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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 information dynamics  

Microsoft Academic Search

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

Jeffrey Yepez

2010-01-01

3

Quantum information dynamics  

NASA Astrophysics Data System (ADS)

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

Yepez, Jeffrey

4

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

NASA Astrophysics Data System (ADS)

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

Prezhdo, Oleg

2011-03-01

5

Quantum and Molecular Dynamics Study for Binding of Macrocyclic Inhibitors to Human ?-Thrombin  

PubMed Central

Molecular dynamics simulations followed by quantum mechanical calculation and Molecular Mechanics Poisson-Boltzmann Surface Area (MM-PBSA) analysis have been carried out to study binding of proline- and pyrazinone-based macrocyclic inhibitors (L86 and T76) to human ?-thrombin. Detailed binding interaction energies between these inhibitors and individual protein fragments are calculated using DFT method based on a new quantum mechanical approach for computing protein-ligand interaction energy. The analysis of detailed interaction energies provides insight on the protein-ligand binding mechanism. Study shows that T76 and L86 bind to thrombin in a very similar “inhibition mode” except that T76 has relatively weaker binding interaction with Glu217. The analysis from quantum calculation of binding interaction is consistent with the MM-PBSA calculation of binding free energy, and the calculated free energies for L86/T76-thrombin binding agree well with the experimental data.

Wu, Emilia L.; Mei, Ye; Han, KeLi; Zhang, John Z. H.

2007-01-01

6

Quantum algorithm for Bose-Einstein condensate quantum fluid dynamics  

Microsoft Academic Search

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.

Jeffrey Yepez; George Vahala; Linda Vahala

2009-01-01

7

Topology, cosmic strings and quantum dynamics - a case study with graphene  

NASA Astrophysics Data System (ADS)

We explore the possibility to study the quantum dynamics of Dirac fermions in presence of a cosmic string by introducing a conical topological defect in gapped graphene in the presence of a Coulomb charge. When the Coulomb charge exceeds a certain critical strength, quantum instability sets in. Below the critical regime and for certain values of the system parameters, the allowed boundary conditions in gapped graphene cone can be classified in terms of a single real quantity. Observables such as local density of states, scattering phase shifts and the bound state spectra are dependent on the value of this real parameter, which has to be determined empirically. For a supercritical Coulomb charge, we analyze the system with a regularized potential as well as with a zigzag boundary condition and find the effect of the sample topology on the observable features of the system.

Chakraborty, Baishali; Gupta, Kumar S.; Sen, Siddhartha

2013-06-01

8

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

9

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

PubMed

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-2Theta(omega-omegac) cusp of the continuum solution in the pinned phase (m>m(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

Krajewski, Florian R; Müser, Martin H

2005-03-22

10

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

NASA Astrophysics Data System (ADS)

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 ?-2?(?-?c) cusp of the continuum solution in the pinned phase (m>mc). 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<=mc), 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.; Müser, Martin H.

2005-03-01

11

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

12

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

13

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

NASA Astrophysics Data System (ADS)

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 (?,?*) 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 (?,?*) 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-Sánchez, Juan Manuel; Gelabert, Ricard; Moreno, Miquel; Lluch, José M.

2008-12-01

14

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

NASA Astrophysics Data System (ADS)

We carried out six-dimensional quantum dynamics calculations for the dissociative adsorption of deuterium chloride (DCl) on Au(111) surface using the initial state-selected time-dependent wave packet approach. The four-dimensional dissociation probabilities are also obtained with the center of mass of DCl fixed at various sites. These calculations were all performed based on an accurate potential energy surface recently constructed by neural network fitting to density function theory energy points. The origin of the extremely small dissociation probability for DCl/HCl (v = 0, j = 0) fixed at the top site compared to other fixed sites is elucidated in this study. The influence of vibrational excitation and rotational orientation of DCl on the reactivity was investigated by calculating six-dimensional dissociation probabilities. The vibrational excitation of DCl enhances the reactivity substantially and the helicopter orientation yields higher dissociation probability than the cartwheel orientation. The site-averaged dissociation probability over 25 fixed sites obtained from four-dimensional quantum dynamics calculations can accurately reproduce the six-dimensional dissociation probability.

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

2014-04-01

15

Studies of quantum fluctuations and competing orders on vortex dynamics in cuprate superconductors  

NASA Astrophysics Data System (ADS)

The existence of competing orders (CO) and the proximity to quantum criticality (QC) in cuprate superconductors create unconventional low energy excitations and significant quantum fluctuations (QF) which can alter the low temperature vortex dynamics of cuprates. We report studies on the effect of QF and CO on vortex dynamics in cuprates at low temperatures, focusing on the four-layer, hole-doped HgBa2Ca3Cu4Ox (Hg-1234). Hg-1234 has two underdoped inner layers that are anti-ferromagnetic and two optimally doped outer layers that are superconducting. Vortex phase diagrams, derived from 3^rd harmonic AC hall probe and high-field DC cantilever magnetization measurements, allow comparison of Hg-1234 with other cuprates such as YBa2Cu3O7-x and La0.1Sr0.9CuO2. Comparison plots of the ab-plane reduced fields (normalized by the paramagnetic field, Hpara), hirr.(t)=Hirr.(t)/Hpara and hC2(t)=HC2(t)/Hpara versus reduced temperature, t, demonstrate that QF and CO indeed affect Hg-1234 more than other cuprates, with Hg-1234 having the smallest extrapolated value of h*? hirr.(0) 0.12, indicating its closest proximity to QC.

Beyer, A. D.; Zapf, V. S.; Park, M.-S.

2005-03-01

16

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

17

Quantum Computation of Fluid Dynamics.  

National Technical Information Service (NTIS)

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

J. Yepez

1998-01-01

18

Quantum Chemical Molecular Dynamics Studies on the Chemical Mechanical Polishing Process of Cu Surface  

NASA Astrophysics Data System (ADS)

The dynamic behavior of the oxidation reaction of the Cu surface during the Cu chemical-mechanical polishing (CMP) process was investigated by a novel tight-binding quantum chemical molecular dynamics method. We confirmed that our tight-binding quantum chemical molecular dynamics method with first-principles parameterization can calculate the structures, and electronic states of various molecules and solids related to the Cu-CMP process as accurately as the density functional calculations, while the CPU time of the new method is around 5,000 times faster than that of the first-principles molecular dynamics calculations. We employed hydrogen peroxide solution as a slurry and the Cu surface as a substrate to simulate the Cu-CMP process by using our accelerated quantum chemical molecular dynamics method. Three types of models were constructed to analyze the effect of the pH of the slurry and Miller plane of the Cu surface on the dynamic behaviors of the oxidation process of the Cu surface. We indicate that the pH of the slurry strongly affects the oxidation process of Cu surface. Moreover, we clarified that the oxidation mechanism depends on the Miller plane of the Cu surfaces.

Yokosuka, Toshiyuki; Sasata, Katsumi; Kurokawa, Hitoshi; Takami, Seiichi; Kubo, Momoji; Imamura, Akira; Miyamoto, Akira

2003-04-01

19

Quantum discord dynamics in structured reservoirs  

Microsoft Academic Search

The non-Markovian master equations are derived to study quantum discord dynamics of two qubits coupled to a common reservoir and two independent reservoirs, respectively. We compare the dynamics under different parameters, such as reservoir spectra and resonant parameters, at high temperature and at zero temperature. The results indicate that the dynamics at these two extreme temperatures share similar characters, as

Z.-K. Su; S.-J. Jiang

2011-01-01

20

Dynamical coherent states and physical solutions of quantum cosmological bounces  

Microsoft Academic Search

A new model is studied which describes the quantum behavior of transitions through an isotropic quantum cosmological bounce in loop quantum cosmology sourced by a free and massless scalar field. As an exactly solvable model even at the quantum level, it illustrates properties of dynamical coherent states and provides the basis for a systematic perturbation theory of loop quantum gravity.

Martin Bojowald

2007-01-01

21

Molecular dynamics with quantum fluctuations  

SciTech Connect

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

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

2010-09-01

22

Quantum dynamics in dual spaces  

SciTech Connect

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

Sudarshan, E.C.G.

1993-12-31

23

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

NASA Astrophysics Data System (ADS)

The dynamics of pigment-pigment and pigment-protein interactions in light-harvesting complexes is studied with an approach that combines molecular dynamics simulations with quantum chemistry calculations and a polaron model analysis. The molecular dynamics simulation of light-harvesting (LH) complexes was performed on an 87 055 atom system comprised of a LH-II complex of Rhodospirillum molischianum embedded in a lipid bilayer and surrounded with appropriate water layers. For each of the 16 B850 bacteriochlorophylls (BChls), we performed 400 ab initio quantum chemistry calculations on geometries that emerged from the molecular dynamical simulations, determining the fluctuations of pigment excitation energies as a function of time. From the results of these calculations we construct a time-dependent Hamiltonian of the B850 exciton system from which we determine within linear response theory the absorption spectrum. Finally, a polaron model is introduced to describe both the excitonic and coupled phonon degrees of freedom by quantum mechanics. The exciton-phonon coupling that enters into the polaron model, and the corresponding phonon spectral function, are derived from the molecular dynamics and quantum chemistry simulations. The model predicts that excitons in the B850 BChl ring are delocalized over five pigments at room temperature. Also, the polaron model permits the calculation of the absorption and circular dichroism spectra of the B850 excitons from the sole knowledge of the autocorrelation function of the excitation energies of individual BChls, which is readily available from the combined molecular dynamics and quantum chemistry simulations. The obtained results are found to be in good agreement with the experimentally measured absorption and circular dichroism spectra.

Damjanovi?, Ana; Kosztin, Ioan; Kleinekathöfer, Ulrich; Schulten, Klaus

2002-03-01

24

Quantum chaos and dynamical entropy  

Microsoft Academic Search

We review the notion of dynamical entropy by Connes, Narnhoferand Thirring and relate it to Quantum Chaos. A particle in a periodicpotential is used as an example. This is worked out in the classical andthe quantum mechanical framework, for the single particle as well as forthe corresponding gas.

F Benatti; T Hudetz; A Knauf

1997-01-01

25

Molecular internal dynamics studied by quantum path interferences in high order harmonic generation  

NASA Astrophysics Data System (ADS)

We investigate how short and long electron trajectory contributions to high harmonic emission and their interferences give access to information about intra-molecular dynamics. In the case of unaligned molecules, we show experimental evidence that the long trajectory contribution is more dependent upon the molecular species than the short one, providing a high sensitivity to cation nuclear dynamics from 100's of as to a few fs after ionisation. Using theoretical approaches based on the strong field approximation and numerical integration of the time dependent Schrödinger equation, we examine how quantum path interferences encode electronic motion when the molecules are aligned. We show that the interferences are dependent upon which ionisation channels are involved and any superposition between them. In particular, quantum path interferences can encode signatures of electron dynamics if the laser field drives a coupling between the channels. Hence, molecular quantum path interferences are a promising method for attosecond spectroscopy, allowing the resolution of ultra-fast charge migration in molecules after ionisation in a self-referenced manner.

Zaïr, Amelle; Siegel, Thomas; Sukiasyan, Suren; Risoud, Francois; Brugnera, Leonardo; Hutchison, Christopher; Diveki, Zsolt; Auguste, Thierry; Tisch, John W. G.; Salières, Pascal.; Ivanov, Misha Y.; Marangos, Jonathan P.

2013-03-01

26

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

NASA Astrophysics Data System (ADS)

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

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

2011-10-01

27

Testing quantum dynamics using signaling  

NASA Astrophysics Data System (ADS)

We consider a physical system in which the description of states and measurements follow the usual quantum mechanical rules. We also assume that the dynamics is linear, but may not be fully quantum (i.e., unitary). We show that in such a physical system, certain complementary evolutions, namely, cloning and deleting operations that give a better fidelity than quantum mechanically allowed ones, in one (inaccessible) region, lead to signaling to a far-apart (accessible) region. To show such signaling, one requires certain two-party quantum correlated states shared between the two regions. Subsequent measurements are performed only in the accessible part to detect such phenomenon.

Sen(de), Aditi; Sen, Ujjwal

2005-07-01

28

Quantum molecular dynamics study on the structures and dc conductivity of warm dense silane  

NASA Astrophysics Data System (ADS)

The ionic and electronic structures of warm dense silane at the densities of 1.795, 2.260, 3.382, and 3.844 g/cm3 have been studied with temperatures from 1000 K to 3 eV using quantum molecular dynamics simulations. At all densities, the structures are melted above 1000 K. The matter states are characterized as polymeric from 1000 to 4000 K and become dense plasma states with further increasing temperature to 1 eV. At two lower densities of 1.795 and 2.260 g/cm3, silane first dissociates and then becomes the polymeric state via a chain state from the initial crystalline structure. At higher densities, however, no dissociation stage was found. These findings can help us understand how the warm dense matter forms. A rise is found for the direct current electric conductivity at T ˜1000 K, indicating the nonmetal-to-metal transition. The conductivity decreases slightly with the increase of temperature, which is due to the more disordered structures at higher temperatures.

Sun, Huayang; Kang, Dongdong; Dai, Jiayu; Zeng, Jiaolong; Yuan, Jianmin

2014-02-01

29

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

PubMed

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

Braams, Bastiaan J; Yu, Hua-Gen

2008-06-01

30

On the duality of quantum filtering and optimal feedback control in quantum open linear dynamical systems  

Microsoft Academic Search

The multi-dimensional quality open linear dynamical system with observation and feedback along a quantum linear transmission line is studied in discrete time. The linear least squares filtering and optimal control strategies are obtained as quantum analogies of the Kalman filter and Bellman dynamical programming. The duality of quantum filtering and optimal feedback control is observed for this particular case.

Simon C. Edwards; Viacheslav P. Belavkin

2003-01-01

31

A windowed-stripe quantum-dot laser structure for self-pulsation generation and lasing dynamic study under femtosecond optical pulse excitation  

Microsoft Academic Search

We demonstrated a new device structure with a central window on the quantum-dot laser stripe to generate the self-pulsation phenomenon. Furthermore, we apply the same device to study laser dynamics under femtosecond optical pulse excitation.

D.-C. Wu; S. Z. Wu; M.-H. Mao

2008-01-01

32

Control by quantum dynamics on graphs  

NASA Astrophysics Data System (ADS)

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

2010-05-01

33

Structure and ultrafast dynamics of liquid water: A quantum mechanics/molecular mechanics molecular dynamics simulations study  

NASA Astrophysics Data System (ADS)

A quantum mechanics/molecular mechanics molecular dynamics simulation was performed for liquid water to investigate structural and dynamical properties of this peculiar liquid. The most important region containing a central reference molecule and all nearest surrounding molecules (first coordination shell) was treated by Hartree-Fock (HF), post-Hartree-Fock [second-order Møller-Plesset perturbation theory (MP2)], and hybrid density functional B3LYP [Becke's three parameter functional (B3) with the correlation functional of Lee, Yang, and Parr (LYP)] methods. In addition, another HF-level simulation (2HF) included the full second coordination shell. Site to site interactions between oxygen-oxygen, oxygen-hydrogen, and hydrogen-hydrogen atoms of all ab initio methods were compared to experimental data. The absence of a second peak and the appearance of a shoulder instead in the gO-O graph obtained from the 2HF simulation is notable, as this feature has been observed so far only for pressurized or heated water. Dynamical data show that the 2HF procedure compensates some of the deficiency of the HF one-shell simulation, reducing the difference between correlated (MP2) and HF results. B3LYP apparently leads to too rigid structures and thus to an artificial slow down of the dynamics.

Xenides, Demetrios; Randolf, Bernhard R.; Rode, Bernd M.

2005-05-01

34

Non-Markovian dynamics of quantum discord  

Microsoft Academic Search

We evaluate the quantum discord dynamics of two qubits in independent and common non-Markovian environments. We compare the dynamics of entanglement with that of quantum discord. For independent reservoirs the quantum discord vanishes only at discrete instants whereas the entanglement can disappear during a finite time interval. For a common reservoir, quantum discord and entanglement can behave very differently with

F. F. Fanchini; A. O. Caldeira; T. Werlang; C. A. Brasil; L. G. E. Arruda

2010-01-01

35

Conditional Quantum Dynamics and Logic Gates  

Microsoft Academic Search

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 nonclassical properties. We describe a simple quantum logic gate, the quantum controlled-NOT, and analyze some of its applications. We discuss two possible physical realizations of the gate, one based

Adriano Barenco; David Deutsch; Artur Ekert; Richard Jozsa

1995-01-01

36

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

37

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

38

Fast method for quantum mechanical molecular dynamics  

NASA Astrophysics Data System (ADS)

As the processing power available for scientific computing grows, first-principles Born-Oppenheimer molecular dynamics simulations are becoming increasingly popular for the study of a wide range of problems in materials science, chemistry, and biology. Nevertheless, the computational cost of Born-Oppenheimer molecular dynamics still remains prohibitively large for many potential applications. Here we show how to avoid a major computational bottleneck: the self-consistent-field optimization prior to force calculations. The optimization-free quantum mechanical molecular dynamics method gives trajectories that are almost indistinguishable from an “exact” microcanonical Born-Oppenheimer molecular dynamics simulation even when low-prefactor linear scaling sparse matrix algebra is used. Our findings show that the computational gap between classical and quantum mechanical molecular dynamics simulations can be significantly reduced.

Niklasson, Anders M. N.; Cawkwell, Marc J.

2012-11-01

39

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

NASA Astrophysics Data System (ADS)

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.

2013-11-01

40

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

41

Theoretical Studies of the Influence of Temperature on Photoluminescence Dynamics in GaInNAs/GaAs Quantum Wells  

NASA Astrophysics Data System (ADS)

Dynamics of excitons in GaInNAs/GaAs quantum wells (QWs) is studied theoretically within a model of hopping excitons. In this model the temporal evolution of photoluminescence (PL) is described by the system of rate equations which takes into account hopping of excitons between randomly generated localizing states. In this work we study the influence of temperature on such characteristic features of PL as the decay and rise time of PL signal as well as their spectral dependences. It is clearly shown that our model reproduces experimental data very well.

Baranowski, Micha?; Kudrawiec, Robert; Misiewicz, Jan

2013-08-01

42

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

SciTech Connect

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

Amaran, Saieswari; Kosloff, Ronnie [Fritz Haber Research Centre and The Department of Physical Chemistry, Hebrew University, Jerusalem 91904 (Israel)] [Fritz Haber Research Centre and The Department of Physical Chemistry, Hebrew University, Jerusalem 91904 (Israel); Tomza, Micha?; Skomorowski, Wojciech; Paw?owski, Filip; Moszynski, Robert [Department of Chemistry, University of Warsaw, Pasteura 1, 02-093 Warsaw (Poland)] [Department of Chemistry, University of Warsaw, Pasteura 1, 02-093 Warsaw (Poland); Rybak, Leonid; Levin, Liat; Amitay, Zohar [The Shirlee Jacobs Femtosecond Laser Research Laboratory, Schulich Faculty of Chemistry, Technion-Israel Institute of Technology, Haifa 32000 (Israel)] [The Shirlee Jacobs Femtosecond Laser Research Laboratory, Schulich Faculty of Chemistry, Technion-Israel Institute of Technology, Haifa 32000 (Israel); Berglund, J. Martin; Reich, Daniel M.; Koch, Christiane P. [Theoretische Physik, Universität Kassel, Heinrich-Plett-Straße 40, 34132 Kassel (Germany)] [Theoretische Physik, Universität Kassel, Heinrich-Plett-Straße 40, 34132 Kassel (Germany)

2013-10-28

43

Molecular Dynamics Simulation Methods including Quantum Effects  

Microsoft Academic Search

\\u000a The progress of computational chemistry in the treatment of liquid systems is outlined, and the combination of the statistical\\u000a methods (in particular molecular dynamics) with quantum mechanics as the main foundation of this progress is emphasised. The\\u000a difficulties of experimental studies of liquid systems without having obtained sophisticated theoretical models describing\\u000a the structural entities and the dynamical behaviour of these

THOMAS S. HOFER; BERNHARD R. RANDOLF; BERND M. RODE

44

Quantum chaotic dynamics and random polynomials  

Microsoft Academic Search

We investigate the distribution of roots of polynomials of high degree with random coefficients which, among others, appear naturally in the context of “quantum chaotic dynamics.” It is shown that under quite general conditions their roots tend to concentrate near the unit circle in the complex plane. In order to further increase this tendency, we study in detail the particular

E. Bogomolny; O. Bohigas; P. Leboeuf

1996-01-01

45

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

SciTech Connect

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

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

2010-01-04

46

The quantum dynamic capacity formula of a quantum channel  

NASA Astrophysics Data System (ADS)

The dynamic capacity theorem characterizes the reliable communication rates of a quantum channel when combined with the noiseless resources of classical communication, quantum communication, and entanglement. In prior work, we proved the converse part of this theorem by making contact with many previous results in the quantum Shannon theory literature. In this work, we prove the theorem with an "ab initio" approach, using only the most basic tools in the quantum information theorist's toolkit: the Alicki-Fannes' inequality, the chain rule for quantum mutual information, elementary properties of quantum entropy, and the quantum data processing inequality. The result is a simplified proof of the theorem that should be more accessible to those unfamiliar with the quantum Shannon theory literature. We also demonstrate that the "quantum dynamic capacity formula" characterizes the Pareto optimal trade-off surface for the full dynamic capacity region. Additivity of this formula reduces the computation of the trade-off surface to a tractable, textbook problem in Pareto trade-off analysis, and we prove that its additivity holds for the quantum Hadamard channels and the quantum erasure channel. We then determine exact expressions for and plot the dynamic capacity region of the quantum dephasing channel, an example from the Hadamard class, and the quantum erasure channel.

Wilde, Mark M.; Hsieh, Min-Hsiu

2012-12-01

47

Scalable Software for Quantum Molecular Dynamics.  

National Technical Information Service (NTIS)

The objective of this project was to develop highly scalable quantum molecular dynamics software for the DoD CHSSI Initiative. Parallel versions of path integral Molecular Dynamics (PIMD) and centroid Molecular Dynamics (CMD) codes for homogeneous systems...

G. A. Voth

2001-01-01

48

A new class of compounds suited to study the torsional dynamics in the quantum regime: the calixarenes  

NASA Astrophysics Data System (ADS)

Inelastic neutron scattering spectroscopy has been used to study the rotational dynamics of methyl groups in the p-tert butylcalix[4]arene(1:1)toluene complex. The neutron scattering function shows several lines between 0.16 and 2.6 meV, and can be satisfactorily reproduced by the single-particle model for rotational tunneling only if the presence of inequivalent sites is assumed, in contrast with the crystallographic determinations. An approach consistent with the room-temperature crystal structure and giving a satisfactory description of the experimental results is obtained by the quantum sine—Gordon model, which describes the dynamics of infinite chains of coupled methyl groups.

Caciuffo, R.; Amoretti, G.; Fillaux, F.; Francescangeli, O.; Melone, S.; Prager, M.; Ugozzoli, F.

1993-01-01

49

Quantum dynamics study of the reaction HD+OH{r_arrow}H+DOH, D+HOH  

SciTech Connect

Accurate time-dependent (TD) quantum wavepacket calculations are reported for the combustion reaction HD+OH. Due to the lack of symmetry, the HD+OH reaction has roughly twice the number of channels of the corresponding H{sub 2}+OH reaction and produces two distinguishable products--HOH and HOD. In order to make the TD calculation possible on workstations with limited memories, we employed a normalized quadrature scheme in the wavepacket propagation by the split-operator propagator. The normalized quadrature scheme eliminates the need to store large matrices during the wavepacket propagation while preserving the unitarity of the split-operator propagator and producing numerically stable results. This approach made TD dynamics calculations possible on small-memory workstations for the title reaction and for other polyatomic reactions. Reaction probabilities, cross sections, rate constants, and reaction branching ratios are reported in this paper for the title reaction. The observed strong dependence of the reaction probabilities on the reactive HD rotation and the relative weak dependence on the nonreactive OH rotation are explained in terms of a steric effect. The isotope effect in the branching ratio is examined and physical explanation is given for the observed branching ratio at low and high kinetic energies.

Zhang, D.H.; Zhang, J.Z.H. [Department of Chemistry, New York University, New York, New York 10003 (United States)] [Department of Chemistry, New York University, New York, New York 10003 (United States); Zhang, Y.; Wang, D.; Zhang, Q. [Department of Physics, Shandong Teacher`s University, Jinan, Shandong (China)] [Department of Physics, Shandong Teacher`s University, Jinan, Shandong (China)

1995-05-15

50

Controlling quantum dynamics phenomena  

NASA Astrophysics Data System (ADS)

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

Rabitz, Herschel

2008-03-01

51

Quantum phases and dynamics of geometric phase in a quantum spin chain under linear quench  

NASA Astrophysics Data System (ADS)

We study the quantum phases of anisotropic XY spin chain in presence and absence of adiabatic quench. A connection between geometric phase and criticality is established from the dynamical behavior of the geometric phase for a quench induced quantum phase transition in a quantum spin chain. We predict XX criticality associated with a sequence of non-contractible geometric phases.

Sarkar, S.; Basu, B.

2012-12-01

52

The Application of Sodium Triple-Quantum Coherence NMR Spectroscopy for the Study of Growth Dynamics in Cartilage Tissue Engineering  

PubMed Central

We studied the tissue growth dynamics for tissue-engineered cartilage at the early growth stage after cell seeding for four weeks using sodium triple-quantum coherence NMR spectroscopy. The following tissue-engineering constructs were studied: 1. Bovine chondrocytes cultured in alginate beads, 2. Bovine chondrocytes cultured as pellets (scaffold-free chondrocyte pellets), 3. Human Marrow Stromal Cells (HMSC) seeded in Collagen/Chitosan based scaffolds of chondrogenic extracellular matrix environment expecting chondrogenic differentiation, named as biomimetic scaffolds. We found that the sodium triple quantum coherence spectroscopy can differentiate between different tissue-engineering constructs and the native tissues based on the fast and the slow relaxation rates as well as based on the average quadrupolar coupling. Both the fast (Tf) and the slow (Ts) relaxation times were found to be longer in the chondrocyte pellets and the biomimetic scaffolds as compared to the chondrocytes suspended in alginate beads and the human articular cartilage tissues. In all cases, it was found that the relaxation rates and the motion of sodium ions, as measured from correlation time, were dependent on the amount of macromolecules, high cell density and the anisotropy of the cartilage tissue engineering constructs. Average quadrupolar couplings were found to be lower in the engineered tissue as compared to the native tissues, presumably due to the lack of order in collagen accumulated in the engineered tissue. These results indicate the use of sodium triple quantum coherence spectroscopy as a tool to investigate anisotropy and growth dynamics of cartilage tissue engineered constructs in a simple and reliable way.

Kotecha, Mrignayani; Ravindran, Sriram; Schmid, Thomas M.; Vaidyanathan, Aishwarya; George, Anne; Magin, Richard L.

2013-01-01

53

Constant pressure path integral molecular dynamics studies of quantum effects in the liquid state properties of n-alkanes  

NASA Astrophysics Data System (ADS)

A computer simulation study of quantum effects in methane, butane, and octane is presented. Each molecular system is examined at three state points in the liquid region using novel extended system, multiple time step, constant pressure, path integral molecular dynamics methodology. In addition, the results of classical calculations are reported to provide a useful reference. Liquid butane is used as a test case on which to compare the predictions of two empirical force fields, CHARMM22 and AMBER95. Comparisons are made to experiment. Briefly, the models predict that quantum effects lead to an increase in molar volume of approximately 2 cm3/mole (i.e., relative to a classical calculation). However, a slight unphysical hydrogen-deuterium isotope effect is, also, observed. This may be caused by an incorrect parametrization of the anisotropy of the potential or by a reduction in the magnitude of the intermolecular induced dipole-induced dipole dispersion coefficient with increasing isotope mass that has not been parametrized in the force fields. In addition, the results show an interesting zero-point energy effect. The intramolecular regions of the radial distribution function exhibit less structure at lower temperatures than at higher temperatures. This is the inverse of the prediction of the model in the classical limit. The quantum effect occurs because the bulk density decreases faster than the intramolecular degrees of freedom lose zero-point energy as temperature increases in the highly harmonic intramolecular potential model employed in the calculations. Nonetheless, the phenomena is not likely to be an artifact and careful experiments could observe it. Finally, the efficiency of the path molecular dynamics methods employed in the studies are demonstrated on both serial and parallel computers.

Balog, E.; Hughes, A. L.; Martyna, G. J.

2000-01-01

54

Non-Markovian dynamics of quantum discord  

Microsoft Academic Search

We evaluate the quantum discord dynamics of two qubits in independent and\\u000acommon non-Markovian environments. We compare the dynamics of entanglement with\\u000athat of quantum discord. For independent reservoirs the quantum discord\\u000avanishes only at discrete instants whereas the entanglement can disappear\\u000aduring a finite time interval. For a common reservoir, quantum discord and\\u000aentanglement can behave very differently with

F. F. Fanchini; T. Werlang; C. A. Brasil; L. G. E. Arruda; A. O. Caldeira

2010-01-01

55

Decoherent dynamics of quantum correlations in qubit-qutrit systems  

NASA Astrophysics Data System (ADS)

We study the dynamics of quantum correlations of qubit-qutrit systems under various decoherent channels. It is shown that the multi-local and local decoherent channels bring different influences for the dynamics of quantum correlations measured by negativity, quantum discord and geometric discord, which depend on the initial state parameters and the properties of the decoherent channels. We put emphasis on the phenomena such as entanglement sudden death, sudden transition between classical and quantum decoherence and stable quantum discord and geometric discord.

Guo, Jin-Liang; Li, Hui; Long, Gui-Lu

2013-11-01

56

Quantum Dynamics of Polariton Condensates  

NASA Astrophysics Data System (ADS)

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

Laussy, Fabrice P.

57

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

58

Non-Markovian dynamics of quantum discord  

SciTech Connect

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

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

2010-05-15

59

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

NASA Astrophysics Data System (ADS)

The dynamics and molecular order of thin lipid (lecithin) films confined to 200, 100 and 20 nm cylindrical pores with varying surface coverage, were investigated by 1H multiple-quantum NMR. The results show that the molecular dynamics in the surface controlled layers are less hindered compared to those in the bulk. Dynamic heterogeneity among terminal CH 3 groups is evident. Enhanced dynamic freedom is observed for films with area per molecule, ˜ 128 Å 2. The results are discussed in terms of changes in the lipid molecular organization with respect to surface concentration, its plausible motional modes and dynamic heterogeneity.

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

2005-03-01

60

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

61

Nonlinear and Nonperturbative Dynamics in Quantum Wells  

NASA Astrophysics Data System (ADS)

Quantum well studies at the Free Electron Laser facility at the University of California, Santa Barbara, motivate a program for the theoretical study of the interaction of intense radiation with electrons in semiconductor heterostructures. Confined in one dimension, and free in the other two, electrons in quantum wells have their energies quantized in parabolic subbands. When laser light is coupled into the well, with polarization in the confinement direction, the matter-radiation system can be approximated as a one dimensional man-made "atom." The optical properties of this system are studied here, both in the perturbative and nonperturbative (weak and strong laser field) regimes. Whereas the classical analog of a driven quantum well has a phase-space which is typically a mixture of resonances and chaotic trajectories (Hamiltonian chaos), the quantum system may be characterized by a time-dependent basis set known as Floquet states. These states' coarse -grained Wigner distributions are ghostly likenesses of the classical phase space structures. The nonintegrability of the classically chaotic system manifests itself quantum mechanically with the appearance of avoided crossings in the spectrum of eigenvalues associated with the Floquet states. Avoided crossings correspond to multi-photon resonances and harmonic generation. The presence of electron-electron interactions provides interesting behavior as well, introducing nonlinearities into the dynamics (in the mean-field approximation). In the weak field regime, perturbation theory predicts an optical response function whose poles do not reside at the intersubband energy spacings, due to dressing of the field by the electron-electron interactions. Dressed optical response formulae are derived in this work up to second order. In the strong field regime, perturbation theory breaks down. However, one may directly integrate the quantum equations of motion to find a strong field steady-state response, if there is dissipation present. When dissipation can be neglected, the dynamics become sensitive to initial conditions, and the nonlinearity due to electron-electron interactions may even lead to chaos.

Galdrikian, Bryan Richard

62

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

63

Volume dynamics and quantum gravity  

NASA Astrophysics Data System (ADS)

Polyhedral grains of space can be given a dynamical structure. In recent work it was shown that Bohr-Sommerfeld quantization of the volume of a tetrahedral grain of space results in a spectrum in excellent agreement with loop gravity. Here we present preliminary investigations of the volume of a 5-faced convex polyhedron. We give for the first time a constructive method for finding these polyhedra given their face areas and normals to the faces and find an explicit formula for the volume. In particular, we are interested in discovering whether the evolution generated by this volume is chaotic or integrable which has important consequences for loop gravity: If the classical volume generates a chaotic flow then the corresponding quantum spectrum will generically be non-degenerate and the volume eigenvalue continues to act as a good label for spin network states. On the other hand, if the volume flow is classically integrable then the degeneracy of the corresponding quantum spectrum will have to be lifted by another observable. We report on progress distinguishing these two cases. Either of these outcomes will impact the direction of future research into volume operators in quantum gravity.

Haggard, Hal

2012-03-01

64

Quantum dynamics of a two-level system in a structured environment: Numerical study beyond perturbation theory  

SciTech Connect

The dissipative quantum dynamics of a two-level system interacting with a structured reservoir consisting of a damped harmonic mode is investigated by means of the numerically exact path integral Monte Carlo method. This approach provides benchmark results in a broad range of parameter space, in particular, in those domains which are not accessible by approximate methods and alternative numerical schemes, that is, strong coupling between system and harmonic mode and from low to high temperatures. For low temperatures the numerical data are quantitatively in agreement with the noninteracting blip approximation only in the regimes of very weak and very strong coupling. It turns out that the entangled dynamics of the two-level system and the harmonic mode is relatively robust so that its signatures are observable up to relatively strong friction and high temperatures. Nonequilibrium initial preparations of the reservoir with respect to the initial state of the system give rise, for strong interactions, to a stepwise decay of the population, thus displaying coherent dynamics of the bath. The impact of an additional Ohmic bath coupled directly to the two-level system is studied as well, including the case where both reservoirs carry different temperatures.

Escher, Johanna Charlotte; Ankerhold, Joachim [Institut fuer Theoretische Physik, Universitaet Ulm, Albert-Einstein-Allee 11, D-89069 Ulm (Germany)

2011-03-15

65

Quantum dynamics of a two-level system in a structured environment: Numerical study beyond perturbation theory  

NASA Astrophysics Data System (ADS)

The dissipative quantum dynamics of a two-level system interacting with a structured reservoir consisting of a damped harmonic mode is investigated by means of the numerically exact path integral Monte Carlo method. This approach provides benchmark results in a broad range of parameter space, in particular, in those domains which are not accessible by approximate methods and alternative numerical schemes, that is, strong coupling between system and harmonic mode and from low to high temperatures. For low temperatures the numerical data are quantitatively in agreement with the noninteracting blip approximation only in the regimes of very weak and very strong coupling. It turns out that the entangled dynamics of the two-level system and the harmonic mode is relatively robust so that its signatures are observable up to relatively strong friction and high temperatures. Nonequilibrium initial preparations of the reservoir with respect to the initial state of the system give rise, for strong interactions, to a stepwise decay of the population, thus displaying coherent dynamics of the bath. The impact of an additional Ohmic bath coupled directly to the two-level system is studied as well, including the case where both reservoirs carry different temperatures.

Escher, Johanna Charlotte; Ankerhold, Joachim

2011-03-01

66

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

Lévêque, Camille; Köppel, Horst; Taïeb, Richard

2014-05-28

67

Quantum Dynamics with AN Ensemble of Hamiltonians  

NASA Astrophysics Data System (ADS)

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

Rahmani, Armin

2013-10-01

68

Dynamic study of highly efficient CdS/CdSe quantum dot-sensitized solar cells fabricated by electrodeposition.  

PubMed

An in situ electrodeposition method is described to fabricate the CdS or/and CdSe quantum dot (QD) sensitized hierarchical TiO(2) sphere (HTS) electrodes for solar cell application. Intensity modulated photocurrent spectroscopy (IMPS), intensity modulated photovoltage spectroscopy (IMVS) and electrochemical impedance spectroscopy (EIS) measurements are performed to investigate the electron transport and recombination of quantum dot-sensitized solar cells (QDSSCs) based on HTS/CdS, HTS/CdSe, and HTS/CdS/CdSe photoelectrodes. This dynamic study reveals that the CdSe/CdS cosensitized solar cell performs ultrafast electron transport and high electron collection efficiency (98%). As a consequence, a power conversion efficiency as high as 4.81% (J(SC) = 18.23 mA cm(-2), V(OC) = 489 mV, FF = 0.54) for HTS/CdS/CdSe photoelectrode based QDSSC is observed under one sun AM 1.5 G illumination (100 mW cm(-2)). PMID:22032641

Yu, Xiao-Yun; Liao, Jin-Yun; Qiu, Kang-Qiang; Kuang, Dai-Bin; Su, Cheng-Yong

2011-12-27

69

Quantum Geometry and Quantum Dynamics at the Planck Scale  

SciTech Connect

Canonical quantum gravity provides insights into the quantum dynamics as well as quantum geometry of space-time by its implications for constraints. Loop quantum gravity in particular requires specific corrections due to its quantization procedure, which also results in a discrete picture of space. The corresponding changes compared to the classical behavior can most easily be analyzed in isotropic models, but perturbations around them are more involved. For one type of corrections, consistent equations have been found which shed light on the underlying space-time structure at the Planck scale: not just quantum dynamics but also the concept of space-time manifolds changes in quantum gravity. Effective line elements provide indications for possible relationships to other frameworks, such as non-commutative geometry.

Bojowald, Martin [Institute for Gravitation and the Cosmos, The Pennsylvania State University, 104 Davey Lab, University Park, PA 16802 (United States)

2009-12-15

70

Dynamics of a Quantum Phase Transition  

SciTech Connect

We present two approaches to the dynamics of a quench-induced phase transition in the quantum Ising model. One follows the standard treatment of thermodynamic second order phase transitions but applies it to the quantum phase transitions. The other approach is quantum, and uses Landau-Zener formula for transition probabilities in avoided level crossings. We show that predictions of the two approaches of how the density of defects scales with the quench rate are compatible, and discuss the ensuing insights into the dynamics of quantum phase transitions.

Zurek, Wojciech H. [Theory Division, LANL, MS-B213, Los Alamos, New Mexico 87545 (United States); Dorner, Uwe [Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU (United Kingdom); Zoller, Peter [Institute for Theoretical Physics, University of Innsbruck, and Institute for Quantum Optics and Quantum Information of the Austrian Academy of Sciences, A-6020 Innsbruck (Austria)

2005-09-02

71

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

72

Quantum Discord Dynamics in Two Different Non-Markovian Reservoirs  

Microsoft Academic Search

The quantum discord dynamics of two non-coupled two-level atoms independently interacting with their reservoir is studied under two kinds of non-Markovian conditions, namely, an off-resonant case with atomic transition frequency and a photonic band gap. In the first case, the phenomenon of the quantum discord loss and the oscillatory behavior of the quantum discord can occur by changing the detuning

Bang-Fu Ding; Xiao-Yun Wang; Jing-Feng Liu; Lin Yan; He-Ping Zhao

2011-01-01

73

Quasiperiodic dynamics of a quantum walk on the line.  

PubMed

We study the dynamics of a generalization of a quantum coin walk on the line, which is a natural model for a diffusion modified by quantum or interference effects. In particular, our results provide surprisingly simple explanations for recurrence phenomena observed by Bouwmeester et al. [Phys. Rev. A 61, 13410 (1999)

Wójcik, Antoni; ?uczak, Tomasz; Kurzy?ski, Pawe?; Grudka, Andrzej; Bednarska, Ma?gorzata

2004-10-29

74

Quantum lattice-gas model for computational fluid dynamics  

Microsoft Academic Search

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

Jeffrey Yepez

2001-01-01

75

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

PubMed

Time independent quantum mechanical (TIQM) scattering calculations have been carried out for the O((1)D) + CH4(X(1)A1) ? CH3(X(2)A2?) + OH(X(2)?) 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. PMID:24985646

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

2014-06-28

76

Exciton Dynamics in Gallium Arsenide Quantum Wells  

NASA Astrophysics Data System (ADS)

The dynamics of excitons is studied using time -resolved photoluminescence. We deduce experimentally, for the first time, the intrinsic homogeneous linewidth of free excitons in GaAs quantum wells. The scattering rate of excitons is directly estimated from temperature dependent linewidth measurements. A theoretical model is presented that correlates the observed photoluminescence linewidth, and hence the scattering rate, to the measured spin relaxation rate of excitons. We show that quantum confinement enhances the spin relaxation rate of weakly scattered electrons by more than two orders of magnitude over that of the bulk. The spin exchange energy is experimentally determined for the first time for GaAs quantum wells. The radiative recombination rate of excitons in GaAs quantum wells is very large due to the macroscopic polarization of the exciton-polariton. Thermalization and scattering reduce the coherence volume of this polarization, resulting in a temperature and intensity dependent photoluminescence lifetime. We derive a theoretical model which is shown to explain the experimental results on the radiative lifetimes.

Srinivas, Vivek

77

Dynamical programming of continuously observed quantum systems  

NASA Astrophysics Data System (ADS)

We develop dynamical programming methods for the purpose of optimal control of quantum states with convex constraints and concave cost and bequest functions of the quantum state. We consider both open loop and feedback control schemes, which correspond, respectively, to deterministic and stochastic master equation dynamics. For the quantum feedback control scheme with continuous nondemolition observations, we exploit the separation theorem of filtering and control aspects for quantum stochastic dynamics to derive a generalized Hamilton-Jacobi-Bellman equation. If the control is restricted to only Hamiltonian terms this is equivalent to a Hamilton-Jacobi equation with an extra linear dissipative term. In this work, we consider, in particular, the case when control is restricted only to observation. A controlled qubit is considered as an example throughout the development of the formalism. Finally, we discuss optimum observation strategies to obtain a pure state from a mixed state of a quantum two-level system.

Belavkin, Viacheslav P.; Negretti, Antonio; Mølmer, Klaus

2009-02-01

78

Quantum Computation of Fluid Dynamics  

Microsoft Academic Search

Presented is a quantum lattice gas for Navier-Stokes fluid dynamicssimulation. The quantum lattice-gas transport equation at the microscopicscale is presented as a generalization of the classical lattice-gastransport equation. A special type of quantum computer network is proposedthat is suitable for implementing the quantum lattice gas. Thequantum computer network undergoes a partial collapse of the wavefunctionat every time step of the

Jeffrey Yepez

1998-01-01

79

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

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

80

Few Body Quantum Dynamics of high-Z Ions studied at the Future Relativistic HESR Storage Ring  

NASA Astrophysics Data System (ADS)

At the FAIR facility for antiprotons and ion research the high energy storage ring HESR, originally conceived for experiments using antiprotons, will be configured to also provide highly-charged heavy ions up to beam energies corresponding to ?=5. This opens a wealth of opportunities for in-ring atomic physics experiments on few- body quantum dynamics ranging from e.g. dynamics of various e^+-e^- pair creation processes to quasi-photoionisation of inner shells of the highest-Z ions. We will discuss various in-ring spectrometers permitting characterization of the pertaining fundamental processes in a kinematically complete fashion.

Hagmann, Siegbert; Stoehlker, Thomas; Litvinov, Yuri; Kozhuharov, Christophor; Hillenbrand, Pierre-Michel; Lestinsky, Michael; Schneider, Dieter; Stiebing, Kurt

2012-06-01

81

Quantum correlated electron dynamics in a quantum-dot sensitized solar cell: Keldysh function approach  

Microsoft Academic Search

In this work we study quantum dynamics of an electron transferred from a quantum dot (QD) to a semiconductor (SM) in a quantum-dot-semiconductor solar cell. The proposed theoretical description includes the following interactions: electron-electron and electron-phonon interactions in a QD, interaction with light, electron-phonon interaction in an SM, and interaction between the electronic states in a QD and an SM

Yuri Dahnovsky

2011-01-01

82

Dynamical coherent states and physical solutions of quantum cosmological bounces  

SciTech Connect

A new model is studied which describes the quantum behavior of transitions through an isotropic quantum cosmological bounce in loop quantum cosmology sourced by a free and massless scalar field. As an exactly solvable model even at the quantum level, it illustrates properties of dynamical coherent states and provides the basis for a systematic perturbation theory of loop quantum gravity. The detailed analysis is remarkably different from what is known for harmonic oscillator coherent states. Results are evaluated with regard to their implications in cosmology, including a demonstration that in general quantum fluctuations before and after the bounce are unrelated. Thus, even within this solvable model the condition of classicality at late times does not imply classicality at early times before the bounce without further assumptions. Nevertheless, the quantum state does evolve deterministically through the bounce.

Bojowald, Martin [Institute for Gravitational Physics and Geometry, Pennsylvania State University, 104 Davey Lab, University Park, Pennsylvania 16802 (United States) and Kavli Institute for Theoretical Physics, University of California, Santa Barbara, California 93106 (United States)

2007-06-15

83

Quantum well lasers - Gain, spectra, dynamics  

Microsoft Academic Search

The present consideration of theoretical and experimental issues in the field of quantum well laser development emphasizes the basic behavior of such aspects of laser operation as the gain, the field spectrum, and the modulation dynamics. The use of quantum well structures is noted to yield improvements in these properties, and brings several novel concepts to bear on the field

Y. Arakawa; A. Yariv

1986-01-01

84

Control of Quantum Dynamics: Issues and Alternatives.  

National Technical Information Service (NTIS)

This paper gives an overview of the logic behind current conceptual issues directed towards controlling quantum dynamics phenomena. The role of theory to translate these concepts mto laboratory designs will be highlighted, along with an explanation of the...

H. Rabitz

1994-01-01

85

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

National Technical Information Service (NTIS)

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

F. Faure

1993-01-01

86

Large nonadiabatic quantum molecular dynamics simulations on parallel computers  

NASA Astrophysics Data System (ADS)

We have implemented a quantum molecular dynamics simulation incorporating nonadiabatic electronic transitions on massively parallel computers to study photoexcitation dynamics of electrons and ions. The nonadiabatic quantum molecular dynamics (NAQMD) simulation is based on Casida's linear response time-dependent density functional theory to describe electronic excited states and Tully's fewest-switches surface hopping approach to describe nonadiabatic electron-ion dynamics. To enable large NAQMD simulations, a series of techniques are employed for efficiently calculating long-range exact exchange correction and excited-state forces. The simulation program is parallelized using hybrid spatial and band decomposition, and is tested for various materials.

Shimojo, Fuyuki; Ohmura, Satoshi; Mou, Weiwei; Kalia, Rajiv K.; Nakano, Aiichiro; Vashishta, Priya

2013-01-01

87

Simulating Quantum Dynamics On A Quantum Computer  

NASA Astrophysics Data System (ADS)

We develop an efficient quantum algorithm for simulating time-dependent Hamiltonian evolution of general input states on a quantum computer. Given conditions on the smoothness of the Hamiltonian, the complexity of the algorithm is close to linear in the evolution time, and therefore is comparable to algorithms for time-independent Hamiltonians. In addition, we show how the complexity can be reduced by optimizing the time steps. The complexity of the algorithm is quantified by calls to an oracle, which yields information about the Hamiltonian, and accounts for all computational resources. In contrast to previous work, which allowed an oracle query to yield an arbitrary number of bits or qubits, we assign a cost for each bit or qubit accessed. This per-bit or per-qubit costing of oracle calls reveals hitherto unnoticed simulation costs. We also account for discretization errors in the time and the representation of the Hamiltonian. We generalize the requirement of sparse Hamiltonians to being a sum of sparse Hamiltonians in various bases for which the transformation to a sparse Hamiltonian may be performed efficiently.

Wiebe, Nathan; Berry, Dominic; Hoyer, Peter; Sanders, Barry

2011-03-01

88

Dynamical spectra of quantum strings in quantum spin ice  

NASA Astrophysics Data System (ADS)

String-like excitations in quantum spin-ice are a fascinating manifestation of quantum fluctuations and may be observable in materials such as Yb2Ti2O7 and Pr2Zr2O7. We study quantum spin-ice under external magnetic fields on both the checkerboard and pyrochlore lattice for experimentally relevant conditions. We show that excitations in quantum spin ice may be string-like, and that stronger quantum fluctuations reduce string tension and lead to deconfined monopoles. Additionally, we discuss the crossover from strings to magnons in the high-field regime. We provide predictions for observing strings via inelastic neutron scattering and THz spectroscopy.

Fuhrman, Wesley; Wan, Yuan; Tchernyshyov, Oleg

2013-03-01

89

Reactivity versus steric effects in fluorinated ketones as esterase inhibitors: a quantum mechanical and molecular dynamics study  

PubMed Central

Carboxylesterases (CEs) are a family of ubiquitous enzymes with broad substrate specificity, and their inhibition may have important implications in pharmaceutical and agrochemical fields. One of the most potent inhibitors both for mammalian and insect CEs are trifluoromethyl ketones (TFMKs), but the mechanism of action of these chemicals is not completely understood. This study examines the balance between reactivity versus steric effects in modulating the activity against human carboxylesterase 1. The intrinsic reactivity of the ketone moiety is determined from quantum mechanical computations, which combine gas phase B3LYP calculations with hydration free energies estimated with the IEF/MST model. In addition, docking and molecular dynamics simulations are used to explore the binding mode of the inhibitors along the deep gorge that delineates the binding site. The results point out that the activity largely depends on the nature of the fluorinated ketone, since the activity is modulated by the balance between the intrinsic electrophilicity of the carbonyl carbon atom and the ratio between keto and hydrate forms. However, the results also suggest that the correct alignment of the alkyl chain in the binding site can exert a large influence on the inhibitory activity, as this effect seems to override the intrinsic reactivity features of the fluorinated ketone. Overall, the results sustain a subtle balance between reactivity and steric effects in modulating the inhibitory activity of TFMK inhibitors.

Rayo, Josep; Munoz, Lourdes; Rosell, Gloria; Hammock, Bruce D.; Guerrero, Angel

2010-01-01

90

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

NASA Astrophysics Data System (ADS)

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

Ishizaki, Akihito; Fleming, Graham R.

2009-06-01

91

Dynamic susceptibility of the Anderson model: A quantum Monte Carlo study  

SciTech Connect

Using a highly accurate method of analytic continuation, we calculated the dynamic susceptibility and NMR relaxation rate 1/{ital T}{sub 1} of magnetic (Anderson or Kondo) impurities over the {ital entire} range {ital T}{much lt}{ital T}{sub {ital K}} to {ital T}{much gt}{ital T}{sub {ital K}}. We find that the susceptibility and NMR relaxation rate are universal functions when properly scaled and that the NMR relaxation rate is directly proportional to the universal Kondo resistivity.

Jarrell, M. (Department of Physics, University of Cincinnati, Cincinnati, Ohio (USA)); Gubernatis, J.E. (Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico (USA)); Silver, R.N. (Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico (USA) Manuel Lujan, Jr. Neutron Scattering Center, Los Alamos National Laboratory, Los Alamos, New Mexico (USA))

1991-09-01

92

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

93

Simulating quantum dynamics on a quantum computer  

NASA Astrophysics Data System (ADS)

We explicitly show how to simulate time-dependent sparse Hamiltonian evolution on a quantum computer, with complexity that is close to linear in the evolution time. The complexity also depends on the magnitude of the derivatives of the Hamiltonian. We propose a range of techniques to simulate Hamiltonians with badly behaved derivatives. These include using adaptive time steps, adapting the order of the integrators, and omitting regions about discontinuities. The complexity of the algorithm is quantified by calls to an oracle, which yields information about the Hamiltonian, and accounts for all computational resources. We explicitly determine the number of bits of output that this oracle needs to provide, and show how to efficiently perform the required 1-sparse unitary operations using these bits. We also account for discretization error in the time, as well as accounting for Hamiltonians that are a sum of terms that are sparse in different bases.

Wiebe, Nathan; Berry, Dominic W.; Høyer, Peter; Sanders, Barry C.

2011-11-01

94

Semiclassical Description of Nonadiabatic Quantum Dynamics  

SciTech Connect

A semiclassical approach is presented that allows us to extend the usual Van Vleck{endash}Gutzwiller formulation to the description of nonadiabatic quantum dynamics on coupled potential-energy surfaces. Based on Schwinger{close_quote}s theory of angular momentum, the formulation employs an exact mapping of the discrete quantum variables onto continuous degrees of freedom. The resulting dynamical problem is evaluated through a semiclassical initial-value representation of the time-dependent propagator. As a first application we have performed semiclassical simulations for a spin-boson model, which reproduce the exact quantum-mechanical results quite accurately. {copyright} {ital 1997} {ital The American Physical Society}

Stock, G.; Thoss, M. [Institute of Physical and Theoretical Chemistry, Technical University of Munich, D-85748 Garching (Germany)] [Institute of Physical and Theoretical Chemistry, Technical University of Munich, D-85748 Garching (Germany)

1997-01-01

95

Real Time Nonequilibrium Dynamics of Quantum Plasmas  

NASA Astrophysics Data System (ADS)

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

de Vega, H. J.

96

Dynamics of fluctuations in a quantum system  

NASA Astrophysics Data System (ADS)

``The noise is the signal" [R. Landauer, Nature (London) 392, 658 (1998), 10.1038/33551] emphasizes the rich information content encoded in fluctuations. This paper assesses the dynamical role of fluctuations of a quantum system driven far from equilibrium, with laser-aligned molecules as a physical realization. Time evolutions of the expectation value and the uncertainty of a standard observable are computed quantum mechanically and classically. We demonstrate the intricate dynamics of the uncertainty that are strikingly independent of those of the expectation value, and their exceptional sensitivity to quantum properties of the system. In general, detecting the time evolution of the fluctuations of a given observable provides information on the dynamics of correlations in a quantum system.

Chen, Yi-Jen; Pabst, Stefan; Li, Zheng; Vendrell, Oriol; Santra, Robin

2014-05-01

97

a Study of the Fundamentals of Modern Lattice Dynamics with AN Application to Quantum Crystals  

NASA Astrophysics Data System (ADS)

We describe some advances made in the effective potential Monte Carlo (EPMC) method. In particular, the effective potential has previously been evaluated by expanding the smeared potential up to finite order; we show that the infinite series can be summed analytically. Previous work also included various forms of an isotropic approximation and the low-coupling approximation; we discard the former but initially retain the latter. We find significant differences with earlier work and argue that the finite-order EPMC method is now obsolete and that the new formalism supersedes it. A deficiency in the EPMC method is that the Gaussian averaging process neglects odd terms in the Taylor expansion of the potential. We describe an improved effective potential theory (IEP) in which this is partially removed by incorporating into the EPMC method, using perturbation theory, a cubic contribution from the potential. We show that IEP theory leads to a marked improvement over the results obtained from the EPMC theory while the EPMC method's speed and computational facility are fully preserved. These fundamental advances in formulating a reliable all-temperature lattice dynamics contain an uncontrolled approximation--the low-coupling approximation (LCA)--routinely used in the implementation of the EPMC theory. We examine the validity of the LCA, by making calculations that do not use it, and find that the LCA is not a good approximation when used with EPMC. We show that the errors caused by making the LCA are properly compensated for only when it is used in conjunction with the IEP theory. We find that at the very lowest temperatures there are small anomalies in the thermal properties. While these are not significant for the heavier rare-gas solids, they probably will be important when IEP is applied to helium. Finally, we examine the validity of a variety of potentials to account for the experimental thermal and elastic properties of solid neon, using IEP theory. We show that so-called realistic potentials are currently not able to account for the experimental results, even when many-body effects are explicitly included. A simple -minded nearest neighbor Lennard-Jones model is shown to give the best account of the thermodynamics of solid neon.

Acocella, Dominic

98

Carrier dynamics in quantum well and quantum dot lasers  

NASA Astrophysics Data System (ADS)

This dissertation concerns the high speed characteristics of semiconductor lasers. From analysis of the frequency dependence of optical modulation characteristics and small signal impedance, it has been possible to extract information about the carrier dynamics and particularly, the carrier capture time. Study of quantum dot high speed characteristics as a function of temperature have led to good understanding of their dynamics. Analysis of the room temperature impedance in quantum dot laser has shown typical capture times of about 30-40ps. The capture times agree reasonably well with values calculated values based on electron-hole scattering being the important capture mechanism. Measured modulation bandwidths of 20GHz at 80K are consistent with pump-probe measurements of capture time of about 10ps. Theoretical calculations show that the capture time is expected to reduce at low temperatures. The onset of severe capture time limitations was at about 150K which resulted in an extracted spacing between the ground and excited electron state of 60 meV, in good agreement with theoretical calculations of 56 meV. Hence, both the magnitude and temperature dependence of the modulation response are consistent with the mechanism for carrier capture being electron-hole scattering. In contrast, maximum modulation bandwidth of very high speed quantum well lasers has shown an increase of less than a factor of two between room temperature and cryogenic temperature. Extremely high speed 1.55?m tunneling injection lasers increased from 20 GHz bandwidth at room temperature to an extrapolated 35 GHz at cryogenic temperature, while the differential gain increased by a factor of fifty. The K-factor and hence the damping limit was almost independent of temperature. This suggest that the gain compression factor is proportional to differential gain. The general result is that for devices which are damping limited, no great improvement in bandwidth is expected from operating at lower temperature. A comparative study was made between a tunneling injection laser (TIL) and three different confinement heterostructure (SCH) 1.55 ?m devices with similar gain regions. The TIL showed more than twice the room temperature modulation bandwidth of the best of the SCH devices, double the differential gain, and the same K-factor. The TIL was limited much less by heating and somewhat less by capture time than the SCH devices. These differences between both their dynamic and DC characteristics are consistent with the tunneling injection mechanism resulting in a cold carrier distribution. Measurements of large-signal modulation characteristics are compared to full numerical rate equantion simulations and show reasonable agreement. An expression is determined for temporal photon density as a function of small signal parameters, and comparison of this expression with full numerical simulation shows that it is valid for output switching ratios up to about 2. The determined maximum digital transmission speed is approximately 23/K (ns) or 1.4/(capture time)(ns) in Gb/sec. This analysis indicates that large signal pulse widths are typically limited to K-factor in quantum well lasers, and are limited by both K-factor and capture time in quantum dot lasers. (Abstract shortened by UMI.)

Klotzkin, David J.

99

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

SciTech Connect

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

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

1990-01-01

100

Dynamic quantum Kerr effect in circuit quantum electrodynamics  

NASA Astrophysics Data System (ADS)

In the dispersive regime of circuit quantum electrodynamics (QED), where the qubit and resonator frequencies differ slightly, photons in the resonator exhibit induced frequency and phase shifts. The qubit-state dependent phase shift is usually measured by monitoring the resonator transmission spectrum at fixed qubit-resonator detuning. In this static scheme, the phase shift can only be monitored in the far-detuned, linear dispersion regime, in order to avoid measurement-induced demolition of the quantum state. By using a dynamic procedure to adiabatically drive the qubit frequency, here we are able to explore the dispersive interaction over a much broader range, and we further monitor the interaction using resonator Wigner tomography. Exotic non-linear effects on different photon states, e.g., Fock states, coherent states and Schrodinger cat states, are thereby directly revealed. Correspondingly, we demonstrate a quantum Kerr effect in the dynamic framework in circuit QED.

Yin, Yi; Wang, Haohua; Mariantoni, Matteo; Barends, Rami; Bialczak, Radoslaw C.; Chen, Yu; Lenander, Mike; Kelly, Julian; Lucero, Erik; Megrant, Anthony; O'Malley, Peter; Sank, Daniel; Wenner, Jim; White, Ted; Cleland, Andrew; Martinis, John

2012-02-01

101

Quantum dynamics of two quantum dots in the vicinity of a photonic band edge: role of structured reservoirs and phonons  

Microsoft Academic Search

We study the population and disentanglement dynamics of two identical quantum dots placed inside the structured electromagnetic reservoir of a photonic crystal and coupled to an independent bath of thermal phonons. A formalism based on the method of generalized-Laplace transforms is developed to study the population and disentanglement dynamics. The effect of resonant dipole dipole interaction between the two quantum

Chiranjeeb Roy

2010-01-01

102

Quantum dynamics in classical thermal baths  

NASA Astrophysics Data System (ADS)

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

Dlamini, Nkosinathi; Sergi, Alessandro

2013-11-01

103

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

Microsoft Academic Search

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

David Gelman; Steven D. Schwartz

2010-01-01

104

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

PubMed

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

Wu, Jianlan; Cao, Jianshu

2013-07-28

105

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

NASA Astrophysics Data System (ADS)

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

Wu, Jianlan; Cao, Jianshu

2013-07-01

106

Distributed CNOT gate via quantum Zeno dynamics  

SciTech Connect

We show how the quantum Zeno effect can be exploited to implement the CNOT gate in two separated cavities with two atomic four-level tripod systems. In respective subspaces of the total Hilbert space, the evolution of the quantum system exhibits different dynamical properties due to the continuous coupling between atoms and cavities. The strictly numerical simulation reveals that a high average gate fidelity can be obtained in the presence of decoherence.

Shao Xiaoqiang; Wang Hongfu; Zhao Yongfang [Center for the Condensed-Matter Science and Technology, Department of Physics, Harbin Institute of Technology, Harbin, Heilongjiang 150001 (China); Chen Li [Department of Physics, College of Science, Yanbian University, Yanji, Jilin 133002 (China); Zhang Shou [Center for the Condensed-Matter Science and Technology, Department of Physics, Harbin Institute of Technology, Harbin, Heilongjiang 150001 (China); Department of Physics, College of Science, Yanbian University, Yanji, Jilin 133002 (China); Yeon, Kyu-Hwang [BK21 Program Physics and Department of Physics, College of Natural Science, Chungbuk National University, Cheonju, Chungbuk 361-763 (Korea, Republic of)

2009-12-15

107

Stochastic solution to quantum dynamics  

NASA Astrophysics Data System (ADS)

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.

1994-02-01

108

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

109

Nuclear quantum dynamics in dense hydrogen  

PubMed Central

Nuclear dynamics in dense hydrogen, which is determined by the key physics of large-angle scattering or many-body collisions between particles, is crucial for the dynamics of planet's evolution and hydrodynamical processes in inertial confinement confusion. Here, using improved ab initio path-integral molecular dynamics simulations, we investigated the nuclear quantum dynamics regarding transport behaviors of dense hydrogen up to the temperatures of 1?eV. With the inclusion of nuclear quantum effects (NQEs), the ionic diffusions are largely higher than the classical treatment by the magnitude from 20% to 146% as the temperature is decreased from 1?eV to 0.3?eV at 10?g/cm3, meanwhile, electrical and thermal conductivities are significantly lowered. In particular, the ionic diffusion is found much larger than that without NQEs even when both the ionic distributions are the same at 1?eV. The significant quantum delocalization of ions introduces remarkably different scattering cross section between protons compared with classical particle treatments, which explains the large difference of transport properties induced by NQEs. The Stokes-Einstein relation, Wiedemann-Franz law, and isotope effects are re-examined, showing different behaviors in nuclear quantum dynamics.

Kang, Dongdong; Sun, Huayang; Dai, Jiayu; Chen, Wenbo; Zhao, Zengxiu; Hou, Yong; Zeng, Jiaolong; Yuan, Jianmin

2014-01-01

110

Nuclear quantum dynamics in dense hydrogen.  

PubMed

Nuclear dynamics in dense hydrogen, which is determined by the key physics of large-angle scattering or many-body collisions between particles, is crucial for the dynamics of planet's evolution and hydrodynamical processes in inertial confinement confusion. Here, using improved ab initio path-integral molecular dynamics simulations, we investigated the nuclear quantum dynamics regarding transport behaviors of dense hydrogen up to the temperatures of 1?eV. With the inclusion of nuclear quantum effects (NQEs), the ionic diffusions are largely higher than the classical treatment by the magnitude from 20% to 146% as the temperature is decreased from 1?eV to 0.3?eV at 10?g/cm(3), meanwhile, electrical and thermal conductivities are significantly lowered. In particular, the ionic diffusion is found much larger than that without NQEs even when both the ionic distributions are the same at 1?eV. The significant quantum delocalization of ions introduces remarkably different scattering cross section between protons compared with classical particle treatments, which explains the large difference of transport properties induced by NQEs. The Stokes-Einstein relation, Wiedemann-Franz law, and isotope effects are re-examined, showing different behaviors in nuclear quantum dynamics. PMID:24968754

Kang, Dongdong; Sun, Huayang; Dai, Jiayu; Chen, Wenbo; Zhao, Zengxiu; Hou, Yong; Zeng, Jiaolong; Yuan, Jianmin

2014-01-01

111

A Quantum Lattice-Gas Model for Computational Fluid Dynamics  

Microsoft Academic Search

Quantum-computing ideas are applied to the practical and ubiquitous problem of fluid dynamics simulation. Presented in this talk is a quantum computing algorithm called a quantum lattice gas. An analytical treatment of the microscopic quantum lattice-gas system is summarized and the predicted effective field theory of the quantum system, at the mesoscopic and macroscopic scales, is given. At the mesoscopic

Jeffrey Yepez

2000-01-01

112

Quantum relaxation dynamics using Bohmian trajectories  

NASA Astrophysics Data System (ADS)

We present a new Bohmian trajectory based treatment of quantum dynamics suitable for dissipative systems. Writing the density matrix in complex-polar form, we derive and define quantum equations of motion for Liouville-space trajectories for a generalized system coupled to a dissipative environment. Our theory includes a vector potential which mixes forward and backwards propagating components and pulls coherence amplitude away from the diagonal region of the density matrix. Quantum effects enter via a double quantum potential, Q(x,y), which is a measure of the local curvature of the density amplitude. We discuss how decoherence can be thought of as a balancing between localization brought on by contact with a thermal environment which increases the local curvature of the density matrix and delocalization due to the internal pressure of the quantum force which seeks to minimize the local curvature. The quantum trajectories are then used to propagate an adaptive Lagrangian grid which carries the density matrix, ?(x,y), and the action, A(x,y), thereby providing a complete hydrodynamiclike description of the dynamics.

Maddox, Jeremy B.; Bittner, Eric R.

2001-10-01

113

Quantum chaotic dynamics and random polynomials  

SciTech Connect

We investigate the distribution of roots of polynomials of high degree with random coefficients which, among others, appear naturally in the context of {open_quotes}quantum chaotic dynamics.{close_quotes} It is shown that under quite general conditions their roots tend to concentrate near the unit circle in the complex plane. In order to further increase this tendency, we study in detail the particular case of self-inversive random polynomials and show that for them a finite portion of all roots lies exactly on the unit circle. Correlation functions of these roots are also computed analytically, and compared to the correlations of eigenvalues of random matrices. The problem of ergodicity of chaotic wavefunctions is also considered. For that purpose we introduce a family of random polynomials whose roots spread uniformly over phase space. While these results are consistent with random matrix theory predictions, they provide a new and different insight into the problem of quantum ergodicity Special attention is devoted to the role of symmetries in the distribution of roots of random polynomials.

Bogomolny, E.; Bohigas, O.; Leboeuf, P. [Institut de Physique Nucleaire, Orsay (France)

1996-12-01

114

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

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

115

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

116

Dynamics of quantum trajectories in chaotic systems  

NASA Astrophysics Data System (ADS)

Quantum trajectories defined in the de Broglie-Bohm theory provide a causal way to interpret physical phenomena. In this letter, we use this formalism to analyze the short-time dynamics induced by unstable periodic orbits in a classically chaotic system, a situation in which scars are known to play a very important role. We find that the topologies of the quantum orbits are much more complicated than that of the scarring and associated periodic orbits, since the former have quantum interference built in. Thus scar wave functions are necessary to analyze the corresponding dynamics. Moreover, these topologies imply different return routes to the vicinity of the initial positions, and this reflects in the existence of different contributions in each peak of the survival probability function.

Wisniacki, D. A.; Borondo, F.; Benito, R. M.

2003-11-01

117

Dynamical Initial Conditions in Quantum Cosmology  

Microsoft Academic Search

Loop quantum cosmology is shown to provide both the dynamical law and initial conditions for the wave function of a universe by one discrete evolution equation. Accompanied by the condition that semiclassical behavior is obtained at large volume, a unique wave function is predicted.

Martin Bojowald

2001-01-01

118

Site-selective spectroscopic study on the dynamics of exciton hopping in an array of inhomogeneously broadened quantum dots  

NASA Astrophysics Data System (ADS)

We investigate the dynamics of exciton hopping in a CdSe/ZnS quantum dot (QD) array composed of an inhomogeneously broadened ensemble. Time- and spectrally resolved fluorescence intensities are measured by varying the excitation photon energy at the absorption edge. This method allows us to observe fluorescence from only the subdistribution of the QD ensemble, thereby allowing the dynamics of exciton hopping, which depends on the initial (donor) exciton energy, to be elucidated. Experimental results along with numerical calculations using a model of a coupled QD array show that when high-energy QDs are selectively excited, exciton energy transfer occurs repeatedly to a site of low energy, leading to a large exciton hopping length. In contrast, when the low-energy end of the QD ensemble is excited, the exciton tends to be trapped in the initial QD. Furthermore, from the analysis of the decay time of fluorescence intensities, it is suggested that there are dark QDs associated with the defect and/or off state of blinking QDs in the ensemble and energy transfer to such a site is mainly followed by quenching.

Miyazaki, Jun; Kinoshita, Shuichi

2012-07-01

119

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

120

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

121

Quantum dynamics in the thermodynamic limit  

SciTech Connect

The description of spontaneous symmetry breaking that underlies the connection between classically ordered objects in the thermodynamic limit and their individual quantum-mechanical building blocks is one of the cornerstones of modern condensed-matter theory and has found applications in many different areas of physics. The theory of spontaneous symmetry breaking, however, is inherently an equilibrium theory, which does not address the dynamics of quantum systems in the thermodynamic limit. Here, we will use the example of a particular antiferromagnetic model system to show that the presence of a so-called thin spectrum of collective excitations with vanishing energy - one of the well-known characteristic properties shared by all symmetry-breaking objects - can allow these objects to also spontaneously break time-translation symmetry in the thermodynamic limit. As a result, that limit is found to be able, not only to reduce quantum-mechanical equilibrium averages to their classical counterparts, but also to turn individual-state quantum dynamics into classical physics. In the process, we find that the dynamical description of spontaneous symmetry breaking can also be used to shed some light on the possible origins of Born's rule. We conclude by describing an experiment on a condensate of exciton polaritons which could potentially be used to experimentally test the proposed mechanism.

Wezel, Jasper van [Theory of Condensed Matter, Cavendish Laboratory, University of Cambridge, Madingley Road, Cambridge CB3 0HE (United Kingdom)

2008-08-01

122

Quantum dynamics in the thermodynamic limit  

NASA Astrophysics Data System (ADS)

The description of spontaneous symmetry breaking that underlies the connection between classically ordered objects in the thermodynamic limit and their individual quantum-mechanical building blocks is one of the cornerstones of modern condensed-matter theory and has found applications in many different areas of physics. The theory of spontaneous symmetry breaking, however, is inherently an equilibrium theory, which does not address the dynamics of quantum systems in the thermodynamic limit. Here, we will use the example of a particular antiferromagnetic model system to show that the presence of a so-called thin spectrum of collective excitations with vanishing energy—one of the well-known characteristic properties shared by all symmetry-breaking objects—can allow these objects to also spontaneously break time-translation symmetry in the thermodynamic limit. As a result, that limit is found to be able, not only to reduce quantum-mechanical equilibrium averages to their classical counterparts, but also to turn individual-state quantum dynamics into classical physics. In the process, we find that the dynamical description of spontaneous symmetry breaking can also be used to shed some light on the possible origins of Born’s rule. We conclude by describing an experiment on a condensate of exciton polaritons which could potentially be used to experimentally test the proposed mechanism.

van Wezel, Jasper

2008-08-01

123

Dynamical renormalization group approach to relaxation in quantum field theory  

NASA Astrophysics Data System (ADS)

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

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

2003-10-01

124

Dynamic holography in quantum well cavities  

NASA Astrophysics Data System (ADS)

High efficiency dynamic holography at 1.55 microns is achieved on a broad-area InP based multiple quantum well devices. The quantum well cavity is sandwiched between a DBR and amorphous mirror, and consists of a number of wells. High energy pulsed writing beams at 1.06 microns generate free carrier gratings which are probed by a 1.55 micron tunable laser in a four wave mixing configuration. Diffraction efficiency into a single order of 30% has been achieved by contribution of a phase grating, mode pulling and asymmetric Fabry-Perot reflection.

Sun, H.; Nolte, D. D.; Hyland, Jim; Harmon, Eric

2013-03-01

125

Lévy flights and nonlocal quantum dynamics  

SciTech Connect

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

Garbaczewski, Piotr; Stephanovich, Vladimir [Institute of Physics, University of Opole, 45-052 Opole (Poland)] [Institute of Physics, University of Opole, 45-052 Opole (Poland)

2013-07-15

126

Memory effects in adiabatic quantum pumping with parasitic nonlinear dynamics  

NASA Astrophysics Data System (ADS)

The charge current adiabatically pumped through a mesoscopic region coupled to a classical variable obeying a nonlinear dynamics is studied within the scattering matrix approach. Due to the nonlinearity in the dynamics of the variable, a hysteretic behavior of the pumping current can be observed for specific characteristics of the pumping cycle. The steps needed to build a quantum pump working as a memory device are discussed together with a possible experimental implementation.

Romeo, F.; Citro, R.

2010-08-01

127

Role of pumping statistics in laser dynamics: Quantum Langevin approach  

Microsoft Academic Search

We study in detail the influence of pumping statistics on the laser dynamics. We apply the technique of quantum Langevin operators and generalize the corresponding noise operators to incorporate the statistical properties of the pump mechanism. These equations are then used to derive expressions for the phase and intensity fluctuations of lasers with various pump statistics. We find that a

Claus Benkert; M. O. Scully; J. Bergou; L. Davidovich; M. Hillery; M. Orszag

1990-01-01

128

Quantum Scaling Laws in the Onset of Dynamical Delocalization  

SciTech Connect

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

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

2006-12-31

129

Classical and quantum dynamics of the impulsively driven hydrogen atom.  

National Technical Information Service (NTIS)

We investigate the classical and quantum dynamics of the hydrogen atom in a Rydberg state subject to a sequence of periodic and random pulses. One goal of this study is to test the validity of classical electron transport theories. We analyze the critical...

M. Melles C. O. Reinhold J. Burgdoerfer

1992-01-01

130

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

131

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

132

Decoherence in a dynamical quantum phase transition  

NASA Astrophysics Data System (ADS)

Motivated by the similarity between adiabatic quantum algorithms and quantum phase transitions, we study the impact of decoherence on the sweep through a second-order quantum phase transition for the prototypical example of the Ising chain in a transverse field and compare it to the adiabatic version of Grover’s search algorithm, which displays a first-order quantum phase transition. For site-independent and site-dependent coupling strengths as well as different operator couplings, the results show (in contrast to first-order transitions) that the impact of decoherence caused by a weak coupling to a rather general environment increases with system size (i.e., number of spins or qubits). This might limit the scalability of the corresponding adiabatic quantum algorithm.

Mostame, Sarah; Schaller, Gernot; Schützhold, Ralf

2010-03-01

133

Dynamics of quantum vortices at finite temperature  

NASA Astrophysics Data System (ADS)

In this thesis, we perform investigations into the behaviour of finite-temperature degenerate Bose gases using a classical-field formalism, focussing in particular on the dynamics of quantum vortices in these systems. We demonstrate that the coherence of the classical field can be characterised by its temporal correlations, and discuss how the phase-symmetry-broken averages familiar from mean-field theories emerge from the field trajectories. We show that a finite-temperature condensate containing a precessing vortex in a cylindrically symmetric trap can be realised as an ergodic equilibrium of the classical-field theory, and demonstrate the identification of the rotationally symmetry-broken condensate orbital and core-filling thermal component from the field correlations. We then consider the nonequilibrium dynamics that result when such a precessing-vortex configuration is subjected to a static trap anisotropy which arrests its rotation, and observe novel coupled relaxation dynamics of the condensed and noncondensed components of the field. Finally, we consider the nucleation of vortices in an initially zero-temperature quasi-two-dimensional condensate stirred by a rotating trap anisotropy. We quantify the emergence of a rotating thermal component of the field, which drives the nucleation of vortices from condensate-surface oscillations, and study the relaxation and rotational equilibration of the initially turbulent collection of vortices. We find that thermal fluctuations of the field prevent the vortices from settling into a rigid crystalline lattice in this reduced dimensionality, and that true condensation in the field is completely destroyed by the disordered motion of vortices. We show, however, that the temporal correlations of the field distinguish the quasi-coherent vortex-liquid phase in the trap centre from the truly thermal material in its periphery.

Wright, Tod M.

2010-11-01

134

Quantum Monte Carlo study of the dynamic structure factor in the gas and crystal phase of hard-sphere bosons  

NASA Astrophysics Data System (ADS)

We investigate the dynamic structure factor of a system of Bose particles at zero temperature using quantum Monte Carlo methods. Interactions are modeled using a hard-sphere potential of size a and simulations are performed for values of the gas parameter na3 ranging from the dilute regime up to densities n where the thermodynamically stable phase is a solid. With increasing density, we observe a crossover of the dispersion of elementary excitations from a Bogoliubov-type spectrum to a phonon-maxon-roton curve and the emergence of a broad multiphonon contribution accompanying the single-quasiparticle peak. In particular, for na3=0.2138, which corresponds to superfluid 4He at equilibrium density, the extracted spectrum turns out to be in good agreement with the experimental energy-momentum dispersion relation in the roton region and for higher momenta. The behavior of the spectral function at the same density in the stable solid and metastable gas phase above the freezing point is also discussed.

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

2013-12-01

135

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

136

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

137

Entropic dynamics and the quantum measurement problem  

NASA Astrophysics Data System (ADS)

We explore the old quantum measurement problem from the perspective of entropic dynamics. The entropic approach contributes two new ideas. First, the dual modes of quantum evolution-either continuous unitary evolution or abrupt wave function collapse during measurement-are unified by virtue of both being special instances of entropic updating of probabilities. The second new idea is that in entropic dynamics particles have only one attribute-position. They have neither momentum nor energy nor any other attributes. The positions have definite albeit unknown values; they are not created by the act of measurement. Other so-called observables can of course be introduced but only as a convenient way to describe more complex position measurements; they are attributes not of the particles but of the probability distributions; their values are effectively created by the act of measurement. We discuss the Born statistical rule for position, which is trivially built into the formalism, and also for more generic observables.

Johnson, David T.; Caticha, Ariel

2012-05-01

138

From Entropic Dynamics to Quantum Theory  

SciTech Connect

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

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

2009-12-08

139

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

140

Assumptions that imply quantum dynamics is linear  

SciTech Connect

A basic linearity of quantum dynamics, that density matrices are mapped linearly to density matrices, is proven very simply for a system that does not interact with anything else. It is assumed that at each time the physical quantities and states are described by the usual linear structures of quantum mechanics. Beyond that, the proof assumes only 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. The basic linearity is linked with previously established results to complete a simple derivation of the linear Schroedinger equation. For this it is assumed that density matrices are mapped one-to-one onto density matrices. An alternative is to assume that pure states are mapped one-to-one onto pure states and that entropy does not decrease.

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

2006-02-15

141

Dynamics of quantum wave packets  

SciTech Connect

This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The objective of this project was to develop ultrafast laser techniques for the creation and measurement of quantum vibrational wave packets in gas phase diatomic molecules. Moreover, the authors sought to manipulate the constitution of these wave packets in terms of harmonic-oscillator basis wavefunctions by manipulating the time-dependent amplitude and phase of the incident ultrashort laser pulse. They specifically investigated gaseous diatomic potassium (K{sub 2}), and discovered variations in the shape of the wave packets as a result of changing the linear chirp in the ultrashort preparation pulse. In particular, they found evidence for wave-packet compression for a specific degree of chirp. Important ancillary results include development of new techniques for denoising and deconvolution of femtosecond time traces and techniques for diagnosing the phase and amplitude of the electric field of femtosecond laser pulses.

Gosnell, T.R.; Taylor, A.J.; Rodriguez, G.; Clement, T.S.

1998-11-01

142

Quasiperiodic Dynamics of a Quantum Walk on the Line  

NASA Astrophysics Data System (ADS)

We study the dynamics of a generalization of a quantum coin walk on the line, which is a natural model for a diffusion modified by quantum or interference effects. In particular, our results provide surprisingly simple explanations for recurrence phenomena observed by Bouwmeester et al. [

Phys. Rev. APLRAAN1050-2947 61, 13410 (1999)10.1103/PhysRevA.61.013410
] in their optical Galton board experiment, and a description of a stroboscopic quantum walk given by Buerschaper and Burnett [quant-ph/0406039] through numerical simulations. We also provide heuristic explanations for the behavior of our model which show, in particular, that its dynamics can be viewed as a discrete version of Bloch oscillations.

Wójcik, Antoni; ?uczak, Tomasz; Kurzy?ski, Pawe?; Grudka, Andrzej; Bednarska, Ma?gorzata

2004-10-01

143

Quantum dynamics as a stochastic process  

NASA Astrophysics Data System (ADS)

The quantum Liouville equation is solved in the Wigner representation using generalized Monte Carlo techniques. For small increments of time, the solution is represented as a sequential classical evolution in phase space followed by a quantum ``jump'' distribution in momentum space, with the latter simulated via a stochastic method. Extending the work initiated by John and Remler [Ann Phys. (N.Y.) 180, 152 (1987)] the technique is developed and validated for higher dimensions. Also, an alternative algorithm is developed and applied to study motion of a quantum system in an anharmonic quartic potential well, with significantly improved results.

John, Sarah; Wilson, John W.

1994-01-01

144

Quantum dynamics in ultracold atomic physics  

NASA Astrophysics Data System (ADS)

We review recent developments in the theory of quantum dynamics in ultracold atomic physics, including exact techniques and methods based on phase-space mappings that are applicable when the complexity becomes exponentially large. Phase-space representations include the truncated Wigner, positive- P and general Gaussian operator representations which can treat both bosons and fermions. These phase-space methods include both traditional approaches using a phase-space of classical dimension, and more recent methods that use a non-classical phase-space of increased dimensionality. Examples used include quantum Einstein-Podolsky-Rosen (EPR) entanglement of a four-mode BEC, time-reversal tests of dephasing in single-mode traps, BEC quantum collisions with up to 106 modes and 105 interacting particles, quantum interferometry in a multi-mode trap with nonlinear absorption, and the theory of quantum entropy in phase-space. We also treat the approach of variational optimization of the sampling error, giving an elementary example of a nonlinear oscillator.

He, Qiong-Yi; Reid, Margaret D.; Opanchuk, Bogdan; Polkinghorne, Rodney; Rosales-Zárate, Laura E. C.; Drummond, Peter D.

2012-02-01

145

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

NASA Astrophysics Data System (ADS)

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

Saito, Hiroki

2014-02-01

146

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

SciTech Connect

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

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

2010-11-15

147

A mixed quantum-classical molecular dynamics study of the hydroxyl stretch in methanol/carbon tetrachloride mixtures: equilibrium hydrogen-bond structure and dynamics at the ground state and the infrared absorption spectrum.  

PubMed

We present a mixed quantum-classical molecular dynamics study of the structure and dynamics of the hydroxyl stretch in methanol/carbon tetrachloride mixtures. One of the methanol molecules is tagged, and its hydroxyl stretch is treated quantum-mechanically, while the remaining degrees of freedom are treated classically. The adiabatic Hamiltonian of the quantum-mechanical hydroxyl is diagonalized on-the-fly to obtain the corresponding adiabatic energy levels and wave functions which depend parametrically on the instantaneous configuration of the classical degrees of freedom. The dynamics of the classical degrees of freedom are in turn affected by the quantum-mechanical state of the tagged hydroxyl stretch via the corresponding Hellmann-Feynman forces. The ability of five different force-field combinations to reproduce the experimental absorption infrared spectrum of the hydroxyl stretch is examined for different isotopomers and on a wide range of compositions. It is found that, in addition to accounting for the anharmonic nature of the hydroxyl stretch, one also has to employ polarizable force fields and account for the damping of the polarizability at short distances. The equilibrium ground-state hydrogen-bonding structure and dynamics is analyzed, and its signature on the absorption infrared spectrum of the hydroxyl stretch is investigated in detail. Five different hydroxyl stretch subpopulations are identified and spectrally assigned: monomers (?), hydrogen-bond acceptors (?), hydrogen-bond donors (?), simultaneous hydrogen-bond donors and acceptors (?), and simultaneous hydrogen-bond donors and double-acceptors (?). The fundamental transition frequencies of the ? and ? subpopulations are found to be narrowly distributed and to overlap, thereby giving rise to a single narrow band whose intensity is significantly diminished by rotational relaxation. The fundamental transition frequency distributions of the ?, ?, and ? subpopulations are found to be broader and to partially overlap, thereby giving rise to a single broad band which is red-shifted relative to the ?? band. The ??? band is also found to be inhomogeneously broadened and unaffected by rotational relaxation. The exchange rates between the different subpopulations and corresponding branching ratios are reported and explained. Finally, nonlinear mapping relations between the hydroxyl transition frequency and bond length and the electric field along the hydroxyl bond axis are established, which can be used to reduce the computational cost of the mixed quantum-classical treatment to that of a purely classical molecular dynamics simulation. PMID:21675789

Kwac, Kijeong; Geva, Eitan

2011-07-28

148

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

149

Quantum lattice-gas model for computational fluid dynamics.  

PubMed

Quantum-computing ideas are applied to the practical and ubiquitous problem of fluid dynamics simulation. Hence, this paper addresses two separate areas of physics: quantum mechanics and fluid dynamics (or specifically, the computational simulation of fluid dynamics). The quantum algorithm is called a quantum lattice gas. An analytical treatment of the microscopic quantum lattice-gas system is carried out to predict its behavior at the mesoscopic scale. At the mesoscopic scale, a lattice Boltzmann equation with a nonlocal collision term that depends on the entire system wave function, governs the dynamical system. Numerical results obtained from an exact simulation of a one-dimensional quantum lattice model are included to illustrate the formalism. A symbolic mathematical method is used to implement the quantum mechanical model on a conventional workstation. The numerical simulation indicates that classical viscous damping is not present in the one-dimensional quantum lattice-gas system. PMID:11308976

Yepez, J

2001-04-01

150

The role of the low-lying dark n?* states in the photophysics of pyrazine: a quantum dynamics study.  

PubMed

The excited state dynamics of pyrazine has attracted considerable attention in the last three decades. It has long been recognized that after UV excitation, the dynamics of the molecule is impacted by strong non-adiabatic effects due to the existence of a conical intersection between the B2u(??*) and B3u(n?*) electronic states. However, a recent study based on trajectory surface hopping dynamics simulations suggested the participation of the Au(n?*) and B2g(n?*) low-lying dark electronic states in the ultrafast radiationless decay of the molecule after excitation to the B2u(??*) state. The purpose of this work was to pursue the investigation of the role of the Au(n?*) and B2g(n?*) states in the photophysics of pyrazine. A linear vibronic coupling model hamiltonian including the four lowest excited electronic states and the sixteen most relevant vibrational degrees of freedom was constructed using high level XMCQDPT2 electronic structure calculations. Wavepacket propagations using the MCTDH method were then performed and used to simulate the absorption spectrum and the electronic state population dynamics of the system. Our results show that the Au(n?*) state plays an important role in the photophysics of pyrazine. PMID:24964033

Sala, Matthieu; Lasorne, Benjamin; Gatti, Fabien; Guérin, Stéphane

2014-07-01

151

Quantum dynamics in fluctuating traps: Master equation, decoherence, and heating  

SciTech Connect

We present a remarkably simple derivation of an exact time-local master equation describing the dynamics of quantum states in harmonic traps subject to arbitrary fluctuating forces. The relation between our master equation and known master equations of irreversible harmonic oscillator dynamics are established. Motivated by recent experiments, we focus on decoherence and in particular on the precise decoherence dynamics of a superposition of wave packets. We determine the decaying purity resulting from the time evolution based on our master equation and study its connection to experimentally accessible observables. Finally, we discuss the heating of the system subjected to arbitrary Gaussian noise.

Grotz, Thimo; Heaney, Libby; Strunz, Walter T. [Theoretische Quantendynamik, Physikalisches Institut, Universitaet Freiburg, Hermann-Herder-Strasse 3, 79104 Freiburg (Germany)

2006-08-15

152

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

NASA Astrophysics Data System (ADS)

The incorporation of semiconductor quantum dots into different heterostructures for applications in nanoscale lasing and amplification has been an active area of research in recent years. Here, we use ultrafast differential transmission spectroscopy to temporally and spectrally resolve density-dependent carrier dynamics in a quantum dots-in-a-well (DWELL) heterostructure. We observe excitation-dependent shifts of the quantum dot energy levels at low densities, while at high densities we observe an anomalous induced absorption at the quantum dot excited state that is correlated with quantum well population dynamics. These studies reveal unique Coulomb interaction-induced phenomena with important implications for DWELL-based lasers and amplifiers.

Prasankumar, R. P.; Chow, W. W.; Urayama, J.; Attaluri, R. S.; Shenoi, R. V.; Krishna, S.; Taylor, A. J.

2010-01-01

153

Wigner dynamics of quantum semi-relativistic oscillator  

NASA Astrophysics Data System (ADS)

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

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

2013-07-01

154

Two-Dimensional Macroscopic Quantum Dynamics in Ybco Josephson Junctions  

NASA Astrophysics Data System (ADS)

We theoretically study classical thermal activation (TA) and macroscopic quantum tunneling (MQT) for a YBa2Cu3O7-?(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.

Kawabata, Shiro; Kato, Takeo; Lombardi, Floriana; Bauch, Thilo

2010-12-01

155

Two-Dimensional Macroscopic Quantum Dynamics in Ybco Josephson Junctions  

NASA Astrophysics Data System (ADS)

We theoretically study classical thermal activation (TA) and macroscopic quantum tunneling (MQT) for a YBa2Cu3O7-?(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.

Kawabata, Shiro; Kato, Takeo; Lombardi, Floriana; Bauch, Thilo

156

Quantum equivalence of a driven triple-well Van der Pol oscillator: A QTM study  

NASA Astrophysics Data System (ADS)

A quantum mechanical analogue of the classically chaotic triple-well oscillator under the influence of an external field and parametric excitation has been studied by using the quantum theory of motion. The on the fly calculations show the correspondence between some dynamical aspects of the classical and quantum oscillators along with a strictly quantum mechanical behaviour in case of diffusion and tunneling. Suitable external conditions have been obtained which can either assist or suppress the movement of quantum particles from one well to another. Quantum interference effects play a critical role in determining the nature of the quantum dynamics and in the presence of strong coupling to the external forces, quantum interference effects reduce drastically leading to decoherence of the quantum wave packet. In such situations, quantum dynamical features qualitatively resemble the corresponding classical dynamical behaviour and a correspondence between classical and quantum dynamics is obtained.

Chakraborty, Debdutta; Chattaraj, Pratim Kumar

2014-06-01

157

Adiabatic dynamics in passage across quantum critical lines and gapless phases.  

PubMed

It is well known that the dynamics of a quantum system is always nonadiabatic in passage through a quantum critical point and the defect density in the final state following a quench shows a power-law scaling with the rate of quenching. However, we propose here a possible situation where the dynamics of a quantum system in passage across quantum critical regions is adiabatic and the defect density decays exponentially. This is achieved by incorporating additional interactions which lead to quantum critical behavior and gapless phases but do not participate in the time evolution of the system. To illustrate the general argument, we study the defect generation in the quantum critical dynamics of a spin-1/2 anisotropic quantum XY spin chain with three spin interactions and a linearly driven staggered magnetic field. PMID:20365412

Chowdhury, Debanjan; Divakaran, Uma; Dutta, Amit

2010-01-01

158

The Dynamics of Quantum Correlations Between Two Atoms in Two Coupled Cavities  

NASA Astrophysics Data System (ADS)

The dynamics of the quantum correlation between two atoms in two single-mode cavities is studied. For the initial Bell state | ? +>, the quantum consonance is equal to the entanglement, and larger than quantum discord. For the initial Bell state | ? +>, the quantum consonance is larger than entanglement, but not larger than quantum discord all the time. As the increase of the cavity-cavity coupling strength, the evolution period of quantum correlation becomes smaller. Consonance is not smooth at some points while cavities are coupled with each other.

Cao, Bao-Liang; Shi, Ying; Jiang, Dong-Guang

2014-06-01

159

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

160

A Survey on the Classical Limit of Quantum Dynamical Entropies  

Microsoft Academic Search

We analyze the behavior of quantum dynamical entropies production from sequences of quantum approximants approaching their (chaotic) classical limit. The model of the quantized hyperbolic automorphisms of the 2-torus is examined in detail and a semi-classical analysis is performed on it using coherent states, fulfilling an appropriate dynamical localization property. Correspondence between quantum dynamical entropies and the Kolmogorov-Sinai invariant is

Valerio Cappellini; Centrum Fizyki Teoretycznej; Polska Akademia Nauk

2007-01-01

161

Optical Nonlinearities and Ultrafast Carrier Dynamics in Semiconductor Quantum Dots  

SciTech Connect

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

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

1998-08-10

162

Trotter-based simulation of quantum-classical dynamics.  

PubMed

Quantum rate processes in condensed phase systems are often computed by combining quantum and classical descriptions of the dynamics. An algorithm for simulating the quantum-classical Liouville equation, which describes the dynamics of a quantum subsystem coupled to a classical bath, is presented in this paper. The algorithm is based on a Trotter decomposition of the quantum-classical propagator, in conjunction with Monte Carlo sampling of quantum transitions, to yield a surface-hopping representation of the dynamics. An expression for the nonadiabatic propagator that is responsible for quantum transitions and associated bath momentum changes is derived in a form that is convenient for Monte Carlo sampling and exactly conserves the total energy of the system in individual trajectories. The expectation values of operators or quantum correlation functions can be evaluated by initial sampling of quantum states and use of quantum-classical Liouville dynamics for the time evolution. The algorithm is tested by calculations on the spin-boson model, for which exact quantum results are available, and is shown to reproduce the exact results for stronger nonadiabatic coupling and much longer times using fewer trajectories than other schemes for simulating quantum-classical Liouville dynamics. PMID:18154283

Kernan, Dónal Mac; Ciccotti, Giovanni; Kapral, Raymond

2008-01-17

163

Quantum wormhole and its dynamics  

NASA Astrophysics Data System (ADS)

The two-dimensional dilaton gravity model is generalized to include a ghost Klein-Gordon field, i.e., a negative gravitational coupling, which supports the existence of static traversible wormhole solutions, and is semiclassically modified by adding local covariant terms of one-loop order. In the semiclassically corrected model, the black hole and the wormhole solutions are given. When a static traversible wormhole is used to transport matter or radiation, we study the back-reaction of the transported matter on the wormhole and the end state of the wormhole in the semiclassical level and compare the results with the classical case. We show that the semiclassical wormhole is stable to such back-reaction: the wormhole starts radiating when the matter arrives and finally return to a static one.

Lee, Hyunjoo; Kim, Sung-Won

2004-07-01

164

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

165

The stability of [Zn(NH(3))(4)](2+) in water: A quantum mechanical/molecular mechanical molecular dynamics study.  

PubMed

To investigate the structural and dynamical properties of the tetraamminezinc(ii) complex (Zn-tetraamine) in aqueous solution, ab initio quantum mechanical/molecular mechanical (QM/MM) molecular dynamics (MD) simulation was performed for 50 ps at the Hartree-Fock (HF) level of theory. A predominant 4-coordinate solvation structure with a maximum probability of the Zn-N distance at approximately 2.1 A was observed, which seems to be involved in the associative mode of water exchange reactions to produce a short-lived, 5-coordinated trigonal bipyramidal structure. Several sets of structural and dynamical parameters such as radial distribution functions (RDF), coordination number distributions (CND), angular distributions (ADF), ligands' mean residence times (MRT) and ion-ligand stretching frequencies have been evaluated in order to get an in depth knowledge of the physical and chemical properties of the tetraamminezinc(ii) complex in aqueous solution. A comparative study of the tetraamminezinc(ii) complex with previously published mono-, di- and triamminezinc(ii) complexes has been also performed, which yielded significant insights into the complex properties as a function of an increasing number of first-shell ammonia ligands. PMID:20544098

Qaiser Fatmi, M; Hofer, Thomas S; Rode, Bernd M

2010-09-01

166

Coupled Dynamics of a Nanomechanical Resonator and Superconducting Quantum Circuits  

NASA Astrophysics Data System (ADS)

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

Suh, Junho

167

Coarse grained open system quantum dynamics  

SciTech Connect

We show that the quantum dynamics of a system comprised of a subspace Q coupled to a larger subspace P can be recast as a reduced set of 'coarse grained' ordinary differential equations with constant coefficients. These equations can be solved by a single diagonalization of a general complex matrix. The method makes no assumptions about the strength of the couplings between the Q and the P subspaces, nor is there any limitation on the initial population in P. The utility of the method is demonstrated via computations in three following areas: molecular compounds, photonic materials, and condensed phases.

Thanopulos, Ioannis [Department of Chemistry, University of British Columbia, Vancouver V6T 1Z3 (Canada); Brumer, Paul [Chemical Physics Theory Group, Department of Chemistry, and Center of Quantum Information and Quantum Control, University of Toronto, Toronto, Ontario M5S 3H6 (Canada); Shapiro, Moshe [Department of Chemistry, University of British Columbia, Vancouver V6T 1Z3 (Canada); Department of Chemical Physics, Weizmann Institute, Rehovot 76100 (Israel)

2008-11-21

168

Clumping and quantum order: quantum gravitational dynamics of NUT charge  

NASA Astrophysics Data System (ADS)

Gravitational instantons with NUT charge are magnetic monopoles upon dimensional reduction. We determine whether NUT charge can proliferate via the Polyakov mechanism and partially screen gravitational interactions. In semiclassical Einstein gravity, Taub-NUT instantons experience a universal attractive force in the path integral that prevents proliferation. This attraction further leads to semiclassical clumping instabilities, similar to the known instabilities of hot flat space and the Kaluza-Klein vacuum. Beyond pure Einstein gravity, NUT proliferation depends on the following question: is the mass of a gravitational instanton in the theory always greater than its NUT charge? Using spinorial methods we show that the answer to this question is `yes' if all matter fields obey a natural Euclidean energy condition. Therefore, the attractive force between instantons in the path integral wins out and gravity is dynamically protected against screening. Semiclassical gravity with a compactified circle can be self-consistently quantum ordered, at the cost of suffering from clumping instabilities.

Hartnoll, Sean A.; Ramirez, David M.

2014-04-01

169

Dynamical Causal Modeling from a Quantum Dynamical Perspective  

NASA Astrophysics Data System (ADS)

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

Demiralp, Emre; Demiralp, Metin

2010-09-01

170

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

171

Quantum critical dynamics simulation of dirty boson systems.  

PubMed

Recently, the scaling result z=d for the dynamic critical exponent at the Bose glass to superfluid quantum phase transition has been questioned both on theoretical and numerical grounds. This motivates a careful evaluation of the critical exponents in order to determine the actual value of z. We study a model of quantum bosons at T=0 with disorder in 2D using highly effective worm Monte Carlo simulations. Our data analysis is based on a finite-size scaling approach to determine the scaling of the quantum correlation time from simulation data for boson world lines. The resulting critical exponents are z=1.8±0.05, ?=1.15±0.03, and ?=-0.3±0.1, hence suggesting that z=2 is not satisfied. PMID:22400943

Meier, Hannes; Wallin, Mats

2012-02-01

172

Transannular Diels-Alder reactivities of 14-membered macrocylic trienes and their relationship with the conformational preferences of the reactants: a combined quantum chemical and molecular dynamics study.  

PubMed

Transannular Diels-Alder (TADA) reactions that occur between the diene and dienophile moieties located on a single macrocyclic triene molecule have been recognized as effective synthetic routes toward realizing complex tricyclic molecules in a single step. In this paper, we report a comprehensive study on the TADA reactions of 14-membered cyclic triene macrocycles to yield A.B.C[6.6.6] tricycles using quantum chemical methods and using classical molecular dynamics simulations. A benchmark study has been performed to examine the reliability of the commonly used ab initio methods and hybrid density functional levels of theory in comparison with results from CCSD(T) calculations to accurately model TADA reactions. The energy barriers obtained using the M06-2X functional were found to be in quantitative agreement with the CCSD(T) level of theory using a reasonably large basis set. Conformational properties of the reactants have been systematically studied using extensive molecular dynamics (MD) simulations. For this purpose, model systems were conceived, and force field parameters corresponding to the dihedral terms in the potential energy function were obtained. Linear relationship between the activation energies corresponding to the TADA reactions and the probability of finding the reactant in certain conformational states was obtained. A clustering method along with optimizations at the molecular mechanics and density functional M06-2X levels has been used to locate the most stable conformation of each of the trienes. PMID:22672100

Prathyusha, V; Ramakrishna, S; Priyakumar, U Deva

2012-06-15

173

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

174

Relativistic quantum dynamics of many-body systems.  

National Technical Information Service (NTIS)

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

F. Coester W. N. Polyzou

2000-01-01

175

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

176

Energy dissipation via quantum chemical hysteresis during high-pressure compression: A first-principles molecular dynamics study of phosphates  

NASA Astrophysics Data System (ADS)

The chemomechanical response of triphosphates (TPs) and zinc phosphates (ZPs) to changes in pressure p and temperature T is studied through first-principles molecular dynamics. The maximum values of p(>20GPa) and T(?1000K) are chosen to mimic roughly the extreme conditions to which phosphates may be exposed during their role as engine antiwear films. In all systems, atoms undergo pressure-induced changes in coordination number. Upon decompression, these chemical changes are partially reversible but nevertheless show strong hysteresis effects. This leads to significant energy dissipation, which contributes to the high friction coefficients of ZP antiwear pads. ZPs remain a covalently cross-linked network after decompression, while TPs revert to a disconnected state. The decompressed TPs have a larger bulk modulus (?35GPa) than the uncompressed TPs (?27GPa) . This increase is due to symmetry-breaking proton transfer reactions, which are irreversible on the time scale of the simulation. Temperature has little effect on the results.

Mosey, Nicholas J.; Woo, Tom K.; Müser, Martin H.

2005-08-01

177

Nuclear spin dynamics in double quantum dots: Multistability, dynamical polarization, criticality, and entanglement  

NASA Astrophysics Data System (ADS)

We theoretically study the nuclear spin dynamics driven by electron transport and hyperfine interaction in an electrically defined double quantum dot in the Pauli-blockade regime. We derive a master-equation-based framework and show that the coupled electron-nuclear system displays an instability towards the buildup of large nuclear spin polarization gradients in the two quantum dots. In the presence of such inhomogeneous magnetic fields, a quantum interference effect in the collective hyperfine coupling results in sizable nuclear spin entanglement between the two quantum dots in the steady state of the evolution. We investigate this effect using analytical and numerical techniques, and demonstrate its robustness under various types of imperfections.

Schuetz, M. J. A.; Kessler, E. M.; Vandersypen, L. M. K.; Cirac, J. I.; Giedke, G.

2014-05-01

178

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

179

Coherent control of quantum dynamics - The dream is alive  

Microsoft Academic Search

A development status evaluation is conducted for current theoretical and experimental efforts to control quantum dynamics. Particular hope is held out for ultrafast laser pulse shaping capabilities which yield subpicosec resolution through either temporal or spatial dispersion. In addition, a rigorous foundation has been achieved for the theoretical framework of quantum dynamics control through the introduction of engineering control concepts.

Warren S. Warren; Herschel Rabitz; Mohammed Dahleh

1993-01-01

180

Quantum dynamical simulations of local field enhancement in metal nanoparticles.  

PubMed

Field enhancements (?) around small Ag nanoparticles (NPs) are calculated using a quantum dynamical simulation formalism and the results are compared with electrodynamic simulations using the discrete dipole approximation (DDA) in order to address the important issue of the intrinsic atomistic structure of NPs. Quite remarkably, in both quantum and classical approaches the highest values of ? are located in the same regions around single NPs. However, by introducing a complete atomistic description of the metallic NPs in optical simulations, a different pattern of the ? distribution is obtained. Knowing the correct pattern of the ? distribution around NPs is crucial for understanding the spectroscopic features of molecules inside hot spots. The enhancement produced by surface plasmon coupling is studied by using both approaches in NP dimers for different inter-particle distances. The results show that the trend of the variation of ? versus inter-particle distance is different for classical and quantum simulations. This difference is explained in terms of a charge transfer mechanism that cannot be obtained with classical electrodynamics. Finally, time dependent distribution of the enhancement factor is simulated by introducing a time dependent field perturbation into the Hamiltonian, allowing an assessment of the localized surface plasmon resonance quantum dynamics. PMID:23449278

Negre, Christian F A; Perassi, Eduardo M; Coronado, Eduardo A; Sánchez, Cristián G

2013-03-27

181

Quantum dynamical simulations of local field enhancement in metal nanoparticles  

NASA Astrophysics Data System (ADS)

Field enhancements (?) around small Ag nanoparticles (NPs) are calculated using a quantum dynamical simulation formalism and the results are compared with electrodynamic simulations using the discrete dipole approximation (DDA) in order to address the important issue of the intrinsic atomistic structure of NPs. Quite remarkably, in both quantum and classical approaches the highest values of ? are located in the same regions around single NPs. However, by introducing a complete atomistic description of the metallic NPs in optical simulations, a different pattern of the ? distribution is obtained. Knowing the correct pattern of the ? distribution around NPs is crucial for understanding the spectroscopic features of molecules inside hot spots. The enhancement produced by surface plasmon coupling is studied by using both approaches in NP dimers for different inter-particle distances. The results show that the trend of the variation of ? versus inter-particle distance is different for classical and quantum simulations. This difference is explained in terms of a charge transfer mechanism that cannot be obtained with classical electrodynamics. Finally, time dependent distribution of the enhancement factor is simulated by introducing a time dependent field perturbation into the Hamiltonian, allowing an assessment of the localized surface plasmon resonance quantum dynamics.

Negre, Christian F. A.; Perassi, Eduardo M.; Coronado, Eduardo A.; Sánchez, Cristián G.

2013-03-01

182

Dynamics of Large Quantum Systems: Equilibration, Thermalization and Interactions  

NASA Astrophysics Data System (ADS)

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

Segal, Dvira; Kulkarni, Manas; Tiwari, Kunal

2013-03-01

183

Quantum Information, Thermofield Dynamics and Thermalized Bosonic Oscillator  

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

184

Quantum dynamical study of the H2 and D2 dissociative adsorption and diffraction from the NiAl (110) alloy surface  

NASA Astrophysics Data System (ADS)

We present quantum dynamics calculations of dissociative adsorption and elastic and rotationally inelastic diffraction of H2 and D2 molecules from the NiAl (110) alloy surface using a six-dimensional potential energy surface obtained with density functional theory (DFT), employing the PW91 generalized gradient approximation. Good agreement with the existing experimental data for both sticking and diffraction is found, thus showing that the electronically adiabatic, rigid-surface model incorporating motion in all H2 degrees of freedom accurately describes the H2/NiAl (110) system with the DFT potential employed. The present results confirm previous classical dynamics predictions such as the variation of the sticking coefficient with incidence energy or the importance of both in-plane and out-of-plane (elastic and rotationally inelastic) diffraction below the dissociation threshold. Nevertheless, quantum interference effects, not represented in classical dynamics calculations, lead to structures in the sticking probability near threshold that are not observed in the classical calculations. In the case of diffraction, very good agreement between theory and experiment has been found for specular, in-plane, and out-of-plane elastic diffraction peaks. In the latter case, quantum dynamics gives a more accurate overall description than classical dynamics, which, however, does a quite reasonable job and predicts the main peaks.

Rivière, P.; Somers, M. F.; Kroes, G. J.; Martín, F.

2006-05-01

185

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

186

Mixed quantum-classical molecular dynamics study of the hydroxyl stretch in methanol/carbon-tetrachloride mixtures II: excited state hydrogen bonding structure and dynamics, infrared emission spectrum, and excited state lifetime.  

PubMed

We present a mixed quantum-classical molecular dynamics study of the hydrogen-bonding structure and dynamics of a vibrationally excited hydroxyl stretch in methanol/carbon-tetrachloride mixtures. The adiabatic Hamiltonian of the quantum-mechanical hydroxyl is diagonalized on-the-fly to obtain the ground and first-excited adiabatic energy levels and wave functions which depend parametrically on the instantaneous configuration of the classical degrees of freedom. The dynamics of the classical degrees of freedom are determined by Hellmann-Feynman forces obtained by taking the expectation value of the force with respect to the ground or excited vibrational wave functions. Polarizable force fields are used which were previously shown to reproduce the experimental infrared absorption spectrum rather well, for different isotopomers and over a wide composition range [Kwac, K.; Geva, E. J. Phys. Chem. B 2011, 115, 9184]. We show that the agreement of the absorption spectra with experiment can be further improved by accounting for the dependence of the dipole moment derivatives on the configuration of the classical degrees of freedom. We find that the propensity of a methanol molecule to form hydrogen bonds increases upon photoexcitation of its hydroxyl stretch, thereby leading to a sizable red-shift of the corresponding emission spectrum relative to the absorption spectrum. Treating the relaxation from the first excited to the ground state as a nonadiabatic process, and calculating its rate within the framework of Fermi's golden rule and the harmonic-Schofield quantum correction factor, we were able to predict a lifetime which is of the same order of magnitude as the experimental value. The experimental dependence of the lifetime on the transition frequency is also reproduced. Nonlinear mapping relations between the hydroxyl transition frequency and bond length in the excited state and the electric field along the hydroxyl bond axis are established. These mapping relations make it possible to reduce the computational cost of the mixed quantum-classical treatment to that of a fully classical treatment. PMID:22283660

Kwac, Kijeong; Geva, Eitan

2012-03-01

187

Quantum dynamics of magnetic and electric dipoles and the geometric phase  

NASA Astrophysics Data System (ADS)

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

Furtado, Claudio; Ribeiro, Carlos Alberto

2004-06-01

188

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

SciTech Connect

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

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

2005-03-01

189

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

190

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

191

Interacting Electrons in a Quantum Dot: Quantum Monte Carlo Studies.  

National Technical Information Service (NTIS)

An efficient optimization method for the quantum Monte Carlo many-body wave functions, called the stochastic gradient approximation (SGA), is presented. Using this method, the states of interacting electrons in a semiconductor quantum dot are studied for ...

A. Harju

1999-01-01

192

Quantum-classical Liouville dynamics in the mapping basis.  

PubMed

The quantum-classical Liouville equation describes the dynamics of a quantum subsystem coupled to a classical environment. It has been simulated using various methods, notably, surface-hopping schemes. A representation of this equation in the mapping Hamiltonian basis for the quantum subsystem is derived. The resulting equation of motion, in conjunction with expressions for quantum expectation values in the mapping basis, provides another route to the computation of the nonadiabatic dynamics of observables that does not involve surface-hopping dynamics. The quantum-classical Liouville equation is exact for the spin-boson system. This well-known model is simulated using an approximation to the evolution equation in the mapping basis, and close agreement with exact quantum results is found. PMID:19044813

Kim, Hyojoon; Nassimi, Ali; Kapral, Raymond

2008-08-28

193

Moyal quantum mechanics: The semiclassical Heisenberg dynamics  

SciTech Connect

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

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

1995-07-01

194

New methods for quantum mechanical reaction dynamics  

SciTech Connect

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

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

1996-12-01

195

Mapping approach to the semiclassical description of nonadiabatic quantum dynamics  

NASA Astrophysics Data System (ADS)

A theoretical formulation is outlined that allows us to extend the semiclassical Van Vleck-Gutzwiller formulation to the description of nonadiabatic quantum dynamics on coupled potential-energy surfaces. In this formulation the problem of a classical treatment of discrete quantum degrees of freedom (DoF) such as electronic states is bypassed by transforming the discrete quantum variables to continuous variables. The mapping approach thus consists of two steps: an exact quantum-mechanical transformation of discrete onto continuous DoF (the ``mapping'') and a standard semiclassical treatment of the resulting dynamical problem. Extending previous work [G. Stock and M. Thoss, Phys. Rev. Lett. 78, 578 (1997)], various possibilities for obtaining a mapping from discrete to continuous DoF are investigated, in particular the Holstein-Primakoff transformation, Schwinger's theory of angular momentum [in Quantum Theory of Angular Momentum, edited by L. C. Biedenharn and H. V. Dam (Academic, New York, 1965)], and the spin-coherent-state representation. Although all these representations are exact on the quantum-mechanical level, the accuracy of their semiclassical evaluation is shown to differ considerably. In particular, it is shown that a generalization of Schwinger's theory appears to be the only transformation that provides an exact description of a general N-level system within a standard semiclassical evaluation. Exploiting the connection between spin-coherent states and Schwinger's representation for a two-level system, furthermore, a semiclassical initial-value representation of the corresponding spin-coherent-state propagator is derived. Although this propagator represents an approximation, its appealing numerical features make it a promising candidate for the semiclassical description of large molecular systems with many DoF. Adopting various spin-boson-type models (i.e., a two-level system coupled to a single or many DoF), computational studies are presented for Schwinger's and the spin-coherent-state representation, respectively. The performance of the semiclassical approximation in the case of regular and chaotic classical dynamics as well as for multimode electronic relaxation dynamics is discussed in some detail.

Thoss, Michael; Stock, Gerhard

1999-01-01

196

Decoherence dynamics of two charge qubits in vertically coupled quantum dots  

SciTech Connect

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

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

2007-12-15

197

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

198

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

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

199

Quantum dynamical study of the H2 and D2 dissociative adsorption and diffraction from the NiAl (110) alloy surface  

Microsoft Academic Search

We present quantum dynamics calculations of dissociative adsorption and elastic and rotationally inelastic diffraction of H2 and D2 molecules from the NiAl (110) alloy surface using a six-dimensional potential energy surface obtained with density functional theory (DFT), employing the PW91 generalized gradient approximation. Good agreement with the existing experimental data for both sticking and diffraction is found, thus showing that

P. Rivière; M. F. Somers; G. J. Kroes; F. Martín

2006-01-01

200

Electronic couplings and on-site energies for hole transfer in DNA: Systematic quantum mechanical\\/molecular dynamic study  

Microsoft Academic Search

The electron hole transfer (HT) properties of DNA are substantially affected by thermal fluctuations of the pi stack structure. Depending on the mutual position of neighboring nucleobases, electronic coupling V may change by several orders of magnitude. In the present paper, we report the results of systematic QM\\/molecular dynamic (MD) calculations of the electronic couplings and on-site energies for the

Alexander A. Voityuk

2008-01-01

201

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

Microsoft Academic Search

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

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

1998-01-01

202

Self-assembled indium arsenide quantum dots: Structure, formation dynamics, optical properties  

Microsoft Academic Search

In this dissertation, we investigate the properties of InAs\\/GaAs quantum dots grown by molecular beam epitaxy. The structure and formation dynamics of InAs quantum dots are studied by a variety of structural characterization techniques. Correlations among the growth conditions, the structural characteristics, and the observed optical properties are explored. The most fundamental structural characteristic of the InAs quantum dots is

Hao Lee

1998-01-01

203

Quantum dynamics of light-driven chiral molecular motors.  

PubMed

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

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

2009-03-21

204

Quantum atomic dynamics in amorphous silicon; a path-integral Monte Carlo simulation  

Microsoft Academic Search

The quantum dynamics of atoms in amorphous silicon has been addressed by using path-integral Monte Carlo simulations. Structural results (radial distribution functions) found from these simulations agree well with experimental data. We study the quantum delocalization of the silicon atoms around their equilibrium positions. This delocalization is larger for coordination defects (fivefold-coordinated Si atoms). Correlations in the atomic displacements are

Carlos P. Herrero

2000-01-01

205

Quantum Dynamical Manifolds of Bound Dirac Polaron Pairs, Dirac Excitons, and Bound Dirac Excitons  

Microsoft Academic Search

Closed-shell Dirac electron pairs and electron-hole pairs in a polarizable medium are studied. The quantum dynamical manifold equations are found for these Dirac polaron pairs (DPPs). This involves finding the quantum differential geometric connection for the system. An exact solution is found in the semiclassical approximation for a frequency dependent polarization field. The hybridization due to the closed shell symmetry

Thomas C. Collins; Dillon F. Scofield

2003-01-01

206

Binding of calcium and other metal ions to the EF-hand loops of calmodulin studied by quantum chemical calculations and molecular dynamics simulations.  

PubMed

Calcium ion binding by the four EF-hand motifs of the protein calmodulin (CaM) is a central event in Ca2+-based cellular signaling. To understand molecular details of this complex process, isolated Ca2+-binding loops can be studied, by use of both experiments and calculations. In this work, we explore the metal specificity of the four Ca2+-binding loops of CaM using density functional theory (DFT) quantum chemical calculations and molecular dynamics simulations. We study CaM complexes with the physiologically important ions of calcium (Ca2+) and magnesium (Mg2+) and also with two other ions, strontium (Sr2+) and lanthanum (La3+). The former is of interest in the area of radioactive waste bioremediation, whereas the latter is often used as a probe of Ca2+-binding sites. We obtain intrinsic metal ion-loop binding energies as well as their components: vacuum, charge-transfer, solvation, entropy, and deformation terms. A detailed analysis of the results reveals that the total binding energy depends on a delicate balance among these energy components. They, in turn, are determined by the cation's charge and size as well as the amino acid composition and flexibility of the loops and the identity of the metal-chelating residues. PMID:17661504

Lepsík, Martin; Field, Martin J

2007-08-23

207

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

208

Quantum Ice : A Quantum Monte Carlo Study  

NASA Astrophysics Data System (ADS)

The magnetic ``ice'' state found in spin ice materials has recently generated great excitement for its magnetic monopole excitations. However the deconfined nature of these monopoles depends crucially on the macroscopic degeneracy of the classical ice ground state. And at very low temperatures we might expect this degeneracy to be lifted by quantum tunneling between different ice configurations. Here we present the results of large-scale Green's function Monte Carlo simulation of ice-type models which include quantum tunneling. We find compelling evidence of an extended quantum U(1)-liquid ground state with deconfined monopole excitations in both the quantum dimer model [1,2] and the quantum ice model on the diamond lattice [3]. This quantum U(1) liquid proves to be remarkably robust against the inclusion of long range dipolar interactions. [0pt] [1] O. Sikora et al., Phys. Rev. Lett. 103, 247001 (2009) [2] O. Sikora et al., Phys. Rev. B 84, 115129 (2011) [3] N. Shannon et al., arXiv:1105.4196

Sikora, Olga; Benton, Owen; Shannon, Nic; Penc, Karlo; McClarty, Paul; Pollmann, Frank; Moessner, Roderich; Fulde, Peter

2012-02-01

209

Quantum versus classical hyperfine-induced dynamics in a quantum dot  

NASA Astrophysics Data System (ADS)

In this article we analyze spin dynamics for electrons confined to semiconductor quantum dots due to the contact hyperfine interaction. We compare mean-field (classical) evolution of an electron spin in the presence of a nuclear field with the exact quantum evolution for the special case of uniform hyperfine coupling constants. We find that (in this special case) the zero-magnetic-field dynamics due to the mean-field approximation and quantum evolution are similar. However, in a finite magnetic field, the quantum and classical solutions agree only up to a certain time scale t

Coish, W. A.; Loss, Daniel; Yuzbashyan, E. A.; Altshuler, B. L.

2007-04-01

210

Quantum many-body dynamics in optomechanical arrays.  

PubMed

We study the nonlinear driven dissipative quantum dynamics of an array of optomechanical systems. At each site of such an array, a localized mechanical mode interacts with a laser-driven cavity mode via radiation pressure, and both photons and phonons can hop between neighboring sites. The competition between coherent interaction and dissipation gives rise to a rich phase diagram characterizing the optical and mechanical many-body states. For weak intercellular coupling, the mechanical motion at different sites is incoherent due to the influence of quantum noise. When increasing the coupling strength, however, we observe a transition towards a regime of phase-coherent mechanical oscillations. We employ a Gutzwiller ansatz as well as semiclassical Langevin equations on finite lattices, and we propose a realistic experimental implementation in optomechanical crystals. PMID:23992065

Ludwig, Max; Marquardt, Florian

2013-08-16

211

Dynamically Disordered Quantum Walk as a Maximal Entanglement Generator  

NASA Astrophysics Data System (ADS)

We show that the entanglement between the internal (spin) and external (position) degrees of freedom of a qubit in a random (dynamically disordered) one-dimensional discrete time quantum random walk (QRW) achieves its maximal possible value asymptotically in the number of steps, outperforming the entanglement attained by using ordered QRW. The disorder is modeled by introducing an extra random aspect to QRW, a classical coin that randomly dictates which quantum coin drives the system’s time evolution. We also show that maximal entanglement is achieved independently of the initial state of the walker, study the number of steps the system must move to be within a small fixed neighborhood of its asymptotic limit, and propose two experiments where these ideas can be tested.

Vieira, Rafael; Amorim, Edgard P. M.; Rigolin, Gustavo

2013-11-01

212

Dynamically disordered quantum walk as a maximal entanglement generator.  

PubMed

We show that the entanglement between the internal (spin) and external (position) degrees of freedom of a qubit in a random (dynamically disordered) one-dimensional discrete time quantum random walk (QRW) achieves its maximal possible value asymptotically in the number of steps, outperforming the entanglement attained by using ordered QRW. The disorder is modeled by introducing an extra random aspect to QRW, a classical coin that randomly dictates which quantum coin drives the system's time evolution. We also show that maximal entanglement is achieved independently of the initial state of the walker, study the number of steps the system must move to be within a small fixed neighborhood of its asymptotic limit, and propose two experiments where these ideas can be tested. PMID:24237496

Vieira, Rafael; Amorim, Edgard P M; Rigolin, Gustavo

2013-11-01

213

Quantum tomography meets dynamical systems and bifurcations theory  

NASA Astrophysics Data System (ADS)

A powerful tool for studying geometrical problems in Hilbert spaces is developed. We demonstrate the convergence and robustness of our method in every dimension by considering dynamical systems theory. This method provides numerical solutions to hard problems involving many coupled nonlinear equations in low and high dimensions (e.g., quantum tomography problem, existence and classification of Pauli partners, mutually unbiased bases, complex Hadamard matrices, equiangular tight frames, etc.). Additionally, this tool can be used to find analytical solutions and also to implicitly prove the existence of solutions. Here, we develop the theory for the quantum pure state tomography problem in finite dimensions but this approach is straightforwardly extended to the rest of the problems. We prove that solutions are always attractive fixed points of a nonlinear operator explicitly given. As an application, we show that the statistics collected from three random orthonormal bases is enough to reconstruct pure states from experimental (noisy) data in every dimension d ? 32.

Goyeneche, D.; de la Torre, A. C.

2014-06-01

214

Quantum state-resolved energy transfer dynamics at gas-liquid interfaces: IR laser studies of CO2 scattering from perfluorinated liquids.  

PubMed

An apparatus for detailed study of quantum state-resolved inelastic energy transfer dynamics at the gas-liquid interface is described. The approach relies on supersonic jet-cooled molecular beams impinging on a continuously renewable liquid surface in a vacuum and exploits sub-Doppler high-resolution laser absorption methods to probe rotational, vibrational, and translational distributions in the scattered flux. First results are presented for skimmed beams of jet-cooled CO(2) (T(beam) approximately 15 K) colliding at normal incidence with a liquid perfluoropolyether (PFPE) surface at E(inc) = 10.6(8) kcal/mol. The experiment uses a tunable Pb-salt diode laser for direct absorption on the CO(2) nu(3) asymmetric stretch. Measured rotational distributions in both 00(0)0 and 01(1)0 vibrational manifolds indicate CO(2) inelastically scatters from the liquid surface into a clearly non-Boltzmann distribution, revealing nonequilibrium dynamics with average rotational energies in excess of the liquid (T(s) = 300 K). Furthermore, high-resolution analysis of the absorption profiles reveals that Doppler widths correspond to temperatures significantly warmer than T(s) and increase systematically with the J rotational state. These rotational and translational distributions are consistent with two distinct gas-liquid collision pathways: (i) a T approximately 300 K component due to trapping-desorption (TD) and (ii) a much hotter distribution (T approximately 750 K) due to "prompt" impulsive scattering (IS) from the gas-liquid interface. By way of contrast, vibrational populations in the CO(2) bending mode are inefficiently excited by scattering from the liquid, presumably reflecting much slower T-V collisional energy transfer rates. PMID:16853084

Perkins, Bradford G; Häber, Thomas; Nesbitt, David J

2005-09-01

215

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

216

GENERAL: Concurrence of Quantum States: Algebraic Dynamical Method Study XXX Models in a Time-Depending Random External Field  

NASA Astrophysics Data System (ADS)

Based on algebraic dynamics and the concept of the concurrence of the entanglement, we investigate the evolutive properties of the two-qubit entanglement that formed by Heisenberg XXX models under a time-depending external held. For this system, the property of the concurrence that is only dependent on the coupling constant J and total values of the external field is proved. Furthermore, we found that the thermal concurrence of the system under a static random external field is a function of the coupling constant J, temperature T, and the magnitude of external held.

Fu, Chuan-Ji; Zhu, Qin-Sheng; Wu, Shao-Yi

2010-06-01

217

Pulse Designed Coherent Dynamics of a Quantum Dot Charge Qubit  

NASA Astrophysics Data System (ADS)

We propose an effective method to design the working parameters of a pulse-driven charge qubit implemented with double quantum dot. It is shown that intrinsic qubit population leakage to undesired states in the control and measurement process can be determined by the simulation of coherent dynamics of the qubit and minimized by choosing proper working parameters such as pulse shape. The result demonstrated here bodes well for future quantum gate operations and quantum computing applications.

Cao, Gang; Wang, Li; Tu, Tao; Li, Hai-Ou; Xiao, Ming; Guo, Guo-Ping

2012-03-01

218

Decoherence-free dynamics of quantum discord for two correlated qubits in finite-temperature reservoirs  

Microsoft Academic Search

We investigate decoherence-free evolution (DFE) of quantum discord (QD) for two initially-correlated qubits in two finite-temperature reservoirs using an exactly solvable model. We study QD dynamics of the two qubits coupled to two independent Ohmic reservoirs when the two qubits are initially prepared in X-type quantum states. It is found that reservoir temperature significantly affects the DFE dynamics. We show

Lan Xu; Ji-Bing Yuan; Qing-Shou Tan; Lan Zhou; Le-Man Kuang

2011-01-01

219

Quantum diffusion in liquid water from ring polymer molecular dynamics.  

PubMed

We have used the ring polymer molecular-dynamics method to study the translational and orientational motions in an extended simple point charge model of liquid water under ambient conditions. We find, in agreement with previous studies, that quantum-mechanical effects increase the self-diffusion coefficient D and decrease the relaxation times around the principal axes of the water molecule by a factor of around 1.5. These results are consistent with a simple Stokes-Einstein picture of the molecular motion and suggest that the main effect of the quantum fluctuations is to decrease the viscosity of the liquid by about a third. We then go on to consider the system-size scaling of the calculated self-diffusion coefficient and show that an appropriate extrapolation to the limit of infinite system size increases D by a further factor of around 1.3 over the value obtained from a simulation of a system containing 216 water molecules. These findings are discussed in light of the widespread use of classical molecular-dynamics simulations of this sort of size to model the dynamics of aqueous systems. PMID:16252959

Miller, Thomas F; Manolopoulos, David E

2005-10-15

220

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

NASA Astrophysics Data System (ADS)

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

Keshavamurthy, S.

2009-03-01

221

Dynamic quantum tunneling in mesoscopic driven Duffing oscillators.  

PubMed

We investigate the dynamic quantum tunneling between two attractors of a mesoscopic driven Duffing oscillator. We find that, in addition to inducing a remarkable quantum shift of the bifurcation point, the mesoscopic nature also results in a perfect linear scaling behavior for the tunneling rate with the driving distance to the shifted bifurcation point. PMID:21867149

Guo, Lingzhen; Zheng, Zhigang; Li, Xin-Qi; Yan, Yijing

2011-07-01

222

Dynamics of quantum discord under decoherence from a spin environment  

Microsoft Academic Search

The effect of decoherence from a spin environment on quantum discord of two-qubit states is investigated. Our results imply that the dynamics of quantum discord depend not only on the white noise in the Werner state, the coupling strength, and the number of the freedom degrees of the environment but also on the tunneling elements of the environment and the

Xiao San Ma; Guang Xing Zhao; Jia Yan Zhang; An Min Wang

2011-01-01

223

Many-body quantum mechanics as a symplectic dynamical system  

Microsoft Academic Search

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

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

1980-01-01

224

Two-dimensional wavepacket dynamics with quantum hydrodynamics  

Microsoft Academic Search

Wyatt and coworkers introduced a new approach (Wyatt, Quantum Dynamics with Trajectories Introduction to Quantum Hydrodynamics, Springer, New York, 2005; Lopreore and Wyatt, Phys Rev Lett, 1999, 82, 5190; Wyatt et al., J Chem Phys, 2001, 114, 5113; Lopreore and Wyatt, J Chem Phys, 2002, 116, 1228; Trahan and Wyatt, J Chem Phys, 2003, 118, 4784; Trahan et al., J

D. Matsumoto; K. Hayashi; T. Ida; M. Mizuno; K. Endo; K. Nishikawa

2007-01-01

225

Design Approach of Dynamically Reconfigurable Single Flux Quantum Logic Gates  

Microsoft Academic Search

Novel reconfigurable superconductive single flux quantum (SFQ) logic devices, the functions of which can be dynamically reconfigured by inputting control signals, have been investigated. The characteristics of single flux quantum circuits can be easily modulated by applying currents or magnetic fields because of the high sensitivity of superconductive circuits. We investigated several design approaches for the realization of dy- namically

Y. Yamanashi; I. Okawa; N. Yoshikawa

2011-01-01

226

Signals faster than light in nonlinear quantum dynamics  

Microsoft Academic Search

Recent ideas and experiments strengthen Gisin's argument that Weinberg's nonlinear generalization of quantum mechanics allows signals faster than light. Employing a classical signal as in quantum teleportation supports Gisin's use of `preparation at a distance' in determining how the nonlinear dynamics of one of two correlated spins responds to measurements on the other, if there is time for the classical

T. F. Jordan; Z.-E. Sariyianni

1999-01-01

227

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

228

Algebraic and geometric aspects of generalized quantum dynamics  

SciTech Connect

We briefly discuss some algebraic and geometric aspects of the generalized Poisson bracket and noncommutative phase space for generalized quantum dynamics, which are analogous to properties of the classical Poisson bracket and ordinary symplectic structure.

Adler, S.L. (Institute for Advanced Study, Princeton, New Jersey 08540 (United States)); Wu, Y. (Department of Physics, University of Utah, Salt Lake City, Utah 84112 (United States))

1994-06-15

229

Dynamic characteristics of photonic crystal quantum dot lasers.  

PubMed

In this paper, we analyze the dynamic characteristics of quantum dot (QD) photonic crystal lasers by solving Maxwell equations coupled to rate equations through linear susceptibility of QDs. Here, we study the effects of the quality factor of the microcavity and temperature on the delay, relaxation oscillation frequency, and output intensity of the lasers. Moreover, we investigate the dependence of the Purcell factor on temperature. We show that when the quality factor of the microcavity is so high that we can consider its linewidth as a delta function in comparison with QDs, the Purcell factor significantly drops with increasing temperature. PMID:24787584

Banihashemi, Mehdi; Ahmadi, Vahid

2014-04-20

230

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

231

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

232

Dynamical localization of two electrons in triple-quantum-dot shuttles  

NASA Astrophysics Data System (ADS)

The dynamical localization phenomena in two-electron quantum-dot shuttles driven by an ac field have been investigated and analyzed by the Floquet theory. The dynamical localization occurs near the anti-crossings in Floquet eigenenergy spectrum. The oscillation of the quantum-dot shuttles may increase the possibility of the dynamical localization. Especially, even if the two electrons are initialized in two neighbor dots, they can be localized there for appropriate intensity of the driven field. The studies may help the understanding of dynamical localization in electron shuttles and expand the application potential of nanoelectromechanical devices.

Qu, Jinxian; Duan, Suqing; Yang, Ning

2012-04-01

233

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; Sørensen, Erik S.; Sachdev, Subir

2014-05-01

234

Quantum dynamics study of the competing ultrafast intersystem crossing and internal conversion in the ``channel 3'' region of benzene  

NASA Astrophysics Data System (ADS)

Time-resolved photoelectron spectroscopy can obtain detailed information about the dynamics of a chemical process on the femtosecond timescale. The resulting signal from such detailed experiments is often difficult to analyze and therefore theoretical calculations are important in providing support. In this paper we continue our work on the competing pathways in the photophysics and photochemistry of benzene after excitation into the ``channel 3'' region [R. S. Minns, D. S. N. Parker, T. J. Penfold, G. A. Worth, and H. H. Fielding, Phys. Chem. Chem. Phys. 12, 15607 (2010)] with details of the calculations shown previously, building on a vibronic coupling Hamiltonian [T. J. Penfold and G. A. Worth, J. Chem. Phys. 131, 064303 (2009)] to include the triplet manifold. New experimental data are also presented suggesting that an oscillatory signal is due to a hot band excitation. The experiments show that signals are obtained from three regions of the potential surfaces, three open channels, which are assigned with the help of simulations showing that following excitation into vibrationally excited-states of S1 the wavepacket not only crosses through the prefulvenoid conical intersection back to the singlet ground state, but also undergoes ultrafast intersystem crossing to low lying triplet states. The model is, however, not detailed enough to capture the full details of the oscillatory signal due to the hot band.

Penfold, T. J.; Spesyvtsev, R.; Kirkby, O. M.; Minns, R. S.; Parker, D. S. N.; Fielding, H. H.; Worth, G. A.

2012-11-01

235

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

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

236

Dynamical control of interference using voltage pulses in the quantum regime.  

PubMed

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. PMID:24828657

Gaury, Benoit; Waintal, Xavier

2014-01-01

237

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

238

Dirac particle in a box, and relativistic quantum Zeno dynamics  

NASA Astrophysics Data System (ADS)

After developing a complete set of eigenfunctions for a Dirac particle restricted to a box, the quantum Zeno dynamics of a relativistic system is considered. The evolution of a continuously observed quantum mechanical system is governed by the theorem put forth by Misra and Sudarshan. One of the conditions for quantum Zeno dynamics to be manifest is that the Hamiltonian is semi-bounded. This Letter analyzes the effects of continuous observation of a particle whose time evolution is generated by the Dirac Hamiltonian. The theorem by Misra and Sudarshan is not applicable here since the Dirac operator is not semi-bounded.

Menon, Govind; Belyi, Sergey

2004-09-01

239

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

SciTech Connect

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

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

2010-09-01

240

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.

Harrison, Christopher B.; Schulten, Klaus

2012-01-01

241

Open quantum dynamics of single-photon optomechanical devices  

NASA Astrophysics Data System (ADS)

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

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

2013-08-01

242

Quantum dynamical semigroups, group representations and convolution semigroups  

NASA Astrophysics Data System (ADS)

Semigroups of operators are known to play an important role in theoretical physics. In particular, quantum dynamical semigroups are fundamental in the theory of open quantum systems. We will describe a class of semigroups of operators which has interesting applications, for instance, in quantum information science. Each of these semigroups of operators is generated, in a suitable way, by a representation (or an antirepresentation) of a group in a Banach space and by a convolution semigroup of probability measures on that group. Some significant examples—including a remarkable type of quantum dynamical semigroups introduced by Kossakowski in the pioneering times of the theory of open quantum systems—and their mutual relations will be discussed.

Aniello, Paolo

2013-03-01

243

A dynamic watermarking scheme for quantum images using quantum wavelet transform  

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

244

Nonlinear dynamics and quantum entanglement in optomechanical systems.  

PubMed

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. PMID:24702337

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

2014-03-21

245

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

Microsoft Academic Search

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

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

2009-01-01

246

Quantum molecular dynamics simulations of hydrogen production and solar cells  

NASA Astrophysics Data System (ADS)

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

Mou, Weiwei

247

Dissipative Dynamics of Quantum Discord of Two Strongly Driven Qubits  

NASA Astrophysics Data System (ADS)

The exact dynamics of quantum discord (QD) of two strongly driven qubits, which are initially prepared in the X-type quantum states and inserted in two independent dissipative cavities or in a common dissipative cavity, are studied. The results indicate that both in the two cases, the evolution of QD is independent of the initial cavity state. For the two independent dissipative cavities, it is found that the phenomenon of sudden transition between classical and quantum decoherence exists and the transition time can be greatly delayed by suitably choosing the initial state parameter of the two qubits, the cavity mode-driving field detunning and the decay rate of the cavity. For the common dissipative cavity, it is shown that for some initial states of the two qubits, the QD can increase for a finite time at first, and then it decreases to a steady value, while for some other initial states, the QD can increase monotonously or with oscillation till a stable value is reached. Moreover, the creation of QD for the two qubits in a common cavity is discussed.

Yang, Bai-yuan; Fang, Mao-fa; Guo, You-neng

2013-11-01

248

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

249

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

NASA Astrophysics Data System (ADS)

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

Fu, Bina; Zhang, Dong H.

2013-05-01

250

Quantum de Laval nozzle: Stability and quantum dynamics of sonic horizons in a toroidally trapped Bose gas containing a superflow  

Microsoft Academic Search

We study an experimentally realizable system containing stable black hole white hole acoustic horizons in toroidally trapped Bose-Einstein condensates---the quantum de Laval nozzle. We numerically obtain stationary flow configurations and assess their stability using Bogoliubov theory, finding both in hydrodynamic and nonhydrodynamic regimes there exist dynamically unstable regions associated with the creation of positive and negative energy quasiparticle pairs in

P. Jain; A. S. Bradley; C. W. Gardiner

2007-01-01

251

Quantum dynamics simulation with classical oscillators  

NASA Astrophysics Data System (ADS)

In a previous paper [J. S. Briggs and A. Eisfeld, Phys. Rev. APLRAAN1050-294710.1103/PhysRevA.85.052111 85, 052111 (2012)] we showed that the time development of the complex amplitudes of N coupled quantum states can be mapped by the time development of positions and velocities of N coupled classical oscillators. Here we examine to what extent this mapping can be realized to simulate the “quantum,” properties of entanglement and qubit manipulation. By working through specific examples, e.g., of quantum gate operation, we seek to illuminate quantum and classical differences which hitherto have been treated more mathematically. In addition, we show that important quantum coupled phenomena, such as the Landau-Zener transition and the occurrence of Fano resonances can be simulated by classical oscillators.

Briggs, John S.; Eisfeld, Alexander

2013-12-01

252

Experimental tests of quantum nonlinear dynamics in atom optics  

Microsoft Academic Search

Cold atoms in optical potentials provide an ideal test bed to explore quantum nonlinear dynamics. Atoms are prepared in a magneto-optic trap or as a dilute Bose–Einstein condensate and subjected to a far detuned optical standing wave that is modulated. They exhibit a wide range of dynamics, some of which can be explained by classical theory while other aspects show

Winfried K Hensinger; Norman R Heckenberg; Gerard J Milburn; Halina Rubinsztein-Dunlop

2003-01-01

253

Open Quantum System Dynamics from a Measurement Perspective: Applications to Coherent Particle Transport and to Quantum~Brownian Motion  

NASA Astrophysics Data System (ADS)

We employ the theoretical framework of positive operator valued measures, to study Markovian open quantum systems. In particular, we discuss how a quantum system influences its environment. Using the theory of indirect measurements, we then draw conclusions about the information we could hypothetically obtain about the system by observing the environment. Although the environment is not actually observed, we can use these results to describe the change of the quantum system due to its interaction with the environment. We apply this technique to two different problems. In the first part, we study the coherently driven dynamics of a particle on a rail of quantum dots. This tunnelling between adjacent quantum dots can be controlled externally. We employ an adiabatic scheme similar to stimulated Raman adiabatic passage, to transfer the particle between different quantum dots. We compare two fundamentally different sources of decoherence. In the second part, we study the dynamics of a free quantum particle, which experiences random collisions with gas particles. Previous studies on this topic applied scattering theory to momentum eigenstates. We present a supplementary approach, where we develop a rigorous measurement interpretation of the collision process to derive a master equation. Finally, we study the collisional decoherence process in terms of the Wigner function. We restrict ourselves to one spatial dimension. Nevertheless, we find some interesting new insight, including that the previously celebrated quantum contribution to position diffusion is not real, but a consequence of the Markovian approximation. Further, we discover that the leading decoherence process is due to phase averaging, rather than induced by the information transfer between the colliding particles.

Kamleitner, Ingo

2010-09-01

254

Analysis of quantum Monte Carlo dynamics for quantum adiabatic evolution in infinite-range spin systems  

NASA Astrophysics Data System (ADS)

We analytically derive deterministic equations of order parameters such as spontaneous magnetization in infinite-range quantum spin systems obeying quantum Monte Carlo dynamics. By means of the Trotter decomposition, we consider the transition probability of Glauber-type dynamics of microscopic states for the corresponding classical system. Under the static approximation, differential equations with respect to macroscopic order parameters are explicitly obtained from the master equation that describes the microscopic-law. We discuss several possible applications of our approach to disordered spin systems for statistical-mechanical informatics. Especially, we argue the ground state searching for infinite-range random spin systems via quantum adiabatic evolution.

Inoue, Jun-Ichi

2011-03-01

255

Acceleration of adiabatic quantum dynamics in electromagnetic fields  

SciTech Connect

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

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

2011-10-15

256

Acceleration of adiabatic quantum dynamics in electromagnetic fields  

NASA Astrophysics Data System (ADS)

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

Masuda, Shumpei; Nakamura, Katsuhiro

2011-10-01

257

Role of wave packet width in quantum molecular dynamics in fusion reactions near barrier  

NASA Astrophysics Data System (ADS)

The dynamical fusion process of 48Ca + 144Sm with different impact parameters near barrier is studied by an extended quantum molecular dynamics (EQMD) model, where width of wavepacket is dynamically treated based on variational principle. The time evolution of different energy components such as potential energy, kinetic energy, Coulomb energy and Pauli potential are analyzed when dynamical or fixed width is assumed in calculation. It is found that the dynamical wavepacket width can enhance the dissipation of incident energy and the fluctuations, which are important to form compound nuclei. Moreover, we compare the fusion barrier dependence on the incident energy when it is determined by both dynamical and fixed wavepacket width.

Cao, X. G.; Ma, Y. G.; Zhang, G. Q.; Wang, H. W.; Anastasi, A.; Curciarello, F.; De Leo, V.

2014-05-01

258

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

259

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

SciTech Connect

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

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

2010-11-15

260

Jensen-Shannon divergence and non-linear quantum dynamics  

NASA Astrophysics Data System (ADS)

Using the statistical inference method, a non-relativistic, spinless, non-linear quantum dynamical equation is derived with the Fisher information metric substituted by the Jensen-Shannon distance information. Among all possible implications, it is shown that the non-linear Schrödinger equation preserves the symplectic structure of the complex Hilbert space, hence a Hamiltonian dynamics. The canonically projected dynamics is obtained on the corresponding projective Hilbert space of pure state density operators.

Molladavoudi, Saeid; Zainuddin, Hishamuddin; Chan, Kar Tim

2012-05-01

261

Correlated Single Quantum Dot Blinking and Interfacial Electron Transfer Dynamics  

PubMed Central

The electron transfer (ET) dynamics from core/multi-shell (CdSe/CdS3MLZnCdS2MLZnS2ML) quantum dots (QDs) to adsorbed Fluorescein (F27) molecules have been studied by single particle spectroscopy to probe the relationship between single QD interfacial electron transfer and blinking dynamics. Electron transfer from the QD to F27 and the subsequent recombination were directly observed by ensemble-averaged transient absorption spectroscopy. Single QD-F27 complexes show correlated fluctuation of fluorescence intensity and lifetime, similar to those observed in free QDs. With increasing ET rate (controlled by F27-to-QD ratio), the lifetime of on states decreases and relative contribution of off states increases. It was shown that ET is active for QDs in on states, the excited state lifetime of which reflects the ET rate, whereas in the off state QD excitons decay by Auger relaxation and ET is not a competitive quenching pathway. Thus, the blinking dynamics of single QDs modulate their interfacial ET activity. Furthermore, interfacial ET provides an additional pathway for generating off states, leading to correlated single QD interfacial ET and blinking dynamics in QD-acceptor complexes. Because blinking is a general phenomenon of single QDs, it appears that the correlated interfacial ET and blinking and the resulting intermittent ET activity are general phenomena for single QDs.

Jin, Shengye; Hsiang, Jung-Cheng; Zhu, Haiming; Song, Nianhui; Dickson, Robert M.; Lian, Tianquan

2011-01-01

262

Correlated Single Quantum Dot Blinking and Interfacial Electron Transfer Dynamics.  

PubMed

The electron transfer (ET) dynamics from core/multi-shell (CdSe/CdS(3ML)ZnCdS(2ML)ZnS(2ML)) quantum dots (QDs) to adsorbed Fluorescein (F27) molecules have been studied by single particle spectroscopy to probe the relationship between single QD interfacial electron transfer and blinking dynamics. Electron transfer from the QD to F27 and the subsequent recombination were directly observed by ensemble-averaged transient absorption spectroscopy. Single QD-F27 complexes show correlated fluctuation of fluorescence intensity and lifetime, similar to those observed in free QDs. With increasing ET rate (controlled by F27-to-QD ratio), the lifetime of on states decreases and relative contribution of off states increases. It was shown that ET is active for QDs in on states, the excited state lifetime of which reflects the ET rate, whereas in the off state QD excitons decay by Auger relaxation and ET is not a competitive quenching pathway. Thus, the blinking dynamics of single QDs modulate their interfacial ET activity. Furthermore, interfacial ET provides an additional pathway for generating off states, leading to correlated single QD interfacial ET and blinking dynamics in QD-acceptor complexes. Because blinking is a general phenomenon of single QDs, it appears that the correlated interfacial ET and blinking and the resulting intermittent ET activity are general phenomena for single QDs. PMID:21915369

Jin, Shengye; Hsiang, Jung-Cheng; Zhu, Haiming; Song, Nianhui; Dickson, Robert M; Lian, Tianquan

2010-08-31

263

Experimental results on quantum chromo dynamics: what is next?  

NASA Astrophysics Data System (ADS)

This review gives a flavour of experimental quantum chromo dynamics (QCD) results obtained at the Large Hadron Collider (LHC) during the first run period in the years 2010-2012. The results cover selected aspects of soft low-pT phenomena, typically described by phenomenological models, as well as high-pT processes which can be studied theoretically with perturbative techniques. In general the phenomenological models required tuning to describe the data in the new energy region of 7-8 TeV, while perturbative QCD (pQCD) is found to work generally quite well for most of the phase space currently studied. The strong force will remain a main topic of research at colliders such as the LHC also in future, with the large data samples allowing for more detailed studies and in particular when the next energy level of 13-14 TeV will be reached.

De Roeck, Albert

2013-12-01

264

Quantum nuclear dynamics in the photophysics of diamondoids.  

PubMed

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

Patrick, Christopher E; Giustino, Feliciano

2013-01-01

265

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.

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

2012-01-01

266

Transport properties of lithium hydride from quantum molecular dynamics and orbital-free molecular dynamics  

SciTech Connect

We have performed a systematic study of lithium hydride in the warm-dense-matter regime for a density range from one to four times ambient solid and for temperatures from 2 to 6 eV using both finite-temperature density-functional theory quantum molecular dynamics (QMD) and orbital-free molecular dynamics (OFMD) with a focus on dynamical properties such as diffusion and viscosity. The validity of various mixing rules, especially those utilizing pressure, were checked for composite properties determined from QMD/OFMD simulations of the pure species against calculations on the fully interacting mixture. These rules produce pressures within about 10% of the full-mixture values but mutual-diffusion coefficients as different as 50%. We found very good agreement overall between the QMD, employing a three-electron pseudopotential, and the OFMD in the local-density approximation, especially at the higher temperatures and densities.

Horner, D. A.; Kress, J. D.; Collins, L. A. [Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Lambert, F. [CEA, DAM, DIF, F-91297 Arpajon (France)

2009-07-01

267

Optimal approach to quantum communication using dynamic programming  

PubMed Central

Reliable preparation of entanglement between distant systems is an outstanding problem in quantum information science and quantum communication. In practice, this has to be accomplished by noisy channels (such as optical fibers) that generally result in exponential attenuation of quantum signals at large distances. A special class of quantum error correction protocols, quantum repeater protocols, can be used to overcome such losses. In this work, we introduce a method for systematically optimizing existing protocols and developing more efficient protocols. Our approach makes use of a dynamic programming-based searching algorithm, the complexity of which scales only polynomially with the communication distance, letting us efficiently determine near-optimal solutions. We find significant improvements in both the speed and the final-state fidelity for preparing long-distance entangled states.

Jiang, Liang; Taylor, Jacob M.; Khaneja, Navin; Lukin, Mikhail D.

2007-01-01

268

Long-distance quantum transport dynamics in macromolecules  

NASA Astrophysics Data System (ADS)

Using renormalization group methods, we develop a rigorous coarse-grained representation of the dissipative dynamics of quantum excitations propagating inside open macromolecular systems. We show that, at very low spatial resolution, this quantum transport theory reduces to a modified Brownian process, in which quantum delocalization effects are accounted for by means of an effective term in the Onsager-Machlup functional. Using this formulation, we derive a simple analytic solution for the time-dependent probability of observing the quantum excitation at a given point in the macromolecule. This formula can be used to predict the migration of natural or charged quantum excitations in a variety of molecular systems, including biological and organic polymers, organic crystalline transistors, or photosynthetic complexes. For illustration purposes, we apply this method to investigate inelastic electronic hole transport in a long homo-DNA chain.

Schneider, E.; Faccioli, P.

2014-04-01

269

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

PubMed Central

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

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

2010-01-01

270

Complex scattering dynamics and the quantum Hall effects  

SciTech Connect

We review both classical and quantum potential scattering in two dimensions in a magnetic field, with applications to the quantum Hall effect. Classical scattering is complex, due to the approach of scattering states to an infinite number of dynamically bound states. Quantum scattering follows the classical behavior rather closely, exhibiting sharp resonances in place of the classical bound states. Extended scatterers provide a quantitative explanation for the breakdown of the QHE at a comparatively small Hall voltage as seen by Kawaji et al., and possibly for noise effects.

Trugman, S.A.

1994-12-16

271

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

272

Quantum dynamic behaviour in a coupled cavities system  

NASA Astrophysics Data System (ADS)

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

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

2012-06-01

273

Dynamic Entanglement and Separability Criteria for Quantum Computing Bit States  

NASA Astrophysics Data System (ADS)

A theoretical framework is demonstrated to evaluate the degree of entanglement of bit states in quantum computing. Separability of general superposition of Hilbert space unit vectors is discussed, and criteria in amplitude as well as in phase are derived. By these criteria the possibility of different quantum gates such as controlled not (CN), controlled controlled not (CCN), controlled rotation (CR), and controlled phase shift (CPS), to create the entanglement is examined. Furthermore, the selection of measurement mode external to the quantum system is incorporated in the formula using Kronecker delta ( ? kx ), introducing the concept of dynamic entanglement. With this the process of wavefunction collapse upon measurement is understood as the result of the activation of the dynamic entanglement. A firefly in a box model is used to show a pure state of ontological uncertainty, which is in a dynamically entangled state in Hilbert space.

Matsueda, Hideaki; Cohen, David W.

2007-12-01

274

A Theoretical Study on Initial Processes of Li-Ion Transport at the Electrolyte/Cathode Interface: A Quantum Chemical Molecular Dynamics Approach  

NASA Astrophysics Data System (ADS)

Initial processes of Li-ion transport at the electrolyte/cathode interface of a Li-ion battery were investigated using an ultra-accelerated quantum chemical molecular dynamics (UA-QCMD) simulator. This simulator was based on our in-house tight-binding quantum chemical (TB-QC) simulator and MD simulator. The parameterization for LiCoO2 crystal and ethylene carbonate (EC) molecule in UA-QCMD was first carried out to show the fine agreement of their electronic structures and interaction energies, with the values determined by first-principles calculations. Li-ion movements in the electrolyte and at the interface between the electrolyte and cathode were simulated. It was found that in the electrolyte, a solvation, that corresponds to the formation of bonds between the Li and surrounded EC molecules was formed. When the Li-ion was moved to the cathode surface, it was observed that the interaction energies of Li-EC molecules was decreased. In such a case, the Li-ion was bound to the oxygen atoms of the cathode.

Tomaru Ogawa,; Masayuki Miyano,; Yasuhiro Suzuki,; Ai Suzuki,; Hideyuki Tsuboi,; Nozomu Hatakeyama,; Akira Endou,; Hiromitsu Takaba,; Momoji Kubo,; Akira Miyamoto,

2010-04-01

275

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

276

A quantum mechanics/molecular dynamics study of electric field gradient fluctuations in the liquid phase. The case of Na+ in aqueous solution.  

PubMed

The (23)Na quadrupolar coupling constant of the Na(+) ion in aqueous solution has been predicted using molecular dynamics simulations and hybrid quantum mechanics/molecular mechanics methods for the calculation of electric field gradients. The developed computational approach is generally expected to provide reliable estimates of the quadrupolar coupling constants of monoatomic species in condensed phases, and we show here that intermolecular polarization and non-electrostatic interactions are of crucial importance as they result in a 100% increased quadrupolar coupling constant of the ion as compared to a simpler pure electrostatic picture. These findings question the reliability of the commonly applied classical Sternheimer approximation for the calculations of the electric field gradient. As it can be expected from symmetry considerations, the quadrupolar coupling constants of the 5- and 6-coordinated Na(+) ions in solution are found to differ significantly. PMID:23247548

Aidas, K?stutis; Ågren, Hans; Kongsted, Jacob; Laaksonen, Aatto; Mocci, Francesca

2013-02-01

277

Interface behaviors of acetylene and ethylene molecules with 1-butyl-3-methylimidazolium acetate ionic liquid: a combined quantum chemistry calculation and molecular dynamics simulation study.  

PubMed

Although imidazolium-based ionic liquids (ILs) combined with oxygen-containing anions were proposed as the potential solvents for the selective separation of acetylene (C(2)H(2)) and ethylene (C(2)H(4)), the detailed mechanism at the molecular level is still not well understood. The present work focuses on a most effective IL for removing C(2)H(2) from a C(2)H(4) stream, 1-butyl-3-methylimidazolium acetate ([BMIM][OAc]), aiming at understanding the first steps of the adsorption process of the molecules at the IL surface. We present a combined quantum mechanical (QM) calculation and molecular dynamics (MD) simulation study on the structure and property of the IL as well as its interaction with C(2)H(2) and C(2)H(4) molecules. The calculated results indicate that C(2)H(2) presents a stronger interaction with the IL than C(2)H(4) and the anion of the IL is mainly responsible for the stronger interaction. QM calculations show a stronger hydrogen-binding linkage between an acidic proton of C(2)H(2)/C(2)H(4) and the basic oxygen atom in [OAc](-) anion, in contrast to the relative weaker association via the C-H···? interaction between C(2)H(2)/C(2)H(4) and the cation. From MD simulations, it is observed that in the interfacial region, the butyl chain of cations and methyl of anions point into the vapor phase. The coming molecules on the IL surface may be initially wrapped by the extensive butyl chain and then devolved to the interface or caught into the bulk by the anion of IL. The introduction of guest molecules significantly influences the anion distribution and orientation on the interface, but the cations are not disturbed because of their larger volume and relatively weaker interaction with the changes in the guest molecules. The theoretical results provide insight into the molecular mechanism of the observed selective separation of C(2)H(2) form a C(2)H(4) stream by ILs. PMID:23211277

Xu, Hao; Han, Zhe; Zhang, Dongju; Zhan, Jinhua

2012-12-01

278

The structure of the hydrated electron. Part 2. A mixed quantum/classical molecular dynamics embedded cluster density functional theory: single-excitation configuration interaction study.  

PubMed

Adiabatic mixed quantum/classical (MQC) molecular dynamics (MD) simulations were used to generate snapshots of the hydrated electron in liquid water at 300 K. Water cluster anions that include two complete solvation shells centered on the hydrated electron were extracted from the MQC MD simulations and embedded in a roughly 18 Ax18 Ax18 A matrix of fractional point charges designed to represent the rest of the solvent. Density functional theory (DFT) with the Becke-Lee-Yang-Parr functional and single-excitation configuration interaction (CIS) methods were then applied to these embedded clusters. The salient feature of these hybrid DFT(CIS)/MQC MD calculations is significant transfer (approximately 18%) of the excess electron's charge density into the 2p orbitals of oxygen atoms in OH groups forming the solvation cavity. We used the results of these calculations to examine the structure of the singly occupied and the lower unoccupied molecular orbitals, the density of states, the absorption spectra in the visible and ultraviolet, the hyperfine coupling (hfcc) tensors, and the infrared (IR) and Raman spectra of these embedded water cluster anions. The calculated hfcc tensors were used to compute electron paramagnetic resonance (EPR) and electron spin echo envelope modulation (ESEEM) spectra for the hydrated electron that compared favorably to the experimental spectra of trapped electrons in alkaline ice. The calculated vibrational spectra of the hydrated electron are consistent with the red-shifted bending and stretching frequencies observed in resonance Raman experiments. In addition to reproducing the visible/near IR absorption spectrum, the hybrid DFT model also accounts for the hydrated electron's 190-nm absorption band in the ultraviolet. Thus, our study suggests that to explain several important experimentally observed properties of the hydrated electron, many-electron effects must be accounted for: one-electron models that do not allow for mixing of the excess electron density with the frontier orbitals of the first-shell solvent molecules cannot explain the observed magnetic, vibrational, and electronic properties of this species. Despite the need for multielectron effects to explain these important properties, the ensemble-averaged radial wavefunctions and energetics of the highest occupied and three lowest unoccupied orbitals of the hydrated electrons in our hybrid model are close to the s- and p-like states obtained in one-electron models. Thus, one-electron models can provide a remarkably good approximation to the multielectron picture of the hydrated electron for many applications; indeed, the two approaches appear to be complementary. PMID:17530823

Shkrob, Ilya A; Glover, William J; Larsen, Ross E; Schwartz, Benjamin J

2007-06-21

279

Theoretical study of dynamic electron-spin-polarization via the doublet-quartet quantum-mixed state (II). Population transfer and magnetic field dependence of the spin polarization.  

PubMed

The population transfer to the spin-sublevels of the unique quartet (S = 3/2) high-spin state of the strongly exchange-coupled (SC) radical-triplet pair (for example, an Acceptor-Donor-Radical triad (A-D-R)) via a doublet-quartet quantum-mixed (QM) state is theoretically investigated by a stochastic Liouville equation. In this work, we have treated the loss of the quantum coherence (de-coherence) due to the de-phasing during the population transfer and neglected the effect of other de-coherence mechanisms. The dependences on the magnitude of the exchange coupling or the fine-structure parameter of the QM state are investigated. The dependence on the velocity of the population transfer (by the electron transfer or the energy-transfer) from the QM state to the SC quartet state is also clarified. It is revealed that the de-coherence during the population transfer mainly originates from the fine-structure term of the QM state in the doublet-triplet exchange coupled systems. This de-coherence leads to the unique dynamic electron polarization (DEP) on the high-field spin sublevels of the SC state, which is similar to the unique DEP pattern of the photo-excited triplet states of the reaction centers of photosystems I and II. The magnetic field dependence of the population transfer leading to the populations of the spin-sublevels of the SC states is also calculated. The possibility of the control of energy transport, spin transport and information technology by using the QM state is discussed based on these results. The knowledge obtained in this work is useful in the spin dynamics of any doublet-triplet exchange coupled systems. PMID:22717738

Matsumoto, Takafumi; Teki, Yoshio

2012-08-01

280

Complexity of controlling quantum many-body dynamics  

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

281

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

SciTech Connect

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

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

2010-05-15

282

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

283

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

NASA Astrophysics Data System (ADS)

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

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

2012-10-01

284

Quantum diffusion dynamics in nonlinear systems: A modified kicked-rotor model  

SciTech Connect

Using a simple method analogous to a quantum rephasing technique, a simple modification to a paradigm of classical and quantum chaos is proposed. The interesting quantum maps thus obtained display remarkably rich quantum dynamics. Emphasis is placed on the destruction of dynamical localization without breaking periodicity, unbounded quantum anomalous diffusion in integrable systems, and transient dynamical localization. Experimental realizations of this work are also discussed.

Gong Jiangbin [Department of Physics and Centre of Computational Science and Engineering, National University of Singapore, 117542 (Singapore); Wang Jiao [Temasek Laboratories and Beijing-Hong Kong-Singapore Joint Center for Nonlinear and Complex Systems (Singapore), National University of Singapore, 117542 (Singapore)

2007-09-15

285

Quench dynamics of isolated many-body quantum systems  

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

286

Loop Quantum Gravity Effective Matter Dynamics  

NASA Astrophysics Data System (ADS)

The cosmological character of Gamma-Ray-Bursts 1 (GRBs), short and intense bursts of 100 keV - 1 MeV photons and 105 - 109 GeV neutrinos 2, makes it plausible to probe quantum gravity -which is expected to become important near Planck scale: EQG ˜ EP : = ? {\\hbar c5 /G} ? 1019 {GeV}. To see why one can look at -for instance- dispersion relations for photons in a space endowed with a structure required by an underlying quantum gravity theory3, say c2 {bar p2} /E2 = 1 + ? E/EQG + {O} (E/EQG )2 with ? a parameter of order one, E the energy and vec p the spatial momentum of the photon. The result is a speed v/c = (1/c)? E/? p = 1 - ? E/EQG + {O} (E/EQG )2 , and a retardation time w.r.t. to speed c propagation: ?t ? ?(E/EQG)(L/c), L being the distance traveled. With E ? 0.20MeV, L ? 1010ly, one gets ?t ? 10-5s. This can be contrasted with the time resolution of GRBs ?t ? 10-3s. Indeed, effective dispersion relations might have observable imprints of physics at Planck scale and may be other aspects of quantum gravity can be probed7. Here we point out how non perturbative quantum general relativity can yield such effective dispersion relations either for photons or neutrinosa...

Alfaro, J.; Morales-Tecotl, H. A.; Urrutia, L. F.

2002-12-01

287

Simulation of Quantum Dynamics Based on the Quantum Stochastic Differential Equation  

PubMed Central

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

2013-01-01

288

Non-Markovian dynamics without using a quantum trajectory  

SciTech Connect

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

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

2011-05-15

289

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

290

A combined INS and DINS study of proton quantum dynamics of ice and water across the triple point and in the supercritical phase  

NASA Astrophysics Data System (ADS)

We report new results of a combined analysis of previous Inelastic Neutron Scattering (INS) and Deep Inelastic Neutron Scattering (DINS) experiments on ice at T = 271 K and water at T = 285 K and T = 673 K. Proton quantum dynamics is discussed in terms of the total mean kinetic energy, , and its three principal direction components, ? (with ?=x,y,z), the lineshape momentum distribution, n(p), and its harmonic lineshape components, nh(p). The results show that the single proton dynamics is ground-state dominated and that x,y and z consist mainly of weighted averages of a mix of bending and librational, librational and stretching mean kinetic energy components, respectively. The stretching component z is redshifted respect to its harmonic component due to additional network mode contributions and softening caused by anharmonicity. The n(p) lineshapes derived at the investigated temperature reflect the anisotropy and quasi-harmonic nature of proton motion in ice and water.

Andreani, C.; Romanelli, G.; Senesi, R.

2013-12-01

291

Dynamics of a Two-Dimensional Quantum Spin Liquid: Signatures of Emergent Majorana Fermions and Fluxes  

NASA Astrophysics Data System (ADS)

We provide a complete and exact theoretical study of the dynamical structure factor of a two-dimensional quantum spin liquid in gapless and gapped phases, as realized in Kitaev's honeycomb model. We show that there are direct signatures—qualitative and quantitative—of the Majorana fermions and gauge fluxes emerging in this model. These include counterintuitive manifestations of quantum number fractionalization, such as a neutron scattering response with a gap even in the presence of gapless excitations, and a sharp component despite the fractionalization of electron spin. Our analysis identifies new varieties of the venerable x-ray edge problem and explores connections to the physics of quantum quenches.

Knolle, J.; Kovrizhin, D. L.; Chalker, J. T.; Moessner, R.

2014-05-01

292

InP quantum dots embedded in GaP: Optical properties and carrier dynamics  

Microsoft Academic Search

The optical emission and dynamics of carriers in Stranski-Krastanow self-organized InP quantum dots embedded in a GaP matrix are studied. InP deposited on GaP (001) using gas-source molecular-beam epitaxy forms quantum dots for InP coverage greater than 1.8 monolayers. Strong photoluminescence from the quantum dots is observed up to room temperature at about 2 eV; photoluminescence from the two-dimensional InP

F. Hatami; W. T. Masselink; L. Schrottke; J. W. Tomm; V. Talalaev; C. Kristukat; A. R. Goñi

2003-01-01

293

Quantum dynamics and entanglement in coherent transport of atomic population  

NASA Astrophysics Data System (ADS)

In this work we look at the quantum dynamics of the process known as either transport without transit, or coherent transfer of atomic population, of a Bose–Einstein condensate from one well of a lattice potential to another, non-adjacent well, without macroscopic occupation of the well between the two. This process has previously been analysed and in this work we extend those analyses by considering the effects of quantum statistics on the dynamics and entanglement properties of the condensate modes in the two relevant wells. In order to do this, we go beyond the mean-field analysis of the Gross–Pitaevskii type approach and utilize the phase-space stochastic methods so well known in quantum optics. In particular, we use the exact positive-P representation where it is suitable, and the approximate truncated Wigner representation otherwise. We find strong agreement between the results of these two methods, with the mean-field dynamics not depending on the initial quantum states of the trapped condensate. We find that the entanglement properties do depend strongly on the initial quantum states, with quantitatively different results found for coherent and Fock states. Comparison of the two methods gives us confidence that the truncated Wigner representation delivers accurate results for this system and is thus a useful method as the collisional nonlinearity increases and the positive-P results fail to converge.

Olsen, M. K.

2014-05-01

294

The quantum nature of the hydrogen bond: insight from path-integral molecular dynamics  

NASA Astrophysics Data System (ADS)

Hydrogen (H) bonds are weak, generally intermolecular bonds, that hold together much of soft matter, the condensed phases of water, network liquids, and many ferroelectric crystals. The small mass of H means H-bonds are inherently quantum mechanical; effects such as zero point motion and tunneling should be considered, although often are not. In particular, a consistent picture of quantum nuclear effects on the strength of H-bonds and consequently the structure of H-bonded systems is still absent. Here, we report ab initio path-integral molecular dynamics studies on the quantum nature of the H-bond. Systematic examination of a range of H-bonded systems shows that quantum nuclei weaken weak H-bonds but strengthen relatively strong ones. This correlation arises from a competition between anharmonic intermolecular bond bending and intramolecular bond stretching. A simple rule of thumb enables predictions to be made for H-bonded bonded materials in general with merely classical knowledge (e.g. H-bond strength or H-bond length). Our work rationalizes the contrasting influence of quantum nuclear dynamics on a wide variety of materials, including liquid water and HF, and highlights the need for flexible molecules in force-field based studies of quantum nuclear dynamics.

Walker, Brent; Li, Xin-Zheng; Michaelides, Angelos

2011-03-01

295

Singularity free gravitational collapse in an effective dynamical quantum spacetime  

NASA Astrophysics Data System (ADS)

We model the gravitational collapse of heavy massive shells including its main quantum corrections. Among these corrections, quantum improvements coming from Quantum Einstein Gravity are taken into account, which provides us with an effective quantum spacetime. Likewise, we consider dynamical Hawking radiation by modeling its back-reaction once the horizons have been generated. Our results point towards a picture of gravitational collapse in which the collapsing shell reaches a minimum non-zero radius (whose value depends on the shell initial conditions) with its mass only slightly reduced. Then, there is always a rebound after which most (or all) of the mass evaporates in the form of Hawking radiation. Since the mass never concentrates in a single point, no singularity appears.

Torres, R.; Fayos, F.

2014-06-01

296

Quantum teleportation of dynamics and effective interactions between remote systems.  

PubMed

Most protocols for quantum information processing consist of a series of quantum gates, which are applied sequentially. In contrast, interactions between matter and fields, for example, as well as measurements such as homodyne detection of light are typically continuous in time. We show how the ability to perform quantum operations continuously and deterministically can be leveraged for inducing nonlocal dynamics between two separate parties. We introduce a scheme for the engineering of an interaction between two remote systems and present a protocol that induces a dynamics in one of the parties that is controlled by the other one. Both schemes apply to continuous variable systems, run continuously in time, and are based on real-time feedback. PMID:23889374

Muschik, Christine A; Hammerer, Klemens; Polzik, Eugene S; Cirac, Ignacio J

2013-07-12

297

Dynamics of Quantum Logic Gates at Room Temperature  

NASA Astrophysics Data System (ADS)

We investigate the dynamics of the quantum control-not gate for the Ising spin system, which is considered today as one of the most promising system for quantum computations [1-3]. The control-not gate is implemented by application of the resonant ?-pulses. Using the equations for the density matrix, numerical calculations are performed which simulate the dynamics of the control-not gate in an ensemble of four-spin molecules, at room temperature. It is shown that the quantum logic can be realized for a two-spin sub-ensemble of a four-spin ensemble, in accordance with basic idea of [3]. 1. G.P. Berman, G.D. Doolen, G.D. Holm, V.I. Tsifrinovich, Phys. Lett. A, 193, (1994) 444. 2. D.P. DiVincenzo, Science, 270, (1995) 255. 3. N.A. Gershenfeld, I.L. Chuang, Science, 275, (1997) 350.

López, G. V.; Berman, G. P.; Doolen, G. D.; Tsifrinovich, V. I.

1998-03-01

298

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

299

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

300

Quantum Molecular Dynamics Simulations of Nanotube Tip Assisted Reactions  

NASA Technical Reports Server (NTRS)

In this report we detail the development and application of an efficient quantum molecular dynamics computational algorithm and its application to the nanotube-tip assisted reactions on silicon and diamond surfaces. The calculations shed interesting insights into the microscopic picture of tip surface interactions.

Menon, Madhu

1998-01-01

301

Threshold and Dynamics in Semiconductor Quantum Well Lasers  

Microsoft Academic Search

The application of semiconductor lasers to optical communications and interconnects requires low threshold current, high-frequency modulation, and low-noise characteristics. Quantum well (QW) lasers have received considerable attention due to the demonstrated low threshold current, predicted superior modulation and spectral dynamics due to the reduction of active layer thickness and corresponding modification of density of states for the injected carriers in

Bin Zhao

1994-01-01

302

Quantum molecular dynamics: Propagating wavepackets and density operators using the  

Microsoft Academic Search

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

Hans-Dieter Meyer; Graham A. Worthy

303

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

304

Formation and Dynamics of Dark Solitons and Vortices in Quantum Electron Plasmas  

SciTech Connect

We present simulation studies of the formation and dynamics of dark solitons and vortices in quantum electron plasmas. The electron dynamics in the latter is governed by a pair of equations comprising the nonlinear Schroedinger and Poisson system of equations, which conserves the number of electrons as well as their momentum and energy. The present governing equations in one spatial dimension admit stationary solutions in the form a dark envelope soliton. The dynamics of the latter reveals its robustness. Furthermore, we numerically demonstrate the existence of cylindrically symmetric two-dimensional quantum electron vortices, which survive during collisions. The nonlinear structures presented here may serve the purpose of transporting information at quantum scales in ultracold micromechanical systems and dense plasmas, such as those created during intense laser-matter interactions.

Shukla, P.K.; Eliasson, B. [Institut fuer Theoretische Physik IV, Ruhr-Universitaet Bochum, D-44780 Bochum (Germany)

2006-06-23

305

Controlling the quantum dynamics of a mesoscopic spin bath in diamond  

PubMed Central

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.

de Lange, Gijs; van der Sar, Toeno; Blok, Machiel; Wang, Zhi-Hui; Dobrovitski, Viatcheslav; Hanson, Ronald

2012-01-01

306

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

307

Quantum Gowdy model within the new loop quantum cosmology improved dynamics  

NASA Astrophysics Data System (ADS)

The linearly polarized Gowdy T3 model can be regarded as compact Bianchi I cosmologies with inhomogeneous modes allowed to travel in one direction. We study a hybrid quantization of this model that combines the loop quantization of the Bianchi I background, adopting the improved dynamics scheme put forward by Ashtekar and Wilson-Ewing, with a Fock quantization for the inhomogeneities. The Hamiltonian constraint operator provides a resolution of the cosmological singularity and superselects separable sectors. We analyze the complicated structure of these sectors. In any of them the Hamiltonian constraint provides an evolution equation with respect to the volume of the associated Bianchi I universe, with a well posed initial value problem. This fact allows us to construct the Hilbert space of physical states and to show that we recover the standard quantum field theory for the inhomogeneities.

Martín-Benito, M.; Garay, L. J.; Mena Marugán, G. A.

2011-09-01

308

Combining quantum wavepacket ab initio molecular dynamics with QM/MM and QM/QM techniques: Implementation blending ONIOM and empirical valence bond theory.  

PubMed

We discuss hybrid quantum-mechanics/molecular-mechanics (QM/MM) and quantum mechanics/quantum mechanics (QM/QM) generalizations to our recently developed quantum wavepacket ab initio molecular dynamics methodology for simultaneous dynamics of electrons and nuclei. The approach is a synergy between a quantum wavepacket dynamics, ab initio molecular dynamics, and the ONIOM scheme. We utilize this method to include nuclear quantum effects arising from a portion of the system along with a simultaneous description of the electronic structure. The generalizations provided here make the approach a potentially viable alternative for large systems. The quantum wavepacket dynamics is performed on a grid using a banded, sparse, and Toeplitz representation of the discrete free propagator, known as the "distributed approximating functional." Grid-based potential surfaces for wavepacket dynamics are constructed using an empirical valence bond generalization of ONIOM and further computational gains are achieved through the use of our recently introduced time-dependent deterministic sampling technique. The ab initio molecular dynamics is achieved using Born-Oppenheimer dynamics. All components of the methodology, namely, quantum dynamics and ONIOM molecular dynamics, are harnessed together using a time-dependent Hartree-like procedure. We benchmark the approach through the study of structural and vibrational properties of molecular, hydrogen bonded clusters inclusive of electronic, dynamical, temperature, and critical quantum nuclear effects. The vibrational properties are constructed through a velocity/flux correlation function formalism introduced by us in an earlier publication. PMID:18698890

Sumner, Isaiah; Iyengar, Srinivasan S

2008-08-01

309

Adaptive Resummation of Markovian Quantum Dynamics  

NASA Astrophysics Data System (ADS)

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

Lucas, Felix; Hornberger, Klaus

2013-06-01

310

Efficient quantum monte carlo energies for molecular dynamics simulations.  

PubMed

A method is presented to treat electrons within the many-body quantum Monte Carlo (QMC) approach "on-the-fly" throughout a molecular dynamics (MD) simulation. Our approach leverages the large (10-100) ratio of the QMC electron to MD ion motion to couple the stochastic, imaginary-time electronic and real-time ionic trajectories. This continuous evolution of the QMC electrons results in highly accurate total energies for the full dynamical trajectory at a fraction of the cost of conventional, discrete sampling. We show that this can be achieved efficiently for both ground and excited states with only a modest overhead to an ab initio MD method. The accuracy of this dynamical QMC approach is demonstrated for a variety of systems, phases, and properties, including optical gaps of hot silicon quantum dots, dissociation energy of a single water molecule, and heat of vaporization of liquid water. PMID:15783668

Grossman, Jeffrey C; Mitas, Lubos

2005-02-11

311

Quantum de Laval nozzle: Stability and quantum dynamics of sonic horizons in a toroidally trapped Bose gas containing a superflow  

Microsoft Academic Search

We study an experimentally realizable system containing stable black\\u000ahole-white hole acoustic horizons in toroidally trapped Bose-Einstein\\u000acondensates - the quantum de Laval nozzle. We numerically obtain stationary\\u000aflow configurations and assess their stability using Bogoliubov theory, finding\\u000aboth in hydrodynamic and non-hydrodynamic regimes there exist dynamically\\u000aunstable regions associated with the creation of positive and negative energy\\u000aquasiparticle pairs

P. Jain; A. S. Bradley; C. W. Gardiner

2007-01-01

312

Quantum de Laval nozzle: Stability and quantum dynamics of sonic horizons in a toroidally trapped Bose gas containing a superflow  

Microsoft Academic Search

We study an experimentally realizable system containing stable black hole-white hole acoustic horizons in toroidally trapped Bose-Einstein condensates--the quantum de Laval nozzle. We numerically obtain stationary flow configurations and assess their stability using Bogoliubov theory, finding both in hydrodynamic and nonhydrodynamic regimes there exist dynamically unstable regions associated with the creation of positive and negative energy quasiparticle pairs in analogy

P. Jain; A. S. Bradley; C. W. Gardiner

2007-01-01

313

Dynamics of quantum correlations for two-qubit coupled to a spin chain with Dzyaloshinskii-Moriya interaction  

Microsoft Academic Search

We study the dynamics of quantum discord and entanglement for two spin qubits coupled to a spin chain with Dzyaloshinsky-Moriya (DM) interaction. We numerically and analytically investigate the time evolution of quantum discord and entanglement for two-qubit initially prepared in a class of $X-$structure state. In the case of evolution from a pure state, quantum correlations decay to zero in

Yi-ying Yan; Li-jun Tian; Li-guo Qin

2011-01-01

314

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

315

General features of the relaxation dynamics of interacting quantum systems  

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

316

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

NASA Astrophysics Data System (ADS)

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

Viola, Lorenza; Tannor, David

2011-08-01

317

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

PubMed Central

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

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

2012-01-01

318

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

319

Asymptotic dynamics in quantum field theory  

NASA Astrophysics Data System (ADS)

A crucial element of scattering theory and the LSZ reduction formula is the assumption that the coupling vanishes at large times. This is known not to hold for the theories of the Standard Model and in general such asymptotic dynamics is not well understood. We give a description of asymptotic dynamics in field theories which incorporates the important features of weak convergence and physical boundary conditions. Applications to theories with three and four point interactions are presented and the results are shown to be completely consistent with the results of perturbation theory.

Horan, Robin; Lavelle, Martin; McMullan, David

2000-07-01

320

Atomic and molecular quantum mechanics by the path integral molecular dynamics method  

NASA Astrophysics Data System (ADS)

The quantum path integral molecular dynamics method was applied to studies of excess electron localization by a Na + ion and by a NaCl molecule. Spatial and energetic characterization of the ground state of the excess electron compare favorably with results of model potential calculations for Na and with SCF Cl calculations for NaCl -.

Scharf, Dafna; Jortner, Joshua; Landman, Uzi

1986-10-01

321

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

322

Initial Conditions Effects in the Population Dynamics of a Driven Semiconductor Quantum Well Structure  

SciTech Connect

We study Rabi oscillations between two subbands of a symmetric double quantum well that is coupled by a strong electromagnetic field. We use the effective nonlinear Bloch equations for the description of the system dynamics and present numerical results for different initial conditions of the system.

Voutsinas, Evangelos; Boviatsis, John [Technological and Educational Institute of Patras, Patras 26334 (Greece)

2007-12-26

323

A Remark on the structure of symmetric quantum dynamical semigroups on von Neumann algebras  

Microsoft Academic Search

We study the structure of the generator of a symmetric, conservative quantum dynamical semigroup with norm-bounded generator on a von Neumann algebra equipped with a faithful semifinite trace. For von Neumann algebras with abelian commutant (i.e. type I von Neumann algebras), we give a necessary and sufficient algebraic condition for the generator of such a semigroup to be written as

Sergio Albeverio; Debashish Goswami

2002-01-01

324

Adiabaticity in nonlinear quantum dynamics: Bose-Einstein Condensate in a time-varying box  

Microsoft Academic Search

A simple model of an atomic Bose-Einstein condensate in a box whose size varies with time is studied to determine the nature of adiabaticity in the nonlinear dynamics obtained within the Gross-Pitaevskii equation (the nonlinear Schrödinger equation). Analytical and numerical methods are used to determine the nature of adiabaticity in this nonlinear quantum system. Criteria for validity of an adiabatic

Y. B. Band; Boris Malomed; Marek Trippenbach

2002-01-01

325

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

326

Asymptotic properties of quantum dynamics in bounded domains at various time scales  

NASA Astrophysics Data System (ADS)

We study a peculiar semiclassical limit of the dynamics of quantum states on a circle and in a box (infinitely deep potential well with rigid walls) as the Planck constant tends to zero and time tends to infinity. Our results describe the dynamics of coherent states on the circle and in the box at all time scales in semiclassical approximation. They give detailed information about all stages of quantum evolution in the semiclassical limit. In particular, we rigorously justify the fact that the spatial distribution of a wave packet is most often close to a uniform distribution. This fact was previously known only from numerical experiments. We apply the results obtained to a problem of classical mechanics: deciding whether the recently suggested functional formulation of classical mechanics is preferable to the traditional one. To do this, we study the semiclassical limit of Husimi functions of quantum states. Both formulations of classical mechanics are shown to adequately describe the system when time is not arbitrarily large. But the functional formulation remains valid at larger time scales than the traditional one and, therefore, is preferable from this point of view. We show that, although quantum dynamics in finite volume is commonly believed to be almost periodic, the probability distribution of the position of a quantum particle in a box has a limit distribution at infinite time if we take into account the inaccuracy in measuring the size of the box.

Volovich, Igor V.; Trushechkin, Anton S.

2012-02-01

327

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 ± 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

328

Unification of dynamical decoupling and the quantum Zeno effect  

SciTech Connect

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

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

2004-03-01

329

Ring-polymer molecular dynamics: quantum effects in chemical dynamics from classical trajectories in an extended phase space.  

PubMed

This article reviews the ring-polymer molecular dynamics model for condensed-phase quantum dynamics. This model, which involves classical evolution in an extended ring-polymer phase space, provides a practical approach to approximating the effects of quantum fluctuations on the dynamics of condensed-phase systems. The review covers the theory, implementation, applications, and limitations of the approximation. PMID:23298242

Habershon, Scott; Manolopoulos, David E; Markland, Thomas E; Miller, Thomas F

2013-01-01

330

Quantum Dynamics in Continuum for Proton Transport I: Basic Formulation.  

PubMed

Proton transport is one of the most important and interesting phenomena in living cells. The present work proposes a multiscale/multiphysics model for the understanding of the molecular mechanism of proton transport in transmembrane proteins. We describe proton dynamics quantum mechanically via a density functional approach while implicitly model other solvent ions as a dielectric continuum to reduce the number of degrees of freedom. The densities of all other ions in the solvent are assumed to obey the Boltzmann distribution. The impact of protein molecular structure and its charge polarization on the proton transport is considered explicitly at the atomic level. We formulate a total free energy functional to put proton kinetic and potential energies as well as electrostatic energy of all ions on an equal footing. The variational principle is employed to derive nonlinear governing equations for the proton transport system. Generalized Poisson-Boltzmann equation and Kohn-Sham equation are obtained from the variational framework. Theoretical formulations for the proton density and proton conductance are constructed based on fundamental principles. The molecular surface of the channel protein is utilized to split the discrete protein domain and the continuum solvent domain, and facilitate the multiscale discrete/continuum/quantum descriptions. A number of mathematical algorithms, including the Dirichlet to Neumann mapping, matched interface and boundary method, Gummel iteration, and Krylov space techniques are utilized to implement the proposed model in a computationally efficient manner. The Gramicidin A (GA) channel is used to demonstrate the performance of the proposed proton transport model and validate the efficiency of proposed mathematical algorithms. The electrostatic characteristics of the GA channel is analyzed with a wide range of model parameters. The proton conductances are studied over a number of applied voltages and reference concentrations. A comparison with experimental data verifies the present model predictions and validates the proposed model. PMID:23550030

Chen, Duan; Wei, Guo-Wei

2013-01-01

331

Quantized Hamilton dynamics describes quantum discrete breathers in a simple way  

NASA Astrophysics Data System (ADS)

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

Igumenshchev, Kirill; Prezhdo, Oleg

2011-08-01

332

Defect formation preempts dynamical symmetry breaking in closed quantum systems  

NASA Astrophysics Data System (ADS)

The theory of spontaneous symmetry breaking—one of the cornerstones of modern condensed-matter physics—underlies the connection between a classically ordered object in the thermodynamic limit and its microscopic quantum-mechanical constituents. However, a large, but not infinitely large, system requires a finite symmetry-breaking perturbation to stabilize a symmetry-broken state over the exact quantum-mechanical ground state, respecting the symmetry. Here, we use the example of a particular antiferromagnetic model system to show that no matter how slowly such a symmetry-breaking perturbation is driven, the adiabatic limit can never be reached. Dynamically induced collective excitations—“quantum defects”—preempt the symmetry-breaking phenomenon and trigger the appearance of a symmetric nonequilibrium state that recursively collapses into the classical equilibrium state, breaking the symmetry at punctured times. The presence of this state allows “quantum-classical” transitions to be investigated and controlled in mesoscopic devices by externally supplying a proper dynamical symmetry-breaking perturbation.

Ortix, Carmine; Rijnbeek, Jorrit; van den Brink, Jeroen

2011-10-01

333

Understanding quantum scattering properties in terms of purely classical dynamics: two-dimensional open chaotic billiards.  

PubMed

We study classical and quantum scattering properties of particles in the ballistic regime in two-dimensional chaotic billiards that are models of electron- or micro-waveguides. To this end we construct the purely classical counterparts of the scattering probability (SP) matrix |S(n,m)|(2) and Husimi distributions specializing to the case of mixed chaotic motion (incomplete horseshoe). Comparison between classical and quantum quantities allows us to discover the purely classical dynamical origin of certain general as well as particular features that appear in the quantum description of the system. On the other hand, at certain values of energy the tunneling of the wave function into classically forbidden regions produces striking differences between the classical and quantum quantities. A potential application of this phenomenon in the field of microlasers is discussed briefly. We also see the manifestation of whispering gallery orbits as a self-similar structure in the transmission part of the classical SP matrix. PMID:12443299

Méndez-Bermúdez, J A; Luna-Acosta, G A; Seba, P; Pichugin, K N

2002-10-01

334

Observing the nonequilibrium dynamics of the quantum transverse-field Ising chain in circuit QED  

NASA Astrophysics Data System (ADS)

Circuit QED architectures of superconducting artificial atoms and microwave resonators are currently moving towards multi-atom, multi-resonator setups with drastically enhanced coherence times, making them increasingly attractive candidates for quantum simulations of interesting interacting quantum many-body systems. Here we propose and analyze a circuit QED design that implements the quantum transverse-field Ising chain coupled to a microwave resonator for readout. Our setup can be used to study quench dynamics, the propagation of localized excitations, and other nonequilibrium features, in a field theory exhibiting a quantum phase transition, and based on a design that is feasible with current technology and could easily be extended to break the integrability of the system.

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

2013-03-01

335

Andreev reflection, a tool to investigate vortex dynamics and quantum turbulence in 3He-B.  

PubMed

Andreev reflection of quasiparticle excitations provides a sensitive and passive probe of flow in superfluid (3)He-B. It is particularly useful for studying complex flows generated by vortex rings and vortex tangles (quantum turbulence). We describe the reflection process and discuss the results of numerical simulations of Andreev reflection from vortex rings and from quantum turbulence. We present measurements of vortices generated by a vibrating grid resonator at very low temperatures. The Andreev reflection is measured using an array of vibrating wire sensors. At low grid velocities, ballistic vortex rings are produced. At higher grid velocities, the rings collide and reconnect to produce quantum turbulence. We discuss spatial correlations of the fluctuating vortex signals measured by the different sensor wires. These reveal detailed information about the formation of quantum turbulence and about the underlying vortex dynamics. PMID:24704872

Fisher, Shaun Neil; Jackson, Martin James; Sergeev, Yuri A; Tsepelin, Viktor

2014-03-25

336

Andreev reflection, a tool to investigate vortex dynamics and quantum turbulence in 3He-B  

PubMed Central

Andreev reflection of quasiparticle excitations provides a sensitive and passive probe of flow in superfluid 3He-B. It is particularly useful for studying complex flows generated by vortex rings and vortex tangles (quantum turbulence). We describe the reflection process and discuss the results of numerical simulations of Andreev reflection from vortex rings and from quantum turbulence. We present measurements of vortices generated by a vibrating grid resonator at very low temperatures. The Andreev reflection is measured using an array of vibrating wire sensors. At low grid velocities, ballistic vortex rings are produced. At higher grid velocities, the rings collide and reconnect to produce quantum turbulence. We discuss spatial correlations of the fluctuating vortex signals measured by the different sensor wires. These reveal detailed information about the formation of quantum turbulence and about the underlying vortex dynamics.

Fisher, Shaun Neil; Jackson, Martin James; Sergeev, Yuri A.; Tsepelin, Viktor

2014-01-01

337

Dynamics of quantum-classical hybrid systems: Effect of matter-wave pressure  

SciTech Connect

Radiation pressure affects the kinetics of a system exposed to radiation and it constitutes the basis of laser cooling. In this article, we study matter-wave pressure through examining the dynamics of a quantum-classical hybrid system. The quantum and classical subsystems are affected mutually via a changing boundary condition. Two systems, that is, an atom and a Bose-Einstein condensate (BEC), are considered as the quantum subsystems, while an oscillating wall is taken as the classical subsystem. We show that the classical subsystem would experience a force proportional to Q{sup -3} from the quantum atom, where Q denotes the distance between the two walls, whereas it acquires an additional force proportional to Q{sup -2} from the BEC due to the atom-atom interaction in the BEC. These forces can be understood as the matter-wave pressure.

Shen, J. [School of Physics and Optoelectronic Technology, Dalian University of Technology, Dalian 116024 (China); Huang, X. L. [School of Physics and Optoelectronic Technology, Dalian University of Technology, Dalian 116024 (China); School of Physics and Electronic Technology, Liaoning Normal University, Dalian 116029 (China); Yi, X. X. [School of Physics and Optoelectronic Technology, Dalian University of Technology, Dalian 116024 (China); Centre for Quantum Technologies and Department of Physics, National University of Singapore, Singapore 117543 (Singapore); Wu Chunfeng; Oh, C. H. [Centre for Quantum Technologies and Department of Physics, National University of Singapore, Singapore 117543 (Singapore)

2010-12-15

338

Dynamical effects of Stark-shifted quantum dots strongly coupled to photonic crystal cavities  

NASA Astrophysics Data System (ADS)

Single semiconductor quantum-dots (QDs) strongly coupled to photonic crystal cavities are a strong candidate for single photon generation, ultra-fast all optical switching and quantum information processing. Recent experiments on coupled-cavity quantum dot systems show possible manipulation of emission wavelength of the dot through optical Stark effect. Interesting dynamical features arise when the Stark pulse duration is comparable to QD-cavity interaction time. Here, we present a theoretical treatment of these dynamical effects and investigate dynamical emission spectrum, energy transfer and single photon generation. We study these effects through numerical solution of the full master equation. We demonstrate that dynamic Stark effects can be used to generate ultra-fast indistinguishable single photons using rapid Stark tuning of the quantum dot. The theoretical limit for the speed is shown to be faster than adiabatic rapid passage technique used for microwave photon generation in circuit QED. A systematic study of role of device parameters such as pulse-shape, dot-cavity coupling and incoherent losses on the efficiency and speed of single photon generation is also presented for possible experimental realization.

Choudhury, Kaushik Roy; Bose, Ranojoy; Waks, Edo

2013-03-01

339

A multilayer multiconfigurational time-dependent Hartree approach for quantum dynamics on general potential energy surfaces  

NASA Astrophysics Data System (ADS)

The multiconfigurational time-dependent Hartree (MCTDH) approach facilitates multidimensional quantum dynamics calculations by representing the wavepacket in an optimal set of time-dependent basis functions, called single-particle functions. Choosing these single-particle functions to be themselves multidimensional wavefunctions which are represented using a MCTDH representation, a multilayer MCTDH scheme has been constructed and used for quantum dynamics calculations treating up to 1000 degrees of freedom rigorously [Wang and Thoss, J. Chem. Phys. 199, 1289 (2003)]. The present work gives a practical scheme which facilitates the application of the multilayer MCTDH approach, which previously has only been employed to study systems described by model-type Hamiltonians, to molecular systems described by more complicated Hamiltonians and general potential energy surfaces. A multilayer extension of the correlation discrete variable representation (CDVR) scheme employed in MCTDH calculations studying quantum dynamics on general potential energy surfaces is developed and tested in a simple numerical application. The resulting multilayer MCTDH/CDVR approach might offer a perspective to rigorously describe the quantum dynamics of larger polyatomic systems.

Manthe, Uwe

2008-04-01

340

A multilayer multiconfigurational time-dependent Hartree approach for quantum dynamics on general potential energy surfaces.  

PubMed

The multiconfigurational time-dependent Hartree (MCTDH) approach facilitates multidimensional quantum dynamics calculations by representing the wavepacket in an optimal set of time-dependent basis functions, called single-particle functions. Choosing these single-particle functions to be themselves multidimensional wavefunctions which are represented using a MCTDH representation, a multilayer MCTDH scheme has been constructed and used for quantum dynamics calculations treating up to 1000 degrees of freedom rigorously [Wang and Thoss, J. Chem. Phys. 199, 1289 (2003)]. The present work gives a practical scheme which facilitates the application of the multilayer MCTDH approach, which previously has only been employed to study systems described by model-type Hamiltonians, to molecular systems described by more complicated Hamiltonians and general potential energy surfaces. A multilayer extension of the correlation discrete variable representation (CDVR) scheme employed in MCTDH calculations studying quantum dynamics on general potential energy surfaces is developed and tested in a simple numerical application. The resulting multilayer MCTDH/CDVR approach might offer a perspective to rigorously describe the quantum dynamics of larger polyatomic systems. PMID:18447430

Manthe, Uwe

2008-04-28

341

Theoretical study of dynamic electron-spin-polarization via the doublet-quartet quantum-mixed state and time-resolved ESR spectra of the quartet high-spin state.  

PubMed

The mechanism of the unique dynamic electron polarization of the quartet (S = 3/2) high-spin state via a doublet-quartet quantum-mixed state and detail theoretical calculations of the population transfer are reported. By the photo-induced electron transfer, the quantum-mixed charge-separate state is generated in acceptor-donor-radical triad (A-D-R). This mechanism explains well the unique dynamic electron polarization of the quartet state of A-D-R. The generation of the selectively populated quantum-mixed state and its transfer to the strongly coupled pure quartet and doublet states have been treated both by a perturbation approach and by exact numerical calculations. The analytical solutions show that generation of the quantum-mixed states with the selective populations after de-coherence and/or accompanying the (complete) dephasing during the charge-recombination are essential for the unique dynamic electron polarization. Thus, the elimination of the quantum coherence (loss of the quantum information) is the key process for the population transfer from the quantum-mixed state to the quartet state. The generation of high-field polarization on the strongly coupled quartet state by the charge-recombination process can be explained by a polarization transfer from the quantum-mixed charge-separate state. Typical time-resolved ESR patterns of the quantum-mixed state and of the strongly coupled quartet state are simulated based on the generation mechanism of the dynamic electron polarization. The dependence of the spectral pattern of the quartet high-spin state has been clarified for the fine-structure tensor and the exchange interaction of the quantum-mixed state. The spectral pattern of the quartet state is not sensitive towards the fine-structure tensor of the quantum-mixed state, because this tensor contributes only as a perturbation in the population transfer to the spin-sublevels of the quartet state. Based on the stochastic Liouville equation, it is also discussed why the selective population in the quantum-mixed state is generated for the "finite field" spin-sublevels. The numerical calculations of the elimination of the quantum coherence (de-coherence and/or dephasing) are demonstrated. A new possibility of the enhanced intersystem crossing pathway in solution is also proposed. PMID:21321715

Teki, Yoshio; Matsumoto, Takafumi

2011-04-01

342

Fast Quantum Gates Using Dynamical and Geometrical Phase  

NASA Astrophysics Data System (ADS)

We propose and analyze an experimentally feasible scheme to design universal set of quantum gates utilizing dynamical and geometrical phases accumulated by a qubit during the excitation. Our scheme provides a possibility to employ strong femtosecond pulses while keeping all advantages of the Rabi solution regime. We design fast quantum gates (picosecond time scale) by choosing proper parameters of the chirped pulses as a way to control nonadiabatic coupling and to satisfy the adiabaticity conditions. We also demonstrate a possibility to control the dynamical and geometrical phases by controlling the relative phase between excitation pulses applied in the Raman configuration. Proposed Hadamard and phase-shift gates allow us to construct a universal set of single qubit gates by controlling the effective pulse area, relative phase and two-photon detuning. Implementation of a controlled-NOT gate based on the proposed excitation scheme is also discussed.

Malinovsky, Vladimir; Hawkins, Patrick; Malinovskaya, Svetlana

2011-06-01

343

Universal short-time quantum critical dynamics in imaginary time  

NASA Astrophysics Data System (ADS)

We propose a scaling theory for the universal imaginary-time quantum critical dynamics for both short and long times. We discover that there exists a universal critical initial slip related to a small initial order parameter M0. In this stage, the order parameter M increases with the imaginary time ? as M ?M0?? with a universal initial-slip exponent ?. For the one-dimensional transverse-field Ising model, we estimate ? to be 0.373, which is markedly distinct from its classical counterpart. Apart from the local order parameter, we also show that the entanglement entropy exhibits universal behavior in the short-time region. As the critical exponents in the early stage and in equilibrium are identical, we apply the short-time dynamics method to determine quantum critical properties. The method is generally applicable in both the Landau-Ginzburg-Wilson paradigm and topological phase transitions.

Yin, Shuai; Mai, Peizhi; Zhong, Fan

2014-04-01

344

Dynamics, synchronization, and quantum phase transitions of two dissipative spins  

SciTech Connect

We analyze the static and dynamic properties of two Ising-coupled quantum spins embedded in a common bosonic bath as an archetype of dissipative quantum mechanics. First, we elucidate the ground-state phase diagram for an Ohmic and a sub-Ohmic bath using a combination of bosonic numerical renormalization group (NRG), analytical techniques, and intuitive arguments. Second, by employing the time-dependent NRG we investigate the system's rich dynamical behavior arising from the complex interplay between spin-spin and spin-bath interactions. Interestingly, spin oscillations can synchronize due to the proximity of the common non-Markovian bath and the system displays highly entangled steady states for certain nonequilibrium initial preparations. We complement our nonperturbative numerical results by exact analytical solutions when available and provide quantitative limits on the applicability of the perturbative Bloch-Redfield approach at weak coupling.

Orth, Peter P.; Le Hur, Karyn [Department of Physics, Yale University, New Haven, Connecticut 06520 (United States); Roosen, David; Hofstetter, Walter [Institut fuer Theoretische Physik, Johann Wolfgang Goethe-Universitaet, 60438 Frankfurt/Main (Germany)

2010-10-01

345

Macroscopic quantum self-trapping in dynamical tunneling.  

PubMed

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

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

2012-08-24

346

A molecular dynamics and quantum mechanics/molecular mechanics study of the catalytic reductase mechanism of methionine sulfoxide reductase A: formation and reduction of a sulfenic acid.  

PubMed

The catalytic mechanism of MsrA in Mycobacterium tuberculosis, in which S-methionine sulfoxide (Met-O) is reduced to methionine (Met), has been investigated using docking, molecular dynamics (MD) simulations, and ONIOM (quantum mechanics/molecular mechanics) methods. In addition, the roles of specific active site residues, including an aspartyl (Asp87) near the recycling cysteine, tyrosyls (Tyr44 and Tyr92), and glutamyl (Glu52), have been examined, as well as the general effects of the protein and active site on the nature and properties of mechanistic intermediates. The mechanism is initiated by the transfer of a proton from the catalytic cysteine's thiol (Cys13SH) via a bridging water to the R group carboxylate of Glu52. The now anionic sulfur of Cys13 nucleophilically attacks the substrate's sulfur with concomitant transfer of a proton from Glu52 to the sulfoxide oxygen, generating a sulfurane. The active site enhances the proton affinity of the sulfurane oxygen, which can readily accept a proton from the phenolic hydroxyls of Tyr44 or Tyr92 to give a sulfonium cation. Subsequently, Asp87 and the recycling cysteine (Cys154) can facilitate nucleophilic attack of a solvent water at the Cys13S center of the sulfonium to give a sulfenic acid (Cys13SOH) and Met. For the subsequent reduction of Cys13SOH with intramolecular disulfide bond formation, Asp87 can help facilitate nucleophilic attack of Cys154S at the sulfur of Cys13SOH by deprotonating its thiol. This reduction is found likely to occur readily upon suitable positioning of the active site hydrogen bond network and the sulfur centers of both Cys13 and Cys154. The calculated rate-limiting barrier is in good agreement with experiment. PMID:23418817

Dokainish, Hisham M; Gauld, James W

2013-03-12

347

Dynamical quantum Hall effect in the parameter space  

PubMed Central

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

Gritsev, V.; Polkovnikov, A.

2012-01-01

348

Gigahertz dynamics of a strongly driven single quantum spin.  

PubMed

Two-level systems are at the core of numerous real-world technologies such as magnetic resonance imaging and atomic clocks. Coherent control of the state is achieved with an oscillating field that drives dynamics at a rate determined by its amplitude. As the strength of the field is increased, a different regime emerges where linear scaling of the manipulation rate breaks down and complex dynamics are expected. By calibrating the spin rotation with an adiabatic passage, we have measured the room-temperature "strong-driving" dynamics of a single nitrogen vacancy center in diamond. With an adiabatic passage to calibrate the spin rotation, we observed dynamics on sub-nanosecond time scales. Contrary to conventional thinking, this breakdown of the rotating wave approximation provides opportunities for time-optimal quantum control of a single spin. PMID:19965386

Fuchs, G D; Dobrovitski, V V; Toyli, D M; Heremans, F J; Awschalom, D D

2009-12-11

349

Dynamic photon emission from multiphoton-excited semiconductor quantum dots  

NASA Astrophysics Data System (ADS)

The dynamic process of multiphoton optical transitions in semiconductor quantum dots (QDs) has been studied by a Monte Carlo scheme. The scheme includes optical transitions of all electrons, initially occupying the valence-band confined states in the QD, among the confined states in valence and conduction bands. The optical transition probabilities are calculated by the time-dependent Schrödinger equation, and nonradiative phonon scattering processes have been included. Assisted by a two-photon excitation by a continuous-wave laser (one photon energy equals half of the QD energy band gap), an assembly of the QDs shows an emission peak around the band gap in the optical emission spectrum, while an ultrafast pulsed laser, whose photon energy is below the QD band gap, also induces a similar narrow but weaker emission peak, which results in a nonstrict multiphoton excitation condition for many potential applications including biophotonics. Extension of the theoretical study to the spherical CdS/Cd0.5Zn0.5S/ZnS-multicoated CdSe QD has reproduced the experimental absorption and multiphoton emission spectra.

Han, T.-T.; Fu, Y.; A?Gren, H.

2008-05-01

350

Quantum Optical Studies of Semiconductors.  

National Technical Information Service (NTIS)

This program has supported students working on developing a fundamental understanding of the quantum features of nano-optical structures in semiconductors. A number of published papers resulted including a report on the first observation of the Raman cohe...

D. G. Steel

2000-01-01

351

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

SciTech Connect

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

Li Jingrui; Woywod, Clemens; Vallet, Valerie; Meier, Christoph [Theoretical Chemistry, Department of Chemistry, Technical University Munich, D-85747 Garching (Germany); Laboratoire de Physique des Lasers, Atomes et Molecules, UMR CNRS 8523, Centre d'Etudes et de Recherches Lasers et Applications, Universite des Sciences et Technologies de Lille, 59655 Villeneuve d'Ascq Cedex (France); LCAR-IRSAMC, Universite Paul Sabatier, 31062 Toulouse (France)

2006-05-14

352

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

353

Full-dimensional quantum dynamics of vibrationally highly excited NHD2.  

PubMed

We report on full-dimensional vibrational quantum dynamics of the highly excited ammonia isotopologue NHD(2) using a newly developed potential energy surface and the MCTDH program package. The calculations allow to realistically simulate an infrared laser induced stereomutation reaction at the pyramidal nitrogen atom in the femtosecond time domain. Our results allow for a thorough qualitative and quantitative understanding of infrared photoinduced stereomutation kinetics, the underlying quantum dynamics, and the reaction mechanisms. Comparison is made with a previous, reduced dimensionality study of the same reaction [R. Marquardt, M. Quack, I. Thanopulos, and D. Luckhaus, J. Chem. Phys. 118, 643 (2003)], and it is shown that slight variances of reduced spaces lead to significantly different kinetics. Because the quantum dynamics depends subtly on variances of reduced spaces, reduced dimensionality treatments are not reliable even for qualitative predictions of the stereomutation kinetics. The first direct comparison between the Multiconfigurational Time Dependent Hartree [M. H. Beck, A. Ja?ckle, G. A. Worth et al., Phys. Rep. 324, 1 (2000)] and Unimolecular Reactions Induced by Monochromatic Infrared Radiation [M. Quack and E. Sutcliffe, QCPE Bulletin 6, 98 (1986)] program packages on a specific, four dimensional quantum dynamical problem allows for their full validation in the present work. PMID:21054027

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

2010-11-01

354

Full-dimensional quantum dynamics of vibrationally highly excited NHD2  

NASA Astrophysics Data System (ADS)

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

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

2010-11-01

355

Quantum de Laval nozzle: Stability and quantum dynamics of sonic horizons in a toroidally trapped Bose gas containing a superflow  

SciTech Connect

We study an experimentally realizable system containing stable black hole-white hole acoustic horizons in toroidally trapped Bose-Einstein condensates--the quantum de Laval nozzle. We numerically obtain stationary flow configurations and assess their stability using Bogoliubov theory, finding both in hydrodynamic and nonhydrodynamic regimes there exist dynamically unstable regions associated with the creation of positive and negative energy quasiparticle pairs in analogy with the gravitational Hawking effect. The dynamical instability takes the form of a two mode squeezing interaction between resonant pairs of Bogoliubov modes. We study the evolution of dynamically unstable flows using the truncated Wigner method, which confirms the two mode squeezed state picture of the analogue Hawking effect for low winding number.

Jain, P. [School of Chemical and Physical Sciences, Victoria University of Wellington (New Zealand); Jack Dodd and Dan Walls Centre for Photonics and Ultra Cold Atoms, University of Otago (New Zealand); Bradley, A. S. [ARC Centre of Excellence for Quantum-Atom Optics, Department of Physics, University of Queensland, Brisbane, QLD 4072 (Australia); Gardiner, C. W. [Jack Dodd and Dan Walls Centre for Photonics and Ultra Cold Atoms, University of Otago (New Zealand)

2007-08-15

356

Quantum de Laval nozzle: Stability and quantum dynamics of sonic horizons in a toroidally trapped Bose gas containing a superflow  

NASA Astrophysics Data System (ADS)

We study an experimentally realizable system containing stable black hole white hole acoustic horizons in toroidally trapped Bose-Einstein condensates—the quantum de Laval nozzle. We numerically obtain stationary flow configurations and assess their stability using Bogoliubov theory, finding both in hydrodynamic and nonhydrodynamic regimes there exist dynamically unstable regions associated with the creation of positive and negative energy quasiparticle pairs in analogy with the gravitational Hawking effect. The dynamical instability takes the form of a two mode squeezing interaction between resonant pairs of Bogoliubov modes. We study the evolution of dynamically unstable flows using the truncated Wigner method, which confirms the two mode squeezed state picture of the analogue Hawking effect for low winding number.

Jain, P.; Bradley, A. S.; Gardiner, C. W.

2007-08-01

357

High-field electron-hole wavepacket dynamics and THz emission in semiconductor quantum wells  

NASA Astrophysics Data System (ADS)

The dynamics of electron-hole wavepackets in quantum wells under ultrafast optical excitation with and without an intense in-plane THz-frequency electric field present is explored. In the absence of the driving field, interference dominated by the 1s exciton and the 2D continuum leads to partial recurrences in the spatial wavepacket dynamics which are manifested in the time-dependent optical properties. In particular, the time-dependent optical emission is studied. When the driving field is on, a strong tunable picosecond burst of upshifted THz radiation at and above the exciton binding energy is predicted due to the coherent wavepacket dynamics.

Citrin, D. S.; Maslov, A.

1998-03-01

358

Three-Dimensional Quantum Gravity as Dynamical Triangulation  

NASA Astrophysics Data System (ADS)

The dynamical triangulation model of 3-dimensional Quantum Gravity is defined and studied. We propose two different algorithms for numerical simulations, leading to consistent results. One is the 3-dimensional generalization of the bonds flip, another is more sophisticated algorithm, based on Schwinger-Dyson equations. We found such care necessary, because our results appear to be quite unexpected. We simulated up to 60000 tetrahedra and observed none of the feared pathologies like factorial growth of the partition function with volume, or collapse to the branched polymer phase. The volume of the Universe grows exponentially when the bare cosmological constant ? approaches the critical value ?c from above, but the closed Universe exists and has peculiar continuum limit. The Universe compressibility diverges as (? - ?c)-2 and the bare Newton constant linearly approaches negative critical value as ? goes to ?c, provided the average curvature is kept at zero. The fractal properties turned out to be the same, as in two dimensions, namely the effective Hausdorff dimension grows logarithmically with the size of the test geodesic sphere.

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

359

Dynamics of quantum spin liquid and spin solid phases in IPA-CuCl3 under an applied magnetic field studied with neutron scattering  

SciTech Connect

Inelastic and elastic neutron scattering is used to study spin correlations in the quasi-one-dimensional quantum antiferromagnet IPA-CuCl3 in strong applied magnetic fields. A condensation of magnons and commensurate transverse long-range ordering is observe at a critical field Hc=9.5 T. The field dependencies of the energies and polarizations of all magnon branches are investigated both below and above the transition point. Their dispersion is measured across the entire one-dimensional Brillouin zone in magnetic fields up to 14 T. The critical wave vector of magnon spectrum truncation Masuda et al., Phys. Rev. Lett. 96, 047210 2006 is found to shift from hc0,35 at HHC to hc=0.25 for HHC. A drastic reduction of magnon bandwidths in the ordered phase Garlea et al., Phys. Rev. Lett. 98, 167202 2007 is observed and studied in detail. New features of the spectrum, presumably related to this bandwidth collapse, are observed just above the transition field.

Zheludev, Andrey I [ORNL; Garlea, Vasile O [ORNL; Masuda, T. [Yokohama City University, Japan; Manaka, H. [Kagoshima University, Kagoshima JAPAN; Regnault, L.-P. [CEA, Grenoble, France; Ressouche, E. [CEA, Grenoble, France; Grenier, B. [CEA, Grenoble, France; Chung, J.-H. [National Institute of Standards and Technology (NIST); Qiu, Y. [National Institute of Standards and Technology (NIST); Habicht, Klaus [Hahn-Meitner Institut, Berlin, Germany; Kiefer, K. [Hahn-Meitner Institut, Berlin, Germany; Boehm, Martin [Institut Laue-Langevin (ILL)

2007-01-01

360

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

SciTech Connect

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

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

2010-01-07

361

Quantum Dynamics of a d-wave Josephson Junction  

NASA Astrophysics Data System (ADS)

Thilo Bauch ^1, Floriana Lombardi ^1, Tobias Lindstr"om ^2, Francesco Tafuri ^3, Giacomo Rotoli ^4, Per Delsing ^1, Tord Claeson ^1 1 Quantum Device Physics Laboratory, Department of Microtechnology and Nanoscience, MC2, Chalmers University of Technology, S-412 96 G"oteborg, Sweden. 2 National Physical Laboratory, Queens Road, Teddington, Middlesex TW11 0LW, UK. 3 Istituto Nazionale per la Fisica della Materia-Dipartimento Ingegneria dell'Informazione, Seconda Universita di Napoli, Aversa (CE), Italy. 4 Dipartimento di Ingegneria Meccanica, Energetica e Gestionale, Universita of L'Aquila, Localita Monteluco, L'Aquila, Italy. We present direct observation of macroscopic quantum properties in an all high critical temperature superconductor d-wave Josephson junction. Although dissipation caused by low energy excitations is expected to strongly suppress quantum effects we demonstrate macroscopic quantum tunneling [1] and energy level quantization [2] in our d-wave Josephson junction. The results clearly indicate that the role of dissipation mechanisms in high temperature superconductors has to be revised, and may also have consequences for a new class of solid state ``quiet'' quantum bit with superior coherence time. We show that the dynamics of the YBCO grain boundary Josephson junctions fabricated on a STO substrate are strongly affected by their environment. As a first approximation we model the environment by the stray capacitance and stray inductance of the junction electrodes. The total system consisting of the junction and stray elements has two degrees of freedom resulting in two characteristic resonance frequencies. Both frequencies have to be considered to describe the quantum mechanical behavior of the Josephson circuit. [1] T. Bauch et al, Phys. Rev. Lett. 94, 087003 (2005). [2] T. Bauch et al, Science 311, 57 (2006).

Bauch, Thilo

2007-03-01

362

Simulation of Chemical Isomerization Reaction Dynamics on a NMR Quantum Simulator  

NASA Astrophysics Data System (ADS)

Quantum simulation can beat current classical computers with minimally a few tens of qubits. Here we report an experimental demonstration that a small nuclear-magnetic-resonance quantum simulator is already able to simulate the dynamics of a prototype laser-driven isomerization reaction using engineered quantum control pulses. 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.

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

2011-07-01

363

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

PubMed Central

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

Grczelschak-Mick, Nicole

2013-01-01

364

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

365

Quantum effects in the dynamics of He probed by inelastic x-ray scattering.  

PubMed

Quantum effects in the teraherz dynamics of supercritical 4He have been studied as a function of both density rho and temperature T; they have been characterized through their effects on the second and third spectral moments of the dynamic structure factor S(Q, omega), measured by the inelastic x-ray scattering (IXS) technique. The IXS spectra were collected in the low-Q region below and around the position of the first diffraction peak Q(m), i.e., in a range relatively unusual in this kind of investigation. The measured spectral moments clearly show a departure from their high-T classical expected values. We observe, moreover, that the amplitude of quantum deviations increases slightly with increasing density. This experimental method allows us to extract, even in a region where the dynamics still maintains a collective character, such typical single particle properties as the mean atomic kinetic energy. PMID:11497568

Verbeni, R; Cunsolo, A; Pratesi, G; Monaco, G; Rosica, F; Masciovecchio, C; Nardone, M; Ruocco, G; Sette, F; Albergamo, F

2001-08-01

366

Effect of carrier dynamics and temperature on two-state lasing in semiconductor quantum dot lasers  

SciTech Connect

It is analytically shown that the both the charge carrier dynamics in quantum dots and their capture into the quantum dots from the matrix material have a significant effect on two-state lasing phenomenon in quantum dot lasers. In particular, the consideration of desynchronization in electron and hole capture into quantum dots allows one to describe the quenching of ground-state lasing observed at high injection currents both qualitatevely and quantitatively. At the same time, an analysis of the charge carrier dynamics in a single quantum dot allowed us to describe the temperature dependences of the emission power via the ground- and excited-state optical transitions of quantum dots.

Korenev, V. V., E-mail: korenev@spbau.ru; Savelyev, A. V.; Zhukov, A. E.; Omelchenko, A. V.; Maximov, M. V. [Saint Petersburg Academic University-Nanotechnology Research and Education Center (Russian Federation)] [Saint Petersburg Academic University-Nanotechnology Research and Education Center (Russian Federation)

2013-10-15

367

The Quantum Electron Dynamics of Materials Subjected to Extreme Environments  

NASA Astrophysics Data System (ADS)

Quantum wavepacket molecular dynamics simulations are used to study the effects of extreme environments on materials. The electron forcefield (eFF) method provides energies and forces from which wavepackets can be propagated in time under conditions ranging from standard temperature and pressure to tens of thousands of Kelvin and hundreds of GPa of pressure with strain rates as high as 1 km per second. Using this technique nanometer scale systems with hundreds of thousands of particles can be simulated for up to hundreds of picoseconds. High strain rate fracture in solids is accompanied by the emission of electrons and photons, though atomistic simulations have thus far been unable to capture such processes. The eFF method for nonadiabatic dynamics accounts for electron emission and large potential differences consistent with the experiments, providing the first atomistic description of the origin of these effects. The effects that we explain are (1) loading of a crack leads to a sudden onset of crack propagation at 7 GPa followed by uniform velocity of the crack at 2500 km/sec after initiation, and (2) voltage fluctuations in the 10--400 mV range, charge creation (up to 1011 carriers/cm 2), and current production (up to 1.3 mA). The development of an effective core potential for eFF enabled this large scale study. Using the eFF wavepacket molecular dynamics method, simulations of the single shock Hugoniot are reported for crystalline polyethylene (PE). The eFF results are in good agreement with previous DFT theories and experimental data which is available up to 80 GPa. We predict shock Hugoniots for PE up to 350 GPa. In addition, we analyze the phase transformations that occur due to heating. Our analysis includes ionization fraction, molecular decomposition, and electrical conductivity during isotropic compression. We find that above a compression of 2.4 g/cm3 the PE structure transforms into a Lennard-Jones fluid, leading to a sharp increase in electron ionization and a significant increase in system conductivity. eFF accurately reproduces shock pressures and temperatures for PE along the single shock Hugoniot.

Theofanis, Patrick Lauren

368

Bulklike hot carrier dynamics in lead sulfide quantum dots.  

PubMed

Hot electronic dynamics in lead sulfide nanocrystals is interrogated by degenerate pump-probe spectroscopy with 20-25 fs pulses over a broad frequency range around three times the nanocrystal band gap. For each nanocrystal diameter, an initial reduction in absorption is seen only at the peak of the quantum confined E1 transition, while increased absorption is seen at all other wavelengths. The signals from the nanocrystals are approximately 300 times weaker than expected for a two-level system with the same absorbance and molar extinction coefficient and are weaker near time zero. These results appear to be inconsistent with quantum confinement of the initially excited high energy states. Arguments based on carrier scattering length, the wave packet size supported by the band structure, and effective mass are advanced to support the hypothesis that, for many direct-gap semiconductor quantum dots, the carrier dynamics at three times the band gap is localized on the 1-2 nm length scale and essentially bulklike except for frequent collisions with the surface. PMID:20550102

Cho, Byungmoon; Peters, William K; Hill, Robert J; Courtney, Trevor L; Jonas, David M

2010-07-14

369

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

SciTech Connect

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

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

2011-09-15

370

Dynamic control of quantum geometric heat flux in a nonequilibrium spin-boson model  

NASA Astrophysics Data System (ADS)

We study the quantum geometric heat flux in the nonequilibrium spin-boson model. By adopting the noninteracting-blip approximation that is able to accommodate the strong system-bath coupling, we show that there exists a nonzero geometric heat flux only when the two-level system is nondegenerate. Moreover, the pumping, no pumping, and dynamic control of geometric heat flux are discussed in detail, compared to the results with Redfield weak-coupling approximation. In particular, the geometric energy transfer induced by modulation of two system-bath couplings is identified, which is exclusive to quantum transport in the strong system-bath coupling regime.

Chen, Tian; Wang, Xiang-Bin; Ren, Jie

2013-04-01

371

From Coulomb-Blockade to Nonlinear Quantum Dynamics in a Superconducting Circuit with a Resonator  

NASA Astrophysics Data System (ADS)

Motivated by recent experiments on superconducting circuits consisting of a dc-voltage-biased Josephson junction in series with a resonator, quantum properties of these devices far from equilibrium are studied. This includes a crossover from a domain of incoherent to a domain of coherent Cooper pair tunneling, where the circuit realizes a driven nonlinear oscillator. Equivalently, weak photon-charge coupling turns into strong correlations captured by a single degree of freedom. Radiated photons offer a new tool to monitor charge flow and current noise gives access to nonlinear dynamics, which allows us to analyze quantum-classical boundaries.

Gramich, Vera; Kubala, Björn; Rohrer, Selina; Ankerhold, Joachim

2013-12-01

372

From Coulomb-blockade to nonlinear quantum dynamics in a superconducting circuit with a resonator.  

PubMed

Motivated by recent experiments on superconducting circuits consisting of a dc-voltage-biased Josephson junction in series with a resonator, quantum properties of these devices far from equilibrium are studied. This includes a crossover from a domain of incoherent to a domain of coherent Cooper pair tunneling, where the circuit realizes a driven nonlinear oscillator. Equivalently, weak photon-charge coupling turns into strong correlations captured by a single degree of freedom. Radiated photons offer a new tool to monitor charge flow and current noise gives access to nonlinear dynamics, which allows us to analyze quantum-classical boundaries. PMID:24483693

Gramich, Vera; Kubala, Björn; Rohrer, Selina; Ankerhold, Joachim

2013-12-13

373

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

SciTech Connect

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

Miller, William H.

2006-04-27

374

Understanding quantum measurement from the solution of dynamical models  

NASA Astrophysics Data System (ADS)

The quantum measurement problem, to wit, understanding why a unique outcome is obtained in each individual experiment, is currently tackled by solving models. After an introduction we review the many dynamical models proposed over the years for elucidating quantum measurements. The approaches range from standard quantum theory, relying for instance on quantum statistical mechanics or on decoherence, to quantum-classical methods, to consistent histories and to modifications of the theory. Next, a flexible and rather realistic quantum model is introduced, describing the measurement of the z-component of a spin through interaction with a magnetic memory simulated by a Curie-Weiss magnet, including N?1 spins weakly coupled to a phonon bath. Initially prepared in a metastable paramagnetic state, it may transit to its up or down ferromagnetic state, triggered by its coupling with the tested spin, so that its magnetization acts as a pointer. A detailed solution of the dynamical equations is worked out, exhibiting several time scales. Conditions on the parameters of the model are found, which ensure that the process satisfies all the features of ideal measurements. Various imperfections of the measurement are discussed, as well as attempts of incompatible measurements. The first steps consist in the solution of the Hamiltonian dynamics for the spin-apparatus density matrix Dˆ(t). Its off-diagonal blocks in a basis selected by the spin-pointer coupling, rapidly decay owing to the many degrees of freedom of the pointer. Recurrences are ruled out either by some randomness of that coupling, or by the interaction with the bath. On a longer time scale, the trend towards equilibrium of the magnet produces a final state Dˆ(t) that involves correlations between the system and the indications of the pointer, thus ensuring registration. Although Dˆ(t) has the form expected for ideal measurements, it only describes a large set of runs. Individual runs are approached by analyzing the final states associated with all possible subensembles of runs, within a specified version of the statistical interpretation. There the difficulty lies in a quantum ambiguity: There exist many incompatible decompositions of the density matrix Dˆ(t) into a sum of sub-matrices, so that one cannot infer from its sole determination the states that would describe small subsets of runs. This difficulty is overcome by dynamics due to suitable interactions within the apparatus, which produce a special combination of relaxation and decoherence associated with the broken invariance of the pointer. Any subset of runs thus reaches over a brief delay a stable state which satisfies the same hierarchic property as in classical probability theory; the reduction of the state for each individual run follows. Standard quantum statistical mechanics alone appears sufficient to explain the occurrence of a unique answer in each run and the emergence of classicality in a measurement process. Finally, pedagogical exercises are proposed and lessons for future works on models are suggested, while the statistical interpretation is promoted for teaching.

Allahverdyan, Armen E.; Balian, Roger; Nieuwenhuizen, Theo M.

2013-04-01

375

Quasilocality and Efficient Simulation of Markovian Quantum Dynamics  

NASA Astrophysics Data System (ADS)

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.

Barthel, Thomas; Kliesch, Martin

2012-06-01

376

Quantum Molecular Dynamics Simulations of Shocked Molecular Liquids  

NASA Astrophysics Data System (ADS)

Quantum Molecular Dynamics (QMD) simulations provide an extremely penetrating probe of a variety of enviroments in which dense matter at elevated temperatures plays a significant role, including solids, fluids, gases, plasmas, and especially mixtures of these various states of matter. In many circumstances, a quantum treatment of the interaction between electrons and ions provides the only reliable procedure for gaining information and understanding on the state and interaction of matter in these extreme conditions in which experiments remain difficult. We shall discuss several applications of QMD including the equation of state and electrical and optical properties of fluid deuterium, the equation of state of oxygen and the shock compression of hydrocarbons. This work was supported under the auspices of the U. S. Department of Energy by Los Alamos and Lawrence Livermore National Laboratories.

Kress, J. D.; Mazevet, S.; Collins, L. A.; Lenosky, T. J.

2001-06-01

377

Dynamics of dipoles and quantum phases in noncommutative coordinates  

NASA Astrophysics Data System (ADS)

The dynamics of a spin-(1/2) neutral particle possessing electric- and magnetic-dipole moments interacting with external electric and magnetic fields in noncommutative coordinates is obtained. Noncommutativity of space is interposed in terms of a semiclassical constrained Hamiltonian system. The relation between the quantum phase acquired by a particle interacting with an electromagnetic field and the (semi)classical force acting on the system is examined and generalized to establish a formulation of the quantum phases in noncommutative coordinates. The general formalism is applied to physical systems yielding the Aharonov-Bohm, Aharonov-Casher, He-McKellar-Wilkens and Anandan phases in noncommutative coordinates. Bounds for the noncommutativity parameter ? are derived comparing the deformed phases with the experimental data on the Aharonov-Bohm and Aharonov-Casher phases.

Dayi, Ö. F.

2009-02-01

378

Dynamic phase diagram for the quantum phase model  

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

379

Quantum dynamics of electron in graphene nanoribbons with edge disorder  

NASA Astrophysics Data System (ADS)

Considering both the finite size and the edge disorder, we explore the dynamic behavior of electrons in graphene nanoribbons (GNRs) with various geometries in terms of quantum diffusion theory. It is shown that in the regime of stronger disorder, the decay exponent ? and the diffusion exponent ? increase with increasing edge disorder, while they decrease in the regime of weaker disorder. This indicates that there exists a localization-quasi-delocalization transition in GNRs upon varying the strength of edge disorder, similar to that in a shell-doped nanowire. In addition, the edge disorder has an influence of varying importance on the electronic transport in GNR, which depends on its width and edge geometry, showing up as a singular quantum size effect. The results can contribute towards understanding of the strange transport properties of graphene sheets and their potential applications.

Yang, C. Y.; Ding, J. W.; Xu, N.

2007-05-01

380

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

PubMed

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

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

2014-06-13

381

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

382

Quantum entanglement due to a modulated dynamical Casimir effect  

NASA Astrophysics Data System (ADS)

We study the creation and entanglement of quasiparticle pairs due to a periodic variation of the mode frequencies of a homogeneous quantum system. Depending on the values of the parameters describing the periodic modulation, the number of created pairs either oscillates or, in a narrow resonant frequency interval, grows exponentially in time. For a system initially in a thermal state, we determine in which cases the final state is quantum mechanically entangled, i.e., where the bipartite state is nonseparable. We include some weak dissipation, expected to be found in any experimental setup, and study the corresponding reduction of the quantum entanglement. Our findings are used to interpret the results of two recent experiments.

Busch, Xavier; Parentani, Renaud; Robertson, Scott

2014-06-01

383

Dynamics and thermodynamics of linear quantum open systems.  

PubMed

We analyze the evolution of the quantum state of networks of quantum oscillators coupled with arbitrary external environments. We show that the reduced density matrix of the network always obeys a local master equation with a simple analytical solution. We use this to study the emergence of thermodynamical laws in the long time regime demonstrating two main results: First, we show that it is impossible to build a quantum absorption refrigerator using linear networks (thus, nonlinearity is an essential resource for such refrigerators recently studied by Levy and Kosloff [Phys. Rev. Lett. 108, 070604 (2012)] and Levy et al. [Phys. Rev. B 85, 061126 (2012)]). Then, we show that the third law imposes constraints on the low frequency behavior of the environmental spectral densities. PMID:23581302

Martinez, Esteban A; Paz, Juan Pablo

2013-03-29

384

Persistence of coherent quantum dynamics at strong dissipation.  

PubMed

The quantum dynamics of a two-state system coupled to a bosonic reservoir with sub-Ohmic spectral density is investigated for strong friction. Numerically exact path integral Monte Carlo methods reveal that a changeover from coherent to incoherent relaxation does not occur for a broad class of spectral distributions. In nonequilibrium coherences associated with substantial system-reservoir entanglement exist even when strong dissipation forces the thermodynamic state of the system to behave almost classically. This may be of relevance for current experiments with nanoscale devices. PMID:23383762

Kast, Denis; Ankerhold, Joachim

2013-01-01

385

Persistence of Coherent Quantum Dynamics at Strong Dissipation  

NASA Astrophysics Data System (ADS)

The quantum dynamics of a two-state system coupled to a bosonic reservoir with sub-Ohmic spectral density is investigated for strong friction. Numerically exact path integral Monte Carlo methods reveal that a changeover from coherent to incoherent relaxation does not occur for a broad class of spectral distributions. In nonequilibrium coherences associated with substantial system-reservoir entanglement exist even when strong dissipation forces the thermodynamic state of the system to behave almost classically. This may be of relevance for current experiments with nanoscale devices.

Kast, Denis; Ankerhold, Joachim

2013-01-01

386

Fast synthesis of the Fredkin gate via quantum Zeno dynamics  

NASA Astrophysics Data System (ADS)

We propose a scheme for fast synthesizing the Fredkin gate with rf SQUID qubits. This scheme utilizes the quantum Zeno dynamics induced by continuous couplings and the non-identical couplings between SQUIDs and superconducting cavity. The effects of decoherence on the performance for the gate are analyzed in virtue of master equation and non-unitary evolution with full Hamiltonian. The strictly numerical simulation shows that the fidelity of this Fredkin gate is relatively high corresponding to current typical experimental parameters. Furthermore, an equivalent physical model is also constructed in an array of coupled cavities.

Shao, Xiao-Qiang; Zheng, Tai-Yu; Zhang, Shou

2012-12-01

387

Nonlinear carrier dynamics in a quantum dash optical amplifier  

NASA Astrophysics Data System (ADS)

The results of experimental pump-probe spectroscopy of a quantum dash optical amplifier biased at transparency are presented. Using strong pump pulses we observe competition between free carrier absorption and two-photon-induced stimulated emission that can have drastic effects on the transmission dynamics. Thus, both an enhancement as well as a suppression of the transmission can be observed even when the amplifier is biased at transparency. A simple theoretical model taking into account two-photon absorption and free carrier absorption is presented that shows good agreement with the measurements.

Lunnemann, Per; Ek, Sara; Yvind, Kresten; Piron, Rozenn; Mørk, Jesper

2012-01-01

388

Spin dynamics in a two-dimensional quantum gas  

NASA Astrophysics Data System (ADS)

We have investigated spin dynamics in a two-dimensional quantum gas. Through spin-changing collisions, two clouds with opposite spin orientations are spontaneously created in a Bose-Einstein condensate. After ballistic expansion, both clouds acquire ring-shaped density distributions with superimposed angular density modulations. The density distributions depend on the applied magnetic field and are well explained by a simple Bogoliubov model. We show that the two clouds are anticorrelated in momentum space. The observed momentum correlations pave the way towards the creation of an atom source with nonlocal Einstein-Podolsky-Rosen entanglement.

Pedersen, Poul L.; Gajdacz, Miroslav; Deuretzbacher, Frank; Santos, Luis; Klempt, Carsten; Sherson, Jacob F.; Hilliard, Andrew J.; Arlt, Jan J.

2014-05-01

389

The Role of Quantum Intramolecular Dynamics in Unimolecular Reactions  

NASA Astrophysics Data System (ADS)

The dynamics of unimolecular reactions can be modelled by classical mechanics for the motion of nuclei on Born-Oppenheimer or other effective potential surfaces, by the corresponding quantum mechanical equations of motion and, perhaps, by quantum statistical treatments. In this paper I provide a synopsis of fundamental, qualitatively important effects arising from the quantum nature of intramolecular dynamics, as opposed to classical mechanics, and illustrate these with theoretical predictions and experimental examples from the work of my group in Zurich. These include quantum nonlinearity in infrared (IR) multiphoton excitation and reaction, non-classical wavepacket spreading in the Fermi resonance coupled modes in CHX3 molecules, effects of zero point energy and angular momentum in unimolecular reactions, nuclear spin symmetry conservation and interconversion and the hypothetical effects arising from the violation of parity and time reversal symmetry in unimolecular reactions. Specific applications to experiments include IR laser chemistry of CF3I and CF3Br, IR spectroscopy and dynamics of CHF3 and predissociation spectra and dynamics of H3+. Hamiltonian systems with a finite number of degrees of freedom have traditionally been divided into two types: those with few degrees of freedom, which were supposed to exhibit some kind of regular ordered motion, approximately soluble by hamiltonian perturbation theory, and those with large numbers of degrees of freedom for which the methods of statistical mechanics should be used. The past few decades have seen a complete change of view, affecting almost all practical applications of classical mechanics. The motion of a hamiltonian system is usually neither completely regular nor properly described by statistical mechanics. It exhibits both regular and chaotic motion for different initial conditions, and the transition between the two types of motion as the initial conditions are varied is subtle and complicated. Variational principles, cantori, and their role in determining the transport properties of chaotic motion in hamiltonian systems and modular smoothing, a method for the rapid calculation of critical functions, which form the fractal boundary between regular and chaotic motion, have appeared in Percival (1987, 1990).

Quack, Martin

1990-08-01

390

Quantum Phase separation dynamics in mixtures of BEC  

NASA Astrophysics Data System (ADS)

We discuss the nonlinear dynamics for Bose-Einstein condensate mixtures. Solitons are LOCALIZED metastable excitations. We found an analogous excitation with an EXTENDED periodic density modulation that occurs during the phase separation for some system parameters. For other parameters, the ``quantum-spinodial'' periodic state is short-lived, at extended times the density evolves into a fascinating pattern with domains that can oscillate, interfere, merge by period halving or by the growth of a dominant domain and reappear, or split into two (bifurcate). On top of this is a gradual separation of the densities of the two components.

Liu, Wu-Ming; Chui, S. T.

2002-03-01

391

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

NASA Astrophysics Data System (ADS)

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

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

2013-01-01

392

Competing quantum effects in the dynamics of a flexible water model.  

PubMed

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 parametrized this model to give the correct liquid structure, diffusion coefficient, and infrared absorption frequencies in quantum (path integral-based) simulations. The model also reproduces the experimental temperature variation of the liquid density and affords reasonable agreement with the experimental melting temperature of hexagonal ice at atmospheric pressure. 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 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 a 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 infrared absorption spectrum. PMID:19603998

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

2009-07-14

393

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

394

Cold Atom Dynamics in a Quantum Optical Lattice Potential  

SciTech Connect

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.

Maschler, Christoph; Ritsch, Helmut [Institut fuer Theoretische Physik, Universitaet Innsbruck, Technikerstrasse 25, A-6020 Innsbruck (Austria)

2005-12-31

395

Quantum Decoherence with Bath Size: Dynamics, Randomness, and Connectivity  

NASA Astrophysics Data System (ADS)

The decoherence of a quantum system S coupled to a quantum environment E is considered, where S+E is a closed quantum system. For typical states X of the Hilbert space, i.e. for states chosen randomly from the Hilbert space unit hypersphere, we derive a scaling relation for the sum of the off-diagonal elements of the reduced density matrix ?S of S. This sum is a measure of the decoherence of S, and decreases as DE-12 as the dimension of the environment Hilbert space DE increases. We present long-time calculations of the time dependent Schr"odinger equation (TDSE) of spin 12 particles comprising S+E in order to test this scaling. The Hamiltonian has uniform or random Heisenberg couplings of a spin chain for S+E. Factors that affect the approach to the predicted scaling relation for the Heisenberg d=1 ring include how quickly and successfully the dynamics drives an initial configuration to an X state, and this depends on the randomness of the coupling strengths in the Hamiltonian and the addition of other connections either within E or between S and E.

Novotny, Mark; Jin, Fengping; Michielsen, Kristel; Miyashita, Seiji; de Raedt, Hans

2013-03-01

396

Time as a dynamical variable in quantum decay  

NASA Astrophysics Data System (ADS)

We present a theoretical analysis of quantum decay in which the survival probability is replaced by a decay rate that is equal to the absolute value squared of the wave function in the time representation. The wave function in the time representation is simply the Fourier transform of the wave function in the energy representation, and it is also the probability amplitude generated by the Positive Operator Valued Measure of a time operator. The present analysis endows time with a dynamical character in quantum decay, and it is applicable only when the unstable system is monitored continuously while it decays. When the analysis is applied to the Gamow state, one recovers the exponential decay law. The analysis allows us to interpret the oscillations in the decay rate of the GSI anomaly, of neutral mesons, and of fluorescence quantum beats as the result of the interference of two resonances in the time representation. In addition, the analysis allows us to show that the time of flight of a resonance coincides with its lifetime.

de la Madrid, Rafael

2013-09-01

397

Schwinger-Dyson equations and dynamic symmetry violation in two-dimensional quantum quadratic gravitation  

Microsoft Academic Search

The dynamic violation of symmetry in two-dimensional quantum gravitation with the action quadratic in the curvature over a\\u000a flat background is studied. The Schwinger-Dyson equation method is used in the ladder approximation. A numerical analysis\\u000a of the equations for the structural functions defining the precise fermion propagator is given. The existence of a critical\\u000a value of the coupling constant, which

Yu. I. Shil’nov; V. V. Chitov; A. T. Kotvitskii

1997-01-01

398

Spinor Bose gases: Symmetries, magnetism, and quantum dynamics  

NASA Astrophysics Data System (ADS)

Spinor Bose gases form a family of quantum fluids manifesting both magnetic order and superfluidity. This article reviews experimental and theoretical progress in understanding the static and dynamic properties of these fluids. The connection between system properties and the rotational symmetry properties of the atomic states and their interactions are investigated. Following a review of the experimental techniques used for characterizing spinor gases, their mean-field and many-body ground states, both in isolation and under the application of symmetry-breaking external fields, are discussed. These states serve as the starting point for understanding low-energy dynamics, spin textures, and topological defects, effects of magnetic-dipole interactions, and various nonequilibrium collective spin-mixing phenomena. The paper aims to form connections and establish coherence among the vast range of works on spinor Bose gases, so as to point to open questions and future research opportunities.

Stamper-Kurn, Dan M.; Ueda, Masahito

2013-07-01

399

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

400

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

NASA Astrophysics Data System (ADS)

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

Rivas, Angel; Martin-Delgado, Miguel A.

2013-03-01

401

Microscopic study of relaxation oscillations in quantum-dot VCSELs  

Microsoft Academic Search

We propose a theoretical model to investigate the switch-on dynamics of electrically pumped quantum dot vertical-cavity surface-emitting lasers. The model is based on the self-consistently combined quantum dot-wetting layer Maxwell–Bloch equations incorporating microscopically calculated Coulomb and phonon-assisted scattering processes between the quantum dot and the quantum dot-embedding wetting layer states. Our approach allows the calculation of the time delay before

Jeong Eun Kim; Matthias-Rene Dachner; Alexander Wilms; Marten Richter; Ermin Malic

2011-01-01

402

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

NASA Astrophysics Data System (ADS)

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

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

2009-12-01

403

State and dynamical parameter estimation for open quantum systems  

NASA Astrophysics Data System (ADS)

Following evolution of an open quantum system one requires full knowledge of its dynamics. In this paper we consider open quantum systems for which the Hamiltonian is ``uncertain.'' In particular, we treat in detail a simple system similar to that considered by Mabuchi [Quant. Semiclass. Opt. 8, 1103 (1996)]: a radiatively damped atom driven by an unknown Rabi frequency ? (as would occur for an atom at an unknown point in a standing light wave). By measuring the environment of the system, knowledge about the system state, and about the uncertain dynamical parameter, can be acquired. We find that these two sorts of knowledge acquisition (quantified by the posterior distribution for ?, and the conditional purity of the system, respectively) are quite distinct processes, which are not strongly correlated. Also, the quality and quantity of knowledge gain depend strongly on the type of monitoring scheme. We compare five different detection schemes (direct, adaptive, homodyne of the x quadrature, homodyne of the y quadrature, and heterodyne) using four different measures of the knowledge gain (Shannon information about ?, variance in ?, long-time system purity, and short-time system purity).

Gambetta, Jay; Wiseman, H. M.

2001-10-01

404

Quantum gravity and spin-1/2 particle effective dynamics  

NASA Astrophysics Data System (ADS)

Quantum gravity phenomenology opens up the possibility of probing Planck scale physics. Thus, by exploiting the generic properties that a semiclassical state of the compound system fermions plus gravity should have, an effective dynamics of spin-1/2 particles is obtained within the framework of loop quantum gravity. Namely, at length scales much larger than Planck length lP˜10-33 cm and below the wavelength of the fermion, the spin-1/2 dynamics in flat spacetime includes Planck scale corrections. In particular we obtain modified dispersion relations in vacuo for fermions. These corrections yield a time of arrival delay of the spin-1/2 particles with respect to a light signal and, in the case of neutrinos, a novel flavor oscillation. To detect these effects the corresponding particles must be highly energetic and should travel long distances. Hence neutrino bursts accompanying gamma ray bursts or ultrahigh energy cosmic rays could be considered. Remarkably, future neutrino telescopes may be capable of testing such effects. This paper provides a detailed account of the calculations and elaborates on results previously reported in a Letter. These are further amended by introducing a real parameter ? aimed at encoding our lack of knowledge of scaling properties of the gravitational degrees of freedom.

Alfaro, Jorge; Morales-Técotl, Hugo A.; Urrutia, Luis F.

2002-12-01

405

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

406

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

407

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

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

408