Universitaet Berlin, Arnimallee 6, D-14195 Berlin (Germany)

2009-07-15

169

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

170

Quantum dynamics of the damped harmonic oscillator  

NASA Astrophysics Data System (ADS)

The quantum theory of the damped harmonic oscillator has been a subject of continual investigation since the 1930s. The obstacle to quantization created by the dissipation of energy is usually dealt with by including a discrete set of additional harmonic oscillators as a reservoir. But a discrete reservoir cannot directly yield dynamics such as Ohmic damping (proportional to velocity) of the oscillator of interest. By using a continuum of oscillators as a reservoir, we canonically quantize the harmonic oscillator with Ohmic damping and also with general damping behaviour. The dynamics of a damped oscillator is determined by an arbitrary effective susceptibility that obeys the Kramers-Kronig relations. This approach offers an alternative description of nano-mechanical oscillators and opto-mechanical systems.

Philbin, T. G.

2012-08-01

171

Melting and lattice dynamics of sodium at high pressures. Ab initio quantum molecular-dynamics analysis  

SciTech Connect

The melting and lattice dynamics of sodium are studied by quantum molecular dynamics simulation, i.e., with allowance for anharmonicity, at pressures up to 1 Mbar and temperatures up to 1000 K. The simulation results agree well with the experimental data and our earlier calculation performed ab initio in the quasi-harmonic approximation. The simulation results demonstrate that anharmonic interactions weakly affect the melting curve and the phonon frequencies of Na up to near-melting temperatures.

Lepeshkin, S. V., E-mail: lepeshkin@lpi.ru [Russian Academy of Sciences, Lebedev Physical Institute (Russian Federation); Magnitskaya, M. V. [Vereshchagin Institute for High Pressure Physics (Russian Federation); Matsko, N. L.; Maksimov, E. G. [Russian Academy of Sciences, Lebedev Physical Institute (Russian Federation)

2012-07-15

172

Quantum molecular dynamics and particle production in heavy ion collisions  

NASA Astrophysics Data System (ADS)

The production of photons, kaons, antikaons and antiprotons in heavy-ion collisions is calculated in the framework of ``quantum'' molecular dynamics (QMD). The Skyrme potentials, with parameters chosen to generate the soft and hard nuclear equations of state(EOS), are used in the propagation of nucleons within QMD. The sensitivity of the production of each type of particle to the EOS is discussed. The mechanisms of production processes are studied. The theoretical results are compared with the available experimental data.

Huang, S. W.; Faessler, A.; Li, G. Q.; Khoa, D. T.; Lehmann, E.; Matin, M. A.; Ohtsuka, N.; Puri, R. K.

173

Loss of coherence and memory effects in quantum dynamics Loss of coherence and memory effects in quantum dynamics  

NASA Astrophysics Data System (ADS)

The last years have witnessed fast growing developments in the use of quantum mechanics in technology-oriented and information-related fields, especially in metrology, in the developments of nano-devices and in understanding highly efficient transport processes. The consequent theoretical and experimental outcomes are now driving new experimental tests of quantum mechanical effects with unprecedented accuracies that carry with themselves the concrete possibility of novel technological spin-offs. Indeed, the manifold advances in quantum optics, atom and ion manipulations, spintronics and nano-technologies are allowing direct experimental verifications of new ideas and their applications to a large variety of fields. All of these activities have revitalized interest in quantum mechanics and created a unique framework in which theoretical and experimental physics have become fruitfully tangled with information theory, computer, material and life sciences. This special issue aims to provide an overview of what is currently being pursued in the field and of what kind of theoretical reference frame is being developed together with the experimental and theoretical results. It consists of three sections: 1. Memory effects in quantum dynamics and quantum channels 2. Driven open quantum systems 3. Experiments concerning quantum coherence and/or decoherence The first two sections are theoretical and concerned with open quantum systems. In all of the above mentioned topics, the presence of an external environment needs to be taken into account, possibly in the presence of external controls and/or forcing, leading to driven open quantum systems. The open system paradigm has proven to be central in the analysis and understanding of many basic issues of quantum mechanics, such as the measurement problem, quantum communication and coherence, as well as for an ever growing number of applications. The theory is, however, well-settled only when the so-called Markovian or memoryless, approximation applies. When strong coupling or long environmental relaxation times make memory effects important for a realistic description of the dynamics, new strategies are asked for and the assessment of the general structure of non-Markovian dynamical equations for realistic systems is a crucial issue. The impact of quantum phenomena such as coherence and entanglement in biology has recently started to be considered as a possible source of the high efficiency of certain biological mechanisms, including e.g. light harvesting in photosynthesis and enzyme catalysis. In this effort, the relatively unknown territory of driven open quantum systems is being explored from various directions, with special attention to the creation and stability of coherent structures away from thermal equilibrium. These investigations are likely to advance our understanding of the scope and role of quantum mechanics in living systems; at the same time they provide new ideas for the developments of next generations of devices implementing highly efficient energy harvesting and conversion. The third section concerns experimental studies that are currently being pursued. Multidimensional nonlinear spectroscopy, in particular, has played an important role in enabling experimental detection of the signatures of coherence. Recent remarkable results suggest that coherence—both electronic and vibrational—survive for substantial timescales even in complex biological systems. The papers reported in this issue describe work at the forefront of this field, where researchers are seeking a detailed understanding of the experimental signatures of coherence and its implications for light-induced processes in biology and chemistry.

Benatti, Fabio; Floreanini, Roberto; Scholes, Greg

2012-08-01

174

Quantum Speed Limit for Non-Markovian Dynamics  

NASA Astrophysics Data System (ADS)

We derive a Margolus-Levitin-type bound on the minimal evolution time of an arbitrarily driven open quantum system. We express this quantum speed limit time in terms of the operator norm of the nonunitary generator of the dynamics. We apply these results to the damped Jaynes-Cummings model and demonstrate that the corresponding bound is tight. We further show that non-Markovian effects can speed up quantum evolution and therefore lead to a smaller quantum speed limit time.

Deffner, Sebastian; Lutz, Eric

2013-07-01

175

Resident electron spin dynamics of II-VI quantum dots  

NASA Astrophysics Data System (ADS)

The spin dynamics of single electrons resident to charged CdSe/ZnSe quantum dots is studied. The spin-orbit mediated spin lifetime is uncovered. It follows a magnetic-field dependence of ?so=190 ms T4/B4. Below about B=2 T, the electron-nuclear hyperfine coupling takes over and the electron spin lifetime shortens. We analyze the temperature dependence of the spin transfer via hyperfine interaction and find that the efficiency for the formation of a nuclear dynamical polarization increases up to 100 K.

Gapon, V.; Puls, J.; Henneberger, F.

2009-05-01

176

Indicators of quantum coherence in light-harvesting dynamics  

Microsoft Academic Search

Characterizing quantum dynamics of electronic excitations in a variety of light-harvesting systems is currently of much interest [1]. In particular, it is important to identify measures that appropriately quantify the strength of coherent dynamics and its impact on different time scales of the light-harvesting process. In this talk I will discuss quantum transport performance measures that are defined based on

Alexandra Olaya-Castro

2011-01-01

177

Nuclear Quantum Effects and Enzyme Dynamics in Dihydrofolate Reductase Catalysis  

Microsoft Academic Search

Mixed quantum\\/classical molecular dynamics simulations of the hydride transfer reaction catalyzed by dihydrofolate reductase are presented. The nuclear quantum effects such as zero point energy and hydrogen tunneling, as well as the motion of the entire solvated enzyme, are included during the generation of the free energy profiles and the real-time dynamical trajectories. The calculated deuterium kinetic isotope effect agrees

Pratul K. Agarwal; Salomon R. Billeter; Sharon Hammes-Schiffer

2002-01-01

178

Quantum Spin Dynamics in Single-Molecule Magnets  

Microsoft Academic Search

This thesis contains a thorough investigation of the quantum spin dynamics in Mn12-ac and Mn6 Single-molecule magnets. In particular, we have investigated the interplay between quantum tunneling of magnetization and nuclear spin dynamics in Mn12-ac by ultra-low temperature NMR experiments. We discuss the effect of quantum tunneling on the nuclear spin-lattice relaxation, the nuclear spin diffusion, the thermalization of the

Andrea Morello

2004-01-01

179

Quantum Information, Thermofield Dynamics and Thermalized Bosonic Oscillator  

NASA Astrophysics Data System (ADS)

We show through Thermofield Dynamics approach that the action of the thermalized quantum logic gate on the thermalized state is equivalent to thermalization of the state that arise from the application of the nonthermalized quantum logic gate. In particular, we study the effect of temperature on a mixed state associated to a system capable of implementing a controlled-NOT (CNOT) quantum logic gate. According to a proposal in the literature, a way of implementing such a logic gate is by using a representation of the qubit states as elements of the Fock space of a bosonic system. We consider such a proposal and use the Thermofield Dynamics to determine the thermalized qubit states. The temperature acts as a quantum noise on pure states, making them a statistical mixture. In this context, we analyze the fidelity as a function of the temperature and using the Mandel parameter, we determine temperature ranges for which the statistics of the system becomes subpoissonian, poissonian and superpoissonian. Finally, we calculate the Wigner function, allowing an analysis of the thermal state in phase space, and we obtain that the increase of temperature decreases nonclassical properties of the system. The temperature range where one has a subpoissonian statistics and high fidelity is determined.

Trindade, M. A. S.; Silva Filho, L. M.; Santos, L. C.; Martins, M. Graças R.; Vianna, J. D. M.

2013-09-01

180

Dynamics of Large Quantum Systems: Equilibration, Thermalization and Interactions  

NASA Astrophysics Data System (ADS)

The question of how/whether large quantum systems equilibrate and/or thermalize when prepared in an out-of-equilibrium state has been of enormous interest given recent experimental progress. We address this question in fermionic [1,2] and bosonic [3] systems, by following the dynamics of the full density matrix. We particularly study the case of two large-twin systems connected by a weak link (a quantum impurity), and we show that the total system equilibrates and thermalizes when the weak link is susceptible to incoherent and inelastic processes. We thus provide an experimentally feasible prescription for equilibrating and thermalizing large finite quantum systems. Our calculations are based on extending methods originally developed to treat subsystem dynamics (such as impurity), namely, the quantum Langevin equation method, the well known fermionic trace formula, and an iterative path integral approach. We also explore the role of interactions. While the fermionic system [1,2] shares many common features with the bosonic analog [3], we will describe certain crucial differences that arise as a result of different statistics.[4pt] [1] M. Kulkarni, K. L. Tiwari, D. Segal, arXiv:1206.2408[0pt] [2] M. Kulkarni, K. L. Tiwari, D. Segal, arXiv:1208.5725[0pt] [3] M. Kulkarni and D. Segal (in preparation)

Segal, Dvira; Kulkarni, Manas; Tiwari, Kunal

2013-03-01

181

Optical detection of quantum dynamics in gallium arsenide neutral donors  

NASA Astrophysics Data System (ADS)

Hydrogenic neutral donors in semiconductors are attractive candidates for the study of quantum dynamics of weakly interacting ensembles in the solid state. States of interest are the hydrogenic orbitals of the single electron that is weakly bound to a positively charged donor. Transitions between hydrogen-like bound electron orbitals fall in the terahertz region of the spectrum. For these atom-like, solid state-embedded quantum systems, photo-excitation to a short lived neutral donor bound exciton (D0X) state is dependent on the orbital state of the neutral donor. State-dependent optical light cattering has previously enabled sensitive readout of quantum dynamics of localized quantum systems such as quantum dots, and quantum nondemolition readout of trapped ions via cycling transitions, especially for spin states. In previous research investigating dynamics of charge states, however, transport measurements based on photoconductivity, selective ionization, or field effect transistor devices have been emphasized. As an alternative optical readout scheme, it is demonstrated that ground state (1S) neutral donors exhibit strong light scattering at the D0X resonance, which fluorescence is quenched when donors are excited out of the ground state with terahertz radiation. The recovery of D0X resonance fluorescence indicates the return of donors to the emitting ground state. Fluorescence recovery is expected to be limited by the long lifetime of the low-lying bound states, where a phonon bottleneck is expected. Measured lifetimes are observed to depend sensitively on parameters affecting free carrier density, including sample temperature and dopant density, as well as excitation fraction and readout laser intensity. Recovery of fluorescence after pulsed resonant terahertz excitation to the 2P- state exhibits strongly nonexponential decay. Two regimes of donor relaxation are observed: an initial fast decay in a tens of ns-scale decay limited, where inelastic scattering with unintentionally-excited free carriers reduces the bound state lifetimes, and a slow hundreds of ns-scale from phonon-limited decay of excited electrons out of the 2P- state. Optical readout of ground state neutral donors demonstrated here is complimentary to photoconductivity, which detects the ionized population. The demonstrated resonance fluorescence-based scheme enables sensitive detection of the internal quantum dynamics of neutral donors. Changes in the spectrum of both the free and donor bound exciton observed as a lineshift and broadening at higher excitation fractions are evidence of terahertz-activated interactions of ground state donors and/or excitons with excited or ionized neighbor donors.

Allen, Dan G.

182

Quantum control of charge carrier dynamics in layered semiconductor heterostructures  

NASA Astrophysics Data System (ADS)

This dissertation presents theoretical studies of charge carrier dynamics in layered semiconductor heterostructures. Carrier dynamics are investigated by solving the Schrodinger equation numerically on a grid. Control methods are used to discover laser pulses that actively manipulate and control dynamics in quantum well systems. Results indicate that a wide array of possible target objectives can be achieved successfully using simple, experimentally feasible electric fields. A tailored laser pulse can drive an electronic wave packet to maximum overlap with a target distribution at a specified time. A genetic algorithm is used to determine the optimal parameters of the excitation pulse. The robustness of the results is analyzed by considering fluctuations in the do field, two types of sample defects, and environmental coupling. In all cases studied, the genetic algorithm can re-optimize the laser field to achieve the control objective. The effects of Coulomb interactions with regard to controlling wave packets in quantum wells are investigated. The goal is to clarify the extent that the attraction between electrons and holes affects control. The primary effect is to modify the energy splittings, which induces small changes in oscillation period and frequency of the wave packet. The results show that the interaction does not substantially affect the control, yet can alter dynamics in some cases. Quantum wells are sources of controllable radiation. Oscillating wave packets in the conduction band typically radiate in the Terahertz frequency regime. The frequency and amplitude of the radiation is tunable by altering excitation conditions. Terahertz fields can be designed by controlling the characteristics of the emission, and used as excitation sources for other applications. Electronic population can be switched adiabatically between quantum wells. A time-dependent do field guides an initial state along a smooth path to a target state. The general requirements for adiabaticity are determined. Successfully meeting the requirements produces a pure state that evolves adiabatically to the final state. This procedure provides an effective method for adiabatic passage with smooth transitions, selectivity, and reversibility.

Shuford, Kevin Lee

183

Quantum dynamics of magnetic and electric dipoles and the geometric phase  

NASA Astrophysics Data System (ADS)

We study the quantum dynamics of a neutral particle that posseses a permanent magnetic and electric dipole moments in the presence of an electromagnetic field. The analysis of this dynamics demonstrates the appearance of a quantum phase that combines the Aharonov-Casher effect and the He-Mckellar-Wilkens effect. We demonstrate that this phase is a special case of the geometric quantum phase. A series of field configurations where this phase would be found is presented. A generalized Casella-type effect is found in one of these configurations. A physical scenario for the quantum phase in an interferometric experiment is proposed.

Furtado, Claudio; Ribeiro, Carlos Alberto

2004-06-01

184

Relativistic Quantum Dynamics of Many-Body Systems  

NASA Astrophysics Data System (ADS)

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

Coester, F.; Polyzou, W. N.

2001-09-01

185

Quantum-mechanical cumulant dynamics near stable periodic orbits in phase space: Application to the classical-like dynamics of quantum accelerator modes  

SciTech Connect

We formulate a general method for the study of semiclassical-like dynamics in stable regions of a mixed phase space, in order to theoretically study the dynamics of quantum accelerator modes. In the simplest case, this involves determining solutions, which are stable when constrained to remain pure-state Gaussian wave packets, and then propagating them using a cumulant-based formalism. Using this methodology, we study the relative longevity, under different parameter regimes, of quantum accelerator modes. Within this attractively simple formalism, we are able to obtain good qualitative agreement with exact wave-function dynamics.

Bach, R.; Burnett, K.; D'Arcy, M.B.; Gardiner, S.A. [Center for Theoretical Physics, Polish Academy of Sciences, 02-668 Warsaw (Poland); Clarendon Laboratory, Department of Physics, University of Oxford, Oxford OX1 3PU (United Kingdom); Atomic Physics Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899-8423 (United States); JILA, University of Colorado and National Institute of Standards and Technology, Boulder, Colorado 80309-0440 (United States)

2005-03-01

186

Moyal quantum mechanics: The semiclassical Heisenberg dynamics  

SciTech Connect

The Moyal description of quantum mechanics, based on the Wigner--Weyl isomorphism between operators and symbols, provides a comprehensive phase space representation of dynamics. The Weyl symbol image of the Heisenberg picture evolution operator is regular in {h_bar} and so presents a preferred foundation for semiclassical analysis. Its semiclassical expansion ``coefficients,`` acting on symbols that represent observables, are simple, globally defined (phase space) differential operators constructed in terms of the classical flow. The first of two presented methods introduces a cluster-graph expansion for the symbol of an exponentiated operator, which extends Groenewold`s formula for the Weyl product of two symbols and has {h_bar} as its natural small parameter. This Poisson bracket based cluster expansion determines the Jacobi equations for the semiclassical expansion of ``quantum trajectories.`` Their Green function solutions construct the regular {h_bar}{down_arrow}0 asymptotic series for the Heisenberg--Weyl evolution map. The second method directly substitutes such a series into the Moyal equation of motion and determines the {h_bar} coefficients recursively. In contrast to the WKB approximation for propagators, the Heisenberg--Weyl description of evolution involves no essential singularity in {h_bar}, no Hamilton--Jacobi equation to solve for the action, and no multiple trajectories, caustics, or Maslov indices. {copyright} 1995 Academic Press, Inc.

Osborn, T.A.; Molzahn, F.H. [Department of Physics, University of Manitoba, Winnipeg, MB, R3T 2N2 (Canada)

1995-07-01

187

New methods for quantum mechanical reaction dynamics  

SciTech Connect

Quantum mechanical methods are developed to describe the dynamics of bimolecular chemical reactions. We focus on developing approaches for directly calculating the desired quantity of interest. Methods for the calculation of single matrix elements of the scattering matrix (S-matrix) and initial state-selected reaction probabilities are presented. This is accomplished by the use of absorbing boundary conditions (ABC) to obtain a localized (L{sup 2}) representation of the outgoing wave scattering Green`s function. This approach enables the efficient calculation of only a single column of the S-matrix with a proportionate savings in effort over the calculation of the entire S-matrix. Applying this method to the calculation of the initial (or final) state-selected reaction probability, a more averaged quantity, requires even less effort than the state-to-state S-matrix elements. It is shown how the same representation of the Green`s function can be effectively applied to the calculation of negative ion photodetachment intensities. Photodetachment spectroscopy of the anion ABC{sup -} can be a very useful method for obtaining detailed information about the neutral ABC potential energy surface, particularly if the ABC{sup -} geometry is similar to the transition state of the neutral ABC. Total and arrangement-selected photodetachment spectra are calculated for the H{sub 3}O{sup -} system, providing information about the potential energy surface for the OH + H{sub 2} reaction when compared with experimental results. Finally, we present methods for the direct calculation of the thermal rate constant from the flux-position and flux-flux correlation functions. The spirit of transition state theory is invoked by concentrating on the short time dynamics in the area around the transition state that determine reactivity. These methods are made efficient by evaluating the required quantum mechanical trace in the basis of eigenstates of the Boltzmannized flux operator.

Thompson, W.H. [Univ. of California, Berkeley, CA (United States). Dept. of Chemistry]|[Lawrence Berkeley Lab., CA (United States)

1996-12-01

188

Quantum Optical Studies of Semiconductors.  

National Technical Information Service (NTIS)

Work on this program focused on the development and application of advanced optical spectroscopy and methodology for the study of the quantum optical properties of semiconductor heterostructures. The work includes the first observation of the nonlinear op...

D. G. Steel

1999-01-01

189

Dynamics of the Anderson model for dilute magnetic alloys: A quantum Monte Carlo and maximum entropy study  

Microsoft Academic Search

In this article we describe the results of a new method for calculating the dynamical properties of the Anderson model. QMC generates data about the Matsubara Green's functions in imaginary time. To obtain dynamical properties, one must analytically continue these data to real time. This is an extremely ill-posed inverse problem similar to the inversion of a Laplace transform from

R. N. Silver; J. E. Gubernatis; D. S. Sivia; M. Jarrell

1990-01-01

190

Decoherence dynamics of two charge qubits in vertically coupled quantum dots  

SciTech Connect

The decoherence dynamics of two charge qubits in a double quantum dot is investigated theoretically. We consider the quantum dynamics of two interacting electrons in a vertically coupled quantum dot driven by an external electric field. We derive the equations of motion for the density matrix, in which the presence of an electron confined in the double dot represents one qubit. A Markovian approach to the dynamical evolution of the reduced density matrix is adopted. We evaluate the concurrence of two qubits in order to study the effect of acoustic phonons on the entanglement. We also show that the disentanglement effect depends on the double dot parameters and increases with the temperature.

Ben Chouikha, W.; Bennaceur, R. [Laboratoire de Physique de la Matiere Condensee, Departement de Physique, Faculte des Sciences de Tunis, 1060 Tunis (Tunisia); Jaziri, S. [Departement de Physique, Faculte des Sciences de Bizerte, Jarzouna 7021 Bizerte (Tunisia)

2007-12-15

191

Dynamical quantum error correction: recent achievements and prospects  

NASA Astrophysics Data System (ADS)

Precisely controlling the dynamics of real-world open quantum systems is a central challenge across quantum science and technology, with implications ranging from quantum physics and chemistry to fault-tolerant quantum computation. Dynamical quantum error correction strategies based on open-loop time-dependent modulation of the system dynamics provide a general perturbative framework for boosting physical-layer fidelities in the non-Markovian regime. I will describe recent progress in designing dynamical error correction schemes able to incorporate various system and control constraints encountered in realistic scenarios. In particular, I will show how to employ dynamical decoupling methods to achieve high-fidelity quantum storage for long times, while minimizing access latency and sequencing complexity, and how to synthesize dynamically corrected quantum gates for simultaneously canceling non-Markovian decoherence and control errors, while accommodating internal always-on dynamics and limited control. In the process, I will make contact with current qubit devices to the extent possible and point to remaining challenges and directions for further explorations.

Viola, Lorenza

2013-03-01

192

Seven-degree-of-freedom, quantum scattering dynamics study of the H{sub 2}D{sup +}+H{sub 2} reaction  

SciTech Connect

A quantum scattering dynamics, time-dependent wavepacket propagation method is applied to study the reaction of H{sub 2}D{sup +}+H{sub 2}{yields}H{sub 3}{sup +}+HD on the Xie-Braams-Bowman potential energy surface. The reduced-dimensional, seven-degree-of-freedom approach is employed in this calculation by fixing one Jacobi and one torsion angle related to H{sub 2}D{sup +} at the lowest saddle point geometry of D{sub 2d} on the potential energy surface. Initial state selected reaction probabilities are presented for various initial rovibrational states. The ground state reaction probability shows no threshold for this reaction, in other words, this reaction can occur without an activation barrier. The vibrational excitation shows that the stretching motion of H{sup +}-HD only has a small effect on the reaction probability; the vibrational excitation of HD in H{sub 2}D{sup +} hinders the reactivity. By contrast, rotational excitation of H{sup +}-HD greatly enhances the reactivity with the reaction probability increased double or triple at high rotational states compared to the ground state. Reactive resonances, seen in all the initial state selected reaction probabilities, are also found in the integral cross section for the ground state of H{sub 2}D{sup +} and H{sub 2}. The thermal rate coefficient is also calculated and is found to be in semiquantitative agreement with experiment; however, quantum scattering approaches including more degrees of freedom, especially including all the angles, are necessary to study this reaction in the future.

Wang Dunyou [College of Physics and Electronics, Shandong Normal University, Jinan, Shandong 250014 (China); Xie Zhen; Bowman, Joel M. [Department of Chemistry and Cherry L. Emerson Center of Scientific Computation, Emory University, Atlanta, Georgia 30322 (United States)

2010-02-28

193

Carrier dynamics in type-II GaSb\\/GaAs quantum dots  

Microsoft Academic Search

The optical properties and dynamics of charge carriers in self-organized arrays of type-II (staggered band lineup) GaSb\\/GaAs quantum dots are studied. Interband absorption from type-II quantum dots is evidenced; the energetic positions of quantum dot absorption peaks coincide with those apparent in photoluminescence spectra. (Sb,As) intermixing with an antimony diffusion length of about 1 nm is found to make an

F. Hatami; M. Grundmann; N. N. Ledentsov; F. Heinrichsdorff; R. Heitz; J. Böhrer; D. Bimberg; S. S. Ruvimov; P. Werner; V. M. Ustinov; P. S. Kop'ev; Zh. I. Alferov

1998-01-01

194

Effects of reagent rotation on the dynamics of the H2+OH reaction: A full dimension quantum study  

NASA Astrophysics Data System (ADS)

We have extended the time-dependent wave packet method to calculate cross sections and rate constants for rotationally excited initial states by using the centrifugal sudden (CS) approximation. A detailed study of the effects of rotational excitation of reagents on the title reaction on the WDSE PES has been carried out. It is found that (a) OH rotational excitation very mildly enhances the total cross section, (b) H2 rotational excitation quite substantially reduce the cross section, and (c) simultaneous OH and H2 rotational excitation has a largely uncorrelated effect. As a result, we found that the thermal rate constant can be obtained fairly accurately by only taking into account the effect of H2 rotation. A model calculation by changing the mass of an O atom reveals that the weak dependence of the cross section on OH rotation is not because the O atom is left relatively stationary by OH rotation. We speculate that it may be a general feature for the diatom-diatom reaction that the nonreactive diatom acts as a spectator not only vibrationally but also rotationally. It was also found that the ``J-shifting'' approximation works quite well for the reaction. On the other hand, the effect of K on the dynamics is found to be much stronger and more complicated than the J effect, making the ``K-shifting'' approximation not good for the reaction.

Zhang, Dong H.; Lee, Soo-Y.

1998-08-01

195

Quantum mechanics based classical molecular dynamics study of water adsorption on (001) SrMO3 surfaces (M = Ti, Zr)  

NASA Astrophysics Data System (ADS)

This paper reports the results of a classical molecular dynamics (CMD) study of molecular water adsorption on MO2- and SrO-terminated SrMO3 (001) surfaces (M = Ti, Zr) at 300 K with ½ ML and 1 ML coverage. Models of the force fields for the water-crystalline oxide interfaces have been proposed. These force fields describe the oxide-oxide, water-oxide and water-water interactions, as well as interactions within the water molecule itself. The water-water and flexible water intramolecular potentials have been adopted from Toukan and Rahman (Phys. Rev. B 31 (1985) 2643-2648). The results of CMD simulations of the structure of the water layers at the oxide surfaces are discussed in terms of the most probable configurations. The power spectra of the water hydrogen velocity autocorrelation functions have been calculated using the CMD trajectories. The calculated power spectra permit us to consider the vibrational modes of the different structural species formed by the water molecules at the oxide surfaces and to analyse the level of binding of these species, both between themselves and to the surface.

Lukyanov, S. I.; Bandura, A. V.; Evarestov, R. A.

2013-05-01

196

Quantum dynamics of light-driven chiral molecular motors.  

PubMed

The results of theoretical studies on quantum dynamics of light-driven molecular motors with internal rotation are presented. Characteristic features of chiral motors driven by a non-helical, linearly polarized electric field of light are explained on the basis of symmetry argument. The rotational potential of the chiral motor is characterized by a ratchet form. The asymmetric potential determines the directional motion: the rotational direction is toward the gentle slope of the asymmetric potential. This direction is called the intuitive direction. To confirm the unidirectional rotational motion, results of quantum dynamical calculations of randomly-oriented molecular motors are presented. A theoretical design of the smallest light-driven molecular machine is presented. The smallest chiral molecular machine has an optically driven engine and a running propeller on its body. The mechanisms of transmission of driving forces from the engine to the propeller are elucidated by using a quantum dynamical treatment. The results provide a principle for control of optically-driven molecular bevel gears. Temperature effects are discussed using the density operator formalism. An effective method for ultrafast control of rotational motions in any desired direction is presented with the help of a quantum control theory. In this method, visible or UV light pulses are applied to drive the motor via an electronic excited state. A method for driving a large molecular motor consisting of an aromatic hydrocarbon is presented. The molecular motor is operated by interactions between the induced dipole of the molecular motor and the electric field of light pulses. PMID:19290336

Yamaki, Masahiro; Nakayama, Shin-ichiro; Hoki, Kunihito; Kono, Hirohiko; Fujimura, Yuichi

2009-01-30

197

Wavepacket dynamics, quantum reversibility, and random matrix theory  

SciTech Connect

We introduce and analyze the physics of 'driving reversal' experiments. These are prototype wavepacket dynamics scenarios probing quantum irreversibility. Unlike the mostly hypothetical 'time reversal' concept, a 'driving reversal' scenario can be realized in a laboratory experiment, and is relevant to the theory of quantum dissipation. We study both the energy spreading and the survival probability in such experiments. We also introduce and study the 'compensation time' (time of maximum return) in such a scenario. Extensive effort is devoted to figuring out the capability of either linear response theory or random matrix theory (RMT) to describe specific features of the time evolution. We explain that RMT modeling leads to a strong non-perturbative response effect that differs from the semiclassical behavior.

Hiller, Moritz [Max Planck Institute for Dynamics and Self-Organization and Department of Physics, University of Goettingen, Bunsenstrasse 10, D-37073 Goettingen (Germany)]. E-mail: mhiller@chaos.gwdg.de; Cohen, Doron [Department of Physics, Ben-Gurion University, Beer-Sheva 84105 (Israel); Geisel, Theo [Max Planck Institute for Dynamics and Self-Organization and Department of Physics, University of Goettingen, Bunsenstrasse 10, D-37073 Goettingen (Germany); Kottos, Tsampikos [Max Planck Institute for Dynamics and Self-Organization and Department of Physics, University of Goettingen, Bunsenstrasse 10, D-37073 Goettingen (Germany); Department of Physics, Wesleyan University, Middletown, CT 06459 (United States)

2006-05-15

198

Fundamental significance of tests that quantum dynamics is linear  

SciTech Connect

Experiments that look for nonlinear quantum dynamics test the fundamental premise of physics that one of two separate systems can influence the physical behavior of the other only if there is a force between them, an interaction that involves momentum and energy. The premise is tested because it is the assumption of a proof that quantum dynamics must be linear. Here, variations of a familiar example are used to show how results of nonlinear dynamics in one system can depend on correlations with the other. Effects of one system on the other, influence without interaction between separate systems, not previously considered possible, would be expected with nonlinear quantum dynamics. Whether it is possible or not is subject to experimental tests together with the linearity of quantum dynamics. Concluding comments and questions consider directions our thinking might take in response to this surprising unprecedented situation.

Jordan, Thomas F. [Department of Physics, University of Minnesota, Duluth, Minnesota 55812 (United States)

2010-09-15

199

Future experiments using forward electron spectroscopy to study the quantum dynamics of high-Z ions at the ESR/CRYRING storage rings  

NASA Astrophysics Data System (ADS)

At the FAIR facility for antiproton and ion research, the new ESR + CRYRING combination of storage rings CRYRING@ESR opens up a wealth of opportunities for in-ring atomic physics experiments on few-body quantum dynamics. The low-energy storage ring CRYRING will serve in its new location at FAIR/ESR for experiments with decelerated antiprotons and highly charged ions. We will discuss selected new experiments in the field of quantum dynamics of high-Z ions, for example for adiabatic superheavy quasi-molecules transiently formed with bare and H-like projectiles. Such experiments will be for the first time possible at the future CRYRING at ESR.

Hillenbrand, P. M.; Hagmann, S.; Stöhlker, Th; Litvinov, Yu; Kozhuharov, C.; Spillmann, U.; Shabaev, V.; Stiebing, K.; Lestinsky, M.; Surzhykov, A.; Voitkiv, A.; Franzke, B.; Fischer, D.; Brandau, C.; Schippers, S.; Mueller, A.; Schneider, D.; Jakubassa, D.; Artiomov, A.; DeFilippo, E.; Ma, X.; Dörner, R.; Rothard, H.

2013-09-01

200

Quantum Simulation of Dynamical Gauge Field Theories with Superconducting Qubits  

NASA Astrophysics Data System (ADS)

We propose a solid-state architecture to quantum simulate dynamical lattice gauge-field theories [1, 2]. Specifically, we consider a superconducting-circuit implementation of U(1) quantum link models [3], where the gauge fields can be expressed in terms of spin operators. We show that a general gauge-invariant Hamiltonian [2] can be simulated using a lattice of coupled non-linear oscillators. To illustrate the method, we study the one-dimensional Schwinger model [4] and the Rokhsar-Kivelson model [5]. These allow us to explore the physics of string breaking and confinement in one and two-dimensional lattices. An analysis of the fidelity accounting for decoherence is given, showing that the dynamics of gauge fields in these models can be observed using current circuit quantum-electrodynamics setups. Finally, we discuss the connection of our implementation with the physics of spin ice [6]. [1] K. G. Wilson, Phys. Rev. D 10, 2445 (1974). [2] J. Kogut and L. Susskind, Phys. Rev. D 11, 395 (1975). [3] S. Chandrasekharan and U.-J Wiese, Nuc. Phys. B, 492, 455 (1997). [4] J. Schwinger, Phys. Rev. 128, 2425 (1962). [5] D. S. Rokhsar and S. A. Kivelson, Phys. Rev. Lett. 61, 2377 (1988). [6] L. Balents, Nature 464, 199 (2010).

Marcos, David; Rabl, Peter; Rico, Enrique; Widmer, Philippe; Hafezi, Mohammad; Wiese, Uwe-Jens; Zoller, Peter

2013-03-01

201

Single-bit feedback and quantum-dynamical decoupling  

SciTech Connect

Synthesizing an effective identity evolution in a target system subjected to unwanted unitary or nonunitary dynamics is a fundamental task for both quantum control and quantum information processing applications. Here, we investigate how single-bit, discrete-time feedback capabilities may be exploited to enact or to enhance quantum procedures for effectively suppressing unwanted dynamics in a finite-dimensional open quantum system. An explicit characterization of the joint unitary propagators correctable by a single-bit feedback strategy for arbitrary evolution time is obtained. For a two-dimensional target system, we show how by appropriately combining quantum feedback with dynamical decoupling methods, concatenated feedback-decoupling schemes may be built, which can operate under relaxed control assumptions and can outperform purely closed-loop and open-loop protocols.

Ticozzi, Francesco [Dipartimento di Ingegneria dell'Informazione, Universita di Padova, via Gradenigo 6/B, 35131 Padova (Italy); Department of Physics and Astronomy, Dartmouth College, 6127 Wilder Laboratory, Hanover, New Hampshire 03755 (United States); Viola, Lorenza [Department of Physics and Astronomy, Dartmouth College, 6127 Wilder Laboratory, Hanover, New Hampshire 03755 (United States)

2006-11-15

202

Dynamic homotopy and landscape dynamical set topology in quantum control  

SciTech Connect

We examine the topology of the subset of controls taking a given initial state to a given final state in quantum control, where 'state' may mean a pure state Double-Vertical-Line {psi}>, an ensemble density matrix {rho}, or a unitary propagator U(0, T). The analysis consists in showing that the endpoint map acting on control space is a Hurewicz fibration for a large class of affine control systems with vector controls. Exploiting the resulting fibration sequence and the long exact sequence of basepoint-preserving homotopy classes of maps, we show that the indicated subset of controls is homotopy equivalent to the loopspace of the state manifold. This not only allows us to understand the connectedness of 'dynamical sets' realized as preimages of subsets of the state space through this endpoint map, but also provides a wealth of additional topological information about such subsets of control space.

Dominy, Jason [Program in Applied and Computational Mathematics, Princeton University, Princeton, New Jersey 08544 (United States); Rabitz, Herschel [Program in Applied and Computational Mathematics, Princeton University, Princeton, New Jersey 08544 (United States); Department of Chemistry, Princeton University, Princeton, New Jersey 08544 (United States)

2012-08-15

203

Macroscopic quantum dynamics of pi junctions with ferromagnetic insulators  

Microsoft Academic Search

We theoretically investigate the macroscopic quantum dynamics of a pi junction with a superconductor (S) and a multiferroic material or a ferromagnetic insulator (FI). By deriving the effective action from a microscopic Hamiltonian, a pi -junction qubit (a S-FI-S superconducting quantum interference device ring) is proposed. In this qubit, a quantum two-level system is spontaneously generated and the effect of

Shiro Kawabata; Satoshi Kashiwaya; Yasuhiro Asano; Yukio Tanaka; Alexander A. Golubov

2006-01-01

204

Dynamics after a sweep through a quantum critical point.  

PubMed

The coherent quantum evolution of a one-dimensional many-particle system after slowly sweeping the Hamiltonian through a critical point is studied using a generalized quantum Ising model containing both integrable and nonintegrable regimes. It is known from previous work that universal power laws of the sweep rate appear in such quantities as the mean number of excitations created by the sweep. Several other phenomena are found that are not reflected by such averages: there are two different scaling behaviors of the entanglement entropy and a relaxation that is power law in time rather than exponential. The final state of evolution after the quench is not characterized by any effective temperature, and the Loschmidt echo converges algebraically for long times, with cusplike singularities in the integrable case that are dynamically broadened by nonintegrable perturbations. PMID:20365512

Pollmann, Frank; Mukerjee, Subroto; Green, Andrew G; Moore, Joel E

2010-02-04

205

Quantum Many-Body Dynamics in Optomechanical Arrays  

NASA Astrophysics Data System (ADS)

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

Ludwig, Max; Marquardt, Florian

2013-08-01

206

A symmetric geometric measure and the dynamics of quantum discord  

NASA Astrophysics Data System (ADS)

A symmetric measure of quantum correlation based on the Hilbert—Schmidt distance is presented in this paper. For two-qubit states, we considerably simplify the optimization procedure so that numerical evaluation can be performed efficiently. Analytical expressions for the quantum correlation are attained for some special states. We further investigate the dynamics of quantum correlation of the system qubits in the presence of independent dissipative environments. Several nontrivial aspects are demonstrated. We find that the quantum correlation can increase even if the system state is suffering from dissipative noise. Sudden changes occur, even twice, in the time evolution of quantum correlation. There exists a certain correspondence between the evolution of quantum correlation in the systems and that in the environments, and the quantum correlation in the systems will be transferred into the environments completely and asymptotically.

Jiang, Feng-Jian; Lü, Hai-Jiang; Yan, Xin-Hu; Shi, Ming-Jun

2013-04-01

207

Classical-Quantum correspondence in isomerization dynamics: quantum eigenstates and classical Arnol'd web  

NASA Astrophysics Data System (ADS)

Recently, there has been a renaissance of sorts in chemical dynamics with researchers critically examining the validity of the two pillars of reaction rate theory - transition state theory and the Rice-Ramsperger-Kassel-Marcus (RRKM) theory. Since both theories have classical dynamics at their foundation, advances in our understanding of nonlinear dynamics and continuing efforts to characterize the phase space structure of systems with three or more degrees of freedom are beginning to yield crucial mechanistic insights into the dynamics. This talk focuses on a mechanistic understanding of the deviations from RRKM theory for a model isomerization problem with three degrees of freedom. Several studies have established that such systems are prime candidates for observing non-RRKM behaviorootnotetextD. M. Leitner, Int. J. Quant. Chem. 75, 523 (1999).. The model is inspired, and generalized, from a much earlier study by De Leon and BerneootnotetextN. De Leon and B. J. Berne, J. Chem. Phys. 75, 3495 (1981).. We try to answer two of the questions posed in this early work by studying the intramolecular vibrational energy flow in the system from both classical and quantum viewpoints. Using a wavelet-based local frequency analysis it is possible to construct a useful representation of the classical phase space (Arnol'd web) highlighting the important dynamical structures. Insights into the dynamics originate from the various nonlinear resonances and phase space traps which potentially result in quantum eigenstates of varying degree of localizationootnotetextD. M. Leitner and M. Gruebele, Mol. Phys. 106, 433 (2008)..

Keshavamurthy, S.

2009-03-01

208

An Eight-Degree-of-Freedom, Time-Dependent Quantum Dynamics Study for the H?+C?H Reaction on a New Modified potential Energy Surface  

SciTech Connect

An eight dimensional time-dependent quantum dynamics wavepacket approach is performed for the study of the H?+C?H ! H + C?H? reaction system on a new modified potential energy surface (PES) [Chem. Phys. Lett. 409, 249 (2005)]. This new potential energy surface is obtained by modifying Wang and Bowman's old PES [ J. Chem. Phys. 101, 8646 (1994)] based on the new ab initio calculation. This new modified PES has a much lower transition state barrier height at 2.29 kcal/mol than Wang and Bowman's old PES at 4.3 kcal/mol. This study shows the reactivity for this diatom-triatom reaction system is enchanced by vibrational excitations of H?; whereas, the vibrational excitations of C?H only have a small effect on the reactivity. Furthermore, the bending excitations of C?H, comparing to the ground state reaction probability, hinder the reactivity. The comparison of the rate constant between this calculation and experimental results agree with each other very well. This comparison indicates that the new modified PES corrects the large barrier height problem in Wang and Bowman's old PES.

Wang, Dunyou; Huo, Winifred M.

2007-10-21

209

Thermodynamics and quantum corrections from molecular dynamics for liquid water  

Microsoft Academic Search

This paper treats the first problem, how to quantum correct the classical mechanical thermodynamic values available from molecular dynamics, Monte Carlo, perturbation, or integral methods in order to compare with experimental quantum reality. A subsequent paper will focus on the second difficulty, the effective computation of free energy and entropy. A simple technique, derived from spectral analysis of the atomic

P. H. Berens; D. H. J. Mackay; G. M. White; K. R. Wilson

1982-01-01

210

ARTICLES Quantum-classical dynamics of nonadiabatic chemical reactions  

Microsoft Academic Search

A reactive flux correlation function formalism for the calculation of rate constants for mixed quantum-classical systems undergoing nonadiabatic dynamics is presented. The linear response formalism accounts for the stationarity of the equilibrium density under quantum-classical dynamics and expresses the rate constant in terms of an ensemble of surface-hopping trajectories. Calculations are carried out on a model two-level system coupled to

Alessandro Sergi; Raymond Kaprala

211

Non-equilibrium quantum dynamics of lattice vibrations  

NASA Astrophysics Data System (ADS)

The problem of the quantum description of the damping of a 1D chain of coupled oscillators with periodic boundary conditions in the Markovian regime is solved. The equations of motion of the normal modes are derived, and the evolution in time of their mean values and variances is explicitly studied. Furthermore, we investigate the effect of the diffusion and the friction on the dynamics of the chain. It is shown that when the off-diagonal elements of the diffusion and friction tensors are taken into account, the most notable contribution of these processes is observed in the mode in which all the oscillators undergo an in-phase vibration.

Hamdouni, Y.; Benrachi, F.

2013-09-01

212

Dynamic compressibility and aging in Wigner crystals and quantum glasses.  

PubMed

We study the nonequilibrium linear response of quantum elastic systems pinned by quenched disorder with Schwinger-Keldysh real-time techniques complemented by a mean-field variational approach. We find (i) a quasiequilibrium regime in which the analytic continuation from the imaginary-time replica results holds provided the marginality condition is enforced, and (ii) an aging regime. The conductivity and compressibility are computed. The latter is found to cross over from its dynamic to static value on a scale set by the waiting time after a quench, an effect which can be probed in experiments in, e.g., Wigner glasses. PMID:16803271

Cugliandolo, Leticia F; Giamarchi, Thierry; Doussal, Pierre Le

2006-06-01

213

The quantum transverse-field Ising chain in circuit quantum electrodynamics: effects of disorder on the nonequilibrium dynamics  

NASA Astrophysics Data System (ADS)

We study several dynamical properties of a recently proposed implementation of the quantum transverse-field Ising chain in the framework of circuit quantum electrodynamics (QED). Particular emphasis is placed on the effects of disorder on the nonequilibrium behavior of the system. We show that small amounts of fabrication-induced disorder in the system parameters do not jeopardize the observation of previously predicted phenomena. Based on a numerical extraction of the mean free path of a wave packet in the system, we also provide a simple quantitative estimate for certain disorder effects on the nonequilibrium dynamics of the circuit QED quantum simulator. We discuss the transition from weak to strong disorder, characterized by the onset of Anderson localization of the system's wave functions, and the qualitatively different dynamics it leads to.

Viehmann, Oliver; von Delft, Jan; Marquardt, Florian

2013-03-01

214

Communication: A six-dimensional state-to-state quantum dynamics study of the H + CH4 --> H2 + CH3 reaction (J = 0)  

NASA Astrophysics Data System (ADS)

We report a quantum state-to-state reaction dynamics study for the title reaction. The calculation was based on an approximation that we introduced to the eight-dimensional model for the X + YCZ3 --> XY + CZ3 type of reactions that restricts the non-reacting CZ3 group in C3V symmetry proposed by Palma and Clary [J. Chem. Phys. 112, 1859 (2000)], by assuming that the CZ3 group can rotate freely with respect to its C3V symmetry axis. With the CH bond length in group fixed at its equilibrium distance, the degree of freedom included in the calculation was reduced to six. Our calculation shows that the six-dimensional treatment can produce reaction probabilities essentially indistinguishable from the seven-dimensional (with CH bond length fixed in the original eight-dimensional model) results. The product vibrational/rotational state distributions and product energy partitioning information are presented for ground initial rovibrational state with the total angular momentum J = 0.

Liu, Shu; Chen, Jun; Zhang, Zhaojun; Zhang, Dong H.

2013-01-01

215

Numerically Exact Dynamics of Functional Quantum Systems - Applications to GaAs Quantum Dot Qubits and 2-DIMENSIONAL Spectra of Very Large Photosyntheitc Complexes  

NASA Astrophysics Data System (ADS)

Functional quantum systems is an emerging research field which includes quantum engineering (the design of technologies that make use of quantum mechanics to outperform their classical counterparts, such as quantum computers, quantum communication devices, quantum thermometers, quantum telescopes, etc.) and the study of natural processes where quantum mechanics provides some improvement that cannot be realized with classical mechanics (possible examples are photosynthesis, animal navigation, the sense of smell, etc.). Being able to predict how a quantum mechanical system changes (ie, how its density matrix changes), given its hamiltonian, is paramount in quantum engineering as one needs to know which hamiltonian will give the desired outcome. Likewise, being able to predict density matrix dynamics in natural systems can help in understanding the system's mechanism, in controlling the system's processes, and can be helpful if designing a technology which attempts to mimic a natural process. State of the art techniques for calculating density matrix dynamics of functional quantum systems in real-time, and with numerically exact accuracy, have been developed over the last year. These techniques will be presented, followed by applications for quantum dot based quantum computing, and for calculating the 2D spectra of large biological systems.

Dattani, Nikesh S.

2013-06-01

216

Quantum speed limit for non-Markovian dynamics.  

PubMed

We derive a Margolus-Levitin-type bound on the minimal evolution time of an arbitrarily driven open quantum system. We express this quantum speed limit time in terms of the operator norm of the nonunitary generator of the dynamics. We apply these results to the damped Jaynes-Cummings model and demonstrate that the corresponding bound is tight. We further show that non-Markovian effects can speed up quantum evolution and therefore lead to a smaller quantum speed limit time. PMID:23862985

Deffner, Sebastian; Lutz, Eric

2013-07-03

217

Modeling Quantum Spin Dynamics in an Ultracold Gas  

NASA Astrophysics Data System (ADS)

A recent experiment in our lab focuses on investigating spin dynamics in the quantum regime, where mean field approaches fail. Previous theoretical models for the quantum dynamical evolution of a spin-1 Bose-Einstein condensate do not include the effects of atomic loss that is unavoidable in experiment. Here, we present results of different loss models including a fully quantum calculation of this complicated many body system using a Monte-Carlo approach. We compare the results of these methods to recent experimental measurements and obtain good agreement.

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

2012-06-01

218

Quantum dynamics of an atom orbiting around an optical nanofiber  

NASA Astrophysics Data System (ADS)

We propose a platform for the investigation of quantum wave-packet dynamics, offering a complementary approach to existing theoretical models and experimental systems. It relies on laser-cooled neutral atoms which orbit around an optical nanofiber in an optical potential produced by a red-detuned guided light field. We show that the atomic center-of-mass motion exhibits genuine quantum effects like collapse and revival of the atomic wave packet. As distinctive advantages, our approach features a tunable dispersion relation as well as straightforward readout for the wave-packet dynamics and can be implemented using existing quantum optics techniques.

Le Kien, Fam; Hakuta, K.; Reitz, D.; Schneeweiss, P.; Rauschenbeutel, A.

2013-06-01

219

Experimental Characterization of Quantum Dynamics Through Many-Body Interactions  

NASA Astrophysics Data System (ADS)

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

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

2013-02-01

220

Accurate numerical verification of the instanton method for macroscopic quantum tunneling: Dynamics of phase slips  

SciTech Connect

We study the quantum dynamics of supercurrents of one-dimensional Bose gases in a ring optical lattice to verify instanton methods applied to coherent macroscopic quantum tunneling (MQT). We directly simulate the real-time quantum dynamics of supercurrents, where a coherent oscillation between two macroscopically distinct current states occurs due to MQT. The tunneling rate extracted from the coherent oscillation is compared with that given by the instanton method. We find that the instanton method is quantitatively accurate when the effective Planck's constant is sufficiently small. We also find phase slips associated with the oscillations.

Danshita, Ippei [Department of Physics, Boston University, Boston, Massachusetts 02215 (United States); Department of Physics, Faculty of Science, Tokyo University of Science, Shinjuku-ku, Tokyo 162-8601 (Japan); Polkovnikov, Anatoli [Department of Physics, Boston University, Boston, Massachusetts 02215 (United States)

2010-09-01

221

Frictionless quantum quenches in ultracold gases: A quantum-dynamical microscope  

SciTech Connect

In this Rapid Communication, a method is proposed to spatially scale up a trapped ultracold gas while conserving the quantum correlations of the initial many-body state. For systems supporting self-similar dynamics, this is achieved by implementing an engineered finite-time quench of the harmonic trap, which induces a frictionless expansion of the gas and acts as a quantum dynamical microscope.

Campo, A. de [Institut fuer Theoretische Physik, Leibniz Universitaet Hannover, Appelstrasse 2 D-30167, Hannover (Germany); Institut fuer Theoretische Physik, Albert-Einstein Allee 11, Universitaet Ulm, D-89069 Ulm (Germany)

2011-09-15

222

A dynamic watermarking scheme for quantum images using quantum wavelet transform  

NASA Astrophysics Data System (ADS)

In this paper, a novel watermarking scheme based on quantum wavelet transform (QWT) is proposed. Firstly, the wavelet coefficients are extracted by executing QWT on quantum image. Then, we utilize a dynamic vector for controlling embedding strength instead of a fixed parameter for embedding process in other schemes. Analysis and results show that the proposed dynamic watermarking scheme has better visual quality under a higher embedding capacity and outperforms the existing schemes in the literature.

Song, Xian-Hua; Wang, Shen; Liu, Shuai; Abd El-Latif, Ahmed A.; Niu, Xia-Mu

2013-08-01

223

Open quantum dynamics of single-photon optomechanical devices  

NASA Astrophysics Data System (ADS)

We study the quantum dynamics of a Michelson interferometer with Fabry-Perot cavity arms and one movable end mirror, and driven by a single photon—an optomechanical device previously studied by Marshall as a device that searches for gravity decoherence. We obtain an exact analytical solution for the system's quantum mechanical equations of motion, including details about the exchange of the single photon between the cavity mode and the external continuum. The resulting time evolution of the interferometer's fringe visibility displays interesting new features when the incoming photon's frequency uncertainty is narrower or comparable to the cavity's line width—only in the limiting case of much broader-band photon does the result return to that of Marshall , but in this case the photon is not very likely to enter the cavity and interact with the mirror, making the experiment less efficient and more susceptible to imperfections. In addition, we show that in the strong-coupling regime, by engineering the incoming photon's wave function, it is possible to prepare the movable mirror into an arbitrary quantum state of a multidimensional Hilbert space.

Hong, Ting; Yang, Huan; Miao, Haixing; Chen, Yanbei

2013-08-01

224

Quantum tunneling dynamics using hydrodynamic trajectories  

Microsoft Academic Search

In this paper we compute quantum trajectories arising from Bohm’s causal description of quantum mechanics. Our computational methodology is based upon a finite-element moving least-squares method (MWLS) presented recently by Wyatt and co-workers [Lopreore and Wyatt, Phys. Rev. Lett. 82, 5190 (1999)]. This method treats the “particles” in the quantum Hamilton–Jacobi equation as Lagrangian fluid elements that carry the phase,

Eric R. Bittner

2000-01-01

225

(Studies in quantum field theory)  

SciTech Connect

During the period 4/1/89--3/31/90 the theoretical physics group supported by Department of Energy Contract No. AC02-78ER04915.A015 and consisting of Professors Bender and Shrauner, Associate Professor Papanicolaou, Assistant Professor Ogilvie, and Senior Research Associate Visser has made progress in many areas of theoretical and mathematical physics. Professors Bender and Shrauner, Associate Professor Papanicolaou, Assistant Professor Ogilvie, and Research Associate Visser are currently conducting research in many areas of high energy theoretical and mathematical physics. These areas include: strong-coupling approximation; classical solutions of non-Abelian gauge theories; mean-field approximation in quantum field theory; path integral and coherent state representations in quantum field theory; lattice gauge calculations; the nature of perturbation theory in large order; quark condensation in QCD; chiral symmetry breaking; the 1/N expansion in quantum field theory; effective potential and action in quantum field theories, including OCD; studies of the early universe and inflation, and quantum gravity.

Not Available

1990-01-01

226

Bipartite entanglement induced by classically-constrained quantum dissipative dynamics  

NASA Astrophysics Data System (ADS)

The properties of some complex many body systems can be modeled by introducing in the dissipative dynamics of each single component a set of kinetic constraints that depend on the state of the neighbor systems. Here, we characterize this kind of dynamics for two quantum systems whose independent dissipative evolutions are defined by a Lindblad equation. The constraints are introduced through a set of projectors that restrict the action of each single dissipative Lindblad channel to the state of the other system. Conditions that guarantee a classical interpretation of the kinetic constraints are found. The generation and evolution of entanglement is studied for two optical qubits systems. Classically constrained dissipation leads to a stationary state whose degree of entanglement depends on the initial state. Nevertheless, independently of the initial conditions, a maximal entangled state is generated when both systems are subjected to the action of local Hamiltonian fields that do not commutate with the constraints. The underlying physical mechanism is analyzed in detail.

Budini, Adrián A.

2013-10-01

227

Quantum molecular dynamics simulations of hydrogen production and solar cells  

NASA Astrophysics Data System (ADS)

The global energy crisis presents two major challenges for scientists around the world: Producing cleaner energy which is sustainable for the environment; And improving the efficiency of energy production as well as consumption. It is crucial and yet elusive to understand the atomistic mechanisms and electronic properties, which are needed in order to tackle those challenges. Quantum molecular dynamics simulations and nonadiabatic quantum molecular dynamics are two of the dominant methods used to address the atomistic and electronic properties in various energy studies. This dissertation is an ensemble of three studies in energy research: (1) Hydrogen production from the reaction of aluminum clusters with water to provide a renewable energy cycle; (2) The photo-excited charge transfer and recombination at a quaterthiophene/zinc oxide interface to improve the power conversion efficiency of hybrid poly(3-hexylthiophene) (P3HT) /ZnO solar cells; and (3) the charge transfer at a rubrene/C60 interface to understand why phenyl groups in rubrene improve the performance of rubrene/C60 solar cells.

Mou, Weiwei

228

Relative Unitary Implementability of Perturbed Quantum Field Dynamics on de-Sitter Space  

NASA Astrophysics Data System (ADS)

In this article, we study the quantum dynamics of a Klein-Gordon field on de-Sitter space. We prove time evolution is not unitarily implementable. We also consider a Klein-Gordon field perturbed by a local potential V. In this case we prove that the deviation from the V=0 dynamics is unitarily implementable.

Poon, Gary

2009-01-01

229

Relative unitary implementability of perturbed quantum field dynamics on de Sitter space  

SciTech Connect

We study the quantum dynamics of a Klein-Gordon field on de Sitter space based on the Euclidean vacuum. We prove time evolution is not unitarily implementable. We also consider a Klein-Gordon field perturbed by a local potential V. In this case we prove that the deviation from the V=0 dynamics is unitarily implementable.

Poon, Gary Kaiman [Department of Physics, SUNY at Buffalo, Amherst, New York 14260 (United States)

2010-04-15

230

Lindblad- and non-Lindblad-type dynamics of a quantum Brownian particle  

SciTech Connect

The dynamics of a typical open quantum system, namely a quantum Brownian particle in a harmonic potential, is studied focusing on its non-Markovian regime. Both an analytic approach and a stochastic wave-function approach are used to describe the exact time evolution of the system. The border between two very different dynamical regimes, the Lindblad and non-Lindblad regimes, is identified and the relevant physical variables governing the passage from one regime to the other are singled out. The non-Markovian short-time dynamics is studied in detail by looking at the mean energy, the squeezing, the Mandel parameter, and the Wigner function of the system.

Maniscalco, S. [School of Pure and Applied Physics, University of KwaZulu-Natal, Durban 4041 (South Africa); INFM, MIUR and Dipartimento di Scienze Fisiche ed Astronomiche dell'Universita di Palermo, via Archirafi 36, 90123 Palermo (Italy); Piilo, J. [School of Pure and Applied Physics, University of KwaZulu-Natal, Durban 4041 (South Africa); Department of Physics, University of Turku, FIN-20014 Turun yliopisto (Finland); Helsinki Institute of Physics, PL 64, FIN-00014 Helsingin yliopisto (Finland); Intravaia, F. [Laboratoire Kastler Brossel, Ecole Normale Superieure, Centre National de la Recherche Scientifique, Universite Pierre et Marie Curie, Case 74, 4 place Jussieu, F-75252 Paris (France); Petruccione, F. [School of Pure and Applied Physics, University of KwaZulu-Natal, Durban 4041 (South Africa); Messina, A. [INFM, MIUR and Dipartimento di Scienze Fisiche ed Astronomiche dell'Universita di Palermo, via Archirafi 36, 90123 Palermo (Italy)

2004-09-01

231

Quantum chemistry and molecular dynamics studies of the entropic elasticity of localized molecular kinks in polyisoprene chains  

NASA Astrophysics Data System (ADS)

We investigate the thermodynamic consequences of the distribution of rotational conformations of polyisoprene on the elastic response of a network chain. In contrast to the classical theory of rubber elasticity, which associates the elastic force with the distribution of end-to-end distances, we find that the distribution of chain contour lengths provides a simple mechanism for an elastic force. Entropic force constants were determined for small contour length extensions of chains constructed as a series of localized kinks, with each kink containing between one and five cis-1,4-isoprene units. The probability distributions for the kink end-to-end distances were computed by two methods: (1) by constructing a Boltzmann distribution from the lengths corresponding to the minimum energy dihedral rotational conformations, obtained by optimizing isoprene using first principles density functional theory, and (2) by sampling the trajectories of molecular dynamics simulations of an isolated molecule composed of five isoprene units. Analogous to the well-known tube model of elasticity, we make the assumption that, for small strains, the chain is constrained by its surrounding tube, and can only move, by a process of reptation, along the primitive path of the contour. Assuming that the chain entropy is Boltzmann's constant times the logarithm of the contour length distribution, we compute the tensile force constants for chain contour length extension as the change in entropy times the temperature. For a chain length typical of moderately crosslinked rubber networks (78 isoprene units), the force constants range between 0.004 and 0.033 N/m, depending on the kink size. For a cross-linked network, these force constants predict an initial tensile modulus of between 3 and 8 MPa, which is comparable to the experimental value of 1 MPa. This mechanism is also consistent with other thermodynamic phenomenology.

Hanson, David E.; Martin, Richard L.

2010-08-01

232

Ab initio-driven trajectory-based nuclear quantum dynamics in phase space  

NASA Astrophysics Data System (ADS)

We derive a Bohmian trajectory-based quantum dynamics approach for the calculation of adiabatic and nonadiabatic quantum effects in ab initio on-the-fly molecular dynamics simulations. The method is designed for calculations in the full, unconstrained, phase space of molecular systems described within density functional theory and time-dependent density functional theory. The problem of solving quantum hydrodynamic equations using trajectories in high dimensions is addressed using an expansion of the nuclear amplitude in atom centered Gaussians that are propagated along the quantum trajectories. In this work, we investigate the adiabatic limit of this theory, even though the full nonadiabatic case is derived. The method is first tested on the H2 molecule and then applied to the study of the proton transfer dynamics in the phase space of the molecular complex (H3N-H-NH3)+.

Tavernelli, Ivano

2013-04-01

233

Dynamic control of coherent pulses via Fano-type interference in asymmetric double quantum wells  

SciTech Connect

We study the temporal and spatial dynamics of two light pulses, a probe and a switch, propagating through an asymmetric double quantum well where tunneling-induced quantum interference may be observed. When such an interference takes place, in the absence of the switch, the quantum well is transparent to the probe which propagates over sufficiently long distances at very small group velocities. In the presence of a relatively strong switch, however, the probe pulse is absorbed due to the quenching of tunneling-induced quantum interference. The probe may be made to vanish even when switch and probe are somewhat delayed with respect to one another. Conversely, our asymmetric double quantum well may be rendered either opaque or transparent to the switch pulse. Such a probe-switch 'reciprocity' can be used to devise a versatile all-optical quantum interference-based solid-state switch for optical communication devices.

Wu Jinhui; Gao Jinyue [College of Physics, Jilin University, Changchun 130023 (China); Key Laboratory of Coherent Light and Atomic and Molecular Spectroscopy of Ministry of Education, Changchun 130023 (China); Xu Jihua; Silvestri, L.; La Rocca, G. C.; Bassani, F. [Scuola Normale Superiore and INFM, Piazza dei Cavalieri 7, 56126 Pisa (Italy); Artoni, M. [Department of Physics and Chemistry of Materials, Brescia University and LENS, Via Valotti 9, 25133 Brescia (Italy)

2006-05-15

234

Acceleration of adiabatic quantum dynamics in electromagnetic fields  

SciTech Connect

We show a method to accelerate quantum adiabatic dynamics of wave functions under electromagnetic field (EMF) by developing the preceding theory [Masuda and Nakamura, Proc. R. Soc. London Ser. A 466, 1135 (2010)]. Treating the orbital dynamics of a charged particle in EMF, we derive the driving field which accelerates quantum adiabatic dynamics in order to obtain the final adiabatic states in any desired short time. The scheme is consolidated by describing a way to overcome possible singularities in both the additional phase and driving potential due to nodes proper to wave functions under EMF. As explicit examples, we exhibit the fast forward of adiabatic squeezing and transport of excited Landau states with nonzero angular momentum, obtaining the result consistent with the transitionless quantum driving applied to the orbital dynamics in EMF.

Masuda, Shumpei [Department of Physics, Tohoku University, Sendai 980 (Japan); Nakamura, Katsuhiro [Faculty of Physics, National University of Uzbekistan, Vuzgorodok, Tashkent 100174 (Uzbekistan); Department of Applied Physics, Osaka City University, Sumiyoshi-ku, Osaka 558-8585 (Japan)

2011-10-15

235

Acceleration of adiabatic quantum dynamics in electromagnetic fields  

NASA Astrophysics Data System (ADS)

We show a method to accelerate quantum adiabatic dynamics of wave functions under electromagnetic field (EMF) by developing the preceding theory [Masuda and Nakamura, Proc. R. Soc. London Ser. APLRAAN1364-502110.1098/rspa.2009.0446 466, 1135 (2010)]. Treating the orbital dynamics of a charged particle in EMF, we derive the driving field which accelerates quantum adiabatic dynamics in order to obtain the final adiabatic states in any desired short time. The scheme is consolidated by describing a way to overcome possible singularities in both the additional phase and driving potential due to nodes proper to wave functions under EMF. As explicit examples, we exhibit the fast forward of adiabatic squeezing and transport of excited Landau states with nonzero angular momentum, obtaining the result consistent with the transitionless quantum driving applied to the orbital dynamics in EMF.

Masuda, Shumpei; Nakamura, Katsuhiro

2011-10-01

236

Quantum dynamics in the bosonic Josephson junction  

SciTech Connect

We employ a semiclassical picture to study dynamics in a bosonic Josephson junction with various initial conditions. Phase diffusion of coherent preparations in the Josephson regime is shown to depend on the initial relative phase between the two condensates. For initially incoherent condensates, we find a universal value for the buildup of coherence in the Josephson regime. In addition, we contrast two seemingly similar on-separatrix coherent preparations, finding striking differences in their convergence to classicality as the number of particles increases.

Chuchem, Maya; Cohen, Doron [Department of Physics, Ben-Gurion University of the Negev, P.O.B. 653, Beer-Sheva 84105 (Israel); Smith-Mannschott, Katrina [Department of Physics, Wesleyan University, Middletown, Connecticut 06459 (United States); MPI for Dynamics and Self-Organization, Bunsenstrasse 10, D-37073 Goettingen (Germany); Hiller, Moritz [Physikalisches Institut, Albert-Ludwigs-Universitaet, Hermann-Herder-Strasse 3, D-79104 Freiburg (Germany); Kottos, Tsampikos [Department of Physics, Wesleyan University, Middletown, Connecticut 06459 (United States); Vardi, Amichay [Department of Chemistry, Ben-Gurion University of the Negev, P.O.B. 653, Beer-Sheva 84105 (Israel); Institute for Theoretical Atomic, Molecular and Optical Physics, Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts 02138 (United States)

2010-11-15

237

Optimal dynamics for quantum-state and entanglement transfer through homogeneous quantum systems  

SciTech Connect

The capability of faithfully transmit quantum states and entanglement through quantum channels is one of the key requirements for the development of quantum devices. Different solutions have been proposed to accomplish such a challenging task, which, however, require either an ad hoc engineering of the internal interactions of the physical system acting as the channel or specific initialization procedures. Here we show that optimal dynamics for efficient quantum-state and entanglement transfer can be attained in generic quantum systems with homogeneous interactions by tuning the coupling between the system and the two attached qubits. We devise a general procedure to determine the optimal coupling, and we explicitly implement it in the case of a channel consisting of a spin-(1/2)XY chain. The quality of quantum-state and entanglement transfer is found to be very good and, remarkably, almost independent of the channel length.

Banchi, L. [Dipartimento di Fisica e Astronomia, Universita di Firenze, via G. Sansone 1, I-50019 Sesto Fiorentino (Italy); Apollaro, T. J. G. [Dipartimento di Fisica e Astronomia, Universita di Firenze, via G. Sansone 1, I-50019 Sesto Fiorentino (Italy); Istituto dei Sistemi Complessi, C.N.R., via Madonna del Piano 10, I-50019 Sesto Fiorentino (Italy); Cuccoli, A. [Dipartimento di Fisica e Astronomia, Universita di Firenze, via G. Sansone 1, I-50019 Sesto Fiorentino (Italy); INFN, Sezione di Firenze, via G. Sansone 1, I-50019 Sesto Fiorentino (Italy); Vaia, R. [Istituto dei Sistemi Complessi, C.N.R., via Madonna del Piano 10, I-50019 Sesto Fiorentino (Italy); Verrucchi, P. [Istituto dei Sistemi Complessi, C.N.R., via Madonna del Piano 10, I-50019 Sesto Fiorentino (Italy); Dipartimento di Fisica e Astronomia, Universita di Firenze, via G. Sansone 1, I-50019 Sesto Fiorentino (Italy); INFN, Sezione di Firenze, via G. Sansone 1, I-50019 Sesto Fiorentino (Italy)

2010-11-15

238

Josephson bifurcation amplifier: Amplifying quantum signals using a dynamical bifurcation  

NASA Astrophysics Data System (ADS)

Quantum measurements of solid-state systems, such as the readout of superconducting quantum bits challenge conventional low-noise amplification techniques. Ideally, the amplifier for a quantum measurement should minimally perturb the measured system while maintaining sufficient sensitivity to overcome the noise of subsequent elements in the amplification chain. Additionally, the drift of materials properties in solid-state systems mandates a fast acquisition rate to permit measurements in rapid succession. In this thesis, we describe the Josephson Bifurcation Amplifier (JBA) which was developed to meet these requirements. The JBA exploits the sensitivity of a dynamical system - a non-linear oscillator tuned near a bifurcation point. In this new scheme, all available degrees of freedom in the dynamical system participate in information transfer and none contribute to unnecessary dissipation resulting in excess noise. We have used a superconducting tunnel junction, also known as a Josephson junction to construct our non-linear oscillator. The Josephson junction is the only electronic circuit element which remains non-linear and non-dissipative at arbitrarily low temperatures. This thesis will describe the theory and experiments demonstrating bifurcation amplification in the JBA and its application to the measurement of superconducting quantum bits. By describing the JBA as a parametrically driven oscillator, we will demonstrate that the ultimate sensitivity of the JBA is limited only by quantum fluctuations. Using this treatment, we will identify the connection between the four main aspects of working with a dynamical bifurcation: parametric amplification, squeezing, quantum activation and the Dynamical Casimir Effect.

Vijayaraghavan, Rajamani

239

Nanoscale quantum dynamics and electrostatic coupling  

NASA Astrophysics Data System (ADS)

Physical nanoscale systems have been analyzed both from an electrostatic point of view and quantum mechanically with respect to quantum computation. We introduce an elaborate code for the efficient numerical simulation of nanoscale electrostatics via a higher-order relaxation algorithm with a large variety of boundary conditions which then is applied to a set of physically relevant problems. Great emphasis is put on screening effects as well as capacitive coupling between spatially separated conducting regions. Specifically, we analyze the depletion of a two-dimensional electron gas using different methods. The effect of surface charges due to the pinning of the Fermi level at a semiconductor surface is shown to play an important role in that it can shift the whole system characteristics, underlining the importance of chemical potentials and work functions. The capacitive coupling is further used to model the interactions in an interacting network of quantum dots, and the use of the capacitance formalism in the quantum mechanical context is explicitly justified. Quantum dot arrays are then analyzed on a general footing with respect to quantum computation and charge qubits based on an extended Hubbard Hamiltonian model. For systems with at most two operative electrons, general restrictions apply, introducing certain constraints on what realizations of this type of charge qubit may eventually look like. Furthermore, the interaction of the macroscopic world with the quantum dot network via quantum gates is discussed. Again, general arguments allow us to rule out certain scenarios of quantum gates. For example it turns out that capacitive coupling alone is not sufficient for full single qubit operation. Alternative ways are discussed, and finally, by using an external magnetic field and its resulting Aharonov-Bohm phases on the array, full single qubit operation based on charge is demonstrated.

Weichselbaum, Andreas

240

Quantum dynamics of two-spin-qubit systems.  

PubMed

The aim of this topical review is a systematic and concise presentation of the results of a series of theoretical works on the quantum dynamics of two-spin-qubit systems towards the elaboration of a physical mechanism of the quantum information transfer between two spin-qubits. For this purpose the main attention is paid to exactly solvable models of two-spin-qubit systems, since the analytical expressions of the elements of their reduced density matrices explicitly exhibit the mutual dependence of the quantum information encoded into the spin-qubits. The treatment of their decoherence due to the interaction with the environment is performed in the Markovian approximation. Rate equations for axially symmetric systems of two coupled spin-qubits non-interacting, as well as interacting, with the environment are exactly solved. It is shown how the solutions of rate equations demonstrate the physical mechanism of the quantum information exchange between the spin-qubits. This mechanism holds also in all two-spin-qubit systems whose rate equations can be solved only by means of numerical calculations. Exact solutions of rate equations for two uncoupled spin-qubits interacting with two separate environments reveal an interesting physical phenomenon in the time evolution of the qubit-qubit entanglement generated by their interaction with the environments: the entanglement sudden death and revival. A two-spin-qubit system with an asymptotically decoherence free subspace was also explicitly constructed. The presented calculations and reasonings can be extended for application to the study of spin-qubit chains or networks. PMID:21828484

Nguyen, Van Hieu

2009-06-12

241

Carrier dynamics in quantum dot and gallium arsenide-based quantum dot cascade laser  

Microsoft Academic Search

Self-organized quantum dots provide unique atomic-like density of states and have important applications in semiconductor lasers. Energy relaxation of charge carriers in quantum dots is important for understanding the physics of devices fabricated from these artificially structured materials. Because the charge carriers relax through discrete energy levels, quantum dots provide a means to study the charge carrier interactions in the

Chuanshun Cao

2004-01-01

242

Quantum Mechanical Modeling and Molecular Dynamic Simulation of Ruthenium (Ru) Polypyridyl Complexes to Study Feasibility of Artificial Photosynthesis  

Microsoft Academic Search

A photochemical reaction is initiated by a charge separation process in the reaction center (RC) complex. Major research in this regard is to analyze the light driven electron transfer and to study the response of the molecule in which the RC is embedded, stabilizing the charge separation process in photosynthesis. In research related to artificial photosynthesis, modeling and simulation of

P. Premkumar; P. K. Krishnan Namboori; M. Sathishkumar; K. I. Ramachandran; Deepa Gopakumar; P. M. Rajasree

2009-01-01

243

Quantum nuclear dynamics in the photophysics of diamondoids.  

PubMed

The unusual electronic properties of diamondoids, the nanoscale relatives of diamond, make them attractive for applications ranging from drug delivery to field emission displays. Identifying the fundamental origin of these properties has proven highly challenging, with even the most advanced quantum many-body calculations unable to reproduce measurements of a quantity as ubiquitous as the optical gap. Here, by combining first-principles calculations and Importance Sampling Monte Carlo methods, we show that the quantum dynamics of carbon nuclei is key to understanding the electronic and optical properties of diamondoids. Quantum nuclear effects dramatically modify the absorption lineshapes and renormalize the optical gaps. These findings allow us to formulate a complete theory of optical absorption in diamondoids, and establish the universal role of quantum nuclear dynamics in nanodiamond across the length scales. PMID:23756460

Patrick, Christopher E; Giustino, Feliciano

2013-01-01

244

Fermi-surface collapse and dynamical scaling near a quantum-critical point  

PubMed Central

Quantum criticality arises when a macroscopic phase of matter undergoes a continuous transformation at zero temperature. While the collective fluctuations at quantum-critical points are being increasingly recognized as playing an important role in a wide range of quantum materials, the nature of the underlying quantum-critical excitations remains poorly understood. Here we report in-depth measurements of the Hall effect in the heavy-fermion metal YbRh2Si2, a prototypical system for quantum criticality. We isolate a rapid crossover of the isothermal Hall coefficient clearly connected to the quantum-critical point from a smooth background contribution; the latter exists away from the quantum-critical point and is detectable through our studies only over a wide range of magnetic field. Importantly, the width of the critical crossover is proportional to temperature, which violates the predictions of conventional theory and is instead consistent with an energy over temperature, E/T, scaling of the quantum-critical single-electron fluctuation spectrum. Our results provide evidence that the quantum-dynamical scaling and a critical Kondo breakdown simultaneously operate in the same material. Correspondingly, we infer that macroscopic scale-invariant fluctuations emerge from the microscopic many-body excitations associated with a collapsing Fermi-surface. This insight is expected to be relevant to the unconventional finite-temperature behavior in a broad range of strongly correlated quantum systems.

Friedemann, Sven; Oeschler, Niels; Wirth, Steffen; Krellner, Cornelius; Geibel, Christoph; Steglich, Frank; Paschen, Silke; Kirchner, Stefan; Si, Qimiao

2010-01-01

245

Efficient Measurement of Quantum Dynamics via Compressive Sensing  

NASA Astrophysics Data System (ADS)

The resources required to characterize the dynamics of engineered quantum systems—such as quantum computers and quantum sensors—grow exponentially with system size. Here we adapt techniques from compressive sensing to exponentially reduce the experimental configurations required for quantum process tomography. Our method is applicable to processes that are nearly sparse in a certain basis and can be implemented using only single-body preparations and measurements. We perform efficient, high-fidelity estimation of process matrices of a photonic two-qubit logic gate. The database is obtained under various decoherence strengths. Our technique is both accurate and noise robust, thus removing a key roadblock to the development and scaling of quantum technologies.

Shabani, A.; Kosut, R. L.; Mohseni, M.; Rabitz, H.; Broome, M. A.; Almeida, M. P.; Fedrizzi, A.; White, A. G.

2011-03-01

246

Mode specificity in the H + H2O --> H2 + OH reaction: A full-dimensional quantum dynamics study  

NASA Astrophysics Data System (ADS)

The initial state-selected time-dependent wave packet approach to an atom-triatom reaction is employed to study the H + H2O --> H2 + OH reaction without the centrifugal sudden approximation. The total reaction probabilities and integral cross sections, which are the exact coupled-channel results, are calculated for the H2O reactant initially in the ground and several vibrationally excited states, including bending excited states, first and second stretching excited states, and simultaneous excitations of both bending and stretching modes. The reactivity enhancements from different initial states of the H2O reagent are presented and discussed in detail. The thermal rate constant for the title reaction and the contributions to this coefficient from individual vibrational states of H2O are also obtained and compared with the previous theoretical and experimental data.

Fu, Bina; Zhang, Dong H.

2013-05-01

247

The quantum correlation dynamics of two qubits in finite-temperature environments with dynamical decoupling pulses  

NASA Astrophysics Data System (ADS)

We investigate the dynamics of quantum correlation between two noninteracting qubits each inserted in its own finite-temperature environment with 1/f spectral density. It is found that the phenomenon of sudden transition between classical and quantum decoherence exists in the system when two qubits are initially prepared in X-type quantum states, and the transition time depends on the initial-state of two qubits, the qubit-environment coupling constant and the temperature of the environment. Furthermore, we explore the influence of dynamical decoupling pulses on the transition time and show that it can be prolonged by applying the dynamical decoupling pulses.

He, Qi-Liang; Xu, Jing-Bo; Yao, Dao-Xin; Zhang, Ye-Qi

2013-07-01

248

Self-consistent magnetization dynamics of a ferromagnetic quantum dot driven by a spin bias  

NASA Astrophysics Data System (ADS)

We present an iterative scheme which combines the non-equilibrium Green's function (NEGF) for evaluating the quantum spin transport in a ferromagnetic quantum dot device and the Landau-Lifshitz (LL) equation for modeling the magnetization dynamics of the dot. For a given initial magnetization, the spin polarization of current and the resulting spin torque in the dot are calculated using the NEGF formalism. The torque acts on the magnetic moment of the dot, and the resultant magnetization dynamics is obtained from the LL equation. The new value of the dot's magnetization is then used as an input for the next round of NEGF calculation, and the whole process is repeated iteratively. The spin torque is thus calculated self-consistently with the dynamics of the magnetic moment of the dot. We apply this self-consistent iterative scheme to study the magnetization dynamics in an exemplary quantum dot system with an induced spin bias in the leads under varying damping conditions.

Siu, Z. B.; Jalil, M. B. A.; Tan, S. G.

2012-04-01

249

Photonic reagent control of dynamically homologous quantum systems  

SciTech Connect

The general objective of quantum control is the manipulation of atomic scale physical and chemical phenomena through the application of external control fields. These tailored fields, or photonic reagents, exhibit systematic properties analogous to those of ordinary laboratory reagents. This analogous behavior is explored further here by considering the controlled response of a family of homologous quantum systems to a single common photonic reagent. A level set of dynamically homologous quantum systems is defined as the family that produces the same value(s) for a target physical observable(s) when controlled by a common photonic reagent. This paper investigates the scope of homologous quantum system control using the level set exploration technique (L-SET). L-SET enables the identification of continuous families of dynamically homologous quantum systems. Each quantum system is specified by a point in a hypercube whose edges are labeled by Hamiltonian matrix elements. Numerical examples are presented with simple finite level systems to illustrate the L-SET concepts. Both connected and disconnected families of dynamically homologous systems are shown to exist.

Beltrani, Vincent; Dominy, Jason; Ho, Tak-San; Rabitz, Herschel [Department of Chemistry, Frick Laboratory, Princeton University, Princeton, New Jersey 08544 (United States); Program in Applied and Computational Mathematics, Princeton University, Princeton, New Jersey 08544 (United States); Department of Chemistry, Frick Laboratory, Princeton University, Princeton, New Jersey 08544 (United States)

2007-03-07

250

Bohmian dynamics on subspaces using linearized quantum force.  

PubMed

In the de Broglie-Bohm formulation of quantum mechanics the time-dependent Schrodinger equation is solved in terms of quantum trajectories evolving under the influence of quantum and classical potentials. For a practical implementation that scales favorably with system size and is accurate for semiclassical systems, we use approximate quantum potentials. Recently, we have shown that optimization of the nonclassical component of the momentum operator in terms of fitting functions leads to the energy-conserving approximate quantum potential. In particular, linear fitting functions give the exact time evolution of a Gaussian wave packet in a locally quadratic potential and can describe the dominant quantum-mechanical effects in the semiclassical scattering problems of nuclear dynamics. In this paper we formulate the Bohmian dynamics on subspaces and define the energy-conserving approximate quantum potential in terms of optimized nonclassical momentum, extended to include the domain boundary functions. This generalization allows a better description of the non-Gaussian wave packets and general potentials in terms of simple fitting functions. The optimization is performed independently for each domain and each dimension. For linear fitting functions optimal parameters are expressed in terms of the first and second moments of the trajectory distribution. Examples are given for one-dimensional anharmonic systems and for the collinear hydrogen exchange reaction. PMID:15267580

Rassolov, Vitaly A; Garashchuk, Sophya

2004-04-15

251

Quantum and semiclassical study of magnetic quantum dots  

NASA Astrophysics Data System (ADS)

We study the energy level structure of two-dimensional charged particles in a circular quantum dot in inhomogeneous magnetic fields. In this system, the magnetic field is zero inside the dot and constant outside. Such a device can be fabricated with present-day technology. We present detailed semiclassical studies of such magnetic quantum dot systems and provide a comparison with exact quantum calculations. In the semiclassical approach we apply the Berry-Tabor formula for the density of states and the Borh-Sommerfeld quantization rules. In both cases we found good agreement with the exact spectrum in the weak magnetic field limit. The energy spectrum for a given missing flux quantum is classified in six possible classes of orbits and summarized in a so-called phase diagram. We also investigate the current flow patterns of different quantum states and show a clear correspondence with classical trajectories.

Kocsis, Bence; Palla, Gergely; Cserti, József

2005-02-01

252

Quantum dynamic behaviour in a coupled cavities system  

NASA Astrophysics Data System (ADS)

The dynamic behaviour of the two-site coupled cavities model which is doped with ta wo-level system is investigated. The exact dynamic solutions in the general condition are obtained via Laplace transform. The simple analytical solutions are obtained in several particular cases, which demonstrate the clear and simple physical picture for the quantum state transition of the system. In the large detuning or hoppling case, the quantum states transferring between qubits follow a slow periodic oscillation induced by the very weak excitation of the cavity mode. In the large coupling case, the system can be interpreted as two Jaynes-Cummings model subsystems which interact through photon hop between the two cavities. In the case of ? ? ? ? g, the quantum states transition of qubits is accompanied by the excitation of the cavity, and the cavity modes have the same dynamic behaviours and the amplitude of probability is equal to 0.25 which does not change with the variation of parameter.

Peng, Jun; Wu, Yun-Wen; Li, Xiao-Juan

2012-06-01

253

Noise-resilient quantum evolution steered by dynamical decoupling.  

PubMed

Realistic quantum computing is subject to noise. Therefore, an important frontier in quantum computing is to implement noise-resilient quantum control over qubits. At the same time, dynamical decoupling can protect the coherence of qubits. Here we demonstrate non-trivial quantum evolution steered by dynamical decoupling control, which simultaneously suppresses noise effects. We design and implement a self-protected controlled-NOT gate on the electron spin of a nitrogen-vacancy centre and a nearby carbon-13 nuclear spin in diamond at room temperature, by employing an engineered dynamical decoupling control on the electron spin. Final state fidelity of 0.91(1) is observed in preparation of a Bell state using the gate. At the same time, the qubit coherence time is elongated at least 30 fold. The design scheme does not require the dynamical decoupling control to commute with the qubit interaction and therefore works for general qubit systems. This work marks a step towards implementing realistic quantum computing systems. PMID:23912335

Liu, Gang-Qin; Po, Hoi Chun; Du, Jiangfeng; Liu, Ren-Bao; Pan, Xin-Yu

2013-01-01

254

Quantum Gravity from Simplices: Analytical Investigations of Causal Dynamical Triangulations  

NASA Astrophysics Data System (ADS)

A potentially powerful approach to quantum gravity has been developed over the last few years under the name of Causal Dynamical Triangulations. Numerical simulations have given very interesting results in the cases of two, three and four spacetime dimension. The aim of this thesis is to give an introduction to the subject (Chapter 1), and try to push the analytical understanding of these models further. This is done by first studying (Chapter 2) the case of a (1+1)-dimensional spacetime coupled to matter, in the form of an Ising model, by means of high- and low-temperature expansions. And after (Chapter 3) by studying a specific model in (2+1) dimensions, whose solution and continuum limit are presented.

Benedetti, Dario

2007-07-01

255

Studies in quantum geometry  

NASA Astrophysics Data System (ADS)

The geometric defects associated with open strings have become a mainstay in the arsenal of the string theorist. These objects are intimately tied to the properties of spacetime. D-branes have been well studied in the nineties and orientifolds are only now been thoroughly investigated. This thesis is built on two different studies. The first, done with Koenraad Schalm and Chuck Doran attempts to analyze the possible Orientifolds and their moduli, starting from Gepner models of the spacetime. The main focus was on elliptical compactifications, as this could be used as building block for more complex geometries. It is noteworthy that the orientifolds place constraints on the possible spacetime geometries, whilst also being characterized by the geometrical nature of the involutions defining them. The second study of this thesis, which was done with Frederik Denef, is on the low energy manifestations of D-branes as supergravity attractor solutions. Four dimensional N = 2 supergravity has regular, stationary, asymptotically flat BPS solutions with intrinsic angular momentum, describing bound states of separate extremal black holes with mutually nonlocal charges. Though the existence and some properties of these solutions were established some time ago, fully explicit analytic solutions were lacking thus far. In this study this gap is filled. We found that in general explicit solutions can be constructed whenever an explicit formula is known in the theory at hand for the Bekenstein-Hawking entropy of a single black hole as a function of its charges, and illustrated this with some simple examples. We also found an example of moduli-dependent black hole entropy.

Bates, Brandon D.

256

Real-time path integrals for quantum dots: Quantum dissipative dynamics with superohmic environment coupling  

NASA Astrophysics Data System (ADS)

Based on a representation of the functional integral as the time evolution of the augmented density matrix we have worked out an implementation of the real-time path integral approach that is applicable to the dynamics of quantum dissipative systems with superohmic coupling to the environment. As a prototype for such a system we consider a laser-driven strongly confined semiconductor quantum dot coupled to acoustic phonons. First applications of this approach to quantum dot systems have already been published. Here, we provide a detailed description of the implementation, including a discussion of numerical issues and extend the formalism from two-level quantum dot models with a pure-dephasing type carrier-phonon coupling to the case of multiple electronic levels. The method allows for numerically exact calculations of the dot dynamics at strong dot-phonon and dot-laser coupling and at long times, usually inaccessible by other approaches.

Vagov, A.; Croitoru, M. D.; Glässl, M.; Axt, V. M.; Kuhn, T.

2011-03-01

257

Quantum Quenches and Off-Equilibrium Dynamical Transition in the Infinite-Dimensional Bose-Hubbard Model  

SciTech Connect

We study the off-equilibrium dynamics of the infinite-dimensional Bose-Hubbard model after a quantum quench. The dynamics can be analyzed exactly by mapping it to an effective Newtonian evolution. For integer filling, we find a dynamical transition separating regimes of small and large quantum quenches starting from the superfluid state. This transition is very similar to the one found for the fermionic Hubbard model by mean field approximations.

Sciolla, Bruno; Biroli, Giulio [Institut de Physique Theorique, CEA/DSM/IPhT-CNRS/URA 2306 CEA-Saclay, F-91191 Gif-sur-Yvette (France)

2010-11-26

258

Dynamic Stabilization of a Quantum Many-Body Spin System  

NASA Astrophysics Data System (ADS)

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

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

2013-08-01

259

Nonlinearity from quantum mechanics: Dynamically unstable Bose-Einstein condensate in a double-well trap  

SciTech Connect

We study theoretically an atomic Bose-Einstein condensate in a double-well trap, both quantum-mechanically and classically, under conditions such that in the classical model an unstable equilibrium dissolves into large-scale oscillations of the atoms between the potential wells. Quantum mechanics alone does not exhibit such nonlinear dynamics, but measurements of the atom numbers in the potential wells may nevertheless cause the condensate to behave essentially classically.

Javanainen, Juha [Department of Physics, University of Connecticut, Storrs, Connecticut 06269-3046 (United States)

2010-05-15

260

Eulerian and Newtonian dynamics of quantum particles  

NASA Astrophysics Data System (ADS)

We derive the classical equations of hydrodynamics (the Euler and continuity equations), from which the Schrödinger equation follows as a limit case. It is shown that the statistical ensemble corresponding to a quantum system and described by the Schrödinger equation can be considered an inviscid gas that obeys the ideal gas law with a quickly oscillating sign-alternating temperature. This statistical ensemble performs the complex movements consisting of smooth average movement and fast oscillations. It is shown that the average movements of the statistical ensemble are described by the Schrödinger equation. A model of quantum motion within the limits of classical mechanics that corresponds to the hydrodynamic system considered is suggested.

Rashkovskiy, S. A.

2013-06-01

261

Quantum Optical Studies of Semiconductors.  

National Technical Information Service (NTIS)

There have been two primary objectives during the current program: (1) The development and application of nonlinear laser spectroscopy to the study of excitation dynamics near the band edge of semiconductor heterostructures; (2) The understanding of pump ...

D. G. Steel

1996-01-01

262

Simulation of Quantum Dynamics Based on the Quantum Stochastic Differential Equation  

PubMed Central

The quantum stochastic differential equation derived from the Lindblad form quantum master equation is investigated. The general formulation in terms of environment operators representing the quantum state diffusion is given. The numerical simulation algorithm of stochastic process of direct photodetection of a driven two-level system for the predictions of the dynamical behavior is proposed. The effectiveness and superiority of the algorithm are verified by the performance analysis of the accuracy and the computational cost in comparison with the classical Runge-Kutta algorithm.

2013-01-01

263

Quantum dynamics of a single vortex  

Microsoft Academic Search

Vortices occur naturally in a wide range of gases and fluids, from macroscopic to microscopic scales. In Bose-Einstein condensates of dilute atomic gases, superfluid helium and superconductors, the existence of vortices is a consequence of the quantum nature of the system. Quantized vortices of supercurrent are generated by magnetic flux penetrating the material, and play a key role in determining

A. Wallraff; A. Lukashenko; J. Lisenfeld; A. Kemp; M. V. Fistul; Y. Koval; A. V. Ustinov

2003-01-01

264

Measuring dynamical randomness of quantum chaos by statistics of Schmidt eigenvalues  

NASA Astrophysics Data System (ADS)

We study statistics of entanglement generated by quantum chaotic dynamics. Using an ensemble of the very large number (?107) of quantum states obtained from the temporally evolving coupled kicked tops, we verify that the estimated one-body distribution of the squared Schmidt eigenvalues for the quantum chaotic dynamics can agree surprisingly well with the analytical one for the universality class of the random matrices described by the fixed trace ensemble (FTE). In order to quantify this agreement, we introduce the L1 norm of the difference between the one-body distributions for the quantum chaos and FTE and use it as an indicator of the dynamical randomness. As we increase the scaled coupling constant, the L1 difference decreases. When the effective Planck constant is not small enough, the decrease saturates, which implies quantum suppression of dynamical randomness. On the other hand, when the effective Planck constant is small enough, the decrease of the L1 difference continues until it is masked by statistical fluctuation due to finiteness of the ensemble. Furthermore, we carry out two statistical analyses, the ?2 goodness of fit test and an autocorrelation analysis, on the difference between the distributions to seek for dynamical remnants buried under the statistical fluctuation. We observe that almost all fluctuating deviations are statistical. However, even for well-developed quantum chaos, unexpectedly, we find a slight nonstatistical deviation near the largest Schmidt eigenvalue. In this way, the statistics of Schmidt eigenvalues enables us to measure dynamical randomness of quantum chaos with reference to the random matrix theory of FTE.

Kubotani, Hiroto; Adachi, Satoshi; Toda, Mikito

2013-06-01

265

Non-Markovian dynamics without using a quantum trajectory  

SciTech Connect

Open quantum systems interacting with structured environments is important and manifests non-Markovian behavior, which was conventionally studied using a quantum trajectory stochastic method. In this paper, by dividing the effects of the environment into two parts, we propose a deterministic method without using a quantum trajectory. This method is more efficient and accurate than the stochastic method in most Markovian and non-Markovian cases. We also extend this method to the generalized Lindblad master equation.

Wu Chengjun; Li Yang; Zhu Mingyi; Guo Hong [CREAM Group, State Key Laboratory of Advanced Optical Communication Systems and Networks, Peking University, School of Electronics Engineering and Computer Science, Peking University, Beijing 100871 (China)

2011-05-15

266

Coupled electron-phonon transport from molecular dynamics with quantum baths.  

PubMed

Based on generalized quantum Langevin equations for the tight-binding wavefunction amplitudes and lattice displacements, electron and phonon quantum transport are obtained exactly using molecular dynamics (MD) in the ballistic regime. The electron-phonon interactions can be handled with a quasi-classical approximation. Both charge and energy transport and their interplay can be studied. We compare the MD results with those of a fully quantum mechanical nonequilibrium Green's function (NEGF) approach for the electron currents. We find a ballistic to diffusive transition of the electron conduction in one-dimensional chains as the chain length increases. PMID:21813980

Lü, J T; Wang, Jian-Sheng

2008-12-09

267

Different dynamics of classical and quantum correlations under decoherence  

NASA Astrophysics Data System (ADS)

The dynamics of classical and quantum correlations under nondissipative and dissipative decoherences are analytically and numerically investigated with both one-side measures and two-side measures. Specifically, two qubits under local amplitude damping decoherence and depolarizing decoherence channels are considered. We show that, under the action of amplitude damping decoherence, both the entanglement and correlations of the different types of initial states with same initial values, suffer different types of dynamics. Moreover, the transfers of the entanglement and correlations between the system and the environment for different types of initial states are also shown to be different. While for the action of depolarizing decoherence, there does not exist sudden change in the decay rates of both the classical and quantum correlations, which is different from some other nondissipative channels. Furthermore, the quantum dissonance can be found to keep unchanged under the action of depolarizing decoherence. Such different dynamic behaviors of different noisy quantum decoherence channels reveal distinct transmission performance of classical and quantum information.

Huang, Peng; Zhu, Jun; Qi, Xiao-xiao; He, Guang-qiang; Zeng, Gui-hua

2012-12-01

268

Quantum circuit analog of the dynamical Casimir effect  

NASA Astrophysics Data System (ADS)

We investigate a quantum-circuit analog of the dynamical Casimir effect discussed in cavity quantum electrodynamics (QED). A double superconducting quantum interference device (SQUID), consisting of a superconducting loop interrupted by a dc-SQUID, is regarded as a harmonic oscillator with a time-dependent frequency imitating the nonadiabatic boundaries in a cavity QED. Squeezing occurs due to parametric processes inherent in the system. We reformulate squeezing based on the Bogoliubov transformation between eigenstates at different times and derive the analytic formula for quantum-state evolutions of the system. The squeezing parameter clearly reveals the relationship between squeezing and nonadiabatic nature of the system. Thus, the squeezing parameter serves as a measure for the dynamical Casimir effect. We demonstrate squeezing for two types of frequency modulation and propose a method for measuring squeezing by using a circuit QED technique under coherent oscillations between an artificial atom and an LC circuit in the presence of dissipation. These observations suggest that a quantum circuit with a Josephson junction is a promising candidate for detecting the dynamical Casimir effect.

Fujii, Toshiyuki; Matsuo, Shigemasa; Hatakenaka, Noriyuki; Kurihara, Susumu; Zeilinger, Anton

2011-11-01

269

A theory of quantum dynamics of a nanomagnet under excitation  

NASA Astrophysics Data System (ADS)

A quantum treatment of magnetization dynamics of a nanomagnet between a thousand and a million spins may be needed as the magnet interacts with quantum control. The advantage of the all-quantum approach over the classical treatment of magnetization is the accounting for the correlation between the magnet and the control agent and the first-principles source of noise. This supplement to the conference talk will concentrate on an overview of the theory with a presentation of the basic ideas which could have wide applications and illustrations with some results. Details of applications to specific models are or will be published elsewhere. A clear concept of the structure of the ground and excited macrospin states as magnetization rotation states and magnons in the Bloch/Dyson sense gives rise to a consistent theory of the magnetization dynamics of a ferromagnet modeled by the Heisenberg Hamiltonian. An example of quantum control is the spin torque transfer, treated here as a sequence of scatterings of each current electron with the localized electrons of the ferromagnet, yields in each encounter a probability distribution of the magnetization recoil state correlated with each outgoing state of the electron. This picture provides a natural Monte Carlo process for simulation of the dynamics in which the probability is determined by quantum mechanics. The computed results of mean motion, noise and damping of the magnetization will be discussed.

Sham, L. J.

2013-09-01

270

Dynamical aspects of carrier transport in quantum well intersubband photodetectors  

Microsoft Academic Search

We report on the dynamics of the transport processes which determine the photoresponse of quantum well intersubband IR detectors. Immediately after intersubband excitation, coherent transport is important. This process can be identified via interference effects between photoexcited carriers. The carriers are re-captured subsequently within a few picoseconds. These fast transport processes give rise to space charges, which induce an additional,

Harald Schneider; Stefan Ehret; G. Bihlmann; Gerhard Boehm

1997-01-01

271

Quantum molecular dynamics: Propagating wavepackets and density operators using the  

Microsoft Academic Search

Quantum molecular dynamics describe the time-evolution of a chem- ical system at the atomic level by directly solving the Schrodinger equation. Time-dependent methods, exemplied by wavepacket prop- agation, are by now developed to a point where they provide an impor- tant insight into the mechanism of many fundamental processes. Of these methods, the most versatile and ecien t is probably

Hans-Dieter Meyer; Graham A. Worthy

272

Thermodynamics and quantum corrections from molecular dynamics for liquid water  

Microsoft Academic Search

In principle, given the potential energy function, the values of thermodynamic variables can be computed from statistical mechanics for a system of molecules. In practice for the liquid state, however, two barriers must be overcome. This paper treats the first problem, how to quantum correct the classical mechanical thermodynamic values available from molecular dynamics, Monte Carlo, perturbation, or integral methods

Peter H. Berens; Donald H. J. Mackay; Gary M. White; Kent R. Wilson

1983-01-01

273

Quantum Dynamics and a Semiclassical Description of the Photon.  

ERIC Educational Resources Information Center

Uses computer graphics and nonstationary, superposition wave functions to reveal the dynamic quantum trajectories of several molecular and electronic transitions. These methods are then coupled with classical electromagnetic theory to provide a conceptually clear picture of the emission process and emitted radiation localized in time and space.…

Henderson, Giles

1980-01-01

274

Quantum Dynamics and a Semiclassical Description of the Photon.  

ERIC Educational Resources Information Center

|Uses computer graphics and nonstationary, superposition wave functions to reveal the dynamic quantum trajectories of several molecular and electronic transitions. These methods are then coupled with classical electromagnetic theory to provide a conceptually clear picture of the emission process and emitted radiation localized in time and space.…

Henderson, Giles

1980-01-01

275

Quantum control of chemical reaction dynamics in a classical way  

Microsoft Academic Search

A simplified approach to quantum control of chemical reaction dynamics based on a classical, local control theory was developed. The amplitude of the control pulse is proportional to the linear momentum of the reaction system within the dipole approximation for the system-radiation field interaction. The kinetic energy of the system is the controlling parameter. That is, the reaction is controlled

Hiroaki Umeda; Yuichi Fujimura

2000-01-01

276

Disjunctive Quantum Logic in Dynamic Perspective  

Microsoft Academic Search

In arXiv: math.LO\\/0011208 we proposed the {\\\\sl intuitionistic or disjunctive representation of quantum logic}, i.e., a representation of the property lattice of physical systems as a complete Heyting algebra of logical propositions on these properties, where this complete Heyting algebra goes equipped with an additional operation, the {\\\\sl operational resolution}, which identifies the properties within the logic of propositions. This

Bob Coecke

2000-01-01

277

Disjunctive Quantum Logic in Dynamic Perspective  

Microsoft Academic Search

In arXiv: math.LO\\/0011208 we proposed the {\\\\sl intuitionistic or disjunctive\\u000arepresentation of quantum logic}, i.e., a representation of the property\\u000alattice of physical systems as a complete Heyting algebra of logical\\u000apropositions on these properties, where this complete Heyting algebra goes\\u000aequipped with an additional operation, the {\\\\sl operational resolution}, which\\u000aidentifies the properties within the logic of propositions. This

Bob Coecke

2002-01-01

278

Comparisons of classical chemical dynamics simulations of the unimolecular decomposition of classical and quantum microcanonical ensembles  

NASA Astrophysics Data System (ADS)

Previous studies have shown that classical trajectory simulations often give accurate results for short-time intramolecular and unimolecular dynamics, particularly for initial non-random energy distributions. To obtain such agreement between experiment and simulation, the appropriate distributions must be sampled to choose initial coordinates and momenta for the ensemble of trajectories. If a molecule's classical phase space is sampled randomly, its initial decomposition will give the classical anharmonic microcanonical (RRKM) unimolecular rate constant for its decomposition. For the work presented here, classical trajectory simulations of the unimolecular decomposition of quantum and classical microcanonical ensembles, at the same fixed total energy, are compared. In contrast to the classical microcanonical ensemble, the quantum microcanonical ensemble does not sample the phase space randomly. The simulations were performed for CH4, C2H5, and Cl----CH3Br using both analytic potential energy surfaces and direct dynamics methods. Previous studies identified intrinsic RRKM dynamics for CH4 and C2H5, but intrinsic non-RRKM dynamics for Cl----CH3Br. Rate constants calculated from trajectories obtained by the time propagation of the classical and quantum microcanonical ensembles are compared with the corresponding harmonic RRKM estimates to obtain anharmonic corrections to the RRKM rate constants. The relevance and accuracy of the classical trajectory simulation of the quantum microcanonical ensemble, for obtaining the quantum anharmonic RRKM rate constant, is discussed.

Manikandan, Paranjothy; Hase, William L.

2012-05-01

279

Computer modeling of static and dynamic behavior of multiple quantum well infrared photodetectors  

Microsoft Academic Search

In this paper we present the results of the theoretical study of static and dynamic properties of multiple Quantum Well Infrared Photodetectors (QWIPs). This study is based on the original model of the QWIPs describing the electron injection from the emitter, transport in the QW structure, and capture (emission) in the QWs in a self-consistent manner. Both static and transient

M. Ershov; V. Ryzhii; K. Saito; C. Hamaguchi

1995-01-01

280

Theoretical study on the excited-state intramolecular proton transfer in the aromatic schiff base salicylidene methylamine: an electronic structure and quantum dynamical approach.  

PubMed

The proton-transfer dynamics in the aromatic Schiff base salicylidene methylamine has been theoretically analyzed in the ground and first singlet (pi,pi) excited electronic states by density functional theory calculations and quantum wave-packet dynamics. The potential energies obtained through electronic calculations that use the time-dependent density functional theory formalism, which predict a barrierless excited-state intramolecular proton transfer, are fitted to a reduced three-dimensional potential energy surface. The time evolution in this surface is solved by means of the multiconfiguration time-dependent Hartree algorithm applied to solve the time-dependent Schrödinger equation. It is shown that the excited-state proton transfer occurs within 11 fs for hydrogen and 25 fs for deuterium, so that a large kinetic isotope effect is predicted. These results are compared to those of the only previous theoretical work published on this system [Zgierski, M. Z.; Grabowska, A. J. Chem. Phys. 2000, 113, 7845], reporting a configuration interaction singles barrier of 1.6 kcal mol(-1) and time reactions of 30 and 115 fs for the hydrogen and deuterium transfers, respectively, evaluated with the semiclassical instanton approach. PMID:16599431

Ortiz-Sanchez, Juan Manuel; Gelabert, Ricard; Moreno, Miquel; Lluch, José M

2006-04-13

281

A quantum reaction dynamics study of the translational, vibrational, and rotational motion effects on the HD +H{sub 3}{sup +} reaction  

SciTech Connect

Time-dependent, quantum reaction dynamics wavepacket approach is employed to investigate the impacts of the translational, vibrational, and rotational motion on the HD+H{sub 3}{sup +}{yields} H{sub 2}D{sup +}+ H{sub 2} reaction using the Xie-Braams-Bowman potential energy surface [Z. Xie, B. J. Braams, and J. M. Bowman, J. Chem. Phys. 122, 224307 (2005)]. We treat this five atom reaction with a seven-degree-of-freedom model by fixing one Jacobi and one torsion angle related to H{sub 3}{sup +} at the lowest saddle point geometry of the potential energy surface. The initial state selected reaction probabilities show that the rotational excitations of H{sup +}-H{sub 2} greatly enhance the reactivity with the reaction probabilities increased double at high rotational states compared to the ground state. However, the vibrational excitations of H{sub 3}{sup +} hinder the reactivity. The ground state reaction probability shows no reaction threshold for this exoergic reaction, and as the translational energy increases, the reaction probability decreases. Furthermore, reactive resonances and zero point energy play very important roles on the reaction dynamics. The obtained integral cross section has the character of an exoergic reaction without a threshold: it decreases with the translational energy increasing. The calculated thermal rate constants using this seven-degree-of-freedom model are in agreement with a later experiment measurement.

Meng Fanbin; Wang Tingting; Wang, Dunyou [College of Physics and Electronics, Shandong Normal University, 88 East Wenhua Road, Jinan 250014 (China)

2011-09-21

282

Quantum dissonance induced by a thermal field and its dynamics in dissipative systems  

NASA Astrophysics Data System (ADS)

In this paper, we study quantum correlation in separable systems termed quantum dissonance [K. Modi, T. Paterek, W. Son, V. Vedral, M. Williamson, Phys. Rev. Lett. 104, 080501 (2010)]. Firstly, we study the emergence of quantum dissonance between two atoms prepared in uncorrelated states and coupled to a single-mode thermal field. We show that even for situations when the thermal field cannot entangle the two atoms, it can nevertheless induce quantum dissonance between them. Then, we investigate the dynamics including the transfer in both Markovian and non-Markovian regimes of quantum dissonance due to dissipation modeled by two independent subsystems each of which consists of a leaky cavity containing a two-level atom and surrounded by a reservoir. The two subsystems possess some amount of atomic quantum dissonance at the beginning but do not interact with each other by any means later on. We show that the quantum dissonance can be transferred among the composite subsystems, but the way it evolves and is transferred may be very different compared to that of entanglement. Finally, we present an efficient method to refrain the unwanted transfer of quantum dissonance from interested systems to reservoirs.

Man, Z. X.; Xia, Y. J.; An, N. B.

2011-10-01

283

Quantum Dynamics of Biological Plasma in the External Coulomb Field  

NASA Astrophysics Data System (ADS)

A quantum solution to the truncated Fisher-Kolmogorov-Petrovskii-Piskunov equation with Coulomb convection and linear diffusion is derived. The quantum radiation of biological systems, individual microorganisms (cells, bacteria), and dust plasma particles in the Coulomb field is studied using the foregoing solution.

Lasukov, V. V.; Lasukova, T. V.; Lasukova, O. V.

2013-10-01

284

Microscopic Studies of Quantum Phase Transitions in Optical Lattices  

NASA Astrophysics Data System (ADS)

In this thesis, I report on experiments that microscopically probe quantum phase transitions of ultracold atoms in optical lattices. We have developed a "quantum gas microscope" that allowed, for the first time, optical imaging and manipulation of single atoms in a quantum-degenerate gas on individual sites of an optical lattice. This system acts as a quantum simulator of strongly correlated materials, which are currently the subject of intense research because of the technological potential of high--T c superconductors and spintronic materials. We have used our microscope to study the superfluid to Mott insulator transition in bosons and a magnetic quantum phase transition in a spin system. In our microscopic study of the superfluid-insulator transition, we have characterized the on-site number statistics in a space- and time-resolved manner. We observed Mott insulators with fidelities as high as 99%, corresponding to entropies of 0.06kB per particle. We also measured local quantum dynamics and directly imaged the shell structure of the Mott insulator. I report on the first quantum magnetism experiments in optical lattices. We have realized a quantum Ising chain in a magnetic field, and observed a quantum phase transition between a paramagnet and antiferromagnet. We achieved strong spin interactions by encoding spins in excitations of a Mott insulator in a tilted lattice. We detected the transition by measuring the total magnetization of the system across the transition using in-situ measurements as well as the Neel ordering in the antiferromagnetic state using noise-correlation techniques. We characterized the dynamics of domain formation in the system. The spin mapping introduced opens up a new path to realizing more exotic states in optical lattices including spin liquids and quantum valence bond solids. As our system sizes become larger, simulating their physics on classical computers will require exponentially larger resources because of entanglement build-up near a quantum phase transition. We have demonstrated a quantum simulator in which all degrees of freedom can be read out microscopically, allowing the simulation of quantum many-body systems with manageable resources. More generally, the ability to image and manipulate individual atoms in optical lattices opens an avenue towards scalable quantum computation.

Bakr, Waseem S.

285

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

SciTech Connect

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

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

2009-09-25

286

Environment-Governed Dynamics in Driven Quantum Systems  

NASA Astrophysics Data System (ADS)

We show that the dynamics of a driven quantum system weakly coupled to the environment can exhibit two distinct regimes. While the relaxation basis is usually determined by the system+drive Hamiltonian (system-governed dynamics), we find that under certain conditions it is determined by specific features of the environment, such as, the form of the coupling operator (environment-governed dynamics). We provide an effective coupling parameter describing the transition between the two regimes and discuss how to observe the transition in a superconducting charge pump.

Gasparinetti, S.; Solinas, P.; Pugnetti, S.; Fazio, R.; Pekola, J. P.

2013-04-01

287

Operational dynamic modeling transcending quantum and classical mechanics.  

PubMed

We introduce a general and systematic theoretical framework for operational dynamic modeling (ODM) by combining a kinematic description of a model with the evolution of the dynamical average values. The kinematics includes the algebra of the observables and their defined averages. The evolution of the average values is drawn in the form of Ehrenfest-like theorems. We show that ODM is capable of encompassing wide-ranging dynamics from classical non-relativistic mechanics to quantum field theory. The generality of ODM should provide a basis for formulating novel theories. PMID:23215365

Bondar, Denys I; Cabrera, Renan; Lompay, Robert R; Ivanov, Misha Yu; Rabitz, Herschel A

2012-11-08

288

Dynamical stabilization and time in open quantum systems  

NASA Astrophysics Data System (ADS)

The meaning of time in an open quantum system is considered under the assumption that both, system and environment, are quantum mechanical objects. The Hamilton operator of the system is non-Hermitian. Its imaginary part is the time operator. As a rule, time and energy vary continuously when controlled by a parameter. At high level density, where many states avoid crossing, a dynamical phase transition takes place in the system under the influence of the environment. It causes a dynamical stabilization of the system what can be seen in many different experimental data. Due to this effect, time is bounded from below: the decay widths (inverse proportional to the lifetimes of the states) do not increase limitless. The dynamical stabilization is an irreversible process.

Rotter, I.

2013-02-01

289

Quantum vortex dynamics in two-dimensional neutral superfluids  

SciTech Connect

We derive an effective action for the vortex-position degree of freedom in a superfluid by integrating out condensate phase- and density-fluctuation environmental modes. When the quantum dynamics of environmental fluctuations is neglected, we confirm the occurrence of the vortex Magnus force and obtain an expression for the vortex mass. We find that this adiabatic approximation is valid only when the superfluid droplet radius R, or the typical distance between vortices, is very much larger than the coherence length xi. We go beyond the adiabatic approximation numerically, accounting for the quantum dynamics of environmental modes and capturing their dissipative coupling to condensate dynamics. For the case of an optical-lattice superfluid, we demonstrate that vortex motion damping can be adjusted by tuning the ratio between the tunneling energy J and the on-site interaction energy U. We comment on the possibility of realizing vortex-Landau-level physics.

Wang, C.-C. Joseph [University of Texas at Austin, Department of Physics, 1 University Station C1600, Austin, Texas 78712-0264 (United States); Duine, R. A.; MacDonald, A. H. [Institute for Theoretical Physics, Utrecht University, Leuvenlaan 4, NL-3584 CE Utrecht (Netherlands)

2010-01-15

290

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

NASA Astrophysics Data System (ADS)

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

Galitski, Victor

2012-02-01

291

Adaptive Resummation of Markovian Quantum Dynamics  

NASA Astrophysics Data System (ADS)

We introduce a method for obtaining analytic approximations to the evolution of Markovian open quantum systems. It is based on resumming a generalized Dyson series in a way that ensures optimal convergence even in the absence of a small parameter. The power of this approach is demonstrated by two benchmark examples: the spatial detection of a free particle and the Landau-Zener problem in the presence of dephasing. The derived approximations are asymptotically exact and exhibit errors on the per mill level over the entire parameter range.

Lucas, Felix; Hornberger, Klaus

2013-06-01

292

Dynamical functions of a 1D correlated quantum liquid  

NASA Astrophysics Data System (ADS)

The dynamical correlation functions in one-dimensional electronic systems show power-law behaviour at low energies and momenta close to integer multiples of the charge and spin Fermi momenta. These systems are usually referred to as Tomonaga-Luttinger liquids. However, near well defined lines of the (k,?) plane the power-law behaviour extends beyond the low-energy cases mentioned above, and also appears at higher energies, leading to singular features in the photoemission spectra and other dynamical correlation functions. The general spectral-function expressions derived in this paper were used in recent theoretical studies of the finite-energy singular features in photoemission of the organic compound tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ) metallic phase. They are based on a so-called pseudofermion dynamical theory (PDT), which allows us to systematically enumerate and describe the excitations in the Hubbard model starting from the Bethe ansatz, as well as to calculate the charge and spin object phase shifts appearing as exponents of the power laws. In particular, we concentrate on the spin-density m\\rightarrow 0 limit and on effects in the vicinity of the singular border lines, as well as close to half filling. Our studies take into account spectral contributions from types of microscopic processes that do not occur for finite values of the spin density. In addition, the specific processes involved in the spectral features of TTF-TCNQ are studied. Our results are useful for the further understanding of the unusual spectral properties observed in low-dimensional organic metals and also provide expressions for the one- and two-atom spectral functions of a correlated quantum system of ultracold fermionic atoms in a 1D optical lattice with on-site two-atom repulsion.

Carmelo, J. M. P.; Bozi, D.; Penc, K.

2008-10-01

293

EDITORIAL: Quantum control theory for coherence and information dynamics Quantum control theory for coherence and information dynamics  

NASA Astrophysics Data System (ADS)

Precisely characterizing and controlling the dynamics of realistic open quantum systems has emerged in recent years as a key challenge across contemporary quantum sciences and technologies, with implications ranging from physics, chemistry and applied mathematics to quantum information processing (QIP) and quantum engineering. Quantum control theory aims to provide both a general dynamical-system framework and a constructive toolbox to meet this challenge. The purpose of this special issue of Journal of Physics B: Atomic, Molecular and Optical Physics is to present a state-of-the-art account of recent advances and current trends in the field, as reflected in two international meetings that were held on the subject over the last summer and which motivated in part the compilation of this volume—the Topical Group: Frontiers in Open Quantum Systems and Quantum Control Theory, held at the Institute for Theoretical Atomic, Molecular and Optical Physics (ITAMP) in Cambridge, Massachusetts (USA), from 1-14 August 2010, and the Safed Workshop on Quantum Decoherence and Thermodynamics Control, held in Safed (Israel), from 22-27 August 2010. Initial developments in quantum control theory date back to (at least) the early 1980s, and have been largely inspired by the well-established mathematical framework for classical dynamical systems. As the above-mentioned meetings made clear, and as the burgeoning body of literature on the subject testifies, quantum control has grown since then well beyond its original boundaries, and has by now evolved into a highly cross-disciplinary field which, while still fast-moving, is also entering a new phase of maturity, sophistication, and integration. Two trends deserve special attention: on the one hand, a growing emphasis on control tasks and methodologies that are specifically motivated by QIP, in addition and in parallel to applications in more traditional areas where quantum coherence is nevertheless vital (such as, for instance, quantum control of chemical reactions or high-resolution magnetic resonance spectroscopy); on the other hand, an unprecedented demand for close coupling between theory and experiment, with theoretical developments becoming more and more attuned to and driven by experimental advances as different quantum technologies continue to evolve at an impressive pace in the laboratory. Altogether, these two trends account for several of the recurrent themes in this volume, as well as in the current quantum control literature as a whole: namely, the quest for control strategies that can attain the highest degree of precision and robustness possible, while striving for efficiency and, ultimately, optimality in achieving the intended control task under realistic operational constraints. From a theory standpoint, this makes it imperative to take into account increasingly more realistic control settings; to assess the quantitative impact of limited control resources and/or system knowledge; and to provide a rigorous and general foundation for existing experimental approaches in order to further enhance applicability and performance. From an experimental standpoint, renewed emphasis is in turn placed on validating theoretical predictions and benchmarking performance, so that the limiting constraints can be singled out for additional theoretical analysis and guidance. This ongoing cross-talk is clearly reflected in this collection, which brings together theoreticians and experimentalists, with a significant fraction of the papers reporting on combined quantum control theory-experiment efforts. While a precise categorization would neither be possible nor desirable, contributions to this volume have been loosely grouped into five broad sections. This grouping has been made in the hope that connections between different problems and/or technical approaches will become more transparent, facilitating the transfer of concepts and methods. The special issue opens with a section devoted to open-loop control methods, with special emphasis on dynamical decoupling (DD), which is becoming an incr

Viola, Lorenza; Tannor, David

2011-08-01

294

The dynamics of quantum discord and entanglement of two atoms coupled to two spatially separate cavities in cavity QED  

NASA Astrophysics Data System (ADS)

In this paper, we study the dynamics of quantum discord and entanglement of two identical two-level atoms A and B coupled with two spatially separate single-mode high- Q cavities a and b in cavity QED, respectively. Making use of geometrical depiction of quantum discord and entanglement of formation (EoF), we show that there exists quantum discord sudden death (DSD) as well as entanglement sudden death (ESD) and the time interval of DSD is shorter than that of ESD in the presented quantum system. In addition, the rate of decreasing of quantum discord is slower than that of entanglement. We have shown that the amount of quantum discord and entanglement and the relative ordering between quantum discord and quantum entanglement depend on the purity p in the presented quantum system. And we have also shown that quantum discord and entanglement of the qubits AB can transfer to the cavities ab and vice versa. Moreover, the transfer of quantum discord is independent of the purity p but that of quantum entanglement is dependent of the purity p. Surprisingly, the sudden changes of quantum discord of qubits and cavities are observed when the initial states of qubits are mixed.

Wu, T.; Ye, L.

2012-10-01

295

Effective dynamics in Bianchi type II loop quantum cosmology  

NASA Astrophysics Data System (ADS)

We numerically investigate the solutions to the effective equations of the Bianchi II model within the “improved” loop quantum cosmology dynamics. The matter source is a massless scalar field. We perform a systematic study of the space of solutions, and focus on the behavior of several geometrical observables. We show that the big bang singularity is replaced by a bounce and the pointlike singularities do not saturate the energy density bound. There are up to three directional bounces in the scale factors, one global bounce in the expansion, the shear presents up to four local maxima and can be zero at the bounce. This allows for solutions with density larger than the maximal density for the isotropic and Bianchi I cases. The asymptotic behavior is shown to behave like that of a Bianchi I model, and the effective solutions connect anisotropic solutions even when the shear is zero at the bounce. All known facts of Bianchi I are reproduced. In the “vacuum limit,” solutions are such that almost all the dynamics is due to the anisotropies. Since Bianchi II plays an important role in the Bianchi IX model and the Belinskii, Khalatnikov, Lifshitz conjecture, our results can provide an intuitive understanding of the behavior in the vicinity of general spacelike singularities, when loop-geometric corrections are present.

Corichi, Alejandro; Montoya, Edison

2012-05-01

296

Quantum dynamics and electronic spectroscopy within the framework of wavelets  

NASA Astrophysics Data System (ADS)

This paper serves as a first-time report on formulating important aspects of electronic spectroscopy and quantum dynamics in condensed harmonic systems using the framework of wavelets, and a stepping stone to our future work on developing anharmonic wavelets. The Morlet wavelet is taken to be the mother wavelet for the initial state of the system of interest. This work reports daughter wavelets that may be used to study spectroscopy and dynamics of harmonic systems. These wavelets are shown to arise naturally upon optical electronic transition of the system of interest. Natural birth of basis (daughter) wavelets emerging on exciting an electronic two-level system coupled, both linearly and quadratically, to harmonic phonons is discussed. It is shown that this takes place through using the unitary dilation and translation operators, which happen to be part of the time evolution operator of the final electronic state. The corresponding optical autocorrelation function and linear absorption spectra are calculated to test the applicability and correctness of the herein results. The link between basis wavelets and the Liouville space generating function is established. An anharmonic mother wavelet is also proposed in the case of anharmonic electron-phonon coupling. A brief description of deriving anharmonic wavelets and the corresponding anharmonic Liouville space generating function is explored. In conclusion, a mother wavelet (be it harmonic or anharmonic) which accounts for Duschinsky mixing is suggested.

Toutounji, Mohamad

2013-03-01

297

Intensity correlations and dynamical processes in cavity quantum electrodynamics  

NASA Astrophysics Data System (ADS)

Dynamical processes in a cavity quantum electrodynamical system are studied with two-level atoms in an optical cavity. The initial condition for the dynamics is either an internal or external step. The internal step is caused by the escape of a photon from the system, and the external step by a change in the driving intensity. After either step there is an oscillatory exchange of energy as the system reaches steady state. The frequency of oscillation decreases with increasing input intensity. The experimental results are compared quantitatively to theoretical calculations and to transmission spectroscopy measurements. After the external step, the output intensity oscillates to a value many times larger than the steady state. Response to the internal step is measured by photon correlations. Antibunched light with sub-Poissonian statistics is observed. Antibunched light with super-Poissonian statistics, as well as bunched light with larger correlations for non-zero times are also observed. All three effects are nonclassical. The latter two have not previously been observed, and violate the Schwarz inequality.

Mielke, Stephen Lawrence

1998-10-01

298

Quantum Trajectory Approach to Molecular Dynamics Simulation with Surface Hopping  

NASA Astrophysics Data System (ADS)

In this work we propose a quantum trajectory approach to the powerful molecular dynamics simulation with surface hopping, from an insight that an effective “observation" is actually implied in the simulation through tracking the forces experienced, just like checking the meter's result in quantum measurement process. This treatment can build the nonadiabatic surface hopping on a physical foundation, instead of the usual fictitious and conceptually inconsistent hopping algorithms. The effects and advantages of the proposed scheme are preliminarily illustrated by a two-surface model system.

Feng, Wei; Xu, Lu-Ting; Li, Xin-Qi; Fang, Wei-Hai

2013-09-01

299

Time scales and relaxation dynamics in quantum-dot lasers  

SciTech Connect

We analyze a three-variable rate equation model that takes into account carrier capture and Pauli blocking in quantum dot semiconductor lasers. The exponential decay of the relaxation oscillations is analyzed from the linearized equations in terms of three key parameters that control the time scales of the laser. Depending on their relative values, we determine two distinct two-variable reductions of the rate equations in the limit of large capture rates. The first case leads to the rate equations for quantum well lasers, exhibiting relaxation oscillations dynamics. The second case corresponds to dots nearly saturated by the carriers and is characterized by the absence of relaxation oscillations.

Erneux, Thomas; Viktorov, Evgeny A.; Mandel, Paul [Universite Libre de Bruxelles, Optique Nonlineaire Theorique, Campus Plaine, Code Postal 231, 1050 Brussels (Belgium)

2007-08-15

300

Dissipative quantum dynamics and nonlinear sigma-model  

NASA Astrophysics Data System (ADS)

Sedov variational principle which is the generalization of the least action principle for the dissipative and irreversible processes and the classical dissipative mechanics in the phase space is considered. Quantum dynamics for the dissipative and irreversible processes is constructed. As an example of the dissipative quantum theory the nonlinear two-dimensional sigma-model is considered. The conformal anomaly of the energy momentum tensor trace for closed bosonic string on the affine-metric manifold is investigated. The two-loop metric beta-function for nonlinear dissipative sigma-model was calculated. The results are compared with the ultraviolet two-loop conterterms for affine-metric sigma model.

Tarasov, V. E.

301

Conditional quantum dynamics with several observers  

SciTech Connect

We consider several observers who monitor different parts of the environment of a single quantum system and use their data to deduce its state. We derive a set of conditional stochastic master equations that describe the evolution of the density matrices each observer ascribes to the system under the Markov approximation, and show that this problem can be reduced to the case of a single 'superobserver', who has access to all the acquired data. The key problem - consistency of the sets of data acquired by different observers - is then reduced to the probability that a given combination of data sets will be ever detected by the superobserver. The resulting conditional master equations are applied to several physical examples: homodyne detection of phonons in quantum Brownian motion, photodetection and homodyne detection of resonance fluorescence from a two-level atom. We introduce relative purity to quantify the correlations between the information about the system gathered by different observers from their measurements of the environment. We find that observers gain the most information about the state of the system and they agree the most about it when they measure the environment observables with eigenstates most closely correlated with the optimally predictable pointer basis of the system.

Dziarmaga, Jacek [Los Alamos National Laboratory, Theoretical Division, MS-B213, Los Alamos, New Mexico 87545 (United States); Instytut Fizyki Uniwersytetu Jagiellonskiego, Ulnicka Reymonta 4, 30-059 Cracow (Poland); Dalvit, Diego A.R.; Zurek, Wojciech H. [Los Alamos National Laboratory, Theoretical Division, MS-B213, Los Alamos, New Mexico 87545 (United States)

2004-02-01

302

Dynamics of quantum correlations in colored-noise environments  

NASA Astrophysics Data System (ADS)

We address the dynamics of entanglement and quantum discord for two noninteracting qubits initially prepared in a maximally entangled state and then subjected to a classical colored noise, i.e., coupled with an external environment characterized by a noise spectrum of the form 1/f?. More specifically, we address systems in which the Gaussian approximation fails, i.e., mere knowledge of the spectrum is not enough to determine the dynamics of quantum correlations. We thus investigate the dynamics for two different configurations of the environment: in the first case, the noise spectrum is due to the interaction of each qubit with a single bistable fluctuator with an undetermined switching rate, whereas in the second case we consider a collection of classical fluctuators with fixed switching rates. In both cases, we found analytical expressions for the time dependence of entanglement and quantum discord, which may also be extended to a collection of fluctuators with random switching rates. The environmental noise is introduced by means of stochastic time-dependent terms in the Hamiltonian, and this allows us to describe the effects of both separate and common environments. We show that the non-Gaussian character of the noise may lead to significant effects, e.g., environments with the same power spectrum, but different configurations give rise to the opposite behavior for quantum correlations. In particular, depending on the characteristics of the environmental noise considered, both entanglement and discord display either a monotonic decay or the phenomena of sudden death and revivals. Our results show that the microscopic structure of the environment, in addition to its noise spectrum, is relevant for the dynamics of quantum correlations and may be a valid starting point for the engineering of non-Gaussian colored environments.

Benedetti, Claudia; Buscemi, Fabrizio; Bordone, Paolo; Paris, Matteo G. A.

2013-05-01

303

Classical and quantum dynamics of a model for atomic-molecular Bose-Einstein condensates  

SciTech Connect

We study a model for a two-mode atomic-molecular Bose-Einstein condensate. Starting with a classical analysis we determine the phase space fixed points of the system. It is found that bifurcations of the fixed points naturally separate the coupling parameter space into four regions. The different regions give rise to qualitatively different dynamics. We then show that this classification holds true for the quantum dynamics.

Santos, G.; Tonel, A.; Foerster, A. [Instituto de Fisica da UFRGS, Av. Bento Goncalves 9500, Porto Alegre, RS (Brazil); Links, J. [Centre for Mathematical Physics, School of Physical Sciences, University of Queensland, Queensland 4072 (Australia)

2006-02-15

304

Quantum computing in the presence of spontaneous emission by a combined dynamical decoupling and quantum-error-correction strategy  

SciTech Connect

A method for quantum computation in the presence of spontaneous emission is proposed. The method combines strong and fast (dynamical decoupling) pulses and a quantum error correcting code that encodes n logical qubits into only n+1 physical qubits. Universal, fault-tolerant, quantum computation is shown to be possible in this scheme using Hamiltonians relevant to a range of promising proposals for the physical implementation of quantum computers.

Khodjasteh, K.; Lidar, D. A. [Department of Physics, University of Toronto, 60 St. George Street, Toronto, Ontario, Canada M5S 1A7 (Canada); Chemical Physics Theory Group, Chemistry Department, University of Toronto, 80 St. George Street, Toronto, Ontario, Canada M5S 3H6 (Canada)

2003-08-01

305

The dynamics of electron-hole collection in quantum well heterostructures  

Microsoft Academic Search

The dynamics of carrier collection in quantum-well heterostructures are studied by photoemission experiments and Monte Carlo simulations. It is shown that carrier scattering decreases rapidly for well sizes not greater than 100 A. The collection mechanism depends sensitively on details of the band structure. The energy distribution function of the carriers after collection exhibits significant structure with respect to multiples

J. Y. Tang; K. Hess; N. Holonyak Jr.; J. J. Coleman; P. D. Dapkus

1982-01-01

306

Dynamic symmetries and entropic inequalities in the probability representation of quantum mechanics  

SciTech Connect

The probability representation of quantum and classical statistical mechanics is discussed. Symplectic tomography, center-of-mass tomography, and spin tomography are studied. The connection of tomographic probabilities with dynamic symmetries like symplectic group is considered. Entropic uncertainty relations and inequalities for spin tomograms are reviewed.

Man'ko, Margarita A.; Man'ko, Vladimir I. [P. N. Lebedev Physical Institute, Leninskii Prospect 53, Moscow 119991 (Russian Federation)

2011-03-21

307

Hybrid approach for including electronic and nuclear quantum effects in molecular dynamics simulations of hydrogen transfer reactions in enzymes  

NASA Astrophysics Data System (ADS)

A hybrid approach for simulating proton and hydride transfer reactions in enzymes is presented. The electronic quantum effects are incorporated with an empirical valence bond approach. The nuclear quantum effects of the transferring hydrogen are included with a mixed quantum/classical molecular dynamics method in which the hydrogen nucleus is described as a multidimensional vibrational wave function. The free energy profiles are obtained as functions of a collective reaction coordinate. A perturbation formula is derived to incorporate the vibrationally adiabatic nuclear quantum effects into the free energy profiles. The dynamical effects are studied with the molecular dynamics with quantum transitions (MDQT) surface hopping method, which incorporates nonadiabatic transitions among the adiabatic hydrogen vibrational states. The MDQT method is combined with a reactive flux approach to calculate the transmission coefficient and to investigate the real-time dynamics of reactive trajectories. This hybrid approach includes nuclear quantum effects such as zero point energy, hydrogen tunneling, and excited vibrational states, as well as the dynamics of the complete enzyme and solvent. The nuclear quantum effects are incorporated during the generation of the free energy profiles and dynamical trajectories rather than subsequently added as corrections. Moreover, this methodology provides detailed mechanistic information at the molecular level and allows the calculation of rates and kinetic isotope effects. An initial application of this approach to the enzyme liver alcohol dehydrogenase is also presented.

Billeter, Salomon R.; Webb, Simon P.; Iordanov, Tzvetelin; Agarwal, Pratul K.; Hammes-Schiffer, Sharon

2001-04-01

308

Anharmonic nuclear dynamics in the mixed quantum-classical limit.  

PubMed

This study employs mixed quantum-classical dynamics (MQCD) formalism to evaluate the linear electronic dipole moment time correlation function (DMTCF) in which a Morse oscillator serves to model the associated vibrations in a mixed quantum-classical (MQC) environment. While the main purpose of this work is to study the applicability of MQCD formalism to anharmonic systems in condensed phase, approximate schemes to physically evaluate the mathematically divergent integrals have been developed in order to deal with the essential singularities that arise while evaluating the Morse oscillator canonical partition function and the DMTCF in MQC systems in the classical limit. The motivation for numerically and analytically evaluating these divergent integrals is that a partition function of any system should lead to a finite value at any temperature and therefore this divergence is unphysical. Additionally, since a partition function is to signify the number of accessible states to the system at hand, divergent results are not physically acceptable. As such, straightforward approximate analytic expressions, at different levels of rigor, for both the classical Morse oscillator partition function and the DMTCF in MQC systems are derived, for the first time. Calculations of Morse oscillator partition function values using different approaches at various temperatures for CO, HCl, and I(2) molecules, showing good results, are presented to test the expressions derived herein. It is found that this divergence, due to singularity, diminishes upon lowering the temperature and only arises at high temperatures. The gradual diminishing of the singularity upon lowering the temperature is sensible since the Morse potential fits the parabolic potential at low temperatures. Model calculations and discussion of the DMTCF and linear absorption spectra in MQC systems using the molecular constants of CO molecule are provided. The linear absorption lineshape is derived by two methods, one of which is asymptotic expansion. PMID:22086187

Toutounji, Mohamad

2011-11-15

309

Nonperturbative quantum dynamics of a new inflation model  

SciTech Connect

We consider an O(N) model coupled self-consistently to gravity in the semiclassical approximation, where the field is subject to {open_quotes}new inflation{close_quotes} type initial conditions. We study the dynamics self-consistently and non-perturbatively with non-equilibrium field theory methods in the large N limit. We find that spinodal instabilities drive the growth of non-perturbatively large quantum fluctuations which shut off the inflationary growth of the scale factor. We find that a very specific combination of these large fluctuations plus the inflaton zero mode assemble into a new effective field. This new field behaves classically and it is the object which actually rolls down. We show how this reinterpretation saves the standard picture of how metric perturbations are generated during inflation and that the spinodal growth of fluctuations dominates the time dependence of the Bardeen variable for superhorizon modes during inflation. We compute the amplitude and index for the spectrum of scalar density and tensor perturbations and argue that in all models of this type the spinodal instabilities are responsible for a {open_quotes}red{close_quotes} spectrum of primordial scalar density perturbations. A criterion for the validity of these models is provided and contact with the reconstruction program is established validating some of the results within a non-perturbative framework. The decoherence aspects and the quantum to classical transition through inflation are studied in detail by following the full evolution of the density matrix and relating the classicality of cosmological perturbations to that of long-wavelength matter fluctuations. {copyright} {ital 1998} {ital The American Physical Society}

Boyanovsky, D. [Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, Pennsylvania 15260 (United States); Cormier, D.; Holman, R.; Kumar, S.P. [Department of Physics, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213 (United States); de Vega, H.J. [LPTHE, Universite Pierre et Marie Curie (Paris VI) et Denis Diderot (Paris VII), Tour 16, 1er. etage, 4, Place Jussieu75252Paris, Cedex 05 (France)

1998-02-01

310

Study of correlations in molecular motion by multiple quantum NMR  

SciTech Connect

Nuclear magnetic resonance is a very useful tool for characterizing molecular configurations through the measurement of transition frequencies and dipolar couplings. The measurement of spectral lineshapes, spin-lattice relaxation times, and transverse relaxation times also provide us with valuable information about correlations in molecular motion. The new technique of multiple quantum nuclear magnetic resonance has numerous advantages over the conventional single quantum NMR techniques in obtaining information about static and dynamic interactions of coupled spin systems. In the first two chapters, the theoretical background of spin Hamiltonians and the density matrix formalism of multiple quantum NMR is discussed. The creation and detection of multiple quantum coherence by multiple pulse sequence are discussed. Prototype multiple quantum spectra of oriented benzene are presented. Redfield relaxation theory and the application of multiple quantum NMR to the study of correlations in fluctuations are presented. A specific example of an oriented methyl group relaxed by paramagnetic impurities is studied in detail. The study of possible correlated motion between two coupled methyl groups by multiple quantum NMR is presented. For a six spin system it is shown that the four-quantum spectrum is sensitive to two-body correlations, and serves a ready test of correlated motion. The study of the spin-lattice dynamics of orienting or tunneling methyl groups (CH/sub 3/ and CD/sub 3/) at low temperatures is presented. The anisotropic spin-lattice relaxation of deuterated hexamethylbenzene, caused by the sixfold reorientation of the molecules, is investigated, and the NMR spectrometers and other experimental details are discussed.

Tang, J.H.

1981-11-01

311

Coupled-Channels Approach for Dissipative Quantum Dynamics in Near-Barrier Collisions  

SciTech Connect

A novel quantum dynamical model based on the dissipative quantum dynamics of open quantum systems is presented. It allows the treatment of both deep-inelastic processes and quantum tunneling (fusion) within a fully quantum mechanical coupled-channels approach. Model calculations show the transition from pure state (coherent) to mixed state (decoherent and dissipative) dynamics during a near-barrier nuclear collision. Energy dissipation, due to irreversible decay of giant-dipole excitations of the interacting nuclei, results in hindrance of quantum tunneling.

Diaz-Torres, A.; Hinde, D. J.; Dasgupta, M. [Department of Nuclear Physics, Research School of Physical Sciences and Engineering, Australian National University, Canberra, ACT 0200 (Australia); Milburn, G. J. [Centre for Quantum Computer Technology, University of Queensland, St. Lucia, Queensland 4072 (Australia); Tostevin, J. A. [Department of Physics, Faculty of Engineering and Physical Sciences, University of Surrey, Guildford, Surrey GU2 7XH (United Kingdom)

2009-03-04

312

Dynamical Horizon Entropy Bound Conjecture in Loop Quantum Cosmology  

NASA Astrophysics Data System (ADS)

The covariant entropy bound conjecture is an important hint for the quantum gravity, with several versions available in the literature. For cosmology, Ashtekar and Wilson-Ewing ever show the consistence between the loop gravity theory and one version of this conjecture. Recently, He and Zhang [J. High Energy Phys. 10 (2007) 077] proposed a version for the dynamical horizon of the universe, which validates the entropy bound conjecture for the cosmology filled with perfect fluid in the classical scenario when the universe is far away from the big bang singularity. However, their conjecture breaks down near big bang region. We examine this conjecture in the context of the loop quantum cosmology. With the example of photon gas, this conjecture is protected by the quantum geometry effects as expected.

Li, Li-Fang; Zhu, Jian-Yang

2012-07-01

313

Optimally combining dynamical decoupling and quantum error correction  

NASA Astrophysics Data System (ADS)

Quantum control and fault-tolerant quantum computing (FTQC) are two of the cornerstones on which the hope of realizing a large-scale quantum computer is pinned, yet only preliminary steps have been taken towards formalizing the interplay between them. Here we explore this interplay using the powerful strategy of dynamical decoupling (DD), and show how it can be seamlessly and optimally integrated with FTQC. To this end we show how to find the optimal decoupling generator set (DGS) for various subspaces relevant to FTQC, and how to simultaneously decouple them. We focus on stabilizer codes, which represent the largest contribution to the size of the DGS, showing that the intuitive choice comprising the stabilizers and logical operators of the code is in fact optimal, i.e., minimizes a natural cost function associated with the length of DD sequences. Our work brings hybrid DD-FTQC schemes, and their potentially considerable advantages, closer to realization.

Paz-Silva, Gerardo A.; Lidar, D. A.

2013-04-01

314

Unification of dynamical decoupling and the quantum Zeno effect  

SciTech Connect

We unify the quantum Zeno effect (QZE) and the 'bang-bang' (BB) decoupling method for suppressing decoherence in open quantum systems: in both cases strong coupling to an external system or apparatus induces a dynamical superselection rule that partitions the open system's Hilbert space into quantum Zeno subspaces. Our unification makes use of von Neumann' s ergodic theorem and avoids making any of the symmetry assumptions usually made in discussions of BB. Thus we are able to generalize the BB to arbitrary fast and strong pulse sequences, requiring no symmetry, and to show the existence of two alternatives to a pulsed BB: continuous decoupling and pulsed measurements. Our unified treatment enables us to derive limits on the efficacy of the BB method: we explicitly show that the inverse QZE implies that the BB can in some cases accelerate, rather than inhibit, decoherence.

Facchi, P.; Pascazio, S. [Dipartimento di Fisica, Universita di Bari I-70126 Bari (Italy); Istituto Nazionale di Fisica Nucleare, Sezione di Bari, I-70126 Bari (Italy); Lidar, D.A. [Chemical Physics Theory Group, Chemistry Department, University of Toronto, 80 St. George Street, Toronto, Ontario, M5S 3H6 (Canada)

2004-03-01

315

A Molecular Dynamics (MD) and Quantum Mechanics/Molecular Mechanics (QM/MM) Study on Ornithine Cyclodeaminase (OCD): A Tale of Two Iminiums  

PubMed Central

Ornithine cyclodeaminase (OCD) is an NAD+-dependent deaminase that is found in bacterial species such as Pseudomonas putida. Importantly, it catalyzes the direct conversion of the amino acid L-ornithine to L-proline. Using molecular dynamics (MD) and a hybrid quantum mechanics/molecular mechanics (QM/MM) method in the ONIOM formalism, the catalytic mechanism of OCD has been examined. The rate limiting step is calculated to be the initial step in the overall mechanism: hydride transfer from the L-ornithine’s C?–H group to the NAD+ cofactor with concomitant formation of a C?=NH2 + Schiff base with a barrier of 90.6 kJ mol?1. Importantly, no water is observed within the active site during the MD simulations suitably positioned to hydrolyze the C?=NH2 + intermediate to form the corresponding carbonyl. Instead, the reaction proceeds via a non-hydrolytic mechanism involving direct nucleophilic attack of the ?-amine at the C?-position. This is then followed by cleavage and loss of the ?-NH2 group to give the ?1-pyrroline-2-carboxylate that is subsequently reduced to L-proline.

Ion, Bogdan F.; Bushnell, Eric A. C.; De Luna, Phil; Gauld, James W.

2012-01-01

316

High accuracy 3D quantum dot tracking with multifocal plane microscopy for the study of fast intracellular dynamics in live cells.  

PubMed

Single particle tracking in three dimensions in a live cell environment holds the promise of revealing important new biological insights. However, conventional microscopy-based imaging techniques are not well suited for fast three-dimensional (3D) tracking of single particles in cells. Previously we developed an imaging modality multifocal plane microscopy (MUM) to image fast intracellular dynamics in three dimensions in live cells. Here, we introduce an algorithm, the MUM localization algorithm (MUMLA), to determine the 3D position of a point source that is imaged using MUM. We validate MUMLA through simulated and experimental data and show that the 3D position of quantum dots can be determined over a wide spatial range. We demonstrate that MUMLA indeed provides the best possible accuracy with which the 3D position can be determined. Our analysis shows that MUM overcomes the poor depth discrimination of the conventional microscope, and thereby paves the way for high accuracy tracking of nanoparticles in a live cell environment. Here, using MUM and MUMLA we report for the first time the full 3D trajectories of QD-labeled antibody molecules undergoing endocytosis in live cells from the plasma membrane to the sorting endosome deep inside the cell. PMID:18835896

Ram, Sripad; Prabhat, Prashant; Chao, Jerry; Ward, E Sally; Ober, Raimund J

2008-10-03

317

Insights in quantum dynamical effects in the infrared spectroscopy of liquid water from a semiclassical study with an ab initio-based flexible and polarizable force field.  

PubMed

The dynamical properties of liquid water play an important role in many processes in nature. In this paper, we focus on the infrared (IR) absorption spectrum of liquid water based on the linearized semiclassical initial value representation (LSC-IVR) with the local Gaussian approximation (LGA) [J. Liu and W. H. Miller, J. Chem. Phys. 131, 074113 (2009)] and an ab initio based, flexible, polarizable Thole-type model (TTM3-F) [G. S. Fanourgakis and S. S. Xantheas, J. Chem. Phys. 128, 074506 (2008)]. Although the LSC-IVR (LGA) gives the exact result for the isolated three-dimensional shifted harmonic stretching model, it yields a blueshifted peak position for the more realistic anharmonic stretching potential. By using the short-time information of the LSC-IVR correlation function; however, it is shown how one can obtain more accurate results for the position of the stretching peak. Due to the physical decay in the condensed phase system, the LSC-IVR (LGA) is a good and practical approximate quantum approach for the IR spectrum of liquid water. The present results offer valuable insight into future attempts to improve the accuracy of the TTM3-F potential or other ab initio-based models in reproducing the IR spectrum of liquid water. PMID:22225165

Liu, Jian; Miller, William H; Fanourgakis, George S; Xantheas, Sotiris S; Imoto, Sho; Saito, Shinji

2011-12-28

318

Insights in quantum dynamical effects in the infrared spectroscopy of liquid water from a semiclassical study with an ab initio-based flexible and polarizable force field  

NASA Astrophysics Data System (ADS)

The dynamical properties of liquid water play an important role in many processes in nature. In this paper, we focus on the infrared (IR) absorption spectrum of liquid water based on the linearized semiclassical initial value representation (LSC-IVR) with the local Gaussian approximation (LGA) [J. Liu and W. H. Miller, J. Chem. Phys. 131, 074113 (2009)] and an ab initio based, flexible, polarizable Thole-type model (TTM3-F) [G. S. Fanourgakis and S. S. Xantheas, J. Chem. Phys. 128, 074506 (2008)]. Although the LSC-IVR (LGA) gives the exact result for the isolated three-dimensional shifted harmonic stretching model, it yields a blueshifted peak position for the more realistic anharmonic stretching potential. By using the short-time information of the LSC-IVR correlation function; however, it is shown how one can obtain more accurate results for the position of the stretching peak. Due to the physical decay in the condensed phase system, the LSC-IVR (LGA) is a good and practical approximate quantum approach for the IR spectrum of liquid water. The present results offer valuable insight into future attempts to improve the accuracy of the TTM3-F potential or other ab initio-based models in reproducing the IR spectrum of liquid water.

Liu, Jian; Miller, William H.; Fanourgakis, George S.; Xantheas, Sotiris S.; Imoto, Sho; Saito, Shinji

2011-12-01

319

Existence of the thermodynamic limit and asymptotic behavior of some irreversible quantum dynamical systems  

NASA Astrophysics Data System (ADS)

This dissertation discusses the properties of two open quantum systems with a general class of irreversible quantum dynamics. First we study Lieb-Robinson bounds in a quantum lattice systems. This bound gives an estimate for the speed of growth of the support of an evolved local observable up to an exponentially small error. In a second model we study the properties of a leaking cavity pumped by a random atomic beam. We begin by describing quantum systems on an infinite lattice with associated finite or infinite dimensional Hilbert space. The generator of the dynamics of this system is of the Lindblad-Kossakowski type and consists of two parts: the Hamiltonian interactions and the dissipative terms. We allow both of them to be time-dependent. This generator satisfies some suitable decay condition in space. We show that the dynamics with a such generator on a finite system is a well-defined quantum dynamics in a sense of a norm-continuous cocycle of unit preserving completely positive maps. Lieb-Robinson bounds for irreversible dynamics were first considered in the classical context and in for a class of quantum lattice systems with finite-range interactions. We extend those results by proving a Lieb-Robinson bound for lattice models with a more general class of quantum dynamics. Then we use Lieb-Robinson bounds for a finite lattice systems to prove the existence of the thermodynamic limit of the dynamics. We show that in a strong limit there exits a strongly continuous cocycle of unit preserving completely positive maps. Which means that the dynamics exists in an infinite system, where Lieb-Robinson bounds also holds. In the second part of the dissertation we consider a system that consists of a beam of two-level atoms that pass one by one through the microwave cavity. The atoms are randomly excited and there is exactly one atom present in the cavity at any given moment. We consider both the ideal and leaky cavity and study the time asymptotic behavior of the state of the cavity. We show that the number of photons increases indefinitely in the case of the ideal cavity. In the case of the leaking cavity the limiting state is independent of the initial state, it is not quasi-free and it is a non-equilibrium steady state. We also compute the associated energy flow.

Vershynina, Anna

320

Quantized Hamilton dynamics describes quantum discrete breathers in a simple way  

SciTech Connect

We study the localization of energy in a nonlinear coupled system, exhibiting so-called breather modes, using quantized Hamilton dynamics (QHD). Already at the lowest order, which is only twice as complex as classical mechanics, this simple semiclassical method incorporates quantum-mechanical effects. The transition between the localized and delocalized regimes is instantaneous in classical mechanics, while it is gradual due to tunneling in both quantum mechanics and QHD. In contrast to classical mechanics, which predicts an abrupt appearance of breathers, quantum mechanics and QHD show an alternation of localized and delocalized behavior in the transient region. QHD includes zero-point energy that is reflected in a shifted energy asymptote for the localized states, providing another improvement on the classical perspective. By detailed analysis of the distribution and transfer of energy within classical mechanics, QHD, and quantum dynamics, we conclude that QHD is an efficient approach that accounts for moderate quantum effects and can be used to identify quantum breathers in large nonlinear systems.

Igumenshchev, Kirill; Prezhdo, Oleg [Department of Chemistry, University of Rochester, Rochester, New York 14627 (United States)

2011-08-15

321

The Dynamics of Quantum Discord and Entanglement of Three Atoms Coupled to Three Spatially Separate Cavities  

NASA Astrophysics Data System (ADS)

In this paper, we study the dynamics of quantum discord and entanglement of three identical two-level atoms simultaneously resonantly interacting with three spatially separate single-mode of high- Q cavities respectively. Taking advantage of the depiction quantum discord and entanglement of formation (EoF), we conclude that the discord and entanglement of atoms and cavities can be mediated by changing some parameters and the maximum values of discord and entanglement are independent on the couplings of cavities and atoms. In particular, there also exists quantum discord sudden death as well as entanglement sudden death and the time interval of the former is shorter than that of the later in the proposed quantum system. It is shown that the discord and entanglement of any two atoms among three atoms can be transferred to the corresponding cavities, and there exists discord and entanglement exchanging between the atoms and the corresponding cavities.

He, Juan; Wu, Tao; Ye, Liu

2013-10-01

322

Macroscopic quantum self-trapping in dynamical tunneling.  

PubMed

It is well known that increasing the nonlinearity due to repulsive atomic interactions in a double-well Bose-Einstein condensate suppresses quantum tunneling between the two sites. Here we find analogous behavior in the dynamical tunneling of a Bose-Einstein condensate between period-one resonances in a single driven potential well. For small nonlinearities we find unhindered tunneling between the resonances, but with an increasing period as compared to the noninteracting system. For nonlinearities above a critical value we generally observe that the tunneling shuts down. However, for certain regimes of modulation parameters we find that dynamical tunneling reemerges for large enough nonlinearities, an effect not present in spatial double-well tunneling. We develop a two-mode model in good agreement with full numerical simulations over a wide range of parameters, which allows the suppression of tunneling to be attributed to macroscopic quantum self-trapping. PMID:23002725

Wüster, Sebastian; D?browska-Wüster, Beata J; Dabrowska-Wüster, Beata J; Davis, Matthew J

2012-08-20

323

FAST TRACK COMMUNICATION: Deterministic constant-temperature dynamics for dissipative quantum systems  

NASA Astrophysics Data System (ADS)

A novel method is introduced in order to treat the dissipative dynamics of quantum systems interacting with a bath of classical degrees of freedom. The method is based upon an extension of the Nosè-Hoover chain (constant temperature) dynamics to quantum-classical systems. Both adiabatic and nonadiabatic numerical calculations on the relaxation dynamics of the spin-boson model show that the quantum-classical Nosè-Hoover chain dynamics represents the thermal noise of the bath in an accurate and simple way. Numerical comparisons, both with the constant-energy calculation and with the quantum-classical Brownian motion treatment of the bath, show that the quantum-classical Nosè-Hoover chain dynamics can be used to introduce dissipation in the evolution of a quantum subsystem even with just one degree of freedom for the bath. The algorithm can be computationally advantageous in modelling, within computer simulation, the dynamics of a quantum subsystem interacting with complex molecular environments.

Sergi, Alessandro

2007-04-01

324

Dynamical quantum Hall effect in the parameter space  

PubMed Central

Geometric phases in quantum mechanics play an extraordinary role in broadening our understanding of fundamental significance of geometry in nature. One of the best known examples is the Berry phase [M.V. Berry (1984), Proc. Royal. Soc. London A, 392:45], which naturally emerges in quantum adiabatic evolution. So far the applicability and measurements of the Berry phase were mostly limited to systems of weakly interacting quasi-particles, where interference experiments are feasible. Here we show how one can go beyond this limitation and observe the Berry curvature, and hence the Berry phase, in generic systems as a nonadiabatic response of physical observables to the rate of change of an external parameter. These results can be interpreted as a dynamical quantum Hall effect in a parameter space. The conventional quantum Hall effect is a particular example of the general relation if one views the electric field as a rate of change of the vector potential. We illustrate our findings by analyzing the response of interacting spin chains to a rotating magnetic field. We observe the quantization of this response, which we term the rotational quantum Hall effect.

Gritsev, V.; Polkovnikov, A.

2012-01-01

325

Dynamical quantum Hall effect in the parameter space.  

PubMed

Geometric phases in quantum mechanics play an extraordinary role in broadening our understanding of fundamental significance of geometry in nature. One of the best known examples is the Berry phase [M.V. Berry (1984), Proc. Royal. Soc. London A, 392:45], which naturally emerges in quantum adiabatic evolution. So far the applicability and measurements of the Berry phase were mostly limited to systems of weakly interacting quasi-particles, where interference experiments are feasible. Here we show how one can go beyond this limitation and observe the Berry curvature, and hence the Berry phase, in generic systems as a nonadiabatic response of physical observables to the rate of change of an external parameter. These results can be interpreted as a dynamical quantum Hall effect in a parameter space. The conventional quantum Hall effect is a particular example of the general relation if one views the electric field as a rate of change of the vector potential. We illustrate our findings by analyzing the response of interacting spin chains to a rotating magnetic field. We observe the quantization of this response, which we term the rotational quantum Hall effect. PMID:22493228

Gritsev, V; Polkovnikov, A

2012-04-09

326

Quench dynamics in the one-dimensional sine-Gordon model: Quantum kinetic equation approach  

NASA Astrophysics Data System (ADS)

We study dynamics after a quantum quench in the one-dimensional sine-Gordon model in its gapless phase. We construct the Dyson equation to leading (quadratic) order in the cosine potential and show that the resulting quantum kinetic equation is atypical in that it involves multi-particle scattering processes. We also show that using an effective action, which generates the Dyson equation by a variational principle, the conserved stress-momentum tensor can be constructed. We solve the dynamics numerically by making a quasi-classical approximation that makes the quantum kinetic equation local in time while retaining the multi-particle nature of the scattering processes. We find that the boson distribution function reaches a steady-state characterized by an effective temperature in the long-wavelength limit. We present an analytic argument for the value of the effective temperature and the time-scales to reach this steady-state.

Tavora, Marco; Mitra, Aditi

2013-03-01

327

Scalar Field Dynamics:. Classical, Quantum and in Between  

NASA Astrophysics Data System (ADS)

Using a Hartree ensemble approximation, we investigate the dynamics of the ?4 model in 1 + 1 dimensions. We find that the fields initially thermalize with a Bose-Einstein distribution for the fields. Gradually, however, the distribution changes towards classical equipartition. Using suitable initial conditions quantum thermalization is achieved much faster than the onset of this undesirable equipartition. We also show how the numerical efficiency of our method can be significantly improved.

Sallé, M.; Smit, J.; Vink, J. C.

2001-07-01

328

Regular and chaotic quantum dynamics in atom-diatom reactive collisions  

SciTech Connect

A new microirreversible 3D theory of quantum multichannel scattering in the three-body system is developed. The quantum approach is constructed on the generating trajectory tubes which allow taking into account influence of classical nonintegrability of the dynamical quantum system. When the volume of classical chaos in phase space is larger than the quantum cell in the corresponding quantum system, quantum chaos is generated. The probability of quantum transitions is constructed for this case. The collinear collision of the Li + (FH) {sup {yields}}(LiF) + H system is used for numerical illustration of a system generating quantum (wave) chaos.

Gevorkyan, A. S., E-mail: g_ashot@sci.a [IIAP/IAPP NAS of Armenia (Armenia); Bogdanov, A. V., E-mail: bogdanov@csa.r [Institute for High Performance Computing and Information Systems (Russian Federation); Nyman, G., E-mail: nyman@chem.gu.s [University of Gothenburg, Department of Chemistry (Sweden)

2008-05-15

329

Coherent-feedback quantum control with a dynamic compensator  

NASA Astrophysics Data System (ADS)

I present an experimental realization of a coherent-feedback control system that was recently proposed for testing basic principles of linear quantum stochastic control theory [M. R. James, H. I. Nurdin, and I. R. Petersen, e-print arXiv:quant-ph/0703150v2, IEEE Transactions on Automatic Control (to be published)]. For a dynamical plant consisting of an optical ring resonator, I demonstrate ˜7dB broadband disturbance rejection of injected laser signals via all-optical feedback with a tailored dynamic compensator. Comparison of the results with a transfer function model pinpoints critical parameters that determine the coherent-feedback control system’s performance.

Mabuchi, Hideo

2008-09-01

330

Exact dynamics of quantum correlations of two qubits coupled to bosonic baths  

NASA Astrophysics Data System (ADS)

Dynamics of the quantum entanglement and quantum discord of two qubits in two independent baths and a common bath with the Lorentzian spectrum are studied exactly in the numerical sense within the hierarchy approach. The effects of the counter-rotating-wave terms from the system–bath coherence on these quantum correlations are systematically discussed and comparisons with previous ones under the rotating-wave approximation are also performed. For two independent baths, beyond the weak system–bath coupling, the counter-rotating-wave terms essentially change evolutions of both the entanglement and quantum discord. With increase of the coupling, revival of the entanglement after a period of complete disentanglement is suppressed dramatically and finally disappears, and the quantum discord becomes smaller monotonically. For the common bath, the entanglement is also suppressed by the counter-rotating-wave terms, but the quantum discord shows quite different behaviors if initiated from spin-correlated states. In the non-Markovian regime, the quantum discord is almost not influenced by the counter-rotating-wave terms and is generally finite in the long-time evolution at arbitrary coupling while in the Markovian regime, it is significantly enhanced with the strong coupling.

Wang, Chen; Chen, Qing-Hu

2013-10-01

331

Investigation of the dynamics of two coupled oscillators with mixed quantum-classical methods.  

PubMed

The dynamics of two coupled oscillators can become quite complex if anharmonic potential energy functions are employed. This type of system therefore represents a good model for an investigation of the performance of mixed quantum-classical methods. In this work, the motion of two coupled particles with a mass ratio of one to ten is studied with three different mixed quantum-classical methods in the presence of anharmonic potential terms for a comparison with exact quantum mechanical calculations. The mixed quantum-classical approaches include the multitrajectory Ehrenfest, the mixed quantum-classical Bohmian (MQCB), and the so-called coupled Schrödinger equations (CSE) formalisms. The analysis shows that while the description of a weakly anharmonic system by the Ehrenfest and MQCB schemes is accurate if proper sampling techniques are applied, both approximations break down rapidly if the anharmonic terms are increased. The performance of the simple CSE prescription, which corresponds to a reduction of the full two-dimensional wave function to two one-dimensional wave functions representing two quantum oscillators coupled via the potential energy in a classical fashion, decreases if the width of the initial wave packet is enlarged. The dependence of the CSE method on the diffuseness of the initial wave packet is therefore opposite to that of the MQCB method, which is more accurate for wide wave packets. Overall, the multitrajectory Ehrenfest ansatz is found to be most successful in reproducing the exact quantum results. PMID:16709095

Li, Jingrui; Woywod, Clemens; Vallet, Valérie; Meier, Christoph

2006-05-14

332

Quantum-gravity induced Lorentz violation and dynamical mass generation  

SciTech Connect

In the eprint by Jean Alexandre [arXiv:1009.5834], a minimal extension of (3+1)-dimensional quantum electrodynamics has been proposed, which includes Lorentz violation (LV) in the form of higher-(spatial)-derivative isotropic terms in the gauge sector, suppressed by a mass scale M. The model can lead to dynamical mass generation for charged fermions. In this article, I elaborate further on this idea and I attempt to connect it to specific quantum-gravity models, inspired from string/brane theory. Specifically, in the first part of the article, I comment briefly on the gauge dependence of the dynamical mass generation in the approximations of J. Alexandre [arXiv:1009.5834.], and I propose a possible avenue for obtaining the true gauge-parameter-independent value of the mass by means of pinch technique argumentations. In the second part of the work, I embed the LV QED model into multibrane world scenarios with a view to provide a geometrical way of enhancing the dynamical mass to phenomenologically realistic values by means of bulk warp metric factors, in an (inverse) Randall-Sundrum hierarchy. Finally, in the third part of this paper, I demonstrate that such Lorentz-violating QED models may represent parts of a low-energy effective action (of Finsler-Born-Infeld type) of open strings propagating in quantum D0-particle stochastic space-time foam backgrounds, which are viewed as consistent quantum-gravity configurations. To capture correctly the quantum-fluctuating nature of the foam background, I replace the D0-recoil-velocity parts of this action by appropriate gradient operators in three-space, keeping the photon field part intact. This is consistent with the summation over world-sheet genera in the first-quantized string approach. I identify a class of quantum orderings which leads to the LV QED action of J. Alexandre, arXiv:1009.5834. In this way I argue, following the logic in that work, that the D-foam can lead to dynamically generated masses for charged-matter (fermionic) excitations interacting with it.

Mavromatos, Nick E. [CERN, Theory Division, CH-1211 Geneva 23 (Switzerland)

2011-01-15

333

Full-dimensional quantum dynamics of vibrationally highly excited NHD2  

NASA Astrophysics Data System (ADS)

We report on full-dimensional vibrational quantum dynamics of the highly excited ammonia isotopologue NHD2 using a newly developed potential energy surface and the MCTDH program package. The calculations allow to realistically simulate an infrared laser induced stereomutation reaction at the pyramidal nitrogen atom in the femtosecond time domain. Our results allow for a thorough qualitative and quantitative understanding of infrared photoinduced stereomutation kinetics, the underlying quantum dynamics, and the reaction mechanisms. Comparison is made with a previous, reduced dimensionality study of the same reaction [R. Marquardt, M. Quack, I. Thanopulos, and D. Luckhaus, J. Chem. Phys. 118, 643 (2003)], and it is shown that slight variances of reduced spaces lead to significantly different kinetics. Because the quantum dynamics depends subtly on variances of reduced spaces, reduced dimensionality treatments are not reliable even for qualitative predictions of the stereomutation kinetics. The first direct comparison between the Multiconfigurational Time Dependent Hartree [M. H. Beck, A. Jäckle, G. A. Worth et al., Phys. Rep. 324, 1 (2000)] and Unimolecular Reactions Induced by Monochromatic Infrared Radiation [M. Quack and E. Sutcliffe, QCPE Bulletin 6, 98 (1986)] program packages on a specific, four dimensional quantum dynamical problem allows for their full validation in the present work.

Marquardt, Roberto; Sanrey, Michael; Gatti, Fabien; Le Quéré, Frédéric

2010-11-01

334

Quantum dynamics of lattice states with compact support in an extended Bose-Hubbard model  

NASA Astrophysics Data System (ADS)

We study the dynamical properties, with special emphasis on mobility, of quantum lattice compactons (QLCs) in a one-dimensional Bose-Hubbard model extended with pair-correlated hopping. These are quantum counterparts of classical lattice compactons (localized solutions with exact zero amplitude outside a given region) of an extended discrete nonlinear Schrödinger equation, which can be derived in the classical limit from the extended Bose-Hubbard model. While an exact one-site QLC eigenstate corresponds to a classical one-site compacton, the compact support of classical several-site compactons is destroyed by quantum fluctuations. We show that it is possible to reproduce the stability exchange regions of the one-site and two-site localized solutions in the classical model with properly chosen quantum states. Quantum dynamical simulations are performed for two different types of initial conditions: “localized ground states” which are localized wave packets built from superpositions of compactonlike eigenstates, and SU(4) coherent states corresponding to classical two-site compactons. Clear signatures of the mobility of classical lattice compactons are seen, but this crucially depends on the magnitude of the applied phase gradient. For small phase gradients, which classically correspond to a slow coherent motion, the quantum time scale is of the same order as the time scale of the translational motion, and the classical mobility is therefore destroyed by quantum fluctuations. For a large phase instead, corresponding to fast classical motion, the time scales separate so that a mobile, localized, coherent quantum state can be translated many sites for particle numbers already of the order of 10.

Jason, Peter; Johansson, Magnus

2013-09-01

335

Theory of quantum control of spin-photon dynamics and spin decoherence in semiconductors  

NASA Astrophysics Data System (ADS)

Single electron spin in a semiconductor quantum dot (QD) and single photon wavepacket propagating in an optical waveguide are investigated as carriers of quantum bit (qubit) for information processing. Cavity quantum electrodynamics of the coupled system composed of charged QD, microcavity and waveguide provides a quantum interface for the interplay of stationary spin qubits and flying photon qubits via cavity assisted optical control. This interface forms the basis for a wide range of essential functions of a quantum network, including transferring, swapping, and entangling qubits at distributed quantum nodes as well as a deterministic source and an efficient detector of a single photon wavepacket with arbitrarily specified shape. The cavity assisted optical process also made possible ultrafast initialization and QND readout of the spin qubit in QD. In addition, the strong optical nonlinearity of dot-cavity-waveguide coupled system enables phase gate and entanglement operation for flying single photon qubits in waveguides. The coherence of the electron spin is the wellspring of these quantum applications being investigated. At low temperature and strong magnetic field, the dominant cause of electron spin decoherence is the coupling with the interacting lattice nuclear spins. We present a quantum solution to the coupled dynamics of the electron with the nuclear spin bath. The decoherence is treated in terms of quantum entanglement of the electron with the nuclear pair-flip excitations driven by the various nuclear interactions. A novel nuclear interaction, mediated by virtue spin-flips of the single electron, plays an important role in single spin free-induction decay (FID). The spin echo not only refocuses the dephasing by inhomogeneous broadening in ensemble dynamics but also eliminates the decoherence by electron-mediated nuclear interaction. Thus, the decoherence times for single spin FID and ensemble spin echo are significantly different. The quantum theory of decoherence also leads to a method of coherence recovery of the electron by disentanglement, realized through maneuvering the nuclear bath evolution by control of the electron spin-flip. The studies form the basis to outline the construction of a solid-state quantum network for scalable and distributed processing of quantum information.

Yao, Wang

336

Correlation effects in quantum spin-Hall insulators: a quantum Monte Carlo study.  

PubMed

We consider the Kane-Mele model supplemented by a Hubbard U term. The phase diagram is mapped out using projective auxiliary field quantum Monte Carlo simulations. The quantum spin liquid of the Hubbard model is robust against weak spin-orbit interaction, and is not adiabatically connected to the spin-Hall insulating state. Beyond a critical value of U>U(c) both states are unstable toward magnetic ordering. In the quantum spin-Hall state we study the spin, charge, and single-particle dynamics of the helical Luttinger liquid by retaining the Hubbard interaction only on a ribbon edge. The Hubbard interaction greatly suppresses charge currents along the edge and promotes edge magnetism but leaves the single-particle signatures of the helical liquid intact. PMID:21469774

Hohenadler, M; Lang, T C; Assaad, F F

2011-03-07

337

Correlation Effects in Quantum Spin-Hall Insulators: A Quantum Monte Carlo Study  

NASA Astrophysics Data System (ADS)

We consider the Kane-Mele model supplemented by a Hubbard U term. The phase diagram is mapped out using projective auxiliary field quantum Monte Carlo simulations. The quantum spin liquid of the Hubbard model is robust against weak spin-orbit interaction, and is not adiabatically connected to the spin-Hall insulating state. Beyond a critical value of U>Uc both states are unstable toward magnetic ordering. In the quantum spin-Hall state we study the spin, charge, and single-particle dynamics of the helical Luttinger liquid by retaining the Hubbard interaction only on a ribbon edge. The Hubbard interaction greatly suppresses charge currents along the edge and promotes edge magnetism but leaves the single-particle signatures of the helical liquid intact.

Hohenadler, M.; Lang, T. C.; Assaad, F. F.

2011-03-01

338

Universal quantum control of two-electron spin quantum bits using dynamic nuclear polarization  

NASA Astrophysics Data System (ADS)

One fundamental requirement for quantum computation is to carry out universal manipulations of quantum bits at rates much faster than the qubit's rate of decoherence. Recently, fast gate operations have been demonstrated in logical spin qubits composed of two electron spins where the rapid exchange of the two electrons permits electrically controllable rotations around one axis of the qubit. However, universal control of the qubit requires arbitrary rotations around at least two axes. Here, we show that by subjecting each electron spin to a magnetic field of different magnitude, we achieve full quantum control of the two-electron logical spin qubit with nanosecond operation times. Using a single device, a magnetic-field gradient of several hundred millitesla is generated and sustained using dynamic nuclear polarization of the underlying Ga and As nuclei. Universal control of the two-electron qubit is then demonstrated using quantum state tomography. The presented technique provides the basis for single- and potentially multiple-qubit operations with gate times that approach the threshold required for quantum error correction.

Foletti, Sandra; Bluhm, Hendrik; Mahalu, Diana; Umansky, Vladimir; Yacoby, Amir

2009-12-01

339

Quantum trajectory dynamics in imaginary time with the momentum-dependent quantum potential  

SciTech Connect

The quantum trajectory dynamics is extended to the wave function evolution in imaginary time. For a nodeless wave function a simple exponential form leads to the classical-like equations of motion of trajectories, representing the wave function, in the presence of the momentum-dependent quantum potential in addition to the external potential. For a Gaussian wave function this quantum potential is a time-dependent constant, generating zero quantum force yet contributing to the total energy. For anharmonic potentials the momentum-dependent quantum potential is cheaply estimated from the global Least-squares Fit to the trajectory momenta in the Taylor basis. Wave functions with nodes are described in the mixed coordinate space/trajectory representation at little additional computational cost. The nodeless wave function, represented by the trajectory ensemble, decays to the ground state. The mixed representation wave functions, with lower energy contributions projected out at each time step, decay to the excited energy states. The approach, illustrated by computing energy levels for anharmonic oscillators and energy level splitting for the double-well potential, can be used for the Boltzmann operator evolution.

Garashchuk, Sophya [Department of Chemistry and Biochemistry, University of South Carolina, Columbia, South Carolina 29208 (United States)

2010-01-07

340

Relaxation Dynamics and Pre-thermalization in an isolated Quantum System  

NASA Astrophysics Data System (ADS)

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

Schmiedmayer, Jörg

2012-02-01

341

Quantum control of chemical reaction dynamics in a classical way  

NASA Astrophysics Data System (ADS)

A simplified approach to quantum control of chemical reaction dynamics based on a classical, local control theory was developed. The amplitude of the control pulse is proportional to the linear momentum of the reaction system within the dipole approximation for the system-radiation field interaction. The kinetic energy of the system is the controlling parameter. That is, the reaction is controlled by accelerating the representative point on a potential energy surface before crossing over a potential barrier and then by deaccelerating it to the target after passing over the potential barrier. The classical treatment was extended to control of wave packet dynamics by replacing the classical momentum by a quantum mechanically averaged momentum on the basis of the Ehrenfest theorem. The present method was applied to a quantum system of a simple one-dimensional, double-well potential for checking its validity. A restriction of the applicability of the simplified method was also discussed. An isomerization of HCN was treated as a model system for wave packet control of a two-dimensional reaction.

Umeda, Hiroaki; Fujimura, Yuichi

2000-09-01

342

Quantum dynamics of an optical cavity coupled to a thin semitransparent membrane: Effect of membrane absorption  

SciTech Connect

We study the quantum dynamics of the cavity optomechanical system formed by a Fabry-Perot cavity with a thin vibrating membrane at its center. We determine in particular to what extent optical absorption by the membrane hinders reaching a quantum regime for the cavity-membrane system. We show that even though membrane absorption may significantly lower the cavity finesse and also heat the membrane, one can still simultaneously achieve ground state cooling of a vibrational mode of the membrane and stationary optomechanical entanglement with state-of-the-art apparatuses.

Biancofiore, C.; Karuza, M.; Galassi, M.; Natali, R.; Vitali, D. [School of Science and Technology, Physics Division, University of Camerino, via Madonna delle Carceri, 9, I-62032 Camerino (Italy) and INFN, Sezione di Perugia (Italy); Tombesi, P.; Di Giuseppe, G. [School of Science and Technology, Physics Division, University of Camerino, via Madonna delle Carceri, 9, I-62032 Camerino (Italy) and INFN, Sezione di Perugia (Italy); CriptoCam S.r.l., via Madonna delle Carceri 9, I-62032 Camerino (Italy)

2011-09-15

343

Ultrafast conditional carrier dynamics in semiconductor quantum dots  

NASA Astrophysics Data System (ADS)

We provide direct evidence that the macroscopic response of the gain dynamics in electrically-pumped In- GaAs/GaAs quantum dots is a superposition of intradot relaxation dynamics from microstates with multiple discrete carrier numbers. The gain recovery in the presence of an optical pre-pump fully depleting the ground-state gain is measured to be faster than without pre-pump. This effect, opposite to expectations from rate equations with mean-field carrier distributions, is due to a conditional gain recovery in which microstates with slow internal dynamics are suppressed by the pre-pump. The effect is evident at 15K and still observable at 300 K, beneficial for high-speed optical signal processing.

Borri, Paola; Langbein, Wolfgang

2011-02-01

344

Localization and Glassy Dynamics Of Many-Body Quantum Systems  

PubMed Central

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

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

2012-01-01

345

Including Quantum Effects in the Dynamics of Complex (i.e., Large)Molecular Systems  

SciTech Connect

The development in the 1950's and 60's of crossed molecular beam methods for studying chemical reactions at the single-collision molecular level stimulated the need and desire for theoretical methods to describe these and other dynamical processes in molecular systems. Chemical dynamics theory has made great strides in the ensuing decades, so that methods are now available for treating the quantum dynamics of small molecular systems essentially completely. For the large molecular systems that are of so much interest nowadays (e.g. chemical reactions in solution, in clusters, in nano-structures, in biological systems, etc.), however, the only generally available theoretical approach is classical molecular dynamics (MD) simulations. Much effort is currently being devoted to the development of approaches for describing the quantum dynamics of these complex systems. This paper reviews some of these approaches, especially the use of semiclassical approximations for adding quantum effects to classical MD simulations, also showing some new versions that should make these semiclassical approaches even more practical and accurate.

Miller, William H.

2006-04-27

346

Spatial mode dynamics in wide-aperture quantum-dot lasers  

SciTech Connect

We present a systematic theoretical study of spatial mode dynamics in wide-aperture semiconductor quantum-dot lasers within the Maxwell-Bloch formalism. Our opto-electro-thermal model self-consistently captures the essential dynamical coupling between field, polarization, and carrier density in both thermal and nonthermal regimes, providing detailed description of the complex spatiotemporal modal intensity structure and spectra in these novel devices and broad area edge-emitting lasers in general. Using linear stability analysis and high resolution adaptive-grid finite element numerical simulation, we show that in the nonthermal regime, the presence of inhomogeneous broadening in quantum-dot active media leads to suppressed filamentation and enhanced spatial coherence compared to conventional quantum well devices with comparable phase-amplitude coupling (alpha parameter). Increasing the degree of inhomogeneous broadening in the active medium leads to further improvement in spatial coherence. In the thermal regime, there is further suppression of filamentation in the inhomogeneously broadened quantum-dot active medium; however, the spatial coherence aided by inhomogeneous broadening is partly lost due to the effect of temperature on cavity detuning. We propose that device designs based on optimized inhomogeneous broadening of quantum-dot gain medium could ultimately lead to diffraction-limited outputs in the quasi-cw regime which are still very difficult to achieve in conventional wide-aperture designs.

Mukherjee, Jayanta; McInerney, John G. [Department of Physics and Tyndall National Institute, Optoelectronics Group, National University of Ireland, University College, Cork (Ireland)

2009-05-15

347

Concatenating dynamical decoupling with decoherence-free subspaces for quantum computation  

SciTech Connect

A scheme to implement a quantum computer subjected to decoherence and governed by an untunable qubit-qubit interaction is presented. By concatenating dynamical decoupling through bang-bang (BB) pulse with decoherence-free subspaces (DFSs) encoding, we protect the quantum computer from environment-induced decoherence that results in quantum information dissipating into the environment. For the inherent qubit-qubit interaction that is untunable in the quantum system, BB control plus DFSs encoding will eliminate its undesired effect which spoils quantum information in qubits. We show how this quantum system can be used to implement universal quantum computation.

Zhang Yong; Zhou Zhengwei; Yu Bo; Guo Guangcan [Key Laboratory of Quantum Information, University of Science and Technology of China, Chinese Academy of Sciences, Hefei, Anhui 230026 (China)

2004-04-01

348

Non-equilibrium dynamics of an unstable quantum pendulum explored in a spin-1 Bose-Einstein condensate  

NASA Astrophysics Data System (ADS)

A pendulum prepared perfectly inverted and motionless is a prototype of unstable equilibrium and corresponds to an unstable hyperbolic fixed point in the dynamical phase space. Here, we measure the non-equilibrium dynamics of a spin-1 Bose-Einstein condensate initialized as a minimum uncertainty spin-nematic state to a hyperbolic fixed point of the phase space. Quantum fluctuations lead to non-linear spin evolution along a separatrix and non-Gaussian probability distributions that are measured to be in good agreement with exact quantum calculations up to 0.25s. At longer times, atomic loss due to the finite lifetime of the condensate leads to larger spin oscillation amplitudes, as orbits depart from the separatrix. This demonstrates how decoherence of a many-body system can result in apparent coherent behaviour. This experiment provides new avenues for studying macroscopic spin systems in the quantum limit and for investigations of important topics in non-equilibrium quantum dynamics.

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

2012-11-01

349

Terahertz Dynamics of Quantum-Confined Electrons in Carbon Nanomaterials  

NASA Astrophysics Data System (ADS)

The terahertz (THz) frequency range. 0.1 - 20 THz, exists between the microwave and infrared ranges and contains abundant information on the dynamics of charge and spin carriers in condensed matter systems. Since its advent two decades ago, THz spectroscopy has been extensively used to study a wide range of solid state materials, including typical semiconductors, conducting polymers, insulators, superconductors, and artificially grown structures such as quantum wells. In these systems, electronic and photonic events tend to occur on the time scale of tens to hundreds of femtoseconds, which results in many important excitations, resonances and dynamical phenomena in the THz frequency range. In this dissertation work, we have developed a typical THz time-domain spectroscopy (TDS) system to investigate the THz dynamics of quantum-confined electrons in two important types of carbon nanomaterial: single-walled carbon nanotubes (SWNTs) and graphene. Polarization dependent THz transmission measurements were conducted on a highly-aligned SWNT film on a sapphire substrate, revealing extremely high anisotropy: virtually no attenuation was observed when the polarization of the THz beam was perpendicular to the nanotube axis, while the THz beam was strongly absorbed when its polarization was parallel to the tube axis. From the measured absorption anisotropy, we calculated the reduced linear dichrosim to be 3, corresponding to a nematic order parameter of 1. These observations are a direct result of the one-dimensional nature of conduction electrons in the nanotubes and at the same time, demonstrate that any misalignment of nanotubes in the film mast have characteristic length scales much smaller than the wavelengths used in these experiments (1.5 mm -- 150 mum). Based on this work, an ideal THz linear polarizer built with parallel stacks of such aligned SWNT films was synthesized, exhibiting a degree of polarization of 99.9% throughout the frequency range 0.2 -- 2.2 THz and a high extinction ratio of 10--3 (or 30 dB). The THz complex conductivity of the thin SWNT film was extracted through a proper model directly from the TDS data without Kramers-Kronig analysis. Both real and imaginary parts of the conductivity showed a non-Drude frequency dependence, indicating the presence of plasmon-dipole resonance at higher frequencies. Finally, the optical conductivity of large-area. graphene grown from solid state carbon source was studied in a wide spectral range (7 cm --1 -- 9500 cm--1) using THz-TDS and Fourier transform infrared spectroscopy. We observed that the Fermi level Ef of graphene could be tuned by both electrical gating and thermal annealing. The optical conductivity measured at different carrier concentrations exhibited Drude-like frequency dependence, and different 2 Ef onsets in the spectrum were probed as well.

Ren, Lei

350

Monte Carlo techniques for real-time quantum dynamics  

SciTech Connect

The stochastic-gauge representation is a method of mapping the equation of motion for the quantum mechanical density operator onto a set of equivalent stochastic differential equations. One of the stochastic variables is termed the 'weight', and its magnitude is related to the importance of the stochastic trajectory. We investigate the use of Monte Carlo algorithms to improve the sampling of the weighted trajectories and thus reduce sampling error in a simulation of quantum dynamics. The method can be applied to calculations in real time, as well as imaginary time for which Monte Carlo algorithms are more-commonly used. The Monte-Carlo algorithms are applicable when the weight is guaranteed to be real, and we demonstrate how to ensure this is the case. Examples are given for the anharmonic oscillator, where large improvements over stochastic sampling are observed.

Dowling, Mark R. [ARC Centre of Excellence for Quantum-Atom Optics, Department of Physics, School of Physical Sciences, University of Queensland, Brisbane, Qld 4072 (Australia)]. E-mail: dowling@physics.uq.edu.au; Davis, Matthew J. [ARC Centre of Excellence for Quantum-Atom Optics, Department of Physics, School of Physical Sciences, University of Queensland, Brisbane, Qld 4072 (Australia); Drummond, Peter D. [ARC Centre of Excellence for Quantum-Atom Optics, Department of Physics, School of Physical Sciences, University of Queensland, Brisbane, Qld 4072 (Australia); Corney, Joel F. [ARC Centre of Excellence for Quantum-Atom Optics, Department of Physics, School of Physical Sciences, University of Queensland, Brisbane, Qld 4072 (Australia)

2007-01-10

351

Dynamic phase diagram for the quantum phase model  

NASA Astrophysics Data System (ADS)

We address the stability of superfluid currents in a system of interacting lattice bosons. We consider various Gutzwiller trial states for the quantum phase model which provides a good approximation for the Bose-Hubbard model in the limit of large interactions and boson populations. We thoroughly analyze the current-carrying stationary states of the dynamics ensuing from a Gaussian ansatz, and derive analytical results for the critical lines signaling their modulational and energetic instability, as well as the maximum of the carried current. We show that these analytical results are in good qualitative agreement with those obtained numerically in previous works on the Bose-Hubbard model, and in the present work for the quantum phase model.

Buonsante, P.; Orefice, L.; Smerzi, A.

2013-06-01

352

Quasilocality and efficient simulation of markovian quantum dynamics.  

PubMed

We consider open many-body systems governed by a time-dependent quantum master equation with short-range interactions. With a generalized Lieb-Robinson bound, we show that the evolution in this very generic framework is quasilocal; i.e., the evolution of observables can be approximated by implementing the dynamics only in a vicinity of the observables' support. The precision increases exponentially with the diameter of the considered subsystem. Hence, time evolution can be simulated on classical computers with a cost that is independent of the system size. Providing error bounds for Trotter decompositions, we conclude that the simulation on a quantum computer is additionally efficient in time. For experiments and simulations in the Schrödinger picture, our result can be used to rigorously bound finite-size effects. PMID:23003931

Barthel, Thomas; Kliesch, Martin

2012-06-05

353

Marginal picture of quantum dynamics related to intrinsic arrival times  

SciTech Connect

We introduce a marginal picture of the evolution of quantum systems, in which the representation vectors are the quantities that evolve and operators and wave packets remain static. The representation vectors can be seen as probe functions that are the evolution of a {delta} function with initial support on q=X in coordinate space. This picture of the dynamics is suited for the determination of intrinsic arrival distributions for quantum systems, providing a clear physical meaning to the 'time eigenstates' used in these calculations. We also analyze Galapon et al.'s 'confined time eigenstates' [Phys. Rev. Lett. 93, 180406 (2004)] from this point of view, and propose alternative probe functions for confined systems without the need of a quantized time.

Torres-Vega, Gabino [Physics Department, Cinvestav, Apartado Postal 14-740, 07000 Mexico City, Distrito Federal (Mexico)

2007-09-15

354

Study of the H+O2 reaction by means of quantum mechanical and statistical approaches: The dynamics on two different potential energy surfaces  

Microsoft Academic Search

The possible existence of a complex-forming pathway for the H+O2 reaction has been investigated by means of both quantum mechanical and statistical techniques. Reaction probabilities, integral cross sections, and differential cross sections have been obtained with a statistical quantum method and the mean potential phase space theory. The statistical predictions are compared to exact results calculated by means of time

Pedro Bargueño; Tomás González-Lezana; Pascal Larrégaray; Laurent Bonnet; Jean-Claude Rayez; Marlies Hankel; Sean C. Smith; Anthony J. H. M. Meijer

2008-01-01

355

The ?-cyclodextrin/benzene complex and its hydrogen bonds - a theoretical study using molecular dynamics, quantum mechanics and COSMO-RS  

PubMed Central

Summary Four highly ordered hydrogen-bonded models of ?-cyclodextrin (?-CD) and its inclusion complex with benzene were investigated by three different theoretical methods: classical quantum mechanics (QM) on AM1 and on the BP/TZVP-DISP3 level of approximation, and thirdly by classical molecular dynamics simulations (MD) at different temperatures (120 K and 273 to 300 K). The hydrogen bonds at the larger O2/O3 rim of empty ?-CDs prefer the right-hand orientation, e.g., O3-H…O2-H in the same glucose unit and bifurcated towards …O4 and O3 of the next glucose unit on the right side. On AM1 level the complex energy was ?2.75 kcal mol?1 when the benzene molecule was located parallel inside the ?-CD cavity and ?2.46 kcal mol?1 when it was positioned vertically. The AM1 HOMO/LUMO gap of the empty ?-CD with about 12 eV is lowered to about 10 eV in the complex, in agreement with data from the literature. AM1 IR spectra displayed a splitting of the O–H frequencies of cyclodextrin upon complex formation. At the BP/TZVP-DISP3 level the parallel and vertical positions from the starting structures converged to a structure where benzene assumes a more oblique position (?20.16 kcal mol?1 and ?20.22 kcal mol?1, resp.) as was reported in the literature. The character of the COSMO-RS ?-surface of ?-CD was much more hydrophobic on its O6 rim than on its O2/O3 side when all hydrogen bonds were arranged in a concerted mode. This static QM picture of the ?-CD/benzene complex at 0 K was extended by MD simulations. At 120 K benzene was mobile but always stayed inside the cavity of ?-CD. The trajectories at 273, 280, 290 and 300 K certainly no longer displayed the highly ordered hydrogen bonds of ?-CD and benzene occupied many different positions inside the cavity, before it left the ?-CD finally at its O2/O3 side.

Grczelschak-Mick, Nicole

2013-01-01

356

Computational relativistic quantum dynamics and its application to relativistic tunneling and Kapitza-Dirac scattering  

NASA Astrophysics Data System (ADS)

Computational methods are indispensable to study the quantum dynamics of relativistic light-matter interactions in parameter regimes where analytical methods become inapplicable. We present numerical methods for solving the time-dependent Dirac equation and the time-dependent Klein-Gordon equation and their implementation on high performance graphics cards. These methods allow us to study tunneling from hydrogen-like highly charged ions in strong laser fields and Kapitza-Dirac scattering in the relativistic regime.

Bauke, Heiko; Klaiber, Michael; Yakaboylu, Enderalp; Hatsagortsyan, Karen Z.; Ahrens, Sven; Müller, Carsten; Keitel, Christoph H.

2013-05-01

357

Dynamical eigenfunctions and critical density in loop quantum cosmology  

NASA Astrophysics Data System (ADS)

We offer a new, physically transparent argument for the existence of the critical, universal maximum matter density in loop quantum cosmology for the case of a flat Friedmann-Lemaître-Robertson-Walker cosmology with scalar matter. The argument is based on the existence of a sharp exponential ultraviolet cutoff in momentum space on the eigenfunctions of the quantum cosmological dynamical evolution operator (the gravitational part of the Hamiltonian constraint), attributable to the fundamental discreteness of spatial volume in loop quantum cosmology. The existence of the cutoff is proved directly from recently found exact solutions for the eigenfunctions for this model. As a consequence, the operators corresponding to the momentum of the scalar field and the spatial volume approximately commute. The ultraviolet cutoff then implies that the scalar momentum, though not a bounded operator, is in effect bounded on subspaces of constant volume, leading to the upper bound on the expectation value of the matter density. The maximum matter density is universal (i.e. independent of the quantum state) because of the linear scaling of the cutoff with volume. These heuristic arguments are supplemented by a new proof in the volume representation of the existence of the maximum matter density. The techniques employed to demonstrate the existence of the cutoff also allow us to extract the large-volume limit of the exact eigenfunctions, confirming earlier numerical and analytical work showing that the eigenfunctions approach superpositions of the eigenfunctions of the Wheeler-DeWitt quantization of the same model. We argue that generic (not just semiclassical) quantum states approach symmetric superpositions of expanding and contracting universes.

Craig, David A.

2013-02-01

358

Ultrafast exciton dynamics in InAs/ZnSe nanocrystal quantum dots.  

PubMed

Colloidal nanocrystal quantum dots with a band gap in the near infra-red have potential application as the emitters for telecommunications or in vivo imaging, or as the photo-absorbing species in next generation solar cells or photodetectors. However, electro- and photoluminescence yields and the efficiency with which photo-generated charges can be extracted from quantum dots depend on the total rate of recombination, which can be dominated by surface-mediated processes. In this study, we use ultrafast transient absorption spectroscopy to characterise the recombination dynamics of photo-generated charges in InAs/ZnSe nanocrystal quantum dots. We find that recombination is dominated by rapid, sub-nanosecond transfer of conduction band electrons to surface states. For the size of dots studied, we also find no evidence of significant multiple exciton generation for photon energies up to 3.2 times the band gap, in agreement with our theoretical modelling. PMID:22968520

Cadirci, Musa; Stubbs, Stuart K; Hardman, Samantha J O; Masala, Ombretta; Allan, Guy; Delerue, Christophe; Pickett, Nigel; Binks, David J

2012-09-11

359

Creating exotic condensates via quantum-phase-revival dynamics in engineered lattice potentials  

SciTech Connect

In the field of ultracold atoms in optical lattices a plethora of phenomena governed by the hopping energy J and the interaction energy U have been studied in recent years. However, the trapping potential typically present in these systems sets another energy scale and the effects of the corresponding time scale on the quantum dynamics have rarely been considered. Here we study the quantum collapse and revival of a lattice Bose-Einstein condensate (BEC) in an arbitrary spatial potential, focusing on the special case of harmonic confinement. Analyzing the time evolution of the single-particle density matrix, we show that the physics arising at the (temporally) recurrent quantum phase revivals is essentially captured by an effective single-particle theory. This opens the possibility of preparing exotic nonequilibrium condensate states with a large degree of freedom by engineering the underlying spatial lattice potential.

Buchhold, Michael; Bissbort, Ulf; Hofstetter, Walter [Institut fuer Theoretische Physik, Johann Wolfgang Goethe-Universitaet, D-60438 Frankfurt/Main (Germany); Will, Sebastian [Fakultaet fuer Physik, Ludwig-Maximilians-Universitaet, D-80799 Muenchen (Germany); Max-Planck-Institut fuer Quantenoptik, D-85748 Garching (Germany)

2011-08-15

360

Quantum-Mechanical Study of the Collision Dynamics of O2(3?g-) + O2(3?g-) on a New ab Initio Potential Energy Surface  

NASA Astrophysics Data System (ADS)

The quantum mechanical theory for the scattering of two identical rigid rotors is reviewed and applied to the collision of O2(3?g-) molecules using a new accurate ab initio potential energy surface (PES) for the quintet state of the composite system. The PES is based on calculations using restricted coupled-cluster theory with singles, doubles, and perturbative triple excitations [RCCSD(T)] [ Bartolomei ; et al. J. Chem. Phys. 2008, 128, 214304. ]. This PES is extended here for large intermolecular distances using the ab initio long-range coefficients of Hettema et al. [ J. Chem. Phys. 1994, 100, 1297. ]. Elastic and rotationally inelastic integral cross sections have been obtained by means of close coupling calculations in the subthermal energy range (center-of-mass velocities below 500 m/s). Results are compared with those obtained using a PES derived from molecular beam experiments [ Aquilanti ; et al. J. Am. Chem. Soc. 1999, 121, 10794. ]. General agreement is found between both PESs, although the experimentally derived PES appears as somewhat more anisotropic at least for the studied energy range. There is, however, a significant difference in the absolute value of the elastic cross sections that is due to differences in the long-range dispersion interaction. The performance of the ab initio PES for higher velocities (relevant to experiments) is also explored by retaining just the isotropic component of the interaction. A satisfactory agreement is found for the shape of the glory pattern but shifted toward lower absolute values of the cross sections.

Pérez-Ríos, Jesús; Bartolomei, Massimiliano; Campos-Martínez, José; Hernández, Marta I.; Hernández-Lamoneda, Ramón

2009-10-01

361

Quantum dynamics of resonant molecule formation in waveguides  

NASA Astrophysics Data System (ADS)

We explore the quantum dynamics of heteronuclear atomic collisions in waveguides and demonstrate the existence of a novel mechanism for the resonant formation of polar molecules. The molecular formation probabilities can be tuned by changing the trap frequencies that characterize the transverse modes of the atomic species. The origin of this effect is the confinement-induced mixing of the relative and center of mass motions in the atomic collision process leading to a coupling of the diatomic continuum to the center of mass excited molecular states in closed transverse channels.

Melezhik, V. S.; Schmelcher, P.

2009-07-01

362

Fast and stable method for simulating quantum electron dynamics  

PubMed

A fast and stable method is formulated to compute the time evolution of a wave function by numerically solving the time-dependent Schrodinger equation. This method is a real-space-real-time evolution method implemented by several computational techniques such as Suzuki's exponential product, Cayley's form, the finite differential method, and an operator named adhesive operator. This method conserves the norm of the wave function, manages periodic conditions and adaptive mesh refinement technique, and is suitable for vector- and parallel-type supercomputers. Applying this method to some simple electron dynamics, we confirmed the efficiency and accuracy of the method for simulating fast time-dependent quantum phenomena. PMID:11088775

Watanabe; Tsukada

2000-08-01

363

INVITED ARTICLE: Wigner's dynamical transition state theory in phase space: classical and quantum  

NASA Astrophysics Data System (ADS)

We develop Wigner's approach to a dynamical transition state theory in phase space in both the classical and quantum mechanical settings. The key to our development is the construction of a normal form for describing the dynamics in the neighbourhood of a specific type of saddle point that governs the evolution from reactants to products in high dimensional systems. In the classical case this is the standard Poincaré Birkhoff normal form. In the quantum case we develop a normal form based on the Weyl calculus and an explicit algorithm for computing this quantum normal form. The classical normal form allows us to discover and compute the phase space structures that govern classical reaction dynamics. From this knowledge we are able to provide a direct construction of an energy dependent dividing surface in phase space having the properties that trajectories do not locally 're-cross' the surface and the directional flux across the surface is minimal. Using this, we are able to give a formula for the directional flux through the dividing surface that goes beyond the harmonic approximation. We relate this construction to the flux flux autocorrelation function which is a standard ingredient in the expression for the reaction rate in the chemistry community. We also give a classical mechanical interpretation of the activated complex as a normally hyperbolic invariant manifold (NHIM), and further describe the structure of the NHIM. The quantum normal form provides us with an efficient algorithm to compute quantum reaction rates and we relate this algorithm to the quantum version of the flux flux autocorrelation function formalism. The significance of the classical phase space structures for the quantum mechanics of reactions is elucidated by studying the phase space distribution of scattering states. The quantum normal form also provides an efficient way of computing Gamov Siegert resonances. We relate these resonances to the lifetimes of the quantum activated complex. We consider several one, two and three degree-of-freedom systems and show explicitly how calculations of the above quantities can be carried out. Our theoretical framework is valid for Hamiltonian systems with an arbitrary number of degrees of freedom and we demonstrate that in several situations it gives rise to algorithms that are computationally more efficient than existing methods.

Waalkens, Holger; Schubert, Roman; Wiggins, Stephen

2008-01-01

364

Atomic physics and quantum optics using superconducting circuits: from the Dynamical Casimir effect to Majorana fermions  

NASA Astrophysics Data System (ADS)

This talk will present an overview of some of our recent results on atomic physics and quantum optics using superconducting circuits. Particular emphasis will be given to photons interacting with qubits, interferometry, the Dynamical Casimir effect, and also studying Majorana fermions using superconducting circuits.[4pt] References available online at our web site:[0pt] J.Q. You, Z.D. Wang, W. Zhang, F. Nori, Manipulating and probing Majorana fermions using superconducting circuits, (2011). Arxiv. J.R. Johansson, G. Johansson, C.M. Wilson, F. Nori, Dynamical Casimir effect in a superconducting coplanar waveguide, Phys. Rev. Lett. 103, 147003 (2009). [0pt] J.R. Johansson, G. Johansson, C.M. Wilson, F. Nori, Dynamical Casimir effect in superconducting microwave circuits, Phys. Rev. A 82, 052509 (2010). [0pt] C.M. Wilson, G. Johansson, A. Pourkabirian, J.R. Johansson, T. Duty, F. Nori, P. Delsing, Observation of the Dynamical Casimir Effect in a superconducting circuit. Nature, in press (Nov. 2011). P.D. Nation, J.R. Johansson, M.P. Blencowe, F. Nori, Stimulating uncertainty: Amplifying the quantum vacuum with superconducting circuits, Rev. Mod. Phys., in press (2011). [0pt] J.Q. You, F. Nori, Atomic physics and quantum optics using superconducting circuits, Nature 474, 589 (2011). [0pt] S.N. Shevchenko, S. Ashhab, F. Nori, Landau-Zener-Stuckelberg interferometry, Phys. Reports 492, 1 (2010). [0pt] I. Buluta, S. Ashhab, F. Nori. Natural and artificial atoms for quantum computation, Reports on Progress in Physics 74, 104401 (2011). [0pt] I.Buluta, F. Nori, Quantum Simulators, Science 326, 108 (2009). [0pt] L.F. Wei, K. Maruyama, X.B. Wang, J.Q. You, F. Nori, Testing quantum contextuality with macroscopic superconducting circuits, Phys. Rev. B 81, 174513 (2010). [0pt] J.Q. You, X.-F. Shi, X. Hu, F. Nori, Quantum emulation of a spin system with topologically protected ground states using superconducting quantum circuit, Phys. Rev. A 81, 063823 (2010).

Nori, Franco

2012-02-01

365

Instability and dynamics of two nonlinearly coupled intense laser beams in a quantum plasma  

NASA Astrophysics Data System (ADS)

We consider nonlinear interactions between two relativistically strong laser beams and a quantum plasma composed of degenerate electron fluids and immobile ions. The collective behavior of degenerate electrons is modeled by quantum hydrodynamic equations composed of the electron continuity, quantum electron momentum (QEM) equation, as well as the Poisson and Maxwell equations. The QEM equation accounts the quantum statistical electron pressure, the quantum electron recoil due to electron tunneling through the quantum Bohm potential, electron-exchange, and electron-correlation effects caused by electron spin, and relativistic ponderomotive forces (RPFs) of two circularly polarized electromagnetic (CPEM) beams. The dynamics of the latter are governed by nonlinear wave equations that include nonlinear currents arising from the relativistic electron mass increase in the CPEM wave fields, as well as from the beating of the electron quiver velocity and electron density variations reinforced by the RPFs of the two CPEM waves. Furthermore, nonlinear electron density variations associated with the driven (by the RPFs) quantum electron plasma oscillations obey a coupled nonlinear Schrödinger and Poisson equations. The nonlinearly coupled equations for our purposes are then used to obtain a general dispersion relation (GDR) for studying the parametric instabilities and the localization of CPEM wave packets in a quantum plasma. Numerical analyses of the GDR reveal that the growth rate of a fastest growing parametrically unstable mode is in agreement with the result that has been deduced from numerical simulations of the governing nonlinear equations. Explicit numerical results for two-dimensional (2D) localized CPEM wave packets at nanoscales are also presented. Possible applications of our investigation to intense laser-solid density compressed plasma experiments are highlighted.

Wang, Yunliang; Shukla, P. K.; Eliasson, B.

2013-01-01

366

Dynamics of e+ + H(ns)?Ps(n?s) + p in dense quantum plasmas  

NASA Astrophysics Data System (ADS)

The dynamics of e+ + H(ns)?Ps(n?s) + p in dense quantum plasmas has been investigated using a distorted-wave theory in momentum space. The interactions among the charged particles in the plasma have been represented by modified Debye–Huckel potentials or exponential cosine screened Coulomb potentials. Making use of simple variationally determined wave functions for the hydrogenic atom, it has been possible to obtain the distorted-wave scattering amplitude in a tractable form. A detailed study has been made on differential and total cross sections in the energy range 25–250 eV. It has been found that screening of the interaction potentials has a significant effect on the scattering dynamics. To the best of our knowledge, such a study on the differential and total cross sections for the electron capture processes in positron–hydrogen collisions in dense quantum plasma is reported first in the literature.

Nayek, Sujay; Ghoshal, Arijit

2013-10-01

367

Quantum dynamics of the O + OH -> H + O2 reaction at low temperatures  

SciTech Connect

We report quantum dynamics calculations of rate coefficients for the O + OH {yields} H + O{sub 2} reaction on two potential energy surfaces (PESs) using a time-independent quantum formalism based on hyperspherical coordinates. Our calculations show that the rate coefficient remains largely constant in the temperature range 10--39 K, in agreement with the conclusions of a recent experimental study [Carty et al., J. Phys. Chem. A 110, 3101 (2006)]. This is in constrast with the quantum calculations of Xu et al. [J. Chem. Phys. 127, 024304 (2007)] which, using the same PES, predicted two orders of magnitude drop in the rate coefficient value from 39 K to 10 K. Implications of our findings to oxygen chemistry in the interstellar medium are discussed.

Kendrick, Brian Kent [Los Alamos National Laboratory; Quemener, Goulven [UNLV; Balakrishnan, Naduvalath [UNLV

2008-01-01

368

Influence of nuclear quantum effects on nonadiabatic dynamics in the condensed phase  

Microsoft Academic Search

Mixing quantum and classical prescriptions of dynamics is an attractive way to approach condensed phase problems in which only a few of the degrees of freedom need to be treated with quantum mechanics while the rest are treated using an effective classical description. The way in which the full quantum problem is reduced so that some variables are treated effectively

David Coker

1998-01-01

369

State-selected dynamics of the complex-forming bimolecular reaction Cl+CH3Cl'-->ClCH3+Cl'-: A four-dimensional quantum scattering study  

Microsoft Academic Search

Time-independent quantum scattering calculations have been carried out on the Walden inversion SN2 reaction Cl-+CH3Cl'(v1,v2,v3)-->ClCH3(v1',v2',v3')+Cl'-. The two C-Cl stretching modes (quantum numbers v3 and v3') and the totally symmetric internal modes of the methyl group (C-H stretching vibration, v1 and v1', and inversion bending vibration, v2 and v2') are treated explicitly. A four-dimensional coupled cluster potential energy surface is employed.

Carsten Hennig; Stefan Schmatz

2004-01-01

370

Spin Dynamics in InAs Quantum Dots  

NASA Astrophysics Data System (ADS)

Spin coherence in InAs Self-Assemble Quantum Dots (SAQD's) could be useful for optical delay lines and quantum information technology. Very uniform dots and a very accurate measurement of dephasing processes are required to realize these possibilities. To this effect we report decoherence times in InAs SAQD. Here we describe measurements of spin dynamics from a 17 layered nominally undoped wafer of InAs SAQDs with a varying dot-size. We used Time Resolved Kerr Rotation (TRKR) for a wavelength resonant with the 3D InAs Stranski-Krastanow strain mediated quantum dots. Response is observed from 0 to 5 T that corresponds to a freely precessing spin with g = 0.45, a 1.2 ns lifetime at B=0 that decreases with B, and a sine-like phase. We attribute this spin to an electron from either the ground state of a negative trion or the excited state of a positive trion. The dots are dots unintentionally doped from background doping in the MBE chamber. Work supported in part by ONR, NSA/ARO, and DARPA/QUIST. JW is an NRC/NRL Postdoctoral Research Associate.

Whitaker, Janica; Bracker, Allan; Gammon, Daniel; Kennedy, Thomas

2006-03-01

371

Dynamic generation of topologically protected self-correcting quantum memory  

NASA Astrophysics Data System (ADS)

We propose a scheme to dynamically realize a quantum memory based on the toric code. The code is generated from qubit systems with typical two-body interactions (Ising, XY, Heisenberg) using periodic, NMR-like, pulse sequences. It allows one to encode the logical qubits without measurements and to protect them dynamically against the time evolution of the physical qubits. A weakly coupled cavity mode mediates a long-range attractive interaction between the stabilizer operators of the toric code, thereby suppressing the creation of thermal anyons. This significantly increases the lifetime of the memory compared to the code with noninteracting stabilizers. We investigate how the fidelity, with which the toric code is realized, depends on the period length T of the pulse sequence and the magnitude of possible pulse errors. We derive an optimal period Topt that maximizes the fidelity.

Becker, Daniel; Tanamoto, Tetsufumi; Hutter, Adrian; Pedrocchi, Fabio L.; Loss, Daniel

2013-04-01

372

Protecting dissipative quantum state preparation via dynamical decoupling  

NASA Astrophysics Data System (ADS)

We show that dissipative quantum state preparation processes can be protected against qubit dephasing by interlacing the state preparation control with dynamical decoupling (DD) control consisting of a sequence of short ? pulses. The inhomogeneous broadening can be suppressed to second order of the pulse interval, and the protection efficiency is nearly independent of the pulse sequence but determined by the average interval between pulses. The DD protection is numerically tested and found to be efficient against inhomogeneous dephasing on two exemplary dissipative state preparation schemes that use collective pumping to realize many-body singlets and linear cluster states, respectively. Numerical simulation also shows that the state preparation can be efficiently protected by ? pulses with completely random arrival time. Our results make possible the application of these state preparation schemes in inhomogeneously broadened systems. DD protection of state preparation against dynamical noises is also discussed using the example of Gaussian noise with a semiclasscial description.

Gong, Z. R.; Yao, Wang

2013-03-01

373

Protection of quantum systems by nested dynamical decoupling  

SciTech Connect

Based on a theorem we establish on dynamical decoupling of time-dependent systems, we present a scheme of nested Uhrig dynamical decoupling (NUDD) to protect multiqubit systems in generic quantum baths to arbitrary decoupling orders, using only single-qubit operations. The number of control pulses in NUDD increases polynomially with the decoupling order. For general multilevel systems, this scheme can preserve a set of unitary Hermitian system operators which mutually either commute or anticommute, and hence all operators in the Lie algebra generated from this set of operators, generating an effective symmetry group for the system up to a given order of precision. NUDD can be implemented with pulses of finite amplitude, up to an error in the second order of the pulse durations.

Wang Zhenyu; Liu Renbao [Department of Physics, Chinese University of Hong Hong, Shatin, N. T. (Hong Kong)

2011-02-15

374

Trajectory-guided configuration interaction simulations of multidimensional quantum dynamics  

SciTech Connect

We propose an approach to modelling multidimensional quantum systems which uses direct-dynamics trajectories to guide wavefunction propagation. First, trajectory simulations are used to generate a sample of dynamically relevant configurations on the potential energy surface (PES). Second, the sampled configurations are used to construct an n-mode representation of the PES using a greedy algorithm. Finally, the time-dependent Schroedinger equation is solved using a configuration interaction expansion of the wavefunction, with individual basis functions derived directly from the 1-mode contributions to the n-mode PES. This approach is successfully demonstrated by application to a 20-dimensional benchmark problem describing tunnelling in the presence of coupled degrees of freedom.

Habershon, Scott [Centre for Computational Chemistry, School of Chemistry, University of Bristol, Bristol BS8 1TS (United Kingdom)

2012-02-07

375

Non-Markovian quantum dynamics: local versus nonlocal.  

PubMed

We analyze non-Markovian evolution of open quantum systems. It is shown that any dynamical map representing the evolution of such a system may be described either by a nonlocal master equation with a memory kernel or equivalently by an equation which is local in time. These two descriptions are complementary: if one is simple, the other is quite involved, or even singular, and vice versa. The price one pays for the local approach is that the corresponding generator keeps the memory about the starting point "t{0}." This is the very essence of non-Markovianity. Interestingly, this generator might be highly singular; nevertheless, the corresponding dynamics is perfectly regular. Remarkably, the singularities of the generator may lead to interesting physical phenomena such as the revival of coherence or sudden death and revival of entanglement. PMID:20366866

Chru?ci?ski, Dariusz; Kossakowski, Andrzej

2010-02-19

376

Protection of quantum systems by nested Uhrig dynamical decoupling  

NASA Astrophysics Data System (ADS)

Based on a theorem we establish on dynamical decoupling of time-dependent systems, we present a scheme of nested Uhrig dynamical decoupling (NUDD) to protect multi-qubit systems in generic quantum baths to arbitrary decoupling orders. This scheme uses only single-qubit operations. Higher order decoupling is achieved at the cost of a polynomial increase in pulse number. For general multi-level systems, this scheme protects a set of unitary Hermitian system operators which mutually either commute or anti-commute, and hence all operators in the Lie algebra generated from this set of operators, generating an effective symmetry group for the system up to a given order of precision. We also show how to implement NUDD with pulses of finite amplitude, up to an error in the second order of the pulse durations.

Wang, Zhen-Yu; Liu, Ren-Bao

2011-03-01

377

Protection of quantum systems by nested dynamical decoupling  

NASA Astrophysics Data System (ADS)

Based on a theorem we establish on dynamical decoupling of time-dependent systems, we present a scheme of nested Uhrig dynamical decoupling (NUDD) to protect multiqubit systems in generic quantum baths to arbitrary decoupling orders, using only single-qubit operations. The number of control pulses in NUDD increases polynomially with the decoupling order. For general multilevel systems, this scheme can preserve a set of unitary Hermitian system operators which mutually either commute or anticommute, and hence all operators in the Lie algebra generated from this set of operators, generating an effective symmetry group for the system up to a given order of precision. NUDD can be implemented with pulses of finite amplitude, up to an error in the second order of the pulse durations.

Wang, Zhen-Yu; Liu, Ren-Bao

2011-02-01

378

Improved isospin dependent quantum molecular dynamics model and its application to fusion reactions near Coulomb barrier  

Microsoft Academic Search

The isospin dependent quantum molecular dynamics model is developed by introducing switch function method which deals with correctly the surface interaction and shell effect in the process of projectile and target approaching. The fusion excitation functions for 40Ca+40Ca, 40Ca+48Ca and 48Ca+48Ca at energies in the vicinity of the Coulomb barrier are studied. The experimental data of the fusion cross sections

Zhao-Qing Feng; Feng-Shou Zhang; Gen-Ming Jin; Xi Huang

2005-01-01

379

Carrier Dynamics in Self-Organized Quantum Dots and Their Application to Infrared Detectors and Sources  

Microsoft Academic Search

Intraband transitions in quantum dots (QDs) can be used for mid- and far-infrared (IR) detectors and sources. Self-organized QD devices usually consist of large bandgap semiconductors with well-established device processing techniques. Polarization selection rules allow absorption and emission in the surface-normal direction. We have conducted extensive theoretical and experimental studies of carrier dynamics in In(Ga)As\\/Ga(Al)As self-organized QDs grown by molecular

Pallab Bhattacharya

2003-01-01

380

Ultrafast electronic dynamics in unipolar n-doped indium gallium arsenide/gallium arsenide self-assembled quantum dots  

NASA Astrophysics Data System (ADS)

Photodetectors based on intraband infrared absorption in the quantum dots have demonstrated improved performance over its quantum well counterpart by lower dark current, relative temperature insensitivity, and its ability for normal incidence operation. Various scattering processes, including phonon emission/absorption and carrier-carrier scattering, are critical in understanding device operation on the fundamental level. In previous studies, our group has investigated carrier dynamics in both low- and high-density regime. Ultrafast electron-hole scattering and the predicted phonon bottleneck effect in intrinsic quantum dots have been observed. Further examination on electron dynamics in unipolar structures is presented in this thesis. We used n-doped quantum dot in mid-infrared photodetector device structure to study the electron dynamics in unipolar structure. Differential transmission spectroscopy with mid-infrared intraband pump and optical interband probe was implemented to measure the electron dynamics directly without creating extra electron-hole pair, Electron relaxation after excitation was measured under various density and temperature conditions. Rapid capture into quantum dot within ˜ 10 ps was observed due to Auger-type electron-electron scattering. Intradot relaxation from the quantum dot excited state to the ground state was also observed on the time scale of 100 ps. With highly doped electron density in the structure, the inter-sublevel relaxation is dominated by Auger-type electron-electron scattering and the phonon bottleneck effect is circumvented. Nanosecond-scale recovery in larger-sized quantum dots was observed, not intrinsic to electron dynamics but due to band-bending and built-in voltage drift. An ensemble Monte Carlo simulation was also established to model the dynamics in quantum dots and in goad agreement with the experimental results. We presented a comprehensive picture of electron dynamics in the unipolar quantum dot structure. Although the phonon bottleneck is circumvented with high doped electron density, relaxation processes in unipolar quantum dots have been measured with time scales longer than that of bipolar systems. The results explain the operation principles of the quantum dot infrared photodetector on a microscopic level and provide basic understanding for future applications and designs.

Wu, Zong-Kwei J.

381

Dynamics of Thermal Effects in the Spin-Wave Theory of Quantum Antiferromagnets  

NASA Astrophysics Data System (ADS)

The main propose of this work [1] is to study the dynamics of quantum antiferromagnets due to the interaction with a thermal environment. To this end we resort to the spin wave theory which has become by now an standard and reference tool in order to have a good approximate description of quantum antiferromagnetic systems in appropriate dimensions. We derive a master equation that allows us to study non-equilibrium dynamics due to the thermal bosons in the environment, and give closed analytic form for the magnon decay rates. Moreover, we show that these ones turn out to be closely related to form factors, which are experimentally accessible by means of neutron and Raman scattering. Furthermore, we compute the time-evolution of the staggered magnetization showing that, for moderate temperatures, the magnetic order is not spoilt even if the coupling is fully isotropic. As far as we know, this is a fundamental aspect of spin wave theory that has remained unexplored. We expect this presentation may be interesting for a broad audience as it is at the crossroads of strongly correlated systems and the physics of quantum open systems, that is so much rooted in quantum information theory.[4pt] [1] A. Rivas and M.A. Martin-Delgado, Ann. Phys. (N.Y.) (in press), and arXiv:1112.315.

Rivas, Angel; Martin-Delgado, Miguel A.

2013-03-01

382

A new method to account for the difference between classical and quantum baths in quantum dissipative dynamics  

NASA Astrophysics Data System (ADS)

We investigate the difference between a quantum and classical bath within the Caldeira-Leggett model for dissipative quantum dynamics. It is well known that a Markovian equation of motion for the reduced dynamics can be derived by taking the classical approximation of the harmonic bath correlation function. However, such approximation is only valid at high temperatures, and it is necessary to include the non-Markovian effect of the quantum bath in more general cases. We show that the equation of motion derived for the classical bath can be extended to the exact quantum one, by simply adding a real stochastic process to take account of the difference between the quantum and classical bath correlation functions. Numerical examples in calculating electron and excitation energy transfer dynamics, as well as absorption spectra of molecular aggregates indicate that the proposed method is a valid approach to extend the existing theories to include the quantum effect of the harmonic bath. The possibility of applying a similar idea to account for the difference between zero and high temperature quantum dissipative dynamics is discussed.

Zhu, Lili; Liu, Hao; Shi, Qiang

2013-09-01

383

Asymptotically decreasing Lieb-Robinson velocity for a class of dissipative quantum dynamics  

NASA Astrophysics Data System (ADS)

We study the velocity of the propagation of information for a class of local dissipative quantum dynamics. This finite velocity is expressed by the so-called Lieb-Robinson bound. Besides the properties of the already studied dynamics, we consider an additional relation that expresses the propagation of certain subspaces. The previously derived bounds did not reflect the dissipative character of the dynamics and yielded the same result as for the reversible case. In this article, we show that for this class the velocity of propagation of information is time dependent and decays in time towards a smaller velocity. In some cases the velocity becomes zero. At the end of the article, the exponential clustering theorem of general frustration free local Markovian dynamics is revisited.

Descamps, Benoît

2013-09-01

384

Theory and simulation of cavity quantum electro-dynamics in multi-partite quantum complex systems  

NASA Astrophysics Data System (ADS)

The cavity quantum electrodynamics of various complex systems is here analyzed using a general versatile code developed in this research. Such quantum multi-partite systems normally consist of an arbitrary number of quantum dots in interaction with an arbitrary number of cavity modes. As an example, a nine-partition system is simulated under different coupling regimes, consisting of eight emitters interacting with one cavity mode. Two-level emitters (e.g. quantum dots) are assumed to have an arrangement in the form of a linear chain, defining the mutual dipole-dipole interactions. It was observed that plotting the system trajectory in the phase space reveals a chaotic behavior in the so-called ultrastrong-coupling regime. This result is mathematically confirmed by detailed calculation of the Kolmogorov entropy, as a measure of chaotic behavior. In order to study the computational complexity of our code, various multi-partite systems consisting of one to eight quantum dots in interaction with one cavity mode were solved individually. Computation run times and the allocated memory for each system were measured.

Alidoosty Shahraki, Moslem; Khorasani, Sina; Aram, Mohammad Hasan

2013-10-01

385

Dynamics of Entropy in Quantum-like Model of Decision Making  

NASA Astrophysics Data System (ADS)

We present a quantum-like model of decision making in games of the Prisoner's Dilemma type. By this model the brain processes information by using representation of mental states in complex Hilbert space. Driven by the master equation the mental state of a player, say Alice, approaches an equilibrium point in the space of density matrices. By using this equilibrium point Alice determines her mixed (i.e., probabilistic) strategy with respect to Bob. Thus our model is a model of thinking through decoherence of initially pure mental state. Decoherence is induced by interaction with memory and external environment. In this paper we study (numerically) dynamics of quantum entropy of Alice's state in the process of decision making. Our analysis demonstrates that this dynamics depends nontrivially on the initial state of Alice's mind on her own actions and her prediction state (for possible actions of Bob.)

Basieva, Irina; Khrennikov, Andrei; Asano, Masanari; Ohya, Masanori; Tanaka, Yoshiharu

2011-03-01

386

Dynamical system analysis of cosmologies with running cosmological constant from quantum Einstein gravity  

NASA Astrophysics Data System (ADS)

We discuss a mechanism that induces a time-dependent vacuum energy on cosmological scales. It is based on the instability-induced renormalization triggered by the low-energy quantum fluctuations in a Universe with a positive cosmological constant. We use the dynamical systems approach to study the qualitative behavior of the Friedmann-Robertson-Walker cosmologies where the cosmological constant is dynamically evolving according with this nonperturbative scaling at low energies. It will be shown that it is possible to realize ‘two regimes’ dark energy phases, where an unstable early phase of power-law evolution of the scale factor is followed by an accelerated expansion era at late times.

Bonanno, Alfio; Carloni, Sante

2012-02-01

387

Linear dynamics subject to thermal fluctuations and non-Gaussian noise: from classical to quantum  

NASA Astrophysics Data System (ADS)

The dynamics of a linear system embedded in a heat bath environment and subject to white non-Gaussian noise is studied. Classical higher-order cumulants in coordinate space are derived for Poissonian noise and their impact on the dynamics and on asymptotic steady-state distributions is analyzed. In the quantum regime, non-Gaussian properties are present in reduced density in coordinate representation, but in energy representation they exist on a transient time scale only, due to symmetry. Within an exactly solvable model, our results provide insight into mechanisms of linear detectors as sensors for non-Gaussian noise at high and low temperatures.

Köpke, M.; Ankerhold, J.

2013-04-01

388

Universal Rephasing Dynamics after a Quantum Quench via Sudden Coupling of Two Initially Independent Condensates  

NASA Astrophysics Data System (ADS)

We consider a quantum quench in which two initially independent condensates are suddenly coupled and study the subsequent “rephasing” dynamics. For weak tunneling couplings, the time evolution of physical observables is predicted to follow universal scaling laws, connecting the short-time dynamics to the long-time nonperturbative regime. We first present a two-mode model valid in two and three dimensions and then move to one dimension, where the problem is described by a gapped sine-Gordon theory. Combining analytical and numerical methods, we compute universal time-dependent expectation values, allowing a quantitative comparison with future experiments.

Dalla Torre, Emanuele G.; Demler, Eugene; Polkovnikov, Anatoli

2013-03-01

389

Dynamics of an interacting dark energy model in Einstein and loop quantum cosmology  

SciTech Connect

We investigate the background dynamics when dark energy is coupled to dark matter in the Universe described by Einstein cosmology and loop quantum cosmology. We introduce a new general form of dark sector coupling, which presents a more complicated dynamical phase space. Differences in the phase space in obtaining the accelerated scaling attractor in Einstein cosmology and loop quantum cosmology are disclosed.

Chen Songbai; Wang Bin; Jing Jiliang [Institute of Physics and Department of Physics, Hunan Normal University, Changsha, Hunan 410081 (China); Key Laboratory of Low Dimensional Quantum Structures and Quantum Control of Ministry of Education, Hunan Normal University, Changsha, Hunan 410081 (China); Department of Physics, Fudan University, Shanghai 200433 (China); Department of Physics, Fudan University, Shanghai 200433 (China); Institute of Physics and Department of Physics, Hunan Normal University, Changsha, Hunan 410081 (China); Key Laboratory of Low Dimensional Quantum Structures and Quantum Control of Ministry of Education, Hunan Normal University, Changsha, Hunan 410081 (China)

2008-12-15

390

Simulating quantum interference in spontaneous decay near plasmonic nanostructures: Population dynamics  

SciTech Connect

It has been recently shown that the placement of a three-level V-type quantum emitter in the proximity of metallic nanostructures can create dynamics similar to that of quantum interference in spontaneous emission. Here we continue this work and present results on the population dynamics of a three-level V-type quantum emitter for various initial conditions in the presence of a two-dimensional array of metal-coated dielectric nanospheres.

Evangelou, Sofia; Yannopapas, Vassilios; Paspalakis, Emmanuel [Materials Science Department, School of Natural Sciences, University of Patras, GR-265 04 Patras (Greece)

2011-05-15

391

Molecular dynamics and quantum chemical studies on the catalytic mechanism of Delta5-3-ketosteroid isomerase: the catalytic diad versus the cooperative hydrogen bond mechanism.  

PubMed

To further understand Delta(5)-3-ketosteroid isomerase (KSI) catalysis, we carried out molecular dynamics (MD) simulations of the KSI dimer ligated with a substrate and reaction intermediate analogue and high level ab initio calculations on relevant enzymatic reaction models. Simulation of the enzyme-substrate complex dimer systems showed asymmetric dynamics between the two monomers, in which the hydrogen bond pattern between the substrate and active site residues in the first and the second subunits supported the cooperative hydrogen bond (CH) and the catalytic diad (CD) mechanisms, respectively. On the other hand, only the CH mechanism was supported in the MD simulation of the enzyme-intermediate complex dimer. From MP2/6-31+G**//RHF/6-31G** calculations, we found the kinetic barriers for the two reaction mechanisms were similar. The CH route afforded a greater stabilization to the enolate intermediate than did the CD counterpart. Thus, the present computational studies indicate that the CH mechanism would be favored over the CD one in the catalytic action of KSI. However, the latter could not be ruled out conclusively because of the explicit appearance of a CD configuration in the MD trajectories of the enzyme-substrate complex and because of the similar intrinsic activation barrier for the CH and CD mechanisms. The appearance of configurations that favor the CD pathway is rationalized in terms of a model in which the KSI-substrate complex does not have a strong preference for one hydrogen bonding pattern over another, while the KSI-intermediate complex favors a cooperative hydrogen bond pattern in order to stabilize the reaction intermediate. This hypothesis is supported by the ab initio calculations which indicate that the CH intermediate is more stable than the CD one by approximately 6.3 kcal/mol. PMID:12537487

Park, Hwangseo; Merz, Kenneth M

2003-01-29

392

PREFACE: Fourth Meeting on Constrained Dynamics and Quantum Gravity  

NASA Astrophysics Data System (ADS)

The formulation of a quantum theory of gravity seems to be the unavoidable endpoint of modern theoretical physics. Yet the quantum description of the gravitational field remains elusive. The year 2005 marks the tenth anniversary of the First Meeting on Constrained Dynamics and Quantum Gravity, held in Dubna (Russia) due to the efforts of Alexandre T. Filippov (JINR, Dubna) and Vittorio de Alfaro (University of Torino, Italy). At the heart of this initiative was the desire for an international forum where the status and perspectives of research in quantum gravity could be discussed from the broader viewpoint of modern gauge field theories. Since the Dubna meeting, an increasing number of scientists has joined this quest. Progress was reported in two other conferences in this series: in Santa Margherita Ligure (Italy) in 1996 and in Villasimius (Sardinia, Italy) in 1999. After a few years of ``working silence'' the time was now mature for a new gathering. The Fourth Meeting on Constrained Dynamics and Quantum Gravity (QG05) was held in Cala Gonone (Sardinia, Italy) from Monday 12th to Friday 16th September 2005. Surrounded by beautiful scenery, 100 scientists from 23 countries working in field theory, general relativity and related areas discussed the latest developments in the quantum treatment of gravitational systems. The QG05 edition covered many of the issues that had been addressed in the previous meetings and new interesting developments in the field, such as brane world models, large extra dimensions, analogue models of gravity, non-commutative techniques etc. The format of the meeting was similar to the previous ones. The programme consisted of invited plenary talks and parallel sessions on cosmology, quantum gravity, strings and phenomenology, gauge theories and quantisation and black holes. A major goal was to bring together senior scientists and younger people at the beginning of their scientific career. We were able to give financial support to both groups. In particular, help was provided to students and scientists from non-EU countries. It is our great pleasure to thank those people and institutions whose help and support was crucial to the success of the meeting. We appreciate the enthusiastic support of our colleagues of the academic community, especially those from the Istituto Nazionale di Fisica Nucleare and the Universities of Cagliari, Pisa, Torino and Mississippi. Financial support was provided by the Istituto Nazionale di Fisica Nucleare, the Universities of Cagliari, Torino, Pisa and Mississippi. This was used largely to support participants, especially younger people. Special thanks go to Pietro Menotti (University of Pisa) and Stefano Sciuto (University of Torino) for their friendship and their universities' financial contributions. It is also a pleasure to acknowledge financial support from the Regione Autonoma della Sardegna and from Tiscali, the communications and Internet company, for providing free telephone cards. Technical support and local organisation was provided by the Sezione di Cagliari of the Istituto Nazionale di Fisica Nucleare. Warmest thanks go to our administrative and technical staff - Maria Assunta Lecca and Simona Renieri, for their untiring assistance, and to Palmasera Village and Hotel Smeraldo for their splendid hospitality. And finally, our gratitude goes to all the participants and especially the many experienced scientists. Their contributions highlighted the meeting and were largely without support. The success of the meeting is due to them and to the enthusiasm of the younger participants. The Editors January 2006 COMMITTEES Organising Committee Mariano Cadoni (Università and INFN Cagliari) Marco Cavaglià (University of Mississippi) Jeanette E. Nelson (Università and INFN Torino) Advisory Committee Orfeu Bertolami (IST Lisboa, Portugal) Luca Bombelli (Univ. Mississippi) Steve Carlip (UC Davis, USA) Alessandro D'Adda (INFN Torino, Italy) Stanley Deser (Brandeis, USA) Georgi Dvali (NYU, USA) Sergio Ferrara (CERN) Gian Francesco Giudice (CERN) Roman Jackiw (MIT, USA)

Cadoni, Mariano; Cavaglia, Marco; Nelson, Jeanette E.

2006-04-01

393

Automatic generation of active coordinates for quantum dynamics calculations: Application to the dynamics of benzene photochemistry  

SciTech Connect

A new practical method to generate a subspace of active coordinates for quantum dynamics calculations is presented. These reduced coordinates are obtained as the normal modes of an analytical quadratic representation of the energy difference between excited and ground states within the complete active space self-consistent field method. At the Franck-Condon point, the largest negative eigenvalues of this Hessian correspond to the photoactive modes: those that reduce the energy difference and lead to the conical intersection; eigenvalues close to 0 correspond to bath modes, while modes with large positive eigenvalues are photoinactive vibrations, which increase the energy difference. The efficacy of quantum dynamics run in the subspace of the photoactive modes is illustrated with the photochemistry of benzene, where theoretical simulations are designed to assist optimal control experiments.

Lasorne, Benjamin; Sicilia, Fabrizio; Bearpark, Michael J.; Robb, Michael A. [Department of Chemistry, Imperial College London, South Kensington, London SW7 2AZ (United Kingdom); Worth, Graham A. [School of Chemistry, University of Birmingham, Edgbaston, Birmingham B15 2TT (United Kingdom); Blancafort, Lluis [Institut de Quimica Computacional and Departament de Quimica, Universitat de Girona, E-17071 Girona (Spain)

2008-03-28

394

Quantum versus classical dynamics in a driven barrier: The role of kinematic effects.  

PubMed

We study the dynamics of the classical and quantum mechanical scattering of a wave packet from an oscillating barrier. Our main focus is on the dependence of the transmission coefficient on the initial energy of the wave packet for a wide range of oscillation frequencies. The behavior of the quantum transmission coefficient is affected by tunneling phenomena, resonances, and kinematic effects emanating from the time dependence of the potential. We show that when kinematic effects dominate (mainly in intermediate frequencies), classical mechanics provides very good approximation of quantum results. In that frequency region, the classical and quantum transmission coefficients are in optimal agreement. Moreover, the transmission threshold (i.e., the energy above which the transmission coefficient becomes larger than a specific small threshold value) is found to exhibit a minimum. We also consider the form of the transmitted wave packet and we find that for low values of the frequency the incoming classical and quantum wave packet can be split into a train of well-separated coherent pulses, a phenomenon that admits purely classical kinematic interpretation. PMID:23031003

Papachristou, P K; Katifori, E; Diakonos, F K; Constantoudis, V; Mavrommatis, E

2012-09-24

395

Quantum Dynamical Behaviour in Complex Systems - A Semiclassical Approach  

SciTech Connect

One of the biggest challenges in Chemical Dynamics is describing the behavior of complex systems accurately. Classical MD simulations have evolved to a point where calculations involving thousands of atoms are routinely carried out. Capturing coherence, tunneling and other such quantum effects for these systems, however, has proven considerably harder. Semiclassical methods such as the Initial Value Representation (SC-IVR) provide a practical way to include quantum effects while still utilizing only classical trajectory information. For smaller systems, this method has been proven to be most effective, encouraging the hope that it can be extended to deal with a large number of degrees of freedom. Several variations upon the original idea of the SCIVR have been developed to help make these larger calculations more tractable; these range from the simplest, classical limit form, the Linearized IVR (LSC-IVR) to the quantum limit form, the Exact Forward-Backward version (EFB-IVR). In this thesis a method to tune between these limits is described which allows us to choose exactly which degrees of freedom we wish to treat in a more quantum mechanical fashion and to what extent. This formulation is called the Tuning IVR (TIVR). We further describe methodology being developed to evaluate the prefactor term that appears in the IVR formalism. The regular prefactor is composed of the Monodromy matrices (jacobians of the transformation from initial to finial coordinates and momenta) which are time evolved using the Hessian. Standard MD simulations require the potential surfaces and their gradients, but very rarely is there any information on the second derivative. We would like to be able to carry out the SC-IVR calculation without this information too. With this in mind a finite difference scheme to obtain the Hessian on-the-fly is proposed. Wealso apply the IVR formalism to a few problems of current interest. A method to obtain energy eigenvalues accurately for complex systems is described. We proposed the use of a semiclassical correction term to a preliminary quantum calculation using, for instance, a variational approach. This allows us to increase the accuracy significantly. Modeling Nonadiabatic dynamics has always been a challenge to classical simulations because the multi-state nature of the dynamics cannot be described accurately by the time evolution on a single average surface, as is the classical approach. We show that using the Meyer-Miller-Stock-Thoss (MMST) representation of the exact vibronic Hamiltonian in combination with the IVR allows us to accurately describe dynamics where the non Born-Oppenheimer regime. One final problem that we address is that of extending this method to the long time regime. We propose the use of a time independent sampling function in the Monte Carlo integration over the phase space of initial trajectory conditions. This allows us to better choose the regions of importance at the various points in time; by using more trajectories in the important regions, we show that the integration can be converged much easier. An algorithm based loosely on the methods of Diffusion Monte Carlo is developed that allows us to carry out this time dependent sampling in a most efficient manner.

Gliebe, Cheryn E; Ananth, Nandini

2008-05-22

396

Gas-Phase Molecular Dynamics: Theoretical Studies in Spectroscopy and Chemical Dynamics  

SciTech Connect

The goal of this program is the development and application of computational methods for studying chemical reaction dynamics and molecular spectroscopy in the gas phase. We are interested in developing rigorous quantum dynamics algorithms for small polyatomic systems and in implementing approximate approaches for complex ones. Particular focus is on the dynamics and kinetics of chemical reactions and on the rovibrational spectra of species involved in combustion processes. This research also explores the potential energy surfaces of these systems of interest using state-of-the-art quantum chemistry methods.

Yu, H.G.; Muckerman, J.T.

2010-06-01

397

Study of the H+O2 reaction by means of quantum mechanical and statistical approaches: the dynamics on two different potential energy surfaces.  

PubMed

The possible existence of a complex-forming pathway for the H+O(2) reaction has been investigated by means of both quantum mechanical and statistical techniques. Reaction probabilities, integral cross sections, and differential cross sections have been obtained with a statistical quantum method and the mean potential phase space theory. The statistical predictions are compared to exact results calculated by means of time dependent wave packet methods and a previously reported time independent exact quantum mechanical approach using the double many-body expansion (DMBE IV) potential energy surface (PES) [Pastrana et al., J. Phys. Chem. 94, 8073 (1990)] and the recently developed surface (denoted XXZLG) by Xu et al. [J. Chem. Phys. 122, 244305 (2005)]. The statistical approaches are found to reproduce only some of the exact total reaction probabilities for low total angular momenta obtained with the DMBE IV PES and some of the cross sections calculated at energy values close to the reaction threshold for the XXZLG surface. Serious discrepancies with the exact integral cross sections at higher energy put into question the possible statistical nature of the title reaction. However, at a collision energy of 1.6 eV, statistical rotationally resolved cross sections managed to reproduce the experimental cross sections for the H+O(2)(v=0,j=1)-->OH(v(')=1,j('))+O process reasonably well. PMID:18601333

Bargueño, Pedro; González-Lezana, Tomás; Larrégaray, Pascal; Bonnet, Laurent; Rayez, Jean-Claude; Hankel, Marlies; Smith, Sean C; Meijer, Anthony J H M

2008-06-28

398

Study of the H+O2 reaction by means of quantum mechanical and statistical approaches: The dynamics on two different potential energy surfaces  

NASA Astrophysics Data System (ADS)

The possible existence of a complex-forming pathway for the H+O2 reaction has been investigated by means of both quantum mechanical and statistical techniques. Reaction probabilities, integral cross sections, and differential cross sections have been obtained with a statistical quantum method and the mean potential phase space theory. The statistical predictions are compared to exact results calculated by means of time dependent wave packet methods and a previously reported time independent exact quantum mechanical approach using the double many-body expansion (DMBE IV) potential energy surface (PES) [Pastrana et al., J. Phys. Chem. 94, 8073 (1990)] and the recently developed surface (denoted XXZLG) by Xu et al. [J. Chem. Phys. 122, 244305 (2005)]. The statistical approaches are found to reproduce only some of the exact total reaction probabilities for low total angular momenta obtained with the DMBE IV PES and some of the cross sections calculated at energy values close to the reaction threshold for the XXZLG surface. Serious discrepancies with the exact integral cross sections at higher energy put into question the possible statistical nature of the title reaction. However, at a collision energy of 1.6 eV, statistical rotationally resolved cross sections managed to reproduce the experimental cross sections for the H+O2(v=0,j=1)-->OH(v'=1,j')+O process reasonably well.

Bargueño, Pedro; González-Lezana, Tomás; Larrégaray, Pascal; Bonnet, Laurent; Rayez, Jean-Claude; Hankel, Marlies; Smith, Sean C.; Meijer, Anthony J. H. M.

2008-06-01

399

Dynamics of Relativistic Electromagnetic One and Two Body, Quantum and Classical Systems.  

NASA Astrophysics Data System (ADS)

I am studying the dynamics of one and two body systems to test the proposed models, find new orbital behavior, and find the effects of relativity and spin. Using a quantum mechanical action principle I develop quantum equations for relativistic and nonrelativistic, spinning and spinless particles. This general derivation allows the models to be compared on even footing. The models studied included the Dirac, Klein-Gordon, Pauli, Schrodinger, Feshbach-Villars, and Kemmer equations. I show how two-body motions give Clausius interaction potentials that include magnetic effects. Using perturbation theory with the Schrodinger problem, the magnetic terms give corrections similar to the hyperfine structure. Assuming the same classical Hamiltonians and quantum Hamiltonians I give classical Lagrangians for each system. I discuss some differences caused by the commutative versus noncommutative algebras. In particular, I study the apparent lack of an explicit laboratory time solution for the free Dirac particle. I develop limits that allow the simpler Hamiltonians to be derived as approximations to the more complex systems. I examine and classify the classical behavior for one and two body relativistic spinless Coulomb systems, and for the two body relativistic Clausius system. I also study the classical behavior of the one body relativistic spinning particle in: no fields (the free particle), constant electric and magnetic fields, and a Coulomb field. I examine two body relativistic spinning systems under Coulomb and Clausius potentials. Magnetic interactions introduce new behavior at short radii. I find small tightly bound orbits including one that is exactly solvable. Using classical quantization methods with the exact solution, I consider the quantum effects of these orbits. The results show composite particles with large apparent mass. The addition of spin seems to make most small orbits unstable because of spin-orbit coupling effects. Finally, I describe some interesting, including some quantum-like, behavior in the dynamics of the classical spin.

Craig, George Steven

400

Dynamics of Quantum Vorticity in a Random Potential  

SciTech Connect

I study the dynamics of a superfluid vortex in a random potential, as in the inner crust of a neutron star. Below a critical flow velocity of the ambient superfluid, a vortex is effectively immobilized by lattice forces even in the limit of zero dissipation. Low-velocity, translatory motion is not dynamically possible, a result with important implications for understanding neutron star precession and the dynamical properties of superfluid nuclear matter.

Link, Bennett [Department of Physics, Montana State University, Bozeman Montana 59717 (United States)

2009-04-03

401

Quantum molecular dynamics; A new algorithm for linear and nonlinear electron transport in disordered materials  

SciTech Connect

Quantum molecular dynamics (QMD) simulations provide the real-time dynamics of electrons and ions through numerical solutions of the time-dependent Schrodinger and Newton equations, respectively. With this technique it is possible to go beyond the structural aspects to study electron dynamics, including linear and nonlinear electron transport, in materials at finite temperatures. The solution of the time-dependent Schrodinger equation for the electron wave function is obtained by a spectral method, which for bulk system is implemented with discrete fast Fourier (FFT) transforms. For systems with broken symmetry due to surfaces or interfaces, the spectral method combines the solution of tridiagonal set of equations with FFT. Using QMD simulations the author have investigated the localization behavior and the mobility of excess electrons at finite temperatures in highly disordered systems such as a dense helium gas and amorphous silicon. Implementation of molecular dynamics on massively parallel architectures are discussed.

Kalia, R.K.; Vashishta, P.; Yang, L.H.; Dech, F.W.; Rowlan, J. (Argonne National Lab., Argonne, IL (US))

1990-01-01

402

Six-dimensional and seven-dimensional quantum dynamics study of the OH + CH4 --> H2O + CH3 reaction  

NASA Astrophysics Data System (ADS)

The reaction dynamics of hydroxyl radical with methane has been investigated using time-dependent wave packet approach within reduced six- and seven-dimensional models. Initial state-selected total reaction probabilities and integral cross sections for the hydrogen abstraction reaction have been computed on the empirical potential energy surface developed by Espinosa-García et al. [J. Chem. Phys. 112, 5731 (2000)]. Excitations of the CH stretching mode and/or the CH3 umbrella mode enhance the reaction. They are, however, both less efficient than translational energy in promoting the reaction, at least at low collision energies. Also, we studied the accuracy of two approximations: centrifugal sudden (CS) and J-shifting (JS), in the calculations of the integral cross sections by a comparison to coupled-channel (CC) calculations. The integral cross sections obtained indicated that the CS approximation works well over the whole energy range studied, and the JS approximation gives accurate cross sections at low collision energies, while noticeably overestimates them at relatively high collision energies. In addition, the OH radical acts as a good spectator as it has a negligible effect on the reaction.

Song, Hongwei; Lee, Soo-Ying; Yang, Minghui; Lu, Yunpeng

2013-10-01

403

Coherent spin-transfer dynamics in diluted magnetic semiconductor quantum wells even after optical excitation with zero net angular momentum  

NASA Astrophysics Data System (ADS)

A quantum kinetic study of correlated spin transfer between optically excited electrons and Mn atoms in a ZnMnSe quantum well is presented. The simulations predict genuine signatures of non-Markovian spin dynamics which are particularly pronounced for special two-color laser excitations with a zero net angular momentum where a Markovian theory predicts an almost zero total electron spin for all times. In contrast, in the quantum kinetic simulations a sizable total electron spin builds up. Subsequently, a coherent oscillatory exchange of spin between the electron and Mn subsystems is observed.

Thurn, C.; Cygorek, M.; Axt, V. M.; Kuhn, T.

2013-10-01

404

Spontaneous activation of CO2 and corrosion pathways on iron surface Fe(100): a quantum mechanical study informed by DFT-based dynamics  

NASA Astrophysics Data System (ADS)

Because of the rapidly increasing interest in technologies for capturing and permanently sequestering CO2 as part of a climate change mitigation strategy, understanding the interaction of CO2 with materials that comprise a sequestration system (steels, cements, silicate minerals, etc.) is of fundamental importance. The majority of models for corrosion of metals involve water-mediated processes, with CO2 dissolved in the aqueous phase playing a minor role in the process. In contrast, recent experiments with mild steels have shown that much greater corrosivity actually occurs in the dense CO2 phase, provided sufficient molecular water is present in the CO2 phase to catalyse certain reactions. In our study, we use DFT-based dynamics to study the internal structure of the the super-critical CO2/(H2O)n system, with n=0-4. While water does not disturb the super-critical CO2 phase, it also gives rise to short-lived CO2...H2O bonds which are likely to facilitate the activation of CO2 on the surface, but otherwise maintains its molecular form. We also use DFT methods to probe the fundamental interactions of CO2 or SO2 and H2O with clean or doped iron surfaces and determine the reactive pathways that lead to CO2 chemisorption, dissociation and further formation of corrosion products in the form of carbonates or sulfites. DFT-based molecular dynamics are employed to sample the configurational space of reactants and products more efficiently. CO2 adsorbs readily on the surface assuming a bent geometry, indicative of charge transfer from the surface to CO2, which closely resembles a CO2- moiety. Once CO2 is adsorbed, it can decompose to adsorbed O+CO, which further reacts with CO2 or SO2 to form corrosion products. Molecularly adsorbed water acts as catalyst to lower these reaction barriers. Clearly, the reactive pathways on the surface are quite different than those in aqueous solution. Battelle operates Pacific Northwest National Laboratory for the US Department of Energy.

Glezakou, V. A.; McGrail, P.; Dang, L. X.

2009-12-01

405

Dynamic light-matter coupling across multiple spatial dimensions in a quantum dots-in-a-well heterostructure  

SciTech Connect

Semiconductor heterostructures incorporating multiple degrees of spatial confinement have recently attracted substantial interest for photonic applications. One example is the quantum dots-in-a-well (DWELL) heterostructure, consisting of zero-dimensional quantum dots embedded in a two-dimensional quantum well and surrounded by three-dimensional bulk material. This structure offers several advantages over conventional photonic devices while providing a model system for the study of light-matter interactions across multiple spatial dimensions. Here, we use ultrafast differential transmission spectroscopy2 to temporally and spectrally resolve density-dependent carrier dynamics in a DWELL heterostructure. We observe excitation-dependent shifts of the quantum dot energy levels at low densities, while at high densities we observe an anomalous induced absorption at the quantum dot excited state that is correlated to quantum well population dynamics. These studies of density-dependent light-matter interactions across multiple coupled spatial dimensions provide clues to the underlying physics governing quantum dot properties, with important implications for DWELL-based photonic devices.

Prasankumar, Rohit P [Los Alamos National Laboratory; Taylor, Antoinette J [Los Alamos National Laboratory; Chow, W W [SNL; Attaluri, R S [UNM; Shenoi, R [UNM

2009-01-01

406

Communication: Multistate quantum dynamics of photodissociation of carbon dioxide between 120 nm and 160 nm  

NASA Astrophysics Data System (ADS)

UV absorption cross section of CO2 is studied using high level ab initio quantum chemistry for electrons and iterative quantum dynamics for nuclear motion on interacting global full dimensional potential energy surfaces. Six electronic states--1, 2, 31A' and 1, 2, 31A''--are considered. At linearity, they correspond to the ground electronic state X~1?g+ and the optically forbidden but vibronically allowed valence states 11?u, 11?u-, and 11?g. In the Franck-Condon region, these states interact via Renner-Teller and conical intersections and are simultaneously involved in an intricate network of non-adiabatic couplings. The absorption spectrum, calculated for many rotational states, reproduces the distinct two-band shape of the experimental spectrum measured at 190 K and the characteristic patterns of the diffuse structures in each band. Quantum dynamics unravel the relative importance of different vibronic mechanisms, while metastable resonance states, underlying the diffuse structures, provide dynamically based vibronic assignments of individual lines.

Grebenshchikov, Sergy Yu.

2012-07-01

407

Communication: multistate quantum dynamics of photodissociation of carbon dioxide between 120 nm and 160 nm.  

PubMed

UV absorption cross section of CO(2) is studied using high level ab initio quantum chemistry for electrons and iterative quantum dynamics for nuclear motion on interacting global full dimensional potential energy surfaces. Six electronic states-1, 2, 3(1)A(') and 1, 2, 3(1)A(")-are considered. At linearity, they correspond to the ground electronic state X?(1)?(g) (+) and the optically forbidden but vibronically allowed valence states 1(1)?(u), 1(1)?(u) (-), and 1(1)?(g). In the Franck-Condon region, these states interact via Renner-Teller and conical intersections and are simultaneously involved in an intricate network of non-adiabatic couplings. The absorption spectrum, calculated for many rotational states, reproduces the distinct two-band shape of the experimental spectrum measured at 190 K and the characteristic patterns of the diffuse structures in each band. Quantum dynamics unravel the relative importance of different vibronic mechanisms, while metastable resonance states, underlying the diffuse structures, provide dynamically based vibronic assignments of individual lines. PMID:22803520

Grebenshchikov, Sergy Yu

2012-07-14

408

Communication: Multistate quantum dynamics of photodissociation of carbon dioxide between 120 nm and 160 nm  

SciTech Connect

UV absorption cross section of CO{sub 2} is studied using high level ab initio quantum chemistry for electrons and iterative quantum dynamics for nuclear motion on interacting global full dimensional potential energy surfaces. Six electronic states-1, 2, 3{sup 1}A{sup Prime} and 1, 2, 3{sup 1}A{sup Double-Prime }-are considered. At linearity, they correspond to the ground electronic state X(tilde sign){sup 1}{Sigma}{sub g}{sup +} and the optically forbidden but vibronically allowed valence states 1{sup 1}{Delta}{sub u}, 1{sup 1}{Sigma}{sub u}{sup -}, and 1{sup 1}{Pi}{sub g}. In the Franc