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1

Quantum State Resolved Studies of Photodesorption Dynamics  

NASA Astrophysics Data System (ADS)

Photodesorption is a fundamental photochemical surface process, in which absorption of light by adsorbed molecules or by the substrate causes ejection of molecules into the gas phase. The goal of the research presented in this dissertation was to investigate the elementary steps of energy transfer and relaxation involved in photodesorption. It was demonstrated that measuring internal and translational state distributions of photodesorbed molecules is a powerful way to gain insight into the physical mechanisms and dynamics of photochemical surface processes. The dynamics of ultraviolet laser (193 and 308 nm) induced desorption of CO from thin epitaxial NiO(111) films, and from Si(100)-c(2 times 4) was studied by detecting desorbed CO molecules in specific quantum states using laser induced fluorescence (LIF) spectroscopy. This technique allowed measuring the final state distributions in desorption angle and velocity, vibrational and rotational quantum states, and the angular momentum alignment, as well as correlations between two or more degrees of freedom. The desorbed molecules have nonthermal amounts of energy in rotational, vibrational, and translational motion. CO photodesorbed from oxidized Ni(111) is characterized by a Maxwell-Boltzmann velocity distribution, and a rotational distribution which is described as a superposition of two Boltzmann distributions. These distributions are the same for the two desorption wavelengths studied, indicating a substrate mediated excitation mechanism. The final state distribution of CO photodesorbed from Si(100) consists of two distinct components. One is rotationally hot but translationally relatively slow and exhibits a preference for cartwheeling alignment. The other component is rotationally quite cold but translationally fast, with a preference for helicoptering alignment. The observed distributions, as well as those previously observed for other photodesorption systems are discussed in terms of a simple dynamical model which circumvents our ignorance of excited-state potential energy surfaces by exploiting the fast electronic relaxation rates encountered at metal and semiconductor surfaces. The model explains rotational Boltzmann distributions, Maxwell-Boltzmann velocity distributions, and rotational-translational correlations characteristic of photodesorbed molecules, as well as spin -orbit state populations of photodesorbed NO. With certain assumptions about adsorption geometries, it can quantitatively explain the measured angular momentum alignment.

Zimmermann, Frank Martin

1995-01-01

2

Quantum wave packet ab initio molecular dynamics: An approach to study quantum dynamics in large systems  

E-print Network

of the methodology, namely, quantum dynamics and ab initio molecular dynamics, are harnessed together using a time-dependent self-consistent field-like coupling procedure. The quantum wave packet dynamics is made computationally. This approach, when combined with full quantum or semiclassical dynamics schemes, has the potential to treat

Iyengar, Srinivasan S.

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

Electron trapping in amorphous silicon: A quantum molecular dynamics study  

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. Using the QMD approach we have investigated the localization behavior of an excess electron in amorphous silicon at finite temperatures. For time scales on the order of a few picoseconds, we find the excess electron is localized inside a void of radius {approximately}3 {Angstrom} at finite temperatures. 12 refs.

Yang, Lin H.; Kalia, R.K.; Vashishta, P.

1990-12-01

5

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

National Technical Information Service (NTIS)

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 s...

J. Miller, K. Miaskiewicz, R. Osman

1993-01-01

6

Quantum molecular dynamics study of warm dense iron  

NASA Astrophysics Data System (ADS)

The equation of state, the self-diffusion coefficient and viscosity of fluid iron in the warm dense regime at densities from 12.5 to 25.0g/cm3, and temperatures from 0.5 to 15.0 eV have been calculated via quantum molecular dynamics simulations. The principal Hugoniot is in good agreement with nuclear explosive experiments up to ˜50Mbar but predicts lower pressures compared with high intensity laser results. The self-diffusion coefficient and viscosity have been simulated and have been compared with the one-component plasma model. The Stokes-Einstein relationship, defined by connections between the viscosity and the self-diffusion coefficient, has been determined and has been found to be fairly well described by classical predictions.

Wang, Cong; Wang, Zhe-Bin; Chen, Qi-Feng; Zhang, Ping

2014-02-01

7

Quantum Monte Carlo study of strongly correlated electrons: Cellular dynamical mean-field theory  

Microsoft Academic Search

We study the Hubbard model using the cellular dynamical mean-field theory (CDMFT) with quantum Monte Carlo (QMC) simulations. We present the algorithmic details of CDMFT with the Hirsch-Fye QMC method for the solution of the self-consistently embedded quantum cluster problem. We use the one- and two-dimensional half filled Hubbard model to gauge the performance of CDMFT+QMC particularly for small clusters

B. Kyung; G. Kotliar; A.-M. S. Tremblay

2006-01-01

8

Quantum dynamical studies on Soybean Lipoxygenase-1 Isaiah Sumner, Prasad Phatak and Srinivasan S. Iyengar  

E-print Network

i t = H Quantum dynamical studies on Soybean Lipoxygenase-1 Isaiah Sumner, Prasad Phatak the hydrogen tunneling problem in the active site of the biological enzyme, soybean lipoxygenase-1. Toward this that hydrogen tunneling plays a crucial role in enzyme catalysis for example in case of Soybean Lipoxygenase-1

Iyengar, Srinivasan S.

9

Quantum dynamics study of H +NH3?H2+NH2 reaction  

NASA Astrophysics Data System (ADS)

We report in this paper a quantum dynamics study for the reaction H +NH3?NH2+H2 on the potential energy surface of Corchado and Espinosa-Garcia [J. Chem. Phys. 106, 4013 (1997)]. The quantum dynamics calculation employs the semirigid vibrating rotor target model [J. Z. H. Zhang, J. Chem. Phys. 111, 3929 (1999)] and time-dependent wave packet method to propagate the wave function. Initial state-specific reaction probabilities are obtained, and an energy correction scheme is employed to account for zero point energy changes for the neglected degrees of freedom in the dynamics treatment. Tunneling effect is observed in the energy dependency of reaction probability, similar to those found in H +CH4 reaction. The influence of rovibrational excitation on reaction probability and stereodynamical effect are investigated. Reaction rate constants from the initial ground state are calculated and are compared to those from the transition state theory and experimental measurement.

Zhang, Xu Qiang; Cui, Qian; Zhang, John Z. H.; Han, Ke Li

2007-06-01

10

Characterization of Majorization Monotone Quantum Dynamics  

E-print Network

In this technical note, the author studies the dynamics of open quantum system in Markovian environment. The author gives necessary and sufficient conditions for such dynamics to be majorization monotone, which are those ...

Yuan, Haidong

11

A study of quantum-classical dynamics in the mapping basis  

NASA Astrophysics Data System (ADS)

Solving quantum dynamics is an exponentially difficult problem. Thus, an exact numerical solution is inaccessible for any condensed matter system. A promising approach is to divide the system into a quantum subsystem containing degrees of freedom which are of greater interest or those which have more profound quantum character (e.g., have smaller mass) and a classical bath containing the rest of the system. Imposing such a partition and treating the bath classically results in quantum-classical dynamics. The quantum-classical Liouville equation is a general equation in the Hilbert space of quantum degrees of freedom while it resides in the phase space of the classical degrees of freedom. Any numerical solution to this equation requires representation of the quantum subsystem in some basis. Solutions to this equation have been already proposed in the subsystem, adiabatic and force bases, each with its own cons and pros. In this work, the quantum-classical equations of motion are cast in the subsystem basis and subsequently mapped to a number of fictitious harmonic oscillators. The result is quantum-classical dynamics in the mapping basis which treats both quantum and classical degrees of freedom on the same footing, i.e., in phase space. Neglecting a portion of the back reaction of the quantum-subsystem to classical bath results in an expression for the time evolution of an operator (density matrix) equal to its Poisson bracket with the Hamiltonian. This equation can be solved in terms of characteristics to provide a computationally tractable method for calculating quantum-classical dynamical properties. The expressions for expectation values and correlation functions in this formalism are derived. Calculations on spin-boson system, barrier crossing models---the so called Tully models---and the Fenna-Mathews-Olson pigments show very good agreement between the results of this method and numerical solutions to the Schrodinger equation.

Nassimi, Ali M.

12

Quantum dynamics in the highly discrete, commensurate Frenkel Kontorova model: A path-integral molecular dynamics study  

SciTech Connect

The commensurate Frenkel Kontorova (FK) model is studied using path-integral molecular dynamics (PIMD). We focus on the highly discrete case, in which the embedding potential has a much greater maximum curvature than the harmonic potential connecting two particles in the FK chain. When efficient sampling methods are used, the dynamical interpretation of adiabatic PIMD appears to represent quite accurately the true time correlation functions of this highly correlated many-body system. We have found that the discrete, quantum FK model shows different behavior than its continuum version. The spectral density does not show the characteristic {omega}{sup -2}{theta}({omega}-{omega}{sub c}) cusp of the continuum solution in the pinned phase (m>m{sub c}). We also identify a dynamical quantum hysteresis in addition to the regular classical hysteresis when an external force is applied to the FK chain. In the unpinned phase (m{<=}m{sub c}), we find a linear response damping coefficient which is finite and only weakly dependent on temperature T at small values of T.

Krajewski, Florian R.; Mueser, Martin H. [Computational Science, Department of Chemistry and Applied Biosciences, ETH Zurich, USI Campus, Via Giuseppe Buffi 13, CH-6900 Lugano (Switzerland); Institut fuer Physik, WA 331, Johannes Gutenberg-Universitaet Mainz, 55099 Mainz (Germany); Department of Applied Mathematics, University of Western Ontario, London, Ontario N6A 5B7 (Canada)

2005-03-22

13

Quantum Spin Dynamics in Molecular Magnets  

Microsoft Academic Search

The detailed theoretical understanding of quantum spin dynamics in various molecular magnets is an important step on the roadway to technological applications of these systems. Quantum effects in both ferromagnetic and antiferromagnetic molecular clusters are, by now, theoretically well understood. Ferromagnetic molecular clusters allow one to study the interplay of incoherent quantum tunneling and thermally activated transitions between states with

Michael N. Leuenberger; Florian Meier; Daniel Loss

2002-01-01

14

A quantum dynamics study of the benzopyran ring opening guided by laser pulses  

NASA Astrophysics Data System (ADS)

The ring-opening photoisomerization of benzopyran, which occurs via a photochemical route involving a conical intersection, has been studied with quantum dynamics calculations using the multi-configuration time-dependent Hartree method (MCTDH). We introduce a mechanistic strategy to control the conversion of benzopyran to merocyanine with laser pulses. We use a six-dimensional model developed in a previous work for the potential energy surfaces (PES) based on an extension of the vibronic-coupling Hamiltonian model (diabatization method by ansatz), which depends on the most active degrees of freedom. The main objective of these quantum dynamics simulations is to provide a set of strategies that could help experimentalists to control the photoreactivity vs. photostability ratio (selectivity). In this work we present: (i) a pump-dump technique used to control the photostability, (ii) a two-step strategy to enhance the reactivity of the system: first, a pure vibrational excitation in the electronic ground state that prepares the system and, second, an ultraviolet excitation that brings the system to the first adiabatic electronic state; (iii) finally the effect of a non-resonant pulse (Stark effect) on the dynamics.

Saab, Mohamad; Doriol, Loďc Joubert; Lasorne, Benjamin; Guérin, Stéphane; Gatti, Fabien

2014-10-01

15

Study of the dynamic behavior of quantum cellular automata in graphane nanoclusters  

NASA Astrophysics Data System (ADS)

The possible creation of architectures of quantum cellular automata formed by simple molecules opens a very promising and interesting area of research due to the possibility of going beyond the current limits of miniaturization and integration of devices. In this research we theoretically study the electronic properties of a quan- tum dot array in graphene nanoribbons and in an array of molecules with graphane structures. The role of quantum dots in the ribbons and in the mole- cules is played by oxide reduction centers that can trap or release electrons. With the knowledge about these properties we design cellular automata archi- tectures with nanoribbons and molecular arrays, with this it will be feasible to store and process logic information at room temperature. The stability of the proposed graphene structures are studied using quan- tum methods of geometric optimization [1]. The electronic properties of the nanoribbons are obtained from first-principle calculations based on pseudo- potentials by using the generalized gradient approximation (GGA) of Perdew- Burke-Ernzerhof [2-3]. With the parameters obtained from the study of the electronic properties of the cells that make up the automata, we can make a simulation of the dynamical response of the system. To do this, we use a set of accelerated algorithms for discrete systems [4] based on the Glauber dynamic [5]. Our results show that the studied system can be scaled so that the propagation of digital information throughout the automata is possible at room temperature.

León, A.; Pacheco, M.

2011-03-01

16

Systematic study of 16O-induced fusions with the improved quantum molecular dynamics model  

E-print Network

The heavy-ion fusion reactions with 16O bombarding on 62Ni, 65Cu, 74Ge, 148Nd, 180Hf, 186W, 208Pb, 238U are systematically investigated with the improved quantum molecular dynamics (ImQMD) model. The fusion cross sections at energies near and above the Coulomb barriers can be reasonably well reproduced by using this semi-classical microscopic transport model with the parameter sets SkP* and IQ3a. The dynamical nucleus-nucleus potentials and the influence of Fermi constraint on the fusion process are also studied simultaneously. In addition to the mean field, the Fermi constraint also plays a key role for the reliable description of fusion process and for improving the stability of fragments in heavy-ion collisions.

Ning Wang; Kai Zhao; Zhuxia Li

2014-11-12

17

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

18

Averaging of quantum dynamical semigroups  

NASA Astrophysics Data System (ADS)

In the framework of the elliptic regularization method, the Cauchy problem for the Schrödinger equation with discontinuous degenerating coefficients is associated with a sequence of regularized Cauchy problems and the corresponding regularized dynamical semigroups. We study a divergent sequence of quantum dynamical semigroups as a random process with values in the space of quantum states defined on a measurable space of regularization parameters with a finitely additive measure. The mathematical expectation of the considered processes determined by the Pettis integral defines a family of averaged dynamical transformations. We investigate the semigroup property and the injectivity and surjectivity of the averaged transformations. We establish the possibility of defining the process by its mathematical expectation at two different instants and propose a procedure for approximating an unknown initial state by solutions of a finite set of variational problems on compact sets.

Sakbaev, V. Zh.

2010-09-01

19

Adiabatic Analysis of Quantum Dynamics  

SciTech Connect

It is extremely difficult to describe reactivity in many dimensions when employing quantum mechanics. We have developed a new visualization method based upon the projection of a wave packet onto the optimum adiabatic basis set along the reaction coordinate. The technique enables a quantitative analysis of the populations of the intermediate states as the reaction proceeds. The method is illustrated by studying the classical and quantum dissociation dynamics of hydrogen molecules on a W(100) surface, using a previously calculated {ital ab initio} potential energy surface. {copyright} {ital 1997} {ital The American Physical Society}

Darling, G.; Kay, M.; Holloway, S. [Surface Science Research Centre, The University of Liverpool, Liverpool L69 3BX (United Kingdom)] [Surface Science Research Centre, The University of Liverpool, Liverpool L69 3BX (United Kingdom)

1997-03-01

20

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

21

Quantum algorithm for Bose-Einstein condensate quantum fluid dynamics  

E-print Network

The dynamics of vortex solitons in a BEC superfluid is studied. A quantum lattice-gas algorithm (localization-based quantum computation) is employed to examine the dynamical behavior of vortex soliton solutions of the Gross-Pitaevskii equation (phi^4 interaction nonlinear Schroedinger equation). Quantum turbulence is studied in large grid numerical simulations: Kolmogorov spectrum associated with a Richardson energy cascade occurs on large flow scales. At intermediate scales a k^{-6} power law emerges, in a classical-quantum transition from vortex filament reconnections to Kelvin wave-acoustic wave coupling. The spontaneous exchange of intermediate vortex rings is observed. Finally, at very small spatial scales a k^{-3} power law emerges, characterizing fluid dynamics occurring within the scale size of the vortex cores themselves, a characteristic Kelvin wave cascade region. Poincare recurrence is studied: in the free non-interacting system, a fast Poincare recurrence occurs for regular arrays of line vortices. The recurrence period is used to demarcate dynamics driving the nonlinear quantum fluid towards turbulence, since fast recurrence is an approximate symmetry of the nonlinear quantum fluid at early times. This class of quantum algorithms is useful for studying BEC superfluid dynamics over a broad range of wave numbers, from quantum flow to a pseudo-classical inviscid flow regime to a Kolmogorov inertial subrange.

Jeffrey Yepez; George Vahala; Linda Vahala

2009-05-06

22

Urea in aqueous solution studied by quantum mechanical charge field-molecular dynamics (QMCF-MD).  

PubMed

This work presents a quantum mechanical charge field-molecular dynamics (QMCF-MD) simulation of urea in dilute aqueous solution. Detailed data for structure and dynamics are provided and compared to previous works of other groups. Radial and angular distributions are employed, as well as higher degree spatial investigations, two-dimensional particle mapping, volume maps and the previously proposed SLICE formalism. Information on dynamical properties are presented in the form of hydrogen bond correlation functions and mean lifetime analysis based on weighted Voronoi decomposition. Dihedral and tilt/theta angle distributions substantiate the previous findings of other groups, that urea is far from being planar within aqueous solution. In addition to the analysis of the complete hydration shell, several specific regions of hydration have been identified, for which individual analysis has been performed in terms of hydrogen bond lifetime correlation functions and re-orientational times. A decomposition study based on Laguerre tessellation further investigates the structure and dynamics of the individual hydration layers. It is found that urea does not show properties found in the case of typical structure breaking agents, such as Rb(+) or Cs(+), which is in accordance with spectroscopic data of Rezus and Bakker. PMID:23636218

Weiss, Alexander K H; Hofer, Thomas S

2013-07-01

23

Direct characterization of quantum dynamics.  

PubMed

The characterization of quantum dynamics is a fundamental and central task in quantum mechanics. This task is typically addressed by quantum process tomography (QPT). Here we present an alternative "direct characterization of quantum dynamics" (DCQD) algorithm. In contrast to all known QPT methods, this algorithm relies on error-detection techniques and does not require any quantum state tomography. We illustrate that, by construction, the DCQD algorithm can be applied to the task of obtaining partial information about quantum dynamics. Furthermore, we argue that the DCQD algorithm is experimentally implementable in a variety of prominent quantum-information processing systems, and show how it can be realized in photonic systems with present day technology. PMID:17155454

Mohseni, M; Lidar, D A

2006-10-27

24

Quantum emitters dynamically coupled to a quantum field  

SciTech Connect

We study theoretically the dynamical response of a set of solid-state quantum emitters arbitrarily coupled to a single-mode microcavity system. Ramping the matter-field coupling strength in round trips, we quantify the hysteresis or irreversible quantum dynamics. The matter-field system is modeled as a finite-size Dicke model which has previously been used to describe equilibrium (including quantum phase transition) properties of systems such as quantum dots in a microcavity. Here we extend this model to address non-equilibrium situations. Analyzing the system’s quantum fidelity, we find that the near-adiabatic regime exhibits the richest phenomena, with a strong asymmetry in the internal collective dynamics depending on which phase is chosen as the starting point. We also explore signatures of the crossing of the critical points on the radiation subsystem by monitoring its Wigner function; then, the subsystem can exhibit the emergence of non-classicality and complexity.

Acevedo, O. L.; Quiroga, L.; Rodríguez, F. J. [Departamento de Física, Universidad de los Andes, A.A. 4976, Bogotá (Colombia); Johnson, N. F. [Department of Physics, University of Miami, Coral Gables, Miami, FL 33124 (United States)

2013-12-04

25

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

E-print Network

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 ...

Wu, Jianlan

26

Hydration of the cyanide ion: an ab initio quantum mechanical charge field molecular dynamics study.  

PubMed

This paper presents an ab initio quantum mechanical charge field molecular dynamics simulation study of the cyanide anion (CN(-)) in aqueous solution where hydrogen bond formation plays a dominant role in the hydration process. Preferential orientation of water hydrogens compared to oxygen atoms was quantified in terms of radial, angular as well as coordination number distributions. All structural results indicate that the water hydrogens are attracted towards CN(-) atoms, thus contributing to the formation of the hydration layer. Moreover, a clear picture of the local arrangement of water molecules around the ellipsoidal CN(-) ion is provided via angular-radial distribution and spatial distribution functions. Apart from the structural analysis, the evaluation of water dynamics in terms of ligand mean residence times and H-bond correlation functions indicates the weak structure making capacity of the CN(-) ion. The similar values of H-bond lifetimes obtained for the NHwat and CHwat bonds indicate an isokinetic behaviour of these H-bonds, since there is a very small difference in the magnitude of the lifetimes. On the other hand, the H-bond lifetimes between water molecules of the hydration shell, and between solute and solvent evidence the slightly stable hydration of the CN(-). Overall, the H-bonding dominates in the hydration process of the cyanide anion enabling it to become soluble in the aqueous environment associated to chemical and biological processes. PMID:25360541

Moin, Syed Tarique; Hofer, Thomas S

2014-12-21

27

Quantum Spin Dynamics in Molecular Magnets  

Microsoft Academic Search

Summary.  ?The detailed theoretical understanding of quantum spin dynamics in various molecular magnets is an important step on the\\u000a roadway to technological applications of these systems. Quantum effects in both ferromagnetic and antiferromagnetic molecular\\u000a clusters are, by now, theoretically well understood. Ferromagnetic molecular clusters allow one to study the interplay of\\u000a incoherent quantum tunneling and thermally activated transitions between states with

Michael N. Leuenberger; Florian Meier; Daniel Loss

2003-01-01

28

A quantum dynamics study of the ultrafast relaxation in a prototypical cu(i)-phenanthroline.  

PubMed

The ultrafast nonadiabatic dynamics of a prototypical Cu(I)-phenanthroline complex, [Cu(dmp)2](+) (dmp = 2,9-dimethyl-1,10-phenanthroline), initiated after photoexcitation into the optically bright metal-to-ligand charge-transfer (MLCT) state (S3) is investigated using quantum nuclear dynamics. In agreement with recent experimental conclusions, we find that the system undergoes rapid (?100 fs) internal conversion from S3 into the S2 and S1 states at or near the Franck-Condon (FC) geometry. This is preceded by a dynamic component with a time constant of ?400 fs, which corresponds to the flattening of the ligands associated with the pseudo Jahn-Teller distortion. Importantly, our simulations demonstrate that this latter aspect is in competition with subpicosecond intersystem crossing (ISC). The mechanism for ISC is shown to be a dynamic effect, in the sense that it arises from the system traversing the pseudo Jahn-Teller coordinate where the singlet and triplet states become degenerate, leading to efficient crossing. These first-principles quantum dynamics simulations, in conjunction with recent experiments, allow us to clearly resolve the mechanistic details of the ultrafast dynamics within [Cu(dmp)2](+), which have been disputed in the literature. PMID:25275666

Capano, G; Chergui, M; Rothlisberger, U; Tavernelli, I; Penfold, T J

2014-10-23

29

Quantum dynamics in simple fluids.  

PubMed

We use quantum-correction factors to calculate approximately the quantum velocity time-correlation function (TCF) of supercritical Lennard-Jones argon from the classical TCF. We find that for this quite classical system, several different quantum-correction schemes yield essentially identical results for the real and imaginary parts of the quantum TCF, and also agree well with the recent forward-backward semiclassical dynamics (FBSD) results of Wright and Makri [J. Chem. Phys. 119, 1634 (2003)]. We also consider a more quantum-mechanical fluid of lighter atoms (neon) at a lower temperature. In this case different quantum-correction schemes give different results. FBSD calculations show that the harmonic quantum correction factor works the best for this system PMID:15267554

Lawrence, C P; Nakayama, A; Makri, N; Skinner, J L

2004-04-01

30

A molecular dynamics study of nuclear quantum effect on the diffusion of hydrogen in condensed phase  

NASA Astrophysics Data System (ADS)

In this paper, the quantum effect of hydrogen molecule on its diffusivity is analyzed using Molecular Dynamics (MD) method. The path integral centroid MD (CMD) method is applied for the reproduction method of time evolution of the molecules. The diffusion coefficient of liquid hydrogen is calculated using the Green-Kubo method. The simulation is performed at wide temperature region and the temperature dependence of the quantum effect of hydrogen molecule is addressed. The calculation results are compared with those of classical MD results. As a result, it is confirmed that the diffusivity of hydrogen molecule is changed depending on temperature by the quantum effect. It is clarified that this result can be explained that the dominant factor by quantum effect on the diffusivity of hydrogen changes from the swollening the potential to the shallowing the potential well around 30 K. Moreover, it is found that this tendency is related to the temperature dependency of the ratio of the quantum kinetic energy and classical kinetic energy.

Nagashima, Hiroki; Tsuda, Shin-ichi; Tsuboi, Nobuyuki; Koshi, Mitsuo; Hayashie, A. Koichi; Tokumasu, Takashi

2014-10-01

31

On quantum potential dynamics  

E-print Network

Non-relativistic de Broglie-Bohm theory describes particles moving under the guidance of the wave function. In de Broglie's original formulation, the particle dynamics is given by a first-order differential equation. In Bohm's reformulation, it is given by Newton's law of motion with an extra potential that depends on the wave function--the quantum potential--together with a constraint on the possible velocities. It was recently argued, mainly by numerical simulations, that relaxing this velocity constraint leads to a physically untenable theory. We provide further evidence for this by showing that for various wave functions the particles tend to escape the wave packet. In particular, we show that for a central classical potential and bound energy eigenstates the particle motion is often unbounded. This work seems particularly relevant for ways of simulating wave function evolution based on Bohm's formulation of the de Broglie-Bohm theory. Namely, the simulations may become unstable due to deviations from the velocity constraint.

Sheldon Goldstein; Ward Struyve

2013-12-06

32

Dynamical evaporation of quantum horizons  

E-print Network

We describe the black hole evaporation process driven by the dynamical evolution of the quantum gravitational degrees of freedom resident at the horizon, as identified by the loop quantum gravity kinematics. Using a parallel with the Brownian motion, we interpret the first law of quantum dynamical horizon in terms of a fluctuation-dissipation relation. In this way, the horizon evolution is described in terms of relaxation to an equilibrium state balanced by the excitation of Planck scale constituents of the horizon. This discrete quantum hair structure associated to the horizon geometry produces a deviation from thermality in the radiation spectrum. We investigate the final stage of the evaporation process and show how the dynamics leads to the formation of a massive remnant, which can eventually decay. Implications for the information paradox are discussed.

Daniele Pranzetti

2012-11-12

33

Quantum dynamics using hydrodynamic trajectories  

NASA Astrophysics Data System (ADS)

In this talk we will give a brief overview of our recent work in developing a causal trajectory approach for simulating quantum dynamics in a variety of systems. These trajectories arise as solutions to the de Broglie/Bohm equations, which replace the Schrödinger wave equation with the continuity equation for the quantum density and a quantum Hamilton-Jacobi equation for a set of ray-like trajectories. Whereas typical applications of this approach have focused upon the use of a "pilot wave" approach whereby the trajectories are obtained from quantum wavefunction, i.e. p[?] =hbar Im[nablalog?], our approach discretizes the density and allowes the discretization points to move according Lagrangian equations of motion derived from the quantum Hamilton-Jacobi equation. We demonstrate the approach via a series of test cases and comment upon the various strengths and difficulties of the approach. In particular, we will discuss what happens when nodes form in the quantum density.

Bittner, Eric

2000-03-01

34

Quantum regression theorem and non-Markovianity of quantum dynamics  

E-print Network

We explore the connection between two recently introduced notions of non-Markovian quantum dynamics and the validity of the so-called quantum regression theorem. While non-Markovianity of a quantum dynamics has been defined looking at the behaviour in time of the statistical operator, which determines the evolution of mean values, the quantum regression theorem makes statements about the behaviour of system correlation functions of order two and higher. The comparison relies on an estimate of the validity of the quantum regression hypothesis, which can be obtained exactly evaluating two points correlation functions. To this aim we consider a qubit undergoing dephasing due to interaction with a bosonic bath, comparing the exact evaluation of the non-Markovianity measures with the violation of the quantum regression theorem for a class of spectral densities. We further study a photonic dephasing model, recently exploited for the experimental measurement of non-Markovianity. It appears that while a non-Markovian dynamics according to either definition brings with itself violation of the regression hypothesis, even Markovian dynamics can lead to a failure of the regression relation.

Giacomo Guarnieri; Andrea Smirne; Bassano Vacchini

2014-06-20

35

Dynamic trapping near a quantum critical point  

E-print Network

The study of dynamics in closed quantum systems has recently been revitalized by the emergence of experimental systems that are well-isolated from their environment. In this paper, we consider the closed-system dynamics of an archetypal model: spins near a second order quantum critical point, which are traditionally described by the Kibble-Zurek mechanism. Imbuing the driving field with Newtonian dynamics, we find that the full closed system exhibits a robust new phenomenon -- dynamic critical trapping -- in which the system is self-trapped near the critical point due to efficient absorption of field kinetic energy by heating the quantum spins. We quantify limits in which this phenomenon can be observed and generalize these results by developing a Kibble-Zurek scaling theory that incorporates the dynamic field. Our findings can potentially be interesting in the context of early universe physics, where the role of the driving field is played by the inflaton or a modulus.

Michael Kolodrubetz; Emanuel Katz; Anatoli Polkovnikov

2014-06-10

36

Dynamic trapping near a quantum critical point  

E-print Network

The study of dynamics in closed quantum systems has recently been revitalized by the emergence of experimental systems that are well-isolated from their environment. In this paper, we consider the closed-system dynamics of an archetypal model: spins near a second order quantum critical point, which are traditionally described by the Kibble-Zurek mechanism. Imbuing the driving field with Newtonian dynamics, we find that the full closed system exhibits a robust new phenomenon -- dynamic critical trapping -- in which the system is self-trapped near the critical point due to efficient absorption of field kinetic energy by heating the quantum spins. We quantify limits in which this phenomenon can be observed and generalize these results by developing a Kibble-Zurek scaling theory that incorporates the dynamic field. Our findings can potentially be interesting in the context of early universe physics, where the role of the driving field is played by the inflaton or a modulus.

Kolodrubetz, Michael; Polkovnikov, Anatoli

2014-01-01

37

Extended-DMFT Study of Quantum Phase Transitions in a Kondo Lattice: Dynamical Large-N limit  

NASA Astrophysics Data System (ADS)

In one approach to the quantum critical heavy fermion metals, Kondo lattice systems are studied through self-consistent Bose-Fermi Kondo Model (BFKM) within the extended dynamical mean field theory. In the case with spin-rotational invariance, this model is still difficult to study theoretically or numerically. Very recently, it has been shown[1,2] that a dynamical large-N generalization provides an access to the quantum critical behavior of the spin-rotationally-invariant BFKM with a sub-ohmic boson spectral function. Here, we carry out a self-consistent EDMFT study of the model in this large-N limit. We determine the extent to which a second-order quantum phase transition exists in this limit for two- and three-dimensional spin fluctuations, as well as the critical exponents of the magnetic dynamics. [1] L. Zhu, S. Kirchner, Q. Si, and A. Georges, Phys. Rev. Lett, in press (cond-mat/0406293). [2] S. Kirchner, L. Zhu, and Q. Si, Physica B, in press (cond-mat/0407307).

Kirchner, Stefan; Zhu, Lijun; Si, Qimiao

2005-03-01

38

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

39

Control by quantum dynamics on graphs  

SciTech Connect

We address the study of controllability of a closed quantum system whose dynamical Lie algebra is generated by adjacency matrices of graphs. We characterize a large family of graphs that renders a system controllable. The key property is a graph-theoretic feature consisting of a particularly disordered cycle structure. Disregarding efficiency of control functions, but choosing subfamilies of sparse graphs, the results translate into continuous-time quantum walks for universal computation.

Godsil, Chris; Severini, Simone [Department of Combinatorics and Optimization, University of Waterloo, Waterloo, Ontario N2L 3G1 (Canada); Department of Physics and Astronomy, University College London, London WC1E 6BT (United Kingdom)

2010-05-15

40

Nonlocal interactions and quantum dynamics  

E-print Network

The problem is considered of describing the dynamics of quantum systems generated by a nonlocal in time interaction. It is shown that the use of the Feynman approach to quantum theory in combination with the canonical approach allows one to extend quantum dynamics to describe the time evolution in the case of such interactions. In this way, using only the current concepts of quantum theory, a generalized equation of motion for state vectors is derived. In the case, where the fundamental interaction generating the dynamics in a system is local in time, this equation is equivalent to the Schr{\\"o}dinger equation. Explicit examples are given for an exactly solvable model. The proposed formalism is shown to provide a new insight into the problem of the description of nonlocal interactions in quantum field theory. It is shown that such a property of the equation of motion as nonlocality in time may be important for describing hadron-hadron interactions at low and intermediate energies.

Renat Kh. Gainutdinov

2001-06-19

41

Ensemble Dynamics with Quantum Forces  

NASA Astrophysics Data System (ADS)

We present a new methodology for approximating the solutions of the time-dependent Schrödinger equation. Our approach is rooted in the de Broglie Bohm interpretation of the quantum theory in which the evolution of a quantum system is characterized by an ensemble of particle trajectories. The paths of these ``Bohmian'' particles are analogous to hydrodynamic trajectories and are determined by the presence of both classical and quantum forces in the system. The quantum force is due to the nonlocal interactions between particles and is related to the curvature of the quantum density. In the present study we invoke an expectation-maximization algorithm to approximate a functional form for the density of a finite ensemble of Bohmian particles. From this density information we then calculate a quantum force and propagate the system forward in time using a Verlet type integration. In what follows we will describe the details of this approach and present some numerical results.

Maddox, Jeremy; Bittner, Eric

2003-03-01

42

Quantum Information Processing with Quantum Zeno Many-Body Dynamics  

Microsoft Academic Search

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

Alex Monras; Oriol Romero-Isart

2008-01-01

43

Kerr rotation studies of single electron spin dynamics in a quantum dot  

NASA Astrophysics Data System (ADS)

Kerr rotation measurements are used to directly and non-destructively probe the dynamics of a single electron spin in a charge-tunable quantum dot. The dot is formed by interface fluctuations of a GaAs quantum well and embedded in a vertical optical cavity. Using Hanle techniques, we perform single electron Kerr rotation measurements at T=10K in order to monitor the depolarization of an optically pumped electron spin within an applied transverse magnetic field. This reveals information about the time averaged transverse spin lifetime, T2^*. At gate voltages for which the charging rate of the dot is relatively low, the results yield a T2^* in agreement with values expected from the hyperfine interaction in these materials. In contrast, at larger charging rates, we find that T2^* is strongly reduced, indicating the importance of additional decoherence mechanisms in that regime. J. Berezovsky, M. H. Mikkelsen, O. Gywat, N. G. Stoltz, L. A. Coldren, and D. D. Awschalom,Science Express, 9 November 2006, (10.1126/science.1133862).

Mikkelsen, M. H.; Berezovsky, J.; Gywat, O.; Stoltz, N. G.; Coldren, L. A.; Awschalom, D. D.

2007-03-01

44

Six-dimensional quantum dynamics study for the dissociative adsorption of HCl on Au(111) surface  

SciTech Connect

The six-dimensional quantum dynamics calculations for the dissociative chemisorption of HCl on Au(111) are carried out using the time-dependent wave-packet approach, based on an accurate PES which was recently developed by neural network fitting to density functional theory energy points. The influence of vibrational excitation and rotational orientation of HCl on the reactivity is investigated by calculating the exact six-dimensional dissociation probabilities, as well as the four-dimensional fixed-site dissociation probabilities. The vibrational excitation of HCl enhances the reactivity and the helicopter orientation yields higher dissociation probability than the cartwheel orientation. A new interesting site-averaged effect is found for the title molecule-surface system that one can essentially reproduce the six-dimensional dissociation probability by averaging the four-dimensional dissociation probabilities over 25 fixed sites.

Liu, Tianhui; Fu, Bina; Zhang, Dong H., E-mail: zhangdh@dicp.ac.cn [State Key Laboratory of Molecular Reaction Dynamics and Center for Theoretical Computational Chemistry, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023 (China)

2013-11-14

45

Theory of controlled quantum dynamics  

Microsoft Academic Search

We introduce a general formalism to obtain localized quantum wavepackets as dynamically controlled systems, in the framework of Nelson stochastic quantization. We show that in general the control is linear, and it amounts to introducing additional time-dependent terms in the potential. In this way one can construct for general systems either coherent packets following classical motion with constant dispersion, or

Salvatore De Martino; Silvio De Siena; Fabrizio Illuminati

1997-01-01

46

Nonlinear Dynamics In Quantum Physics -- Quantum Chaos and Quantum Instantons  

E-print Network

We discuss the recently proposed quantum action - its interpretation, its motivation, its mathematical properties and its use in physics: quantum mechanical tunneling, quantum instantons and quantum chaos.

H. Kröger

2003-02-21

47

Experimental realization of quantum zeno dynamics.  

PubMed

It is generally impossible to probe a quantum system without disturbing it. However, it is possible to exploit the back action of quantum measurements and strong couplings to tailor and protect the coherent evolution of a quantum system. This is a profound and counterintuitive phenomenon known as quantum Zeno dynamics. Here we demonstrate quantum Zeno dynamics with a rubidium Bose-Einstein condensate in a five-level Hilbert space. We harness measurements and strong couplings to dynamically disconnect different groups of quantum states and constrain the atoms to coherently evolve inside a two-level subregion. In parallel to the foundational importance due to the realization of a dynamical superselection rule and the theory of quantum measurements, this is an important step forward in protecting and controlling quantum dynamics and, broadly speaking, quantum information processing. PMID:24476716

Schäfer, F; Herrera, I; Cherukattil, S; Lovecchio, C; Cataliotti, F S; Caruso, F; Smerzi, A

2014-01-01

48

Excited state dynamics in SO2. III. An ab initio quantum study of single- and multi-photon ionization  

NASA Astrophysics Data System (ADS)

We present an ab initio quantum study of the photoelectron spectra of sulfur dioxide, based on wavepacket propagations on manifolds of ionic, and excited/Rydberg states. We obtain excellent agreement for two different cases. First, the one photon ionization case where we can reproduce all details of the experimental spectrum and demonstrate the influence of the conical intersection between two of the ionic states. Then the multiphoton ionization regime, in which the dynamics of the wave packet on the two lowest singlet states is directly mapped in the spectra via a pump-probe scheme, as proposed in the experimental companion paper [I. Wilkinson et al., J. Chem. Phys. 140, 204301 (2014)].

Lévęque, Camille; Köppel, Horst; Taďeb, Richard

2014-05-01

49

Quantum Spin Dynamics and Quantum Computation  

E-print Network

We describe a simulation method for a quantum spin model of a generic, general purpose quantum computer. The use of this quantum computer simulator is illustrated through several implementations of Grover's database search algorithm. Some preliminary results on the stability of quantum algorithms are presented.

H. De Raedt; A. H. Hams; K. Michielsen; S. Miyashita; K. Saito

1999-11-09

50

Nonequilibrium quench dynamics in quantum quasicrystals  

E-print Network

We study the nonequilibrium dynamics of a quasiperiodic quantum Ising chain after a sudden change in the strength of the transverse field at zero temperature. In particular we consider the dynamics of the entanglement entropy and the relaxation of the magnetization. The entanglement entropy increases with time as a power-law, and the magnetization is found to exhibit stretched-exponential relaxation. These behaviors are explained in terms of anomalously diffusing quasiparticles, which are studied in a wave packet approach. The nonequilibrium magnetization is shown to have a dynamical phase transition.

Ferenc Igloi; Gergo Roosz; Yu-Cheng Lin

2012-10-27

51

Orbits of hybrid systems as qualitative indicators of quantum dynamics  

E-print Network

Hamiltonian theory of hybrid quantum-classical systems is used to study dynamics of the classical subsystem coupled to different types of quantum systems. It is shown that the qualitative properties of orbits of the classical subsystem clearly indicate if the quantum subsystem does or does not have additional conserved observables.

N. Buric; D. B. Popovic; M. Radonjic; S. Prvanovic

2014-03-03

52

Robustness of controlled quantum dynamics  

NASA Astrophysics Data System (ADS)

The control of multilevel quantum systems is sensitive to implementation errors in the control field and uncertainties associated with system Hamiltonian parameters. A small variation in the control field spectrum or the system Hamiltonian can cause an otherwise optimal field to deviate from controlling desired quantum state transitions and reaching a particular objective. An accurate analysis of robustness is thus essential in understanding and achieving model-based quantum control, such as in the control of chemical reactions based on ab initio or experimental estimates of the molecular Hamiltonian. In this paper, theoretical foundations for quantum control robustness analysis are presented from both a distributional perspective—in terms of moments of the transition amplitude, interferences, and transition probability—and a worst-case perspective. Based on this theory, analytical expressions and a computationally efficient method for determining the robustness of coherently controlled quantum dynamics are derived. The robustness analysis reveals that there generally exists a set of control pathways that are more resistant to destructive interferences in the presence of control field and system parameter uncertainty. These robust pathways interfere and combine to yield a relatively accurate transition amplitude and high transition probability when uncertainty is present.

Koswara, Andy; Chakrabarti, Raj

2014-10-01

53

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

2013-04-01

54

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

NASA Astrophysics Data System (ADS)

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/cm3 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.

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

2013-04-01

55

Quantum molecular dynamics study of expanded beryllium: Evolution from warm dense matter to atomic fluid  

NASA Astrophysics Data System (ADS)

By performing quantum molecular dynamics (QMD) simulations, we investigate the equation of states, electrical and optical properties of the expanded beryllium at densities two to one-hundred lower than the normal solid density, and temperatures ranging from 5000 to 30000 K. With decreasing the density of Be, the optical response evolves from the one characteristic of a simple metal to the one of an atomic fluid. By fitting the optical conductivity spectra with the Drude-Smith model, it is found that the conducting electrons become localized at lower densities. In addition, the negative derivative of the electrical resistivity on temperature at density about eight lower than the normal solid density demonstrates that the metal to nonmetal transition takes place in the expanded Be. To interpret this transition, the electronic density of states is analyzed systematically. Furthermore, a direct comparison of the Rosseland opacity obtained by using QMD and the standard opacity code demonstrates that QMD provides a powerful tool to validate plasma models used in atomic physics approaches in the warm dense matter regime.

Li, Dafang; Liu, Haitao; Zeng, Siliang; Wang, Cong; Wu, Zeqing; Zhang, Ping; Yan, Jun

2014-07-01

56

Quantum molecular dynamics study of expanded beryllium: evolution from warm dense matter to atomic fluid.  

PubMed

By performing quantum molecular dynamics (QMD) simulations, we investigate the equation of states, electrical and optical properties of the expanded beryllium at densities two to one-hundred lower than the normal solid density, and temperatures ranging from 5000 to 30000 K. With decreasing the density of Be, the optical response evolves from the one characteristic of a simple metal to the one of an atomic fluid. By fitting the optical conductivity spectra with the Drude-Smith model, it is found that the conducting electrons become localized at lower densities. In addition, the negative derivative of the electrical resistivity on temperature at density about eight lower than the normal solid density demonstrates that the metal to nonmetal transition takes place in the expanded Be. To interpret this transition, the electronic density of states is analyzed systematically. Furthermore, a direct comparison of the Rosseland opacity obtained by using QMD and the standard opacity code demonstrates that QMD provides a powerful tool to validate plasma models used in atomic physics approaches in the warm dense matter regime. PMID:25081816

Li, Dafang; Liu, Haitao; Zeng, Siliang; Wang, Cong; Wu, Zeqing; Zhang, Ping; Yan, Jun

2014-01-01

57

The universal quantum driving force to speed up a quantum computation -- The unitary quantum dynamics  

E-print Network

It is shown in the paper that the unitary quantum dynamics in quantum mechanics is the universal quantum driving force to speed up a quantum computation. This assertion supports strongly in theory that the unitary quantum dynamics is the fundamental and universal principle in nature. On the other hand, the symmetric structure of Hilbert space of a composite quantum system is the quantum-computing resource that is not owned by classical computation. A new quantum-computing speedup theory is set up on the basis of the unitary quantum dynamics. Both the unitary quantum dynamics and the symmetric structure and property of the Hilbert space of the quantum system are mainly responsible for an exponential quantum-computing speedup for a general efficient quantum algorithm. The inherent importance for the unitary quantum dynamics to speed up a quantum computation lies in the unique ability of the unitary quantum dynamics to build the effective interaction between the symmetric structure of the Hilbert space of the quantum system and the mathematical symmetric structure of a problem to be solved on the quantum system. This unique ability could result in an essential difference of computational power between quantum and classical computations by combining the symmetric structure and property of the Hilbert space. The new quantum-computing speedup theory also provides reasonable mechanisms for exponential quantum-computing speedup for the existing efficient quantum algorithms based on the quantum parallel principle. These existing quantum algorithms including the hidden-subgroup-problem quantum algorithms and conventional quantum search algorithms have the common character that the symmetric structure of the Hilbert space does not have any effective effect on these quantum algorithms. This could be the main reason why these quantum algorithms are quite special and considered to be semiclassical.

Xijia Miao

2011-05-18

58

Excitons in a photosynthetic light-harvesting system: A combined molecular dynamics, quantum chemistry, and polaron model study  

E-print Network

electronic excitation to the photo- synthetic reaction center 1­4 . In the case of purple bacte- ria, lightExcitons in a photosynthetic light-harvesting system: A combined molecular dynamics, quantum. The molecular dynamics simulation of light-harvesting LH complexes was per- formed on an 87 055 atom system

Kosztin, Ioan

59

Ultrafast exciton dynamics in CdSe quantum dots studied from bleaching recovery and fluorescence transients.  

PubMed

We have performed ultrafast absorption bleach recovery and fluorescence upconversion measurements ( approximately 100 fs time resolution) for three CdSe samples, with nanoparticle diameters of 2.7, 2.9, and 4.3 nm. The two types of experiments provide complementary information regarding the contributions of the different processes involved in the fast relaxation of electrons and holes in the CdSe quantum dots. Transient absorption and emission experiments were conducted for the 1S [1Se-1S3/2(h)] transition, 1S(e) and 1S3/2(h) representing the lowest electron (e) and hole (h) levels. The bleach recovery of the 1S transition shows a approximately 400-500 fs initial rise, which is followed by a size-dependent approximately 10-90 ps decay and finally a long-lived (approximately ns) decay. The fluorescence upconversion signal for the 1S transition shows quite different temporal behavior: a two times slower rise time (approximately 700-1000 fs) and, when the fluorescence upconversion signal has risen to about 20% of its maximum intensity, the signal displays a slight leveling off (bend), followed by a continued rise until the maximum intensity is reached. This bend is well reproducible and power and concentration independent. Simulations show that the bend in the rise is caused by a very fast decay component with a typical time of about 230-430 fs. Considering that the 1S quantum dot excitation is comprised of five exciton substates (F=+/-2, +/-1L, 0L, +/-1U, and 0U), we attribute the disparity in the rise of the bleaching and emission transients to the results from the dynamics of the different excitons involved in respectively the bleaching and fluorescence experiments. More specifically, in transient absorption, population changes of the F=+/-1U excitons are probed, in emission population effects for the F=+/-2 ("dark") and the F=+/-1L ("bright") exciton states are monitored. It is discussed that the fast (approximately 400-500 fs) rise of the bleach recovery is representative of the feeding of the F=+/-1U exciton (by filling of the 1S(e) electron level) and that the slower (approximately 700-1000 fs) feeding of the emissive +/-2, +/-1L excitons is determined by the relaxation of the hole levels within the 1S3/2 fine structure. Finally, the approximately 230-430 fs component, typical of the bend in the fluorescence transient, is attributed to the thermalization of the close-lying +/-2 ("dark") and +/-1L ("bright") excitons. PMID:16471595

Wang, Haiyu; de Mello Donegá, Celso; Meijerink, Andries; Glasbeek, Max

2006-01-19

60

Dynamical Generation of Noiseless Quantum Subsystems  

NASA Astrophysics Data System (ADS)

We combine dynamical decoupling and universal control methods for open quantum systems with coding procedures. By exploiting a general algebraic approach, we show how appropriate encodings of quantum states result in obtaining universal control over dynamically generated noise-protected subsystems with limited control resources. In particular, we provide a constructive scheme based on two-body Hamiltonians for performing universal quantum computation over large noiseless spaces which can be engineered in the presence of arbitrary linear quantum noise.

Viola, Lorenza; Knill, Emanuel; Lloyd, Seth

2000-10-01

61

Metric perturbation theory of quantum dynamics  

E-print Network

A theory of quantum dynamics based on a discrete structure underlying the space time manifold is developed for single particles. It is shown that at the micro domain the interaction of particles with the underlying discrete structure results in the quantum space time manifold. Regarding the resulting quantum space-time as perturbation from the Lorentz metric it is shown it is possible to discuss the dynamics of particles in the quantum domain.

Antony L Tambyrajah

2006-10-06

62

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

63

Quantum Discord: A Dynamic Approach in Geometric Picture  

E-print Network

We present a dynamic approach to study the quantum discord and classical correlation. By local filtering operation, the evaluation of quantum discord is closely related to quantum channel and channel capacity. As a consequence, the traditional optimization over horizontal-or-vertical von Neumann measurements is replaced by that over horizontal-and-vertical three-element POVM measurement, from which more rigorous results of quantum discord are obtained.

Mingjun Shi; Fengjian Jiang; Jiangfeng Du

2011-07-22

64

Communication: Quantum dynamics in classical spin baths  

NASA Astrophysics Data System (ADS)

A formalism for studying the dynamics of quantum systems embedded in classical spin baths is introduced. The theory is based on generalized antisymmetric brackets and predicts the presence of open-path off-diagonal geometric phases in the evolution of the density matrix. The weak coupling limit of the equation can be integrated by standard algorithms and provides a non-Markovian approach to the computer simulation of quantum systems in classical spin environments. It is expected that the theory and numerical schemes presented here have a wide applicability.

Sergi, Alessandro

2013-07-01

65

Quantum Dynamics in Classical Spin Baths  

E-print Network

A formalism for studying the dynamics of quantum systems embedded in classical spin baths is introduced. The theory is based on generalized antisymmetric brackets and predicts the presence of open-path off-diagonal geometric phases in the evolution of the density matrix. The weak coupling limit of the equation can be integrated by standard algorithms and provides a non-Markovian approach to the computer simulation of quantum systems in classical spin environments. It is expected that the theory and numerical schemes presented here have a wide applicability.

Alessandro Sergi

2013-06-14

66

Communication: quantum dynamics in classical spin baths.  

PubMed

A formalism for studying the dynamics of quantum systems embedded in classical spin baths is introduced. The theory is based on generalized antisymmetric brackets and predicts the presence of open-path off-diagonal geometric phases in the evolution of the density matrix. The weak coupling limit of the equation can be integrated by standard algorithms and provides a non-Markovian approach to the computer simulation of quantum systems in classical spin environments. It is expected that the theory and numerical schemes presented here have a wide applicability. PMID:23883002

Sergi, Alessandro

2013-07-21

67

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

68

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

69

Monitoring Entanglement Evolution and Collective Quantum Dynamics  

E-print Network

We generalize a recently developed scheme for monitoring coherent quantum dynamics with good time-resolution and low backaction [Reuther et al., Phys. Rev. Lett. 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 demonstrate that this scheme also allows one to observe quantum dynamics with many frequency scales, such as that of a qubit undergoing Landau-Zener transitions. Moreover, we propose how to measure the entanglement between two qubits as well as the collective dynamics of qubit arrays.

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

2010-07-30

70

Advances in Quantum Trajectory Approaches to Dynamics  

NASA Astrophysics Data System (ADS)

The quantum fluid dynamics (QFD) formulation is based on the separation of the amplitude and phase of the complex wave function in Schrodinger's equation. The approach leads to conservation laws for an equivalent "gas continuum". The Lagrangian [1] representation corresponds to following the particles of the fluid continuum, i. e. calculating "quantum trajectories". The Eulerian [2] representation on the other hand, amounts to observing the dynamics of the gas continuum at the points of a fixed coordinate frame. The combination of several factors leads to a most encouraging computational efficiency. QFD enables the numerical analysis to deal with near monotonic amplitude and phase functions. The Lagrangian description concentrates the computation effort to regions of highest probability as an optimal adaptive grid. The Eulerian representation allows the study of multi-coordinate problems as a set of one-dimensional problems within an alternating direction methodology. An explicit time integrator limits the increase in computational effort with the number of discrete points to linear. Discretization of the space via local finite elements [1,2] and global radial functions [3] will be discussed. Applications include wave packets in four-dimensional quadratic potentials and two coordinate photo-dissociation problems for NOCl and NO2. [1] "Quantum fluid dynamics (QFD) in the Lagrangian representation with applications to photo-dissociation problems", F. Sales, A. Askar and H. A. Rabitz, J. Chem. Phys. 11, 2423 (1999) [2] "Multidimensional wave-packet dynamics within the fluid dynamical formulation of the Schrodinger equation", B. Dey, A. Askar and H. A. Rabitz, J. Chem. Phys. 109, 8770 (1998) [3] "Solution of the quantum fluid dynamics equations with radial basis function interpolation", Xu-Guang Hu, Tak-San Ho, H. A. Rabitz and A. Askar, Phys. Rev. E. 61, 5967 (2000)

Askar, Attila

2001-03-01

71

Why quantum dynamics is linear  

NASA Astrophysics Data System (ADS)

A seed George planted 45 years ago is still producing fruit now. In 1961, George set out the fundamental proposition that quantum dynamics is described most generally by linear maps of density matrices. Since the first sprout from George's seed appeared in 1962, we have known that George's fundamental proposition can be used to derive the linear Schrodinger equation in cases where it can be expected to apply. Now we have a proof of George's proposition that density matrices are mapped linearly to density matrices, that there can be no nonlinear generalization of this. That completes the derivation of the linear Schrodinger equation. The proof of George's proposition replaces Wigner's theorem that a symmetry transformation is represented by a linear or antilinear operator. The assumption needed to prove George's proposition is just that the dynamics does not depend on anything outside the system but must allow the system to be described as part of a larger system. This replaces the physically less compelling assumption of Wigner's theorem that absolute values of inner products are preserved. The history of this question is reviewed. Nonlinear generalizations of quantum mechanics have been proposed. They predict small but clear nonlinear effects, which very accurate experiments have not seen. This begs the question. Is there a reason in principle why nonlinearity is not found? Is it impossible? Does quantum dynamics have to be linear? Attempts to prove this have not been decisive, because either their assumptions are not compelling or their arguments are not conclusive. The question has been left unsettled. The simple answer, based on a simple assumption, was found in two steps separated by 44 years.

Jordan, Thomas F.

2009-11-01

72

Nuclear quantum effect on intramolecular hydrogen bond of hydrogen maleate anion: An ab initio path integral molecular dynamics study  

NASA Astrophysics Data System (ADS)

Ab initio path integral molecular dynamics simulation was performed to understand the nuclear quantum effect on the hydrogen bond of hydrogen malonate anion. Static calculation predicted the proton transfer barrier as 0.12 kcal/mol. Conventional ab initio molecular dynamics simulation at 300 K found proton distribution with a double peak on the proton transfer coordinate. Inclusion of thermal effect alone elongates the hydrogen bond length, which increases the barrier height. Inclusion of nuclear quantum effect washes out this barrier, and distributes a single broad peak in the center. H/D isotope effect on the proton transfer is also discussed.

Kawashima, Yukio; Tachikawa, Masanori

2013-05-01

73

Seven-degree-of-freedom, quantum scattering dynamics study of the H2D++H2 reaction  

NASA Astrophysics Data System (ADS)

A quantum scattering dynamics, time-dependent wavepacket propagation method is applied to study the reaction of H2D++H2-->H3++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 H2D+ at the lowest saddle point geometry of D2d 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+-HD only has a small effect on the reaction probability; the vibrational excitation of HD in H2D+ hinders the reactivity. By contrast, rotational excitation of H+-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 H2D+ and H2. 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; Xie, Zhen; Bowman, Joel M.

2010-02-01

74

Classical dynamics of quantum entanglement.  

PubMed

We analyze numerically the dynamical generation of quantum entanglement in a system of two interacting particles, started in a coherent separable state, for decreasing values of ?. As ??0 the entanglement entropy, computed at any finite time, converges to a finite nonzero value. The limit law that rules the time dependence of entropy is well reproduced by purely classical computations. Its general features can be explained by simple classical arguments, which expose the different ways entanglement is generated in systems that are classically chaotic or regular. PMID:22587162

Casati, Giulio; Guarneri, Italo; Reslen, Jose

2012-03-01

75

Dynamical Correspondence in a Generalized Quantum Theory  

E-print Network

A dynamical correspondence allocates a skew order derivation (generator of a one-parameter positive group) on an ordered Banach space to each element of the space. It is well-known that its existence distinguishes the selfadjoint parts of the von Neumann algebras among Jordan algebras of a more general type - the JBW algebras. The paper shows that this remains valid, if the JBW algebras are replaced by a broader class of nonassociative algebras which arises from recent studies of the quantum logics with a conditional probability calculus and particularly of those that rule out third-order interference. The conditional probability calculus is a mathematical model of the L\\"uders-von Neumann quantum measurement process, and third-order interference is a property of the conditional probabilities which was discovered by R. Sorkin in 1994 and which is ruled out by quantum mechanics.

Gerd Niestegge

2014-02-02

76

Excited state dynamics in SO2. III. An ab initio quantum study of single- and multi-photon ionization.  

PubMed

We present an ab initio quantum study of the photoelectron spectra of sulfur dioxide, based on wavepacket propagations on manifolds of ionic, and excited/Rydberg states. We obtain excellent agreement for two different cases. First, the one photon ionization case where we can reproduce all details of the experimental spectrum and demonstrate the influence of the conical intersection between two of the ionic states. Then the multiphoton ionization regime, in which the dynamics of the wave packet on the two lowest singlet states is directly mapped in the spectra via a pump-probe scheme, as proposed in the experimental companion paper [I. Wilkinson et al., J. Chem. Phys. 140, 204301 (2014)]. PMID:24880276

Lévęque, Camille; Köppel, Horst; Taďeb, Richard

2014-05-28

77

A molecular dynamics study of intramolecular proton transfer reaction of malonaldehyde in solutions based upon mixed quantum-classical approximation. I. Proton transfer reaction in water  

NASA Astrophysics Data System (ADS)

In order to investigate proton transfer reaction in solution, mixed quantum-classical molecular dynamics calculations have been carried out based on our previously proposed quantum equation of motion for the reacting system [A. Yamada and S. Okazaki, J. Chem. Phys. 128, 044507 (2008)]. Surface hopping method was applied to describe forces acting on the solvent classical degrees of freedom. In a series of our studies, quantum and solvent effects on the reaction dynamics in solutions have been analysed in detail. Here, we report our mixed quantum-classical molecular dynamics calculations for intramolecular proton transfer of malonaldehyde in water. Thermally activated proton transfer process, i.e., vibrational excitation in the reactant state followed by transition to the product state and vibrational relaxation in the product state, as well as tunneling reaction can be described by solving the equation of motion. Zero point energy is, of course, included, too. The quantum simulation in water has been compared with the fully classical one and the wave packet calculation in vacuum. The calculated quantum reaction rate in water was 0.70 ps-1, which is about 2.5 times faster than that in vacuum, 0.27 ps-1. This indicates that the solvent water accelerates the reaction. Further, the quantum calculation resulted in the reaction rate about 2 times faster than the fully classical calculation, which indicates that quantum effect enhances the reaction rate, too. Contribution from three reaction mechanisms, i.e., tunneling, thermal activation, and barrier vanishing reactions, is 33:46:21 in the mixed quantum-classical calculations. This clearly shows that the tunneling effect is important in the reaction.

Yamada, Atsushi; Kojima, Hidekazu; Okazaki, Susumu

2014-08-01

78

A molecular dynamics study of intramolecular proton transfer reaction of malonaldehyde in solutions based upon mixed quantum-classical approximation. I. Proton transfer reaction in water.  

PubMed

In order to investigate proton transfer reaction in solution, mixed quantum-classical molecular dynamics calculations have been carried out based on our previously proposed quantum equation of motion for the reacting system [A. Yamada and S. Okazaki, J. Chem. Phys. 128, 044507 (2008)]. Surface hopping method was applied to describe forces acting on the solvent classical degrees of freedom. In a series of our studies, quantum and solvent effects on the reaction dynamics in solutions have been analysed in detail. Here, we report our mixed quantum-classical molecular dynamics calculations for intramolecular proton transfer of malonaldehyde in water. Thermally activated proton transfer process, i.e., vibrational excitation in the reactant state followed by transition to the product state and vibrational relaxation in the product state, as well as tunneling reaction can be described by solving the equation of motion. Zero point energy is, of course, included, too. The quantum simulation in water has been compared with the fully classical one and the wave packet calculation in vacuum. The calculated quantum reaction rate in water was 0.70 ps(-1), which is about 2.5 times faster than that in vacuum, 0.27 ps(-1). This indicates that the solvent water accelerates the reaction. Further, the quantum calculation resulted in the reaction rate about 2 times faster than the fully classical calculation, which indicates that quantum effect enhances the reaction rate, too. Contribution from three reaction mechanisms, i.e., tunneling, thermal activation, and barrier vanishing reactions, is 33:46:21 in the mixed quantum-classical calculations. This clearly shows that the tunneling effect is important in the reaction. PMID:25173023

Yamada, Atsushi; Kojima, Hidekazu; Okazaki, Susumu

2014-08-28

79

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

80

Dynamics of multipartite quantum correlations under decoherence  

E-print Network

Quantum discord is an optimal resource for the quantification of classical and non-classical correlations as compared to other related measures. Geometric measure of quantum discord is another measure of quantum correlations. Recently, the geometric quantum discord for multipartite states has been introduced by Jianwei Xu [arxiv:quant/ph.1205.0330]. Motivated from the recent study [Ann. Phys. 327 (2012) 851] for the bipartite systems, I have investigated global quantum discord (QD) and geometric quantum discord (GQD) under the influence of external environments for different multipartite states. Werner-GHZ type three-qubit and six-qubit states are considered in inertial and non-inertial settings. The dynamics of QD and GQD is investigated under amplitude damping, phase damping, depolarizing and flipping channels. It is seen that the quantum discord vanishes for p>0.75 in case of three-qubit GHZ states and for p>0.5 for six qubit GHZ states. This implies that multipartite states are more fragile to decoherence for higher values of N. Surprisingly, a rapid sudden death of discord occurs in case of phase flip channel. However, for bit flip channel, no sudden death happens for the six-qubit states. On the other hand, depolarizing channel heavily influences the QD and GQD as compared to the amplitude damping channel. It means that the depolarizing channel has the most destructive influence on the discords for multipartite states. From the perspective of accelerated observers, it is seen that effect of environment on QD and GQD is much stronger than that of the acceleration of non-inertial frames. The degradation of QD and GQD happens due to Unruh effect. Furthermore, QD exhibits more robustness than GQD when the multipartite systems are exposed to environment.

M. Ramzan

2012-05-14

81

NONLINEAR DYNAMICS IN QUANTUM PHYSICS - QUANTUM CHAOS AND QUANTUM INSTANTONS  

Microsoft Academic Search

We discuss the recently proposed quantum action - its interpretation, its moti- vation, its mathematical properties and its use in physics: quantum mechanical tunneling, quantum instantons and quantum chaos. 1. Introduction. Modern physics returns to some of its origins dating back to the first part of the last century. Examples are entanglement, according to Schrodinger the most peculiar property occuring

Helmut Kroger

82

Coherent State Functional Integral in Loop Quantum Cosmology:. Alternative Dynamics  

NASA Astrophysics Data System (ADS)

Coherent state functional integral for the minisuperspace model of loop quantum cosmology is studied. By the well-established canonical theory, the transition amplitude in the path integral representation of loop quantum cosmology with alternative dynamics can be formulated through group averaging. The effective action and Hamiltonian with higher-order quantum corrections are thus obtained. It turns out that for a nonsymmetric Hamiltonian constraint operator, the Moyal (star)-product emerges naturally in the effective Hamiltonian. For the corresponding symmetric Hamiltonian operator, the resulted effective theory implies a possible quantum cosmological effect in large scale limit in the alternative dynamical scenario, which coincides with the result in canonical approach. Moreover, the first-order modified Friedmann equation still contains the particular information of alternative dynamics and hence admits the possible phenomenological distinction between the different proposals of quantum dynamics.

Qin, Li; Ma, Yongge

2012-05-01

83

Online characterization of quantum dynamics using quantum error correction  

E-print Network

Characterizing noisy quantum processes is important to quantum computation and communication (QCC), since quantum systems are generally open. To date, all methods of characterization of quantum dynamics (CQD), typically implemented by quantum process tomography, are offline, i.e., QCC and CQD are not concurrent, as they require distinct state preparations. Here we introduce an online method, "Quantum error correction based characterization of dynamics" (QECCD), in which the initial state is any element from the code space of a quantum error correcting code (QECC) that can protect the state from the (otherwise uncharacterized) noise. The statistics of stabilizer measurements, with possible unitary pre-processing operations, are used to characterize the noise, while the observed syndrome can be used to correct the noisy state. Our method requires $\\mathcal{O}(d^{2} \\log(d))$ configurations to characterize arbitrary noise restricted to a $d$-dimensional subspace of a Hamming space of dimension $2^{n} \\geq d$. QECCD answers in the affirmative the question of whether it is possible to fully characterize quantum dynamics using quantum error detection techniques (Mohseni and Lidar, PRL 2006).

S. Omkar; R. Srikanth; S. Banerjee

2014-05-05

84

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

85

Quantum dynamical study of the O(1D) + CH4 ? CH3 + OH atmospheric reaction  

NASA Astrophysics Data System (ADS)

Time independent quantum mechanical (TIQM) scattering calculations have been carried out for the O(1D) + CH4(X1A1) ? CH3(X2A2?) + OH(X2?) atmospheric reaction, using an ab initio ground potential energy surface where the CH3 group is described as a pseudo-atom. Total and state-to-state reaction probabilities for a total angular momentum J = 0 have been determined for collision energies up to 0.5 eV. The vibrational and rotational state OH product distributions show no specific behavior. The rate coefficient has been calculated by means of the J-shifting approach in the 10-500 K temperature range and slightly depends on T at ordinary temperatures (as expected for a barrierless reaction). Quantum effects do not influence the vibrational populations and rate coefficient in an important way, and a rather good agreement has been found between the TIQM results and the quasiclassical trajectory and experimental ones. This reinforces somewhat the reliability of the pseudo-triatomic approach under the reaction conditions explored.

Ben Bouchrit, R.; Jorfi, M.; Ben Abdallah, D.; Jaidane, N.; González, M.; Bussery-Honvault, B.; Honvault, P.

2014-06-01

86

Nonlinear Schrödinger equation and dissipative quantum dynamics in periodic fields  

Microsoft Academic Search

The nonlinear dynamics of dissipative quantum systems in periodic fields is studied in the framework of a Gisin-like nonlinear Schrödinger equation with deterministic nonunitary quantum friction terms describing the system-bath couplings. The virtue of this nonunitary evolution is that it is compatible with Dirac's superposition principle and the Hilbert-space structure of quantum kinematics. Floquet theory and the generalized Van Vleck

Youhong Huang; Shih-I. Chu; Joseph O. Hirschfelder

1989-01-01

87

Conditional Quantum Dynamics and Logic Gates  

E-print Network

Quantum logic gates provide fundamental examples of conditional quantum dynamics. They could form the building blocks of general quantum information processing systems which have recently been shown to have many interesting non--classical properties. We describe a simple quantum logic gate, the quantum controlled--NOT, and analyse some of its applications. We discuss two possible physical realisations of the gate; one based on Ramsey atomic interferometry and the other on the selective driving of optical resonances of two subsystems undergoing a dipole--dipole interaction.

A. Barenco; D. Deutsch; A. Ekert; R. Jozsa

1995-03-24

88

Universal crossovers and critical dynamics of quantum phase transitions: A renormalization group study of the pseudogap Kondo problem  

NASA Astrophysics Data System (ADS)

The pseudogap Kondo problem, describing a magnetic impurity embedded in an electronic environment with a power-law density of states, displays continuous quantum phase transitions between free and screened moment phases. In this paper we employ renormalization group techniques to analytically calculate universal crossover functions, associated to these transitions, for various observables. Quantitative agreement with the results of Numerical Renormalization Group (NRG) simulations is obtained for temperature-dependent static and zero-temperature dynamic quantities, at and away from criticality. In the notoriously difficult realm of finite-temperature low-frequency dynamics, usually inaccessible to both NRG and perturbative methods, we show that progress can be made by a suitable renormalization procedure in the framework of the Callan-Symanzik equations. Our general strategy can be extended to other zero-temperature phase transitions, both in quantum impurity models and bulk systems.

Fritz, Lars; Florens, Serge; Vojta, Matthias

2006-10-01

89

NUMERICAL SIMULATION OF TRAPPED DIPOLAR QUANTUM GASES: COLLAPSE STUDIES AND VORTEX DYNAMICS  

E-print Network

of the condensate, and the dynamics of vortices. 1. Introduction In the last decade, lots of progress has been made magnetic/electric dipolar interaction between particles are significant [22, 16]. In such condensates two experiments to cool down the gas to sufficiently low temper- atures. The dimensionless parameters 1, 2

Sparber, Christof

90

Clock Quantum Monte Carlo: an imaginary-time method for real-time quantum dynamics  

E-print Network

In quantum information theory, there is an explicit mapping between general unitary dynamics and Hermitian ground state eigenvalue problems known as the Feynman-Kitaev Clock. A prominent family of methods for the study of quantum ground states are quantum Monte Carlo methods, and recently the full configuration interaction quantum Monte Carlo (FCIQMC) method has demonstrated great promise for practical systems. We combine the Feynman-Kitaev Clock with FCIQMC to formulate a new technique for the study of quantum dynamics problems. Numerical examples using quantum circuits are provided as well as a technique to further mitigate the sign problem through time-dependent basis rotations. Moreover, this method allows one to combine the parallelism of Monte Carlo techniques with the locality of time to yield an effective parallel-in-time simulation technique.

McClean, Jarrod R

2014-01-01

91

Chemical reaction dynamics of PeCB and TCDD decomposition: A tight-binding quantum chemical molecular dynamics study with first-principles parameterization  

NASA Astrophysics Data System (ADS)

The decomposition reaction dynamics of 2,3,4,4',5-penta-chlorinated biphenyl (2,3,4,4',5-PeCB), 3,3',4,4',5-penta-chlorinated biphenyl (3,3',4,4',5-PeCB), and 2,3,7,8-tetra-chlorinated dibenzo-p-dioxin (2,3,7,8-TCDD) was clarified for the first time at atomic and electronic levels, using our novel tight-binding quantum chemical molecular dynamics method with first-principles parameterization. The calculation speed of our new method is over 5000 times faster than that of the conventional first-principles molecular dynamics method. We confirmed that the structure, energy, and electronic states of the above molecules calculated by our new method are quantitatively consistent with those by first-principles calculations. After the confirmation of our methodology, we investigated the decomposition reaction dynamics of the above molecules and the calculated dynamic behaviors indicate that the oxidation of the 2,3,4,4',5-PeCB, 3,3',4,4',5-PeCB, and 2,3,7,8-TCDD proceeds through an epoxide intermediate, which is in good agreement with the previous experimental reports and consistent with our static density functional theory calculations. These results proved that our new tight-binding quantum chemical molecular dynamics method with first-principles parameterization is an effective tool to clarify the chemical reaction dynamics at reaction temperatures.

Suzuki, Ai; Selvam, Parasuraman; Kusagaya, Tomonori; Takami, Seiichi; Kubo, Momoji; Imamura, Akira; Miyamoto, Akira

92

QSAR, docking, dynamic simulation and quantum mechanics studies to explore the recognition properties of cholinesterase binding sites.  

PubMed

A set of 84 known N-aryl-monosubstituted derivatives (42 amides: series 1 and 2, and 42 imides: series 3 an 4, from maleic and succinic anhydrides, respectively) that display inhibitory activity toward both acetylcholinesterase and butyrylcholinesterase (ChEs) was considered for Quantitative structure-activity relationship (QSAR) studies. These QSAR studies employed docking data from both ChEs that were previously submitted to molecular dynamics (MD) simulations. Donepezil and galanthamine stereoisomers were included to analyze their quantum mechanics properties and for validating the docking procedure. Quantum parameters such as frontier orbital energies, dipole moment, molecular volume, atomic charges, bond length and reactivity parameters were measured, as well as partition coefficients, molar refractivity and polarizability were also analyzed. In order to evaluate the obtained equations, four compounds: 1a (4-oxo-4-(phenylamino)butanoic acid), 2a ((2Z)-4-oxo-4-(phenylamino)but-2-enoic acid), 3a (2-phenylcyclopentane-1,3-dione) and 4a (2-phenylcyclopent-4-ene-1,3-dione) were employed as independent data set, using only equations with r(m(test))˛>0.5. It was observed that residual values gave low value in almost all series, excepting in series 1 for compounds 3a and 4a, and in series 4 for compounds 1a, 2a and 3a, giving a low value for 4a. Consequently, equations seems to be specific according to the structure of the evaluated compound, that means, series 1 fits better for compound 1a, series 3 or 4 fits better for compounds 3a or 4a. Same behavior was observed in the butyrylcholinesterase (BChE). Therefore, obtained equations in this QSAR study could be employed to calculate the inhibition constant (Ki) value for compounds having a similar structure as N-aryl derivatives described here. The QSAR study showed that bond lengths, molecular electrostatic potential and frontier orbital energies are important in both ChE targets. Docking studies revealed that despite the multiple conformations obtained through MD simulations on both ChEs, the ligand recognition properties were conserved. In fact, the complex formed between ChEs and the best N-aryl compound reproduced the binding mode experimentally reported, where the ligand was coupled into the choline-binding site and stabilized through ?-? interactions with Trp82 or Trp86 for BChE and AChE, respectively, suggesting that this compound could be an efficient inhibitor and supporting our model. PMID:24321698

Correa-Basurto, J; Bello, M; Rosales-Hernández, M C; Hernández-Rodríguez, M; Nicolás-Vázquez, I; Rojo-Domínguez, A; Trujillo-Ferrara, J G; Miranda, René; Flores-Sandoval, C A

2014-02-25

93

Quantum dynamics of magnetically controlled network for Bloch electrons  

E-print Network

We study quantum dynamics of wave packet motion of Bloch electrons in quantum networks with the tight-binding approach for different types of nearest-neighbor interactions. For various geometrical configurations, these networks can function as some optical devices, such as beam splitters and interferometers. When the Bloch electrons with the Gaussian wave packets input these devices, various quantum coherence phenomena can be observed, e.g., the perfect quantum state transfer without reflection in a Y-shaped beam, the multi- mode entanglers of electron wave by star shaped network and Bloch electron interferometer with the lattice Aharonov-Bohm effects. Behind these conceptual quantum devices are the physical mechanism that, for hopping parameters with some specific values, a connected quantum networks can be reduced into a virtual network, which is a direct sum of some irreducible subnetworks. Thus, the perfect quantum state transfer in each subnetwork in this virtual network can be regarded as a coherent bea...

Yang, S; Sun, C P

2006-01-01

94

Coherent Electron Spin Dynamics in Quantum Dots  

NASA Astrophysics Data System (ADS)

The coherent spin dynamics of electrons in confined in quantum dots is discussed. A new measurement technique, mode-locking of electron spin precession by and with a pulsed excitation laser is used to address the coherence, which otherwise would be masked in ensemble studies by dephasing. The background of nuclei leads to a refocusing such that all optically excited electron spins become synchronized with the laser. With this tool spin coherence times in the microseconds range are demonstrated at cryogenic temperatures. The mode locking can be tailored by the laser excitation protocol such that strong signals at arbitrary times can be generated in Faraday rotation experiments.

Bayer, Manfred; Greilich, Alex; Yakovlev, Dmitri R.

95

Generalized dynamic scaling for quantum critical relaxation in imaginary time  

NASA Astrophysics Data System (ADS)

We study the imaginary-time relaxation critical dynamics of a quantum system with a vanishing initial correlation length and an arbitrary initial order parameter M0. We find that in quantum critical dynamics, the behavior of M0 under scale transformations deviates from a simple power law, which was proposed for very small M0 previously. A universal characteristic function is then suggested to describe the rescaled initial magnetization, similar to classical critical dynamics. This characteristic function is shown to be able to describe the quantum critical dynamics in both short- and long-time stages of the evolution. The one-dimensional transverse-field Ising model is employed to numerically determine the specific form of the characteristic function. We demonstrate that it is applicable as long as the system is in the vicinity of the quantum critical point. The universality of the characteristic function is confirmed by numerical simulations of models belonging to the same universality class.

Zhang, Shuyi; Yin, Shuai; Zhong, Fan

2014-10-01

96

Communication: state-to-state quantum dynamics study of the OH + CO ? H + CO2 reaction in full dimensions (J = 0).  

PubMed

A full dimensional state-to-state quantum dynamics study is carried out for the prototypical complex-formation OH + CO ? H + CO(2) reaction in the ground rovibrational initial state on the Lakin-Troya-Schatz-Harding potential energy surface by using the reactant-product decoupling method. With three heavy atoms and deep wells on the reaction path, the reaction represents a huge challenge for accurate quantum dynamics study. This state-to-state calculation is the first such a study on a four-atom reaction other than the H(2) + OH ? H(2)O + H and its isotope analogies. The product CO(2) vibrational and rotational state distributions, and product energy partitioning information are presented for ground initial rovibrational state with the total angular momentum J = 0. PMID:22010691

Liu, Shu; Xu, Xin; Zhang, Dong H

2011-10-14

97

Communication: State-to-state quantum dynamics study of the OH + CO --> H + CO2 reaction in full dimensions (J = 0)  

NASA Astrophysics Data System (ADS)

A full dimensional state-to-state quantum dynamics study is carried out for the prototypical complex-formation OH + CO --> H + CO2 reaction in the ground rovibrational initial state on the Lakin-Troya-Schatz-Harding potential energy surface by using the reactant-product decoupling method. With three heavy atoms and deep wells on the reaction path, the reaction represents a huge challenge for accurate quantum dynamics study. This state-to-state calculation is the first such a study on a four-atom reaction other than the H2 + OH <--> H2O + H and its isotope analogies. The product CO2 vibrational and rotational state distributions, and product energy partitioning information are presented for ground initial rovibrational state with the total angular momentum J = 0.

Liu, Shu; Xu, Xin; Zhang, Dong H.

2011-10-01

98

Carrier dynamics in the quantum kinetics regime  

NASA Astrophysics Data System (ADS)

Theory has predicted that, on a short time scale, the dynamics of optically excited carriers in semiconductors can no longer be described by the semiclassical Boltzmann equation. The carriers rather behave like quantum mechanical waves and the Boltzmann kinetics have to be replaced by quantum kinetics. Here we briefly review recent experiments on the quantum kinetics of electron-LO-phonon scattering. The focus of this review, however, is on more recent experiments at elevated carrier densities which are within the regime of the quantum kinetics of carrier-carrier scattering.

Hügel, W. A.; Heinrich, M. F.; Wegener, M.

1999-12-01

99

Fault-tolerant quantum dynamical decoupling.  

PubMed

Dynamical decoupling pulse sequences have been used to extend coherence times in quantum systems ever since the discovery of the spin-echo effect. Here we introduce a method of recursively concatenated dynamical decoupling pulses, designed to overcome both decoherence and operational errors. This is important for coherent control of quantum systems such as quantum computers. For bounded-strength, non-Markovian environments, such as for the spin-bath that arises in electron- and nuclear-spin based solid-state quantum computer proposals, we show that it is strictly advantageous to use concatenated pulses, as opposed to standard periodic dynamical decoupling pulse sequences. Namely, the concatenated scheme is both fault tolerant and superpolynomially more efficient, at equal cost. We derive a condition on the pulse noise level below which concatenation is guaranteed to reduce decoherence. PMID:16383882

Khodjasteh, K; Lidar, D A

2005-10-28

100

Dynamical error suppression for quantum information processing  

NASA Astrophysics Data System (ADS)

Quantum information theory is based on the premise of manipulating quantum systems. Decoherence and noisy control directly limit this manipulation. Quantum error correction theory aims to understand the sources of errors in manipulation of quantum systems and to remedy the problems caused by the errors in an efficient manner. In this thesis I focus on error correction mechanisms that are based on a realistic and physical picture of the interactions of the quantum system with the environment. In chapters 1, 2, and 3, I provide a brief introduction to quantum information processing, quantum error correction, and dynamical decoupling. In chapters 4 and 5, I consider error correction of a set of qubits in the presence of spontaneous emission as the main source of errors. These results have been published in [KL:02] and [KL:03]. The quantum trajectories picture is used for describing the error processes. Two error correction schemes are provided in this scenario and are both built on simple quantum error detecting codes for detecting quantum jump errors. The qubit number overhead in this encoding is reduced in the first method [KL:02] by exploiting the symmetry of the conditional dynamics that can be used to create a decoherence free subspace. In the second method [KL:03], the conditional dynamics is canceled by applying parallel population swapping operations on the qubits. For both methods, I describe means of integrating the proposed error correction schemes with various proposals to achieve fault tolerant quantum computation. Chapters 6 and 7 are based on dynamical decoupling: a method for removal of undesired interaction terms from a Hamiltonian evolution by application of fixed unitary quantum operators. These results have been published in [KL:05] and [KL:06]. I describe general concatenated pulse sequences that are constructed recursively from simple dynamical decoupling pulse sequences. I show that using the concatenated dynamical decoupling sequences is (i) significantly more efficient than repeating traditional sequences and (ii) these sequences are more robust with respect to natural control errors [KL:05]. A comprehensive leading order analysis of dynamical decoupling efficiency is provided in the process [KL:06]. In chapter 8 (not yet published), I describe the construction of self-correcting pulse sequences for a single qubit.

Khodjasteh Lakelayeh, Kaveh

101

Quantum dynamical study of femtosecond photodesorption of CO from TiO2(110)  

NASA Astrophysics Data System (ADS)

The photodesorption of CO from TiO2(110) by femtosecond pulses is investigated with the Surrogate Hamiltonian approach. The aim of the study is to resolve the relaxation mechanism and forecast the lifetime of the exited state based on a microscopic description of the excitation and relaxation processes. The parameters characterizing the system are obtained from ab initio and Density Functional Theory-calculations with one parameter estimated from physical considerations and convergence studies. Two electronic states are considered and the relaxation is assumed to be due to the interaction of the excited adsorbate with electron hole pairs in the surface. Desorption probabilities and velocity distributions of the desorbing molecules are calculated and an exited state lifetime is predicted. Throughout this paper atomic units, i.e., ? = me = e = a0 = 1, have been used unless otherwise stated.

Asplund, Erik; Klüner, Thorsten

2014-08-01

102

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

103

Dynamical regimes of dissipative quantum systems  

NASA Astrophysics Data System (ADS)

We reveal several distinct regimes of the relaxation dynamics of a small quantum system coupled to an environment within the plane of the dissipation strength and the reservoir temperature. This is achieved by discriminating between coherent dynamics with damped oscillatory behavior on all time scales, partially coherent behavior being nonmonotonic at intermediate times but monotonic at large ones, and purely monotonic incoherent decay. Surprisingly, elevated temperature can render the system "more coherent" by inducing a transition from the partially coherent to the coherent regime. This provides a refined view on the relaxation dynamics of open quantum systems.

Kennes, D. M.; Kashuba, O.; Meden, V.

2013-12-01

104

Adsorption of TCDD with 1-butyl-3-methylimidazolium dicyanamide ionic liquid: a combined molecular dynamics simulation and quantum chemistry study.  

PubMed

The effective abatement of flue gas emissions, especially polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs), is one of the challenging issues in the field of environmental science currently. Imidazolium-based dicyanamide ionic liquids (ILs) were proposed to have potential in controlling the emissions of PCDD/Fs. However, the relevant mechanism at the molecular level still remains unclear. To address this subject, we here present a combined molecular dynamics (MD) simulation and quantum chemical (QM) study on the adsorption of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), the most toxic congener among PCDD/F family, by 1-butyl-3-methylimidazolium dicyanamide IL, a representative imidazolium dicyanoamide ILs, which were demonstrated to possess high capture capability for PCDD/Fs. The MD simulation results show that TCDD molecules can be effectively adsorbed on the IL surface to form a dense layer, but cannot enter the interior of the IL. The results of QM calculations show that the adsorption of TCDDs on the IL surface occurs via intra-molecular hydrogen bond interactions. The calculated interaction energy of the anion with TCDD molecule is two times more than that of the cation, implying that the IL anion dominates the interaction with TCDD molecules, while the cation plays a secondary role. Based on the calculated results, we propose that imidazolium dicyanamide IL films/membranes may be better materials than the corresponding bulk for capturing TCDD. The present theoretical results may be helpful to designing the functional ILs which effectively capture and concentrate PCDD/F compounds. PMID:23336926

Pan, Wenxiao; Qi, Yuanyuan; Wang, Ruoxi; Han, Zhe; Zhang, Dongju; Zhan, Jinhua

2013-04-01

105

Quantum Dynamics Study of the Isotopic Effect on Capture Reactions: HD, D2 + CH3  

NASA Technical Reports Server (NTRS)

Time-dependent wave-packet-propagation calculations are reported for the isotopic reactions, HD + CH3 and D2 + CH3, in six degrees of freedom and for zero total angular momentum. Initial state selected reaction probabilities for different initial rotational-vibrational states are presented in this study. This study shows that excitations of the HD(D2) enhances the reactivities; whereas the excitations of the CH3 umbrella mode have the opposite effects. This is consistent with the reaction of H2 + CH3. The comparison of these three isotopic reactions also shows the isotopic effects in the initial-state-selected reaction probabilities. The cumulative reaction probabilities (CRP) are obtained by summing over initial-state-selected reaction probabilities. The energy-shift approximation to account for the contribution of degrees of freedom missing in the six dimensionality calculation is employed to obtain approximate full-dimensional CRPs. The rate constant comparison shows H2 + CH3 reaction has the biggest reactivity, then HD + CH3, and D2 + CH3 has the smallest.

Wang, Dunyou; Kwak, Dochan (Technical Monitor)

2002-01-01

106

Quantum versus classical hyperfine-induced dynamics in a quantum dot* W. A. Coisha  

E-print Network

Quantum versus classical hyperfine-induced dynamics in a quantum dot* W. A. Coisha and Daniel Loss spin dynamics for electrons confined to semiconductor quantum dots due to the contact hyperfine.1063/1.2722783 I. INTRODUCTION Prospects for future quantum information processing with quantum-dot

Yuzbashyan, Emil

107

Quantum Computation and Quantum Spin Dynamics Hans De Raedt, Kristel Michielsen, and Anthony Hams  

E-print Network

quantum computers by simulating quantum spin models representing quantum computer hardware. ExamplesQuantum Computation and Quantum Spin Dynamics Hans De Raedt, Kristel Michielsen, and Anthony Hams@yuragi.t.u-tokyo.ac.jp, saitoh@spin.t.u-tokyo.ac.jp We analyze the stability of quantum computations on physically realiz- able

108

Dynamical Localization in Disordered Quantum Spin Systems  

NASA Astrophysics Data System (ADS)

We say that a quantum spin system is dynamically localized if the time-evolution of local observables satisfies a zero-velocity Lieb-Robinson bound. In terms of this definition we have the following main results: First, for general systems with short range interactions, dynamical localization implies exponential decay of ground state correlations, up to an explicit correction. Second, the dynamical localization of random xy spin chains can be reduced to dynamical localization of an effective one-particle Hamiltonian. In particular, the isotropic xy chain in random exterior magnetic field is dynamically localized.

Hamza, Eman; Sims, Robert; Stolz, Günter

2012-10-01

109

Nonlinear Schrödinger equation and dissipative quantum dynamics in periodic fields  

NASA Astrophysics Data System (ADS)

The nonlinear dynamics of dissipative quantum systems in periodic fields is studied in the framework of a Gisin-like nonlinear Schrödinger equation with deterministic nonunitary quantum friction terms describing the system-bath couplings. The virtue of this nonunitary evolution is that it is compatible with Dirac's superposition principle and the Hilbert-space structure of quantum kinematics. Floquet theory and the generalized Van Vleck nearly degenerate perturbation method are used to facilitate both analytical and numerical solutions. Closed-form analytic solutions can be obtained in the long-time average approximation or within the rotating-wave approximation. The methods are applied to the study of dissipative quantum dynamics of two-level systems driven by intense periodic fields. It is found that the system asymptotically approaches a limit cycle (whose orientation is subject to the quantum friction constraint), regardless of the strength of the perturbed fields and the nonlinearity constant, indicating quantum suppression of classical chaos. Further, each point of the limit cycle is found to be an attractor and ?(t) exhibits a fractal-like evolution pattern in the course of time. The structure of the limit cycle depends strongly upon field intensity and frequency as well as the order of nonlinear multiphoton transitions. The power spectrum of the Bloch vector trajectory exhibits a dynamical symmetry inherent in the dissipative system and in the asymptotic limit cycle. A theoretical analysis is presented for the understanding of the origin and the role of the dynamical symmetry.

Huang, Youhong; Chu, Shih-I.; Hirschfelder, Joseph O.

1989-10-01

110

Dynamics of continuous-time quantum walks in restricted geometries  

NASA Astrophysics Data System (ADS)

We study quantum transport on finite discrete structures and we model the process by means of continuous-time quantum walks. A direct and effective comparison between quantum and classical walks can be attained based on the average displacement of the walker as a function of time. Indeed, a fast growth of the average displacement can be advantageously exploited to build up efficient search algorithms. By means of analytical and numerical investigations, we show that the finiteness and the inhomogeneity of the substrate jointly weaken the quantum-walk performance. We further highlight the interplay between the quantum-walk dynamics and the underlying topology by studying the temporal evolution of the transfer probability distribution and the lower bound of long-time averages.

Agliari, E.; Blumen, A.; Mülken, O.

2008-11-01

111

Stochastic solution to quantum dynamics  

NASA Technical Reports Server (NTRS)

The quantum Liouville equation in the Wigner representation is solved numerically by using Monte Carlo methods. For incremental time steps, the propagation is implemented as a classical evolution in phase space modified by a quantum correction. The correction, which is a momentum jump function, is simulated in the quasi-classical approximation via a stochastic process. The technique, which is developed and validated in two- and three- dimensional momentum space, extends an earlier one-dimensional work. Also, by developing a new algorithm, the application to bound state motion in an anharmonic quartic potential shows better agreement with exact solutions in two-dimensional phase space.

John, Sarah; Wilson, John W.

1994-01-01

112

Quantum Dynamics of Nonlinear Cavity Systems  

E-print Network

We investigate the quantum dynamics of three different configurations of nonlinear cavity systems. To begin, we carry out a quantum analysis of a dc superconducting quantum interference device (SQUID) mechanical displacement detector comprised of a SQUID with a mechanically compliant loop segment. The SQUID is approximated by a nonlinear current-dependent inductor, inducing a flux tunable nonlinear Duffing term in the cavity equation of motion. Expressions are derived for the detector signal and noise response where it is found that a soft-spring Duffing self-interaction enables a closer approach to the displacement detection standard quantum limit, as well as cooling closer to the ground state. Next, we make use of a superconducting transmission line formed from an array of dc-SQUIDs for investigating analogue Hawking radiation. Biasing the array with a space-time varying flux modifies the propagation velocity of the transmission line, leading to an effective metric with a horizon. This setup allows for quantum effects such as backreaction and analogue space-time fluctuations on the Hawking process. Finally, we look at a quantum parametric amplifier with dynamical pump mode, viewed as a zero-dimensional model of Hawking radiation from an evaporating black hole. The conditions are derived under which the spectrum of particles generated from vacuum fluctuations deviates from the thermal spectrum predicted for the conventional parametric amplifier. We find that significant deviation occurs once the pump mode (black hole) has released nearly half of its initial energy in the signal (Hawking radiation) and idler (in-falling particle) modes. As a model of black hole dynamics, this finding lends support to the view that late-time Hawking radiation contains information about the quantum state of the black hole and is entangled with the black hole's quantum gravitational degrees of freedom.

Paul D. Nation

2010-09-16

113

The HD molecule in small and medium cages of clathrate hydrates: Quantum dynamics studied by neutron scattering measurements and computation.  

PubMed

We report inelastic neutron scattering (INS) measurements on molecular hydrogen deuteride (HD) trapped in binary cubic (sII) and hexagonal (sH) clathrate hydrates, performed at low temperature using two different neutron spectrometers in order to probe both energy and momentum transfer. The INS spectra of binary clathrate samples exhibit a rich structure containing sharp bands arising from both the rotational transitions and the rattling modes of the guest molecule. For the clathrates with sII structure, there is a very good agreement with the rigorous fully quantum simulations which account for the subtle effects of the anisotropy, angular and radial, of the host cage on the HD microscopic dynamics. The sH clathrate sample presents a much greater challenge, due to the uncertainties regarding the crystal structure, which is known only for similar crystals with different promoter, but nor for HD (or H2) plus methyl tert-butyl ether (MTBE-d12). PMID:25296815

Colognesi, Daniele; Powers, Anna; Celli, Milva; Xu, Minzhong; Ba?i?, Zlatko; Ulivi, Lorenzo

2014-10-01

114

The HD molecule in small and medium cages of clathrate hydrates: Quantum dynamics studied by neutron scattering measurements and computation  

NASA Astrophysics Data System (ADS)

We report inelastic neutron scattering (INS) measurements on molecular hydrogen deuteride (HD) trapped in binary cubic (sII) and hexagonal (sH) clathrate hydrates, performed at low temperature using two different neutron spectrometers in order to probe both energy and momentum transfer. The INS spectra of binary clathrate samples exhibit a rich structure containing sharp bands arising from both the rotational transitions and the rattling modes of the guest molecule. For the clathrates with sII structure, there is a very good agreement with the rigorous fully quantum simulations which account for the subtle effects of the anisotropy, angular and radial, of the host cage on the HD microscopic dynamics. The sH clathrate sample presents a much greater challenge, due to the uncertainties regarding the crystal structure, which is known only for similar crystals with different promoter, but nor for HD (or H2) plus methyl tert-butyl ether (MTBE-d12).

Colognesi, Daniele; Powers, Anna; Celli, Milva; Xu, Minzhong; Ba?i?, Zlatko; Ulivi, Lorenzo

2014-10-01

115

Dynamics and quantumness of excitation energy transfer through a complex quantum network  

NASA Astrophysics Data System (ADS)

Understanding the mechanisms of efficient and robust energy transfer in organic systems provides us with insights for the optimal design of artificial systems. In this paper, we explore the dynamics of excitation energy transfer (EET) through a complex quantum network by a toy model consisting of three sites coupled to environments. We study how the coherent evolution and the noise-induced decoherence work together to reach efficient EET and illustrate the role of the phase factor attached to the coupling constant in the EET. By comparing the differences between the Markovian and non-Markovian dynamics, we discuss the effect of environment and the spatial structure of system on the dynamics and the efficiency of EET. A intuitive picture is given to show how the exciton is transferred through the system. Employing the simple model, we show the robustness of EET efficiency under the influence of the environment and elucidate the important role of quantum coherence in EET. We go further to study the quantum feature of the EET dynamics by quantumness and show the importance of quantum coherence from a different perspective. We calculate the energy current in the EET and its quantumness, and results for different system parameters are presented and discussed.

Qin, M.; Shen, H. Z.; Zhao, X. L.; Yi, X. X.

2014-10-01

116

Combining dynamical decoupling with fault-tolerant quantum computation  

NASA Astrophysics Data System (ADS)

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; Lidar, Daniel A.; Preskill, John

2011-07-01

117

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

118

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

119

SUPERADIABATIC TRANSITIONS IN QUANTUM MOLECULAR DYNAMICS  

E-print Network

crossing of two electronic energy levels, for one nuclear degree of freedom. We derive the general form. In turn, the nuclear quantum dynamical motion is determined by an effective potential given by the energy electronic energy levels at an avoided crossing. We treat a two-level system with one nuclear degree

Betz, Volker

120

Evaluation of quantum transition rates from quantum-classical molecular dynamics simulations  

E-print Network

scat- tering events.11­16 Currently, various quantum-classical mo- lecular dynamics MD schemes17Evaluation of quantum transition rates from quantum-classical molecular dynamics simulations Oleg V NA MD is investigated and a specific prescription for incorporating quantum decoherence into NA

121

Computer Simulation of Quantum Dynamics in a Classical Spin Environment  

E-print Network

In this paper a formalism for studying the dynamics of quantum systems coupled to classical spin environments is reviewed. The theory is based on generalized antisymmetric brackets and naturally predicts open-path off-diagonal geometric phases in the evolution of the density matrix. It is shown that such geometric phases must also be considered in the quantum-classical Liouville equation for a classical bath with canonical phase space coordinates; this occurs whenever the adiabatics basis is complex (as in the case of a magnetic field coupled to the quantum subsystem). When the quantum subsystem is weakly coupled to the spin environment, non-adiabatic transitions can be neglected and one can construct an effective non-Markovian computer simulation scheme for open quantum system dynamics in classical spin environments. In order to tackle this case, integration algorithms based on the symmetric Trotter factorization of the classical-like spin propagator are derived. Such algorithms are applied to a model comprising a quantum two-level system coupled to a single classical spin in an external magnetic field. Starting from an excited state, the population difference and the coherences of this two-state model are simulated in time while the dynamics of the classical spin is monitored in detail. It is the author's opinion that the numerical evidence provided in this paper is a first step toward developing the simulation of quantum dynamics in classical spin environments into an effective tool. In turn, the ability to simulate such a dynamics can have a positive impact on various fields, among which, for example, nano-science.

Alessandro Sergi

2014-04-24

122

Hydration dynamics in water clusters via quantum molecular dynamics simulations  

NASA Astrophysics Data System (ADS)

We have investigated the hydration dynamics in size selected water clusters with n = 66, 104, 200, 500, and 1000 water molecules using molecular dynamics simulations. To study the most fundamental aspects of relaxation phenomena in clusters, we choose one of the simplest, still realistic, quantum mechanically treated test solute, an excess electron. The project focuses on the time evolution of the clusters following two processes, electron attachment to neutral equilibrated water clusters and electron detachment from an equilibrated water cluster anion. The relaxation dynamics is significantly different in the two processes, most notably restoring the equilibrium final state is less effective after electron attachment. Nevertheless, in both scenarios only minor cluster size dependence is observed. Significantly different relaxation patterns characterize electron detachment for interior and surface state clusters, interior state clusters relaxing significantly faster. This observation may indicate a potential way to distinguish surface state and interior state water cluster anion isomers experimentally. A comparison of equilibrium and non-equilibrium trajectories suggests that linear response theory breaks down for electron attachment at 200 K, but the results converge to reasonable agreement at higher temperatures. Relaxation following electron detachment clearly belongs to the linear regime. Cluster relaxation was also investigated using two different computational models, one preferring cavity type interior states for the excess electron in bulk water, while the other simulating non-cavity structure. While the cavity model predicts appearance of several different hydrated electron isomers in agreement with experiment, the non-cavity model locates only cluster anions with interior excess electron distribution. The present simulations show that surface isomers computed with the cavity predicting potential show similar dynamical behavior to the interior clusters of the non-cavity type model. Relaxation associated with cavity collapse presents, however, unique dynamical signatures.

Turi, László

2014-05-01

123

Dynamics and conductivity near quantum criticality  

NASA Astrophysics Data System (ADS)

Relativistic O(N) field theories are studied near the quantum-critical point in two space dimensions. We compute dynamical correlations by large-scale Monte Carlo simulations and numerical analytic continuation. In the ordered side, the scalar spectral function exhibits a universal peak at the Higgs mass. For N=3 and 4, we confirm its ?3 rise at low frequency. On the disordered side, the spectral function exhibits a sharp gap. For N=2, the dynamical conductivity rises above a threshold at the Higgs mass (density gap), in the superfluid (Mott insulator) phase. For charged bosons (Josephson arrays), the power-law rise above the Higgs mass increases from two to four. Approximate charge-vortex duality is reflected in the ratio of imaginary conductivities on either side of the transition. We determine the critical conductivity to be ?c*=0.3(ą0.1)×4e2/h and describe a generalization of the worm algorithm to N>2. We use a singular value decomposition error analysis for the numerical analytic continuation.

Gazit, Snir; Podolsky, Daniel; Auerbach, Assa; Arovas, Daniel P.

2013-12-01

124

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

125

Avoiding irreversible dynamics in quantum systems  

NASA Astrophysics Data System (ADS)

Devices that exploit laws of quantum physics offer revolutionary advances in computation and communication. However, building such devices presents an enormous challenge, since it would require technologies that go far beyond current capabilities. One of the main obstacles to building a quantum computer and devices needed for quantum communication is decoherence or noise that originates from the interaction between a quantum system and its environment, and which leads to the destruction of the fragile quantum information. Encoding into decoherence-free subspaces (DFS) provides an important strategy for combating decoherence effects in quantum systems and constitutes the focus of my dissertation. The theory of DFS relies on the existence of certain symmetries in the decoherence process, which allow some states of a quantum system to be completely decoupled from the environment and thus to experience no decoherence. In this thesis I describe various approaches to DFS that are developed in the current literature. Although the general idea behind various approaches to DFS is the same, I show that different mathematical definitions of DFS actually have different physical meaning. I provide a rigorous definition of DFS for every approach, explaining its physical meaning and relation to other definitions. I also examine the theory of DFS for Markovian systems. These are systems for which the environment has no memory, i.e., any change in the environment affects the quantum system instantaneously. Examples of such systems include many systems in quantum optics that have been proposed for implementation of a quantum computer, such as atomic and molecular gases, trapped ions, and quantum dots. Here I develop a rigorous theory that provides necessary and sufficient conditions for the existence of DFS. This theory allows us to identify a special new class of DFS that was not known before. Under particular circumstances, dynamics of a quantum system can connive together with the interactions between the system and its environment in a special way to reduce decoherence. This property is used to discover new DFS that rely on rather counterintuitive phenomenon, which I call an "incoherent generation of coherences." I also provide examples of physical systems that support such states. These DFS can be used to suppress & coherence, but may not be sufficient for performing full quantum computation. I also explore the possibility of physically generating the DFS that are useful for quantum computation. For quantum computation we need to preserve at least two quantum states to encode the quantum analogue of classical bits. Here I aim to generate DFS in a system composed from a large collection of atoms or molecules and I need to determine how one should position atoms or molecules in 3D space so that the overall system possesses a DFS with at least two states (i.e., non-trivial DFS). I show that for many Markovian systems, non-trivial DFS can exist only when particles are located in exactly the same position in space. This, of course, is not possible in the real world. For these systems, I also show that states in DFS are states with infinite lifetime. However, for all practical applications we just need long-lived states. Thus in reality, we do just need to bring quantum particles close together to generate an imperfect DFS, i.e. a collection of long-lived states. This can be achieved, for example, for atoms within a single molecule.

Karasik, Raisa Iosifovna

126

Quantum Dynamics of Energy Transfer under Shock Conditions  

Microsoft Academic Search

Classical molecular dynamics (MD) simulations predict efficient energy transfer from translational to vibrational modes near shock fronts in molecular solids. The validity of the classical description of collisional energy transfer under shock conditions has not been tested for extended systems. In this research effort, quantum mechanical (QM) simulations are used to study energy transfer in a system consisting of three

R. C. Mowrey; M. L. Elert; C. T. White

2006-01-01

127

Quantum dynamics of a nanomagnet in a rotating field  

NASA Astrophysics Data System (ADS)

The quantum dynamics of a two-state spin system in a rotating magnetic field has been studied. Analytical and numerical results for the transition probability have been obtained along the lines of the Landau-Zener-Stueckelberg theory. The effect of various kinds of noise on the evolution of the system has been analyzed.

Calero, Carlos; Chudnovsky, E. M.; Garanin, D. A.

2005-07-01

128

Quantum dynamical maps and Markovianity  

E-print Network

It is known that the time evolution of a subsystem from an initial state to two later times, t1, t2 (t2 > t1), are both completely positive (CP) but it is shown here that in the intermediate times between t1 and t2, in general, it need not be CP. This reveals the key to the Markov (if CP) and nonMarkov (if NCP) avataras of the intermediate dynamics. This is brought out based on A and B dynamical maps - without resorting to Master equation approach. The choice of tensor product form for the global initial state points towards the system-environment interaction dynamics as the sole cause for Markovianity/non-Markovianity. A succinct summary of the results is given in the form of a table.

A. R. Usha Devi; A. K. Rajagopal; Sudha

2011-04-23

129

Quantum algorithm for simulating the dynamics of an open quantum system  

SciTech Connect

In the study of open quantum systems, one typically obtains the decoherence dynamics by solving a master equation. The master equation is derived using knowledge of some basic properties of the system, the environment, and their interaction: One basically needs to know the operators through which the system couples to the environment and the spectral density of the environment. For a large system, it could become prohibitively difficult to even write down the appropriate master equation, let alone solve it on a classical computer. In this paper, we present a quantum algorithm for simulating the dynamics of an open quantum system. On a quantum computer, the environment can be simulated using ancilla qubits with properly chosen single-qubit frequencies and with properly designed coupling to the system qubits. The parameters used in the simulation are easily derived from the parameters of the system + environment Hamiltonian. The algorithm is designed to simulate Markovian dynamics, but it can also be used to simulate non-Markovian dynamics provided that this dynamics can be obtained by embedding the system of interest into a larger system that obeys Markovian dynamics. We estimate the resource requirements for the algorithm. In particular, we show that for sufficiently slow decoherence a single ancilla qubit could be sufficient to represent the entire environment, in principle.

Wang Hefeng; Ashhab, S.; Nori, Franco [Advanced Science Institute, RIKEN, Wako-shi, Saitama 351-0198 (Japan); Department of Physics, University of Michigan, Ann Arbor, Michigan 48109-1040 (United States)

2011-06-15

130

Quantum algorithm for simulating the dynamics of an open quantum system  

NASA Astrophysics Data System (ADS)

In the study of open quantum systems, one typically obtains the decoherence dynamics by solving a master equation. The master equation is derived using knowledge of some basic properties of the system, the environment, and their interaction: One basically needs to know the operators through which the system couples to the environment and the spectral density of the environment. For a large system, it could become prohibitively difficult to even write down the appropriate master equation, let alone solve it on a classical computer. In this paper, we present a quantum algorithm for simulating the dynamics of an open quantum system. On a quantum computer, the environment can be simulated using ancilla qubits with properly chosen single-qubit frequencies and with properly designed coupling to the system qubits. The parameters used in the simulation are easily derived from the parameters of the system + environment Hamiltonian. The algorithm is designed to simulate Markovian dynamics, but it can also be used to simulate non-Markovian dynamics provided that this dynamics can be obtained by embedding the system of interest into a larger system that obeys Markovian dynamics. We estimate the resource requirements for the algorithm. In particular, we show that for sufficiently slow decoherence a single ancilla qubit could be sufficient to represent the entire environment, in principle.

Wang, Hefeng; Ashhab, S.; Nori, Franco

2011-06-01

131

Quantum algorithm for simulating the dynamics of an open quantum system  

E-print Network

In the study of open quantum systems, one typically obtains the decoherence dynamics by solving a master equation. The master equation is derived using knowledge of some basic properties of the system, the environment and their interaction: one basically needs to know the operators through which the system couples to the environment and the spectral density of the environment. For a large system, it could become prohibitively difficult to even write down the appropriate master equation, let alone solve it on a classical computer. In this paper, we present a quantum algorithm for simulating the dynamics of an open quantum system. On a quantum computer, the environment can be simulated using ancilla qubits with properly chosen single-qubit frequencies and with properly designed coupling to the system qubits. The parameters used in the simulation are easily derived from the parameters of the system+environment Hamiltonian. The algorithm is designed to simulate Markovian dynamics, but it can also be used to simulate non-Markovian dynamics provided that this dynamics can be obtained by embedding the system of interest into a larger system that obeys Markovian dynamics. We estimate the resource requirements for the algorithm. In particular, we show that for sufficiently slow decoherence a single ancilla qubit could be sufficient to represent the entire environment, in principle.

Hefeng Wang; S. Ashhab; Franco Nori

2011-03-17

132

Exploring the quantum frontier of spin dynamics  

NASA Astrophysics Data System (ADS)

Our familiar classical concept of a spin is that of a system characterized by the direction in which the spin is pointing. In this picture, we may think of the dynamics of a spin as the motion of a classical gyroscope, wich we can aptly describe the spin dynamics as the motion of a point on a sphere. This classical description of the spin dynamics, formalized in the Landau-Lifshits-Gilbert equation, has proved extremely successful in the field micro- and nanomagnetism. However, as the size of the system is further decreased (e.g., when considering molecular magnets such as the Fe8 or Mn12 systems, which have a spin S=10), quantum effects such as tunneling, interference, entanglement, coherence, etc., play an essential role, and one must adopt a fully quantum mechanical description of the spin system. The landscape in which the system evolves is then no longer a mere sphere, but rather it is the projective Hilbert space (wich is the projective complex space <=P^2S for a spin S), as space of considerably greater richness and complexity than the sphere of classical spin dynamics. A very appealing tool to describe a quantum spin system is Majorana's stellar representation, which is the extension for a spin S of the Bloch sphere description of a spin .5ex1 -.1em/ -.15em.25ex2 . I shall discuss how this representation can help us in improving our understanding of fundamental quantum processes and concept such as Landau-Zener transitions, Rabi oscillations, Berry phase, diabolical points and illustrate this on the example of spin dynamics of molecular magnets.

Bruno, Patrick

2011-03-01

133

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

SciTech Connect

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. -- Highlights: •The sudden transition phenomenon from finite-temperature environments is studied. •The transition time depends on the environment temperature and the system parameters. •The transition time can be prolonged by applying the dynamical decoupling pulses.

He, Qi-Liang [Zhejiang Institute of Modern Physics and Physics Department, Zhejiang University, Hangzhou 310027 (China)] [Zhejiang Institute of Modern Physics and Physics Department, Zhejiang University, Hangzhou 310027 (China); Xu, Jing-Bo, E-mail: phyxjb@yahoo.com.cn [Zhejiang Institute of Modern Physics and Physics Department, Zhejiang University, Hangzhou 310027 (China)] [Zhejiang Institute of Modern Physics and Physics Department, Zhejiang University, Hangzhou 310027 (China); Yao, Dao-Xin [State Key Laboratory of Optoelectronic Materials and Technologies, Sun Yat-sen University, Guangzhou 510275 (China) [State Key Laboratory of Optoelectronic Materials and Technologies, Sun Yat-sen University, Guangzhou 510275 (China); Department of Physics and Astronomy, University of Tennessee, Knoxville, TN 37996 (United States); Zhang, Ye-Qi [Zhejiang Institute of Modern Physics and Physics Department, Zhejiang University, Hangzhou 310027 (China)] [Zhejiang Institute of Modern Physics and Physics Department, Zhejiang University, Hangzhou 310027 (China)

2013-07-15

134

Universal quench dynamics of interacting quantum impurity systems  

NASA Astrophysics Data System (ADS)

The equilibrium physics of quantum impurities frequently involves a universal crossover from weak to strong reservoir-impurity coupling, characterized by single-parameter scaling and an energy scale TK (Kondo temperature) that breaks scale invariance. For the noninteracting resonant level model, the nonequilibrium time evolution of the Loschmidt echo after a local quantum quench was recently computed explicitly [R. Vasseur, K. Trinh, S. Haas, and H. Saleur, Phys. Rev. Lett. 110, 240601 (2013), 10.1103/PhysRevLett.110.240601]. It shows single-parameter scaling with variable TKt. Here, we scrutinize whether similar universal dynamics can be observed in various interacting quantum impurity systems. Using density matrix and functional renormalization group approaches, we analyze the time evolution resulting from abruptly coupling two noninteracting Fermi or interacting Luttinger liquid leads via a quantum dot or a direct link. We also consider the case of a single Luttinger liquid lead suddenly coupled to a quantum dot. We investigate whether the field-theory predictions for the universal scaling as well as for the large-time behavior successfully describe the time evolution of the Loschmidt echo and the entanglement entropy of microscopic models. Our study shows that for the considered local quench protocols the above quantum impurity models fall into a class of problems for which the nonequilibrium dynamics can largely be understood based on the knowledge of the corresponding equilibrium physics.

Kennes, D. M.; Meden, V.; Vasseur, R.

2014-09-01

135

An application of quantum fluid dynamics  

NASA Astrophysics Data System (ADS)

Hydrodynamics is often applied to quantum phenomena such as heavy-ion collisions. But here it should be noted that local equilibrium is not always realized in these collision processes and also the quantum effect is not fully taken into account in hydrodynamics. In this sense, a fluid-dynamical treatment of quantum many-body systems which does not presuppose local equilibrium is required. As an attempt in this direction, we derive simultaneous equations governing the motion of local variables such as the particle density ?( r, t) and velocity field ?( r, t) by averaging a many-body wave function. The equations obtained will be shown to unify into a single nonlinear Schrödinger-type equation. Hence this is worthy of being called a quantum fluid dynamics (QFD). In deriving the QFD, we have employed the time-dependent Hartree-Fock and the generalized scaling approximation. Particularly, in order to attain self-containedness, we have assumed a certain relation which is valid in the case of the locally isotropic strain tensor. The introduction of anisotropy requires other local variables reflecting explicitly the deviation from local equilibrium and thus has been left as a future task.

Himi, Masashi; Fukushima, Kenji

1984-12-01

136

Dynamic Dimensionality Identification for Quantum Control  

NASA Astrophysics Data System (ADS)

The control of quantum systems with shaped laser pulses presents a paradox since the relative ease with which solutions are discovered appears incompatible with the enormous variety of pulse shapes accessible with a standard pulse shaper. Quantum landscape theory indicates that the relevant search dimensionality is not dictated by the number of pulse shaper elements, but rather is related to the number of states participating in the controlled dynamics. The actual dimensionality is encoded within the sensitivity of the observed yield to all of the pulse shaper elements. To investigate this proposition, the Hessian matrix is measured for controlled transitions amongst states of atomic rubidium, and its eigendecomposition reveals a dimensionality consistent with that predicted by landscape theory. Additionally, this methodology furnishes a low-dimensional picture that captures the essence of the light-matter interaction and the ensuing system dynamics.

Roslund, Jonathan; Rabitz, Herschel

2014-04-01

137

Dynamic dimensionality identification for quantum control.  

PubMed

The control of quantum systems with shaped laser pulses presents a paradox since the relative ease with which solutions are discovered appears incompatible with the enormous variety of pulse shapes accessible with a standard pulse shaper. Quantum landscape theory indicates that the relevant search dimensionality is not dictated by the number of pulse shaper elements, but rather is related to the number of states participating in the controlled dynamics. The actual dimensionality is encoded within the sensitivity of the observed yield to all of the pulse shaper elements. To investigate this proposition, the Hessian matrix is measured for controlled transitions amongst states of atomic rubidium, and its eigendecomposition reveals a dimensionality consistent with that predicted by landscape theory. Additionally, this methodology furnishes a low-dimensional picture that captures the essence of the light-matter interaction and the ensuing system dynamics. PMID:24765949

Roslund, Jonathan; Rabitz, Herschel

2014-04-11

138

A Dynamics for Discrete Quantum Gravity  

NASA Astrophysics Data System (ADS)

This paper is based on the causal set approach to discrete quantum gravity. We first describe a classical sequential growth process (CSGP) in which the universe grows one element at a time in discrete steps. At each step the process has the form of a causal set (causet) and the "completed" universe is given by a path through a discretely growing chain of causets. We then quantize the CSGP by forming a Hilbert space H on the set of paths. The quantum dynamics is governed by a sequence of positive operators ? n on H that satisfy normalization and consistency conditions. The pair ( H,{ ? n }) is called a quantum sequential growth process (QSGP). We next discuss a concrete realization of a QSGP in terms of a natural quantum action. This gives an amplitude process related to the "sum over histories" approach to quantum mechanics. Finally, we briefly discuss a discrete form of Einstein's field equation and speculate how this may be employed to compare the present framework with classical general relativity theory.

Gudder, S.

2014-10-01

139

Open Systems Dynamics for Propagating Quantum Fields  

E-print Network

In this dissertation, I explore interactions between matter and propagating light. The electromagnetic field is modeled as a reservoir of quantum harmonic oscillators successively streaming past a quantum system. Each weak and fleeting interaction entangles the light and the system, and the light continues its course. Within the framework of open quantum systems, the light is eventually traced out, leaving the reduced quantum state of the system as the primary mathematical subject. Two major results are presented. The first is a master equation approach for a quantum system interacting with a traveling wave packet prepared with a definite number of photons. In contrast to quasi-classical states, such as coherent or thermal fields, these N-photon states possess temporal mode entanglement, and local interactions in time have nonlocal consequences. The second is a model for a three-dimensional light-matter interface for an atomic ensemble interacting with a paraxial laser beam and its application to the generation of QND spin squeezing. Both coherent and incoherent dynamics due to spatially inhomogeneous atom-light coupling across the ensemble are accounted for. Measurement of paraxially scattered light can generate squeezing of an atomic spin wave, while diffusely scattered photons lead to spatially local decoherence.

Ben Q. Baragiola

2014-08-18

140

Phantom field dynamics in loop quantum cosmology  

SciTech Connect

We consider a dynamical system of phantom scalar field under exponential potential in the background of loop quantum cosmology. In our analysis, there is neither stable node nor repeller unstable node but only two saddle points, hence no big rip singularity. Physical solutions always possess potential energy greater than the magnitude of the negative kinetic energy. We found that the universe bounces after accelerating even in the domination of the phantom field. After bouncing, the universe finally enters the oscillatory regime.

Samart, Daris; Gumjudpai, Burin [Fundamental Physics and Cosmology Research Unit, Tah Poe Academia Institute (TPTP), Department of Physics, Naresuan University, Phitsanulok, 65000 (Thailand)

2007-08-15

141

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

2013-07-01

142

Multiple quantum NMR dynamics in pseudopure states  

NASA Astrophysics Data System (ADS)

We investigate numerically the multiple quantum (MQ) NMR dynamics in systems of nuclear spins 1/2 coupled by dipole-dipole interactions in the case of the pseudopure initial state. Simulations of the MQ NMR with real molecular structures such as six dipolar-coupled proton spins of benzene, hydroxyl proton chains in calcium hydroxyapatite, and fluorine chains in calcium fluorapatite open the way to experimental NMR testing of the obtained results. It was found that multiple-spin correlations are created faster in such experiments than in the usual MQ NMR experiments and can be used for the investigation of many-spin dynamics of nuclear spins in solids.

Furman, G. B.

2009-01-01

143

Dynamics of Quantum Dot Photonic Crystal Lasers  

E-print Network

Quantum dot photonic crystal membrane lasers were fabricated and the large signal modulation characteristics were studied. We find that the modulation characteristics of quantum dot lasers can be significantly improved using cavities with large spontaneous emission coupling factor. Our experiments show, and simulations confirm, that the modulation rate is limited by the rate of carrier capture into the dots to around 30GHz in our present system.

Bryan Ellis; Ilya Fushman; Dirk Englund; Bingyang Zhang; Yoshihisa Yamamoto; Jelena Vuckovic

2007-03-07

144

Quantum Dynamics Scattering Study of AB+CDE Reactions: A Seven Dimensional Treatment for the H2+C2H Reaction  

NASA Technical Reports Server (NTRS)

A time-dependent wave-packet approach is presented for the quantum dynamics study of the AB+CDE reaction system for zero total angular momentum. A seven-degree-of-freedom calculation is employed to study the chemical reaction of H2+C2H yields H + C2H2 by treating C2H as a linear molecule. Initial state selected reaction probabilities are presented for various initial ro-vibrational states. This study shows that vibrational excitation of H2 enhances the reaction probability, whereas the excitation of C2H has only a small effect on the reactivity. An integral cross section is also reported for the initial ground states of H2 and C2H. The theoretical and experimental results agree with each other very well when the calculated seven dimensional results are adjusted to account for the lower transition state barrier heights found in recent ab initio calculations.

Wang, Dunyou

2003-01-01

145

Quantum dot potentials: Symanzik scaling, resurgent expansions, and quantum dynamics  

SciTech Connect

This article is concerned with a special class of the ''double-well-like'' potentials that occur naturally in the analysis of finite quantum systems. Special attention is paid, in particular, to the so-called Fokker-Planck potential, which has a particular property: the perturbation series for the ground-state energy vanishes to all orders in the coupling parameter, but the actual ground-state energy is positive and dominated by instanton configurations of the form exp(-a/g), where a is the instanton action. The instanton effects are most naturally taken into account within the modified Bohr-Sommerfeld quantization conditions whose expansion leads to the generalized perturbative expansions (so-called resurgent expansions) for the energy eigenvalues of the Fokker-Planck potential. Until now, these resurgent expansions have been mainly applied for small values of coupling parameter g, while much less attention has been paid to the strong-coupling regime. In this contribution, we compare the energy values, obtained by directly resumming generalized Bohr-Sommerfeld quantization conditions, to the strong-coupling expansion, for which we determine the first few expansion coefficients in powers of g{sup -2/3}. Detailed calculations are performed for a wide range of coupling parameters g and indicate a considerable overlap between the regions of validity of the weak-coupling resurgent series and of the strong-coupling expansion. Apart from the analysis of the energy spectrum of the Fokker-Planck Hamiltonian, we also briefly discuss the computation of its eigenfunctions. These eigenfunctions may be utilized for the numerical integration of the (single-particle) time-dependent Schroedinger equation and, hence, for studying the dynamical evolution of the wave packets in the double-well-like potentials.

Surzhykov, Andrey; Lubasch, Michael; Jentschura, Ulrich D. [Max-Planck-Institut fuer Kernphysik, Saupfercheckweg 1, 69117 Heidelberg (Germany); Zinn-Justin, Jean [DAPNIA, Commissariat a l'Energie Atomique, Centre de Saclay, 91191 Gif-Sur-Yvette (France)

2006-11-15

146

Quantum dynamical framework for Brownian heat engines  

NASA Astrophysics Data System (ADS)

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.

Agarwal, G. S.; Chaturvedi, S.

2013-07-01

147

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

2013-07-01

148

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

149

Oscillatory dynamics and non-Markovian memory in dissipative quantum systems.  

PubMed

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. PMID:23521236

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

2013-03-01

150

Oscillatory dynamics and non-markovian memory in dissipative quantum systems  

E-print Network

The nonequilibrium dynamics of a small quantum system coupled to a dissipative environment is studied. We show that (1) the oscillatory dynamics close to a coherent-to-incoherent transition is surprisingly different from the one of the classical damped harmonic oscillator and that (2) non-markovian memory plays a prominent role in the time evolution after a quantum quench.

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

2012-11-01

151

Simulation of chemical reaction dynamics on an NMR quantum computer  

E-print Network

Quantum simulation can beat current classical computers with minimally a few tens of qubits and will likely become the first practical use of a quantum computer. One promising application of quantum simulation is to attack challenging quantum chemistry problems. Here we report an experimental demonstration that a small nuclear-magnetic-resonance (NMR) quantum computer is already able to simulate the dynamics of a prototype chemical reaction. The experimental results agree well with classical simulations. We conclude that the quantum simulation of chemical reaction dynamics not computable on current classical computers is feasible in the near future.

Dawei Lu; Nanyang Xu; Ruixue Xu; Hongwei Chen; Jiangbin Gong; Xinhua Peng; Jiangfeng Du

2011-05-21

152

Non-equilibrium quantum dynamics after local quenches  

E-print Network

We study the quantum dynamics resulting from preparing a one-dimensional quantum system in the ground state of initially two decoupled parts which are then joined together (local quench). Specifically we focus on the transverse Ising chain and compute the time-dependence of the magnetization profile, m_l(t), and correlation functions at the critical point, in the ferromagnetically ordered phase and in the paramagnetic phase. At the critical point we find finite size scaling forms for the nonequilibrium magnetization and compare predictions of conformal field theory with our numerical results. In the ferromagnetic phase the magnetization profiles are well matched by our predictions from a quasi-classical calculation.

Uma Divakaran; Ferenc Iglói; Heiko Rieger

2011-05-26

153

Two-dimensional macroscopic quantum dynamics in YBCO Josephson junctions  

E-print Network

We theoretically study classical thermal activation (TA) and macroscopic quantum tunneling (MQT) for a YBCO Josephson junction coupled with an LC circuit. The TA and MQT escape rate are calculated by taking into account the two-dimensional nature of the classical and quantum phase dynamics. We find that the MQT escape rate is largely suppressed by the coupling to the LC circuit. On the other hand, this coupling leads to the slight reduction of the TA escape rate. These results are relevant for the interpretation of a recent experiment on the MQT and TA phenomena in YBCO bi-epitaxial Josephson junctions.

Shiro Kawabata; Takeo Kato; Floriana Lombardi; Thilo Bauch

2009-11-06

154

Quantum mechanics and low energy nucleon dynamics  

E-print Network

We discuss the problem of consistency of quantum mechanics as applied to low energy nucleon dynamics with the symmetries of QCD. It is shown that the dynamics consistent with these symmetries is not governed by the Schrodinger equation. We present a new way to formulate the effective theory of nuclear forces as an inevitable consequence of the basic principles of quantum mechanics and the symmetries of strong interactions. We show that being formulated in this way the effective theory of nuclear forces can be put on the same firm theoretical grounds as the quantum mechanics of atomic phenomena. In this case the effective theory allows one to describe with a given accuracy not only two-nucleon scattering, but also the evolution of nucleon systems, and places the constraints on the off-shell behavior of the two-nucleon interaction. In this way we predict the off-shell behavior of the S wave two-nucleon T-matrix at very low energies when the pionless theory is applicable. Further extensions and applications of this approach are discussed.

Renat Kh. Gainutdinov; Aigul A. Mutygullina

2003-04-03

155

Quantum Process Tomography Quantifies Coherence Transfer Dynamics in Vibrational Exciton  

PubMed Central

Quantum coherence has been a subject of great interest in many scientific disciplines. However, detailed characterization of the quantum coherence in molecular systems, especially its transfer and relaxation mechanisms, still remains a major challenge. The difficulties arise in part because the spectroscopic signatures of the coherence transfer are typically overwhelmed by other excitation relaxation processes. We use quantum process tomography (QPT) via two-dimensional infrared spectroscopy to quantify the rate of the elusive coherence transfer between two vibrational exciton states. QPT retrieves the dynamics of the dissipative quantum system directly from the experimental observables. It thus serves as an experimental alternative to theoretical models of the system-bath interaction, and can be used to validate these theories. Our results for coupled carbonyl groups of a diketone molecule in chloroform, used as a benchmark system, reveal the non-secular nature of the interaction between the exciton and the Markovian bath and open the door for the systematic studies of the dissipative quantum systems dynamics in detail. PMID:24079417

Chuntonov, Lev; Ma, Jianqiang

2013-01-01

156

Chaos and Nonlinear Dynamics in a Quantum Artificial Economy  

E-print Network

Chaos and nonlinear economic dynamics are addressed for a quantum coupled map lattice model of an artificial economy, with quantized supply and demand equilibrium conditions. The measure theoretic properties and the patterns that emerge in both the economic business volume dynamics' diagrams as well as in the quantum mean field averages are addressed and conclusions are drawn in regards to the application of quantum chaos theory to address signatures of chaotic dynamics in relevant discrete economic state variables.

Carlos Pedro Gonçalves

2012-02-29

157

Optimal control of molecular motion expressed through quantum fluid dynamics  

NASA Astrophysics Data System (ADS)

A quantum fluid-dynamic (QFD) control formulation is presented for optimally manipulating atomic and molecular systems. In QFD the control quantum system is expressed in terms of the probability density ? and the quantum current j. This choice of variables is motivated by the generally expected slowly varying spatial-temporal dependence of the fluid-dynamical variables. The QFD approach is illustrated for manipulation of the ground electronic state dynamics of HCl induced by an external electric field.

Dey, Bijoy K.; Rabitz, Herschel; Askar, Attila

2000-04-01

158

Dynamical evolution of quantum oscillators towards equilibrium  

E-print Network

A pure quantum state of large number N of oscillators, interacting via harmonic coupling, evolves such that any small subsystem n<quantum dynamics alone, with no necessity to bring in any additional statistical postulates. Mixedness of equilibrated subsystems consisting of 1, 2, ....., n<

A R Usha Devi; A K Rajagopal

2009-01-11

159

Clocks And Dynamics In Quantum Mechanics  

E-print Network

We argue that (1) our perception of time through change and (2) the gap between reality and our observation of it are at the heart of both quantum mechanics and the dynamical mechanism of physical systems. We suggest that the origin of quantum uncertainty lies with the absence of infinities or infinitesimals in observational data and that our concept of time derives from observing changing data (events). We argue that the fundamentally important content of the Superposition Principle is not the "probability amplitude" of posterior state observation but future state availability conditional only on prior information. Since event detection also implies posterior conditions (e.g. a specific type of detectable event occurred) as well as prior conditions, the probabilities of detected outcomes are also conditional on properties of the posterior properties of the observation. Such posterior conditions cannot affect the prior state availabilities and this implies violation of counter-factual definiteness. A componen...

York, Michael

2014-01-01

160

Quantum fluid dynamics based current-density functional study of a helium atom in a strong time-dependent magnetic field  

NASA Astrophysics Data System (ADS)

Evolution of the helium atom in a strong time-dependent (TD) magnetic field ( B) of strength up to 1011 G is investigated through a quantum fluid dynamics (QFD) based current-density functional theory (CDFT). The TD-QFD-CDFT computations are performed through numerical solution of a single generalized nonlinear Schrödinger equation employing vector exchange-correlation potentials and scalar exchange-correlation density functionals that depend both on the electronic charge-density and the current-density. The results are compared with that obtained from a B-TD-QFD-DFT approach (based on conventional TD-DFT) under similar numerical constraints but employing only scalar exchange-correlation potential dependent on electronic charge-density only. The B-TD-QFD-DFT approach, at a particular TD magnetic field-strength, yields electronic charge- and current-densities as well as exchange-correlation potential resembling with that obtained from the time-independent studies involving static (time-independent) magnetic fields. However, TD-QFD-CDFT electronic charge- and current-densities along with the exchange-correlation potential and energy differ significantly from that obtained using B-TD-QFD-DFT approach, particularly at field-strengths >109 G, representing dynamical effects of a TD field. The work concludes that when a helium atom is subjected to a strong TD magnetic field of order >109 G, the conventional TD-DFT based approach differs "dynamically" from the CDFT based approach under similar computational constraints.

Vikas, Hash(0x125f4490)

2011-02-01

161

Quantum tomography meets dynamical systems and bifurcations theory  

E-print Network

A powerful tool for studying geometrical problems in Hilbert space is developed. In particular, we study the quantum pure state tomography problem in finite dimensions from the point of view of dynamical systems and bifurcations theory. First, we introduce a generalization of the Hellinger metric for probability distributions which allows us to find a geometrical interpretation of the quantum state tomography problem. Thereafter, we prove that every solution to the state tomography problem is an attractive fixed point of the so-called physical imposition operator. Additionally, we demonstrate that multiple states corresponding to the same experimental data are associated to bifurcations of this operator. Such a kind of bifurcations only occurs when informationally incomplete set of observables are considered. Finally, we prove that the physical imposition operator has a non-contractive Lipschitz constant 2 for the Bures metric. This value of the Lipschitz constant manifests the existence of the quantum tomography problem for pure states.

D. Goyeneche; A. C. de la Torre

2014-01-07

162

Quantum Gravity, Dynamical Phase Space and String Theory  

E-print Network

In a natural extension of the relativity principle we argue that a quantum theory of gravity involves two fundamental scales associated with both dynamical space-time as well as dynamical momentum space. This view of quantum gravity is explicitly realized in a new formulation of string theory which involves dynamical phase space and in which space-time is a derived concept. This formulation naturally unifies symplectic geometry of Hamiltonian dynamics, complex geometry of quantum theory and real geometry of general relativity. The space-time and momentum space dynamics, and thus dynamical phase space, is governed by a new version of the Renormalization Group.

Laurent Freidel; Robert G. Leigh; Djordje Minic

2014-05-15

163

Diffusion and interactions of carbon dioxide and oxygen in the vicinity of the active site of Rubisco: Molecular dynamics and quantum chemical studies  

NASA Astrophysics Data System (ADS)

Molecular dynamics (MD) at the molecular mechanical level and geometry optimisation at the quantum mechanical level have been performed to investigate the transport and fixation of oxygen and carbon dioxide in the cavity of ribulose-1,5-bisphosphate carboxylase/oxygenase, or Rubisco. Multiple MD simulations have been carried out to study the diffusive behaviour of O2 and CO2 molecules from the Mg2+ cation in Rubisco at 298 K and 1 bar, being one step in the overall process of carboxylation/oxygenation in Rubisco. In addition to this work, in order to gain additional perspective on the role of chemical reaction rates and thermodynamics, oxygen, and carbon dioxide uptake mechanisms have also been investigated by the aid of quantum chemical calculations. The results indicate that the activation barrier for carboxylation is slightly lower than that of oxygenation. This agrees qualitatively with experimental findings, and rationalises the observed competition between both catalytic processes in nature. Finally, the longer-lived persistence of CO2 in the vicinity of the active centre (i.e., slower self-diffusion) may serve to explain, in part, why carboxylation is the more kinetically favoured on an overall basis compared to oxygenation.

El-Hendawy, Morad M.; Garate, José-Antonio; English, Niall J.; O'Reilly, Stephen; Mooney, Damian A.

2012-10-01

164

Dynamical Causal Modeling from a Quantum Dynamical Perspective  

SciTech Connect

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 [Department of Psychology, University of Michigan, 1012 East Hall, 530 Church Street, Ann Arbor, MI 48109-1043 (United States); Demiralp, Metin [Istanbul Technical University, Informatics Institute, Group for Science and Methods of Computing, Maslak, 34469, Istanbul (Turkey)

2010-09-30

165

Non-Adiabatic Quantum Dynamics of Grover's Adiabatic Search Algorithm  

E-print Network

We study quantum dynamics of Grover's adiabatic search algorithm with the equivalent two-level system. Its adiabatic and non-adiabatic evolutions are visualized as trajectories of Bloch vectors on a Bloch sphere. We find the change in the non-adiabatic transition probability from exponential decay for short running time to inverse-square decay for long running time. The size dependence of the critical running time is expressed in terms of Lambert $W$ function. The transitionless driving Hamiltonian is obtained to make a quantum state follow the adiabatic path. We demonstrate that a constant Hamiltonian, approximate to the exact time-dependent driving Hamiltonian, can alter the non-adiabatic transition probability from the inverse square decay to the inverse fourth power decay with running time. This may open up a new way of reducing errors in adiabatic quantum computation.

Sangchul Oh; Sabre Kais

2014-06-27

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

Quantum algorithm design using dynamic learning  

E-print Network

We present a dynamic learning paradigm for "programming" a general quantum computer. A learning algorithm is used to find the control parameters for a coupled qubit system, such that the system at an initial time evolves to a state in which a given measurement corresponds to the desired operation. This can be thought of as a quantum neural network. We first apply the method to a system of two coupled superconducting quantum interference devices (SQUIDs), and demonstrate learning of both the classical gates XOR and XNOR. Training of the phase produces a gate congruent to the CNOT modulo a phase shift. Striking out for somewhat more interesting territory, we attempt learning of an entanglement witness for a two qubit system. Simulation shows a reasonably successful mapping of the entanglement at the initial time onto the correlation function at the final time for both pure and mixed states. For pure states this mapping requires knowledge of the phase relation between the two parts; however, given that knowledge, this method can be used to measure the entanglement of an otherwise unknown state. The method is easily extended to multiple qubits or to quNits.

E. C. Behrman; J. E. Steck; P. Kumar; K. A. Walsh

2008-08-11

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

Quantum dynamics of fast chemical reactions  

SciTech Connect

The aims of this research are to explore, develop, and apply theoretical methods for the evaluation of the dynamics of gas phase collision processes, primarily chemical reactions. The primary theoretical tools developed for this work have been quantum scattering theory, both in time dependent and time independent forms. Over the past several years, the authors have developed and applied methods for the direct quantum evaluation of thermal rate constants, applying these to the evaluation of the hydrogen isotopic exchange reactions, applied wave packet propagation techniques to the dissociation of Rydberg H{sub 3}, incorporated optical potentials into the evaluation of thermal rate constants, evaluated the use of optical potentials for state-to-state reaction probability evaluations, and, most recently, have developed quantum approaches for electronically non-adiabatic reactions which may be applied to simplify calculations of reactive, but electronically adiabatic systems. Evaluation of the thermal rate constants and the dissociation of H{sub 3} were reported last year, and have now been published.

Light, J.C. [Univ. of Chicago, IL (United States)

1993-12-01

170

Automated Synthesis of Dynamically Corrected Quantum Gates  

E-print Network

We address the problem of constructing dynamically corrected gates for non-Markovian open quantum systems in settings where limitations on the available control inputs and/or the presence of control noise make existing analytical approaches unfeasible. By focusing on the important case of singlet-triplet electron spin qubits, we show how ideas from optimal control theory may be used to automate the synthesis of dynamically corrected gates that simultaneously minimize the system's sensitivity against both decoherence and control errors. Explicit sequences for effecting robust single-qubit rotations subject to realistic timing and pulse-shaping constraints are provided, which can deliver substantially improved gate fidelity for state-of-the-art experimental capabilities.

Kaveh Khodjasteh; Hendrik Bluhm; Lorenza Viola

2012-05-01

171

Dynamical patterns in spatially extended quantum-CNN  

Microsoft Academic Search

In this paper, we aim to merge the concept of quantum computing with the paradigm of Cellular Nonlinear Network (CNN) in order to show if and when spatial dynamical complex behaviors can emerge from the interaction of spatially extended quantum cells constituting a quantum cellular nonlinear network (Q-CNN).

Arturo Buscarino; Luigi Fortuna; Mattia Frasca; Angelo Sarra Fiore

2010-01-01

172

Quantum ice: a quantum Monte Carlo study.  

PubMed

Ice states, in which frustrated interactions lead to a macroscopic ground-state degeneracy, occur in water ice, in problems of frustrated charge order on the pyrochlore lattice, and in the family of rare-earth magnets collectively known as spin ice. Of particular interest at the moment are "quantum spin-ice" materials, where large quantum fluctuations may permit tunnelling between a macroscopic number of different classical ground states. Here we use zero-temperature quantum Monte Carlo simulations to show how such tunnelling can lift the degeneracy of a spin or charge ice, stabilizing a unique "quantum-ice" ground state-a quantum liquid with excitations described by the Maxwell action of (3+1)-dimensional quantum electrodynamics. We further identify a competing ordered squiggle state, and show how both squiggle and quantum-ice states might be distinguished in neutron scattering experiments on a spin-ice material. PMID:22401117

Shannon, Nic; Sikora, Olga; Pollmann, Frank; Penc, Karlo; Fulde, Peter

2012-02-10

173

Quantum Ice : a quantum Monte Carlo study  

E-print Network

Ice states, in which frustrated interactions lead to a macroscopic ground-state degeneracy, occur in water ice, in problems of frustrated charge order on the pyrochlore lattice, and in the family of rare-earth magnets collectively known as spin ice. Of particular interest at the moment are "quantum spin ice" materials, where large quantum fluctuations may permit tunnelling between a macroscopic number of different classical ground states. Here we use zero-temperature quantum Monte Carlo simulations to show how such tunnelling can lift the degeneracy of a spin or charge ice, stabilising a unique "quantum ice" ground state --- a quantum liquid with excitations described by the Maxwell action of 3+1-dimensional quantum electrodynamics. We further identify a competing ordered "squiggle" state, and show how both squiggle and quantum ice states might be distinguished in neutron scattering experiments on a spin ice material.

Nic Shannon; Olga Sikora; Frank Pollmann; Karlo Penc; Peter Fulde

2011-05-20

174

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

175

Modeling quantum fluid dynamics at nonzero temperatures  

PubMed Central

The detailed understanding of the intricate dynamics of quantum fluids, in particular in the rapidly growing subfield of quantum turbulence which elucidates the evolution of a vortex tangle in a superfluid, requires an in-depth understanding of the role of finite temperature in such systems. The Landau two-fluid model is the most successful hydrodynamical theory of superfluid helium, but by the nature of the scale separations it cannot give an adequate description of the processes involving vortex dynamics and interactions. In our contribution we introduce a framework based on a nonlinear classical-field equation that is mathematically identical to the Landau model and provides a mechanism for severing and coalescence of vortex lines, so that the questions related to the behavior of quantized vortices can be addressed self-consistently. The correct equation of state as well as nonlocality of interactions that leads to the existence of the roton minimum can also be introduced in such description. We review and apply the ideas developed for finite-temperature description of weakly interacting Bose gases as possible extensions and numerical refinements of the proposed method. We apply this method to elucidate the behavior of the vortices during expansion and contraction following the change in applied pressure. We show that at low temperatures, during the contraction of the vortex core as the negative pressure grows back to positive values, the vortex line density grows through a mechanism of vortex multiplication. This mechanism is suppressed at high temperatures. PMID:24704874

Berloff, Natalia G.; Brachet, Marc; Proukakis, Nick P.

2014-01-01

176

Quantum Dynamics of Supergravity on R^3 x S^1  

E-print Network

We study the quantum dynamics of N=1 supergravity in four dimensions with a compact spatial circle. Supersymmetry ensures that the perturbative contributions to the Casimir energy on the circle cancel. However, instanton contributions remain. These render supersymmetric compactification on a circle unstable and the background dynamically decompactifies back to four dimensions. The calculation provides a testing ground for some old ideas in Euclidean quantum gravity. In particular, we show that gravitational instantons are associated to a new, infra-red scale which is naturally exponentially suppressed relative to the Planck scale and arises from the logarithmic running of the Gauss-Bonnet term. There are also some interesting technical details, including the non-cancellation of bosonic and fermionic determinants around the background of a self-dual gravitational instanton, despite the existence of supersymmetry.

David Tong; Carl Turner

2014-08-14

177

Dynamical evolutions and coherences in a quantum heat engine  

NASA Astrophysics Data System (ADS)

The effect of spontaneously generated coherence (SGC) on the quantum heat engine (QHE) consisting of a laser system is studied in terms of its dynamical evolution and the generation of coherences. The QHE is coupled to the two thermal photon reservoirs, a squeezed thermal bath as well as to a cavity mode. The coherence associated with the transition interacting with squeezed reservoir and the average thermal photon number of the hot (as well as cold) reservoir shows a non monotonous behavior between them. The dynamics along with generated coherences of the system and the laser power emitted depend sensitively on the hot, cold and squeezed reservoir parameters.

Osman, Kariman I.; Joshi, Amitabh

2014-09-01

178

Dynamics of plasmonic field polarization induced by quantum coherence in quantum dot-metallic nanoshell structures.  

PubMed

When a hybrid system consisting of a semiconductor quantum dot and a metallic nanoparticle interacts with a laser field, the plasmonic field of the metallic nanoparticle can be normalized by the quantum coherence generated in the quantum dot. In this Letter, we study the states of polarization of such a coherent-plasmonic field and demonstrate how these states can reveal unique aspects of the collective molecular properties of the hybrid system formed via coherent exciton-plasmon coupling. We show that transition between the molecular states of this system can lead to ultrafast polarization dynamics, including sudden reversal of the sense of variations of the plasmonic field and formation of circular and elliptical polarization. PMID:25166055

Sadeghi, S M

2014-09-01

179

Quantum dynamics of the abstraction reaction of h with cyclopropane.  

PubMed

The dynamics of the abstraction reaction of H atoms with the cyclopropane molecule is studied using quantum mechanical scattering theory. The quantum scattering calculations are performed in hyperspherical coordinates with a two-dimensional (2D) potential energy surface. The ab initio energy calculations are carried out with CCSD(T)-F12a/cc-pVTZ-F12 level of theory with the geometry and frequency calculations at the MP2/cc-pVTZ level. The contribution to the potential energy surface from the spectator modes is included as the projected zero-point energy correction to the ab initio energy. The 2D surface is fitted with a 29-parameter double Morse potential. An R-matrix propagation scheme is carried out to solve the close-coupled equations. The adiabatic energy barrier and reaction enthalpy are compared with high level computational calculations as well as experimental data. The calculated reaction rate constants shows very good agreement when compared with the experimental data, especially at lower temperature highlighting the importance of quantum tunnelling. The reaction probabilities are also presented and discussed. The special features of performing quantum dynamics calculation on the chemical reaction of a cyclic molecule are discussed. PMID:25271568

Shan, Xiao; Clary, David C

2014-10-30

180

Quantum Dynamical Semigroups for Diffusion Models with Hartree Interaction  

Microsoft Academic Search

We consider a class of evolution equations in Lindblad form, which model the dynamics of dissipative quantum mechanical systems with mean-field interaction. Particularly, this class includes the so-called Quantum Fokker-Planck-Poisson model. The existence and uniqueness of global-in-time, mass preserving solutions is proved, thus establishing the existence of a nonlinear conservative quantum dynamical semigroup. The mathematical difficulties stem from combining an

Anton Arnold; Christof Sparber

2004-01-01

181

Exponential rise of dynamical complexity in quantum computing through projections.  

PubMed

The ability of quantum systems to host exponentially complex dynamics has the potential to revolutionize science and technology. Therefore, much effort has been devoted to developing of protocols for computation, communication and metrology, which exploit this scaling, despite formidable technical difficulties. Here we show that the mere frequent observation of a small part of a quantum system can turn its dynamics from a very simple one into an exponentially complex one, capable of universal quantum computation. After discussing examples, we go on to show that this effect is generally to be expected: almost any quantum dynamics becomes universal once 'observed' as outlined above. Conversely, we show that any complex quantum dynamics can be 'purified' into a simpler one in larger dimensions. We conclude by demonstrating that even local noise can lead to an exponentially complex dynamics. PMID:25300692

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

2014-01-01

182

Exponential rise of dynamical complexity in quantum computing through projections  

PubMed Central

The ability of quantum systems to host exponentially complex dynamics has the potential to revolutionize science and technology. Therefore, much effort has been devoted to developing of protocols for computation, communication and metrology, which exploit this scaling, despite formidable technical difficulties. Here we show that the mere frequent observation of a small part of a quantum system can turn its dynamics from a very simple one into an exponentially complex one, capable of universal quantum computation. After discussing examples, we go on to show that this effect is generally to be expected: almost any quantum dynamics becomes universal once ‘observed’ as outlined above. Conversely, we show that any complex quantum dynamics can be ‘purified’ into a simpler one in larger dimensions. We conclude by demonstrating that even local noise can lead to an exponentially complex dynamics. PMID:25300692

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

2014-01-01

183

Exponential rise of dynamical complexity in quantum computing through projections  

NASA Astrophysics Data System (ADS)

The ability of quantum systems to host exponentially complex dynamics has the potential to revolutionize science and technology. Therefore, much effort has been devoted to developing of protocols for computation, communication and metrology, which exploit this scaling, despite formidable technical difficulties. Here we show that the mere frequent observation of a small part of a quantum system can turn its dynamics from a very simple one into an exponentially complex one, capable of universal quantum computation. After discussing examples, we go on to show that this effect is generally to be expected: almost any quantum dynamics becomes universal once ‘observed’ as outlined above. Conversely, we show that any complex quantum dynamics can be ‘purified’ into a simpler one in larger dimensions. We conclude by demonstrating that even local noise can lead to an exponentially complex dynamics.

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

2014-10-01

184

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

185

Measurement and Information Extraction in Complex Dynamics Quantum Computation  

NASA Astrophysics Data System (ADS)

Quantum Information processing has several di.erent applications: some of them can be performed controlling only few qubits simultaneously (e.g. quantum teleportation or quantum cryptography) [1]. Usually, the transmission of large amount of information is performed repeating several times the scheme implemented for few qubits. However, to exploit the advantages of quantum computation, the simultaneous control of many qubits is unavoidable [2]. This situation increases the experimental di.culties of quantum computing: maintaining quantum coherence in a large quantum system is a di.cult task. Indeed a quantum computer is a many-body complex system and decoherence, due to the interaction with the external world, will eventually corrupt any quantum computation. Moreover, internal static imperfections can lead to quantum chaos in the quantum register thus destroying computer operability [3]. Indeed, as it has been shown in [4], a critical imperfection strength exists above which the quantum register thermalizes and quantum computation becomes impossible. We showed such e.ects on a quantum computer performing an e.cient algorithm to simulate complex quantum dynamics [5,6].

Casati, Giulio; Montangero, Simone

186

Ultra-cold Atom CollisionsUltra-cold Atom Collisions and Quantum Dynamics atand Quantum Dynamics at  

E-print Network

Ultra-cold Atom CollisionsUltra-cold Atom Collisions and Quantum Dynamics atand Quantum Dynamics are available at Ben-Gurion University to carry out research in ultra-cold atomic and molecular physics groups working on similar problems, including groups headed by Ami Vardi, Bilha Segev, Doron Cohen, Yshai

Band, Yehuda B.

187

Protecting adiabatic quantum computation by dynamical decoupling  

NASA Astrophysics Data System (ADS)

Adiabatic quantum computation (AQC) relies heavily on a systems ability to remain in its ground state with high probability throughout the entirety of the adiabatic evolution. System-environment interactions present during the evolution manifest decoherence, thereby increases the probability of excitation. In this work, it is shown that the existence of such noise-producing terms can be dramatically reduced by Dynamical Decoupling (DD). In particular, we consider a multi-qubit system subjected to a classical bath modeled by random Gaussian-correlated noise. The performance of deterministic schemes such as Concatenated Dynamical Decoupling (CDD) and Nested Uhrig Dynamical Decoupling (NUDD) are analyzed for Grover's search algorithm and the two-qubit Satisfiability (2-SAT) problem. The CDD evolution substantially increases noise suppression with increasing concatenation level. In contrast, improvements in performance are only observed for specific sequence orders in the NUDD scheme. These results are verified for both adiabatic evolutions in terms of the total adiabatic run time and minimum pulse interval.

Quiroz, Gregory; Lidar, Daniel

2012-02-01

188

Analysis and improvement of the dynamic watermarking scheme for quantum images using quantum wavelet transform  

NASA Astrophysics Data System (ADS)

We investigate the dynamic watermarking scheme for quantum images using quantum wavelet transform (QWT) proposed by Song et al. (Quantum Inf Process 12(12):3689-3706, 2013). It is aimed to embed the watermark image into the wavelet coefficients of the quantum carrier image. However, in our opinion, the key procedures of the protocol are wrong. At last, a possible improvement strategy is presented.

Yang, Yu-Guang; Xu, Peng; Tian, Ju; Zhang, Hua

2014-09-01

189

Clocks And Dynamics In Quantum Mechanics  

E-print Network

We argue that (1) our perception of time through change and (2) the gap between reality and our observation of it are at the heart of both quantum mechanics and the dynamical mechanism of physical systems. We suggest that the origin of quantum uncertainty lies with the absence of infinities or infinitesimals in observational data and that our concept of time derives from observing changing data (events). We argue that the fundamentally important content of the Superposition Principle is not the "probability amplitude" of posterior state observation but future state availability conditional only on prior information. Since event detection also implies posterior conditions (e.g. a specific type of detectable event occurred) as well as prior conditions, the probabilities of detected outcomes are also conditional on properties of the posterior properties of the observation. Such posterior conditions cannot affect the prior state availabilities and this implies violation of counter-factual definiteness. A component of a quantum system may be chosen to represent a clock and changes in other components can then be expected to be correlated with clocks with which they are entangled. Instead of traditional time-dependent equations of motion we provide a specific mechanism whereby evolution of data is instead quasi-causally related to the relative \\availability\\ of states and equations of motion are expressed in terms of quantized clock variables. We also suggest that time-reversal symmetry-breaking in weak interactions is an artifice of a conventional choice of co-ordinate time-function. Analysis of a "free" particle suggests that conventional co-ordinate space-time emerges from how we measure the separation of objects and events.

Michael York

2014-05-05

190

Protecting conditional quantum gates by robust dynamical decoupling  

E-print Network

Dephasing -- phase randomization of a quantum superposition state -- is a major obstacle for the realization of high fidelity quantum logic operations. Here, we implement a two-qubit Controlled-NOT gate using dynamical decoupling (DD), despite the gate time being more than one order of magnitude longer than the intrinsic coherence time of the system. For realizing this universal conditional quantum gate, we have devised a concatenated DD sequence that ensures robustness against imperfections of DD pulses that otherwise may destroy quantum information or interfere with gate dynamics. We compare its performance with three other types of DD sequences. These experiments are carried out using a well-controlled prototype quantum system -- trapped atomic ions coupled by an effective spin-spin interaction. The scheme for protecting conditional quantum gates demonstrated here is applicable to other physical systems, such as nitrogen vacancy centers, solid state nuclear magnetic resonance, and circuit quantum electrodynamics.

Ch. Piltz; B. Scharfenberger; A. Khromova; A. F. Varón; Ch. Wunderlich

2012-08-10

191

Quantum Monte Carlo study of quantum dots in magnetic fields  

Microsoft Academic Search

We have studied the ground state energies and quantum numbers of confined two-dimensional (2D) electrons in weak and intermediate magnetic field strengths using quantum Monte Carlo methods. These 2D quantum dots are of theoretical interest, because it is possible to go from a weakly to a strongly correlated system by tuning the relative strength of the external potential to the

Wolfgang Geist; Lang Zeng; Mei-Yin Chou

2004-01-01

192

Quantum dynamics in condensed phases : charge carrier mobility, decoherence, and excitation energy transfer  

E-print Network

In this thesis, we develop analytical models for quantum systems and perform theoretical investigations on several dynamical processes in condensed phases. First, we study charge-carrier mobilities in organic molecular ...

Cheng, Yuan-Chung, Ph. D. Massachusetts Institute of Technology

2006-01-01

193

Dynamical identification of open quantum systems  

E-print Network

I propose a quantum trajectories approach to parametric identification of the effective Hamiltonian for a Markovian open quantum system, and discuss an application motivated by recent experiments in cavity quantum electrodynamics. This example illustrates a strategy for quantum parameter estimation that efficiently utilizes the information carried by correlations between measurements distributed in time.

Hideo Mabuchi

1996-08-13

194

The Cracking of N-Heptane in the Gas Phase State and in the HZSM-5 Zeolite: A Quantum Molecular Dynamics Study  

SciTech Connect

Quantum molecular dynamics is used to investigate the cracking of a representative hydrocarbon of the paraffin family (n-heptane), analyzing the effects of temperature in the fragmentation of n-heptane when this compound is in the gas phase and inside a typical industrial catalyst (zeolite HZSM-5). The hydrocarbon structural and electronic features in the two environments are determined and compared. The results substantiate current views and exhibit the basic aspects in the cracking of n-heptane.

Zaragoza, I P.; Santamaria, Ruben

2002-10-10

195

Quantum Geometry of the Dynamical Space-time  

E-print Network

Quantum theory of field (extended) objects without a priori space-time geometry has been represented. Intrinsic coordinates in the tangent fibre bundle over complex projective Hilbert state space $CP(N-1)$ are used instead of space-time coordinates. The fate of quantum system modeled by the generalized coherent states is rooted in this manifold. Dynamical (state-dependent) space-time arises only at the stage of the quantum "yes/no" measurement. The quantum measurement of the gauge ``field shell'' of the generalized coherent state is described in terms of the affine parallel transport of the local dynamical variables in $CP(N-1)$.

Peter Leifer

2006-11-20

196

Protected quantum computing: interleaving gate operations with dynamical decoupling sequences.  

PubMed

Implementing precise operations on quantum systems is one of the biggest challenges for building quantum devices in a noisy environment. Dynamical decoupling attenuates the destructive effect of the environmental noise, but so far, it has been used primarily in the context of quantum memories. Here, we experimentally demonstrate a general scheme for combining dynamical decoupling with quantum logical gate operations using the example of an electron-spin qubit of a single nitrogen-vacancy center in diamond. We achieve process fidelities >98% for gate times that are 2 orders of magnitude longer than the unprotected dephasing time T2. PMID:24580577

Zhang, Jingfu; Souza, Alexandre M; Brandao, Frederico Dias; Suter, Dieter

2014-02-01

197

Quantum approach of mesoscopic magnet dynamics with spin transfer torque  

NASA Astrophysics Data System (ADS)

We present a theory of magnetization dynamics driven by spin-polarized current in terms of the quantum master equation. In the spin coherent state representation, the master equation becomes a Fokker-Planck equation, which naturally includes the spin transfer and quantum fluctuation. The current electron scattering state is correlated to the magnet quantum states, giving rise to quantum correction to the electron transport properties in the usual semiclassical theory. In the large-spin limit, the magnetization dynamics is shown to obey the Hamilton-Jacobi equation or the Hamiltonian canonical equations.

Wang, Yong; Sham, L. J.

2013-05-01

198

Quantum dynamics in a camel-back potential of a dc SQUID E. Hoskinson1  

E-print Network

Quantum dynamics in a camel-back potential of a dc SQUID E. Hoskinson1 , F. Lecocq1 , N. Didier2 Josephson junctions (dc SQUID), with near-zero current bias and flux bias near half a flux quantum. We SQUID and the rf SQUID phase qubit have been extensively studied [2­6]. In each of these devices

Paris-Sud XI, UniversitĂŠ de

199

Confined quantum Zeno dynamics of a watched atomic arrow  

NASA Astrophysics Data System (ADS)

In a quantum world, a watched arrow never moves. This is the quantum Zeno effect. Repeatedly asking a quantum system `are you still in your initial state?' blocks its coherent evolution through measurement back-action. Quantum Zeno dynamics (QZD; refs , ) gives more freedom to the system. Instead of pinning it to a single state, it sets a border in its evolution space. Repeatedly asking the system `are you beyond the border?' makes this limit impenetrable. As the border can be designed by choosing the measured observable, QZD allows one to dynamically tailor the system's Hilbert space. Recent proposals, particularly in the cavity quantum electrodynamics context, highlight the interest of QZD for quantum state engineering tasks, which are the key to quantum-enabled technologies and quantum information processing. We report the observation of QZD in the 51-dimensional Hilbert space of a large angular momentum J = 25. Continuous selective interrogation limits the evolution of this angular momentum to an adjustable multi-dimensional subspace. This confined dynamics leads to the production of non-classical `Schrödinger cat' states, quantum superpositions of angular momenta pointing in different directions. These states are promising for sensitive metrology of electric and magnetic fields. This QZD approach could also be generalized to cavity and circuit quantum electrodynamics experiments by replacing the angular momentum with a photonic harmonic oscillator.

Signoles, Adrien; Facon, Adrien; Grosso, Dorian; Dotsenko, Igor; Haroche, Serge; Raimond, Jean-Michel; Brune, Michel; Gleyzes, Sébastien

2014-10-01

200

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

201

Dynamics of multipartite quantum correlations in the qubit-reservoir system  

NASA Astrophysics Data System (ADS)

We study the dynamics of multipartite quantum correlations in terms of genuinely multipartite (GM) concurrence and global quantum discord in an N qubits system interacting with independent reservoirs. For the initial mixed GHZ-like state, we show that the multipartite quantum correlations initially in the qubits system can be completely transferred to the reservoirs. During this process, the GM entanglement exhibits sudden death for qubits and sudden birth for reservoirs, but the global quantum discord presents the asymptotic behavior. In this sense, the global quantum discord is more robust than GM entanglement in the evolution process. We put research emphasis on the effects induced by the amplitude ? of the initial state, purity p and the qubits number N. In addition, a sharp comparison between the dynamics of GM entanglement and that of global quantum discord in both Markovian and non-Markovian regimes is made.

Guo, Jin-Liang; Mi, Ying-Juan

2014-02-01

202

Quantum fluid dynamics approach for electronic structure calculation: application to the study of ground-state properties of rare gas atoms  

NASA Astrophysics Data System (ADS)

We explore the usefulness of a quantum fluid dynamics (QFD) approach for quantitative electronic structure calculations of many-electron systems. By combining QFD and density functional theory, a single time-dependent nonlinear QFD equation can be derived. The equation is further transformed into a diffusion-type form by an imaginary-time evolution method, whose asymptotic solution reaches a global minimum and the many-body ground-state wavefunction. The time-dependent generalized pseudospectral method is extended to solve the diffusion equation in spherical coordinates, allowing optimal and nonuniform spatial discretization and accurate and efficient solution of the diffusion function in space and time. The procedure is applied to the study of electronic energies, densities and other ground-state properties of noble gas atoms (He, Ne, Ar, Kr, Xe). The results are in good agreement with other best available values. The method offers a conceptually appealing and computationally practical procedure for the treatment of many-electron systems beyond the Hartree-Fock level.

Roy, Amlan K.; Chu, Shih-I.

2002-05-01

203

Dynamic homotopy and landscape dynamical set topology in quantum control  

NASA Astrophysics Data System (ADS)

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 |??, an ensemble density matrix ?, 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; Rabitz, Herschel

2012-08-01

204

Critical behavior of dynamically triangulated quantum gravity in four dimensions  

NASA Astrophysics Data System (ADS)

We performed a detailed study of the phase transition region in four-dimensional simplicial quantum gravity, using the dynamical triangulation approach. The phase transition between the gravity and antigravity phases turned out to be asymmetrical, so that we observed the scaling laws only when the Newton constant approached the critical value from the perturbative side. The curvature susceptibility diverges with the scaling index - 0.6. The physical (i.e. measured with heavy particle propagation) Hausdorff dimension of the manifolds, which is 2.3 in the gravity phase and 4.6 in the antigravity phase, turned out to be 4 at the critical point, within the measurement accuracy. These facts indicate the existence of the continuum limit in four-dimensional euclidean quantum gravity.

Agishtein, M. E.; Migdal, A. A.

1992-10-01

205

Quantum Dynamics of Lorentzian Spacetime Foam  

E-print Network

A simple spacetime wormhole, which evolves classically from zero throat radius to a maximum value and recontracts, can be regarded as one possible mode of fluctuation in the microscopic ``spacetime foam'' first suggested by Wheeler. The dynamics of a particularly simple version of such a wormhole can be reduced to that of a single quantity, its throat radius; this wormhole thus provides a ``minisuperspace model'' for a structure in Lorentzian-signature foam. The classical equation of motion for the wormhole throat is obtained from the Einstein field equations and a suitable equation of state for the matter at the throat. Analysis of the quantum behavior of the hole then proceeds from an action corresponding to that equation of motion. The action obtained simply by calculating the scalar curvature of the hole spacetime yields a model with features like those of the relativistic free particle. In particular the Hamiltonian is nonlocal, and for the wormhole cannot even be given as a differential operator in closed form. Nonetheless the general solution of the Schr\\"odinger equation for wormhole wave functions, i.e., the wave-function propagator, can be expressed as a path integral. Too complicated to perform exactly, this can yet be evaluated via a WKB approximation. The result indicates that the wormhole, classically stable, is quantum-mechanically unstable: A Feynman-Kac decomposition of the WKB propagator yields no spectrum of bound states. Though an initially localized wormhole wave function may oscillate for many classical expansion/recontraction periods, it must eventually leak to large radius values. The possibility of such a mode unstable against growth, combined with

Ian Redmount; Wai-Mo Suen

1993-09-14

206

Non-Markovian Quantum State Diffusion and Open System Dynamics  

Microsoft Academic Search

We present a non-Markovian quantum trajectory method that allows to determine the dynamics of a quantum system coupled to\\u000a an environment of harmonic oscillators. When averaged over the classical noise we recover the reduced density operator without\\u000a approximation, in particular without Markov approximation. In the Markov limit, our result reduces to standard quantum state\\u000a diffusion. We use coherent states to

Walter T. Strunz; Lajos Diósi; Nicolas Gisin

2000-01-01

207

Classical and Quantum Dynamics of Energy Transfer under Shock Conditions  

Microsoft Academic Search

Classical molecular dynamics (MD) simulations of shocks in molecular solids predict rapid excitation of bond motion indicating efficient translational to vibrational coupling. The validity of the MD description of collisional energy transfer near shock fronts has not been carefully tested. The importance of quantum effects under shock conditions is explored in classical MD and quantum mechanical (QM) simulations of a

R. C. Mowrey; M. L. Elert; C. T. White

2005-01-01

208

Quantum Metrology: Dynamics versus Entanglement Sergio Boixo,1,2  

E-print Network

Quantum Metrology: Dynamics versus Entanglement Sergio Boixo,1,2 Animesh Datta,1 Matthew J. Davis,3 measurements. Practical interest in using nonlinear interactions for quantum metrology comes from the fact that-mechanical character as linear (k 1) metrology schemes but is n times faster. Even though this Letter is mainly about

Queensland, University of

209

Trajectory-based solution of the nonadiabatic quantum dynamics equations: an on-the-fly approach for molecular dynamics simulations.  

PubMed

The non-relativistic quantum dynamics of nuclei and electrons is solved within the framework of quantum hydrodynamics using the adiabatic representation of the electronic states. An on-the-fly trajectory-based nonadiabatic molecular dynamics algorithm is derived, which is also able to capture nuclear quantum effects that are missing in the traditional trajectory surface hopping approach based on the independent trajectory approximation. The use of correlated trajectories produces quantum dynamics, which is in principle exact and computationally very efficient. The method is first tested on a series of model potentials and then applied to study the molecular collision of H with H(2) using on-the-fly TDDFT potential energy surfaces and nonadiabatic coupling vectors. PMID:21264437

Curchod, Basile F E; Tavernelli, Ivano; Rothlisberger, Ursula

2011-02-28

210

Quantum molecular dynamic simulations of warm dense carbon monoxide.  

PubMed

Using quantum molecular dynamic simulations, we have studied the thermophysical properties of warm dense carbon monoxide under extreme conditions. The principal Hugoniot pressure up to 286 GPa, which is derived from the equation of state, is calculated and compared with available experimental and theoretical data. The chemical decomposition of carbon monoxide has been predicted at 8 GPa by means of pair correlation function and the charge density distribution. Based on Kubo-Greenwood formula, the dc electrical conductivity and the optical reflectivity are determined, and the nonmetal-metal transition for shock compressed carbon monoxide is observed around 40 GPa. PMID:21842937

Zhang, Yujuan; Wang, Cong; Li, Dafang; Zhang, Ping

2011-08-14

211

Relativistic hydrodynamic scaling from the dynamics of quantum field theory.  

PubMed

Relativistic hydrodynamic scaling or boost invariance is a particularly important hydrodynamic regime, describing collective flows of relativistic many body systems and is used in the interpretation of experiments from high-energy cosmic rays to relativistic heavy-ion collisions. We show evidence for the emergence of hydrodynamic scaling from the dynamics of relativistic quantum field theory. We consider a scalar lambdaphi(4) model in 1+1 dimensions in the Hartree approximation and study the relativistic collisions of two kinks and the decay of a localized high-energy density region. We find that thermodynamic scalar isosurfaces show approximate boost invariance at high-energy densities. PMID:12225137

Bettencourt, Luís M A; Cooper, Fred; Pao, Karen

2002-09-01

212

Complexity of controlling quantum many-body dynamics  

E-print Network

We demonstrate that arbitrary time evolutions of many-body quantum systems can be reversed even in cases when only part of the Hamiltonian can be controlled. The reversed dynamics obtained via optimal control—contrary to ...

Caneva, T.

213

Photoabsorption of acridine yellow and proflavin bound to human serum albumin studied by means of quantum mechanics/molecular dynamics.  

PubMed

Attempting to unravel mechanisms in optical probing of proteins, we have performed pilot calculations of two cationic chromophores-acridine yellow and proflavin-located at different binding sites within human serum albumin, including the two primary drug binding sites as well as a heme binding site. The computational scheme adopted involves classical molecular dynamics simulations of the ligands bound to the protein and subsequent linear response polarizable embedding density functional theory calculations of the excitation energies. A polarizable embedding potential consisting of point charges fitted to reproduce the electrostatic potential and isotropic atomic polarizabilities computed individually for every residue of the protein was used in the linear response calculations. Comparing the calculated aqueous solution-to-protein shifts of maximum absorption energies to available experimental data, we concluded that the cationic proflavin chromophore is likely not to bind albumin at its drug binding site 1 nor at its heme binding site. Although agreement with experimental data could only be obtained in qualitative terms, our results clearly indicate that the difference in optical response of the two probes is due to deprotonation, and not, as earlier suggested, to different binding sites. The ramifications of this finding for design of molecular probes targeting albumin or other proteins is briefly discussed. PMID:23356863

Aidas, K?stutis; Olsen, Jógvan Magnus H; Kongsted, Jacob; Ĺgren, Hans

2013-02-21

214

The dynamical-quantization approach to open quantum systems  

NASA Astrophysics Data System (ADS)

The dynamical-quantization approach to open quantum systems does consist in quantizing the Brownian motion starting directly from its stochastic dynamics under the framework of both Langevin and Fokker-Planck equations, without alluding to any model Hamiltonian. On the ground of this non-Hamiltonian quantization method, we can derive a non-Markovian Caldeira-Leggett quantum master equation as well as a non-Markovian quantum Smoluchowski equation. The former is solved for the case of a quantum Brownian particle in a gravitational field whilst the latter for a harmonic oscillator. In both physical situations, we come up with the existence of a non-equilibrium thermal quantum force and investigate its classical limit at high temperatures as well as its quantum limit at zero temperature. Further, as a physical application of our quantum Smoluchowski equation, we take up the tunneling phenomenon of a non-inertial quantum Brownian particle over a potential barrier. Lastly, we wish to point out, corroborating conclusions reached in our previous paper [A. O. Bolivar, Ann. Phys. 326 (2011) 1354], that the theoretical predictions in the present article uphold the view that our non-Hamiltonian quantum mechanics is able to capture novel features inherent in quantum Brownian motion, thereby overcoming shortcomings underlying the Caldeira-Leggett Hamiltonian model.

Bolivar, A. O.

2012-03-01

215

The dynamics of quantum criticality revealed by quantum Monte Carlo and holography  

NASA Astrophysics Data System (ADS)

Understanding the dynamics of quantum systems without long-lived excitations (quasiparticles) constitutes an important yet challenging problem. Although numerical techniques can yield results for the dynamics in imaginary time, their reliable continuation to real time has proved difficult. We tackle this issue using the superfluid-insulator quantum critical point of bosons on a two-dimensional lattice, where quantum fluctuations destroy quasiparticles. We present quantum Monte Carlo simulations for two separate lattice realizations. Their low-frequency conductivities turn out to have the same universal dependence on imaginary frequency and temperature. Using the structure of the real-time dynamics of conformal field theories described by the holographic gauge/gravity duality, we then make progress on the problem of analytically continuing the numerical data to real time. Our method yields quantitative and experimentally testable results on the frequency-dependent conductivity near the quantum critical point. Extensions to other observables and universality classes are discussed.

Witczak-Krempa, William; Sřrensen, Erik S.; Sachdev, Subir

2014-05-01

216

Dynamical control of interference using voltage pulses in the quantum regime  

NASA Astrophysics Data System (ADS)

As a general trend, nanoelectronics experiments are shifting towards frequencies so high that they become comparable to the device’s internal characteristic time scales, resulting in new opportunities for studying the dynamical aspects of quantum mechanics. Here we theoretically study how a voltage pulse (in the quantum regime) propagates through an electronic interferometer (Fabry-Perot or Mach-Zehnder). We show that extremely fast pulses provide a conceptually new tool for manipulating quantum information: the possibility to dynamically engineer the interference pattern of a quantum system. Striking physical signatures are associated with this new regime: restoration of the interference in presence of large bias voltages; negative currents with respect to the direction of propagation of the voltage pulse; and oscillation of the total transmitted charge with the total number of injected electrons. The present findings have been made possible by the recent unlocking of our capability for simulating time-resolved quantum nanoelectronics of large systems.

Gaury, Benoit; Waintal, Xavier

2014-05-01

217

Dynamical behavior of interacting dark energy in loop quantum cosmology  

E-print Network

The dynamical behaviors of interacting dark energy in loop quantum cosmology are discussed in this paper. Based on defining three dimensionless variables, we simplify the equations of the fixed points. The fixed points for interacting dark energy can be determined by the Friedmann equation coupled with the dynamical equations {in Einstein cosmology}. But in loop quantum cosmology, besides the Friedmann equation, the conversation equation also give a constrain on the fixed points. The difference of stability properties for the fixed points in loop quantum cosmology and the ones in Einstein cosmology also have been discussed.

Kui Xiao; Jian-Yang Zhu

2010-06-28

218

Quantum and classical dynamics simulations of ATP hydrolysis in solution  

PubMed Central

ATP hydrolysis is a key reaction in living cells that drives many cellular processes. The reaction, which involves gamma phosphate cleavage from ATP, converting it to ADP, has been suggested to occur via an associative or dissociative mechanism dependent upon the surrounding environment. Prior quantum chemical studies suffered from short simulation timescales failing to capture free energy contributions due to relaxation of the surrounding aqueous environment. We have developed a highly parallelized QM/MM implementation in the NAMD and OpenAtom simulation packages, using the dual grid, dual length scale method for combined plane-wave and Eular exponential spline-based QM/MM simulations. This approach, using message-driven parallel quantum and classical dynamics, permits sufficient timescale simulations for quantum chemical events such as ATP hydrolysis, and is found to accurately and reliably include the free energy contributions of solvent relaxation to hydrolysis. In this paper we describe the application of the dual grid, dual length plane-wave-based QM/MM method to study both the associative and dissociative mechanisms of ATP hydrolysis, accounting for the free energy contribution from solvent relaxation, as well as for the key role of Mg2+ in the reaction. PMID:23293550

Harrison, Christopher B.; Schulten, Klaus

2012-01-01

219

Surface-hopping dynamics and decoherence with quantum equilibrium structure.  

PubMed

In open quantum systems, decoherence occurs through interaction of a quantum subsystem with its environment. The computation of expectation values requires a knowledge of the quantum dynamics of operators and sampling from initial states of the density matrix describing the subsystem and bath. We consider situations where the quantum evolution can be approximated by quantum-classical Liouville dynamics and examine the circumstances under which the evolution can be reduced to surface-hopping dynamics, where the evolution consists of trajectory segments exclusively evolving on single adiabatic surfaces, with probabilistic hops between these surfaces. The justification for the reduction depends on the validity of a Markovian approximation on a bath averaged memory kernel that accounts for quantum coherence in the system. We show that such a reduction is often possible when initial sampling is from either the quantum or classical bath initial distributions. If the average is taken only over the quantum dispersion that broadens the classical distribution, then such a reduction is not always possible. PMID:18447424

Grunwald, Robbie; Kim, Hyojoon; Kapral, Raymond

2008-04-28

220

Confined quantum Zeno dynamics of a watched atomic arrow  

E-print Network

In a quantum world, a watched arrow never moves. This is the Quantum Zeno Effect (QZE). Repeatedly asking a quantum system "are you still in your initial state?" blocks its coherent evolution through measurement back-action. Quantum Zeno Dynamics (QZD) leaves more freedom to the system. Instead of pinning it to a single state, it sets a border in its evolution space. Repeatedly asking the system "did you cross the border?" makes it impenetrable. Since the border can be designed at will by choosing the measured observable, QZD allows one to tailor the system's evolution space. Recent proposals, particularly in the Cavity Quantum Electrodynamics (CQED) context, highlight the interest of QZD for quantum state engineering tasks, which are the key to quantumenabled technologies and quantum information processing. We report the observation of QZD in the 51-dimension Hilbert space of a large angular momentum J = 25. Continuous selective interrogation limits the evolution of this angular momentum to an adjustable multi-dimensional subspace. This confined dynamics leads to the production of non-classical "Schr\\"odinger cat" states, quantum superpositions of angular momentums pointing in different directions. These states are promising for sensitive metrology of electric and magnetic fields. This QZD approach could be generalized to other systems, opening novel perspectives for quantum information processing.

Adrien Signoles; Adrien Facon; Dorian Grosso; Igor Dotsenko; Serge Haroche; Jean-Michel Raimond; Michel Brune; Sébastien Gleyzes

2014-02-01

221

A Time-Dependent Quantum Dynamics Study of the H2 + CH3 yields H + CH4 Reaction  

NASA Technical Reports Server (NTRS)

We present a time-dependent wave-packet propagation calculation for the H2 + CH3 yields H + CH4 reaction in six degrees of freedom and for zero total angular momentum. Initial state selected reaction probability for different initial rotational-vibrational states are presented in this study. The cumulative reaction probability (CRP) is obtained by summing over initial-state-selected reaction probability. The energy-shift approximation to account for the contribution of degrees of freedom missing in the 6D calculation is employed to obtain an approximate full-dimensional CRP. Thermal rate constant is compared with different experiment results.

Wang, Dunyou; Kwak, Dochan (Technical Monitor)

2002-01-01

222

Nonlinear Dynamics and Quantum Entanglement in Optomechanical Systems  

NASA Astrophysics Data System (ADS)

To search for and exploit quantum manifestations of classical nonlinear dynamics is one of the most fundamental problems in physics. Using optomechanical systems as a paradigm, we address this problem from the perspective of quantum entanglement. We uncover strong fingerprints in the quantum entanglement of two common types of classical nonlinear dynamical behaviors: periodic oscillations and quasiperiodic motion. There is a transition from the former to the latter as an experimentally adjustable parameter is changed through a critical value. Accompanying this process, except for a small region about the critical value, the degree of quantum entanglement shows a trend of continuous increase. The time evolution of the entanglement measure, e.g., logarithmic negativity, exhibits a strong dependence on the nature of classical nonlinear dynamics, constituting its signature.

Wang, Guanglei; Huang, Liang; Lai, Ying-Cheng; Grebogi, Celso

2014-03-01

223

Fisher-Shannon product and quantum revivals in wavepacket dynamics  

NASA Astrophysics Data System (ADS)

We show the usefulness of the Fisher-Shannon information product in the study of the sequence of collapses and revivals that take place along the time evolution of quantum wavepackets. This fact is illustrated in two models, a quantum bouncer and a graphene quantum ring.

García, T.; de los Santos, F.; Romera, E.

2014-01-01

224

Dynamics of quantum discord in a two-qubit system under classical noise  

NASA Astrophysics Data System (ADS)

We study the quantum discord dynamics of two noninteracting qubits that are, respectively, subject to classical noise. The results show that the dynamics of quantum discord are dependent on both the coupling between the qubits and classical noise, and the average switching rate of the classical noise. In the weak-coupling Markovian region, quantum discord exhibits exponent decay without revival, and can be well protected by increasing the average classical noise switching rate. While in the strong-coupling non-Markovian region, quantum discord reveals slowly decayed oscillations with quick revival by decreasing the average switching rate of the classical noise. Thus, our results provide a new method of protecting quantum discord in a two-qubit system by controlling the coupling between the qubits and classical noise, and the average switching rate of the classical noise.

Guo, You-Neng; Fang, Mao-Fa; Liu, Xiang; Yang, Bai-Yuan

2014-03-01

225

Full-dimensional quantum dynamics study of exchange processes for the D + H2O and D + HOD reactions  

NASA Astrophysics Data System (ADS)

The exchange processes of D + H2O and D + HOD reactions are studied using initial state-selected time-dependent wave packet approach in full dimension. The total reaction probabilities for different partial waves, together with the integral cross sections, are obtained both by the centrifugal sudden (CS) approximation and exact coupled-channel (CC) calculations, for the H2O(HOD) reactant initially in the ground rovibrational state. In the CC calculations, small resonance peaks in the reaction probabilities and quick diminishing of the resonance peaks with the increase of total angular momenta J do not lead to clear step-like features just above the threshold in the cross sections for the title reactions, which are different in other isotopically substituted reactions where the hydrogen atom was included as the reactant instead of the deuterium atom [B. Fu, Y. Zhou, and D. H. Zhang, Chem. Sci. 3, 270 (2012); B. Fu and D. H. Zhang, J. Phys. Chem. A 116, 820 (2012)]. It is interesting that the shape resonance-induced features resulting from the reaction tunneling are significantly diminished accordingly in the reactions of the deuterium atom and H2O or HOD, owing to the weaker tunneling capability of the reagent deuterium atom in the title reactions than the reagent hydrogen atom in other reactions. In the CS calculations, the resonance peaks persist in many partial waves but cannot survive the partial-wave summations. The cross sections for the D' + H2O --> D'OH + H and D' + HOD --> D'OD + H reactions are substantially larger than those for the D' + HOD --> HOD' + D reaction, indicating that the D'/H exchange reactions are much more favored than the D'/D exchange.

Fu, Bina; Zhang, Dong H.

2012-05-01

226

Quantum chaos, dynamical correlations, and the effect of noise on localization  

Microsoft Academic Search

Localization in the quantum kicked rotator (QKR) problem leads to nontrivial dynamical correlations that are absent in the classical limit. These correlations are related to the spectral properties of the model. The effect of noise on coherence is studied. Also, its effect on the dynamical correlations is investigated, and thus one is able to determine analytically the diffusion that is

Doron Cohen

1991-01-01

227

Validity of the site-averaging approximation for modeling the dissociative chemisorption of H2 on Cu(111) surface: A quantum dynamics study on two potential energy surfaces.  

PubMed

A new finding of the site-averaging approximation was recently reported on the dissociative chemisorption of the HCl/DCl+Au(111) surface reaction [T. Liu, B. Fu, and D. H. Zhang, J. Chem. Phys. 139, 184705 (2013); T. Liu, B. Fu, and D. H. Zhang, J. Chem. Phys. 140, 144701 (2014)]. Here, in order to investigate the dependence of new site-averaging approximation on the initial vibrational state of H2 as well as the PES for the dissociative chemisorption of H2 on Cu(111) surface at normal incidence, we carried out six-dimensional quantum dynamics calculations using the initial state-selected time-dependent wave packet approach, with H2 initially in its ground vibrational state and the first vibrational excited state. The corresponding four-dimensional site-specific dissociation probabilities are also calculated with H2 fixed at bridge, center, and top sites. These calculations are all performed based on two different potential energy surfaces (PESs). It is found that the site-averaging dissociation probability over 15 fixed sites obtained from four-dimensional quantum dynamics calculations can accurately reproduce the six-dimensional dissociation probability for H2 (v = 0) and (v = 1) on the two PESs. PMID:25416886

Liu, Tianhui; Fu, Bina; Zhang, Dong H

2014-11-21

228

Quantum dynamics of Shi Ying Lin a  

E-print Network

�5]. On the other hand, the title reaction is highly exothermic (DE = �6.5 eV) without an intrinsic barrier quantum states due to the two heavy atoms in the system and the large exothermicity, an accu- rate quantum it to compute the integral cross section and the rate constant for this reaction. Good agreement

Honvault, Pascal

229

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

230

Quantum Gravity, Dynamical Energy-Momentum Space and Vacuum Energy  

E-print Network

We argue that the combination of the principles of quantum theory and general relativity allow for a dynamical energy-momentum space. We discuss the freezing of vacuum energy in such a dynamical energy-momentum space and present a phenomenologically viable seesaw formula for the cosmological constant in this context.

Lay Nam Chang; Djordje Minic; Tatsu Takeuchi

2010-04-23

231

Arbitrarily accurate dynamical control in open quantum systems.  

PubMed

We show that open-loop dynamical control techniques may be used to synthesize unitary transformations in open quantum systems in such a way that decoherence is perturbatively compensated for to a desired (in principle arbitrarily high) level of accuracy, which depends only on the strength of the relevant errors and the achievable rate of control modulation. Our constructive and fully analytical solution employs concatenated dynamically corrected gates, and is applicable independently of detailed knowledge of the system-environment interactions and environment dynamics. Explicit implications for boosting quantum gate fidelities in realistic scenarios are addressed. PMID:20366973

Khodjasteh, Kaveh; Lidar, Daniel A; Viola, Lorenza

2010-03-01

232

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

233

Markovian and non-Markovian dynamics in quantum and classical systems  

E-print Network

We discuss the conceptually different definitions used for the non-Markovianity of classical and quantum processes. The well-established definition for non-Markovianity of a classical stochastic process represents a condition on the Kolmogorov hierarchy of the n-point joint probability distributions. Since this definition cannot be transferred to the quantum regime, quantum non-Markovianity has recently been defined and quantified in terms of the underlying quantum dynamical map, using either its divisibility properties or the behavior of the trace distance between pairs of initial states. Here, we investigate and compare these definitions and their relations to the classical notion of non-Markovianity by employing a large class of non-Markovian processes, known as semi-Markov processes, which admit a natural extension to the quantum case. A number of specific physical examples is constructed which allow to study the basic features of the classical and the quantum definitions and to evaluate explicitly the me...

Vacchini, Bassano; Laine, Elsi-Mari; Piilo, Jyrki; Breuer, Heinz-Peter

2011-01-01

234

THE JOURNAL OF CHEMICAL PHYSICS 134, 074107 (2011) Multistage ab initio quantum wavepacket dynamics for electronic structure  

E-print Network

THE JOURNAL OF CHEMICAL PHYSICS 134, 074107 (2011) Multistage ab initio quantum wavepacket dynamics for electronic structure and dynamics in open systems: Momentum representation, coupled electron-nuclear dynamics dynamics (MS-AIWD) treatment for the study of delocalized electronic systems as well as electron transport

Iyengar, Srinivasan S.

235

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

2009-07-01

236

TOPICAL REVIEW: Quantum dynamics of two-spin-qubit systems  

NASA Astrophysics Data System (ADS)

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.

Nguyen, Van Hieu

2009-07-01

237

Quantum Dynamics, Minkowski-Hilbert space, and A Quantum Stochastic Duhamel Principle  

E-print Network

In this paper we shall re-visit the well-known Schr\\"odinger and Lindblad dynamics of quantum mechanics. However, these equations shall be realized as the consequence of a more general, underlying dynamical process. In both cases we shall see that the evolution of a quantum state $P_\\psi=\\varrho(0)$ may be given the not so well-known pseudo-quadratic form $\\partial_t\\varrho(t)=\\mathbf{V}^\\star\\varrho(t)\\mathbf{V}$ where $\\mathbf{V}$ is a vector operator in a complex Minkowski space and the pseudo-adjoint $\\mathbf{V}^\\star$ is induced by the Minkowski metric $\\boldsymbol{\\eta}$. The interesting thing about this formalism is that its derivation has very deep roots in a new understanding of the differential calculus of time. This Minkowski-Hilbert representation of quantum dynamics is called the \\emph{Belavkin Formalism}; a beautiful, but not well understood theory of mathematical physics that understands that both deterministic and stochastic dynamics may be `unraveled' into a second-quantized Minkowski space. Working in such a space provided the author with the means to construct a QS (quantum stochastic) Duhamel principle and simple applications to a Schr\\"odinger dynamics perturbed by a continual measurement process are considered. What is not known, but presented here, is the role of the Lorentz transform in quantum measurement and the appearance of Riemannian geometry in quantum measurement is also discussed.

Matthew F. Brown

2014-07-10

238

Linear Optics Simulation of Quantum Non-Markovian Dynamics  

PubMed Central

The simulation of open quantum dynamics has recently allowed the direct investigation of the features of system-environment interaction and of their consequences on the evolution of a quantum system. Such interaction threatens the quantum properties of the system, spoiling them and causing the phenomenon of decoherence. Sometimes however a coherent exchange of information takes place between system and environment, memory effects arise and the dynamics of the system becomes non-Markovian. Here we report the experimental realisation of a non-Markovian process where system and environment are coupled through a simulated transverse Ising model. By engineering the evolution in a photonic quantum simulator, we demonstrate the role played by system-environment correlations in the emergence of memory effects. PMID:23236588

Chiuri, Andrea; Greganti, Chiara; Mazzola, Laura; Paternostro, Mauro; Mataloni, Paolo

2012-01-01

239

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

PubMed

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 YbRh(2)Si(2), 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. PMID:20668246

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

2010-08-17

240

Computational Improvements to Quantum Wave Packet ab Initio Molecular Dynamics Using a Potential-Adapted,  

E-print Network

combined with an on-the-fly interpolation scheme, allows us to determine the quantum dynamical interactionComputational Improvements to Quantum Wave Packet ab Initio Molecular Dynamics Using a Potential between quantum wave packet dynamics and ab initio molecular dynamics. Atom-centered density

Iyengar, Srinivasan S.

241

Decoherence and Quantum-Classical Master Equation Dynamics  

Microsoft Academic Search

The conditions under which quantum-classical Liouville dynamics may be\\u000areduced to a master equation are investigated. Systems that can be partitioned\\u000ainto a quantum-classical subsystem interacting with a classical bath are\\u000aconsidered. Starting with an exact non-Markovian equation for the diagonal\\u000aelements of the density matrix, an evolution equation for the subsystem density\\u000amatrix is derived. One contribution to this

Robbie Grunwald; Raymond Kapral

2006-01-01

242

Decoherence and quantum-classical master equation dynamics  

Microsoft Academic Search

The conditions under which quantum-classical Liouville dynamics may be reduced to a master equation are investigated. Systems that can be partitioned into a quantum-classical subsystem interacting with a classical bath are considered. Starting with an exact non-Markovian equation for the diagonal elements of the density matrix, an evolution equation for the subsystem density matrix is derived. One contribution to this

Robbie Grunwald; Raymond Kapral

2007-01-01

243

Dynamical localization effect in a coupled quantum dot array driven by an AC magnetic field  

NASA Astrophysics Data System (ADS)

We have studied the transport properties of a ring-coupled quantum dot array driven by an AC magnetic field, which is connected to two leads, and we give the response of the transport current to the dynamical localization. We found that when the ratio of the magnetic flux to the total quantum dots number is a root of the zeroth order Bessel function, dynamical localization and collapse of quasi-energy occurs and importantly, the transport current displays a dip which is the signal of dynamical localization. The dynamical localization effect is strengthened as a result of the increase of the quantum dot number, and it is weakened on account of the increase of the dots-lead hopping rate.

Xia, Jun-Jie; Nie, Yi-Hang

2011-09-01

244

Operators versus functions: from quantum dynamical semigroups to tomographic semigroups  

NASA Astrophysics Data System (ADS)

Quantum mechanics can be formulated in terms of phase-space functions, according to Wigner's approach. A generalization of this approach consists in replacing the density operators of the standard formulation with suitable functions, the so-called generalized Wigner functions or (group-covariant) tomograms, obtained by means of group-theoretical methods. A typical problem arising in this context is to express the evolution of a quantum system in terms of tomograms. In the case of a (suitable) open quantum system, the dynamics can be described by means of a quantum dynamical semigroup 'in disguise', namely, by a semigroup of operators acting on tomograms rather than on density operators. We focus on a special class of quantum dynamical semigroups, the twirling semigroups, that have interesting applications, e.g., in quantum information science. The 'disguised counterparts' of the twirling semigroups, i.e., the corresponding semigroups acting on tomograms, form a class of semigroups of operators that we call tomographic semigroups. We show that the twirling semigroups and the tomographic semigroups can be encompassed in a unique theoretical framework, a class of semigroups of operators including also the probability semigroups of classical probability theory, so achieving a deeper insight into both the mathematical and the physical aspects of the problem.

Aniello, Paolo

2013-11-01

245

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

246

Bohmian dynamics on subspaces using linearized quantum force  

NASA Astrophysics Data System (ADS)

In the de Broglie-Bohm formulation of quantum mechanics the time-dependent Schrödinger 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.

Rassolov, Vitaly A.; Garashchuk, Sophya

2004-04-01

247

Quantum dynamics of a dissipative and confined cyclotron motion  

NASA Astrophysics Data System (ADS)

We study the dissipative dynamics of a charged oscillator in a magnetic field by coupling (a la Caldeira and Leggett) it to a heat bath consisting of non-interacting harmonic oscillators. We derive here the autocorrelation functions of the position and momentum and study its behavior at various limiting situations. The equilibrium (steady state) dispersions of position and momentum are obtained from their respective autocorrelation functions. We analyze the equilibrium position and momentum dispersions at low and high temperatures for both low and high magnetic field strengths. We obtain the classical diffusive behavior (at long times) as well as the equilibrium momentum dispersion of the free quantum charged particle in a magnetic field, in the limit of vanishing oscillator potential ?0. We establish the relations between the reduced partition function and the equilibrium dispersions of the dissipative and confined cyclotron problem.

Kumar, Jishad

2014-01-01

248

Semiclassical approximations to quantum dynamical time correlation Jianshu Cao and Gregory A. Voth  

E-print Network

Semiclassical approximations to quantum dynamical time correlation functions Jianshu Cao-6323 Received 8 September 1995; accepted 28 September 1995 Semiclassical approximations for quantum time is developed to calculate quantum time correlation functions. This approach holds considerable promise

Cao, Jianshu

249

Can the ring polymer molecular dynamics method be interpreted as real time quantum dynamics?  

NASA Astrophysics Data System (ADS)

The ring polymer molecular dynamics (RPMD) method has gained popularity in recent years as a simple approximation for calculating real time quantum correlation functions in condensed media. However, the extent to which RPMD captures real dynamical quantum effects and why it fails under certain situations have not been clearly understood. Addressing this issue has been difficult in the absence of a genuine justification for the RPMD algorithm starting from the quantum Liouville equation. To this end, a new and exact path integral formalism for the calculation of real time quantum correlation functions is presented in this work, which can serve as a rigorous foundation for the analysis of the RPMD method as well as providing an alternative derivation of the well established centroid molecular dynamics method. The new formalism utilizes the cyclic symmetry of the imaginary time path integral in the most general sense and enables the expression of Kubo-transformed quantum time correlation functions as that of physical observables pre-averaged over the imaginary time path. Upon filtering with a centroid constraint function, the formulation results in the centroid dynamics formalism. Upon filtering with the position representation of the imaginary time path integral, we obtain an exact quantum dynamics formalism involving the same variables as the RPMD method. The analysis of the RPMD approximation based on this approach clarifies that an explicit quantum dynamical justification does not exist for the use of the ring polymer harmonic potential term (imaginary time kinetic energy) as implemented in the RPMD method. It is analyzed why this can cause substantial errors in nonlinear correlation functions of harmonic oscillators. Such errors can be significant for general correlation functions of anharmonic systems. We also demonstrate that the short time accuracy of the exact path integral limit of RPMD is of lower order than those for finite discretization of path. The present quantum dynamics formulation also serves as the basis for developing new quantum dynamical methods that utilize the cyclic nature of the imaginary time path integral.

Jang, Seogjoo; Sinitskiy, Anton V.; Voth, Gregory A.

2014-04-01

250

Dynamical quantum error correction of unitary operations with bounded controls  

NASA Astrophysics Data System (ADS)

Dynamically corrected gates were recently introduced [K. Khodjasteh and L. Viola, Phys. Rev. Lett. 102, 080501 (2009)] as a tool to achieve decoherence-protected quantum gates based on open-loop Hamiltonian engineering. Here, we further expand the framework of dynamical quantum error correction, with emphasis on elucidating under what conditions decoherence suppression can be ensured while performing a generic target quantum gate, using only available bounded-strength control resources. Explicit constructions for physically relevant error models are detailed, including arbitrary linear decoherence and pure dephasing on qubits. The effectiveness of dynamically corrected gates in an illustrative non-Markovian spin-bath setting is investigated numerically, confirming the expected fidelity performance in a wide parameter range. Robustness against a class of systematic control errors is automatically incorporated in the perturbative error regime.

Khodjasteh, Kaveh; Viola, Lorenza

2009-09-01

251

Optimized Dynamical Decoupling in ?-Type n-Level Quantum Systems  

E-print Network

In this paper, we first design a type of Bang-Bang (BB) operation group to reduce the phase decoherence in a {\\Xi}-type n-level quantum system based on the dynamical decoupling mechanism. Then, we derive two kinds of dynamical decoupling schemes: periodic dynamical decoupling (PDD) and Uhrig dynamical decoupling (UDD). We select the non-diagonal element of density matrix as a reference index, and investigate the behavior of quantum coherence of the {\\Xi}-type n-level atom under these two dynamical decoupling schemes proposed. At last, we choose a {\\Xi}-type six-level atom as a system controlled, and use the decoupling schemes proposed to suppress the phase decoherence. The simulation experiments and the comparison results are given.

Linping Chan; Shuang Cong

2014-02-21

252

Noise-resilient quantum evolution steered by dynamical decoupling  

NASA Astrophysics Data System (ADS)

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.

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

2013-08-01

253

Dynamical symmetry and analytical solutions of the non-autonomous quantum master equation of the dissipative two-level system: decoherence of quantum register  

E-print Network

Based on the non-autonomous quantum master equation, we investigate the dissipative and decoherence properties of the two-level atom system interacting with the environment of thermal quantum radiation fields. For this system, by a novel algebraic dynamic method, the dynamical symmetry of the system is found, the quantum master equation is converted into a Schr\\"{o}dinger-like equation and the non-Hermitian rate (quantum Liouville) operator of the master equation is expressed as a linear function of the dynamical u(2) generators. Furthermore, the integrability of the non-autonomous master equation has been proved for the first time. Based on the time-dependent analytical solutions, the asymptotic behavior of the solution has been examined and the approach to the equilibrium state has been proved. Finally, we have studied the decoherence property of the multiple two-level atom system coupled to the thermal radiation fields, which are related to the quantum register.

Shun-Jin Wang; Jun-Hong An; Hong-Gang Luo; Cheng-Long Jia

2005-05-10

254

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

255

Towards many-dimensional real-time quantum theory for heavy-particle dynamics. II. Beyond semiclassics by quantum smoothing of the singularity in quantum-classical correspondence  

NASA Astrophysics Data System (ADS)

A theory of many-dimensional real-time quantum dynamics is studied in terms of action decomposed function (ADF), a class of quantum wave function. In the preceding companion paper [S. Takahashi and K. Takatsuka, Phys. Rev. A 89, 012108 (2014), 10.1103/PhysRevA.89.012108], we showed that semiclassical dynamics for ADF in the Lagrange picture of phase flow can be described in terms of what we call deviation determinant and associated quantum phases without use of the stability matrix. Consequently, the Hessian of the involved potential functions is not required in this formalism. This paper is devoted to an analysis of the mechanism of quantum diffusion (quantum smoothing) that removes the singularity inherent in the semiclassical ADF: We derive a Lorentzian form for the amplitude factor of ADF. The real part of its denominator comes from the deviation determinant, while the imaginary part reflects quantum diffusion and is proportional to the Planck constant. The presence of the nonzero imaginary part smooths out the singularity and removes the divergence. Besides, this imaginary part can be obtained through a Wronskian relation with the deviation vectors, which can be solved rather easily at each space-time point on a classical trajectory. A number of theoretical advantages of the Lorentzian form and the Wronskian relation are illustrated theoretically and numerically. It turns out that there is no essential difficulty in applications to many-dimensional heavy-particle systems such as molecules. The theory is examined with stringent numerical tests.

Takatsuka, Kazuo; Takahashi, Satoshi

2014-01-01

256

Chaotic Dynamics and Transport in Classical and Quantum Systems  

NASA Astrophysics Data System (ADS)

This book offers a modern updated review on the most important activities in today dynamical systems and statistical mechanics by some of the best experts in the domain. It gives a contemporary and pedagogical view on theories of classical and quantum chaos and complexity in hamiltonian and ergodic systems and their applications to anomalous transport in fluids, plasmas, oceans and atom-optic devices and to control of chaotic transport. The book is issued from lecture notes of the International Summer School on "Chaotic Dynamics and Transport in Classical and Quantum Systems" held in Cargčse (Corsica) 18th to the 30th August 2003.

Collet, P.; Courbage, M.; Metens, S.; Neishtadt, A.; Zaslavsky, G.

257

Quantum dissipation and neural net dynamics.  

PubMed

Inspired by the dissipative quantum model of brain, we model the states of neural nets in terms of collective modes by the help of the formalism of Quantum Field Theory. We exhibit an explicit neural net model which allows to memorize a sequence of several informations without reciprocal destructive interference, namely we solve the overprinting problem in such a way last registered information does not destroy the ones previously registered. Moreover, the net is able to recall not only the last registered information in the sequence, but also anyone of those previously registered. PMID:10379551

Pessa, E; Vitiello, G

1999-05-01

258

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

259

Non-adiabatic molecular dynamics with quantum solvent effects Oleg V. Prezhdo*, Craig Brooksby  

E-print Network

Non-adiabatic molecular dynamics with quantum solvent effects Oleg V. Prezhdo*, Craig Brooksby) molecular dynamics (MD) to include quantum effects of solvent environments are described. In a standard NA-MD to incorporate the following quantum effects of the solvent. (1) Branching, i.e. the ability of solvent quantum

260

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

261

Experimental study of quantum simulation for quantum chemistry with a nuclear magnetic resonance simulator.  

PubMed

Quantum computers have been proved to be able to mimic quantum systems efficiently in polynomial time. Quantum chemistry problems, such as static molecular energy calculations and dynamical chemical reaction simulations, become very intractable on classical computers with scaling up of the system. Therefore, quantum simulation is a feasible and effective approach to tackle quantum chemistry problems. Proof-of-principle experiments have been implemented on the calculation of the hydrogen molecular energies and one-dimensional chemical isomerization reaction dynamics using nuclear magnetic resonance systems. We conclude that quantum simulation will surpass classical computers for quantum chemistry in the near future. PMID:22946038

Lu, Dawei; Xu, Nanyang; Xu, Boruo; Li, Zhaokai; Chen, Hongwei; Peng, Xinhua; Xu, Ruixue; Du, Jiangfeng

2012-10-13

262

Quantum Hall effect in a one-dimensional dynamical system  

SciTech Connect

We construct a periodically time-dependent Hamiltonian with a phase transition in the quantum Hall universality class. One spatial dimension can be eliminated by introducing a second incommensurate driving frequency, so that we can study the quantum Hall effect in a one-dimensional (1D) system. This reduction to 1D is very efficient computationally and would make it possible to perform experiments on the 2D quantum Hall effect using cold atoms in a 1D optical lattice.

Dahlhaus, J. P.; Edge, J. M.; Beenakker, C. W. J. [Instituut-Lorentz, Universiteit Leiden, P.O. Box 9506, NL-2300 RA Leiden (Netherlands); Tworzydlo, J. [Institute of Theoretical Physics, University of Warsaw, Hoza 69, PL-00-681 Warsaw (Poland)

2011-09-15

263

Markovian and non-Markovian dynamics in quantum and classical systems  

E-print Network

We discuss the conceptually different definitions used for the non-Markovianity of classical and quantum processes. The well-established definition for non-Markovianity of a classical stochastic process represents a condition on the Kolmogorov hierarchy of the n-point joint probability distributions. Since this definition cannot be transferred to the quantum regime, quantum non-Markovianity has recently been defined and quantified in terms of the underlying quantum dynamical map, using either its divisibility properties or the behavior of the trace distance between pairs of initial states. Here, we investigate and compare these definitions and their relations to the classical notion of non-Markovianity by employing a large class of non-Markovian processes, known as semi-Markov processes, which admit a natural extension to the quantum case. A number of specific physical examples is constructed which allow to study the basic features of the classical and the quantum definitions and to evaluate explicitly the measures for quantum non-Markovianity. Our results clearly demonstrate several fundamental distinctions between the classical and the quantum notion of non-Markovianity, as well as between the various quantum measures for non-Markovianity.

Bassano Vacchini; Andrea Smirne; Elsi-Mari Laine; Jyrki Piilo; Heinz-Peter Breuer

2011-06-01

264

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

2009-01-14

265

Quantum-like dynamics of decision-making  

NASA Astrophysics Data System (ADS)

In cognitive psychology, some experiments for games were reported, and they demonstrated that real players did not use the “rational strategy” provided by classical game theory and based on the notion of the Nasch equilibrium. This psychological phenomenon was called the disjunction effect. Recently, we proposed a model of decision making which can explain this effect (“irrationality” of players) Asano et al. (2010, 2011) [23,24]. Our model is based on the mathematical formalism of quantum mechanics, because psychological fluctuations inducing the irrationality are formally represented as quantum fluctuations Asano et al. (2011) [55]. In this paper, we reconsider the process of quantum-like decision-making more closely and redefine it as a well-defined quantum dynamics by using the concept of lifting channel, which is an important concept in quantum information theory. We also present numerical simulation for this quantum-like mental dynamics. It is non-Markovian by its nature. Stabilization to the steady state solution (determining subjective probabilities for decision making) is based on the collective effect of mental fluctuations collected in the working memory of a decision maker.

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

2012-03-01

266

Universal dynamics of a soliton after a quantum quench  

E-print Network

In a quantum quench, one prepares a system in an eigenstate of a given Hamiltonian, and then lets it evolve after suddenly changing a control parameter of the Hamiltonian. By observing this evolution, one aims at understanding whether and how a quantum system reaches a (thermal) equilibrium. Typically, the initial state is taken to be the ground state and/or in an extended state: we propose a different experimentally feasible protocol, in which the system is prepared in an excited state corresponding to a collective solitonic excitation. If we are interested only in the single particle density, in the hydrodynamic regime the time evolution can be reduced to a semi-classical non-linear differential equation. The study of such equation shows that the short time dynamics after the quench is universal, and simple analytical predictions can be given for the velocities and profiles. Numerical support for these results is presented using the the Calogero model and the non-linear Schrodinger equation (NLSE), relevant for the implementation of the proposed protocol with ultracold bosons. The effect of non-integrable terms (power-law non-linearity and a parabolic potential) in the NLSE is also investigated, and shown to not spoil the universality.

Fabio Franchini; Andrey Gromov; Manas Kulkarni; Andrea Trombettoni

2014-08-15

267

Reaction-Diffusion Processes, Critical Dynamics and Quantum Chains  

E-print Network

The master equation describing non-equilibrium one-dimensional problems like diffusion limited reactions or critical dynamics of classical spin systems can be written as a Schr\\"odinger equation in which the wave function is the probability distribution and the Hamiltonian is that of a quantum chain with nearest neighbor interactions. Since many one-dimensional quantum chains are integrable, this opens a new field of applications. At the same time physical intuition and probabilistic methods bring new insight into the understanding of the properties of quantum chains. A simple example is the asymmetric diffusion of several species of particles which leads naturally to Hecke algebras and $q$-deformed quantum groups. Many other examples are given. Several relevant technical aspects like critical exponents, correlation functions and finite-size scaling are also discussed in detail.

Francisco C. Alcaraz; Michel Droz; Malte Henkel; Vladimir Rittenberg

1993-02-23

268

Controllable coupling and quantum correlation dynamics of two double quantum dots coupled via a transmission line resonator  

E-print Network

We propose a theoretical scheme to generate a controllable and switchable coupling between two double-quantum-dot (DQD) spin qubits by using a transmission line resonator (TLR) as a bus system. We study dynamical behaviors of quantum correlations described by entanglement correlation (EC) and discord correlation (DC) between two DQD spin qubits when the two spin qubits and the TLR are initially prepared in $X$-type quantum states and a coherent state, respectively. We demonstrate that in the EC death regions there exist DC stationary states in which the stable DC amplification or degradation can be generated during the dynamical evolution. It is shown that these DC stationary states can be controlled by initial-state parameters, the coupling, and detuning between qubits and the TLR. We reveal the full synchronization and anti-synchronization phenomena in the EC and DC time evolution, and show that the EC and DC synchronization and anti-synchronization depends on the initial-state parameters of the two DQD spin qubits. These results shed new light on dynamics of quantum correlations.

Qin-Qin Wu; Qing-Shou Tan; Le-Man Kuang

2010-11-25

269

Dynamical quantum repeater using cavity QED and optical coherent states  

NASA Astrophysics Data System (ADS)

In the framework of cavity QED, we propose a quantum repeater scheme that uses coherent light and atoms coupled to optical cavities. In contrast to conventional schemes, we exploit solely the cavity QED evolution for the entire quantum repeater scheme and, thus, avoid any explicit execution of quantum logical gates. The entanglement distribution between the repeater nodes is realized with the help of pulses of coherent light interacting with the atom-cavity system in each repeater node. In our previous paper [D. Gonta and P. van Loock, Phys. Rev. APLRAAN1050-294710.1103/PhysRevA.86.052312 86, 052312 (2012)], we already proposed a dynamical protocol to purify a bipartite entangled state using the evolution of atomic chains coupled to optical cavities. Here, we incorporate parts of this protocol in our repeater scheme, combining it with dynamical versions of entanglement distribution and swapping.

Gon?a, Denis; van Loock, Peter

2013-11-01

270

Theory of dynamic nuclear polarization and feedback in quantum dots  

NASA Astrophysics Data System (ADS)

An electron confined in a quantum dot interacts with its local nuclear spin environment through the hyperfine contact interaction. This interaction combined with external control and relaxation or measurement of the electron spin allows for the generation of dynamic nuclear polarization. The quantum nature of the nuclear bath, along with the interplay of coherent external fields and incoherent dynamics in these systems renders a wealth of intriguing phenomena seen in recent experiments such as electron Zeeman frequency focusing, hysteresis, and line dragging. We develop in detail a fully quantum, self-consistent theory that can be applied to such experiments and that moreover has predictive power. Our theory uses the operator sum representation formalism in order to incorporate the incoherent dynamics caused by the additional, Markovian bath, which in self-assembled dots is the vacuum field responsible for electron-hole optical recombination. The beauty of this formalism is that it reduces the complexity of the problem by encoding the joint dynamics of the external coherent and incoherent driving in an effective dynamical map that only acts on the electron spin subspace. This, together with the separation of time scales in the problem, allows for a tractable and analytically solvable formalism. The key role of entanglement between the electron spin and the nuclear spins in the formation of dynamic nuclear polarization naturally follows from our solution. We demonstrate the theory in detail for an optical pulsed experiment and present an in-depth discussion and physical explanation of our results.

Economou, Sophia E.; Barnes, Edwin

2014-04-01

271

Theory of dynamic nuclear polarization and feedback in quantum dots  

E-print Network

An electron confined in a quantum dot interacts with its local nuclear spin environment through the hyperfine contact interaction. This interaction combined with external control and relaxation or measurement of the electron spin allows for the generation of dynamic nuclear polarization. The quantum nature of the nuclear bath, along with the interplay of coherent external fields and incoherent dynamics in these systems renders a wealth of intriguing phenomena seen in recent experiments such as electron Zeeman frequency focusing, hysteresis, and line dragging. We develop in detail a fully quantum, self-consistent theory that can be applied to such experiments and that moreover has predictive power. Our theory uses the operator sum representation formalism in order to incorporate the incoherent dynamics caused by the additional, Markovian bath, which in self-assembled dots is the vacuum field responsible for electron-hole optical recombination. The beauty of this formalism is that it reduces the complexity of the problem by encoding the joint dynamics of the external coherent and incoherent driving in an effective dynamical map that only acts on the electron spin subspace. This together with the separation of timescales in the problem allows for a tractable and analytically solvable formalism. The key role of entanglement between the electron spin and the nuclear spins in the formation of dynamic nuclear polarization naturally follows from our solution. We demonstrate the theory in detail for an optical pulsed experiment and present an in-depth discussion and physical explanation of our results.

Sophia E. Economou; Edwin Barnes

2013-12-19

272

Matching-pursuit/split-operator Fourier-transform simulations of nonadiabatic quantum dynamics  

E-print Network

for simulations of adiabatic quantum dynamics in multidimensional systems. The MP/SOFT propagation schemeMatching-pursuit/split-operator Fourier-transform simulations of nonadiabatic quantum dynamics March 2005 A rigorous and practical approach for simulations of nonadiabatic quantum dynamics

Wu, Yinghua

273

Quantum wavepacket ab initio molecular dynamics: Generalizations using an extended Lagrangian treatment of diabatic states coupled  

E-print Network

,7 The quantum dynamics scheme in QWAIMD has also been used to develop a technique known as multistage ab initioQuantum wavepacket ab initio molecular dynamics: Generalizations using an extended Lagrangian a methodology that accurately computes quantum dynamical effects in a subsystem while simultaneously treating

Iyengar, Srinivasan S.

274

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

E-print Network

, as well as the dynamics of the complete enzyme and solvent. The nuclear quantum effects are incorporated and nuclear quantum effects, as well as the dynamics of the sol- vent and protein. The incorporationHybrid approach for including electronic and nuclear quantum effects in molecular dynamics

Hammes-Schiffer, Sharon

275

Quantum Dynamics of Energy Transfer under Shock Conditions  

Microsoft Academic Search

Classical molecular dynamics (MD) simulations of shocks in molecular solids predict rapid excitation of bond motion indicating efficient translational to vibrational coupling. The validity of the MD description of collisional energy transfer near shock fronts has not been carefully tested. The probability of vibrational excitation under shock conditions is explored in two-dimensional quantum mechanical (QM) simulations of H2 colliding with

R. C. Mowrey; M. L. Elert; C. T. White

2006-01-01

276

Chaotic Dynamics and Transport in Classical and Quantum Systems  

Microsoft Academic Search

This book offers a modern updated review on the most important activities in today dynamical systems and statistical mechanics by some of the best experts in the domain. It gives a contemporary and pedagogical view on theories of classical and quantum chaos and complexity in hamiltonian and ergodic systems and their applications to anomalous transport in fluids, plasmas, oceans and

P. Collet; M. Courbage; S. Metens; A. Neishtadt; G. Zaslavsky

2005-01-01

277

Quantum Potential and Random Phase-Space Dynamics  

Microsoft Academic Search

We analyze limitations upon any kinetic theory inspired derivation of a probabilistic coun- terpart of the Schrodinger picture quantum dynamics. Neither dissipative nor non-dissipative stochastic phase-space processes based on the white-noise (Brownian motion) kinetics are valid candidates unless additional constraints (a suitable form of the energy conservation law) are prop- erly incorporated in the formalism.

Piotr Garbaczewski

278

Semiclassical dynamics of excess quantum noise  

NASA Astrophysics Data System (ADS)

A semiclassical theoretical framework is presented to describe the essential features of the excess quantum noise that occurs in systems with nonorthogonal eigenmodes. Excess noise is shown to be always spectrally colored, instead of white, so that the Petermann excess noise factor is best written as K(?) instead of K. The consequences of this spectral coloring are analyzed for lasers, both below and above the lasing threshold.

van Exter, M. P.; van Druten, N. J.; van der Lee, A. M.; Dutra, S. M.; Nienhuis, G.; Woerdman, J. P.

2001-04-01

279

Stochastic Differential Equations for Quantum Dynamics of Spin-Boson Networks  

E-print Network

The quantum dynamics of open many-body systems poses a challenge for computational approaches. Here we develop a stochastic scheme based on the positive P phase-space representation to study the nonequilibrium dynamics of coupled spin-boson networks that are driven and dissipative. Such problems are at the forefront of experimental research in cavity and solid state realizations of quantum optics, as well as cold atom physics, trapped ions and superconducting circuits. We demonstrate and test our method on a driven, dissipative two-site system, each site involving a spin coupled to a photonic mode, with photons hopping between the sites, where we find good agreement with Monte Carlo Wavefunction simulations. In addition to numerically reproducing features recently observed in an experiment [Phys. Rev. X 4, 031043 (2014)], we also predict a novel steady state quantum dynamical phase transition for an asymmetric configuration of drive and dissipation.

Stephan Mandt; Darius Sadri; Andrew A. Houck; Hakan E. Türeci

2014-10-12

280

Controlling the quantum dynamics of a mesoscopic spin bath in diamond  

E-print Network

Understanding and mitigating decoherence is a key challenge for quantum science and technology. The main source of decoherence for solid-state spin systems is the uncontrolled spin bath environment. Here, we demonstrate quantum control of a mesoscopic spin bath in diamond at room temperature that is composed of electron spins of substitutional nitrogen impurities. The resulting spin bath dynamics are probed using a single nitrogen-vacancy (NV) centre electron spin as a magnetic field sensor. We exploit the spin bath control to dynamically suppress dephasing of the NV spin by the spin bath. Furthermore, by combining spin bath control with dynamical decoupling, we directly measure the coherence and temporal correlations of different groups of bath spins. These results uncover a new arena for fundamental studies on decoherence and enable novel avenues for spin-based magnetometry and quantum information processing.

G. de Lange; T. van der Sar; M. S. Blok; Z. H. Wang; V. V. Dobrovitski; R. Hanson

2011-04-24

281

Exploring the control landscape for nonlinear quantum dynamics  

NASA Astrophysics Data System (ADS)

Manipulation of a quantum system can be viewed in the framework of a control landscape defined as the physical objective as a functional of the control. Control landscape analyses have thus far considered linear quantum dynamics. This paper extends the analysis of control landscape topology to nonlinear quantum dynamics with the objective of steering a finite-level quantum system from an initial state to a final target state. The analysis rests on the assumptions that (i) the final state is reachable from the initial state, (ii) the differential mapping from the control to the state is surjective, and (iii) the control resources are unconstrained. Under these assumptions, landscape critical points (i.e., where the slope vanishes) for nonlinear quantum dynamics only appear as the global maximum and minimum; thus, the landscape is free of traps. Moreover, the landscape Hessian (i.e., the second derivative with respect to the control) at the global maximum has finite rank, indicating the presence of a large level set of optimal controls that preserve the value of the maximum. Extensive numerical simulations on finite-level models of the Gross-Pitaevskii equation confirm the trap-free nature of the landscape as well as the Hessian rank analysis, using either an applied electric field or a tunable condensate two-body interaction strength as the control. In addition, the control mechanisms arising in the numerical simulations are qualitatively assessed. These results are a generalization of previous findings for the linear Schrödinger equation, and show promise for successful control in a wide range of nonlinear quantum dynamics applications.

Yan, Julia; Hocker, David; Long, Ruixing; Ho, Tak-San; Rabitz, Herschel

2014-06-01

282

Quantum wavepacket ab initio molecular dynamics: Simulating quantum nuclear effects in complex systems  

NASA Astrophysics Data System (ADS)

A methodology, Quantum Wavepacket Ab Initio Molecular Dynamics (QWAIMD), for the efficient, simultaneous dynamics of electrons and nuclei is presented. This approach allows for the quantum-dynamical treatment of a subset of nuclei in complex, molecular systems while treating the remaining nuclei and electrons within in the ab initio molecular dynamics (AIMD) paradigm. Developments of QWAIMD discussed within include: (a) a novel sampling algorithm dubbed Time-Dependent Deterministic Sampling (TDDS), which increases the computational efficiency by several orders of magnitude; (b) generalizations to hybrid QM/QM and QM/MM electronic structure methods via a combination of the ONIOM and empirical valence bond approaches, which may allow for the accurate simulation of large molecules; and (c) a novel velocity-flux autocorrelation function to calculate the vibrational density-of-states of quantum-classical systems. These techniques are benchmarked on calculations of small, hydrogen-bound clusters. Furthermore, since many chemical processes occur over time-scales inaccessible to computation, a scheme is discussed and benchmarked here which can bias both QWAIMD and classical-AIMD dynamics to sample these long time-scale events, like proton transfer in enzyme catalysis. Finally, hydrogen tunneling in an enzyme, soybean lipoxygenase-1 (SLO-1) is examined by calculating the orbitals (eigenstates) of the transferring proton along the reaction coordinate. This orbital analysis is then supplemented by using quantum measurement theory to reexamine the transfer.

Sumner, Isaiah

283

Experimental reconstruction of work distribution and study of fluctuation relations in a closed quantum system.  

PubMed

We report the experimental reconstruction of the nonequilibrium work probability distribution in a closed quantum system, and the study of the corresponding quantum fluctuation relations. The experiment uses a liquid-state nuclear magnetic resonance platform that offers full control on the preparation and dynamics of the system. Our endeavors enable the characterization of the out-of-equilibrium dynamics of a quantum spin from a finite-time thermodynamics viewpoint. PMID:25325627

Batalhăo, Tiago B; Souza, Alexandre M; Mazzola, Laura; Auccaise, Ruben; Sarthour, Roberto S; Oliveira, Ivan S; Goold, John; De Chiara, Gabriele; Paternostro, Mauro; Serra, Roberto M

2014-10-01

284

Experimental Reconstruction of Work Distribution and Study of Fluctuation Relations in a Closed Quantum System  

NASA Astrophysics Data System (ADS)

We report the experimental reconstruction of the nonequilibrium work probability distribution in a closed quantum system, and the study of the corresponding quantum fluctuation relations. The experiment uses a liquid-state nuclear magnetic resonance platform that offers full control on the preparation and dynamics of the system. Our endeavors enable the characterization of the out-of-equilibrium dynamics of a quantum spin from a finite-time thermodynamics viewpoint.

Batalhăo, Tiago B.; Souza, Alexandre M.; Mazzola, Laura; Auccaise, Ruben; Sarthour, Roberto S.; Oliveira, Ivan S.; Goold, John; De Chiara, Gabriele; Paternostro, Mauro; Serra, Roberto M.

2014-10-01

285

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

286

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

287

Timescales in Quantum Open Systems: Dynamics of Time Correlation Functions and Stochastic Quantum Trajectory Methods in Non-Markovian Systems  

Microsoft Academic Search

The dynamics of a system in interaction with another system, the later considered as a reservoir, is studied in many different\\u000a domains in physics. This approach is useful not only to address fundamental questions like quantum decoherence decoherence\\u000a and the measurement problem [1] but also to deal with practical and theoretical problems appearing in the emerging fields\\u000a of nanotechnology nanotechnology

Daniel Alonso; Inés de Vega

2010-01-01

288

Study of atmospheric dynamics  

NASA Technical Reports Server (NTRS)

In order to better understand the dynamics of the global atmosphere, a data set of precision temperature measurements was developed using the NASA built Microwave Sounding Unit. Modeling research was carried out to validate global model outputs using various satellite data. Idealized flows in a rotating annulus were studied and applied to the general circulation of the atmosphere. Dynamic stratospheric ozone fluctuations were investigated. An extensive bibliography and several reprints are appended.

Mcnider, Richard T.; Christy, John R.; Cox, Gregory N.

1993-01-01

289

Quantum and nanoscale modelling of exciton dynamics in polymeric systems.  

PubMed

One of the factors that limit the efficiency of polymer-based optoelectronic devices, such as photovoltaic solar cells and light emitting diodes, is the exciton diffusion within the polymeric network. Due to the amorphous nature the of polymeric materials, the diffusion of excitons is limited by the energetic and spatial disorder in such systems, which is a consequence not only of the chemical structure of the polymer but also from its morphology at nanoscale. To get a deep understanding on how such effects influence exciton dynamics we performed a quantum molecular dynamics simulations to determine the energetic disorder within the polymer system, and Monte Carlo simulations to study exciton diffusion in three-dimensional (3D) polymer networks that present both spatial and energetic disorder at nanometre scale. Our results show clearly that exciton diffusion in poly(p-phenylenevinylene) (PPV) occurs preferentially in the direction parallel to the electrodes surface for a polymer-based optoelectronic devices with the orientation of the conjugated strands similar to those obtained by the spin-coating technique and the decay of such excitons occurs preferentially in longer strands which allow us to get insight on exciton behaviour in polymeric systems that are not possible to be obtained directly from the experiments. PMID:20352770

Barbosa, H M C; Correia, H M G; Ramos, M M D

2010-02-01

290

Quantum-Gravity Induced Lorentz Violation and Dynamical Mass Generation  

E-print Network

In Ref. [1] (by J. Alexandre) 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 [1], 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 note, 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.

Nick E. Mavromatos

2010-11-15

291

Massive Quantum Memories by Periodically Inverted Dynamic Evolutions  

E-print Network

We introduce a general scheme to realize perfect quantum state reconstruction and storage in systems of interacting qubits. This novel approach is based on the idea of controlling the residual interactions by suitable external controls that, acting on the inter-qubit couplings, yield time-periodic inversions in the dynamical evolution, thus cancelling exactly the effects of quantum state diffusion. We illustrate the method for spin systems on closed rings with XY residual interactions, showing that it enables the massive storage of arbitrarily large numbers of local states, and we demonstrate its robustness against several realistic sources of noise and imperfections.

S. M. Giampaolo; F. Illuminati; A. Di Lisi; G. Mazzarella

2005-06-27

292

Hierarchy of Stochastic Pure States for Open Quantum System Dynamics  

NASA Astrophysics Data System (ADS)

We derive a hierarchy of stochastic evolution equations for pure states (quantum trajectories) for open quantum system dynamics with non-Markovian structured environments. This hierarchy of pure states (HOPS) is generally applicable and provides the exact reduced density operator as an ensemble average over normalized states. The corresponding nonlinear equations are presented. We demonstrate that HOPS provides an efficient theoretical tool and apply it to the spin-boson model, the calculation of absorption spectra of molecular aggregates, and energy transfer in a photosynthetic pigment-protein complex.

Suess, D.; Eisfeld, A.; Strunz, W. T.

2014-10-01

293

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

294

Overview of some results in my thermodynamics, quantum mechanics, and molecular dynamics simulations research  

Microsoft Academic Search

Described here in sectional form are some simultaneous developments and results in [A] Continuum thermodynamics with applications, including electrochemical systems, [B] Statistical thermodynamics [C] Foundational studies in mechanics, quantum mechanics and radiation, and [D] Molecular dynamics and NEMD simulations of complex systems which are chemical reaction theories deduced from computer simulations. These topics were investigated over a two decade period

Christopher G. Jesudason

2009-01-01

295

Entanglement and dynamic stability of Nash equilibria in a symmetric quantum game  

Microsoft Academic Search

We study the evolutionary stability of Nash equilibria (NE) in a symmetric quantum game played by the recently proposed scheme of applying ‘identity’ and ‘Pauli spin-flip’ operators on an initial state with classical probabilities. We show that in this symmetric game dynamic stability of a NE can be changed when the game changes its form, for example, from classical to

A. Iqbal; A. H. Toor

2001-01-01

296

First-principles quantum molecular dynamics study of TixZr1-xN(111)/SiNy heterostructures and comparison with experimental results  

NASA Astrophysics Data System (ADS)

The heterostructures of five monolayers B1-TixZr1-xN(111), x = 1.0, 0.6, 0.4 and 0.0 (where B1 is a NaCl-type structure) with one monolayer of a Si3N4-like Si2N3 interfacial layer were investigated by means of first-principles quantum molecular dynamics and a structure optimization procedure using the Quantum ESPRESSO code. Slabs consisting of stoichiometric TiN and ZrN and random, as well as segregated, B1-TixZr1-xN(111) solutions were considered. The calculations of the B1-TixZr1-xN solid solutions, as well as of the heterostructures, showed that the pseudo-binary TiN-ZrN system exhibits a miscibility gap. The segregated heterostructures in which Zr atoms surround the SiyNz interface were found to be the most stable. For the Zr-rich heterostructures, the total energy of the random solid solution was lower compared to that of the segregated one, whereas for the Ti-rich heterostructures the opposite tendency was observed. Hard and super hard Zr-Ti-Si-N coatings with thicknesses from 2.8 to 3.5 ?m were obtained using a vacuum arc source with high frequency stimulation. The samples were annealed in a vacuum and in air at 1200 °C. Experimental investigations of Zr-Ti-N, Zr-Ti-Si-N and Ti-Si-N coatings with different Zr, Ti and Si concentrations were carried out for comparison with results obtained from TixZr1-xN(111)/SiNy systems. During annealing, the hardness of the best series samples was increased from (39.6 ą 1.4) to 53.6 GPa, which seemed to indicate that a spinodal segregation along grain interfaces was finished. A maximum hardness of 40.8 GPa before and 55 GPa after annealing in air at 500 °C was observed for coatings with a concentration of elements of Si ? (7-8) at.%, Ti ? 22 at.% and Zr ? 70 at.%.

Ivashchenko, Volodymyr; Veprek, Stan; Pogrebnjak, Alexander; Postolnyi, Bogdan

2014-04-01

297

Quantum Dynamical Applications of Salem's Theorem  

NASA Astrophysics Data System (ADS)

We consider the survival probability of a state that evolves according to the Schrödinger dynamics generated by a self-adjoint operator H. We deduce from a classical result of Salem that upper bounds for the Hausdorff dimension of a set supporting the spectral measure associated with the initial state imply lower bounds on a subsequence of time scales for the survival probability. This general phenomenon is illustrated with applications to the Fibonacci operator and the critical almost Mathieu operator. In particular, this gives the first quantitative dynamical bound for the critical almost Mathieu operator.

Damanik, David; Del Rio, Rafael

2009-07-01

298

Dynamical dipole gamma radiation in heavy-ion collisions on the basis of a quantum molecular dynamics model  

SciTech Connect

Dynamical dipole gamma-ray emission in heavy-ion collisions is explored in the framework of the quantum molecular dynamics model. The studies are focused on systems of {sup 40}Ca bombarding {sup 48}Ca and its isotopes at different incident energies and impact parameters. Yields of gamma rays are calculated and the centroid energy and dynamical dipole emission width of the gamma spectra are extracted to investigate the properties of gamma emission. In addition, sensitivities of dynamical dipole gamma-ray emission to the isospin and the symmetry energy coefficient of the equation of state are studied. The results show that detailed study of dynamical dipole gamma radiation can provide information on the equation of state and the symmetry energy around the normal nuclear density.

Wu, H. L. [Shanghai Institute of Applied Physics, Chinese Academy of Sciences, P.O. Box 800-204, Shanghai 201800 (China); Graduate School of the Chinese Academy of Sciences, Beijing 100080 (China); Tian, W. D.; Ma, Y. G.; Cai, X. Z.; Chen, J. G.; Fang, D. Q.; Guo, W.; Wang, H. W. [Shanghai Institute of Applied Physics, Chinese Academy of Sciences, P.O. Box 800-204, Shanghai 201800 (China)

2010-04-15

299

Indicators of quantum coherence in light-harvesting dynamics  

NASA Astrophysics Data System (ADS)

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 the probability for the dynamics to successfully distinguish different initial photo-excitation conditions. I will also discuss how initial state distinguisability can provide information on spatially correlated phonon fluctuations as well as on the non-markovian character of the quantum dynamics. The prototype systems considered here are cryptophyte light-harvesting antennae isolated from marine algae [2, 3]. Experimental quantification of state distinguishability can be realized by monitoring the evolution of selected off-diagonal density matrix elements and therefore it could be achieved with current two-dimensional spectroscopy techniques. [4pt] [1] A. Olaya-Castro and G. D. Scholes, "Energy transfer from F"orster-Dexter theory to quantum coherent light-harvesting", to appear in Int. Rev. Phys. Chem. (2010) [0pt] [2] E. Collini, C.Y. Wong, K.E. Wilk, P.M.G. Curmi, P. Brumer and G.D. Scholes, "Coherently wired light-harvesting in photosynthetic marine algae at ambient temperature" Nature, 463, 644-647 (2010) [0pt] [3] A. Kolli, A Nazir, F. Fassioli, R. Dinshaw, G D Scholes, and A Olaya-Castro, "Energy transfer dynamics in cryptophyte antennae proteins", submitted for publication (2010)

Olaya-Castro, Alexandra

2011-03-01

300

Dynamic control of plasmon generation by an individual quantum system.  

PubMed

Controlling light on the nanoscale in a similar way as electric currents has the potential to revolutionize the exchange and processing of information. Although light can be guided on this scale by coupling it to plasmons, that is, collective electron oscillations in metals, their local electronic control remains a challenge. Here, we demonstrate that an individual quantum system is able to dynamically gate the electrical plasmon generation. Using a single molecule in a double tunnel barrier between two electrodes we show that this gating can be exploited to monitor fast changes of the quantum system itself and to realize a single-molecule plasmon-generating field-effect transistor operable in the gigahertz range. This opens new avenues toward atomic scale quantum interfaces bridging nanoelectronics and nanophotonics. PMID:25181332

Große, Christoph; Kabakchiev, Alexander; Lutz, Theresa; Froidevaux, Romain; Schramm, Frank; Ruben, Mario; Etzkorn, Markus; Schlickum, Uta; Kuhnke, Klaus; Kern, Klaus

2014-10-01

301

Optimally combining dynamical decoupling and quantum error correction.  

PubMed

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. PMID:23559088

Paz-Silva, Gerardo A; Lidar, D A

2013-01-01

302

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

303

Quantum Monte Carlo studies of quantum dots in magnetic fields  

Microsoft Academic Search

We have studied the ground and excited states of confined two-dimensional (2D) electrons in various magnetic field strengths by the variational and diffusion Monte Carlo methods. These 2D quantum dots are of great theoretical interest, because it is possible to go from a weakly to a strongly correlated system by tuning the relative strength of the external potential to the

Wolfgang Geist; Lang Zeng; Mei-Yin Chou; Cyrus Umrigar; Francesco Pederiva

2003-01-01

304

Interaction effects in the mesoscopic regime: A quantum Monte Carlo study of irregular quantum dots  

E-print Network

Interaction effects in the mesoscopic regime: A quantum Monte Carlo study of irregular quantum dots-state properties of isolated irregular quantum dots. Quantum Monte Carlo techniques are used to calculate- mation overpredicts the effects of interactions in quantum dots. DOI: 10.1103/PhysRevB.71.241306 PACS

Baranger, Harold U.

305

Dynamics of charge carrier recombination and capture in laser nanostructures with InGaAsSb/AlGaAsSb quantum wells  

SciTech Connect

Time dynamics of photoluminescence intensity was studied in InGaAsSb/AlGaAsSb quantum wells with different compositions of the barrier solid solution and with different width of the quantum wells. The time of charge carrier capture in quantum wells, the energy relaxation times, lifetime related to resonant Auger recombination were estimated.

Vinnichenko, Maxim Ya.; Vorobjev, Leonid E.; Firsov, Dmitry A.; Mashko, Marina O.; Sofronov, Anton N. [St. Petersburg State Polytechnical University, 195251, Polytechnicheskaya str. 29, St. Petersburg (Russian Federation); Shterengas, Leon; Belenky, Gregory [Department of Electrical and Computer Engineering, State University of New York at Stony Brook, New York 11794 (United States)

2013-12-04

306

Dynamics of Symmetry Breaking during Quantum Real-Time Evolution in a Minimal Model System.  

PubMed

One necessary criterion for the thermalization of a nonequilibrium quantum many-particle system is ergodicity. It is, however, not sufficient in cases where the asymptotic long-time state lies in a symmetry-broken phase but the initial state of nonequilibrium time evolution is fully symmetric with respect to this symmetry. In equilibrium, one particular symmetry-broken state is chosen as a result of an infinitesimal symmetry-breaking perturbation. From a dynamical point of view the question is: Can such an infinitesimal perturbation be sufficient for the system to establish a nonvanishing order during quantum real-time evolution? We study this question analytically for a minimal model system that can be associated with symmetry breaking, the ferromagnetic Kondo model. We show that after a quantum quench from a completely symmetric state the system is able to break its symmetry dynamically and discuss how these features can be observed experimentally. PMID:25396355

Heyl, Markus; Vojta, Matthias

2014-10-31

307

Fingerprints of Classical Instability in Open Quantum Dynamics  

E-print Network

The dynamics near a hyperbolic point in phase space is modelled by an inverted harmonic oscillator. We investigate the effect of the classical instability on the open quantum dynamics of the oscillator, introduced through the interaction with a thermal bath, using both the survival probability function and the rate of von Neumann entropy increase, for large times. In this parameter range we prove, using influence functional techniques, that the survival probability function decreases exponentially at a rate, K', depending not only on the measure of instability in the model but also on the strength of interaction with the environment. We also show that K' determines the rate of von Neumann entropy increase and that this result is independent of the temperature of the environment. This generalises earlier results which are valid in the limit of vanishing dissipation. The validity of inferring similar rates of survival probability decrease and entropy increase for quantum chaotic systems is also discussed.

Paul A. Miller; Sarben Sarkar

1998-07-03

308

Recurrence properties of quantum observables in wave packet dynamics  

E-print Network

We investigate the recurrence properties of the time series of quantum mechanical expectation values, in terms of two representative models for a single-mode radiation field interacting with a nonlinear medium. From recurrence-time distributions, return maps and recurrence plots, we conclude that the dynamics of appropriate observables pertaining to the field can vary from quasiperiodicity to hyperbolicity, depending on the extent of the nonlinearity and of the departure from coherence of the initial state of the field. We establish that, in a simple bipartite model in which the field is effectively an open quantum system, a decaying exponential recurrence-time distribution, characteristic of a hyperbolic dynamical system, is associated with chaotic temporal evolution as characterized by a positive Liapunov exponent.

C. Sudheesh; S. Lakshmibala; V. Balakrishnan

2009-12-29

309

Recurrence properties of quantum observables in wave packet dynamics  

E-print Network

We investigate the recurrence properties of the time series of quantum mechanical expectation values, in terms of two representative models for a single-mode radiation field interacting with a nonlinear medium. From recurrence-time distributions, return maps and recurrence plots, we conclude that the dynamics of appropriate observables pertaining to the field can vary from quasiperiodicity to hyperbolicity, depending on the extent of the nonlinearity and of the departure from coherence of the initial state of the field. We establish that, in a simple bipartite model in which the field is effectively an open quantum system, a decaying exponential recurrence-time distribution, characteristic of a hyperbolic dynamical system, is associated with chaotic temporal evolution as characterized by a positive Liapunov exponent.

Sudheesh, C; Balakrishnan, V

2009-01-01

310

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. PMID:22493228

Gritsev, V.; Polkovnikov, A.

2012-01-01

311

Non-Markovian Dynamical Maps: Numerical Processing of Open Quantum Trajectories Javier Cerrillo and Jianshu Cao*  

E-print Network

of an open quantum system encode the key information of its underlying dynamical correlations, which in turn of quantum dissipation and predicts the noncanonical equilibrium distribution due to the system to reconstruct the dynamical operators (the system Hamiltonian and memory kernel) from quantum trajectories

Cao, Jianshu

312

Solutions of mixed quantum-classical dynamics in multiple dimensions using classical trajectories  

E-print Network

evolution schemes to describe the dynamics of a system exhibiting important quantum effects. The firstSolutions of mixed quantum-classical dynamics in multiple dimensions using classical trajectories The multithreads algorithm for solving the mixed quantum-classical Liouville equation is extended to systems

Schofield, Jeremy

313

Density-dependent carrier dynamics in a quantum dots-in-a-well heterostructure  

E-print Network

transmission spectroscopy to temporally and spectrally resolve density-dependent carrier dynamics in a quantumDensity-dependent carrier dynamics in a quantum dots-in-a-well heterostructure R. P. Prasankumar,1 The incorporation of semiconductor quantum dots into different heterostructures for applications in nanoscale lasing

Krishna, Sanjay

314

Shannon Entropy Based Time-Dependent Deterministic Sampling for Efficient "On-the-Fly" Quantum Dynamics  

E-print Network

Shannon Entropy Based Time-Dependent Deterministic Sampling for Efficient "On-the-Fly" Quantum of various regions on a potential energy surface and to be employed in "on-the-fly" quantum dynamics. Shannon to be performed during on-the-fly quantum dynamics is fewer when the Shannon entropy based sampling functions

Iyengar, Srinivasan S.

315

Mixed quantum-classical molecular dynamics: Aspects of the multithreads algorithm  

E-print Network

Mixed quantum-classical molecular dynamics: Aspects of the multithreads algorithm Chun-Cheng Wan years to develop procedures that incorporate quantum transitions into a clas- sical evolution scheme.1 avenue for incorporating quantum ef- fects into classical molecular dynamics is based on the mixed

Schofield, Jeremy

316

Non-relativistic Gravity in Entropic Quantum Dynamics  

SciTech Connect

Symmetries and transformations are explored in the framework of entropic quantum dynamics. This discussion leads to two conditions that are required for any transformation to qualify as a symmetry. The heart of this work lies in the application of these conditions to the extended Galilean transformation, which admits features of both special and general relativity. The effective gravitational potential representative of the strong equivalence principle arises naturally.

Johnson, David T.; Caticha, Ariel [Department of Physics, University at Albany-SUNY, Albany, NY 12222 (United States)

2011-03-14

317

Non-Markovian Quantum Dynamics and Classical Chaos  

E-print Network

We study the influence of a chaotic environment in the evolution of an open quantum system. We show that there is an inverse relation between chaos and non-Markovianity. In particular we remark the deep relation of the short time non-Markovian behavior with the revivals of the average fidelity amplitude -- a fundamental quantity used to measure sensitivity to perturbations, and identify quantum chaos. The long time behavior is established as a finite size effect which vanishes for large enough environments.

Garcia-Mata, I; Wisniacki, D A

2012-01-01

318

Relativistic Quantum Dynamics: A non-traditional perspective on space, time, particles, fields, and action-at-a-distance  

E-print Network

This book is an attempt to build a consistent relativistic quantum theory of interacting particles. In the first part of the book "Quantum electrodynamics" we follow rather traditional approach to particle physics. Our discussion proceeds systematically from the principle of relativity and postulates of quantum measurements to the renormalization in quantum electrodynamics. In the second part of the book "The quantum theory of particles" this traditional approach is reexamined. We find that formulas of special relativity should be modified to take into account particle interactions. We also suggest reinterpreting quantum field theory in the language of physical "dressed" particles. This formulation eliminates the need for renormalization and opens up a new way for studying dynamical and bound state properties of quantum interacting systems. The developed theory is applied to realistic physical objects and processes including the hydrogen atom, the decay law of moving unstable particles, the dynamics of interacting charges, relativistic and quantum gravitational effects. These results force us to take a fresh look at some core issues of modern particle theories, in particular, the Minkowski space-time unification, the role of quantum fields and renormalization and the alleged impossibility of action-at-a-distance. A new perspective on these issues is suggested. It can help to solve the old problem of theoretical physics -- a consistent unification of relativity and quantum mechanics.

Eugene V. Stefanovich

2005-04-08

319

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

320

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

321

Quantum dynamics of the avian compass  

E-print Network

The ability of migratory birds to orient relative to the Earth's magnetic field is believed to involve a coherent superposition of two spin states of a radical electron pair. However, the mechanism by which this coherence can be maintained in the face of strong interactions with the cellular environment has remained unclear. This Letter addresses the problem of decoherence between two electron spins due to hyperfine interaction with a bath of spin 1/2 nuclei. Dynamics of the radical pair density matrix are derived and shown to yield a simple mechanism for sensing magnetic field orientation. Rates of dephasing and decoherence are calculated ab initio and found to yield millisecond coherence times, consistent with behavioral experiments.

Zachary B. Walters

2012-08-13

322

Quantum dynamics of the avian compass  

NASA Astrophysics Data System (ADS)

The ability of migratory birds to orient relative to the Earth's magnetic field is believed to involve a coherent superposition of two spin states of a radical electron pair. However, the mechanism by which this coherence can be maintained in the face of strong interactions with the cellular environment has remained unclear. This paper addresses the problem of decoherence between two electron spins due to hyperfine interaction with a bath of spin-1/2 nuclei. Dynamics of the radical pair density matrix are derived and shown to yield a simple mechanism for sensing magnetic field orientation. Rates of dephasing and decoherence are calculated ab initio and found to yield millisecond coherence times, consistent with behavioral experiments.

Walters, Zachary B.

2014-10-01

323

Dynamics of quantum turbulence of different spectra  

PubMed Central

Turbulence in a superfluid in the zero-temperature limit consists of a dynamic tangle of quantized vortex filaments. Different types of turbulence are possible depending on the level of correlations in the orientation of vortex lines. We provide an overview of turbulence in superfluid 4He with a particular focus on recent experiments probing the decay of turbulence in the zero-temperature regime below 0.5 K. We describe extensive measurements of the vortex line density during the free decay of different types of turbulence: ultraquantum and quasiclassical turbulence in both stationary and rotating containers. The observed decays and the effective dissipation as a function of temperature are compared with theoretical models and numerical simulations. PMID:24704876

Walmsley, Paul; Zmeev, Dmitry; Pakpour, Fatemeh; Golov, Andrei

2014-01-01

324

Comparative Study of the Performance of Quantum Annealing and Simulated Annealing  

E-print Network

Relations of simulated annealing and quantum annealing are studied by a mapping from the transition matrix of classical Markovian dynamics of the Ising model to a quantum Hamiltonian and vice versa. It is shown that these two operators, the transition matrix and the Hamiltonian, share the eigenvalue spectrum. Thus, if simulated annealing with slow temperature change does not encounter a difficulty caused by an exponentially long relaxation time at a first-order phase transition, the same is true for the corresponding process of quantum annealing in the adiabatic limit. One of the important differences between the classical-to-quantum mapping and the converse quantum-to-classical mapping is that the Markovian dynamics of a short-range Ising model is mapped to a short-range quantum system, but the converse mapping from a short-range quantum system to a classical one results in long-range interactions. This leads to a difference in efficiencies that simulated annealing can be efficiently simulated by quantum annealing but the converse is not necessarily true. We conclude that quantum annealing is easier to implement and is more flexible than simulated annealing. We also point out that the present mapping can be extended to accommodate explicit time dependence of temperature, which is used to justify the quantum-mechanical analysis of simulated annealing by Somma, Batista, and Ortiz. Additionally, an alternative method to solve the non-equilibrium dynamics of the one-dimensional Ising model is provided through the classical-to-quantum mapping.

Hidetoshi Nishimori; Junichi Tsuda; Sergey Knysh

2014-09-23

325

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. PMID:23400242

Grczelschak-Mick, Nicole

2013-01-01

326

Quantum-fluid-dynamics approach for strong-field processes: Application to the study of multiphoton ionization and high-order harmonic generation of He and Ne atoms in intense laser fields  

NASA Astrophysics Data System (ADS)

We explore the feasibility of extending the quantum-fluid dynamics (QFD) approach for quantitative investigation of nonlinear optical processes of many-electron quantum systems in intense laser fields. Through the amalgamation of the QFD and density-functional theory (DFT), a single time-dependent hydrodynamical equation of motion can be derived. This equation has the form of a generalized nonlinear Schrödinger equation (GNLSE) but includes the many-body effects through a local time-dependent exchange-correlation potential. The time-dependent generalized pseudospectral method is extended to the solution of the GNLSE in spherical coordinates, allowing nonuniform spatial discretization and efficient, accurate solution of the hydrodynamical density and wave function in space and time. The procedure is applied to the study of multiphoton ionization (MPI) and high-order harmonic generation (HHG) of He and Ne atoms in intense laser fields. Excellent agreement with other recent self-interaction-free time-dependent DFT calculations is obtained for He, while for Ne, good agreement is achieved. Four different exchange-correlation energy functionals are used in the study with an aim to explore the roles of exchange and correlation on MPI/HHG processes in details. The method offers a conceptually appealing and computationally practical approach for nonperturbative treatment of strong-field processes of many-electron systems beyond the time-dependent Hartree-Fock level.

Roy, Amlan K.; Chu, Shih-I.

2002-04-01

327

Long and short time quantum dynamics: III. Transients  

NASA Astrophysics Data System (ADS)

The quantum transport equations for fast transients have the structure of a Generalized Master Equations for the single-particle distribution, with causal memory terms. Nonequilibrium Green's functions are reduced to GME if the Generalized Kadanoff-Baym Ansatz is applied. This Ansatz has been used with success both to non-linear transport and to optical transients in semi-conductors; further progress is linked with its extension to a family of the Causal Ansatzes, differing primarily in renormalization of the propagators. For the switch-on non-equilibrium states, generated by a perturbation from equilibrium, the renormalization to the dark dressed Green's function followed by calculation of the induced self-energies is a productive direction. It also circumvents the problem of correlated initial conditions, far from a general solution otherwise. Such initial conditions appear as incompatible with a Causal Ansatz in general. The presently available formalism permits to study a transient process in the whole time range using the complete NGF, but making a flexible Ansatz-based reduction appropriate to the stage of dynamic evolution.

Špi?ka, Václav; Velický, Bed?ich; Kalvová, And?la

2005-10-01

328

Canonical versus noncanonical equilibration dynamics of open quantum systems  

NASA Astrophysics Data System (ADS)

In statistical mechanics, any quantum system in equilibrium with its weakly coupled reservoir is described by a canonical state at the same temperature as the reservoir. Here, by studying the equilibration dynamics of a harmonic oscillator interacting with a reservoir, we evaluate microscopically the condition under which the equilibration to a canonical state is valid. It is revealed that the non-Markovian effect and the availability of a stationary state of the total system play a profound role in the equilibration. In the Markovian limit, the conventional canonical state can be recovered. In the non-Markovian regime, when the stationary state is absent, the system equilibrates to a generalized canonical state at an effective temperature; whenever the stationary state is present, the equilibrium state of the system cannot be described by any canonical state anymore. Our finding of the physical condition on such noncanonical equilibration might have significant impact on statistical physics. A physical scheme based on circuit QED is proposed to test our results.

Yang, Chun-Jie; An, Jun-Hong; Luo, Hong-Gang; Li, Yading; Oh, C. H.

2014-08-01

329

Canonical versus noncanonical equilibration dynamics of open quantum systems.  

PubMed

In statistical mechanics, any quantum system in equilibrium with its weakly coupled reservoir is described by a canonical state at the same temperature as the reservoir. Here, by studying the equilibration dynamics of a harmonic oscillator interacting with a reservoir, we evaluate microscopically the condition under which the equilibration to a canonical state is valid. It is revealed that the non-Markovian effect and the availability of a stationary state of the total system play a profound role in the equilibration. In the Markovian limit, the conventional canonical state can be recovered. In the non-Markovian regime, when the stationary state is absent, the system equilibrates to a generalized canonical state at an effective temperature; whenever the stationary state is present, the equilibrium state of the system cannot be described by any canonical state anymore. Our finding of the physical condition on such noncanonical equilibration might have significant impact on statistical physics. A physical scheme based on circuit QED is proposed to test our results. PMID:25215704

Yang, Chun-Jie; An, Jun-Hong; Luo, Hong-Gang; Li, Yading; Oh, C H

2014-08-01

330

Advantages of randomization in coherent quantum dynamical control  

NASA Astrophysics Data System (ADS)

Control scenarios have been identified where the use of randomized design may substantially improve the performance of dynamical decoupling methods (Santos and Viola 2006 Phys. Rev. Lett. 97 150501). Here, by focusing on the suppression of internal unwanted interactions in closed quantum systems, we review and further elaborate on the advantages of randomization at long evolution times. By way of illustration, special emphasis is devoted to isolated Heisenberg chains of coupled spin-1/2 particles. In particular, for nearest-neighbor interactions, two types of decoupling cycles are contrasted: inefficient averaging, whereby the number of control actions increases exponentially with the system size, and efficient averaging associated to a fixed-size control group. The latter allows for analytical and numerical studies of efficient decoupling schemes created by exploiting and merging together randomization and deterministic strategies, such as symmetrization, concatenation and cyclic permutations. Notably, sequences capable of removing interactions up to third order in the achievable control timescale are explicitly constructed, and a numerical algorithm to search for optimal decoupling sequences is proposed. The consequences of faulty controls in deterministic versus randomized schemes are also analyzed.

Santos, Lea F.; Viola, Lorenza

2008-08-01

331

Energy conserving approximations to the quantum potential: Dynamics with linearized quantum force  

NASA Astrophysics Data System (ADS)

Solution of the Schrödinger equation within the de Broglie-Bohm formulation is based on propagation of trajectories in the presence of a nonlocal quantum potential. We present a new strategy for defining approximate quantum potentials within a restricted trial function by performing the optimal fit to the log-derivatives of the wave function density. This procedure results in the energy-conserving dynamics for a closed system. For one particular form of the trial function leading to the linear quantum force, the optimization problem is solved analytically in terms of the first and second moments of the weighted trajectory distribution. This approach gives exact time-evolution of a correlated Gaussian wave function in a locally quadratic potential. The method is computationally cheap in many dimensions, conserves total energy and satisfies the criterion on the average quantum force. Expectation values are readily found by summing over trajectory weights. Efficient extraction of the phase-dependent quantities is discussed. We illustrate the efficiency and accuracy of the linear quantum force approximation by examining a one-dimensional scattering problem and by computing the wavepacket reaction probability for the hydrogen exchange reaction and the photodissociation spectrum of ICN in two dimensions.

Garashchuk, Sophya; Rassolov, Vitaly A.

2004-01-01

332

Energy conserving approximations to the quantum potential: dynamics with linearized quantum force.  

PubMed

Solution of the Schrodinger equation within the de Broglie-Bohm formulation is based on propagation of trajectories in the presence of a nonlocal quantum potential. We present a new strategy for defining approximate quantum potentials within a restricted trial function by performing the optimal fit to the log-derivatives of the wave function density. This procedure results in the energy-conserving dynamics for a closed system. For one particular form of the trial function leading to the linear quantum force, the optimization problem is solved analytically in terms of the first and second moments of the weighted trajectory distribution. This approach gives exact time-evolution of a correlated Gaussian wave function in a locally quadratic potential. The method is computationally cheap in many dimensions, conserves total energy and satisfies the criterion on the average quantum force. Expectation values are readily found by summing over trajectory weights. Efficient extraction of the phase-dependent quantities is discussed. We illustrate the efficiency and accuracy of the linear quantum force approximation by examining a one-dimensional scattering problem and by computing the wavepacket reaction probability for the hydrogen exchange reaction and the photodissociation spectrum of ICN in two dimensions. PMID:15268241

Garashchuk, Sophya; Rassolov, Vitaly A

2004-01-15

333

Non-Markovianity and Indivisible Quantum dynamics of a Apin-S System  

NASA Astrophysics Data System (ADS)

Using a measure for the divisibility of a dynamical map, we study the non-Markovian character of a quantum evolution of a spin-S system, which is in an external field and weakly coupled to a bosonic bath with a certain temperature. The finite-temperature dynamics of the open system is obtained by the time-convolutionless master equation in the secular approximation. Besides the influence of the environmental spectral density function, the external field and low temperatures can affect the quantum non-Markovianity. It is found out that the non-Markovian feature of a dynamical map of a high-dimensional spin system is noticeable in contrast to that of a low-dimension spin system.

Hao, Xiang; Xu, Xue-Fen; Zhu, Shi-Qun

2013-09-01

334

Renormalization group study of random quantum magnets  

E-print Network

We have developed a very efficient numerical algorithm of the strong disorder renormalization group method to study the critical behaviour of the random transverse-field Ising model, which is a prototype of random quantum magnets. With this algorithm we can renormalize an N-site cluster within a time N*log(N), independently of the topology of the graph and we went up to N~4*10^6. We have studied regular lattices with dimension D<=4 as well as Erdos-Renyi random graphs, which are infinite dimensional objects. In all cases the quantum critical behaviour is found to be controlled by an infinite disorder fixed point, in which disorder plays a dominant role over quantum fluctuations. As a consequence the renormalization procedure as well as the obtained critical properties are asymptotically exact for large systems. We have also studied Griffiths singularities in the paramagnetic and the ferromagnetic phases and generalized the numerical algorithm for another random quantum systems.

István A. Kovács; Ferenc Iglói

2011-09-20

335

Computational Studies of Quantum Spin Systems  

E-print Network

These lecture notes introduce quantum spin systems and several computational methods for studying their ground-state and finite-temperature properties. Symmetry-breaking and critical phenomena are first discussed in the simpler setting of Monte Carlo studies of classical spin systems, to illustrate finite-size scaling at continuous and first-order phase transitions. Exact diagonalization and quantum Monte Carlo (stochastic series expansion) algorithms and their computer implementations are then discussed in detail. Applications of the methods are illustrated by results for some of the most essential models in quantum magnetism, such as the S=1/2 Heisenberg antiferromagnet in one and two dimensions, as well as extended models useful for studying quantum phase transitions between antiferromagnetic and magnetically disordered states.

Anders W. Sandvik

2011-01-17

336

The Emergence of Classical Dynamics in a Quantum World  

E-print Network

Ever since the advent of quantum mechanics, it has been clear that the atoms composing matter do not obey Newton's laws. Instead, their behavior is described by the Schroedinger equation. Surprisingly though, until recently, no clear explanation was given for why everyday objects, which are merely collections of atoms, are observed to obey Newton's laws. It would seem that, if quantum mechanics explains all the properties of atoms accurately, they, too, should obey quantum mechanics. This reasoning led some scientists to believe in a distinct macroscopic, or ``big and complicated,'' world in which quantum mechanics fails and classical mechanics takes over, although there has never been experimental evidence for such a failure. Even those who insisted that Newtonian mechanics would somehow emerge from the underlying quantum mechanics as the system became increasingly macroscopic were hindered by the lack of adequate experimental and theoretical tools. In the last decade, however, this quantum-to-classical transition has become accessible to experimental study and quantitative description, and the resulting insights are the subject of this article.

Tanmoy Bhattacharya; Salman Habib; Kurt Jacobs

2004-07-14

337

Novel method for solving the quantum nonlinear dynamics of photons: use of a classical input.  

PubMed

In order to investigate the nonlinear dynamics of photons, one must in principle solve a quantum many-particle problem, which usually requires intensive computation. In this study, we show that the spatial wave function of photons after nonlinear interaction can be obtained with less computation by assuming a classical input pulse and calculating a correlation function in the output field. This method is particularly useful when nonlinear optical media have many mechanical degrees of freedom, where quantum many-particle problems become extremely difficult. PMID:17677844

Koshino, Kazuki

2007-06-01

338

Hydride Transfer in Liver Alcohol Dehydrogenase: Quantum Dynamics, Kinetic Isotope Effects, and Role of Enzyme Motion  

E-print Network

of the transferring hydrogen are incorporated with a mixed quantum/classical molecular dynamics method in which dynamical effects are determined by calculating the transmission coefficients with a reactive flux scheme based on real-time molecular dynamics with quantum transitions (MDQT) surface hopping trajectories

Hammes-Schiffer, Sharon

339

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. PMID:22355756

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

2012-01-01

340

Scaling and relaxational dynamics near Kondo-destroying quantum critical points  

NASA Astrophysics Data System (ADS)

We study the finite-temperature dynamical scaling in the vicinity of the Kondo-destroying quantum critical points in two quantum impurity models. For the pseudogap Anderson model, we use a combination of renormalization group, continuous time quantum Monte Carlo and large-N techniques to obtain the complete scaling functions of the local susceptibility and single-electron Green's function both in the coherent ( ?>T) and relaxational ( ?quantum critical point of heavy fermion metals [2]. For the Bose-Fermi Kondo model, we report related results derived from the continuous time quantum Monte Carlo and large-N methods. [4pt] [1] M. T. Glossop, S. Kirchner, J. H. Pixley, and Q.Si, ``Critical Kondo destruction in a pseudogap Anderson model: scaling and relaxational dynamics,'' to be published (2009). [0pt] [2] S. Friedemann et al., to be published (2009).

Pixley, Jedediah; Glossop, Matthew; Kirchner, Stefan; Si, Qimiao

2010-03-01

341

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

342

Monte Carlo techniques for real-time quantum dynamics  

E-print Network

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 method is 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.

Mark R. Dowling; Matthew J. Davis; Peter D. Drummond; Joel F. Corney

2005-07-01

343

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

2012-06-01

344

Quantum Control of Ultra-cold Atoms: Uncovering a Novel Connection between Two Paradigms of Quantum Nonlinear Dynamics  

E-print Network

Controlling the translational motion of cold atoms using optical lattice potentials is of both theoretical and experimental interest. By designing two on-resonance time sequences of kicking optical lattice potentials, a novel connection between two paradigms of nonlinear mapping systems, i.e., the kicked rotor model and the kicked Harper model, is established. In particular, it is shown that Hofstadter's butterfly quasi-energy spectrum in periodically driven quantum systems may soon be realized experimentally, with the effective Planck constant tunable by varying the time delay between two sequences of control fields. Extensions of this study are also discussed. The results are intended to open up a new generation of cold-atom experiments of quantum nonlinear dynamics

Jiao Wang; Anders S. Mouritzen; Jiangbin Gong

2008-03-27

345

A study of molecular vibrational relaxation mechanism in condensed phase based upon mixed quantum-classical molecular dynamics. II. Noncollisional mechanism for the relaxation of a polar solute in supercritical water  

Microsoft Academic Search

Mixed quantum-classical molecular dynamics method has been applied to vibrational relaxation of a hydrophilic model NO in supercritical water at various densities along an isotherm above the critical temperature. The relaxation rate was determined based on Fermi's golden rule at each state point and showed an inverse S-shaped curve as a function of bulk density. The hydration number was also

Masahiro Sato; Susumu Okazaki

2005-01-01

346

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

2012-11-21

347

Real-time dynamics of dissipative quantum systems  

SciTech Connect

The first part of this thesis motivates a real time approach to the dynamics of dissipative quantum systems. We review previous imaginary time methods for calculating escape rates and discuss their applications to the analysis of data in macroscopic quantum tunneling experiments. In tunneling experiments on heavily damped Superconducting Quantum Interference Devices, the instanton method gave results that compare reasonably well with data. In tunneling experiments on weakly damped Current Biased Josephson Junctions, two problems arise. First, the classical limit of the instanton result disagrees with the classical rate of thermal activation. Second, the instanton method cannot predict the microwave enhancement of escape rates. In the third chapter, we discuss our real time approach to the dynamics of dissipative systems in terms of a kinetic equation for the reduced density matrix. We demonstrate some known equilibrium properties of dissipative systems through the kinetic equation and derived the bath induced widths and energy shifts. In the low damping limit, the kinetic equation reduces to a much simpler master equation. The classical limit of the master equation is completely equivalent to the Fokker-Planck equation that describes thermal activation. In the fourth chapter, we apply the master equation to the problem of tunneling and resonance enhancement of tunneling in weakly damped current biased Josephson junctions. In the classical regime, microwaves of the appropriate frequency induce resonances between many neighboring levels and an asymmetrical resonance peak is measured. We can calibrate the junction parameters by fitting the stationary solution of the master equation to the classical resonance data. In the quantum regime, the stationary solution of the master equation, predicts well-resolved resonance peaks which agree very well with the observed data.

Chow, K.S.

1988-01-01

348

Controlling the dynamics of spontaneous emission from quantum dots by photonic crystals  

NASA Astrophysics Data System (ADS)

Control of spontaneously emitted light lies at the heart of quantum optics. It is essential for diverse applications ranging from miniature lasers and light-emitting diodes, to single-photon sources for quantum information, and to solar energy harvesting. To explore such new quantum optics applications, a suitably tailored dielectric environment is required in which the vacuum fluctuations that control spontaneous emission can be manipulated. Photonic crystals provide such an environment: they strongly modify the vacuum fluctuations, causing the decay of emitted light to be accelerated or slowed down, to reveal unusual statistics, or to be completely inhibited in the ideal case of a photonic bandgap. Here we study spontaneous emission from semiconductor quantum dots embedded in inverse opal photonic crystals. We show that the spectral distribution and time-dependent decay of light emitted from excitons confined in the quantum dots are controlled by the host photonic crystal. Modified emission is observed over large frequency bandwidths of 10%, orders of magnitude larger than reported for resonant optical microcavities. Both inhibited and enhanced decay rates are observed depending on the optical emission frequency, and they are controlled by the crystals' lattice parameter. Our experimental results provide a basis for all-solid-state dynamic control of optical quantum systems.

Lodahl, Peter; Floris van Driel, A.; Nikolaev, Ivan S.; Irman, Arie; Overgaag, Karin; Vanmaekelbergh, Daniël; Vos, Willem L.

2004-08-01

349

Quantum dynamics in continuum for proton transport--generalized correlation.  

PubMed

As a key process of many biological reactions such as biological energy transduction or human sensory systems, proton transport has attracted much research attention in biological, biophysical, and mathematical fields. A quantum dynamics in continuum framework has been proposed to study proton permeation through membrane proteins in our earlier work and the present work focuses on the generalized correlation of protons with their environment. Being complementary to electrostatic potentials, generalized correlations consist of proton-proton, proton-ion, proton-protein, and proton-water interactions. In our approach, protons are treated as quantum particles while other components of generalized correlations are described classically and in different levels of approximations upon simulation feasibility and difficulty. Specifically, the membrane protein is modeled as a group of discrete atoms, while ion densities are approximated by Boltzmann distributions, and water molecules are represented as a dielectric continuum. These proton-environment interactions are formulated as convolutions between number densities of species and their corresponding interaction kernels, in which parameters are obtained from experimental data. In the present formulation, generalized correlations are important components in the total Hamiltonian of protons, and thus is seamlessly embedded in the multiscale/multiphysics total variational model of the system. It takes care of non-electrostatic interactions, including the finite size effect, the geometry confinement induced channel barriers, dehydration and hydrogen bond effects, etc. The variational principle or the Euler-Lagrange equation is utilized to minimize the total energy functional, which includes the total Hamiltonian of protons, and obtain a new version of generalized Laplace-Beltrami equation, generalized Poisson-Boltzmann equation and generalized Kohn-Sham equation. A set of numerical algorithms, such as the matched interface and boundary method, the Dirichlet to Neumann mapping, Gummel iteration, and Krylov space techniques, is employed to improve the accuracy, efficiency, and robustness of model simulations. Finally, comparisons between the present model predictions and experimental data of current-voltage curves, as well as current-concentration curves of the Gramicidin A channel, verify our new model. PMID:22482542

Chen, Duan; Wei, Guo-Wei

2012-04-01

350

Quantum dynamics in continuum for proton transport--Generalized correlation  

PubMed Central

As a key process of many biological reactions such as biological energy transduction or human sensory systems, proton transport has attracted much research attention in biological, biophysical, and mathematical fields. A quantum dynamics in continuum framework has been proposed to study proton permeation through membrane proteins in our earlier work and the present work focuses on the generalized correlation of protons with their environment. Being complementary to electrostatic potentials, generalized correlations consist of proton-proton, proton-ion, proton-protein, and proton-water interactions. In our approach, protons are treated as quantum particles while other components of generalized correlations are described classically and in different levels of approximations upon simulation feasibility and difficulty. Specifically, the membrane protein is modeled as a group of discrete atoms, while ion densities are approximated by Boltzmann distributions, and water molecules are represented as a dielectric continuum. These proton-environment interactions are formulated as convolutions between number densities of species and their corresponding interaction kernels, in which parameters are obtained from experimental data. In the present formulation, generalized correlations are important components in the total Hamiltonian of protons, and thus is seamlessly embedded in the multiscale/multiphysics total variational model of the system. It takes care of non-electrostatic interactions, including the finite size effect, the geometry confinement induced channel barriers, dehydration and hydrogen bond effects, etc. The variational principle or the Euler-Lagrange equation is utilized to minimize the total energy functional, which includes the total Hamiltonian of protons, and obtain a new version of generalized Laplace-Beltrami equation, generalized Poisson-Boltzmann equation and generalized Kohn-Sham equation. A set of numerical algorithms, such as the matched interface and boundary method, the Dirichlet to Neumann mapping, Gummel iteration, and Krylov space techniques, is employed to improve the accuracy, efficiency, and robustness of model simulations. Finally, comparisons between the present model predictions and experimental data of current-voltage curves, as well as current-concentration curves of the Gramicidin A channel, verify our new model. PMID:22482542

Chen, Duan; Wei, Guo-Wei

2012-01-01

351

Decoherence and quantum-classical master equation dynamics.  

PubMed

The conditions under which quantum-classical Liouville dynamics may be reduced to a master equation are investigated. Systems that can be partitioned into a quantum-classical subsystem interacting with a classical bath are considered. Starting with an exact non-Markovian equation for the diagonal elements of the density matrix, an evolution equation for the subsystem density matrix is derived. One contribution to this equation contains the bath average of a memory kernel that accounts for all coherences in the system. It is shown to be a rapidly decaying function, motivating a Markovian approximation on this term in the evolution equation. The resulting subsystem density matrix equation is still non-Markovian due to the fact that bath degrees of freedom have been projected out of the dynamics. Provided the computation of nonequilibrium average values or correlation functions is considered, the non-Markovian character of this equation can be removed by lifting the equation into the full phase space of the system. This leads to a trajectory description of the dynamics where each fictitious trajectory accounts for decoherence due to the bath degrees of freedom. The results are illustrated by computations of the rate constant of a model nonadiabatic chemical reaction. PMID:17381198

Grunwald, Robbie; Kapral, Raymond

2007-03-21

352

Equation of state of dense plasmas: Orbital-free molecular dynamics as the limit of quantum molecular dynamics for high-Z elements  

NASA Astrophysics Data System (ADS)

The applicability of quantum molecular dynamics to the calculation of the equation of state of a dense plasma is limited at high temperature by computational cost. Orbital-free molecular dynamics, based on a semiclassical approximation and possibly on a gradient correction, is a simulation method available at high temperature. For a high-Z element such as lutetium, we examine how orbital-free molecular dynamics applied to the equation of state of a dense plasma can be regarded as the limit of quantum molecular dynamics at high temperature. For the normal mass density and twice the normal mass density, we show that the pressures calculated with the quantum approach converge monotonically towards those calculated with the orbital-free approach; we observe a faster convergence when the orbital-free approach includes the gradient correction. We propose a method to obtain an equation of state reproducing quantum molecular dynamics results up to high temperatures where this approach cannot be directly implemented. With the results already obtained for low-Z plasmas, the present study opens the way for reproducing the quantum molecular dynamics pressure for all elements up to high temperatures.

Danel, J.-F.; Blottiau, P.; Kazandjian, L.; Piron, R.; Torrent, M.

2014-10-01

353

A new time-frequency method to reveal quantum dynamics of atomic hydrogen in intense laser pulses: Synchrosqueezing Transform  

E-print Network

This study introduces a new adaptive time-frequency (TF) analysis technique, synchrosqueezing transform (SST), to explore the dynamics of a laser-driven hydrogen atom at an {\\it ab initio} level, upon which we have demonstrated its versatility as a new viable venue for further exploring quantum dynamics. For a signal composed of oscillatory components which can be characterized by instantaneous frequency, the SST enables rendering the decomposed signal based on the phase information inherited in the linear TF representation with mathematical support. Compared with the classical type TF methods, the SST clearly depicts several intrinsic quantum dynamical processes such as selection rules, AC Stark effects, and high harmonic generation.

Sheu, Yae-lin; Wu, Hau-tieng; Li, Peng-Cheng; Chu, Shih-I

2014-01-01

354

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

SciTech Connect

The main 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, and extends them to understand some important properties of materials in condensed phases and interstellar medium as well as in combustion environments.

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

2012-05-29

355

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

356

Euler & Lagrange versus Heisenberg & Schroedinger: Dynamical Pictures in Classical and Quantum Mechanics  

E-print Network

Using quantum-classical analogies, we find that dynamical pictures of quantum mechanics have precise counterparts in classical mechanics. In particular, the Eulerian and Lagrangian descriptions of fluid dynamics in classical mechanics are the analogs of the Schroedinger and Heisenberg pictures in quantum mechanics, respectively. Similarities between classical and quantum dynamical pictures are explored within the framework of the Koopman-von Neumann formalism. These allow for a natural definition of various dynamical pictures in classical mechanics as well as the application of classical concepts to quantum dynamics. As an illustration, we use the interaction picture to find the classical evolution of an ensemble of particles of equal initial momenta and arbitrary configuration density under the action of a constant force in one dimension. As a second example, we discuss the extension of the ideas of sensitivity to initial conditions and chaos in classical mechanics to quantum mechanics.

M. Hossein Partovi

2013-05-22

357

Fast and stable method for simulating quantum electron dynamics  

NASA Astrophysics Data System (ADS)

A fast and stable method is formulated to compute the time evolution of a wave function by numerically solving the time-dependent Schrödinger 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.

Watanabe, Naoki; Tsukada, Masaru

2000-08-01

358

Quantum mechanics-classical molecular dynamics approach to EXAFS  

NASA Astrophysics Data System (ADS)

Recently developed approach to the simulation of configuration-averaged EXAFS spectra using the combination of quantum mechanics and classical Molecular Dynamics (MD) methods is presented on the example of the Ti K-edge in SrTiO3 at T = 300 K. The method allows one to significantly reduce the number of fitting parameters required in the EXAFS signal calculation and to account entirely for disorder contributions. We show also that the sensitivity of configuration-averaged EXAFS spectra to the force field model employed in the MD simulations allows one to use them as additional information for the force field parameters fitting.

Kuzmin, Alexei; Evarestov, Robert A.

2009-11-01

359

Multimodal Properties and Dynamics of Gradient Echo Quantum Memory  

NASA Astrophysics Data System (ADS)

We investigate the properties of a recently proposed gradient echo memory (GEM) scheme for information mapping between optical and atomic systems. We show that GEM can be described by the dynamic formation of polaritons in k space. This picture highlights the flexibility and robustness with regards to the external control of the storage process. Our results also show that, as GEM is a frequency-encoding memory, it can accurately preserve the shape of signals that have large time-bandwidth products, even at moderate optical depths. At higher optical depths, we show that GEM is a high fidelity multimode quantum memory.

Hétet, G.; Longdell, J. J.; Sellars, M. J.; Lam, P. K.; Buchler, B. C.

2008-11-01

360

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

361

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

SciTech Connect

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 Schroedinger 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 [International Centre for Advanced Studies in Physical Sciences and Institute for Theoretical Physics, Faculty of Physics and Astronomy, Ruhr University Bochum, D-44780 Bochum (Germany); Department of Physics, School of Mathematics and Physics, University of Science and Technology Beijing, Beijing 100083 (China); Shukla, P. K. [International Centre for Advanced Studies in Physical Sciences and Institute for Theoretical Physics, Faculty of Physics and Astronomy, Ruhr University Bochum, D-44780 Bochum (Germany); Department of Mechanical and Aerospace Engineering and Center for Energy Research, University of California San Diego, La Jolla, California 92093 (United States); School of Chemistry and Physics, KwaZulu-Natal University, Durban 4000 (South Africa); Eliasson, B. [International Centre for Advanced Studies in Physical Sciences and Institute for Theoretical Physics, Faculty of Physics and Astronomy, Ruhr University Bochum, D-44780 Bochum (Germany)

2013-01-15

362

Competing quantum effects in the dynamics of a flexible water model  

E-print Network

Numerous studies have identified large quantum mechanical effects in the dynamics of liquid water. In this paper, we suggest that these effects may have been overestimated due to the use of rigid water models and flexible models in which the intramolecular interactions were described using simple harmonic functions. To demonstrate this, we introduce a new simple point charge model for liquid water, q-TIP4P/F, in which the O--H stretches are described by Morse-type functions. We have parameterized this model to give the correct liquid structure, diffusion coefficient, and infra-red absorption frequencies in quantum (path integral-based) simulations. By comparing classical and quantum simulations of the liquid, we find that quantum mechanical fluctuations increase the rates of translational diffusion and orientational relaxation in our model by a factor of around 1.15. This effect is much smaller than that observed in all previous simulations of simple empirical water models, which have found a quantum effect of at least 1.4 regardless of the quantum simulation method or the water model employed. The small quantum effect in our model is a result of two competing phenomena. Intermolecular zero point energy and tunneling effects destabilize the hydrogen bonding network, leading to a less viscous liquid with a larger diffusion coefficient. However this is offset by intramolecular zero point motion, which changes the average water monomer geometry resulting in a larger dipole moment, stronger intermolecular interactions, and slower diffusion. We end by suggesting, on the basis of simulations of other potential energy models, that the small quantum effect we find in the diffusion coefficient is associated with the ability of our model to produce a single broad O-H stretching band in the infra-red absorption spectrum.

Scott Habershon; Thomas E. Markland; David E. Manolopoulos

2010-11-04

363

Non-Markovian Quantum Dynamics and Classical Chaos  

E-print Network

We study the influence of a chaotic environment in the evolution of an open quantum system. We show that there is an inverse relation between chaos and non-Markovianity. In particular, we remark on the deep relation of the short time non-Markovian behavior with the revivals of the average fidelity amplitude-a fundamental quantity used to measure sensitivity to perturbations and to identify quantum chaos. The long time behavior is established as a finite size effect which vanishes for large enough environments.

I. Garcia-Mata; C. Pineda; D. A. Wisniacki

2012-04-16

364

Non-Markovian quantum dynamics and classical chaos  

NASA Astrophysics Data System (ADS)

We study the influence of a chaotic environment in the evolution of an open quantum system. We show that there is an inverse relation between chaos and non-Markovianity. In particular, we remark on the deep relation of the short time non-Markovian behavior with the revivals of the average fidelity amplitude—a fundamental quantity used to measure sensitivity to perturbations and to identify quantum chaos. The long time behavior is established as a finite size effect which vanishes for large enough environments.

García-Mata, Ignacio; Pineda, Carlos; Wisniacki, Diego

2012-08-01

365

Cold atom dynamics in a quantum optical lattice potential  

E-print Network

We study a generalized cold atom Bose Hubbard model, where the periodic optical potential is formed by a cavity field with quantum properties. On the one hand the common coupling of all atoms to the same mode introduces cavity mediated long range atom-atom interactions and on the other hand atomic backaction on the field introduces atom-field entanglement. This modifies the properties of the associated quantum phase transitions and allows for new correlated atom-field states including superposition of different atomic quantum phases. After deriving an approximative Hamiltonian including the new long range interaction terms we exhibit central physical phenomena at generic configurations of few atoms in few wells. We find strong modifications of population fluctuations and next-nearest neighbor correlations near the phase transition point.

Christoph Maschler; Helmut Ritsch

2005-08-23

366

Quantum Mechanics and Discrete Time from "Timeless" Classical Dynamics  

E-print Network

We study classical Hamiltonian systems in which the intrinsic proper time evolution parameter is related through a probability distribution to the physical time, which is assumed to be discrete. - This is motivated by the ``timeless'' reparametrization invariant model of a relativistic particle with two compactified extradimensions. In this example, discrete physical time is constructed based on quasi-local observables. - Generally, employing the path-integral formulation of classical mechanics developed by Gozzi et al., we show that these deterministic classical systems can be naturally described as unitary quantum mechanical models. The emergent quantum Hamiltonian is derived from the underlying classical one. It is closely related to the Liouville operator. We demonstrate in several examples the necessity of regularization, in order to arrive at quantum models with bounded spectrum and stable groundstate.

H. -T. Elze

2003-07-03

367

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

368

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

369

On the rate of convergence for the mean field approximation of many-body quantum dynamics  

E-print Network

We consider the time evolution of quantum states by many-body Schr\\"odinger dynamics and study the rate of convergence of their reduced density matrices in the mean field limit. If the prepared state at initial time is of coherent or factorized type and the number of particles $n$ is large enough then it is known that $1/n$ is the correct rate of convergence at any time. We show in the simple case of bounded pair potentials that the previous rate of convergence holds in more general situations with possibly correlated prepared states. In particular, it turns out that the coherent structure at initial time is unessential and the important fact is rather the speed of convergence of all reduced density matrices of the prepared states. We illustrate our result with several numerical simulations and examples of multi-partite entangled quantum states borrowed from quantum information.

Zied Ammari; Marco Falconi; Boris Pawilowski

2014-11-23

370

Influence of external magnetic field on dynamics of open quantum systems  

SciTech Connect

The influence of an external magnetic field on the non-Markovian dynamics of an open two-dimensional quantum system is investigated. The fluctuations of collective coordinate and momentum and transport coefficients are studied for a charged harmonic oscillator linearly coupled to a neutral bosonic heat bath. It is shown that the dissipation of collective energy slows down with increasing strength of the external magnetic field. The role of magnetic field in the diffusion processes is illustrated by several examples.

Kalandarov, Sh. A. [Joint Institute for Nuclear Research, 141980 Dubna (Russian Federation); Institute of Nuclear Physics, 702132 Tashkent (Uzbekistan); Institut fuer Theoretische Physik der Justus-Liebig-Universitaet, D-35392 Giessen (Germany); Kanokov, Z. [Joint Institute for Nuclear Research, 141980 Dubna (Russian Federation); National University, 700174 Tashkent (Uzbekistan); Adamian, G. G. [Joint Institute for Nuclear Research, 141980 Dubna (Russian Federation); Institute of Nuclear Physics, 702132 Tashkent (Uzbekistan); Antonenko, N. V. [Joint Institute for Nuclear Research, 141980 Dubna (Russian Federation)

2007-03-15

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

Trajectory-guided configuration interaction simulations of multidimensional quantum dynamics  

NASA Astrophysics Data System (ADS)

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 Schrödinger 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

2012-02-01

373

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

374

Multiple quantum NMR dynamics in dipolar ordered spin systems  

NASA Astrophysics Data System (ADS)

We investigate analytically and numerically the multiple-quantum (MQ) NMR dynamics in systems of nuclear spins 1/2 coupled by the dipole-dipole interactions in the case of the dipolar ordered initial state. We suggest two different methods of MQ NMR. One of them is based on the measurement of the dipolar temperature in the quasiequilibrium state which is established after the time of order ?loc-1 ( ?loc is the dipolar local field) after the MQ NMR experiment. The other method uses an additional resonance (?/4)y pulse after the preparation period of the standard MQ NMR experiment in solids. Many-spin clusters and correlations are created faster in such experiments than in the usual MQ NMR experiments and can be used for the investigation of many-spin dynamics of nuclear spins in solids.

Doronin, S. I.; Fel'Dman, E. B.; Kuznetsova, E. I.; Furman, G. B.; Goren, S. D.

2007-10-01

375

Dynamical invariants and nonadiabatic geometric phases in open quantum systems  

SciTech Connect

We introduce an operational framework to analyze nonadiabatic Abelian and non-Abelian, cyclic and noncyclic, geometric phases in open quantum systems. In order to remove the adiabaticity condition, we generalize the theory of dynamical invariants to the context of open systems evolving under arbitrary convolutionless master equations. Geometric phases are then defined through the Jordan canonical form of the dynamical invariant associated with the superoperator that governs the master equation. As a by-product, we provide a sufficient condition for the robustness of the phase against a given decohering process. We illustrate our results by considering a two-level system in a Markovian interaction with the environment, where we show that the nonadiabatic geometric phase acquired by the system can be constructed in such a way that it is robust against both dephasing and spontaneous emission.

Sarandy, M. S. [Departamento de Ciencias Exatas, Polo Universitario de Volta Redonda, Universidade Federal Fluminense, Avenida dos Trabalhadores 420, Volta Redonda, 27255-125 Rio de Janeiro (Brazil); Duzzioni, E. I. [Centro de Ciencias Naturais e Humanas, Universidade Federal do ABC, R. Santa Adelia 166, Santo Andre 09210-170, Sao Paulo (Brazil); Moussa, M. H. Y. [Instituto de Fisica de Sao Carlos, Universidade de Sao Paulo, Caixa Postal 369, Sao Carlos, 13560-970, Sao Paulo (Brazil)

2007-11-15

376

High resolution kinetic beam schemes in generalized coordinates for ideal quantum gas dynamics  

Microsoft Academic Search

A class of high resolution kinetic beam schemes in multiple space dimensions in general coordinates system for the ideal quantum gas is presented for the computation of quantum gas dynamical flows. The kinetic Boltzmann equation approach is adopted and the local equilibrium quantum statistics distribution is assumed. High-order accurate methods using essentially non-oscillatory interpolation concept are constructed. Computations of shock

Yu-Hsin Shi; J. C. Huang; J. Y.. Yang

2007-01-01

377

arXiv:quant-ph/0107036v16Jul2001 Efficient Quantum Computing of Complex Dynamics  

E-print Network

of the effect of static imperfections in the quantum computer hardware shows that the main elements of the phasearXiv:quant-ph/0107036v16Jul2001 Efficient Quantum Computing of Complex Dynamics Giuliano Benenti in gate operations. PACS numbers: 03.67.Lx, 05.45.Mt, 24.10.Cn When applied to computation, quantum

Shepelyansky, Dima

378

Dynamically protected cat-qubits: a new paradigm for universal quantum computation  

E-print Network

present a new hardware-efficient paradigm for universal quantum computation which is based on encodingDynamically protected cat-qubits: a new paradigm for universal quantum computation Mazyar Mirrahimi quantum memory towards a hardware-efficient protected logical qubit with which we can perform universal

Devoret, Michel H.

379

(Dynamical) quantum typicality: What is it and what are its physical and computational implications ?  

E-print Network

(Dynamical) quantum typicality: What is it and what are its physical and computational implications ? Jochen Gemmer University of OsnabrĂźck, Kassel, May 13th, 2014 J.Gemmer quantum typicality #12;Outline Thermal relaxation in closed quantum systems? Typicality in a nutshell Numerical experiment: model

Steinhoff, Heinz-JĂźrgen

380

Quantum Mechanics as a Generalization of Nambu Dynamics to the Weyl-Wigner Formalism *, **  

E-print Network

, j Quantum Mechanics as a Generalization of Nambu Dynamics to the Weyl-Wigner Formalism *, ** Iwo obtain the phase-space formulation of quantum mechanics. The noncanonical bracket for the Wigner function-72072 Tiibingen #12;I I, 10 I. Bialynicki-Birula and P.1. Morrison . Quantum Mechanics

Morrison, Philip J.,

381

Theoretical studies of chemical reaction dynamics  

SciTech Connect

This collaborative program with the Theoretical Chemistry Group at Argonne involves theoretical studies of gas phase chemical reactions and related energy transfer and photodissociation processes. Many of the reactions studied are of direct relevance to combustion; others are selected they provide important examples of special dynamical processes, or are of relevance to experimental measurements. Both classical trajectory and quantum reactive scattering methods are used for these studies, and the types of information determined range from thermal rate constants to state to state differential cross sections.

Schatz, G.C. [Argonne National Laboratory, IL (United States)

1993-12-01

382

Disordered quantum dots: A diffusion quantum Monte Carlo study  

Microsoft Academic Search

We report diffusion quantum Monte Carlo (DQMC) calculations of disordered quantum dots in the presence of an external magnetic field. The addition spectra, spin configuration, Hund's rule, and many-body densities are investigated up to 13 electrons. The data from DQMC is in excellent agreement with exact diagonalization for disorder-free quantum dots, and in marked difference with those obtained from unrestricted

A. D. Güçlü; Jian-Sheng Wang; Hong Guo

2003-01-01

383

A dynamical time operator in Dirac's relativistic quantum mechanics  

NASA Astrophysics Data System (ADS)

A self-adjoint dynamical time operator is introduced in Dirac's relativistic formulation of quantum mechanics and shown to satisfy a commutation relation with the Hamiltonian analogous to that of the position and momentum operators. The ensuing time-energy uncertainty relation involves the uncertainty in the instant of time when the wave packet passes a particular spatial position and the energy uncertainty associated with the wave packet at the same time, as envisaged originally by Bohr. The instantaneous rate of change of the position expectation value with respect to the simultaneous expectation value of the dynamical time operator is shown to be the phase velocity, in agreement with de Broglie's hypothesis of a particle associated wave whose phase velocity is larger than c. Thus, these two elements of the original basis and interpretation of quantum mechanics are integrated into its formal mathematical structure. Pauli's objection is shown to be resolved or circumvented. Possible relevance to current developments in electron channeling, in interference in time, in Zitterbewegung-like effects in spintronics, graphene and superconducting systems and in cosmology is noted.

Bauer, M.

2014-03-01

384

Dynamical Scaling Behavior in Non-Equilibrium Quantum Phase Transitions  

NASA Astrophysics Data System (ADS)

This thesis focuses on the emergence of universal dynamical scaling in quantum critical spin systems driven out of equilibrium, with emphasis on quench dynamics which involves isolated standard critical points, multi-critical points, and non-isolated critical points (that is, critical regions). One of our main conclusions is that the so-called Kibble-Zurek scaling holds for a large class of physical observables throughout the whole quench process when isolated standard critical points are involved, irrespective of the quench path. However, for both isolated multi-critical points and non-isolated critical points, the knowledge of equilibrium critical exponents is not enough to predict non-equilibrium dynamical scaling. Instead, our analysis shows that the resulting power-law scalingdepends sensitively on the control path, and that anomalous critical exponents may emerge depending on the universality class. In particular, we argue that for a multi-critical point the observed anomalous behavior originates in the fact that the dynamical excitation process takes place asymmetrically with respect to the static multi-critical point, requiring the introduction of genuinely non-static exponents. We further explore the robustness of universal dynamical scaling behavior with respect to initialization in a large class of states with finite energy above the ground state, including thermal mixtures. We find that the critical exponents of the ground-state quantum phase transition can be encoded in the dynamical scaling exponents despite the finite energy of the initial state. In particular, we identify conditions on the initial distribution of quasi-particle excitation which ensure the Kibble-Zurek scaling to persist. The emergence of effective thermal equilibrium behavior following a sudden quench towards criticality is also investigated, with focus on the long-time expectation value of the quasi-particle number operator. We find that effective thermalization fails to occur in quenches towards a multi-critical point, in contrast to quenches to a standard critical point. We argue that the observed lack of thermalization originates in this case in the asymmetry of the impulse region that is also responsible for anomalous multi-critical dynamical scaling.

Deng, Shusa

385

Quantum recurrence and fractional dynamic localization in ac-driven perfect state transfer Hamiltonians  

NASA Astrophysics Data System (ADS)

Quantum recurrence and dynamic localization are investigated in a class of ac-driven tight-binding Hamiltonians, the Krawtchouk quantum chain, which in the undriven case provides a paradigmatic Hamiltonian model that realizes perfect quantum state transfer and mirror inversion. The equivalence between the ac-driven single-particle Krawtchouk Hamiltonian Hˆ(t) and the non-interacting ac-driven bosonic junction Hamiltonian enables to determine in a closed form the quasi energy spectrum of Hˆ(t) and the conditions for exact wave packet reconstruction (dynamic localization). In particular, we show that quantum recurrence, which is predicted by the general quantum recurrence theorem, is exact for the Krawtchouk quantum chain in a dense range of the driving amplitude. Exact quantum recurrence provides perfect wave packet reconstruction at a frequency which is fractional than the driving frequency, a phenomenon that can be referred to as fractional dynamic localization.

Longhi, Stefano

2014-06-01

386

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

387

Quantum dynamics of Raman-coupled Bose-Einstein condensates using Laguerre-Gaussian beams  

SciTech Connect

We investigate the quantum dynamics of Raman-coupled Bose-Einstein condensates driven by laser beams that carry orbital angular momentum. By adiabatically eliminating the excited atomic state we obtain an effective two-state Hamiltonian for the coupled condensates, and quantization of the matter-wave fields results in collapse and revivals in the quantum dynamics. We show that the revival period depends on whether the initial nonrotating condensate displays broken U(1) symmetry or not, and that the difference may be detected by measuring the motion of quantized vortices that are nested in the density profile of the Raman-coupled condensates. We further study the steady-state population transfer using a linear sweep of the two-photon detuning, by which the atomic population is coherently transferred from an initial nonrotating state to the final vortex state.

Kanamoto, Rina; Wright, Ewan M.; Meystre, Pierre [Department of Physics and College of Optical Sciences, University of Arizona, Tucson, Arizona 85721 (United States)

2007-06-15

388

Non-Markovian Dynamics of Quantum and Classical Correlations in the Presence of System-Bath Coherence  

E-print Network

We present a detailed study of the dynamics of correlations in non-Markovian environments, applying the hierarchy equations approach. This theoretical treatment is able to take the system-bath interaction into consideration carefully. It is shown that crosses and sudden changes of classical and quantum correlations can happen if we gradually reduce the strength of the interactions between qubits. For some special initial states, sudden transitions between classical and quantum correlations even occur.

Li, Chuan-Feng; Yuan, Hong-Yuan; Ge, Rong-Chun; Guo, Guang-Can

2010-01-01

389

Non-Markovian Dynamics of Quantum and Classical Correlations in the Presence of System-Bath Coherence  

E-print Network

We present a detailed study of the dynamics of correlations in non-Markovian environments, applying the hierarchy equations approach. This theoretical treatment is able to take the system-bath interaction into consideration carefully. It is shown that crosses and sudden changes of classical and quantum correlations can happen if we gradually reduce the strength of the interactions between qubits. For some special initial states, sudden transitions between classical and quantum correlations even occur.

Chuan-Feng Li; Hao-Tian Wang; Hong-Yuan Yuan; Rong-Chun Ge; Guang-Can Guo

2010-11-23

390

Non-Markovian Dynamics of Quantum and Classical Correlations in the Presence of System-Bath Coherence  

NASA Astrophysics Data System (ADS)

We present a detailed study on the dynamics of two-qubit correlations in non-Markovian environments, applying the hierarchy equations approach. This treatment is free from the limitation of perturbative, Markovian or rotating wave approximations. It is shown that crossovers and sudden changes in the classical and quantum correlations can appear when the strength of the interaction between qubits is gradually reduced. For some special initial states, there are even sudden transitions between the classical and quantum correlations.

Li, Chuan-Feng; Wang, Hao-Tian; Yuan, Hong-Yuan; Ge, Rong-Chun; Guo, Guang-Can

2011-12-01

391

Entanglement and quantum discord dynamics of two atoms under practical feedback control  

SciTech Connect

We study the dynamics of two identical atoms resonantly coupled to a single-mode cavity under practical feedback control, and focus on the detection inefficiency. The entanglement is induced to vanish in finite time by the inefficiency of detection. Counterintuitively, the asymptotic entanglement and quantum discord can be increased by the inefficiency of detection. The noise of detection triggers the control field to create entanglement and discord when no photons are emitted from the atoms. Furthermore, sudden change happens to the dynamics of entanglement.

Li Yang; Luo Bin; Guo Hong [CREAM Group, State Key Laboratory of Advanced Optical Communication Systems and Networks, School of Electronics Engineering and Computer Science, and Center for Computational Science and Engineering (CCSE), Peking University, Beijing 100871 (China)

2011-07-15

392

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

2014-05-01

393

On the Consistency of Approximate Quantum Dynamics Simulation Methods for Vibrational Spectra in the Condensed Phase  

E-print Network

Including quantum mechanical effects on the dynamics of nuclei in the condensed phase is challenging, because the complexity of exact methods grows exponentially with the number of quantum degrees of freedom. Efforts to circumvent these limitations can be traced down to two approaches: methods that treat a small subset of the degrees of freedom with rigorous quantum mechanics, considering the rest of the system as a static or classical environment, and methods that treat the whole system quantum mechanically, but using approximate dynamics. Here we perform a systematic comparison between these two philosophies for the description of quantum effects in vibrational spectroscopy, taking the Embedded Local Monomer (LMon) model and a mixed quantum-classical (MQC) model as representatives of the first family of methods, and centroid molecular dynamics (CMD) and thermostatted ring polymer molecular dynamics (TRPMD) as examples of the latter. We use as benchmarks D$_2$O doped with HOD and pure H$_2$O at three distinc...

Rossi, Mariana; Paesani, Francesco; Bowman, Joel; Ceriotti, Michele

2014-01-01

394

Probabilistic quantum phase-space simulation of Bell violations and their dynamical evolution  

E-print Network

Quantum simulations of Bell inequality violations are numerically obtained using probabilistic phase space methods, namely the positive P-representation. In this approach the moments of quantum observables are evaluated as moments of variables that have values outside the normal eigenvalue range. There is thus a parallel with quantum weak measurements and weak values. Nevertheless, the representation is exactly equivalent to quantum mechanics. A number of states violating Bell inequalities are sampled, demonstrating that these quantum paradoxes can be treated with probabilistic methods. We treat quantum dynamics by simulating the time evolution of the Bell state formed via parametric down-conversion, and discuss multi-mode generalizations.

Laura Rosales-Zárate; Bogdan Opanchuk; Peter D. Drummond; Margaret D. Reid

2014-05-06

395

Dynamics of interacting dark energy model in Einstein and Loop Quantum Cosmology  

E-print Network

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 us 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.

Songbai Chen; Bin Wang; Jiliang Jing

2008-08-26

396

Quantum Dynamics Using Lie Algebras, with Explorations in the Chaotic Behavior of Oscillators  

E-print Network

Quantum Dynamics Using Lie Algebras, with Explorations in the Chaotic Behavior of Oscillators Ryan Thomas Sayer All Rights Reserved #12;ABSTRACT Quantum Dynamics Using Lie Algebras, with Explorations the generators of the Lie algebra comprising the Hamiltonian. We obtain cou- pled ODE's for the time evolution

Hart, Gus

397

Treatment of quantum zero-point energy constraint in simulations of molecular dynamics  

Microsoft Academic Search

Purpose – It has been well known that the quantum zero-point energy (ZPE) cannot be conserved in simulations of atoms and molecules dynamics based on classical mechanics. The purpose of this paper is to examine fundamental issues related to the treatment of quantum ZPE constraint in simulations of atoms and molecules dynamics. Design\\/methodology\\/approach – The ZPE is well known to

Shigeru Tada

2011-01-01

398

Use of dynamical coupling for improved quantum state transfer A. O. Lyakhov and C. Bruder  

E-print Network

Use of dynamical coupling for improved quantum state transfer A. O. Lyakhov and C. Bruder propose a method to improve quantum state transfer in transmission lines. The idea is to localize the information on the last qubit of a transmission line, by dynamically varying the coupling constants between

Bruder, Christoph

399

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 (Universitŕ and INFN Cagliari) Marco Cavagliŕ (University of Mississippi) Jeanette E. Nelson (Universitŕ 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

400

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

401

Electronic structure and carrier dynamics in InAs/InP double-cap quantum dots  

E-print Network

1 Electronic structure and carrier dynamics in InAs/InP double-cap quantum dots P. Miska1.2 , J The carrier dynamics in InAs double-cap quantum dots (DC-QDs) grown on InP(113)B are investigated. The shape are named double-cap quantum dots (DC-QDs) and emit at 1.55 Âľm at room temperature [10]. The optical

Boyer, Edmond

402

Nonadiabatic quantum molecular dynamics with hopping. II. Role of nuclear quantum effects in atomic collisions  

NASA Astrophysics Data System (ADS)

The role of electron-nuclear correlations, i.e., quantum effects in the nuclear motion in atomic collisions with complex targets, is discussed using the recently developed nonadiabatic quantum molecular dynamics with hopping method [Fischer, Handt, and Schmidt, paper I of this series, Phys. Rev. A 90, 012525 (2014), 10.1103/PhysRevA.90.012525]. It is shown that the excitation process is nearly unaffected by electron-nuclear correlations as long as integral quantities are considered (total kinetic energy loss), whereas the relaxation mechanism of the molecular target is greatly affected (total fragmentation probability). To describe highly differential quantities (kinetic energy loss as a function of the scattering angle), however, the consideration of nuclear quantum effects during the initial excitation process is indispensable, even in collisions where one would expect purely classical behavior of the nuclei due to their small de Broglie wavelength. The calculations reproduce and explain in detail old but still unexplained experimental data of differential energy-loss spectroscopy in He +He and He +H2 collisions.

Fischer, M.; Handt, J.; Schmidt, R.

2014-07-01

403

Characterization of control noise effects in optimal quantum unitary dynamics  

E-print Network

The control of quantum mechanical unitary transformations naturally calls for a degree of resilience to control field noise. While consideration of noise effects in quantum systems has been an area of active study, the relationship between optimal solutions and those that are both optimal and robust to noise is still not generally understood. This work defines measures for quantifying the effects of field noise upon targeted unitary transformations. Robustness to noise is assessed in the framework of the quantum control landscape, which is the mapping from the control to the unitary transformation performance measure. Within that framework, more robust optimal controls are associated with regions of low landscape curvature. The utility of this perspective when considering the effects of noise is demonstrated through numerical simulations of the overlap between directions of significant curvature on the landscape and noise correlation functions. These simulations demonstrate both the rich and varied nature of optimal and robust controls, as well as reveal distinct noise spectral regimes that support robust control solutions for a class of transformations considered in quantum information processing.

David Hocker; Constantin Brif; Matthew D. Grace; Ashley Donovan; Tak-San Ho; Katharine W. Moore Tibbetts; Rebing Wu; Herschel Rabitz

2014-05-23

404

Study photonic crystals defect model property with quantum theory  

NASA Astrophysics Data System (ADS)

In this paper, we have presented a quantum theory approach to study one-dimensional photonic crystals with and without defect layer. We give quantum dispersion relation, quantum transmissivity, reflectivity and absorptivity, and compare them with the classical dispersion relation, transmissivity, reflectivity and absorptivity. By the calculation, we find that the classical and quantum dispersion relation, transmissivity reflectivity and absorptivity are identical. With the quantum theory new approach, we can study two-dimensional and three-dimensional photonic crystals in the future.

Wu, Xiang-Yao; Ma, Ji; Liu, Xiao-Jing; Yang, Jing-Hai; Li, Hong; Zhang, Si-Qi; Gao, Hai-Xin; Li, Heng-Mei; Yuan, Hong-Chun

2014-06-01

405

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

406

Decay dynamics of neutral and charged excitonic complexes in single InAs/GaAs quantum dots  

E-print Network

Decay dynamics of neutral and charged excitonic complexes in single InAs/GaAs quantum dots M X, XX, X+, and XX+ of 26 different single InAs/GaAs quantum dots are reported. The ratios.1063/1.2844886 Single quantum dots QDs provide the key for quantum computing1,2 and quantum cryptography.3 For real

Nabben, Reinhard

407

Ultrafast interfacial charge transfer dynamics in dye-sensitized and quantum dot solar cell  

NASA Astrophysics Data System (ADS)

Dye sensitized solar cell (DSSC) appeared to be one of the good discovery for the solution of energy problem. We have been involved in studying ultrafast interfacial electron transfer dynamics in DSSC using femtosecond laser spectroscopy. However it has been realized that it is very difficult to design and develop higher efficient one, due to thermodynamic limitation. Again in DSSC most of the absorbed photon energy is lost as heat within the cell, which apart from decreasing the efficiency also destabilizes the device. It has been realized that quantum dot solar cell (QDSC) are the best bet where the sensitizer dye molecules can be replaced by suitable quantum dot (QD) materials in solar cell. The quantum-confinement effect in semiconductors modifies their electronic structure, which is a very important aspect of these materials. For photovoltaic applications, a long-lived charge separation remains one of the most essential criteria. One of the problems in using QDs for photovoltaic applications is their fast charge recombination caused by nonradiative Auger processes, which occur predominantly at lower particle sizes due to an increase in the Coulomb interaction between electrons and holes. Various approaches, such as the use of metal-semiconductor composites, semiconductor-polymer composite, and semiconductor core-shell heterostructures, have been attempted to minimize the fast recombination between electrons and holes. To make higher efficient solar devices it has been realised that it is very important to understand charge carrier and electron transfer dynamics in QD and QD sensitized semiconductor nanostructured materials. In the present talk, we are going to discuss on recent works on ultrafast electron transfer dynamics in dye-sensitized TiO2 nanoparticles/film [1-12] and charge (electron/hole) transfer dynamics in quantum dot core-shell nano-structured materials [13-17].

Ghosh, Hirendra N.

2013-02-01

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 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. [Department of Chemistry, Technical University of Munich, Lichtenbergstr. 4, 85747 Garching (Germany)

2012-07-14

409

Quantum chemical study on influence of intermolecular hydrogen bonding on the geometry, the atomic charges and the vibrational dynamics of 2,6-dichlorobenzonitrile.  

PubMed

FT-IR (4000-400 cm(-1)) and FT-Raman (4000-200 cm(-1)) spectral measurements on solid 2,6-dichlorobenzonitrile (2,6-DCBN) have been done. The molecular geometry, harmonic vibrational frequencies and bonding features in the ground state have been calculated by density functional theory at the B3LYP/6-311++G (d,p) level. A comparison between the calculated and the experimental results covering the molecular structure has been made. The assignments of the fundamental vibrational modes have been done on the basis of the potential energy distribution (PED). To investigate the influence of intermolecular hydrogen bonding on the geometry, the charge distribution and the vibrational spectrum of 2,6-DCBN; calculations have been done for the monomer as well as the tetramer. The intermolecular interaction energies corrected for basis set superposition error (BSSE) have been calculated using counterpoise method. Based on these results, the correlations between the vibrational modes and the structure of the tetramer have been discussed. Molecular electrostatic potential (MEP) contour map has been plotted in order to predict how different geometries could interact. The Natural Bond Orbital (NBO) analysis has been done for the chemical interpretation of hyperconjugative interactions and electron density transfer between occupied (bonding or lone pair) orbitals to unoccupied (antibonding or Rydberg) orbitals. UV spectrum was measured in methanol solution. The energies and oscillator strengths were calculated by Time Dependent Density Functional Theory (TD-DFT) and matched to the experimental findings. TD-DFT method has also been used for theoretically studying the hydrogen bonding dynamics by monitoring the spectral shifts of some characteristic vibrational modes involved in the formation of hydrogen bonds in the ground and the first excited state. The (13)C nuclear magnetic resonance (NMR) chemical shifts of the molecule were calculated by the Gauge independent atomic orbital (GIAO) method and compared with experimental results. Standard thermodynamic functions have been obtained and changes in thermodynamic properties on going from monomer to tetramer have been presented. PMID:24287056

Agarwal, Parag; Bee, Saba; Gupta, Archana; Tandon, Poonam; Rastogi, V K; Mishra, Soni; Rawat, Poonam

2014-01-01

410

An Experimental Proposal to Test Dynamic Quantum Non-locality with Single-Atom Interferometry  

E-print Network

Quantum non-locality based on the well-known Bell inequality is of kinematic nature. A different type of quantum non-locality, the non-locality of the quantum equation of motion, is recently put forward with connection to the Aharonov-Bohm effect [Nature Phys. 6, 151 (2010)]. Evolution of the displacement operator provides an example to manifest such dynamic quantum non-locality. We propose an experiment using single-atom interferometry to test such dynamic quantum non-locality. We show how to measure evolution of the displacement operator with clod atoms in a spin-dependent optical lattice potential and discuss signature to identify dynamic quantum non-locality under a realistic experimental setting.

Zhu, Shi-Liang; Zhang, Dan-Wei; Duan, Lu-Ming

2010-01-01

411

An experimental proposal to test dynamic quantum non-locality with single-atom interferometry  

NASA Astrophysics Data System (ADS)

Quantum non-locality based on the well-known Bell inequality is of kinematic nature. A different type of quantum non-locality, the non-locality of the quantum equation of motion, is recently put forward with connection to the Aharonov-Bohm effect (Popescu S., Nat. Phys., 6 (2010) 151). Evolution of the displacement operator provides an example to manifest such dynamic quantum non-locality. We propose an experiment using single-atom interferometry to test such dynamic quantum non-locality. We show how to measure evolution of the displacement operator with cold atoms in a spin-dependent optical lattice potential and discuss signature to identify dynamic quantum non-locality under a realistic experimental setting.

Zhu, Shi-Liang; Xue, Zheng-Yuan; Zhang, Dan-Wei; Duan, Lu-Ming

2011-06-01

412

Quantum critical dynamics of the boson system in the Ginzburg-Landau model  

NASA Astrophysics Data System (ADS)

The quantum critical dynamics of the quantum phase transitions is considered. In the framework of the unified theory, based on the Keldysh technique, we consider the crossover from the classical to the quantum description of the boson many-body system dynamics close to the second order quantum phase transition. It is shown that in this case the upper critical space dimension of this model is dc+=2, therefore the quantum critical dynamics approach is useful in case of d<2. In the one-dimension system the phase coherence time does diverge at the quantum critical point, gc, and has the form of ??-ln?g-gc?/?g-gc?, the correlation radius diverges as rc??g-gc?(?=0.6).

Vasin, M. G.

2014-12-01

413

Teaching Quantum ChromoDynamics using Rubik's Cube  

NASA Astrophysics Data System (ADS)

A potential relationship between the combinatorial aspects of Quantum Chromodynamics and Rubik's cube algebra was first noted in 1982. The Scientific American cover story's mathematics failed to complete the analogy, but clearly demonstrated the value of a graphical, tangible tool for communicating the algebraic relationships of quarks in QCD. Symmetry breaking and restrictions imposed on Rubik's cube algebra were (http://arxiv.org/abs/physics/9712042) defined in a way which provides unified algebra. Construction of standard model particles as well as strong and weak interactions between quarks can be demonstrated with or without student participation. Quantum ElectroDynamics requires extension to a multi-cube superposition approach in which each particle naturally inhabits a separate cube. The three families of particles have been shown to be both necessary and sufficient. The restricted cube, symbolized by a Cyrillic Ya, is the only known non-commutative matrix algebra which passes Seiberg's causality criterion. Many topics of current research can be quickly and clearly introduced to the audience, e.g. a tripartite string (1-brane) has six intrinsic extra dimensions and is one-to-one and onto the standard model of particle physics. The restricted cube algebra has proven to be an active engagement technique well-suited to introducing QC/ED to physics students and the public. Several cubes will be available for reference and demonstrations.

Lundberg, Wayne R.

2008-04-01

414

Dynamic-local-field approximation for the quantum solids  

NASA Technical Reports Server (NTRS)

A local-molecular-field description for the ground-state properties of the quantum solids is presented. The dynamical behavior of atoms contributing to the local field, which acts on an arbitrary pair of test particles, is incorporated by decoupling the pair correlations between these field atoms. The energy, pressure, compressibility, single-particle-distribution function, and the rms atomic deviations about the equilibrium lattice sites are calculated for H2, He-3, and He-4 over the volume range from 5 to 24.5 cu cm/mole. The results are in close agreement with existing Monte Carlo calculations wherever comparisons are possible. At very high pressure, the results agree with simplified descriptions which depend on negligible overlap of the system wave function between neighboring lattice sites.

Etters, R. D.; Danilowicz, R. L.

1974-01-01

415

Mapping the Schrodinger picture of open quantum dynamics  

E-print Network

For systems described by finite matrices, an affine form is developed for the maps that describe evolution of density matrices for a quantum system that interacts with another. This is established directly from the Heisenberg picture. It separates elements that depend only on the dynamics from those that depend on the state of the two systems. While the equivalent linear map is generally not completely positive, the homogeneous part of the affine maps is, and is shown to be composed of multiplication operations that come simply from the Hamiltonian for the larger system. The inhomogeneous part is shown to be zero if and only if the map does not increase the trace of the square of any density matrix. Properties are worked out in detail for two-qubit examples.

Thomas F. Jordan; Anil Shaji; E. C. G. Sudarshan

2005-05-16

416

Quantum molecular dynamics simulation of hydrogen diffusion in zirconium hydride  

NASA Astrophysics Data System (ADS)

The behavior of hydrogen in zirconium hydride in the high-temperature range has been investigated using the quantum molecular dynamics method. The ? phases of compositions ZrH1.75 and ZrH2 and the liquid phase are considered. The self-diffusion coefficients of hydrogen are calculated as a function of the temperature in the range from 1000 to 6000 K. For the ZrH1.75 and ZrH2 hydrides, the obtained values are close to each other. At temperatures of 1000-2000 K, the hydrogen diffusion is determined not only by the mobility of hydrogen atoms but also by the transition from the energetically favorable tetrahedral positions into the excited state. The obtained values of the diffusion coefficients in the temperature range of 1000-1200 K are in good agreement with the experimental data.

Yanilkin, A. V.

2014-09-01

417

Exact Quantum Dynamics Calculations Using Phase Space Wavelets  

NASA Astrophysics Data System (ADS)

In a series of earlier papers, the authors introduced the first exact quantum dynamics method that defeats the exponential scaling of CPU effort with system dimensionality. The method used a ``weylet'' basis set (orthogonalized Weyl-Heisenberg wavelets), combined with a phase space truncation scheme first proposed by M. Davis and E. Heller. Here, we use a related, but much simpler, wavelet basis consisting of momentum-symmetrized phase space Gaussians. Despite being non-orthogonal, symmetrized Gaussians exhibit collective locality, allowing for effective phase space truncation and the defeat of exponential scaling. A ``universal'' and remarkably simple code has been written, which is dimensionally independent, and which also exploits massively parallel algorithms. The codes have been used to calculate the vibrational spectra of several molecules of varying dimensionality.

Halverson, Thomas; Poirier, Bill

2013-06-01

418

Efficient semiclassical quantum nuclear effects for shock compression studies  

NASA Astrophysics Data System (ADS)

A fast methodology is described for atomistic simulations of shock-compressed materials that incorporates quantum nuclear effects in a self-consistent fashion. We introduce a modification of the multiscale shock technique (MSST) that couples to a quantum thermal bath described by a colored noise Langevin thermostat. The new approach, which we call QB-MSST, is of comparable computational cost to MSST and self-consistently incorporates quantum heat capacities and Bose-Einstein harmonic vibrational distributions. As a first test, we study shock-compressed methane using the ReaxFF potential. The Hugoniot curves predicted from the new approach are found comparable with existing experimental data. We find that the self-consistent nature of the method results in the onset of chemistry at 40% lower pressure on the shock Hugoniot than observed with classical molecular dynamics. The temperature shift associated with quantum heat capacity is determined to be the primary factor in this shift.[4pt] In collaboration with Tingting Qi, Department of Materials Science and Engineering, Stanford University.

Reed, Evan

2013-03-01

419

Stable and unstable dynamics of Overhauser fields in a double quantum dot  

NASA Astrophysics Data System (ADS)

Nonlinear dynamics of nuclear spin ensembles driven by a two-electron system in a double quantum dot in the Pauli spin blockade (SB) regime is studied experimentally in conjunction with numerical simulation. Dynamic nuclear spin polarization (DNP) is systematically studied by evaluating the current level and its fluctuations. We interpret large current noise in the SB regime as stable feedback noise, where identical Overhauser fields of the two dots are preferred. In contrast, stepwise increases of current in the shallow Coulomb blockade region can be understood as unstable dynamics with significant imbalance of the Overhauser fields, which cancels the external magnetic field in one of the two dots. There, an extremely small transverse Overhauser field can easily lift the SB transport, giving the highest current level, when longitudinal components cancel the applied field.

Sharmin, Sonia; Muraki, Koji; Fujisawa, Toshimasa

2014-03-01

420

Quantum dynamics of ultrafast charge transfer at an oligothiophene-fullerene heterojunction.  

PubMed

Following up on our recent study of ultrafast charge separation at oligothiophene-fullerene interfaces [H. Tamura, I. Burghardt, and M. Tsukada, J. Phys. Chem. C 115, 10205 (2011)], we present here a detailed quantum dynamical perspective on the charge transfer process. To this end, electron-phonon coupling is included non-perturbatively, by an explicit quantum dynamical treatment using the multi-configuration time-dependent Hartree (MCTDH) method. Based upon a distribution of electron-phonon couplings determined from electronic structure studies, a spectral density is constructed and employed to parametrize a linear vibronic coupling Hamiltonian. The diabatic coupling is found to depend noticeably on the inter-fragment distance, whose effect on the dynamics is here investigated. MCTDH calculations of the nonadiabatic transfer dynamics are carried out for the two most relevant electronic states and 60 phonon modes. The electron transfer process is found to be ultrafast and mediated by electronic coherence, resulting in characteristic oscillatory features during a period of about 100 fs. PMID:23249077

Tamura, Hiroyuki; Martinazzo, Rocco; Ruckenbauer, Matthias; Burghardt, Irene

2012-12-14