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1

A quantum molecular dynamics study of aqueous solvation dynamics.

Ring polymer molecular dynamics experiments have been carried out to examine effects derived from nuclear quantum fluctuations at ambient conditions on equilibrium and non-equilibrium dynamical characteristics of charge solvation by a popular simple, rigid, water model, SPC/E , and for a more recent, and flexible, q-TIP4P/F model, to examine the generality of conclusions. In particular, we have recorded the relaxation of the solvent energy gap following instantaneous, ±e charge jumps in an initially uncharged Lennard-Jones-like solute. In both charge cases, quantum effects are reflected in sharper decays at the initial stages of the relaxation, which produce up to a ?20% reduction in the characteristic timescales describing the solvation processes. For anionic solvation, the magnitude of polarization fluctuations controlling the extent of the water proton localization in the first solvation shell is somewhat more marked than for cations, bringing the quantum solvation process closer to the classical case. Effects on the solvation response from the explicit incorporation of flexibility in the water Hamiltonian are also examined. Predictions from linear response theories for the overall relaxation profile and for the corresponding characteristic timescales are reasonably accurate for the solvation of cations, whereas we find that they are much less satisfactory for the anionic case. PMID:24182048

Videla, Pablo E; Rossky, Peter J; Laria, D

2013-10-28

2

A quantum molecular dynamics study of aqueous solvation dynamics

NASA Astrophysics Data System (ADS)

Ring polymer molecular dynamics experiments have been carried out to examine effects derived from nuclear quantum fluctuations at ambient conditions on equilibrium and non-equilibrium dynamical characteristics of charge solvation by a popular simple, rigid, water model, SPC/E, and for a more recent, and flexible, q-TIP4P/F model, to examine the generality of conclusions. In particular, we have recorded the relaxation of the solvent energy gap following instantaneous, ±e charge jumps in an initially uncharged Lennard-Jones-like solute. In both charge cases, quantum effects are reflected in sharper decays at the initial stages of the relaxation, which produce up to a ˜20% reduction in the characteristic timescales describing the solvation processes. For anionic solvation, the magnitude of polarization fluctuations controlling the extent of the water proton localization in the first solvation shell is somewhat more marked than for cations, bringing the quantum solvation process closer to the classical case. Effects on the solvation response from the explicit incorporation of flexibility in the water Hamiltonian are also examined. Predictions from linear response theories for the overall relaxation profile and for the corresponding characteristic timescales are reasonably accurate for the solvation of cations, whereas we find that they are much less satisfactory for the anionic case.

Videla, Pablo E.; Rossky, Peter J.; Laria, D.

2013-10-01

3

Studying Photoluminescence Dynamics of Single Quantum Dots Photon by Photon

NASA Astrophysics Data System (ADS)

Colloidal semiconductor nanocrystals, or quantum dots (QDs), have been the focus of much research effort in the past decade. The development of these colloidal dots has allowed the concepts of quantum confinement and dimensional control of electronic and optical properties to find entirely new areas of application, for instance in fluorescent labeling of biological specimens. At the single-particle level, however, colloidal QDs exhibit surprisingly complicated time-dependent behavior in their photoluminescence (PL) characteristics. The PL dynamics of the biologically compatible CdSe/ZnS/streptavidin quantum dots were studied using time-resolved single-molecule spectroscopy. Statistical tests of the photon-counting data suggested that the simple ``on/off'' discrete state model is inconsistent with experimental results. Instead, a continuous emission state distribution model was found to be more appropriate. Autocorrelation analysis of lifetime and intensity fluctuations showed a nonlinear correlation between them. These results were consistent with the model that charged quantum dots were also emissive, and that time-dependent charge migration gave rise to the observed photo-luminescence dynamics.

Yang, Haw; Zhang, Kai; Fu, Aihua; Alivisatos, Paul; Hayden, Carl

2006-03-01

4

The study of classical dynamical systems using quantum theory

NASA Astrophysics Data System (ADS)

We have developed a method for complementing an arbitrary classical dynamical system to a quantum system using the Lorenz and Rössler systems as examples. The Schrödinger equation for the corresponding quantum statistical ensemble is described in terms of the Hamilton-Jacobi formalism. We consider both the original dynamical system in the coordinate space and the conjugate dynamical system corresponding to the momentum space. Such simultaneous consideration of mutually complementary coordinate and momentum frameworks provides a deeper understanding of the nature of chaotic behavior in dynamical systems. We have shown that the new formalism provides a significant simplification of the Lyapunov exponents calculations. From the point of view of quantum optics, the Lorenz and Rössler systems correspond to three modes of a quantized electromagnetic field in a medium with cubic nonlinearity. From the computational point of view, the new formalism provides a basis for the analysis of complex dynamical systems using quantum computers.

Bogdanov, Yu. I.; Bogdanova, N. A.

2014-12-01

5

Computer studies of multiple-quantum spin dynamics

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

Murdoch, J.B.

1982-11-01

6

Nuclear magnetometry studies of spin dynamics in quantum Hall systems

NASA Astrophysics Data System (ADS)

We performed a nuclear magnetometry study on quantum Hall ferromagnet with a bilayer total filling factor of ?tot=2 . We found not only a rapid nuclear relaxation but also a sudden change in the nuclear-spin polarization distribution after a one-second interaction with a canted antiferromagnetic phase. We discuss the possibility of observing cooperative phenomena coming from nuclear-spin ensemble triggered by hyperfine interaction in quantum Hall system.

Fauzi, M. H.; Watanabe, S.; Hirayama, Y.

2014-12-01

7

Quantum molecular dynamics study of warm dense iron.

The equation of state, the self-diffusion coefficient and viscosity of fluid iron in the warm dense regime at densities from 12.5 to 25.0 g/cm(3), and temperatures from 0.5 to 15.0 eV have been calculated via quantum molecular dynamics simulations. The principal Hugoniot is in good agreement with nuclear explosive experiments up to ? 50 Mbar but predicts lower pressures compared with high intensity laser results. The self-diffusion coefficient and viscosity have been simulated and have been compared with the one-component plasma model. The Stokes-Einstein relationship, defined by connections between the viscosity and the self-diffusion coefficient, has been determined and has been found to be fairly well described by classical predictions. PMID:25353580

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

2014-02-01

8

Femtosecond two-photon photoassociation of hot magnesium atoms: A quantum dynamical study using) Femtosecond two-photon photoassociation of hot magnesium atoms: A quantum dynamical study using thermal random; published online 31 October 2013) Two-photon photoassociation of hot magnesium atoms by femtosecond laser

Koch, Christiane

9

Ab initio quantum mechanical charge field molecular dynamics (QMCF-MD) were successfully applied to Cu(II) embedded in water to elucidate structure and to understand dynamics of ligand exchange mechanism. From the simulation studies, it was found that using an extended large quantum mechanical region including two shells of hydration is required for a better description of the dynamics of exchanging water molecules. The structural features characterized by radial distribution function, angular distribution function and other analytical parameters were consistent with experimental data. The major outcome of this study was the dynamics of exchange mechanism and reactions in the first hydration shell that could not be studied so far. The dynamical data such as mean residence time of the first shell water molecules and other relevant data from the simulations are close to the results determined experimentally. Another major characteristic of hydrated Cu(II) is the Jahn-Teller distortion which was also successfully reproduced, leading to the final conclusion that the dominating aqua complex is a 6-coordinated species. The ab initio QMCF-MD formalism proved again its capabilities of unraveling even ambiguous properties of hydrated species that are far difficult to explore by any conventional quantum mechanics/molecular mechanics (QM/MM) approach or experiment.

Moin, Syed Tarique; Hofer, Thomas S.; Weiss, Alexander K. H.; Rode, Bernd M. [Theoretical Chemistry Division, Institute of General, Inorganic and Theoretical Chemistry, University of Innsbruck, Innrain 80-82, A-6020 Innsbruck (Austria)

2013-07-07

10

Quantum dynamics study of the Cl+D2 reaction: Time-dependent wave packet calculations

NASA Astrophysics Data System (ADS)

The quantum dynamics of the Cl+D2 reaction has been studied by means of time-dependent quantum wave packet calculations on the G3 and BW2 potential energy surfaces. Initial state-specific total reaction probabilities and integral cross sections are calculated, and the thermal rate constant is obtained. On the G3 surface, the effect of the reagent's rotational excitation on the reactivity is negative, while on the BW2 surface, the rotation of reagent has positive effect on the reactivity. Comparison of the thermal rate constants on the G3 and BW2 surfaces with experimental measurement is shown.

Yang, Ben-Hui; Tang, Bi-Yu; Yin, Hong-Ming; Han, Ke-Li; Zhang, John Z. H.

2000-11-01

11

Energetics and Dynamics of GaAs Epitaxial Growth via Quantum Wave Packet Studies

NASA Technical Reports Server (NTRS)

The dynamics of As(sub 2) molecule incorporation into the flat Ga-terminated GaAs(100) surface is studied computationally. The time-dependent Schrodinger equation is solved on a two-dimensional potential energy surface obtained using density functional theory calculations. The probabilities of trapping and subsequent dissociation of the molecular As(sub 2) bond are calculated as a function of beam translational energy and vibrational quantum number of As(sub 2).

Dzegilenko, Fedor N.; Saini, Subhash (Technical Monitor)

1998-01-01

12

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

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

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

2011-10-28

13

A theoretical study of the photodissociation dynamics of H2S in its first absorption band is presented. The potential energy surfaces underlying the dynamics of the breakup process have been modeled so as to reproduce the principal features of all the available experimental data. The modeling is performed using time dependent quantum dynamical methods and involves the exact numerical solution of

Richard N. Dixon; C. Clay Marston; Gabriel G. Balint-Kurti

1990-01-01

14

Characterization of majorization monotone quantum dynamics

In this article I study the dynamics of open quantum system in Markovian environment. I give necessary and sufficient conditions for such dynamics to be majorization monotone, which are those dynamics always mixing the states.

Haidong Yuan

2015-03-25

15

Dynamical imperfections in quantum computers

We study the effects of dynamical imperfections in quantum computers. By considering an explicit example, we identify different regimes ranging from the low-frequency case, where the imperfections can be considered as static but with renormalized parameters, to the high-frequency fluctuations, where the effects of imperfections are completely wiped out. We generalize our results by proving a theorem on the dynamical evolution of a system in the presence of dynamical perturbations.

Facchi, Paolo; Pascazio, Saverio [Dipartimento di Fisica, Universita di Bari, I-70126 Bari, Italy and INFN, Sezione di Bari, I-70126 Bari (Italy); Montangero, Simone; Fazio, Rosario [NEST-INFM and Scuola Normale Superiore, Piazza dei Cavalieri 7, 56126 Pisa (Italy)

2005-06-15

16

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

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

1993-12-01

17

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

18

Characterization of Majorization Monotone Quantum Dynamics

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

Yuan, Haidong

19

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

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, E-mail: bina@dicp.ac.cn, E-mail: zhangdh@dicp.ac.cn; Zhang, Dong H., E-mail: bina@dicp.ac.cn, 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)

2014-04-14

20

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

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

21

We propose a dynamical approach to quantum memories using an oscillator-cavity model. This overcomes the known difficulties of achieving high quantum input-output fidelity with storage times long compared to the input signal duration. We use a generic model of the memory response, which is applicable to any linear storage medium ranging from a superconducting device to an atomic medium. The temporal switching or gating of the device may either be through a control field changing the coupling, or through a variable detuning approach, as in more recent quantum memory experiments. An exact calculation of the temporal memory response to an external input is carried out. This shows that there is a mode-matching criterion which determines the optimum input and output mode shape. This optimum pulse shape can be modified by changing the gate characteristics. In addition, there is a critical coupling between the atoms and the cavity that allows high fidelity in the presence of long storage times. The quantum fidelity is calculated both for the coherent state protocol, and for a completely arbitrary input state with a bounded total photon number. We show how a dynamical quantum memory can surpass the relevant classical memory bound, while retaining a relatively long storage time.

Q. Y. He; M. D. Reid; E. Giacobino; J. Cviklinski; P. D Drummond

2008-08-14

22

Efficient Quantum Computing of Complex Dynamics

We propose a quantum algorithm which uses the number of qubits in an optimal way and efficiently simulates a physical model with rich and complex dynamics described by the quantum sawtooth map. The numerical study of the effect of static imperfections in the quantum computer hardware shows that the main elements of the phase space structures are accurately reproduced up

Giuliano Benenti; Giulio Casati; Simone Montangero; Dima L. Shepelyansky

2001-01-01

23

NASA Astrophysics Data System (ADS)

The dynamics of pyrrole excited at wavelengths in the range 242-217 nm are studied using a combination of time-resolved photoelectron spectroscopy and wavepacket propagations performed using the multi-configurational time-dependent Hartree method. Excitation close to the origin of pyrrole's electronic spectrum, at 242 and 236 nm, is found to result in an ultrafast decay of the system from the ionization window on a single timescale of less than 20 fs. This behaviour is explained fully by assuming the system to be excited to the A2(???) state, in accord with previous experimental and theoretical studies. Excitation at shorter wavelengths has previously been assumed to result predominantly in population of the bright A1(???) and B2(???) states. We here present time-resolved photoelectron spectra at a pump wavelength of 217 nm alongside detailed quantum dynamics calculations that, together with a recent reinterpretation of pyrrole's electronic spectrum [S. P. Neville and G. A. Worth, J. Chem. Phys. 140, 034317 (2014)], suggest that population of the B1(???) state (hitherto assumed to be optically dark) may occur directly when pyrrole is excited at energies in the near UV part of its electronic spectrum. The B1(???) state is found to decay on a timescale of less than 20 fs by both N-H dissociation and internal conversion to the A2(???) state.

Wu, Guorong; Neville, Simon P.; Schalk, Oliver; Sekikawa, Taro; Ashfold, Michael N. R.; Worth, Graham A.; Stolow, Albert

2015-02-01

24

A comparative study of imaginary time path integral based methods for quantum dynamics.

The recently introduced approximate many-body quantum simulation method, ring polymer molecular dynamics (RPMD), is compared to the centroid molecular dynamics method (CMD). Comparisons of simulation results for liquid para-hydrogen at two state points and liquid ortho-deuterium at one state point are presented. The calculated quantum correlation functions for the two methods are shown to be in good agreement with one another for a large portion of the time spectrum. However, as the quantum mechanical nature of the system increases, RPMD is less accurate in predicting the kinetic energy of the system than is CMD. A simplified and highly efficient algorithm is proposed which largely corrects this deficiency. PMID:16674214

Hone, Tyler D; Rossky, Peter J; Voth, Gregory A

2006-04-21

25

Quantum Dynamics in Biological Systems

NASA Astrophysics Data System (ADS)

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

Shim, Sangwoo

26

NASA Astrophysics Data System (ADS)

A combination of computational chemistry and molecular dynamics (MD) approaches was used to study two polymer-nanoparticle composite (PNPC) systems, first a model bead spring polymer with spherical nanoparticles and generalized interactions, and second, a Poly(dimethylsiloxane) (PDMS)-silica system with accurate quantum chemistry (QC) based force fields. The following molecular processes, which are fundamental to the reinforcement of polymer-nanoparticle composites (PNPC), were studied: (1) the effect of nanoparticle-polymer interactions and polymer molecular weight on nanoparticle dispersion and distribution, (2) the free energy and conformational changes when stretching individual PDMS chains in a melt, and (3) the effect of silica fillers with different surface modifications on the properties of PDMS chains at the interface. In the model PNPC consisting of spherical nanoparticles in a bead-spring polymer melt, it was found that when the polymer-nanoparticle interactions were relatively weak the polymer matrix promoted nanoparticle aggregation. Increasingly attractive nanoparticle-polymer interactions led to strong adsorption of the polymer chains on the surface of the nanoparticles and promoted dispersion of the nanoparticles and were independent of polymer molecular weight. A classical force field for PDMS and its oligomers has been derived on the basis of intermolecular binding energies, molecular geometries, molecular electrostatic potentials, and conformational energies obtained from quantum chemistry calculations and in MD simulations and it accurately reproduces the properties of PDMS melts of various molecular weights. MD simulations using umbrella sampling methods to sample the free energy of stretching a PDMS oligomer in a melt of PDMS oligomers found that the restoring forces were mainly a result of the changes in entropy of the chain as the chain was contracted or stretched, and only at severe extensions did energetic contributions due to deformation of internal bends make a significant contribution to the free energy. Finally, MD simulations of PDMS with silica and modified silica surfaces that accurately predicted the changes in PDMS dynamics with the addition of SiO2 observed in quasielastic neutron scattering experiments. Surface modifications of the silica particles affected the PDMS chain dynamics but no significant hydrogen bonding was observed in the MD simulations of PDMS near silica surfaces.

Smith, James Sherwood

27

NASA Astrophysics Data System (ADS)

The solvation of Li(I) in liquid ammonia has been investigated by an ab initio quantum mechanical charge-field molecular dynamics (QMCF-MD) simulation. Being the first simulation of a metal cation in liquid ammonia employing this methodology, the work yields a wide range of accurate structural and dynamical data. Li(I) is tetrahedrally coordinated by four ammonia molecules in the first solvation shell at a distance of 2.075 Å. Two ligand exchange attempts have been observed within 12 ps of simulation time. The second solvation shell shows a more labile structure with numerous successful exchanges. The results are in excellent agreement with experiments.

Prasetyo, Niko; Canaval, Lorenz R.; Wijaya, Karna; Armunanto, Ria

2015-01-01

28

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

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

Nagashima, Hiroki; Tokumasu, Takashi [Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, Miyagi (Japan); Tsuda, Shin-ichi [Shinshu University, 77-7 Minamibori, Nagano, Nagano (Japan); Tsuboi, Nobuyuki [Kyushu Institute of Technology, 1-1 Sensui-cho, Tobata-ku, Kitakyushu, Fukuoka (Japan); Koshi, Mitsuo [Yokohama National University, 79-7 Tokiwadai, Hodogaya, Yokohama, Kanagawa (Japan); Hayashie, A. Koichi [AoyamaGakuin University, 5-10-1 Fuchinobe, Chuo-ku, Sagamihara, Kanagawa (Japan)

2014-10-06

29

Quantum emitters dynamically coupled to a quantum field

NASA Astrophysics Data System (ADS)

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

Acevedo, O. L.; Quiroga, L.; Rodríguez, F. J.; Johnson, N. F.

2013-12-01

30

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

The ionic and electronic structures of warm dense silane at the densities of 1.795, 2.260, 3.382, and 3.844 g/cm(3) 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/cm(3), 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. PMID:25353443

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

2014-02-01

31

Molecular dynamics with quantum fluctuations

NASA Astrophysics Data System (ADS)

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, Ionu?; Mandelshtam, Vladimir A.

2010-09-01

32

Nonequilibrium dynamics of quantum glasses

NASA Astrophysics Data System (ADS)

The physics of low temperature glasses and the optimisation problems are two apparently unrelated subjects that are, however, formally connected. First, I shall summarize the picture of the glass transition and the glassy nonequilibrium behaviour that follows from the application of analytic techniques (real-time dynamics, TAP, replicas) that we extended to include quantum fluctuations. This study predicts a generic crossover from a second order classical transition to a first order transition close to the quantum critical point, as observed experimentally in a dipolar diluted magnet. It also shows the emergence of effective temperatures in the nonequilibrium phase that, in particular, induce a pseudo-decoherent dynamic effect. Second, I shall describe how some algorithms used to solve typical optimisation problems can be mapped onto diluted quantum spin-glass models. I shall briefly discuss the K-satisfiability problem and an heuristic algorithm used to search its solution (or to prove that there is no solution) from the viewpoint of disordered systems.

Cugliandolo, Leticia

2001-03-01

33

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

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

2009-10-14

34

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

Sheldon Goldstein; Ward Struyve

2014-11-05

35

NASA Astrophysics Data System (ADS)

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

Goldstein, Sheldon; Struyve, Ward

2015-01-01

36

Wigner Flow Reveals Topological Order in Quantum Phase Space Dynamics

NASA Astrophysics Data System (ADS)

The behavior of classical mechanical systems is characterized by their phase portraits, the collections of their trajectories. Heisenberg’s uncertainty principle precludes the existence of sharply defined trajectories, which is why traditionally only the time evolution of wave functions is studied in quantum dynamics. These studies are quite insensitive to the underlying structure of quantum phase space dynamics. We identify the flow that is the quantum analog of classical particle flow along phase portrait lines. It reveals hidden features of quantum dynamics and extra complexity. Being constrained by conserved flow winding numbers, it also reveals fundamental topological order in quantum dynamics that has so far gone unnoticed.

Steuernagel, Ole; Kakofengitis, Dimitris; Ritter, Georg

2013-01-01

37

Computer Visualization of Many-Particle Quantum Dynamics

NASA Astrophysics Data System (ADS)

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

Ozhigov, A. Y.

2009-03-01

38

Formation of carbon monoxide by radiative association: a quantum dynamical study

NASA Astrophysics Data System (ADS)

Rate coefficients for the formation of carbon monoxide (CO) by radiative association of carbon and oxygen atoms are computed using quantum dynamical simulations. At temperatures above 10 K CO radiative association is dominated by C(3P) and O(3P) approaching on the A1? potential energy curve. The rate coefficient is estimated as k=A(T/300 K)?exp-?/T with A= 1.39 × 10-18 cm3 s-1, ?=-0.016 and ?= 92.2 for temperatures between 6 and 127.2 K, and A= 1.36 × 10-17 cm3 s-1, ?= 0.41 and ?= 340 for temperatures between 127.2 and 15 000 K. Furthermore we computed the rate coefficients for approaching on the X1?+ curve. For temperatures below 200 K it is between 0.7 × 10-22 and 4 × 10-22 cm3 s-1.

Franz, Jan; Gustafsson, Magnus; Nyman, Gunnar

2011-07-01

39

Quantum nature of the big bang: Improved dynamics

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

Abhay Ashtekar; Tomasz Pawlowski; Parampreet Singh

2006-01-01

40

NASA Astrophysics Data System (ADS)

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

2013-10-01

41

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

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

1995-08-17

42

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

Quantum entanglement via two-qubit quantum Zeno dynamics Xiang-Bin Wang,1,2,3

Quantum entanglement via two-qubit quantum Zeno dynamics Xiang-Bin Wang,1,2,3 J. Q. You,1. Quantum entanglement is an important resource for quan- tum information processing QIP . Two-qubit joint the quantum Zeno effect of two optical qubits. Here we study a two-qubit quantum Zeno dynamics with threshold

Nori, Franco

44

Control by quantum dynamics on graphs

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

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

2010-05-15

45

Dynamical Correspondence in a Generalized Quantum Theory

NASA Astrophysics Data System (ADS)

In order to figure out why quantum physics needs the complex Hilbert space, many attempts have been made to distinguish the C*-algebras and von Neumann algebras in more general classes of abstractly defined Jordan algebras (JB- and JBW-algebras). One particularly important distinguishing property was identified by Alfsen and Shultz and is the existence of a dynamical correspondence. It reproduces the dual role of the selfadjoint operators as observables and generators of dynamical groups in quantum mechanics. In the paper, this concept is extended to another class of nonassociative algebras, arising from recent studies of the quantum logics with a conditional probability calculus and particularly of those that rule out third-order interference. The conditional probability calculus is a mathematical model of the Lüders-von Neumann quantum measurement process, and third-order interference is a property of the conditional probabilities which was discovered by Sorkin (Mod Phys Lett A 9:3119-3127, 1994) and which is ruled out by quantum mechanics. It is shown then that the postulates that a dynamical correspondence exists and that the square of any algebra element is positive still characterize, in the class considered, those algebras that emerge from the selfadjoint parts of C*-algebras equipped with the Jordan product. Within this class, the two postulates thus result in ordinary quantum mechanics using the complex Hilbert space or, vice versa, a genuine generalization of quantum theory must omit at least one of them.

Niestegge, Gerd

2015-03-01

46

Quantum and classical dynamics in biochemical reactions

The classic experiment of deVault and Chance touched off a long series of theoretical and experimental studies of the interplay between quantum and classical dynamics in photosynthetic electron transfer. More recently these issues have also been addressed in experiments on ligand binding reactions in heme proteins and through the study of kinetic isotope effects in enzymatic proton transfer. Theoretical effort

William Bialek; William J. Bruno; Julian Joseph; José Nelson Onuchic

1989-01-01

47

Efficient quantum computing of complex dynamics.

We propose a quantum algorithm which uses the number of qubits in an optimal way and efficiently simulates a physical model with rich and complex dynamics described by the quantum sawtooth map. The numerical study of the effect of static imperfections in the quantum computer hardware shows that the main elements of the phase space structures are accurately reproduced up to a time scale which is polynomial in the number of qubits. The errors generated by these imperfections are more significant than the errors of random noise in gate operations. PMID:11736427

Benenti, G; Casati, G; Montangero, S; Shepelyansky, D L

2001-11-26

48

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

49

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

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

2013-04-01

50

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

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

2014-01-01

51

NASA Astrophysics Data System (ADS)

We have calculated the equations of state, the viscosity and self-diffusion coefficients, and electronic transport coefficients of beryllium in the warm dense regime for densities from 4.0 to 6.0 g/cm3 and temperatures from 1.0 to 10.0 eV by using quantum molecular dynamics simulations. The principal Hugoniot curve is in agreement with underground nuclear explosive and high-power laser experimental results up to ˜20 Mbar. The calculated viscosity and self-diffusion coefficients are compared with the one-component plasma model, using effective charges given by the average-atom model. The Stokes-Einstein relationship, which connects viscosity and self-diffusion coefficients, is found to hold fairly well in the strong coupling regime. The Lorenz number, which is the ratio between thermal and electrical conductivities, is computed via Kubo-Greenwood formula and compared to the well-known Wiedemann-Franz law in the warm dense region.

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

2013-04-01

52

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

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

2014-01-01

53

Computation and Dynamics: Classical and Quantum

NASA Astrophysics Data System (ADS)

We discuss classical and quantum computations in terms of corresponding Hamiltonian dynamics. This allows us to introduce quantum computations which involve parallel processing of both: the data and programme instructions. Using mixed quantum-classical dynamics we look for a full cost of computations on quantum computers with classical terminals.

Kisil, Vladimir V.

2010-05-01

54

Anomalies in non-Markovian quantum dynamics

NASA Astrophysics Data System (ADS)

The non-Markovian dynamics of general finite dimensional open quantum systems is studied. In the framework of the continuous time quantum random walk inverse power law tailed distributions of the waiting times between two consecutive interactions with the external environment are considered. Hindered time evolution appears over long time scales if the distribution of the long waiting times increases up to the critical decay 1/t. More generally, arbitrarily slow relaxations to the asymptotic configurations are found in the scenario of dynamical maps of a qudit. Similar features characterize the time evolution of the entanglement of X states.

Giraldi, Filippo; Petruccione, Francesco

2015-02-01

55

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

Reynolds, J.

1997-10-08

56

It is suggested that charged tachyons of extremely large mass M could not only contribute to the dark matter needed to fit astrophysical observations, but could also provide an explanation for gamma ray bursts and ultra high energy cosmic rays. The present paper defines a quantum field theory of tachyons, the latter similar to ordinary leptons, but with momenta larger than energy.

H. M. Fried; Y. Gabellini

2005-05-31

57

Theory of controlled quantum dynamics

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

58

Quantum effects in light and heavy liquid water: A rigid-body centroid molecular dynamics study.

The centroid molecular dynamics (CMD) method is applied to the study of liquid water in the context of the rigid-body approximation. This rigid-body CMD technique, which is significantly more efficient than the standard CMD method, is implemented on the TIP4P model for water and used to examine isotopic effects in the equilibrium and dynamical properties of liquid H(2)O and D(2)O. The results obtained with this approach compare remarkably well with those determined previously with path integrals simulations as well as those obtained from the standard CMD method employing flexible models. In addition, an examination of the impact of quantization on the rotational and librational motion of the water molecule is also reported. PMID:15367027

Hernández de la Peña, L; Kusalik, P G

2004-09-22

59

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

Quantum Computation and Quantum Spin Dynamics

We analyze the stability of quantum computations on physically realizable quantum computers by simulating quantum spin models representing quantum computer hardware. Examples of logically identical implementations of the controlled-NOT operation are used to demonstrate that the results of a quantum computation are unstable with respect to the physical realization of the quantum computer. We discuss the origin of these instabilities

Hans de Raedt; Kristel Michielsen; Anthony Hams; Seiji Miyashita; Keiji Saito

2001-01-01

61

Molecular Dynamics with Quantum Fluctuations

NASA Astrophysics Data System (ADS)

A new Quantum Dynamics approach, called Gaussian Molecular Dynamics (GMD), is introduced. As in the Centroid Molecular Dynamics (CMD), 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. GMD is furthermore used to estimate the diffusion constant and the spectrum of the velocity auto-correlation function of low pressure para-hydrogen at 14K and respectively 25K. The results are consistent with known experimental and theoretical results, such as CMD and RPMD.

Georgescu, Ionut; Deckman, Jason; Mandelshtam, Vladimir

2011-03-01

62

Quantum Information Processing with Quantum Zeno Many-Body Dynamics

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

63

Quantum Stochastic Processes: A Case Study

We present a detailed study of a simple quantum stochastic process, the quantum phase space Brownian motion, which we obtain as the Markovian limit of a simple model of open quantum system. We show that this physical description of the process allows us to specify and to construct the dilation of the quantum dynamical maps, including conditional quantum expectations. The quantum phase space Brownian motion possesses many properties similar to that of the classical Brownian motion, notably its increments are independent and identically distributed. Possible applications to dissipative phenomena in the quantum Hall effect are suggested.

Michel Bauer; Denis Bernard

2011-01-18

64

Non-Hermitian quantum-classical dynamics

There are many instances when quantum systems have both light and heavy degrees of freedom, with masses $m$ and $M$, respectively. Here, the case in which the dynamics is governed by a non-Hermitian Hamiltonian is considered. Since a small parameter $\\mu=(m/M)^{1/2}$ arises naturally, a rigorous procedure (based on the partial Wigner representation of quantum mechanics and the linear expansion of the equations of motion in $\\mu$) can be applied to the non-Hermitian quantum equation in order to obtain the classical limit over the heavy degrees of freedom. Such a procedure does not depend on the adoption on any particular basis set and provides an exact equation when the dependence in the heavy degrees of freedom is quadratic for the Hermitian part of the total non-Hermitian Hamiltonian and linear for the anti-Hermitian part. Once the non-Hermitian quantum-classical equations of motion are represented in the adiabatic basis selected from the Hermitian part of the total Hamiltonian, piecewise-deterministic algorithms can be developed and their adiabatic limit can be conveniently integrated in the case of weak coupling between light and heavy degrees of freedom. In order to illustrate the formalism, the quantum-classical non-Hermitian dynamics of a Heisenberg two-spin chain with spin independently coupled to a harmonic oscillator is studied. Two decays operator (one depending only on the quantum degrees of freedom and the other only on the classical coordinates) are explicitly considered. It is shown that the algorithms provided can propagate efficiently the quantum-classical non-Hermitian dynamics of these models, simulating the loss of probability and the damping that one would expect in an open quantum system.

Alessandro Sergi

2015-02-21

65

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

NASA Astrophysics Data System (ADS)

A quantum scattering dynamics, time-dependent wavepacket propagation method is applied to study the reaction of H2D++H2?H3++HD on the Xie-Braams-Bowman potential energy surface. The reduced-dimensional, seven-degree-of-freedom approach is employed in this calculation by fixing one Jacobi and one torsion angle related to H2D+ at the lowest saddle point geometry of D2d on the potential energy surface. Initial state selected reaction probabilities are presented for various initial rovibrational states. The ground state reaction probability shows no threshold for this reaction, in other words, this reaction can occur without an activation barrier. The vibrational excitation shows that the stretching motion of H+-HD only has a small effect on the reaction probability; the vibrational excitation of HD in H2D+ hinders the reactivity. By contrast, rotational excitation of H+-HD greatly enhances the reactivity with the reaction probability increased double or triple at high rotational states compared to the ground state. Reactive resonances, seen in all the initial state selected reaction probabilities, are also found in the integral cross section for the ground state of H2D+ and H2. The thermal rate coefficient is also calculated and is found to be in semiquantitative agreement with experiment; however, quantum scattering approaches including more degrees of freedom, especially including all the angles, are necessary to study this reaction in the future.

Wang, Dunyou; Xie, Zhen; Bowman, Joel M.

2010-02-01

66

Quantum dynamical semigroups and the theory of quantum measurements

NASA Astrophysics Data System (ADS)

The possible use of non-Hamiltonian type quantum evolution equations to find a solution to the problem of Wave Packet Reduction is discussed. A particular class of equations usually referred to as Quantum Dynamical Semigroup is considered.

Ghirardi, G. C.; Rimini, A.; Weber, T.

1988-07-01

67

Quantum dynamical study of the He + NeH+ reaction on a new analytical potential energy surface.

An analytical potential energy surface (PES) for the ground state of the [HeHNe](+) system has been constructed from a set of 19,605 ab initio data points, obtained from coupled cluster singles and doubles with perturbative triples correction calculations and the aug-cc-pVQZ basis set. The PES is based on the many-body expansion form proposed by Aguado and Paniagua (J. Chem. Phys. 1992, 96, 1265), and it has a root-mean-square error of 0.03 kcal/mol. The minimum energy pathways (MEPs) for different Ne-H-He angles are calculated, and it is found that the MEP for 180° (linear) goes through the deepest potential energy well. Preliminary quantum dynamical studies are performed for the He + NeH(+) (v = 0-2, j = 0-3) ? HeH(+) + Ne reaction in the 0.0-0.5 eV collision energy range. Quantum calculations are carried out using a time-dependent wave packet method within the centrifugal sudden approximation. Reaction probabilities exhibit strong oscillatory behavior arising because of the metastable [HeHNe](+). Vibrational excitation has been found to enhance the reaction cross sections. PMID:24256154

Koner, Debasish; Panda, Aditya N

2013-12-12

68

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

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

H. Kröger

2003-02-21

69

Robustness of Controlled Quantum Dynamics

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

Andy Koswara; Raj Chakrabarti

2014-09-29

70

NASA Astrophysics Data System (ADS)

Creation of shallow junction for the future generation LSI is a crucial step in semiconductor industry and low-energy boron implantation process is considered to be a key technology. In this study, we have statistically investigated the effects of orientation of implantation on the dynamic behavior of boron implantation process into hydrogen-terminated Si(001) 2× 1 surface by using our original tight-binding quantum chemical molecular dynamics method, which is over 5,000 times faster than conventional first-principle molecular dynamics method. It was found that depth profile of boron implantation can be controlled by orientation of boron implantation and the shallowest implantation depth was obtained in the case of tilt angle equal to 7° among the investigated tilt angles of 0°, 7°, 15°, 22.5°, 30° and 45° at the initial boron energy of 100 eV. At the boron implantation process of over 1 keV energy the tilt angle of 7° has been employed experimentally and the same tilt angle was predicted to be the best even at low-energy region of 100 eV. Furthermore, we investigated the effect of rotation angle on the depth profile and at all the investigated tilt angles the average implantation depth becomes shallower for rotation angle of 45° that is along < 011> direction, than for rotation angle of 0° that is along < 001>. Hence, the shallowest depth profile was obtained in the case of tilt angle of 7° and rotation angle of 45°, where the distribution of intruded boron atom was more concentrated than for the same tilt angle but rotation angle of 0°. The effect of tilt and rotation angles on the boron implantation process has not been clarified experimentally at low-energy boron implantation process of less than 1 keV and hence we concluded that theoretical optimization of low-energy boron implantation process has been succeeded by means of our original tight-binding quantum chemical molecular dynamics method.

Tsuboi, Hideyuki; Sagawa, Ai; Iga, Hideki; Sasata, Katsumi; Masuda, Tsuyoshi; Koyama, Michihisa; Kubo, Momoji; Broclawik, Ewa; Yabuhara, Hidehiko; Miyamoto, Akira

2005-04-01

71

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

2008-02-01

72

Dynamic trapping near a quantum critical point

NASA Astrophysics Data System (ADS)

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

Kolodrubetz, Michael; Katz, Emanuel; Polkovnikov, Anatoli

2015-02-01

73

High fidelity quantum gates via dynamical decoupling.

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

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

2010-12-01

74

Metric perturbation theory of quantum dynamics

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

Antony L Tambyrajah

2006-10-06

75

Quantum jump dynamics in cavity QED

NASA Astrophysics Data System (ADS)

We study the stochastic dynamics of the electromagnetic field in a lossless cavity interacting with a beam of two-level atoms, given that the atomic states are measured after they have crossed the cavity. The atoms first interact at the exit of the cavity with a classical laser field E and then enter into a detector which measures their states. Each measurement disentangles the field and the atoms and changes in a random way the state |?(t)> of the cavity field. For weak atom-field coupling, the evolution of |?(t)> when many atoms cross the cavity and the detector is characterized by a succession of quantum jumps occurring at random times, separated by quasi-Hamiltonian evolutions, both of which depend on the laser field E. For E=0, the dynamics is the same as in the Monte Carlo wave function model of Dalibard et al. [Phys. Rev. Lett. 68, 580 (1992)] and Carmichael, An Open System Approach to Quantum Optics, Lecture Notes in Physics Vol. 18 (Springer, Berlin, 1991)]. The density matrix of the quantum field, obtained by averaging the projector |?(t)> evolves under the monitoring of the atoms and the measurements toward squeezed states |?,re2i?>, moving in the ?-complex plane but with almost constant squeezing parameters r and ?. The values of r and ? are determined analytically. On the other hand, for E=0, the dynamics transforms the initial state into Fock states |n> with fluctuating numbers of photons n, as shown in Kist et al. [J. Opt. B: Quantum Semiclassical Opt. 1, 251 (1999)]. In the last part, we derive the quantum jump dynamics from the linear quantum jump model proposed in Spehner and Bellissard [J. Stat. Phys. 104, 525 (2001)], for arbitrary open quantum systems having a Lindblad-type evolution. A careful derivation of the infinite jump rates limit, where the dynamics can be approximated by a diffusion process of the quantum state, is also presented.

Spehner, D.; Orszag, M.

2002-07-01

76

Non-Markovian dynamics of quantum discord

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

77

Quantum nature of the big bang: Improved dynamics

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

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

2006-10-15

78

Dynamical Quantum Geometry (DQG Programme)

In this brief note (written as a lengthy letter), we describe the construction of a representation for the Weyl-algebra underlying Loop Quantum Geometry constructed from a diffeomorphism variant state, which corresponds to a ''condensate'' of Loop Quantum Geometry, resembling a static spatial geometry. We present the kinematical GNS-representation and the gauge- and diffeomorphism invariant Hilbert space representation and show that the expectation values of the geometric operators take essentialy classical values plus quantum corrections, which is similar to a ''local condensate'' of quantum geometry. We describe the idea for the construction of a scale dependent asymptotic map into a family of scale dependent lattice gauge theories, where scale separates the essential geometry and a low energy effective theory, which is described as degrees of freedom in the lattice gauge theory. If this idea can be implemented then it is likely to turn out that this Hilbert space contains in addition to gravity also gauge coupled ''extra degrees of freedom'', which may not be dynamically irrelevant.

Tim A. Koslowski

2007-09-21

79

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

Xijia Miao

2011-11-22

80

Characterization of quantum dynamics using quantum error correction

NASA Astrophysics Data System (ADS)

Characterizing noisy quantum processes is important to quantum computation and communication (QCC), since quantum systems are generally open. To date, all methods of characterization of quantum dynamics (CQD), typically implemented by quantum process tomography, are off-line, i.e., QCC and CQD are not concurrent, as they require distinct state preparations. Here we introduce a method, "quantum error correction based characterization of dynamics," in which the initial state is any element from the code space of a quantum error correcting code that can protect the state from arbitrary errors acting on the subsytem subjected to unknown dynamics. The statistics of stabilizer measurements, with possible unitary preprocessing operations, are used to characterize the noise, while the observed syndrome can be used to correct the noisy state. Our method requires at most 2 (4n-1 ) configurations to characterize arbitrary noise acting on n qubits.

Omkar, S.; Srikanth, R.; Banerjee, Subhashish

2015-01-01

81

NASA Astrophysics Data System (ADS)

The ozonolysis of limonene is one of the most important processes for secondary organic aerosol formation and a detailed understanding of the atmospheric chemistry of d-limonene is highly urgent. In this paper, the reaction of d-limonene with O 3 has been studied using high level molecular orbital theory. A detailed description of the possible ozonolysis mechanism in the presence of H 2O or NO is provided. The main products obtained are keto-limonene, limononic acid and 7OH-lim, which are low vapor pressure compounds. On the basis of the quantum chemical information, the direct dynamic calculation is performed and the rate constants are calculated over a temperature range of 200˜800 K using the transition state theory and canonical varitional transition state theory with small-curvature tunneling effect. The four-parameter formula of rate constants with the temperature is fitted and the lifetimes of the reaction species in the troposphere are estimated according to the rate constants, which can provide helpful information to the model simulation study.

Sun, Tingli; Wang, Yudong; Zhang, Chenxi; Sun, Xiaomin; Wang, Wenxing

2011-03-01

82

Quantum dynamical calculations are reported for the title reaction, for both product arrangement channels and using potential energy surfaces corresponding to the three electronic states, 1 1A', 2 1A', and 1 1A'', which correlate with both reactants and products. The calculations have been performed for J=0 using the time-dependent real wavepacket approach by Gray and Balint-Kurti [J. Chem. Phys. 108,

Huan Yang; Ke-Li Han; Shinkoh Nanbu; Hiroki Nakamura; Gabriel G. Balint-Kurti; Hong Zhang; Sean C. Smith; Marlies Hankel

2008-01-01

83

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

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

2014-02-25

84

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

Blancafort, Lluis [Institut de Quimica Computacional, Department de Quimica, Universitat de Girona, Campus de Montilivi, 17071 Girona (Spain); Gatti, Fabien [CTMM, Institut Charles Gerhardt Montpellier (UMR 5253), CC 1501, Universite Montpellier 2, 34095 Montpellier Cedex 05 (France); Meyer, Hans-Dieter [Theoretische Chemie, Ruprecht-Karls-Universitaet, Im Neuenheimer Feld 229, 69120 Heidelberg (Germany)

2011-10-07

85

Coherent State Functional Integral in Loop Quantum Cosmology: Alternative Dynamics

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

Li Qin; Yongge Ma

2012-06-06

86

Dynamics of multipartite quantum correlations under decoherence

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

M. Ramzan

2012-05-14

87

Quantum Geometry and Quantum Dynamics at the Planck Scale

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

88

Momentum and spin in entropic quantum dynamics

NASA Astrophysics Data System (ADS)

We study quantum theory as an example of entropic inference. Our goal is to remove conceptual difficulties that arise in quantum mechanics. Since probability is a common feature of quantum theory and of any inference problem, we briefly introduce probability theory and the entropic methods to update probabilities when new information becomes available. Nelson's stochastic mechanics and Caticha's derivation of quantum theory are discussed in the subsequent chapters. Our first goal is to understand momentum and angular momentum within an entropic dynamics framework and to derive the corresponding uncertainty relations. In this framework momentum is an epistemic concept -- it is not an attribute of the particle but of the probability distributions. We also show that the Heisenberg's uncertainty relation is an osmotic effect. Next we explore the entropic analog of angular momentum. Just like linear momentum, angular momentum is also expressed in purely informational terms. We then extend entropic dynamics to curved spaces. An important new feature is that the displacement of a particle does not transform like a vector. It involves second order terms that account for the effects of curvature . This leads to a modified Schrodinger equation for curved spaces that also take into account the curvature effects. We also derive Schrodinger equation for a charged particle interacting with external electromagnetic field on general Riemannian manifolds. Finally we develop the entropic dynamics of a particle of spin 1/2. The particle is modeled as a rigid point rotator interacting with an external EM field. The configuration space of such a rotator is R 3 x S3 (S 3 is the 3-sphere). The model describes the regular representation of SU(2) which includes all the irreducible representations (spin 0, 1/2, 1, 3/2,...) including spin 1/2.

Nawaz, Shahid

89

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

NASA Astrophysics Data System (ADS)

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

Asplund, Erik; Klüner, Thorsten

2014-08-01

90

Selective dynamical decoupling for quantum state transfer

NASA Astrophysics Data System (ADS)

State transfer across discrete quantum networks is one of the elementary tasks of quantum information processing. Its aim is the faithful placement of information into a specific position in the network. However, all physical systems suffer from imperfections, which can severely limit the transfer fidelity. We present selective dynamical decoupling schemes which are capable of stabilizing imperfect quantum state transfer protocols on the model of a bent linear qubit chain. The efficiency of the schemes is tested and verified in numerical simulations on a number of realistic cases. The simulations demonstrate that these selective dynamical decoupling schemes are capable of suppressing unwanted errors in quantum state transfer protocols efficiently.

Frydrych, H.; Hoskovec, A.; Jex, I.; Alber, G.

2015-01-01

91

Nuclear magnetic resonance (NMR) spectroscopy is omnipresent in chemical analysis. However, chirality of a molecule can only be detected indirectly by NMR, e.g., by monitoring its interaction with another chiral object. In the present study, we investigate the spectroscopic behavior of chiral molecules placed into a chiral solvent. In this case, the solvent-solute interaction is much weaker, but the application range of such NMR analysis is wider than for a specific chemical shift agent. Two alcohols and an amine were used as model systems, and differences in NMR chemical shifts dependent on the solute-solvent chirality combination were experimentally detected. Combined quantum mechanic/molecular mechanic (QM/MM) computations were applied to reveal the underlying solute-solvent interactions. NMR shielding was calculated using the density functional theory (DFT). While the experimental observations could not be reproduced quantitatively, the modeling provided a qualitative agreement and detailed insight into the essence of solvent-solute chiral interactions. The potentials of mean force (PMF) obtained using molecular dynamics (MD) and the weighted histogram analysis method (WHAM) indicate that the chiral interaction brings about differences in conformer ratios, which are to a large extent responsible for the NMR shifts. The MD results also predicted slight changes in the solvent structure, including the radial distribution function (RDF), to depend on the solvent/solute chirality combination. Apart from the conformer distribution, an effective average solvent electrostatic field was tested as another major factor contributing to the chiral NMR effect. The possibility to simulate spectral effects of chiral solvents from the first-principles opens up the way to NMR spectroscopic determination of the absolute configuration for a larger scale of compounds, including those not forming specific complexes. PMID:25411905

Kessler, Ji?í; Dra?ínský, Martin; Bou?, Petr

2014-12-01

92

Quantum dynamics study of the isotopic effect on capture reactions: HD, D2+CH3

NASA Astrophysics Data System (ADS)

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

Wang, Dunyou

2003-01-01

93

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

NASA Technical Reports Server (NTRS)

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

Wang, Dunyou; Kwak, Dochan (Technical Monitor)

2002-01-01

94

Quantum dynamics of magnetically controlled network for Bloch electrons

We study quantum dynamics of wave packet motion of Bloch electrons in quantum networks with the tight-binding approach for different types of nearest-neighbor interactions. For various geometrical configurations, these networks can function as some optical devices, such as beam splitters and interferometers. When the Bloch electrons with the Gaussian wave packets input these devices, various quantum coherence phenomena can be observed, e.g., the perfect quantum state transfer without reflection in a Y-shaped beam, the multi- mode entanglers of electron wave by star shaped network and Bloch electron interferometer with the lattice Aharonov-Bohm effects. Behind these conceptual quantum devices are the physical mechanism that, for hopping parameters with some specific values, a connected quantum networks can be reduced into a virtual network, which is a direct sum of some irreducible subnetworks. Thus, the perfect quantum state transfer in each subnetwork in this virtual network can be regarded as a coherent beam splitting process. Analytical and numerical investigations show the controllability of wave packet motion in these quantum networks by the magnetic flux through some loops of these networks, or by adjusting the couplings on nodes. We find the essential differences in these quantum coherence effects when the different wave packets enter these quantum networks initially. With these quantum coherent features, they are expected to be used as quantum information processors for the fermion system based on the possible engineered solid state systems, such as the array of quantum dots that can be implemented experimentally.

S. Yang; Z. Song; C. P. Sun

2006-03-01

95

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

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

Jarrod R. McClean; Alán Aspuru-Guzik

2014-10-07

96

Clock quantum Monte Carlo technique: An imaginary-time method for real-time quantum dynamics

NASA Astrophysics Data System (ADS)

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

McClean, Jarrod R.; Aspuru-Guzik, Alán

2015-01-01

97

We present a method based on the path integral Monte Carlo formalism for the calculation of ground-state time correlation functions in quantum systems. The key point of the method is the consideration of time as a complex variable whose phase ? acts as an adjustable parameter. By using high-order approximations for the quantum propagator, it is possible to obtain Monte Carlo data all the way from purely imaginary time to ? values near the limit of real time. As a consequence, it is possible to infer accurately the spectral functions using simple inversion algorithms. We test this approach in the calculation of the dynamic structure function S(q, ?) of two one-dimensional model systems, harmonic and quartic oscillators, for which S(q, ?) can be exactly calculated. We notice a clear improvement in the calculation of the dynamic response with respect to the common approach based on the inverse Laplace transform of the imaginary-time correlation function. PMID:25796238

Rota, R; Casulleras, J; Mazzanti, F; Boronat, J

2015-03-21

98

Non-equilibrium dynamics of an unstable quantum pendulum

A pendulum prepared perfectly inverted and motionless is a prototype of unstable equilibria and corresponds to an unstable hyperbolic fixed point in the dynamical phase space. Unstable fixed points are central to understanding Hamiltonian chaos in classical systems. In many-body quantum systems, mean-field approximations fail in the vicinity of unstable fixed points and lead to dynamics driven by quantum fluctuations. Here, we measure the non-equilibrium dynamics of a many-body quantum pendulum initialized to a hyperbolic fixed point of the phase space. The experiment uses a spin-1 Bose condensate, which exhibits Josephson dynamics in the spin populations that correspond in the mean-field limit to motion of a non-rigid mechanical pendulum. The condensate is initialized to a minimum uncertainty spin state, and quantum fluctuations lead to non-linear spin evolution along a separatrix and non-Gaussian probability distributions that are measured to be in good agreement with exact quantum calculations up to 0.25 s. At longer times, atomic loss due to the finite lifetime of the condensate leads to larger spin oscillation amplitudes compared to no loss case as orbits depart from the separatrix. This demonstrates how decoherence of a many-body system can result in more apparent coherent behaviour. This experiment provides new avenues for studying macroscopic spin systems in the quantum limit and for investigations of important topics in non-equilibrium quantum dynamics.

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

2012-05-09

99

Thermodynamics of quantum systems under dynamical control

In this review the debated rapport between thermodynamics and quantum mechanics is addressed in the framework of the theory of periodically-driven/controlled quantum-thermodynamic machines. The basic model studied here is that of a two-level system (TLS), whose energy is periodically modulated while the system is coupled to thermal baths. When the modulation interval is short compared to the bath memory time, the system-bath correlations are affected, thereby causing cooling or heating of the TLS, depending on the interval. In steady state, a periodically-modulated TLS coupled to two distinct baths constitutes the simplest quantum heat machine (QHM) that may operate as either an engine or a refrigerator, depending on the modulation rate. We find their efficiency and power-output bounds and the conditions for attaining these bounds. An extension of this model to multilevel systems shows that the QHM power output can be boosted by the multilevel degeneracy. These results are used to scrutinize basic thermodynamic principles: (i) Externally-driven/modulated QHMs may attain the Carnot efficiency bound, but when the driving is done by a quantum device ("piston"), the efficiency strongly depends on its initial quantum state. Such dependence has been unknown thus far. (ii) The refrigeration rate effected by QHMs does not vanish as the temperature approaches absolute zero for certain quantized baths, e.g., magnons, thous challenging Nernst's unattainability principle. (iii) System-bath correlations allow more work extraction under periodic control than that expected from the Szilard-Landauer principle, provided the period is in the non-Markovian domain. Thus, dynamically-controlled QHMs may benefit from hitherto unexploited thermodynamic resources.

D. Gelbwaser-Klimovsky; Wolfgang Niedenzu; Gershon Kurizki

2015-03-04

100

Open systems dynamics for propagating quantum fields

NASA Astrophysics Data System (ADS)

In this dissertation, I explore interactions between matter and propagating light. The electromagnetic field is modeled as a Markovian reservoir of quantum harmonic oscillators successively streaming past a quantum system. Each weak and fleeting interaction entangles the light and the system, and the light continues its course. In the context of quantum tomography or metrology one attempts, using measure- ments of the light, to extract information about the quantum state of the system. An inevitable consequence of these measurements is a disturbance of the system's quantum state. These ideas focus on the system and regard the light as ancillary. It serves its purpose as a probe or as a mechanism to generate interesting dynamics or system states but is eventually traced out, leaving the reduced quantum state of the system as the primary mathematical subject. What, then, when the state of light itself harbors intrinsic self-entanglement? One such set of states, those where a traveling wave packet is prepared with a defi- nite number of photons, is a focal point of this dissertation. These N-photon states are ideal candidates as couriers in quantum information processing device. In con- trast to quasi-classical states, such as coherent or thermal fields, N-photon states possess temporal mode entanglement, and local interactions in time have nonlocal consequences. The reduced state of a system probed by an N-photon state evolves in a non-Markovian way, and to describe its dynamics one is obliged to keep track of the field's evolution. I present a method to do this for an arbitrary quantum system using a set of coupled master equations. Many models set aside spatial degrees of freedom as an unnecessary complicating factor. By doing so the precision of predictions is limited. Consider a ensemble of cold, trapped atomic spins dispersively probed by a paraxial laser beam. Atom-light coupling across the ensemble is spatially inhomogeneous as is the radiation pattern of scattered light. To achieve strong entanglement between the atoms and photons, one must match the spatial mode of the collective radiation from the ensemble to the mode of the laser beam while minimizing the effects of decoherence due to optical pumping. In this dissertation, I present a three-dimensional model for a quantum light-matter interface for propagating quantum fields specifically equipped to address these issues. The reduced collective atomic state is described by a stochastic master equation that includes coherent collective scattering into paraxial modes, decoher- ence by local inhomogeneous diffuse scattering, and measurement backaction due to continuous observation of the light. As the light is measured, backaction transmutes atom-light entanglement into entanglement between the atoms of the ensemble. This formalism is used to study the impact of spatial modes in the squeezing of a collec- tive atomic spin wave via continuous measurement. The largest squeezing occurs precisely in parameter regimes with significant spatial inhomogeneities, far from the limit in which the interface is well approximated by a one-dimensional, homogeneous model.

Baragiola, Ben Quinn

101

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

102

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

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

2014-10-01

103

NASA Astrophysics Data System (ADS)

A comparison of the hydration characteristics of di- and trivalent europium ions in aqueous solution is presented. The established quantum mechanical charge-field molecular dynamics (QMCF-MD) approach yielded two 30 ps simulations. Significant differences among the two species were found in the Eu-O radial distribution functions, both in good agreement with experiments. The first shell coordination numbers of 8.1 and 8.9 were observed for Eu(II) and Eu(III), respectively. The mean residence time of first shell ligands differ by more than one order of magnitude, the divalent ion's hydration shell being more flexible, which is underlined by a weak ion-water bond strength.

Canaval, Lorenz R.; Rode, Bernd M.

2015-01-01

104

Dynamics of fluctuations in a quantum system

"\\textit{The noise is the signal}"[R. Landauer, Nature \\textbf{392}, 658 (1998)] 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.

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

2014-05-09

105

NASA Astrophysics Data System (ADS)

A novel molecular dynamics methodology recently proposed by our group [Rega et al., Chem. Phys. Lett. 422, 367 (2006)], which is based on an integrated hybrid potential rooted in high level quantum mechanical methods using localized basis functions and nonperiodic boundary conditions, has been applied to study acrolein in aqueous solution. The solute structural rearrangement and its hydrogen-bonding pattern due to the interactions with water have been analyzed in some detail. Moreover, the solvent effects on the UV n ??? vertical transition and on the NMR C13 and O17 shielding constants of acrolein have been investigated theoretically by performing a posteriori quantum mechanical calculations on a statistically significant number of snapshots extracted from both gas-phase and aqueous solution simulations. Results show that such effective computational strategy can be successfully used to improve our understanding, at atomic level, of important spectroscopic observables.

Brancato, Giuseppe; Rega, Nadia; Barone, Vincenzo

2006-10-01

106

Universal simulation of Markovian quantum dynamics

We consider the problem of constructing a "universal set" of Markovian processes, such that any Markovian open quantum system, described by a one-parameter semigroup of quantum channels, can be efficiently simulated through sequential simulations of processes from the universal set. In particular, for quantum systems of dimension $d$, we explicitly construct a universal set of semigroup generators, parametrized by $d^2-3$ continuous parameters. Consequently, we show that in order to simulate the dynamics of an arbitrary $d$ dimensional Markovian quantum system it is necessary and sufficient to be able to implement unitary operations on the system, and quantum channels from the semigroups generated by elements of the universal set of generators. As such, we specify the minimum set of resources necessary for the simulation of arbitrary Markovian open quantum systems, and furthermore, assuming these resources we provide an explicit algorithm for the efficient simulation of such systems.

Ryan Sweke; Ilya Sinayskiy; Denis Bernard; Francesco Petruccione

2015-03-17

107

NASA Astrophysics Data System (ADS)

Time-dependent, quantum reaction dynamics wavepacket approach is employed to investigate the impacts of the translational, vibrational, and rotational motion on the HD + H_3^+ ? H2D+ + H2 reaction using the Xie-Braams-Bowman potential energy surface [Z. Xie, B. J. Braams, and J. M. Bowman, J. Chem. Phys. 122, 224307 (2005)], 10.1063/1.1927529. We treat this five atom reaction with a seven-degree-of-freedom model by fixing one Jacobi and one torsion angle related to H_3^+ at the lowest saddle point geometry of the potential energy surface. The initial state selected reaction probabilities show that the rotational excitations of H+-H2 greatly enhance the reactivity with the reaction probabilities increased double at high rotational states compared to the ground state. However, the vibrational excitations of H_3^+ hinder the reactivity. The ground state reaction probability shows no reaction threshold for this exoergic reaction, and as the translational energy increases, the reaction probability decreases. Furthermore, reactive resonances and zero point energy play very important roles on the reaction dynamics. The obtained integral cross section has the character of an exoergic reaction without a threshold: it decreases with the translational energy increasing. The calculated thermal rate constants using this seven-degree-of-freedom model are in agreement with a later experiment measurement.

Meng, Fanbin; Wang, Tingting; Wang, Dunyou

2011-09-01

108

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

Lorenza Viola; David Tannor

2011-01-01

109

Optimal dynamic discrimination of similar quantum systems

NASA Astrophysics Data System (ADS)

The techniques for identifying and separating similar molecules have always been very important to chemistry and other branches of science and engineering. Similar quantum systems share comparable Hamiltonians, so their eigenenergy levels, transition dipole moments, and therefore their ordinary observable properties are alike. Traditional analytical methods have mostly been restricted by working with the subtle differences in the physical and chemical properties of the similar species. Optimal Dynamic Discrimination (ODD) aims at magnifying the dissimilarity of the agents by actively controlling their quantum evolution, drawing on the extremely rich information embedded in their dynamics. ODD is developed based on the tremendous flexibility of Optimal Control Theory (OCT) and on the practical implementation of closed-loop learning control, which has become a more and more indispensable tool for controlling quantum processes. The ODD experimental paradigm is designed to combat a number of factors that are detrimental to the discrimination of similar molecules: laser pulse noise, signal detection errors, finite time resolution in the signals, and environmental decoherence effects. It utilizes either static signals or time series signal, the latter capable of providing more information. Simulations are performed in this dissertation progressing from the wave function to the density matrix formulation, in order to study the decoherence effects. Analysis of the results reveals the roles of the adverse factors, unravels the underlying mechanisms of ODD, and provides insights on laboratory implementation. ODD emphasizes the incorporation of algorithmic development and laboratory design, and seeks to bridge the gap between theoretical/computational chemistry and experimental chemistry, with the help from applied mathematics and computer science.

Li, Baiqing

2005-07-01

110

Quantum dynamics of bio-molecular systems in noisy environments

We discuss three different aspects of the quantum dynamics of bio-molecular systems and more generally complex networks in the presence of strongly coupled environments. Firstly, we make a case for the systematic study of fundamental structural elements underlying the quantum dynamics of these systems, identify such elements and explore the resulting interplay of quantum dynamics and environmental decoherence. Secondly, we critically examine some existing approaches to the numerical description of system-environment interaction in the non-perturbative regime and present a promising new method that can overcome some limitations of existing methods. Thirdly, we present an approach towards deciding and quantifying the non-classicality of the action of the environment and the observed system-dynamics. We stress the relevance of these tools for strengthening the interplay between theoretical and experimental research in this field.

M. B. Plenio; S. F. Huelga

2012-02-05

111

Statistical dynamics of a non-Abelian anyonic quantum walk

We study the single particle dynamics of a mobile non-Abelian anyon hopping around many pinned anyons on a surface. The dynamics is modelled by a discrete time quantum walk and the spatial degree of freedom of the mobile anyon becomes entangled with the fusion degrees of freedom of the collective system. Each quantum trajectory makes a closed braid on the world lines of the particles establishing a direct connection between statistical dynamics and quantum link invariants. We find that asymptotically a mobile Ising anyon becomes so entangled with its environment that its statistical dynamics reduces to a classical random walk with linear dispersion in contrast to particles with Abelian statistics which have quadratic dispersion.

Lauri Lehman; Vaclav Zatloukal; Gavin K. Brennen; Jiannis K. Pachos; Zhenghan Wang

2010-09-04

112

Geometric origin of dynamically induced freezing of quantum evolution

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

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

2006-02-15

113

Quantum spin dynamics as a model for quantum computer operation

: We study effects of the physical realization of quantum computers on their logical operation. Through simulation of physical\\u000a models of quantum computer hardware, we analyze the difficulties that are encountered in programming physical realizations\\u000a of quantum computers. Examples of logically identical implementations of the controlled-NOT operation and Grover's database\\u000a search algorithm are used to demonstrate that the results of

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

2002-01-01

114

The photoexcited electrons transfer dynamics of the CdS quantum dots (QDs) deposited in TiO{sub 2} nanowire array films are studied using surface photovoltage (SPV) and transient photovoltage (TPV) techniques. By comparing the SPV results with different thicknesses of QDs layers, we can separate the dynamic characteristics of photoexcited electrons injection and trapping. It is found that the TPV signals of photoexcited electrons trapped in the CdS QDs occur at timescales of about 2?×?10{sup ?8} s, which is faster than that of the photoexcited electrons injected from CdS into TiO{sub 2}. More than 90 nm of the thickness of the CdS QDs layer will seriously affect the photoexcited electrons transfer and injection.

Pang, Shan; Cheng, Ke; Yuan, Zhanqiang; Xu, Suyun; Cheng, Gang; Du, Zuliang, E-mail: zld@henu.edu.cn [Key Laboratory for Special Functional Materials of Ministry of Education, Henan University, Kaifeng 475004, Henan (China)

2014-05-19

115

Superadiabatic dynamics in open quantum systems

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

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

2014-05-08

116

Fractal dynamics in chaotic quantum transport

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

117

Controlling quantum critical dynamics of isolated systems

NASA Astrophysics Data System (ADS)

Controlling the non adiabatic dynamics of isolated quantum systems driven through a critical point is of interest in a variety of fields ranging from quantum simulation to finite-time thermodynamics. We briefly review the different methods for designing protocols which minimize excitation (defect) production in a closed quantum critical system driven out of equilibrium. We chart out the role of specific driving schemes for this procedure, point out their experimental relevance, and discuss their implementation in the context of ultracold atom and spin systems.

del Campo, A.; Sengupta, K.

2015-02-01

118

An instability of unitary quantum dynamics

Instabilities of equilibrium quantum mechanics are common and well-understood. They are manifested for example in phase transitions, where a quantum system becomes so sensitive to perturbations that a symmetry can be spontaneously broken. Here, we consider the possibility that the time evolution governing quantum dynamics may be similarly subject to an instability, at which its unitarity spontaneously breaks down owing to an extreme sensitivity towards perturbations. We find that indeed such an instability exists, and we explore its immediate consequences. Interpretations of the results both in terms of extreme sensitivity to the influence of environmental degrees of freedom, and in terms of a possible fundamental violation of unitarity are discussed.

Jasper van Wezel

2015-02-26

119

Efficient Measurement of Quantum Dynamics via Compressive Sensing

The resources required to characterize the dynamics of engineered quantum systems—such as quantum computers and quantum sensors—grow exponentially with system size. Here we adapt techniques from compressive sensing to ...

Shabani, A.

120

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

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

121

Exploring the capabilities of quantum optimal dynamic discrimination

NASA Astrophysics Data System (ADS)

Optimal dynamic discrimination (ODD) uses closed-loop learning control techniques to discriminate between similar quantum systems. ODD achieves discrimination by employing a shaped control (laser) pulse to simultaneously exploit the unique quantum dynamics particular to each system, even when they are quite similar. In this work, ODD is viewed in the context of multiobjective optimization, where the competing objectives are the degree of similarity of the quantum systems and the level of controlled discrimination that can be achieved. To facilitate this study, the D-MORPH gradient algorithm is extended to handle multiple quantum systems and multiple objectives. This work explores the trade-off between laser resources (e.g., the length of the pulse, fluence, etc.) and ODD's ability to discriminate between similar systems. A mechanism analysis is performed to identify the dominant pathways utilized to achieve discrimination between similar systems.

Beltrani, Vincent; Ghosh, Pritha; Rabitz, Herschel

2009-04-01

122

Combining dynamical decoupling with fault-tolerant quantum computation

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

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

2011-07-15

123

Efficient Quantum State Estimation by Continuous Weak Measurement and Dynamical Control

We demonstrate a fast, robust and non-destructive protocol for quantum state estimation based on continuous weak measurement in the presence of a controlled dynamical evolution. Our experiment uses optically probed atomic spins as a testbed, and successfully reconstructs a range of trial states with fidelities of ~90%. The procedure holds promise as a practical diagnostic tool for the study of complex quantum dynamics, the testing of quantum hardware, and as a starting point for new types of quantum feedback control.

Greg A. Smith; Andrew Silberfarb; Ivan H. Deutsch; Poul S. Jessen

2006-06-13

124

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

125

Nuclear quantum dynamics in dense hydrogen

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. PMID:24968754

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

2014-01-01

126

Hydration dynamics in water clusters via quantum molecular dynamics simulations

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, E-mail: turi@chem.elte.hu [Department of Physical Chemistry, Eötvös Loránd University, Budapest 112, P. O. Box 32, H-1518 (Hungary)

2014-05-28

127

NASA Technical Reports Server (NTRS)

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

Wang, Dunyou

2003-01-01

128

Phase space representation of quantum dynamics

We discuss a phase space representation of quantum dynamics of systems with many degrees of freedom. This representation is based on a perturbative expansion in quantum fluctuations around one of the classical limits. We explicitly analyze expansions around three such limits: (i) corpuscular or Newtonian limit in the coordinate-momentum representation, (ii) wave or Gross-Pitaevskii limit for interacting bosons in the coherent state representation, and (iii) Bloch limit for the spin systems. We discuss both the semiclassical (truncated Wigner) approximation and further quantum corrections appearing in the form of either stochastic quantum jumps along the classical trajectories or the nonlinear response to such jumps. We also discuss how quantum jumps naturally emerge in the analysis of non-equal time correlation functions. This representation of quantum dynamics is closely related to the phase space methods based on the Wigner-Weyl quantization and to the Keldysh technique. We show how such concepts as the Wigner function, Weyl symbol, Moyal product, Bopp operators, and others automatically emerge from the Feynmann's path integral representation of the evolution in the Heisenberg representation. We illustrate the applicability of this expansion with various examples mostly in the context of cold atom systems including sine-Gordon model, one- and two-dimensional Bose-Hubbard model, Dicke model and others.

Polkovnikov, Anatoli, E-mail: asp@bu.ed [Department of Physics, Boston University, Boston, MA 02215 (United States)

2010-08-15

129

Entangled quantum probes for dynamical environmental noise

We address the use of entangled qubits as quantum probes to characterize the dynamical noise induced by complex environments. In particular, we show that entangled probes improve estimation of the correlation time for a broad class of environmental noises compared to any sequential strategy involving single qubit preparation. The effect is present when the noise is faster than a threshold value, a regime which may always be achieved by tuning the coupling between the quantum probe and the environment inducing the noise. Our scheme exploits time-dependent sensitivity of quantum systems to decoherence and does not require dynamical control on the probes. We derive the optimal interaction time and the optimal probe preparation, showing that it corresponds to multiqubit GHZ states when entanglement is useful. We also show robustness of the scheme against depolarization or dephasing of the probe, and discuss simple measurements approaching optimal precision.

Matteo A. C. Rossi; Matteo G. A. Paris

2015-03-11

130

Quantum optical device accelerating dynamic programming

In this paper we discuss analogue computers based on quantum optical systems accelerating dynamic programming for some computational problems. These computers, at least in principle, can be realized by actually existing devices. We estimate an acceleration in resolving of some NP-hard problems that can be obtained in such a way versus deterministic computers

D. Grigoriev; A. Kazakov; S. Vakulenko

2010-11-23

131

Effective Evolution Equations from Quantum Dynamics

In these notes we review the material presented at the summer school on "Mathematical Physics, Analysis and Stochastics" held at the University of Heidelberg in July 2014. We consider the time-evolution of quantum systems and in particular the rigorous derivation of effective equations approximating the many-body Schr\\"odinger dynamics in certain physically interesting regimes.

Niels Benedikter; Marcello Porta; Benjamin Schlein

2015-02-09

132

Fractal dynamics in chaotic quantum transport

NASA Astrophysics Data System (ADS)

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

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

2013-08-01

133

Fractal dynamics in chaotic quantum transport.

Despite several experiments on chaotic quantum transport in two-dimensional systems such as semiconductor quantum dots, corresponding quantum simulations within a real-space model have been out of reach so far. Here we carry out quantum transport calculations in real space and real time for a two-dimensional stadium cavity that shows chaotic dynamics. By applying a large set of magnetic fields we obtain a complete picture of magnetoconductance that indicates fractal scaling. In the calculations of the fractality we use detrended fluctuation analysis-a widely used method in time-series analysis-and show its usefulness in the interpretation of the conductance curves. Comparison with a standard method to extract the fractal dimension leads to consistent results that in turn qualitatively agree with the previous experimental data. PMID:24032907

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

2013-08-01

134

Fractal Dynamics in Chaotic Quantum Transport

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

Ville Kotimaki; Esa Rasanen; Holger Hennig; Eric J. Heller

2013-07-28

135

Dynamic diffusion as approximation of quantum behavior

The approximation of quantum unitary dynamics of a particle by a swarm of point wise classical samples of this particle is proposed. Quantum mechanism of speedup rests on the creation and annihilation of absolutely rigid bons, which join samples in dot wise symplexes so that the density of swarm approximate the quantum probability. This mechanism does not require differentiation of a density that is adventage of this method over Bohm's quantum hydrodynamics: our method is applicable to many particles in entangled states. In multi particle case the limitation of total number of samples gives the natural model of decoherence, e.g. the divergency from the exact solution of Shredinger equation. Intensity of creation - annihilation of bonds between samples substantially depends on the grain of spatial resolution, which makes impossible to pass to the limits as in a classical substance; this is the price for the scalability of a model to many particles.

Yuri Ozhigov

2010-11-08

136

Dynamics and conductivity near quantum criticality

NASA Astrophysics Data System (ADS)

Relativistic O(N) field theories are studied near the quantum-critical point in two space dimensions. We compute dynamical correlations by large-scale Monte Carlo simulations and numerical analytic continuation. In the ordered side, the scalar spectral function exhibits a universal peak at the Higgs mass. For N=3 and 4, we confirm its ?3 rise at low frequency. On the disordered side, the spectral function exhibits a sharp gap. For N=2, the dynamical conductivity rises above a threshold at the Higgs mass (density gap), in the superfluid (Mott insulator) phase. For charged bosons (Josephson arrays), the power-law rise above the Higgs mass increases from two to four. Approximate charge-vortex duality is reflected in the ratio of imaginary conductivities on either side of the transition. We determine the critical conductivity to be ?c*=0.3(±0.1)×4e2/h and describe a generalization of the worm algorithm to N>2. We use a singular value decomposition error analysis for the numerical analytic continuation.

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

2013-12-01

137

Quantum dynamics of Josephson vortices

to the external magnetic field H ~ IH H vortex #12;Measurement technique % & ' ( ' !)*+ ,-. / ! Âµ.' . . ' . A width versus temperature IH=15 ÂµÂµÂµÂµA IH=45 ÂµÂµÂµÂµA Quantum tunneling at T energy levels Energy level separation 41 2 2 res 1- cI I E increasing H IH=50 ÂµÂµÂµÂµA IH=5 ÂµÂµÂµÂµA Fit

Fominov, Yakov

138

Dynamical competition between quantum Hall and quantum spin Hall effects

NASA Astrophysics Data System (ADS)

In this paper, we investigate the occurrence of quantum phase transitions in topological systems out of equilibrium. More specifically, we consider graphene with a sizable spin-orbit coupling, irradiated by circularly polarized light. In the absence of light, the spin-orbit coupling drives a quantum spin Hall phase where edge currents with opposite spins counterpropagate. On the other hand, the light generates a time-dependent vector potential, which leads to a hopping parameter with staggered time-dependent phases around the benzene ring. The model is a dynamical version of the Haldane model, which considers a static staggered flux with zero total flux through each plaquette. Since the light breaks time-reversal symmetry, a quantum Hall (QH) phase protected by an integer topological invariant arises. An important difference with the static QH phase is the existence of counterpropagating edge states at different momenta, which are made possible by zero- and two-photon resonances. By numerically solving the complete problem, with spin-orbit coupling and light, and investigating different values of the driving frequency ? , we show that the spectrum exhibits nontrivial gaps not only at zero energy but also at ? /2 . This additional gap is created by photon resonances between the valence and conduction band of graphene, and the symmetry of the spectrum forces it to lie at ? /2 . By increasing the intensity of the irradiation, the topological state in the zero energy gap undergoes a dynamical phase transition from a quantum spin Hall to a quantum Hall phase, whereas the gap around ? /2 remains in the quantum Hall regime.

Quelle, A.; Morais Smith, C.

2014-11-01

139

Quantitative analysis of quantum dot dynamics and emission spectra in cavity quantum electrodynamics

We present detuning-dependent spectral and decay-rate measurements to study the difference between spectral and dynamical properties of single quantum dots embedded in micropillar and photonic-crystal cavities. For the micropillar cavity, the dynamics is well described by the dissipative Jaynes-Cummings model, while systematic deviations are observed for the emission spectra. The discrepancy for the spectra is attributed to coupling of other exciton lines to the cavity and interference of different propagation paths towards the detector of the fields emitted by the quantum dot. In contrast, quantitative information about the system can readily be extracted from the dynamical measurements. In the case of photonic crystal cavities we observe an anti crossing in the spectra when detuning a single quantum dot through resonance, which is the spectral signature of strong coupling. However, time-resolved measurements reveal that the actual coupling strength is significantly smaller than anticipated from the spectral...

Madsen, K H

2012-01-01

140

NASA Astrophysics Data System (ADS)

Finding the consequences of symmetry for open-system quantum dynamics is a problem with broad applications, including describing thermal relaxation, deriving quantum limits on the performance of amplifiers, and exploring quantum metrology in the presence of noise. The symmetry of the dynamics may reflect a symmetry of the fundamental laws of nature or a symmetry of a low-energy effective theory, or it may describe a practical restriction such as the lack of a reference frame. In this paper, we apply some tools of harmonic analysis together with ideas from quantum information theory to this problem. The central idea is to study the decomposition of quantum operations—in particular, states, measurements, and channels—into different modes, which we call modes of asymmetry. Under symmetric processing, a given mode of the input is mapped to the corresponding mode of the output, implying that one can only generate a given output if the input contains all of the necessary modes. By defining monotones that quantify the asymmetry in a particular mode, we also derive quantitative constraints on the resources of asymmetry that are required to simulate a given asymmetric operation. We present applications of our results for deriving bounds on the probability of success in nondeterministic state transitions, such as quantum amplification, and a simplified formalism for studying the degradation of quantum reference frames.

Marvian, Iman; Spekkens, Robert W.

2014-12-01

141

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

142

Quantum algorithm for simulating the dynamics of an open quantum system

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

143

Role of controllability in optimizing quantum dynamics

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

144

Quantum dynamics in the thermodynamic limit

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

145

NASA Astrophysics Data System (ADS)

The dynamics of the dihydrogen molecule when confined in carbon nanotubes with different chiralities and diameters are studied by using a 5 dimensional model considering the most relevant degrees of freedom of the system. The nuclear eigenstates are calculated for an (8,0) and a (5,0) carbon nanotubes by the State-Average Multiconfigurational Time-dependent Hartree, and then studied using qualitative tools (mapping of the total wave functions onto given subspaces) and more rigorous analysis (different kinds of overlaps with reference functions). The qualitative analysis is seen to fail due to a strong coupling between the internal and translational degrees of freedom. Using more accurate tools allows us to gain a deeper insight into the behaviour of confined species.

Mondelo-Martell, M.; Huarte-Larrañaga, F.

2015-02-01

146

Lévy flights and nonlocal quantum dynamics

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

147

Steered quantum dynamics for energy minimization.

We introduce a quantum optimal control algorithm for energy minimization that combines the diffeomorphic modulation under observable response preserving homotopy (D-MORPH) gradient and the Broyden Fletcher Goldfarb Shanno (BFGS) iterative scheme for nonlinear optimization. An extended set of controls defining the time-dependent mass, dipole moment, and external perturbational field are optimized to find an effective Hamiltonian that steers the dynamics of the system into the global minimum without getting trapped into local minima. The algorithm is illustrated as applied to energy minimization on rugged surfaces and golf potentials comparable to those previously explored for testing quantum annealing methodologies. PMID:25122515

Soley, Micheline; Markmann, Andreas; Batista, Victor S

2015-01-22

148

The resonance Raman spectroscopic study of the excited state structural dynamics of 1,3-dimethyluracil (DMU), 5-bromo-1,3-dimethyluracil (5BrDMU), uracil, and thymine in water and acetonitrile were reported. Density functional theory calculations were carried out to help elucidate the ultraviolet electronic transitions associated with the A-, and B-band absorptions and the vibrational assignments of the resonance Raman spectra. The effect of the methylation at N1, N3 and C5 sites of pyrimidine ring on the structural dynamics of uracils in different solvents were explored on the basis of the resonance Raman intensity patterns. The relative resonance Raman intensities of DMU and 5BrDMU are computed at the B3LYP-TD level. Huge discrepancies between the experimental resonance Raman intensities and the B3LYP-TD predicted ones were observed. The underlying mechanism was briefly discussed. The decay channel through the S1((1)n?*)/S2((1)??*) conical intersection and the S1((1)n?*)/T1((3)??*) intersystem crossing were revealed by using the CASSCF(8,7)/6-31G(d) level of theory calculations. PMID:23971973

Li, Ming-Juan; Liu, Ming-Xia; Zhao, Yan-Ying; Pei, Ke-Mei; Wang, Hui-Gang; Zheng, Xuming; Fang, Wei Hai

2013-10-01

149

NASA Astrophysics Data System (ADS)

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

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

2012-10-01

150

The Bayesian approach to quantum mechanics of Caves, Fuchs and Schack is presented. Its conjunction of realism about physics along with anti-realism about much of the structure of quantum theory is elaborated; and the position defended from common objections: that it is solipsist; that it is too instrumentalist; that it cannot deal with Wigner's friend scenarios. Three more substantive problems are raised: Can a reasonable ontology be found for the approach? Can it account for explanation in quantum theory? Are subjective probabilities on their own adequate in the quantum domain? The first question is answered in the affirmative, drawing on elements from Nancy Cartwright's philosophy of science. The second two are not: it is argued that these present outstanding difficulties for the project. A quantum Bayesian version of Moore's paradox is developed to illustrate difficulties with the subjectivist account of pure state assignments.

Christopher G. Timpson

2008-04-13

151

Multiple quantum NMR dynamics in pseudopure states.

We investigate numerically the multiple quantum (MQ) NMR dynamics in systems of nuclear spins 1/2 coupled by dipole-dipole interactions in the case of the pseudopure initial state. Simulations of the MQ NMR with real molecular structures such as six dipolar-coupled proton spins of benzene, hydroxyl proton chains in calcium hydroxyapatite, and fluorine chains in calcium fluorapatite open the way to experimental NMR testing of the obtained results. It was found that multiple-spin correlations are created faster in such experiments than in the usual MQ NMR experiments and can be used for the investigation of many-spin dynamics of nuclear spins in solids. PMID:21814001

Furman, G B

2009-01-14

152

Multiple quantum NMR dynamics in pseudopure states

NASA Astrophysics Data System (ADS)

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

Furman, G. B.

2009-01-01

153

Renormalization group approach to quantum Hamiltonian dynamics

NASA Astrophysics Data System (ADS)

Ken Wilson developed powerful renormalization group procedures for constructing effective theories and solving a broad class of difficult physical problems. His insights allowed him to later advance the Hamiltonian approach to quantum dynamics of particles and fields in the Minkowski space-time, motivated by QCD. The latter advances are described in this article, concluding with a remark on Ken's related interest in difficult systemic issues of society.

G?azek, Stanis?aw D.

2015-03-01

154

Intersatellite quantum communication feasibility study

NASA Astrophysics Data System (ADS)

The shift in the Communication paradigm from the bit to the qubit is increasingly exploited in terrestrial long range links and networks, with strong potentials in secure communications, quantum computing and metrology. The space-to-ground quantum key distribution was also considered as feasible. A new different scenario for the quantum communications is that of the intersatellite link. In this study we focus on the extension of intersatellite communications into the quantum domain. The long distances involved and the fast relative motion are severe constraints, partially compensated by the absence of beam degradation due to the propagation in the atmosphere as well as the relatively low background noise level. We address the conception of the optical terminal and the predicted performances in the case of constellations of LEO and MEO satellite including the quantum communications and quantum teleportation.

Tomaello, Andrea; Dall'Arche, Alberto; Naletto, Giampiero; Villoresi, Paolo

2011-08-01

155

A Dynamics for Discrete Quantum Gravity

NASA Astrophysics Data System (ADS)

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

Gudder, S.

2014-10-01

156

Quantum dynamical framework for Brownian heat engines.

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

Agarwal, G S; Chaturvedi, S

2013-07-01

157

Quantum dynamical framework for Brownian heat engines

NASA Astrophysics Data System (ADS)

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

Agarwal, G. S.; Chaturvedi, S.

2013-07-01

158

). #12;W.D. Li, X.J. Zhou, Y.Q. Wang, J.Q. Liang, W.M. Liu,W.D. Li, X.J. Zhou, Y.Q. Wang, J.Q. Liang, W, Z. D. Zhang, W. M. Liu,Z. X. Liang, Z. D. Zhang, W. M. Liu, Dynamics of a bright soliton in Bose Phase Transition of Cold AtomsCold Atoms Wu-Ming Liu (Institute of Physics, Chinese Academy of Sciences

Wang, Wei Hua

159

NASA Astrophysics Data System (ADS)

We employ the initial state-selected time-dependent wave packet approach to an atom-triatom reaction to study the H + HOD ? OH + HD/OD + H2 reaction without the centrifugal sudden approximation, based on an accurate potential energy surface which was recently developed by neural network fitting to high level ab initio energy points. The total reaction probabilities and integral cross sections, which are the exact coupled-channel results, are calculated for the HOD reactant initially in the ground and several vibrationally excited states, including the bending excited state, OD stretching excited states, OH stretching excited states, and combined excitations of them. The reactivity enhancements from different initial states of HOD are presented, which feature strong bond-selective effects of the reaction dynamics. The current results for the product branching ratios, reactivity enhancements, and relative cross sections are largely improved over the previous calculations, in quantitatively good agreement with experiment. The thermal rate constant for the title reaction and the contributions from individual vibrational states of HOD are also obtained.

Fu, Bina; Zhang, Dong H.

2015-02-01

160

Quantum statistical and dynamical effects in vortex systems

We review some recent developments in the quantum statistical mechanics and in the quantum dynamics of the vortex system in high temperature- and in conventional high-resistivity thin-film superconductors.

G. Blatter; B. Ivlev; Yu. Kagan; V. Vinokur; Theoretische Physik

1994-01-01

161

Boundary dynamics and topology change in quantum mechanics

We show how to use boundary conditions to drive the evolution on a Quantum Mechanical system. We will see how this problem can be expressed in terms of a time-dependent Schr\\"{o}dinger equation. In particular we will need the theory of self-adjoint extensions of differential operators in manifolds with boundary. An introduction of the latter as well as meaningful examples will be given. It is known that different boundary conditions can be used to describe different topologies of the associated quantum systems. We will use the previous results to study how this topology change can be accomplished in a dynamical way.

J. M. Pérez-Pardo; M. Barbero-Liñán; A. Ibort

2015-01-12

162

Quantitative analysis of quantum dot dynamics and emission spectra in cavity quantum electrodynamics

NASA Astrophysics Data System (ADS)

We present detuning-dependent spectral and decay-rate measurements to study the difference between the spectral and dynamical properties of single quantum dots embedded in micropillar and photonic crystal cavities. For the micropillar cavity, the dynamics is well described by the dissipative Jaynes-Cummings model, whereas systematic deviations are observed for the emission spectra. The discrepancy for the spectra is attributed to the coupling of other exciton lines to the cavity and interference of different propagation paths toward the detector of the fields emitted by the quantum dot. In contrast, quantitative information about the system can readily be extracted from the dynamical measurements. In the case of photonic crystal cavities, we observe an anti-crossing in the spectra when detuning a single quantum dot through resonance, which is the spectral signature of a strong coupling. However, time-resolved measurements reveal that the actual coupling strength is significantly smaller than anticipated from the spectral measurements and that the quantum dot is rather weakly coupled to the cavity. We suggest that the observed Rabi splitting is due to cavity feeding by other quantum dots and/or multi-exciton complexes giving rise to collective emission effects.

Madsen, K. H.; Lodahl, P.

2013-02-01

163

Automated synthesis of dynamically corrected quantum gates

NASA Astrophysics Data System (ADS)

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

Khodjasteh, Kaveh; Bluhm, Hendrik; Viola, Lorenza

2012-10-01

164

Path integral formulation for quantum nonadiabatic dynamics and the mixed quantum-classical limit

This work identifies geometric effects on dynamics due to nonadiabatic couplings in Born Oppenheimer systems and provides a systematic method for deriving corrections to mixed quantum-classical methods. Specifically, an exact path integral formulation of the quantum nonadiabatic dynamics of Born Oppenheimer systems is described. Stationary phase approximations to the propagator for full quantum dynamics are derived. It is shown that quantum corrections to mixed quantum classical methods can be obtained through stationary phase approximations to the full quantum dynamics. A rigorous description of the quantum corrections due to electronic nonadiabatic coupling on the nuclear dynamics within the Ehrenfest framework is obtained. The fewest switches surface hopping method is shown to be obtained as a quasiclassical approximation to the dynamics and natural semiclassical extensions to include classically forbidden nonadiabatic transitions are suggested.

Vinod Krishna

2007-02-25

165

Open quantum reaction-diffusion dynamics: absorbing states and relaxation

We consider an extension of classical stochastic reaction-diffusion (RD) dynamics to open quantum systems. We study a class of models of hard core particles on a one-dimensional lattice whose dynamics is generated by a quantum master operator and where particle hopping is coherent while reactions, such as pair annihilation or pair coalescence, are dissipative. These are quantum open generalisations of the $A+A \\to \\varnothing$ and $A+A \\to A$ classical RD models. We characterise the relaxation of the state towards the stationary regime via a decomposition of the system Hilbert space into transient and recurrent subspaces. We provide a complete classification of the structure of the recurrent subspace (and the non-equilibrium steady states) in terms of the dark states associated to the quantum master operator and its general spectral properties. We also show that, in one dimension, relaxation towards these absorbing dark states is slower than that predicted by a mean-field analysis due to fluctuation effects, in analogy with what occurs in classical RD systems. Numerical simulations of small systems suggest that the decay of the density in one dimension, in both the open quantum $A+A \\to \\varnothing$ and $A+A \\to A$ cases, may go asymptotically as $t^{-b}$ with $1/2 < b < 1$.

Merlijn van Horssen; Juan P. Garrahan

2014-11-28

166

Quantum Process Tomography Quantifies Coherence Transfer Dynamics in Vibrational Exciton

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

Chuntonov, Lev; Ma, Jianqiang

2013-01-01

167

Open quantum reaction-diffusion dynamics: Absorbing states and relaxation

NASA Astrophysics Data System (ADS)

We consider an extension of classical stochastic reaction-diffusion (RD) dynamics to open quantum systems. We study a class of models of hard-core particles on a one-dimensional lattice whose dynamics is generated by a quantum master operator. Particle hopping is coherent while reactions, such as pair annihilation or pair coalescence, are dissipative. These are quantum open generalizations of the A +A ?? and A +A ?A classical RD models. We characterize the relaxation of the state towards the stationary regime via a decomposition of the system Hilbert space into transient and recurrent subspaces. We provide a complete classification of the structure of the recurrent subspace (and the nonequilibrium steady states) in terms of the dark states associated to the quantum master operator and its general spectral properties. We also show that, in one dimension, relaxation towards these absorbing dark states is slower than that predicted by a mean-field analysis due to fluctuation effects, in analogy with what occurs in classical RD systems. Numerical simulations of small systems suggest that the decay of the density in one dimension, in both the open quantum A +A ?? and A +A ?A systems, behaves asymptotically as t-b with 1 /2 **
**

van Horssen, Merlijn; Garrahan, Juan P.

2015-03-01

168

Dynamics of Quantum Adiabatic Evolution Algorithm for Number Partitioning

NASA Technical Reports Server (NTRS)

We have developed a general technique to study the dynamics of the quantum adiabatic evolution algorithm applied to random combinatorial optimization problems in the asymptotic limit of large problem size n. We use as an example the NP-complete Number Partitioning problem and map the algorithm dynamics to that of an auxiliary quantum spin glass system with the slowly varying Hamiltonian. We use a Green function method to obtain the adiabatic eigenstates and the minimum exitation gap, gmin = O(n2(sup -n/2)), corresponding to the exponential complexity of the algorithm for Number Partitioning. The key element of the analysis is the conditional energy distribution computed for the set of all spin configurations generated from a given (ancestor) configuration by simultaneous flipping of a fixed number of spins. For the problem in question this distribution is shown to depend on the ancestor spin configuration only via a certain parameter related to the energy of the configuration. As the result, the algorithm dynamics can be described in terms of one-dimensional quantum diffusion in the energy space. This effect provides a general limitation of a quantum adiabatic computation in random optimization problems. Analytical results are in agreement with the numerical simulation of the algorithm.

Smelyanskiy, Vadius; vonToussaint, Udo V.; Timucin, Dogan A.; Clancy, Daniel (Technical Monitor)

2002-01-01

169

Dynamics of Quantum Adiabatic Evolution Algorithm for Number Partitioning

NASA Technical Reports Server (NTRS)

We have developed a general technique to study the dynamics of the quantum adiabatic evolution algorithm applied to random combinatorial optimization problems in the asymptotic limit of large problem size n. We use as an example the NP-complete Number Partitioning problem and map the algorithm dynamics to that of an auxiliary quantum spin glass system with the slowly varying Hamiltonian. We use a Green function method to obtain the adiabatic eigenstates and the minimum excitation gap. g min, = O(n 2(exp -n/2), corresponding to the exponential complexity of the algorithm for Number Partitioning. The key element of the analysis is the conditional energy distribution computed for the set of all spin configurations generated from a given (ancestor) configuration by simultaneous flipping of a fixed number of spins. For the problem in question this distribution is shown to depend on the ancestor spin configuration only via a certain parameter related to 'the energy of the configuration. As the result, the algorithm dynamics can be described in terms of one-dimensional quantum diffusion in the energy space. This effect provides a general limitation of a quantum adiabatic computation in random optimization problems. Analytical results are in agreement with the numerical simulation of the algorithm.

Smelyanskiy, V. N.; Toussaint, U. V.; Timucin, D. A.

2002-01-01

170

Optical Nonlinearities and Ultrafast Carrier Dynamics in Semiconductor Quantum Dots

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

171

Simulation of chemical reaction dynamics on an NMR quantum computer

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

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

2011-05-21

172

Quantum Gravity, Dynamical Phase Space and String Theory

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

Laurent Freidel; Robert G. Leigh; Djordje Minic

2014-05-15

173

Quantum turbulence visualized by particle dynamics

NASA Astrophysics Data System (ADS)

The Lagrangian dynamics of micrometer-sized solid particles of hydrogen and deuterium is investigated in thermal counterflow of superfluid He4 at length scales ?exp straddling about two orders of magnitude across the average distance ? between quantized vortices by using the particle tracking velocimetry technique. The normalized probability distribution functions of the particle velocities and accelerations change from the shapes typical of quantum turbulence, characterized by power-law tails, at length scales ?exp??, to forms similar to those obtained in classical turbulent flows, at ?exp??, although the power-law behavior of the acceleration distribution tails is less clear than that observed for the particle velocities. Moreover, the acceleration distribution follows a nearly log-normal, classical-like shape, at ? ??exp?Lint, where Lint denotes the integral length scale, providing thus, within the just defined inertial range, experimental evidence of the existence of classical-like, macroscopic vortical structures in thermal counterflow of superfluid He4, which is traditionally regarded as a quantum flow with no obvious classical analog. Additionally, we report our observations of the added mass effect in quantum turbulence and discuss them in the framework of a developed model of particle dynamics.

La Mantia, M.; Skrbek, L.

2014-07-01

174

PHYSICAL REVIEW A 85, 023826 (2012) Dynamic quantum Kerr effect in circuit quantum electrodynamics

PHYSICAL REVIEW A 85, 023826 (2012) Dynamic quantum Kerr effect in circuit quantum electrodynamics-state cavity quantum electrodynamics (QED) systems [2Â5], with strongly enhanced coupling strength between regime to avoid measurement-induced demolition of the qubit quantum state. Here we explore the qubit

Martinis, John M.

175

Chaos and Nonlinear Dynamics in a Quantum Artificial Economy

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

Carlos Pedro Gonçalves

2012-02-29

176

Relativistic Quantum Metrology in Open System Dynamics

Quantum metrology studies the ultimate limit of precision in estimating a physical quantity if quantum strategies are exploited. Here we investigate the evolution of a two-level atom as a detector which interacts with a massless scalar field using the master equation approach for open quantum system. We employ local quantum estimation theory to estimate the Unruh temperature when probed by a uniformly accelerated detector in the Minkowski vacuum. In particular, we evaluate the Fisher information (FI) for population measurement, maximize its value over all possible detector preparations and evolution times, and compare its behavior with that of the quantum Fisher information (QFI). We find that the optimal precision of estimation is achieved when the detector evolves for a long enough time. Furthermore, we find that in this case the FI for population measurement is independent of initial preparations of the detector and is exactly equal to the QFI, which means that population measurement is optimal. This result demonstrates that the achievement of the ultimate bound of precision imposed by quantum mechanics is possible. Finally, we note that the same configuration is also available to the maximum of the QFI itself. PMID:25609187

Tian, Zehua; Wang, Jieci; Fan, Heng; Jing, Jiliang

2015-01-01

177

Quantum Dynamics of a Bose Superfluid Vortex

NASA Astrophysics Data System (ADS)

Quantum vortex dynamics remain poorly understood despite decades of theoretical investigation. The vortex is a topological soliton, arising from the same medium as the quasiparticles with which it interacts. Hence the coupling between the vortex ``zero mode'' and the quasiparticles has no term linear in the quasiparticle variables -- the lowest order coupling is quadratic. We present a fully quantum-mechanical derivation of the vortex equation of motion valid at low temperatures where the normal fluid density is small. The resulting equation of motion is naturally expressed as a function of the dimensionless frequency ?= ?/kBT. The usual Hall-Vinen/Iordanskii equations are valid when ?1 (the ``classical regime''), but elsewhere, the equations are strongly memory dependent. We will discuss the experimental implications of this frequency dependence in Bose superfluids and cold atomic gases.

Thompson, Lara; Stamp, Philip

2012-02-01

178

Signature of Quantum Depletion in the Dynamic Structure Factor of Atomic Gases

We study the linear response and the dynamic structure factor of weakly interacting Bose gases at low temperatures. Going beyond lowest order in the weak coupling expansion allows us to determine the contribution of the thermal and quantum depletion of the condensate to the dynamic structure factor. We find that the quantum depletion produces a pronounced peak in the dynamic structure factor, which allows for its detection via a spectroscopic analysis.

H. P. Buchler; G. Blatter

2003-12-19

179

Dynamical Causal Modeling from a Quantum Dynamical Perspective

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

180

Quantum and classical molecular dynamics simulations of liquid methane

NASA Astrophysics Data System (ADS)

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

Pathania, Y.; Ahluwalia, P. K.

2013-02-01

181

Emergence of coherence and the dynamics of quantum phase transitions.

The dynamics of quantum phase transitions pose one of the most challenging problems in modern many-body physics. Here, we study a prototypical example in a clean and well-controlled ultracold atom setup by observing the emergence of coherence when crossing the Mott insulator to superfluid quantum phase transition. In the 1D Bose-Hubbard model, we find perfect agreement between experimental observations and numerical simulations for the resulting coherence length. We, thereby, perform a largely certified analog quantum simulation of this strongly correlated system reaching beyond the regime of free quasiparticles. Experimentally, we additionally explore the emergence of coherence in higher dimensions, where no classical simulations are available, as well as for negative temperatures. For intermediate quench velocities, we observe a power-law behavior of the coherence length, reminiscent of the Kibble-Zurek mechanism. However, we find nonuniversal exponents that cannot be captured by this mechanism or any other known model. PMID:25775515

Braun, Simon; Friesdorf, Mathis; Hodgman, Sean S; Schreiber, Michael; Ronzheimer, Jens Philipp; Riera, Arnau; Del Rey, Marco; Bloch, Immanuel; Eisert, Jens; Schneider, Ulrich

2015-03-24

182

A Central Limit Theorem in Many-Body Quantum Dynamics

NASA Astrophysics Data System (ADS)

We study the many body quantum evolution of bosonic systems in the mean field limit. The dynamics is known to be well approximated by the Hartree equation. So far, the available results have the form of a law of large numbers. In this paper we go one step further and we show that the fluctuations around the Hartree evolution satisfy a central limit theorem. Interestingly, the variance of the limiting Gaussian distribution is determined by a time-dependent Bogoliubov transformation describing the dynamics of initial coherent states in a Fock space representation of the system.

Arous, Gérard Ben; Kirkpatrick, Kay; Schlein, Benjamin

2013-07-01

183

Non-equilibrium dynamics of artificial quantum matter

NASA Astrophysics Data System (ADS)

The rapid progress of the field of ultracold atoms during the past two decades has set new milestones in our control over matter. By cooling dilute atomic gases and molecules to nano-Kelvin temperatures, novel quantum mechanical states of matter can be realized and studied on a table-top experimental setup while bulk matter can be tailored to faithfully simulate abstract theoretical models. Two of such models which have witnessed significant experimental and theoretical attention are (1) the two-component Fermi gas with resonant s-wave interactions, and (2) the single-component Fermi gas with dipole-dipole interactions. This thesis is devoted to studying the non-equilibrium collective dynamics of these systems using the general framework of quantum kinetic theory. We present a concise review of the utilized mathematical methods in the first two chapters, including the Schwinger-Keldysh formalism of non-equilibrium quantum fields, two-particle irreducible (2PI) effective actions and the framework of quantum kinetic theory. We study the collective dynamics of the dipolar Fermi gas in a quasi-two-dimensional optical trap in chapter 3 and provide a detailed account of its dynamical crossover from the collisionless to the hydrodynamical regime. Chapter 4 is devoted to studying the dynamics of the attractive Fermi gas in the normal phase. Starting from the self-consistent T-matrix (pairing fluctuation) approximation, we systematically derive a set of quantum kinetic equations and show that they provide a globally valid description of the dynamics of the attractive Fermi gas, ranging from the weak-coupling Fermi liquid phase to the intermediate non-Fermi liquid pairing pseudogap regime and finally the strong-coupling Bose liquid phase. The shortcomings of the self-consistent T-matrix approximation in two spatial dimensions are discussed along with a proposal to overcome its unphysical behaviors. The developed kinetic formalism is finally utilized to reproduce and interpret the findings of a recent experiment done on the collective dynamics of trapped two-dimensional ultracold gases.

Babadi, Mehrtash

184

Coherent spin dynamics in semiconductor quantum dots

NASA Astrophysics Data System (ADS)

We briefly review recent achievements in experimental and theoretical studies of the spin dynamics of electrons and trions under optical pulse-train excitation. The microscopic origin of spin coherence generation, control and detection by means of light is uncovered. The specific features of spin-Faraday, Kerr, and ellipticity signals are analyzed. We show that these effects provide complementary information about spin dynamics. The equilibrium spin dynamics probed by the spin noise spectroscopy is also discussed.

Glazov, M. M.

2013-04-01

185

Quantum Ice : a quantum Monte Carlo study

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

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

2011-12-13

186

Interaction Matrix Element Fluctuations in Ballistic Quantum Dots: Dynamical Effects

We study matrix element fluctuations of the two-body screened Coulomb interaction and of the one-body surface charge potential in ballistic quantum dots, comparing behavior in actual chaotic billiards with analytic results previously obtained in a normalized random wave model. We find that the matrix element variances in actual chaotic billiards typically exceed by a factor of 3 or 4 the predictions of the random wave model, for dot sizes commonly used in experiments. We discuss dynamical effects that are responsible for this enhancement. These dynamical effects have an even more striking effect on the covariance, which changes sign when compared with random wave predictions. In billiards that do not display hard chaos, an even larger enhancement of matrix element fluctuations is possible. These enhanced fluctuations have implications for peak spacing statistics and spectral scrambling for quantum dots in the Coulomb blockade regime.

L. Kaplan; Y. Alhassid

2009-09-17

187

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

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

David Tong; Carl Turner

2014-10-15

188

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 ...

Chu, Shih-I; Roy, Amlan K.

2002-03-18

189

We theoretically study the nuclear spin dynamics driven by electron transport and hyperfine interaction in an electrically-defined double quantum dot (DQD) 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.

Martin J. A. Schuetz; Eric M. Kessler; Lieven M. K. Vandersypen; J. Ignacio Cirac; Geza Giedke

2014-05-30

190

Polymer Quantum Dynamics of the Taub Universe

Within the framework of non-standard (Weyl) representations of the canonical commutation relations, we investigate the polymer quantization of the Taub cosmological model. The Taub model is analyzed within the Arnowitt-Deser-Misner reduction of its dynamics, by which a time variable arises. While the energy variable and its conjugate momentum are treated as ordinary Heisenberg operators, the anisotropy variable and its conjugate momentum are represented by the polymer technique. The model is analyzed at both classical and quantum level. As a result, classical trajectories flatten with respect to the potential wall, and the cosmological singularity is not probabilistically removed. In fact, the dynamics of the wave packets is characterized by an interference phenomenon, which, however, is not able to stop the evolution towards the classical singularity.

Marco Valerio Battisti; Orchidea Maria Lecian; Giovanni Montani

2008-11-17

191

Automated Synthesis of Dynamically Corrected Quantum Gates

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

Kaveh Khodjasteh; Hendrik Bluhm; Lorenza Viola

2012-10-10

192

NASA Astrophysics Data System (ADS)

The spin-forbidden predissociation reaction of the ground state N2O is studied by quantum dynamics calculations. Ab initio calculations are carried out to obtain the potential energy surfaces (PES') of the singlet ground state of N2O and three triplet ones correlating with the asymptote N2+O(3P) and the spin-orbit coupling (SOC) elements among them. The decay rate of individual singlet vibrational state to the 3A' state are estimated by applying Fermi golden rule. For the 1A' state, totally 1692 vibrational eigenstates with the even parity for the total angular momentum J=0 are obtained, and time-dependent wave packet calculations on the triplet PES are performed to obtain the autocorrelation functions whose Fourier transforms provides the decay rates. The resultant decay rates for 887 singlet vibrational states in the energy range 67.3?E?83.7 kcal/mol are analyzed in terms of a random matrix/transition state theory. Incomplete energy randomization of the vibrational energy in the singlet state even near the singlet state dissociation threshold is concluded from the analyses of calculated decay rate distributions.

Nakamura, Hisao; Kato, Shigeki

1999-05-01

193

Hidden Symmetries of Dynamics in Classical and Quantum Physics

This article reviews the role of hidden symmetries of dynamics in the study of physical systems, from the basic concepts of symmetries in phase space to the forefront of current research. Such symmetries emerge naturally in the description of physical systems as varied as non-relativistic, relativistic, with or without gravity, classical or quantum, and are related to the existence of conserved quantities of the dynamics and integrability. In recent years their study has grown intensively, due to the discovery of non-trivial examples that apply to different types of theories and different numbers of dimensions. Applications encompass the study of integrable systems such as spinning tops, the Calogero model, systems described by the Lax equation, the physics of higher dimensional black holes, the Dirac equation, supergravity with and without fluxes, providing a tool to probe the dynamics of non-linear systems.

Marco Cariglia

2014-11-05

194

Quantum dynamics of fast chemical reactions

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

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

1993-12-01

195

Quantum dynamics of a plane pendulum

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

196

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

197

The photophysics and photochemistry of thioacetamide (CH3CSNH2) after excitation to the S2 electronic state were investigated by using resonance Raman spectroscopy in conjunction with the complete active space self-consistent field (CASSCF) method and density functional theory (DFT) calculations. The A-band resonance Raman spectra in acetonitrile, methanol, and water were obtained at 299.1, 282.4, 266.0, 252.7, and 245.9 nm excitation wavelengths to probe the structural dynamics of thioacetamide in the S2 state. CASSCF calculations were done to determine the transition energies and structures of the lower-lying excited states, the conical intersection points CI(S2/S1) and CI(S1/S0), and intersystem crossing points. The structural dynamics of thioacetamide in the S2 state was revealed to be along eight Franck-Condon active vibrational modes ?15, ?11, ?14, ?10, ?8, ?12, ?18, and ?19, mostly in the CC/CS/CN stretches and the CNH8,9/CCH5,6,7/CCN/CCS in-plane bends as indicated by the corresponding normal mode descriptions. The S2 ? S1 decay process via the S2/S1 conical intersection point as the major channel were excluded. The thione-thiol photoisomerization reaction mechanism of thioacetamide via the S2,FC ? S'1,min excited state proton transfer (ESPT) reaction channel was proposed. PMID:25559740

Chen, Xiao; Zhao, Yanying; Zhang, Haibo; Xue, Jiadan; Zheng, Xuming

2015-02-01

198

Modeling quantum fluid dynamics at nonzero temperatures

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

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

2014-01-01

199

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

200

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

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

2006-01-01

201

Coherent control of quantum dynamics - The dream is alive

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

202

Exponential rise of dynamical complexity in quantum computing through projections.

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

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

2014-01-01

203

Exponential rise of dynamical complexity in quantum computing through projections

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

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

2014-01-01

204

A quantifier of genuine multipartite quantum correlations and its dynamics

NASA Astrophysics Data System (ADS)

By using measurement-induced disturbance (S Luo 2008 Phys. Rev. A 77 022301), we propose a quantifier for genuine multipartite quantum correlations. The connection between this quantum correlations measure and the quantum advantage in multiport dense coding for pure three-qubit states is established. It is also used to investigate the dynamics of quantum correlations in a four-partite system. The phenomena of generation of quantum correlations and holding of quantum correlations in some time windows are found. As a byproduct, the monogamy score based on measurement-induced disturbance is related to the generalized geometric measure for pure three-qubit states.

Wang, Xin; Qiu, Liang

2015-03-01

205

We apply two approximate solutions of the quantum-classical Liouville equation (QCLE) in the mapping representation to the simulation of the laser-induced response of a quantum subsystem coupled to a classical environment. These solutions, known as the Poisson Bracket Mapping Equation (PBME) and the Forward-Backward (FB) trajectory solutions, involve simple algorithms in which the dynamics of both the quantum and classical degrees of freedom are described in terms of continuous variables, as opposed to standard surface-hopping solutions in which the classical degrees of freedom hop between potential energy surfaces dictated by the discrete adiabatic state of the quantum subsystem. The validity of these QCLE-based solutions is tested on a non-trivial electron transfer model involving more than two quantum states, a time-dependent Hamiltonian, strong subsystem-bath coupling, and an initial energy shift between the donor and acceptor states that depends on the strength of the subsystem-bath coupling. In particular, we calculate the time-dependent population of the photoexcited donor state in response to an ultrafast, on-resonance pump pulse in a three-state model of an electron transfer complex that is coupled asymmetrically to a bath of harmonic oscillators through the optically dark acceptor state. Within this approach, the three-state electron transfer complex is treated quantum mechanically, while the bath oscillators are treated classically. When compared to the more accurate QCLE-based surface-hopping solution and to the numerically exact quantum results, we find that the PBME solution is not capable of qualitatively capturing the population dynamics, whereas the FB solution is. However, when the subsystem-bath coupling is decreased (which also decreases the initial energy shift between the donor and acceptor states) or the initial shift is removed altogether, both the PBME and FB results agree better with the QCLE-based surface-hopping results. These findings highlight the challenges posed by various conditions such as a time-dependent external field, the strength of the subsystem-bath coupling, and the degree of asymmetry on the accuracy of the PBME and FB algorithms.

Rekik, Najeh; Freedman, Holly; Hanna, Gabriel [Department of Chemistry, University of Alberta, Edmonton, Alberta T6G 2G2 (Canada); Hsieh, Chang-Yu [Department of Chemistry, University of Toronto, Toronto, Ontario M5S 3H6 (Canada)

2013-04-14

206

Dynamic sensitivity of photon-dressed atomic ensemble with quantum criticality

We study the dynamic sensitivity of an atomic ensemble dressed by a single-mode cavity field (called a photon-dressed atomic ensemble), which is described by the Dicke model near the quantum critical point. It is shown that when an extra atom in a pure initial state passes through the cavity, the photon-dressed atomic ensemble will experience a quantum phase transition showing an explicit sudden change in its dynamics characterized by the Loschmidt echo of this quantum critical system. With such dynamic sensitivity, the Dicke model can resemble the cloud chamber for detecting a flying particle by the enhanced trajectory due to the classical phase transition.

Huang Jinfeng; Kuang Leman [Key Laboratory of Low-Dimensional Quantum Structures and Quantum Control of Ministry of Education and Department of Physics, Hunan Normal University, Changsha 410081 (China); Li Yong [Department of Physics, The University of Hong Kong, Pokfulam Road, Hong Kong (China); Liao Jieqiao; Sun, C. P. [Institute of Theoretical Physics, Chinese Academy of Sciences, Beijing 100190 (China)

2009-12-15

207

Loop quantum cosmology of Bianchi IX: Effective dynamics

We study numerically the solutions to the effective equations of Bianchi IX spacetimes within Loop Quantum Cosmology. We consider Bianchi IX models with and without inverse triad corrections whose matter content is a scalar field without mass. The solutions are classified using the classical observables. We show that both effective theories --with lapse N=V and N=1-- solve the big bang singularity and reproduce the classical dynamics far from the bounce. Moreover, due to the spatial compactness, there is an infinity number of bounces and recollapses. We study the limit of large volume and show that both effective theories reproduce the same dynamics, thus recovering general relativity. We implement a procedure to identify amongst the Bianchi IX solutions, those that behave like k=0,1 FLRW as well as Bianchi I, II, and VII_0 models. The effective solutions exhibit Bianchi I phases with Bianchi II transitions and also Bianchi VII_0 phases, which had not been studied before, at the quantum nor effective level. We comment on the possible implications of these results for a quantum modification to the classical BKL behaviour.

Alejandro Corichi; Edison Montoya

2015-02-09

208

We investigate the thermodynamic consequences of the distribution of rotational conformations of polyisoprene on the elastic response of a network chain. In contrast to the classical theory of rubber elasticity, which associates the elastic force with the distribution of end-to-end distances, we find that the distribution of chain contour lengths provides a simple mechanism for an elastic force. Entropic force constants were determined for small contour length extensions of chains constructed as a series of localized kinks, with each kink containing between one and five cis-1,4-isoprene units. The probability distributions for the kink end-to-end distances were computed by two methods: (1) by constructing a Boltzmann distribution from the lengths corresponding to the minimum energy dihedral rotational conformations, obtained by optimizing isoprene using first principles density functional theory, and (2) by sampling the trajectories of molecular dynamics simulations of an isolated molecule composed of five isoprene units. Analogous to the well-known tube model of elasticity, we make the assumption that, for small strains, the chain is constrained by its surrounding tube, and can only move, by a process of reptation, along the primitive path of the contour. Assuming that the chain entropy is Boltzmann's constant times the logarithm of the contour length distribution, we compute the tensile force constants for chain contour length extension as the change in entropy times the temperature. For a chain length typical of moderately crosslinked rubber networks (78 isoprene units), the force constants range between 0.004 and 0.033 N/m, depending on the kink size. For a cross-linked network, these force constants predict an initial tensile modulus of between 3 and 8 MPa, which is comparable to the experimental value of 1 MPa. This mechanism is also consistent with other thermodynamic phenomenology. PMID:20815590

Hanson, David E; Martin, Richard L

2010-08-28

209

Thermal Rates of Hydrogen Exchange of Methane with Zeolite: A Direct ab Initio Dynamics Study ab initio dynamics study on the kinetics of the hydrogen exchange of methane with a zeolite model in cracking, isomerization, and alkylation of hydro- carbons. It has been established that such chemical

Truong, Thanh N.

210

Arrow of time in generalized quantum theory and its classical limit dynamics

In this paper we have studied a generalized quantum theory and its consistent classical limit, which possess a well-defined arrow of time in their dynamics. The original quantum theory is defined as analytically dependent on complex time and specified by non-Hermitian Hamiltonian structure.

V. V. Asadov; O. V. Kechkin

2006-08-21

211

Geometry and Dynamics of Quantum State Diffusion

Riemannian metric on real 2n-dimensional space associated with the equation governing complex diffusion of pure states of an open quantum system is introduced and studied. Examples of a qubit under the influence of dephasing and thermal environments are used to show that the curvature of the diffusion metric is a good indicator of the properties of the environment dominated evolution and its stability.

Nikola Buric

2007-04-11

212

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

213

Dynamics in the quantum/classical limit based on selective use of the quantum potential

NASA Astrophysics Data System (ADS)

A classical limit of quantum dynamics can be defined by compensation of the quantum potential in the time-dependent Schrödinger equation. The quantum potential is a non-local quantity, defined in the trajectory-based form of the Schrödinger equation, due to Madelung, de Broglie, and Bohm, which formally generates the quantum-mechanical features in dynamics. Selective inclusion of the quantum potential for the degrees of freedom deemed "quantum," defines a hybrid quantum/classical dynamics, appropriate for molecular systems comprised of light and heavy nuclei. The wavefunction is associated with all of the nuclei, and the Ehrenfest, or mean-field, averaging of the force acting on the classical degrees of freedom, typical of the mixed quantum/classical methods, is avoided. The hybrid approach is used to examine evolution of light/heavy systems in the harmonic and double-well potentials, using conventional grid-based and approximate quantum-trajectory time propagation. The approximate quantum force is defined on spatial domains, which removes unphysical coupling of the wavefunction fragments corresponding to distinct classical channels or configurations. The quantum potential, associated with the quantum particle, generates forces acting on both quantum and classical particles to describe the backreaction.

Garashchuk, Sophya; Dell'Angelo, David; Rassolov, Vitaly A.

2014-12-01

214

Clocks And Dynamics In Quantum Mechanics

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

Michael York

2014-07-11

215

Switching Quantum Dynamics for Fast Stabilization

Control strategies for dissipative preparation of target quantum states, both pure and mixed, and subspaces are obtained by switching between a set of available semigroup generators. We show that the class of problems of interest can be recast, from a control--theoretic perspective, into a switched-stabilization problems for linear dynamics. This is attained by a suitable affine transformation of the coherence-vector representation. In particular, we propose and compare stabilizing time-based and state-based switching rules for entangled state preparation, showing that the latter not only ensure faster convergence with respect to non-switching methods, but can designed so that it retains robustness with respect to initialization, as long as the target is a pure state or a subspace.

Pierre Scaramuzza; Francesco Ticozzi

2015-02-25

216

Moyal quantum mechanics: The semiclassical Heisenberg dynamics

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

217

An Integrated Hierarchical Dynamic Quantum Secret Sharing Protocol

NASA Astrophysics Data System (ADS)

Generalizing the notion of dynamic quantum secret sharing (DQSS), a simplified protocol for hierarchical dynamic quantum secret sharing (HDQSS) is proposed and it is shown that the protocol can be implemented using any existing protocol of quantum key distribution, quantum key agreement or secure direct quantum communication. The security of this proposed protocol against eavesdropping and collusion attacks is discussed with specific attention towards the issues related to the composability of the subprotocols that constitute the proposed protocol. The security and qubit efficiency of the proposed protocol is also compared with that of other existing protocols of DQSS. Further, it is shown that it is possible to design a semi-quantum protocol of HDQSS and in principle, the protocols of HDQSS can be implemented using any quantum state. It is also noted that the completely orthogonal-state-based realization of HDQSS protocol is possible and that HDQSS can be experimentally realized using a large number of alternative approaches.

Mishra, Sandeep; Shukla, Chitra; Pathak, Anirban; Srikanth, R.; Venugopalan, Anu

2015-02-01

218

Protecting conditional quantum gates by robust dynamical decoupling.

Dephasing--phase randomization of a quantum superposition state--is a major obstacle for the realization of high fidelity quantum logic operations. Here, we implement a two-qubit controlled-NOT gate using dynamical decoupling (DD), despite the gate time being more than 1 order of magnitude longer than the intrinsic coherence time of the system. For realizing this universal conditional quantum gate, we have devised a concatenated DD sequence that ensures robustness against imperfections of DD pulses that otherwise may destroy quantum information or interfere with gate dynamics. We compare its performance with three other types of DD sequences. These experiments are carried out using a well-controlled prototype quantum system--trapped atomic ions coupled by an effective spin-spin interaction. The scheme for protecting conditional quantum gates demonstrated here is applicable to other physical systems, such as nitrogen vacancy centers, solid state nuclear magnetic resonance, and circuit quantum electrodynamics. PMID:25167390

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

2013-05-17

219

New methods for quantum mechanical reaction dynamics

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

220

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

221

Matrix metalloproteinases (MMPs) consist of a class of proteins required for normal tissue function. Their over expression is associated with many disease states and hence the interest in MMPs as drug targets. Almost all MMP inhibitors have been reported to fail in clinical trials due to lack of specificity. Zinc in the binding site of metalloproteinases performs essential biological functions and contributes to the binding affinity of inhibitors. The multiple possibilities for coordination geometry and the consequent charge on the zinc atom indicate that parameters developed are not directly transferable across different families of zinc metalloproteinases with different zinc coordination geometries, active sites and ligand architectures which makes it difficult to evaluate metal-ligand interactions. In order to assist in drug design endeavors for MMP targets, a computationally tractable pathway is presented, comprising docking of small molecule inhibitors against the target MMPs, derivation of quantum mechanical charges on the zinc ion in the active site and the amino acids coordinating with zinc including the inhibitor molecule, molecular dynamics simulations on the docked ligand-MMP complexes and evaluation of binding affinities of the ligand-MMP complexes via an accurate scoring function for zinc containing metalloprotein-ligand complexes. The above pathway was applied to study the interaction of inhibitor Batimastat with MMPs, which resulted in a high correlation between the predicted binding free energies and experiment, suggesting the potential applicability of the pathway. We then proceeded to formulate a few design principles which identify the key protein residues for generating molecules with high affinity and specificity against each of the MMPs. PMID:25611160

Singh, Tanya; Adekoya, Olayiwola Adedotun; Jayaram, B

2015-03-17

222

NASA Astrophysics Data System (ADS)

The predissociation of N2O into the 13A' and 13A? dissociative states for the total angular momentum J>0 is studied by quantum dynamics calculations. The effective Hamiltonian for describing the predissociation is derived from time-dependent wave packet propagation calculations on the triplet potential energy surfaces. The decay rates of individual rovibrational states in the singlet manifold are obtained by diagonalizing the effective Hamiltonian represented in terms of the singlet rovibrational wave functions. The Fermi golden rule is also applied to test its validity in estimating the decay rate distribution. For J=1 and 2, the rovibrational Hamiltonian is constructed by recoupling the coupled state wave functions obtained by a filter diagonalization. For higher values of J, a random coupling model deduced from the calculations for J=1 and 2 is introduced to estimate the decay rate distributions. In order to compare the calculated decay rate distributions with those by a random matrix/transition state theory (RM/TST), the transition states are defined as the eigenvectors of decay rate matrix whose eigenvalues are used for calculating the RM/TST distributions. It is found that the fluctuation of decay rate distribution decreases with increasing J though the calculated distribution shows significant deviation from the RM/TST prediction even for J=20. A simple model is employed to interpret the origin of the decrease of fluctuation in decay rates with J and the deviation from RM/TST. It is concluded that a sharp decay rate distribution comes from an increase of the absolute number of singlet rovibrational states accessible to the transition state due to the K-mixing, though such a K-mixing is limited. The deviation of calculated distribution from the RM/TST one is thus attributed to incomplete energy randomization in the singlet state N2O.

Nakamura, Hisao; Kato, Shigeki

2000-01-01

223

(Studies in quantum field theory)

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

Not Available

1990-01-01

224

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

225

Dynamical quantum error correction: recent achievements and prospects

NASA Astrophysics Data System (ADS)

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

Viola, Lorenza

2013-03-01

226

Quantum approach of mesoscopic magnet dynamics with spin transfer torque

NASA Astrophysics Data System (ADS)

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

Wang, Yong; Sham, L. J.

2013-05-01

227

Quantum Geometry of the Dynamical Space-time

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

Peter Leifer

2006-11-25

228

Genetic simulation of quantum dynamics by the principle of quantum state selection

The simple genetic algorithm is proposed for the simulation of quantum many body dynamics. It uses the selection of entangled quantum states and has the inbuilt absolute decoherence that comes from the limitation of classical memory. It utilizes the "pre-quantum field" in the form of interacting between the different "quantum worlds". It is shown how this selection model can be applied to the problem of molecular association in chemical reactions.

Yuri Ozhigov

2008-01-24

229

Dynamic Homotopy and Landscape Dynamical Set Topology in Quantum Control

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

Jason Dominy; Herschel Rabitz

2012-08-13

230

Dynamic homotopy and landscape dynamical set topology in quantum control

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

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

2012-08-15

231

Quantum Simulation of Dynamical Gauge Field Theories with Superconducting Qubits

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

232

Optimal approach to quantum communication using dynamic programming

Optimal approach to quantum communication using dynamic programming Liang Jiang* , Jacob M. Taylor efficient protocols. Our approach makes use of a dynamic programming- based searching algorithm and asset management to control and estimation of dynamical systems (1). In this article we use

Nehorai, Arye

233

Domain Wall Dynamics near a Quantum Critical Point

dynamics of atomic-size domain walls (DWs). On the atomic level, a DW is a structure that is stable it passes through a DW while the transverse component is almost completely reflected. #12;80 Domain Wall Dynamics near a Quantum Critical Point In this chapter, we focus on the dynamic stability of the DW

234

Critical behavior of dynamically triangulated quantum gravity in four dimensions

NASA Astrophysics Data System (ADS)

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

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

1992-10-01

235

Quantum tomography meets dynamical systems and bifurcations theory

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., E-mail: dardo.goyeneche@cefop.udec.cl [Departamento de Fisíca, Universidad de Concepción, Casilla 160-C, Concepción, Chile and Center for Optics and Photonics, Universidad de Concepción, Casilla 4012, Concepción (Chile); Torre, A. C. de la [Departamento de Física, Universidad Nacional de Mar del Plata, IFIMAR-CONICET, Dean Funes 3350, 7600 Mar del Plata (Argentina)

2014-06-15

236

Confined quantum Zeno dynamics of a watched atomic arrow

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

237

Dynamic characteristics of photonic crystal quantum dot lasers.

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

238

Quantum molecular dynamic simulations of warm dense carbon monoxide.

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

239

Wave Node Dynamics and Revival Symmetry in Quantum Rotors

NASA Astrophysics Data System (ADS)

Symmetries and dynamics of wave nodes in space and time expose principles of quantum theory and its relativistic underpinning. Among these are key principles behind recently discovered dephasing and rephasing phenomena known as revivals. A reexamination of basic Eberly revivals, Berry 'quantum fractal' landscapes, and the 'quantum carpets' of Schleich and co-workers reveals a simple Farey arithmetic and Cn-group revival structure in one of the earliest quantum wave models, the Bohr rotor. These principles may be useful for interpreting modern time-dependent rovibrational spectra. The nodal dynamics of the Bohr rotor is seen to have a quasi-fractal structure similar to that of earlier systems involving chaotic circle maps. The fractal structure is an overlay of discrete versions of Bohr's rotor model. Each N-point Bohr rotor acts like a base-N quantum 'odometer' which performs rational fraction arithmetic. Such systems may have applications for optical information technology and quantum computing.

Harter, William G.

2001-12-01

240

Quantum walks and quantum simulation of wavepacket dynamics with twisted photons

The "quantum walk" has emerged recently as a paradigmatic process for the dynamic simulation of complex quantum systems, entanglement production and quantum computation. Hitherto, photonic implementations of quantum walks have mainly been based on multi-path interferometric schemes in real space. Here, we report the experimental realization of a discrete quantum walk taking place in the orbital angular momentum space of light, both for a single photon and for two simultaneous photons. In contrast to previous implementations, the whole process develops in a single light beam, with no need of interferometers; it requires optical resources scaling linearly with the number of steps; and it allows flexible control of input and output superposition states. Exploiting the latter property, we also simulated the quantum dynamics of Gaussian wavepackets, exploring the system dispersion relation in momentum space and the associated spin-orbit topological features. Our demonstration introduces a novel versatile photonic platform for quantum simulations.

Filippo Cardano; Francesco Massa; Hammam Qassim; Ebrahim Karimi; Sergei Slussarenko; Domenico Paparo; Corrado de Lisio; Fabio Sciarrino; Enrico Santamato; Robert W. Boyd; Lorenzo Marrucci

2014-07-21

241

Quantum Dynamics of Lorentzian Spacetime Foam

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

Ian Redmount; Wai-Mo Suen

1993-09-14

242

Dynamical symmetries for superintegrable quantum systems

We study the dynamical symmetries of a class of two-dimensional superintegrable systems on a 2-sphere, obtained by a procedure based on the Marsden-Weinstein reduction, by considering its shape-invariant intertwining operators. These are obtained by generalizing the techniques of factorization of one-dimensional systems. We firstly obtain a pair of noncommuting Lie algebras su(2) that originate the algebra so(4). By considering three spherical coordinate systems, we get the algebra u(3) that can be enlarged by 'reflexions' to so(6). The bounded eigenstates of the Hamiltonian hierarchies are associated to the irreducible unitary representations of these dynamical algebras.

Calzada, J. A. [Universidad de Valladolid, Departmento de Matematica Aplicada (Spain)], E-mail: juacal@eis.uva.es; Negro, J., E-mail: jnegro@fta.uva.es; Olmo, M. A. del [Universidad de Valladolid, Departmento de Fisica Teorica (Spain)], E-mail: olmo@fta.uva.es

2007-03-15

243

Complexity of controlling quantum many-body dynamics

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

Caneva, T.

244

Noether's theorem for dissipative quantum dynamical semi-groups

NASA Astrophysics Data System (ADS)

Noether's theorem on constants of the motion of dynamical systems has recently been extended to classical dissipative systems (Markovian semi-groups) by Baez and Fong [J. Math. Phys. 54, 013301 (2013)]. We show how to extend these results to the fully quantum setting of quantum Markov dynamics. For finite-dimensional Hilbert spaces, we construct a mapping from observables to completely positive maps that leads to the natural analogue of their criterion of commutativity with the infinitesimal generator of the Markov dynamics. Using standard results on the relaxation of states to equilibrium under quantum dynamical semi-groups, we are able to characterise the constants of the motion under quantum Markov evolutions in the infinite-dimensional setting under the usual assumption of existence of a stationary strictly positive density matrix. In particular, the Noether constants are identified with the fixed point of the Heisenberg picture semi-group.

Gough, John E.; Ratiu, Tudor S.; Smolyanov, Oleg G.

2015-02-01

245

129A Lecture Notes Quantum ElectroDynamics

and relatistic theory of electromagnetism is called Quantum ElectroDynamics, or QED for shot. It combines Dirac this explicitly. 2.1 Classical Maxwell Field The vector potential A and the scalar potential are combined

Murayama, Hitoshi

246

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

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

247

Quantum versus classical hyperfine-induced dynamics in a quantum dota)

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

248

Domain-wall dynamics near a quantum critical point Shengjun Yuan and Hans De Raedt

opportunities to study the quantum dynamics of atomic-size domain walls DWs . On the atomic level, a DW wave speeds up when it passes through a DW while the transverse component is almost completely reflected. In this paper, we focus on the dynamic stability of the DW in the Heisenberg-Ising ferromagnetic

249

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

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

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

2010-04-15

250

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

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

Gary Poon

2009-06-09

251

Loop quantum cosmology of Bianchi IX: Effective dynamics

We study numerically the solutions to the effective equations of Bianchi IX spacetimes within Loop Quantum Cosmology. We consider Bianchi IX models with and without inverse triad corrections whose matter content is a scalar field without mass. The solutions are classified using the classical observables. We show that both effective theories --with lapse N=V and N=1-- solve the big bang singularity and reproduce the classical dynamics far from the bounce. Moreover, due to the spatial compactness, there is an infinity number of bounces and recollapses. We study the limit of large volume and show that both effective theories reproduce the same dynamics, thus recovering general relativity. We implement a procedure to identify amongst the Bianchi IX solutions, those that behave like k=0,1 FLRW as well as Bianchi I, II, and VII_0 models. The effective solutions exhibit Bianchi I phases with Bianchi II transitions and also Bianchi VII_0 phases, which had not been studied before, at the quantum nor effective level. W...

Corichi, Alejandro

2015-01-01

252

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

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

Maniscalco, S

2004-01-01

253

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

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

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

2004-09-01

254

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

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

S. Maniscalco; J. Piilo; F. Intravaia; F. Petruccione; A. Messina

2004-10-01

255

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

256

Higher-order solutions to non-Markovian quantum dynamics via hierarchical functional derivative

Solving realistic quantum systems coupled to an environment is a challenging task. Here we develop a hierarchical functional derivative (HFD) approach for efficiently solving the non-Markovian quantum trajectories of an open quantum system embedded in a bosonic bath. An explicit expression for arbitrary order HFD equation is derived systematically. Moreover, it is found that for an analytically solvable model, this hierarchical equation naturally terminates at a given order and thus becomes exactly solvable. This HFD approach provides a systematic method to study the non-Markovian quantum dynamics of an open system coupled to a bosonic environment.

Da-Wei Luo; Chi-Hang Lam; Lian-Ao Wu; Ting Yu; Hai-Qing Lin; J. Q. You

2015-01-26

257

Editorial: Focus on Dynamics and Thermalization in Isolated Quantum Many-Body Systems

NASA Astrophysics Data System (ADS)

The dynamics and thermalization of classical systems have been extensively studied in the past. However, the corresponding quantum phenomena remain, to a large extent, uncharted territory. Recent experiments with ultracold quantum gases have at last allowed exploration of the coherent dynamics of isolated quantum systems, as well as observation of non-equilibrium phenomena that challenge our current understanding of the dynamics of quantum many-body systems. These experiments have also posed many new questions. How can we control the dynamics to engineer new states of matter? Given that quantum dynamics is unitary, under which conditions can we expect observables of the system to reach equilibrium values that can be predicted by conventional statistical mechanics? And, how do the observables dynamically approach their statistical equilibrium values? Could the approach to equilibrium be hampered if the system is trapped in long-lived metastable states characterized, for example, by a certain distribution of topological defects? How does the dynamics depend on the way the system is perturbed, such as changing, as a function of time and at a given rate, a parameter across a quantum critical point? What if, conversely, after relaxing to a steady state, the observables cannot be described by the standard equilibrium ensembles of statistical mechanics? How would they depend on the initial conditions in addition to the other properties of the system, such as the existence of conserved quantities? The search for answers to questions like these is fundamental to a new research field that is only beginning to be explored, and to which researchers with different backgrounds, such as nuclear, atomic, and condensed-matter physics, as well as quantum optics, can make, and are making, important contributions. This body of knowledge has an immediate application to experiments in the field of ultracold atomic gases, but can also fundamentally change the way we approach and understand many-body quantum systems. This focus issue of New Journal Physics brings together both experimentalists and theoreticians working on these problems to provide a comprehensive picture of the state of the field. Focus on Dynamics and Thermalization in Isolated Quantum Many-Body Systems Contents Spin squeezing of high-spin, spatially extended quantum fields Jay D Sau, Sabrina R Leslie, Marvin L Cohen and Dan M Stamper-Kurn Thermodynamic entropy of a many-body energy eigenstate J M Deutsch Ground states and dynamics of population-imbalanced Fermi condensates in one dimension Masaki Tezuka and Masahito Ueda Relaxation dynamics in the gapped XXZ spin-1/2 chain Jorn Mossel and Jean-Sébastien Caux Canonical thermalization Peter Reimann Minimally entangled typical thermal state algorithms E M Stoudenmire and Steven R White Manipulation of the dynamics of many-body systems via quantum control methods Julie Dinerman and Lea F Santos Multimode analysis of non-classical correlations in double-well Bose-Einstein condensates Andrew J Ferris and Matthew J Davis Thermalization in a quasi-one-dimensional ultracold bosonic gas I E Mazets and J Schmiedmayer Two simple systems with cold atoms: quantum chaos tests and non-equilibrium dynamics Cavan Stone, Yassine Ait El Aoud, Vladimir A Yurovsky and Maxim Olshanii On the speed of fluctuations around thermodynamic equilibrium Noah Linden, Sandu Popescu, Anthony J Short and Andreas Winter A quantum central limit theorem for non-equilibrium systems: exact local relaxation of correlated states M Cramer and J Eisert Quantum quench dynamics of the sine-Gordon model in some solvable limits A Iucci and M A Cazalilla Nonequilibrium quantum dynamics of atomic dark solitons A D Martin and J Ruostekoski Quantum quenches in the anisotropic spin-1?2 Heisenberg chain: different approaches to many-body dynamics far from equilibrium Peter Barmettler, Matthias Punk, Vladimir Gritsev, Eugene Demler and Ehud Altman Crossover from adiabatic to sudden interaction quenches in the Hubbard model: prethermalization and non-equilibrium dynamics Mic

Cazalilla, M. A.; Rigol, M.

2010-05-01

258

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

259

NASA Astrophysics Data System (ADS)

Quantum dynamics calculations via the local reflection matrix method are performed to investigate the effects of the vibration and initial translational energy on the dissociative adsorption of H2 approaching a defective Pt(111) surface at different incident angles and adsorption sites. The sticking probability plot for H2 incident on the top site at 15° shows that as the translational energy is increased, the probability rapidly rises to unity which suggests that H2 is easily adsorbed on the Pt surface. The plot also shows that even though the adsorption process is non-activated, there is a probability that H2 will not be adsorbed on the Pt surface at low translational energies due to quantum mechanical effects. For the rest of the configurations, an S-shaped region is observed in the plots suggesting an activated adsorption process. The plots show that when the initial translational energy (Et) is less that the barrier, H2 sticks to the Pt surface by tunneling through the barrier and when Et is greater than the barrier, H2 sticks on the Pt surface by using its available energy to overcome the barrier. The plots also show significant vibration assisted sticking (VAS) effect for all cases. VAS effect is most prominent for H2 approaching the vacant site at incident angles 15 and 30°.

Natividad, Michelle T.; Arboleda, Nelson B.; Kasai, Hideaki

2014-12-01

260

Quantum and classical dynamics in adiabatic computation

NASA Astrophysics Data System (ADS)

Adiabatic transport provides a powerful way to manipulate quantum states. By preparing a system in a readily initialized state and then slowly changing its Hamiltonian, one may achieve quantum states that would otherwise be inaccessible. Moreover, a judicious choice of final Hamiltonian whose ground state encodes the solution to a problem allows adiabatic transport to be used for universal quantum computation. However, the dephasing effects of the environment limit the quantum correlations that an open system can support and degrade the power of such adiabatic computation. We quantify this effect by allowing the system to evolve over a restricted set of quantum states, providing a link between physically inspired classical optimization algorithms and quantum adiabatic optimization. This perspective allows us to develop benchmarks to bound the quantum correlations harnessed by an adiabatic computation. We apply these to the D-Wave Vesuvius machine with revealing—though inconclusive—results.

Crowley, P. J. D.; Ä?uri?, T.; Vinci, W.; Warburton, P. A.; Green, A. G.

2014-10-01

261

Many-Body Quantum Spin Dynamics with Monte Carlo Trajectories on a Discrete Phase Space

NASA Astrophysics Data System (ADS)

Interacting spin systems are of fundamental relevance in different areas of physics, as well as in quantum information science and biology. These spin models represent the simplest, yet not fully understood, manifestation of quantum many-body systems. An important outstanding problem is the efficient numerical computation of dynamics in large spin systems. Here, we propose a new semiclassical method to study many-body spin dynamics in generic spin lattice models. The method is based on a discrete Monte Carlo sampling in phase space in the framework of the so-called truncated Wigner approximation. Comparisons with analytical and numerically exact calculations demonstrate the power of the technique. They show that it correctly reproduces the dynamics of one- and two-point correlations and spin squeezing at short times, thus capturing entanglement. Our results open the possibility to study the quantum dynamics accessible to recent experiments in regimes where other numerical methods are inapplicable.

Schachenmayer, J.; Pikovski, A.; Rey, A. M.

2015-01-01

262

NASA Astrophysics Data System (ADS)

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

Dattani, Nikesh S.

2013-06-01

263

Nonlinear dynamics and quantum entanglement in optomechanical systems.

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

264

Confined quantum Zeno dynamics of a watched atomic arrow

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

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

2014-05-06

265

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

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

2011-09-21

266

Quantum dynamics of CO-H2 in full dimensionality.

Accurate rate coefficients for molecular vibrational transitions due to collisions with H2, critical for interpreting infrared astronomical observations, are lacking for most molecules. Quantum calculations are the primary source of such data, but reliable values that consider all internal degrees of freedom of the collision complex have only been reported for H2-H2 due to the difficulty of the computations. Here we present essentially exact, full-dimensional dynamics computations for rovibrational quenching of CO due to H2 impact. Using a high-level six-dimensional potential surface, time-independent scattering calculations, within a full angular momentum coupling formulation, were performed for the de-excitation of vibrationally excited CO. Agreement with experimentally determined results confirms the accuracy of the potential and scattering computations, representing the largest of such calculations performed to date. This investigation advances computational quantum dynamical studies representing initial steps towards obtaining CO-H2 rovibrational quenching data needed for astrophysical modelling. PMID:25800802

Yang, Benhui; Zhang, P; Wang, X; Stancil, P C; Bowman, J M; Balakrishnan, N; Forrey, R C

2015-01-01

267

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

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

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

2011-09-15

268

Programmable quantum simulation by dynamic Hamiltonian engineering

NASA Astrophysics Data System (ADS)

Quantum simulation is a promising near term application for quantum information processors with the potential to solve computationally intractable problems using just a few dozen interacting qubits. A range of experimental platforms have recently demonstrated the basic functionality of quantum simulation applied to quantum magnetism, quantum phase transitions and relativistic quantum mechanics. However, in all cases, the physics of the underlying hardware restricts the achievable inter-particle interactions and forms a serious constraint on the versatility of the simulators. To broaden the scope of these analog devices, we develop a suite of pulse sequences that permit a user to efficiently realize average Hamiltonians that are beyond the native interactions of the system. Specifically, this approach permits the generation of all symmetrically coupled translation-invariant two-body Hamiltonians with homogeneous on-site terms, a class which includes all spin-1/2 XYZ chains, but generalized to include long-range couplings. Our work builds on previous work proving that universal simulation is possible using both entangling gates and single-qubit unitaries. We show that determining the appropriate ‘program’ of unitary pulse sequences which implements an arbitrary Hamiltonian transformation can be formulated as a linear program over functions defined by those pulse sequences, running in polynomial time and scaling efficiently in hardware resources. Our analysis extends from circuit model quantum information to adiabatic quantum evolutions, representing an important and broad-based success in applying functional analysis to the field of quantum information.

Hayes, David; Flammia, Steven T.; Biercuk, Michael J.

2014-08-01

269

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

270

A study of Quantum Correlation for Three Qubit States under the effect of Quantum Noisy Channels

We study the dynamics of quantum dissension for three qubit states in various dissipative channels such as amplitude damping, dephasing and depolarizing. Our study is solely based on Markovian environments where quantum channels are without memory and each qubit is coupled to its own environment. We start with mixed GHZ, mixed W, mixture of separable states, a mixed biseparable state, as the initial states and mostly observe that the decay of quantum dissension is asymptotic in contrast to sudden death of quantum entanglement in similar environments. This is a clear indication of the fact that quantum correlation in general is more robust against the effect of noise. However, for a given class of initial mixed states we find a temporary leap in quantum dissension for a certain interval of time. More precisely, we observe the revival of quantum correlation to happen for certain time period. This signifies that the measure of quantum correlation such as quantum discord, quantum dissension, defined from the information theoretic perspective is different from the correlation defined from the entanglement-separability paradigm and can increase under the effect of the local noise. We also study the effects of these channels on the monogamy score of each of these initial states. Interestingly, we find that for certain class of states and channels, there is change from negative values to positive values of the monogamy score with classical randomness as well as with time. This gives us an important insight in obtaining states which are freely sharable (polygamous state) from the states which are not freely sharable (monogamous). This is indeed a remarkable feature, as we can create monogamous states from polygamous states Monogamous states are considered to have more signatures of quantum ness and can be used for security purpose.

Pratik K. Sarangi; Indranil Chakrabarty

2014-11-27

271

Quantum computation in continuous time using dynamic invariants

NASA Astrophysics Data System (ADS)

We introduce an approach for quantum computing in continuous time based on the Lewis-Riesenfeld dynamic invariants. This approach allows, under certain conditions, for the design of quantum algorithms running on a nonadiabatic regime. We show that the relaxation of adiabaticity can be achieved by processing information in the eigenlevels of a time dependent observable, namely, the dynamic invariant operator. Moreover, we derive the conditions for which the computation can be implemented by time independent as well as by adiabatically varying Hamiltonians. We illustrate our results by providing the implementation of both Deutsch-Jozsa and Grover algorithms via dynamic invariants.

Sarandy, M. S.; Duzzioni, E. I.; Serra, R. M.

2011-09-01

272

Quantum heat bath for spin-lattice dynamics

NASA Astrophysics Data System (ADS)

Quantization of spin-wave excitations necessitates the reconsideration of the classical fluctuation-dissipation relation (FDR) used for temperature control in spin-lattice dynamics simulations of ferromagnetic metals. In this paper, Bose-Einstein statistics is used to reinterpret the Langevin dynamics of both lattice and spins, allowing quantum statistics to be mimicked in canonical molecular dynamics simulations. The resulting quantum heat baths are tested by calculating the specific heats and magnetization over a wide temperature range, from 0 K to above the Curie temperature, with molecular dynamics (MD), spin dynamics (SD), and spin-lattice dynamics (SLD) simulations. The results are verified with experimental data and available theoretical analysis. Comparison with classical results also shows the importance of quantization effects for spin excitations in all the ferromagnetically ordered configurations.

Woo, C. H.; Wen, Haohua; Semenov, A. A.; Dudarev, S. L.; Ma, Pui-Wai

2015-03-01

273

Phenol-benzene complexation dynamics: Quantum chemistry calculation, molecular dynamics simulations the nature and dynamics of the phenol-benzene complex in the mixed solvent, benzene/CCl4. Under thermal used for the phenol-benzene interaction in the MD simulations is in good accord with the highest level

Fayer, Michael D.

274

NASA Astrophysics Data System (ADS)

A quantum sampling algorithm for the interpolation of diabatic potential energy matrices by the Grow method is introduced. The new procedure benefits from penetration of the wave packet into classically forbidden regions, and the accurate quantum mechanical description of nonadiabatic transitions. The increased complexity associated with running quantum dynamics is reduced by using approximate low order expansions of the nuclear wave function within a Multi-configuration time-dependent Hartree scheme during the Grow process. The sampling algorithm is formulated and applied for three representative test cases, demonstrating the recovery of analytic potentials by the interpolated ones, and the convergence of a dynamic observable.

Godsi, Oded; Collins, Michael A.; Peskin, Uri

2010-03-01

275

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

276

Programmable quantum simulation by dynamic Hamiltonian engineering

Quantum simulation is a promising near term application for mesoscale quantum information processors, with the potential to solve computationally intractable problems at the scale of just a few dozen interacting quantum systems. Recent experiments in a range of technical platforms have demonstrated the basic functionality of quantum simulation applied to quantum magnetism, quantum phase transitions, and relativistic quantum mechanics. In all cases, the underlying hardware platforms restrict the achievable inter-particle interaction, forming a serious constraint on the ability to realize a versatile, programmable quantum simulator. In this work, we address this problem by developing novel sequences of unitary operations that engineer desired effective Hamiltonians in the time-domain. The result is a hybrid programmable analog simulator permitting a broad class of interacting spin-lattice models to be generated starting only with an arbitrary long-range native inter-particle interaction and single-qubit addressing. Specifically, our approach permits the generation of all symmetrically coupled translation-invariant two-body Hamiltonians with homogeneous on-site terms, a class which includes all spin-1/2 XYZ chains, but generalized to include long-range couplings. Building on previous work proving that universal simulation is possible using both entangling gates and single-qubit unitaries, we show that determining the "program" of unitary pulses to implement an arbitrary spin Hamiltonian can be formulated as a linear program that runs in polynomial time and scales efficiently in hardware resources. Our analysis extends from circuit model quantum information to adiabatic quantum evolutions, where our approach allows for the creation of non-native ground state solutions to a computation.

David L. Hayes; Steven T. Flammia; Michael J. Biercuk

2014-06-18

277

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

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

Matthew F. Brown

2014-07-10

278

NASA Astrophysics Data System (ADS)

Exciton dephasing and relaxation dynamics are studied in a GaAs quantum dot ensemble using optical twodimensional Fourier transform spectroscopy. We measure the temperature and excitation-density dependence of the exciton ground-state homogeneous lineshape of quantum dots within the ensemble and show that acoustic phonon sidebands are absent. The linewidth increases nonlinearly with temperature from 6 to 50 K and the behavior is well-described by an Arrhenius equation with an offset. The absence of a phonon-activation peak in the spectra reveals that elastic exciton-phonon scattering is the primary dephasing mechanism and the results can be explained qualitatively using an extension of the independent Boson model that includes quadratic coupling in the phonon displacement coordinates. At temperatures >= 35 K, spectral features associated with phonon-assisted population transfer of excitons out of the quantum dots and into quantum wells states begin to appear.

Moody, Galan; Siemens, Mark E.; Bristow, Alan D.; Dai, Xingcan; Karaiskaj, Denis; Bracker, Allan S.; Gammon, Daniel; Cundiff, Steven T.

2012-03-01

279

Lectures on dynamical models for quantum measurements

NASA Astrophysics Data System (ADS)

In textbooks, ideal quantum measurements are described in terms of the tested system only by the collapse postulate and Born's rule. This level of description offers a rather flexible position for the interpretation of quantum mechanics. Here we analyse an ideal measurement as a process of interaction between the tested system S and an apparatus A, so as to derive the properties postulated in textbooks. We thus consider within standard quantum mechanics the measurement of a quantum spin component ?z by an apparatus A, being a magnet coupled to a bath. We first consider the evolution of the density operator of S + A describing a large set of runs of the measurement process. The approach describes the disappearance of the off-diagonal terms ("truncation") of the density matrix as a physical effect due to A, while the registration of the outcome has classical features due to the large size of the pointer variable, the magnetization. A quantum ambiguity implies that the density matrix at the final time can be decomposed on many bases, not only the one of the measurement. This quantum oddity prevents to connect individual outcomes to measurements, a difficulty known as the "measurement problem". It is shown that it is circumvented by the apparatus as well, since the evolution in a small time interval erases all decompositions, except the one on the measurement basis. Once one can derive the outcome of individual events from quantum theory, the so-called collapse of the wavefunction or the reduction of the state appears as the result of a selection of runs among the original large set. Hence nothing more than standard quantum mechanics is needed to explain features of measurements. The employed statistical formulation is advocated for the teaching of quantum theory.

Nieuwenhuizen, Theo M.; Perarnau-Llobet, Marti; Balian, Roger

2014-06-01

280

Linear Optics Simulation of Quantum Non-Markovian Dynamics

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

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

2012-01-01

281

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

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

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. PMID:20668246

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

2010-01-01

283

Carrier dynamics in site- and structure-controlled InGaN/GaN quantum dots

NASA Astrophysics Data System (ADS)

We report on the carrier dynamics in InGaN/GaN dot-in-nanowire quantum dots, revealed by a systematic mapping between the optical properties and structural parameters of the quantum dots. Such a study is made possible by using quantum dots with precisely controlled locations and sizes. We show that the carrier dynamics is governed by two competing mechanisms: (1) Excitons are protected from surface recombination by a potential barrier formed due to strain relaxation at the sidewall surface. (2) Excitons can overcome the potential barrier by tunneling and thermal activation. This carrier dynamics model successfully explains the following surprising experimental findings on individual quantum dots. First, there exist strong statistical correlations among multiple optical properties of many individual quantum dots, despite variations of these properties resulting from inevitable structural variations among the quantum dots. Second, the antibunching property of the quantum dot emission exhibits an abnormal ladle-shaped dependence on the decay time and temperature. Our results can guide the way toward nitride-based high-temperature single-photon emitters and nanophotonic devices.

Zhang, Lei; Hill, Tyler A.; Teng, Chu-Hsiang; Demory, Brandon; Ku, Pei-Cheng; Deng, Hui

2014-12-01

284

Excited-state quantum phase transitions and periodic dynamics

NASA Astrophysics Data System (ADS)

We investigate signatures of the excited-state quantum phase transition in the periodic dynamics of the Lipkin-Meshkov-Glick model and the Tavis-Cummings model. In the thermodynamic limit, expectation values of observables in eigenstates of the system can be calculated using classical trajectories. Motivated by this, we suggest a method based on the time evolution of the finite-size system to find singularities in observables, which arise due to the excited-state quantum phase transition.

Engelhardt, G.; Bastidas, V. M.; Kopylov, W.; Brandes, T.

2015-01-01

285

Controlling quantum systems by embedded dynamical decoupling schemes

A dynamical decoupling method is presented which is based on embedding a deterministic decoupling scheme into a stochastic one. This way it is possible to combine the advantages of both methods and to increase the suppression of undesired perturbations of quantum systems significantly even for long interaction times. As a first application the stabilization of a quantum memory is discussed which is perturbed by one-and two-qubit interactions.

Oliver Kern; Gernot Alber

2005-06-05

286

Dynamical invariants for quantum control of four-level systems

NASA Astrophysics Data System (ADS)

We present a Lie-algebraic classification and detailed construction of the dynamical invariants, also known as Lewis-Riesenfeld invariants, of the four-level systems including two-qubit systems which are most relevant and sufficiently general for quantum control and computation. These invariants not only solve the time-dependent Schrödinger equation of four-level systems exactly but also enable the control, and hence quantum computation based on which, of four-level systems fast and beyond adiabatic regimes.

Güngördü, Utkan; Wan, Yidun; Fasihi, Mohammad Ali; Nakahara, Mikio

2012-12-01

287

The dynamical properties of liquid water play an important role in many processes in Nature. In this paper we focus on the infrared (IR) absorption spectrum of liquid water based on the linearized semiclassical initial value representation (LSC-IVR) with the local Gaussian approximation (LGA) [Liu and Miller, J. Chem. Phys. 131, 074113 (2009)] and an ab initio based, flexible, polarizable Thole-type model (TTM3-F) [Fanourgakis and Xantheas, J. Chem. Phys. 128, 074506 (2008)]. Although the LSC-IVR (LGA) gives the exact result for the isolated 3-dimensional shifted harmonic stretching model, it yields a blue-shifted peak position for the more realistic anharmonic stretching potential. By using the short time information of the LSCIVR correlation function, however, it is shown how one can obtain more accurate results for the position of the stretching peak. Due to the physical decay in the condensed phase system, the LSC-IVR (LGA) is a good and practical approximate quantum approach for the IR spectrum of liquid water. The present results offer valuable insight into future attempts to improve the accuracy of the TTM3-F potential in reproducing the IR spectrum of liquid water.

Liu, Jianbo; Miller, William H.; Fanourgakis, G. S.; Xantheas, Sotiris S.; Imoto, Sho; Saito, Shinji

2011-12-28

288

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

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

2011-12-28

289

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. PMID:23202934

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

2012-01-01

290

Quantum Dynamics of a Bose Superfluid Vortex

We derive a fully quantum-mechanical equation of motion for a vortex in a 2-dimensional Bose superfluid in the temperature regime where the normal fluid density ?[subscript n](T) is small. The coupling between the vortex ...

Thompson, Lara

291

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

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

292

Microscopic Studies of Quantum Phase Transitions in Optical Lattices

NASA Astrophysics Data System (ADS)

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

Bakr, Waseem S.

2011-12-01

293

Simulating the dynamical quantum Hall effect with superconducting qubits

NASA Astrophysics Data System (ADS)

We propose an experimental scheme to simulate the dynamical quantum Hall effect and the related interaction-induced topological transition with a superconducting-qubit array. We show that a one-dimensional Heisenberg model with tunable parameters can be realized in an array of superconducting qubits. The quantized plateau, which is a feature of the dynamical quantum Hall effect, will emerge in the Berry curvature of the superconducting qubits as a function of the coupling strength between nearest-neighbor qubits. We numerically calculate the Berry curvatures of two-, four-, and six-qubit arrays and find that the interaction-induced topological transition can be easily observed with the simplest two-qubit array. Furthermore, we analyze some practical conditions in typical experiments for observing this dynamical quantum Hall effect.

Yang, Xu-Chen; Zhang, Dan-Wei; Xu, Peng; Yu, Yang; Zhu, Shi-Liang

2015-02-01

294

Simulating dynamical quantum Hall effect with superconducting qubits

We propose an experimental scheme to simulate the dynamical quantum Hall effect and the related interaction-induced topological transition with a superconducting-qubit array. We show that a one-dimensional Heisenberg model with tunable parameters can be realized in an array of superconducting qubits. The quantized plateaus, which is a feature of the dynamical quantum Hall effect, will emerge in the Berry curvature of the superconducting qubits as a function of the coupling strength between nearest neighbor qubits. We numerically calculate the Berry curvatures of two-, four- and six-qubit arrays, and find that the interaction-induced topological transition can be easily observed with the simplest two-qubit array. Furthermore, we analyze some practical conditions in typical experiments for observing such dynamical quantum Hall effect.

Xu-Chen Yang; Dan-Wei Zhang; Peng Xu; Yang Yu; Shi-Liang Zhu

2015-01-20

295

Optimal approach to quantum communication using dynamic programming

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 via 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 new, 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.

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

2007-10-31

296

Optimal approach to quantum communication using dynamic programming

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. PMID:17959783

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

2007-01-01

297

A Quantum Cosmological Model With Static and Dynamic Wormholes

Quantization is performed of a Friedmann-Robertson-Walker universe filled with a conformally invariant scalar field and a perfect fluid with equation of state $p=\\alpha \\rho$. A well-known discrete set of static quantum wormholes is shown to exist for radiation ($\\alpha =1/3$), and a novel continuous set is found for cosmic strings ($\\alpha = -1/3$), the latter states having throat radii of any size. In both cases wave-packet solutions to the Wheeler-DeWitt equation are obtained with all the properties of evolving quantum wormholes. In the case of a radiation fluid, a detailed analysis of the quantum dynamics is made in the context of the Bohm-de Broglie interpretation. It is shown that a repulsive quantum force inversely proportional to the cube of the scale factor prevents singularities in the quantum domain. For the states considered, there are no particle horizons either.

N. A. Lemos; G. A. Monerat

2002-10-17

298

Efficient measurement of quantum dynamics via compressive sensing.

The resources required to characterize the dynamics of engineered quantum systems--such as quantum computers and quantum sensors--grow exponentially with system size. Here we adapt techniques from compressive sensing to exponentially reduce the experimental configurations required for quantum process tomography. Our method is applicable to processes that are nearly sparse in a certain basis and can be implemented using only single-body preparations and measurements. We perform efficient, high-fidelity estimation of process matrices of a photonic two-qubit logic gate. The database is obtained under various decoherence strengths. Our technique is both accurate and noise robust, thus removing a key roadblock to the development and scaling of quantum technologies. PMID:21469772

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

2011-03-11

299

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

300

Path Integrals and Alternative Effective Dynamics in Loop Quantum Cosmology

The alternative dynamics of loop quantum cosmology is examined by the path integral formulation. We consider the spatially flat FRW models with a massless scalar field, where the alternative quantization inherit more features from full loop quantum gravity. The path integrals can be formulated in both timeless and deparameterized frameworks. It turns out that the effective Hamiltonians derived from the two different viewpoints are equivalent to each other. Moreover, the first-order modified Friedmann equations are derived and predict quantum bounces for contracting universe, which coincide with those obtained in canonical theory.

Li Qin; Guo Deng; Yongge Ma

2012-06-06

301

We investigate the influence of the electron-phonon interaction on the decay dynamics of a quantum dot coupled to an optical microcavity. We show that the electron-phonon interaction has important consequences on the dynamics, especially when the quantum dot and cavity are tuned out of resonance, in which case the phonons may add or remove energy leading to an effective non-resonant coupling between quantum dot and cavity. The system is investigated using two different theoretical approaches: (i) a second-order expansion in the bare phonon coupling constant, and (ii) an expansion in a polaron-photon coupling constant, arising from the polaron transformation which allows an accurate description at high temperatures. In the low temperature regime we find excellent agreement between the two approaches. An extensive study of the quantum dot decay dynamics is performed, where important parameter dependencies are covered. We find that in general the electron-phonon interaction gives rise to a greatly increased bandwidth of the coupling between quantum dot and cavity. At low temperature an asymmetry in the quantum dot decay rate is observed, leading to a faster decay when the quantum dot has a larger energy than to the cavity. We explain this as due to the absence of phonon absorption processes. Furthermore, we derive approximate analytical expressions for the quantum dot decay rate, applicable when the cavity can be adiabatically eliminated. The expressions lead to a clear interpretation of the physics and emphasizes the important role played by the effective phonon density, describing the availability of phonons for scattering, in quantum dot decay dynamics. Based on the analytical expressions we present the parameter regimes where phonon effects are expected to be important. Also, we include all technical developments in appendices.

P. Kaer; T. R. Nielsen; P. Lodahl; A. -P. Jauho; J. Mork

2012-08-16

302

Quantum correlation dynamics in photosynthetic processes assisted by molecular vibrations

During the long course of evolution, nature has learnt how to exploit quantum effects. In fact, recent experiments reveal the existence of quantum processes whose coherence extends over unexpectedly long time and space ranges. In particular, photosynthetic processes in light-harvesting complexes display a typical oscillatory dynamics ascribed to quantum coherence. Here, we consider the simple model where a dimer made of two chromophores is strongly coupled with a quasi-resonant vibrational mode. We observe the occurrence of wide oscillations of genuine quantum correlations, between electronic excitations and the environment, represented by vibrational bosonic modes. Such a quantum dynamics has been unveiled through the calculation of the negativity of entanglement and the discord, indicators widely used in quantum information for quantifying the resources needed to realize quantum technologies. We also discuss the possibility of approximating additional weakly-coupled off-resonant vibrational modes, simulating the disturbances induced by the rest of the environment, by a single vibrational mode. Within this approximation, one can show that the off-resonant bath behaves like a classical source of noise.

G. L. Giorgi; M. Roncaglia; F. A. Raffa; M. Genovese

2015-01-30

303

Noise-resilient quantum evolution steered by dynamical decoupling

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

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

2013-01-01

304

Dynamical phase transitions as a resource for quantum enhanced metrology

We consider the general problem of estimating an unknown control parameter of an open quantum system. We establish a direct relation between the evolution of both system and environment and the precision with which the parameter can be estimated. We show that when the open quantum system undergoes a first-order dynamical phase transition the quantum Fisher information (QFI), which gives the upper bound on the achievable precision of any measurement of the system and environment, becomes quadratic in observation time (cf. "Heisenberg scaling"). In fact, the QFI is identical to the variance of the dynamical observable that characterises the phases that coexist at the transition, and enhanced scaling is a consequence of the divergence of the variance of this observable at the transition point. This identification allows to establish the finite time scaling of the QFI. Near the transition the QFI is quadratic in time for times shorter than the correlation time of the dynamics. In the regime of enhanced scaling the optimal measurement whose precision is given by the QFI involves measuring both system and output. As a particular realisation of these ideas, we describe a theoretical scheme for quantum enhanced phase estimation using the photons being emitted from a quantum system near the coexistence of dynamical phases with distinct photon emission rates.

Katarzyna Macieszczak; Madalin Guta; Igor Lesanovsky; Juan P. Garrahan

2014-11-14

305

Quantum effects in the dynamics of proton glasses

NASA Astrophysics Data System (ADS)

The dynamics of proton and deuteron glasses has been studied via the NMR spin-lattice relaxation (T1) of 87Rb and O-D...O deuterons down to T=1.6 K in Rb0.50(NH4)0.50H2PO4,Rb0.58(ND4)0.42D2PO4, and Rb0.68(ND4)0.32D2AsO4. In the glassy phase the relaxation rate was found to be anomalously short and temperature independent as T-->0, whereas this effect is absent in pure ferroelectric RbH2PO4. The temperature independence of T1 at low temperatures demonstrates the presence of phonon-assisted tunneling of the proton and the deuteron between the two potential minima in the H bond. The proton and deuteron glass phases are thus quantum rather than classical glasses.

Dolinšek, J.; Ar?on, D.; Zalar, B.; Pirc, R.; Blinc, R.; Kind, R.

1996-09-01

306

Quantum dynamics of the driven and dissipative Rabi model

NASA Astrophysics Data System (ADS)

The Rabi model considers a two-level system (or spin 1/2) coupled to a quantized harmonic oscillator and describes the simplest interaction between matter and light. The recent experimental progress in solid-state circuit quantum electrodynamics has engendered theoretical efforts to quantitatively describe the mathematical and physical aspects of the light-matter interaction beyond the rotating-wave approximation. We develop a stochastic Schrödinger equation approach which enables us to access the strong-coupling limit of the Rabi model and study the effects of dissipation and ac drive in an exact manner. We include the effect of Ohmic noise on the non-Markovian spin dynamics, resulting in Kondo-type correlations, as well as cavity losses. We compute the time evolution of spin variables in various conditions. As a consideration for future work, we discuss the possibility of reaching a steady state with one polariton in realistic experimental conditions.

Henriet, Loïc; Ristivojevic, Zoran; Orth, Peter P.; Le Hur, Karyn

2014-08-01

307

Quantum dynamics and state-dependent affine gauge fields on CP(N-1)

Gauge fields frequently used as an independent construction additional to so-called wave fields of matter. This artificial separation is of course useful in some applications (like Berry's interactions between the "heavy" and "light" sub-systems) but it is restrictive on the fundamental level of "elementary" particles and entangled states. It is shown that the linear superposition of action states and non-linear dynamics of the local dynamical variables form an oscillons of energy representing non-local particles - "lumps" arising together with their "affine gauge potential" agrees with Fubini-Study metric. I use the conservation laws of local dynamical variables (LDV's) during affine parallel transport in complex projective Hilbert space $CP(N-1)$ for twofold aim. Firstly, I formulate the variation problem for the ``affine gauge potential" as system of partial differential equations \\cite{Le1}. Their solutions provide embedding quantum dynamics into dynamical space-time whose state-dependent coordinates related to the qubit spinor subjected to Lorentz transformations of "quantum boosts" and "quantum rotations". Thereby, the problem of quantum measurement being reformulated as the comparison of LDV's during their affine parallel transport in $CP(N-1)$, is inherently connected with space-time emergences. Secondly, the important application of these fields is the completeness of quantum theory. The EPR and Schr\\"odinger's Cat paradoxes are discussed from the point of view of the restored Lorentz invariance due to the affine parallel transport of local Hamiltonian of the soliton-like field.

Peter Leifer

2008-04-11

308

Charge and excitonic-energy transfer phenomena are fundamental for energy conversion in solar cells as well as artificial photosynthesis. Currently, much interest is being paid to light-harvesting and energy transduction processes in supramolecular structures, where nuclear dynamics has a major influence on electronic quantum dynamics. For this reason, the simulation of long range electron transfer in supramolecular structures, under environmental conditions described within an atomistic framework, has been a difficult problem to study. This work describes a coupled quantum mechanics/molecular mechanics method that aims at describing long range charge transfer processes in supramolecular systems, taking into account the atomistic details of large molecular structures, the underlying nuclear motion, and environmental effects. The method is applied to investigate the relevance of electron-nuclei interaction on the mechanisms for photo-induced electron-hole pair separation in dye-sensitized interfaces as well as electronic dynamics in molecular structures. PMID:25767107

da Silva, Robson; Hoff, Diego A; Rego, Luis G C

2015-04-10

309

NASA Astrophysics Data System (ADS)

Charge and excitonic-energy transfer phenomena are fundamental for energy conversion in solar cells as well as artificial photosynthesis. Currently, much interest is being paid to light-harvesting and energy transduction processes in supramolecular structures, where nuclear dynamics has a major influence on electronic quantum dynamics. For this reason, the simulation of long range electron transfer in supramolecular structures, under environmental conditions described within an atomistic framework, has been a difficult problem to study. This work describes a coupled quantum mechanics/molecular mechanics method that aims at describing long range charge transfer processes in supramolecular systems, taking into account the atomistic details of large molecular structures, the underlying nuclear motion, and environmental effects. The method is applied to investigate the relevance of electron–nuclei interaction on the mechanisms for photo-induced electron–hole pair separation in dye-sensitized interfaces as well as electronic dynamics in molecular structures.

da Silva, Robson; Hoff, Diego A.; Rego, Luis G. C.

2015-04-01

310

We study the quantum corrections to the Gross-Pitaevskii equation for two weakly linked Bose-Einstein condensates. The goals are: 1) to investigate dynamical regimes at the borderline between the classical and quantum behaviour of the bosonic field; 2) to search for new macroscopic quantum coherence phenomena not observable with other superfluid/superconducting systems. Quantum fluctuations renormalize the classical Josephson oscillation frequencies. Large amplitude phase oscillations are modulated, exhibiting collapses and revivals. We describe a new inter-well oscillation mode, with a vanishing (ensemble averaged) mean value of the observables, but with oscillating mean square fluctuations. Increasing the number of condensate atoms, we recover the classical Gross-Pitaevskii (Josephson) dynamics, without invoking the symmetry-breaking of the Gauge invariance.

Augusto Smerzi; Srikanth Raghavan

1999-07-12

311

Study of correlations in molecular motion by multiple quantum NMR

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

Tang, J.H.

1981-11-01

312

Nonlocal Memory Effects in the Dynamics of Open Quantum Systems

NASA Astrophysics Data System (ADS)

We explore the possibility to generate nonlocal dynamical maps of an open quantum system through local system-environment interactions. Employing a generic decoherence process induced by a local interaction Hamiltonian, we show that initial correlations in a composite environment can lead to nonlocal open system dynamics which exhibit strong memory effects, although the local dynamics is Markovian. In a model of two entangled photons interacting with two dephasing environments, we find a direct connection between the degree of memory effects and the amount of correlation in the initial environmental state. The results demonstrate that, contrary to conventional wisdom, enlarging an open system can change the dynamics from Markovian to non-Markovian.

Laine, Elsi-Mari; Breuer, Heinz-Peter; Piilo, Jyrki; Li, Chuan-Feng; Guo, Guang-Can

2012-05-01

313

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

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

2012-10-13

314

Interacting bosons in a disordered lattice: Dynamical characterization of the quantum phase diagram

NASA Astrophysics Data System (ADS)

We study the quantum dynamics of interacting bosons in a three-dimensional disordered lattice. We show that the superfluid current induced by an adiabatic acceleration of the disordered lattice undergoes a dynamical instability signaling the onset of the Bose-glass phase. The dynamical superfluid-Bose-glass phase diagram is found in very good agreement with static superfluid fraction calculation. A different boundary is obtained when the disorder is suddenly quenched in a moving periodic lattice. In this case we do not observe a dynamical instability but rather a depletion of the superfluid density. Our analysis is based on a dynamical Gutzwiller approach which we show to reproduce the quantum Monte Carlo static phase diagram in the strong interaction limit.

Buonsante, Pierfrancesco; Pezzè, Luca; Smerzi, Augusto

2015-03-01

315

Coupled electron-phonon transport from molecular dynamics with quantum baths

NASA Astrophysics Data System (ADS)

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

Lü, J. T.; Wang, Jian-Sheng

2009-01-01

316

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

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

Lü, J T; Wang, Jian-Sheng

2009-01-14

317

Theoretical studies of chemical reaction dynamics

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

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

1993-12-01

318

Thermal dynamic modeling study

NASA Technical Reports Server (NTRS)

Some thermal dynamic requirements associated with the space shuttle vehicle are reviewed. Pertinent scaling laws are discussed and recommendations are offered regarding the need for conducting reduced-scale dynamic tests of major components at elevated temperatures. Items considered are the development and interpretation of thermal dynamic structural scaling laws, the identification of major related problem areas and a presentation of viable model fabrication, instrumentation, and test procedures.

Ojalvo, I. U.

1972-01-01

319

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

320

Coherent Quantum Dynamics: What Fluctuations Can Tell

Coherent states provide a natural connection of quantum systems to their classical limit and are employed in various fields of physics. Here we derive general systematic expansions, with respect to quantum parameters, of expectation values of products of arbitrary operators within both oscillator coherent states and SU(2) coherent states. In particular, we generally prove that the energy fluctuations of an arbitrary Hamiltonian are in leading order entirely due to the time dependence of the classical variables. These results add to the list of wellknown properties of coherent states and are applied here to the Lipkin-Meshkov-Glick model, the Dicke model, and to coherent intertwiners in spin networks as considered in Loop Quantum Gravity.

Schliemann, John

2015-01-01

321

Controlling the quantum dynamics of a mesoscopic spin bath in diamond

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. PMID:22536480

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

2012-01-01

322

Quantum and classical correlations in high temperature dynamics of two coupled large spins

NASA Astrophysics Data System (ADS)

We study dynamical correlations of two coupled large spins depending on the time and on the spin quantum numbers. In the high-temperature approximation, we obtain analytical expressions for the mutual informations, quantum and classical parts of correlations. The latter was obtained performing the non-orthogonal projective (POVM) measurements onto the spin coherent states of two spins or one spin, as well as by means of the orthogonal projective measurement of von Neumann. Contribution from quantum correlations is much less than that from classical ones and decreasing with the increase in spin quantum numbers at short times. However, it is not so in a time equal to half of the quantum period.

Zobov, V. E.

2013-01-01

323

Eulerian and Newtonian dynamics of quantum particles

NASA Astrophysics Data System (ADS)

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

Rashkovskiy, S. A.

2013-06-01

324

Optimized dynamical decoupling in a model quantum memory.

Any quantum system, such as those used in quantum information or magnetic resonance, is subject to random phase errors that can dramatically affect the fidelity of a desired quantum operation or measurement. In the context of quantum information, quantum error correction techniques have been developed to correct these errors, but resource requirements are extraordinary. The realization of a physically tractable quantum information system will therefore be facilitated if qubit (quantum bit) error rates are far below the so-called fault-tolerance error threshold, predicted to be of the order of 10(-3)-10(-6). The need to realize such low error rates motivates a search for alternative strategies to suppress dephasing in quantum systems. Here we experimentally demonstrate massive suppression of qubit error rates by the application of optimized dynamical decoupling pulse sequences, using a model quantum system capable of simulating a variety of qubit technologies. We demonstrate an analytically derived pulse sequence, UDD, and find novel sequences through active, real-time experimental feedback. The latter sequences are tailored to maximize error suppression without the need for a priori knowledge of the ambient noise environment, and are capable of suppressing errors by orders of magnitude compared to other existing sequences (including the benchmark multi-pulse spin echo). Our work includes the extension of a treatment to predict qubit decoherence under realistic conditions, yielding strong agreement between experimental data and theory for arbitrary pulse sequences incorporating nonidealized control pulses. These results demonstrate the robustness of qubit memory error suppression through dynamical decoupling techniques across a variety of qubit technologies. PMID:19396139

Biercuk, Michael J; Uys, Hermann; VanDevender, Aaron P; Shiga, Nobuyasu; Itano, Wayne M; Bollinger, John J

2009-04-23

325

Material Phase Causality or a Dynamics-Statistical Interpretation of Quantum Mechanics

The internal phase dynamics of a quantum system interacting with an electromagnetic field is revealed in details. Theoretical and experimental evidences of a causal relation of the phase of the wave function to the dynamics of the quantum system are presented sistematically for the first time. A dynamics-statistical interpretation of the quantum mechanics is introduced.

Koprinkov, I. G. [Department of Applied Physics, Technical University of Sofia, 1756 Sofia (Bulgaria)

2010-11-25

326

Dynamics of a three-photon state interacting with a quantum dot

In this paper, we study the dynamics of the interaction of a three-photon state and a quantum dot embedded in a semiconductor cavity. In the first place, we consider an ideal cavity in which the effects due to the environment are neglected. Under this conditions, the most important feature of the dynamics is its periodicity, which may be seen on the temporal evolution of the light state. The entanglement dynamics, which is studied through the negativity and the linear entropy, shows a periodic behaviour too. On the other hand, when considering the interaction between the cavity and the environment, taking into account both an incoherent pumping and a photon leakage, the dynamics is no longer periodic. Instead, it may be seen that the entanglement reach stationary values, which depend on the incoherent pumping and photon leakage rates. Finally, we discuss the possibility of using this sort of systems for quantum information processing.

Juan Camilo López Carreño; Juan Pablo Restrepo Cuartas; Herbert Vinck Posada

2014-06-11

327

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

328

Theory of dynamic nuclear polarization and feedback in quantum dots

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

Sophia E. Economou; Edwin Barnes

2014-04-06

329

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

The main goal of this program is the development and application of computational methods for studying chemical reaction dynamics and molecular spectroscopy in the gas phase. We are interested in developing rigorous quantum dynamics algorithms for small polyatomic systems and in implementing approximate approaches for complex ones. Particular focus is on the dynamics and kinetics of chemical reactions and on the rovibrational spectra of species involved in combustion processes. This research also explores the potential energy surfaces of these systems of interest using state-of-the-art quantum chemistry methods, and extends them to understand some important properties of materials in condensed phases and interstellar medium as well as in combustion environments.

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

2012-05-29

330

Quantum-structure dependent excitonic carrier dynamics of InxGa1-xN\\/GaN multi-quantum-wells

Excitonic carrier dynamics taking place in InxGa1-xN\\/GaN multi-quantum-well systems have been studied by low temperature picosecond time resolved photoluminescence (LT-TRPL), HR-TEM, XPS, Dynamic TOF-SIMS, and quantum mechanical simulation methods. Both time-integrated and time-resolved photoluminescence spectra of InxGa1-xN\\/GaN multi-quantum-wells with different well thickness and Indium composition were measured at 10 K. We assigned the natural radiative lifetime of each sample from

Sangsu Hong; Yong Seok Kim; Young Joon Yoon; June Sik Park; Bae Kyun Kim; Alexander Fomin; Gyu Han Lee; Je Won Kim; Hyung Koun Cho; Taiha Joo

2006-01-01

331

Dynamical "breaking" of time reversal symmetry and converse quantum ergodicity

It is a common assumption that quantum systems with time reversal invariance and classically chaotic dynamics have energy spectra distributed according to GOE-type of statistics. Here we present a class of systems which fail to follow this rule. We show that for convex billiards of constant width with time reversal symmetry and "almost" chaotic dynamics the energy level distribution is of GUE-type. The effect is due to the lack of ergodicity in the "momentum" part of the phase space and, as we argue, is generic in two dimensions. Besides, we show that certain billiards of constant width in multiply connected domains are of interest in relation to the quantum ergodicity problem. These billiards are quantum ergodic, but not classically ergodic.

Boris Gutkin

2007-04-25

332

Quantum Dynamics and a Semiclassical Description of the Photon.

ERIC Educational Resources Information Center

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

Henderson, Giles

1980-01-01

333

Theoretical method for analyzing quantum dynamics of correlated photons

We present a theoretical method for the efficient analysis of quantum nonlinear dynamics of correlated photons. Since correlated photons can be regarded as a superposition of uncorrelated photons, semiclassical analysis can be applied to this problem. The proposed method is demonstrated for a V-type three-level atom as a nonlinear optical system.

Koshino, Kazuki; Nakatani, Masatoshi [College of Liberal Arts and Sciences, Tokyo Medical and Dental University, 2-8-30 Konodai, Ichikawa 272-0827 (Japan) and PRESTO, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi 332-0012 (Japan)

2009-05-15

334

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

335

Simulation of quantum dynamics based on the quantum stochastic differential equation.

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. PMID:23781156

Li, Ming

2013-01-01

336

Torsion as a dynamic degree of freedom of quantum gravity

The gauge approach to gravity based on the local Lorentz group with a general independent affine connection A_{\\mu cd} is developed. We consider SO(1,3) gauge theory with a Lagrangian quadratic in curvature as a simple model of quantum gravity. The torsion is proposed to represent a dynamic degree of freedom of quantum gravity at scales above the Planckian energy. The Einstein-Hilbert theory is induced as an effective theory due to quantum corrections of torsion via generating a stable gravito-magnetic condensate. We conjecture that torsion possesses an intrinsic quantum nature and can be confined. A minimal Abelian projection for the Lorentz gauge model has been constructed, and an effective theory of the cosmic knot at the Planckian scale is proposed.

Sang-Woo Kim; D. G. Pak

2008-03-05

337

Reaction-Diffusion Processes, Critical Dynamics and Quantum Chains

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

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

1993-02-23

338

Quantum Yang-Mills-Weyl Dynamics in the Schrödinger paradigm

NASA Astrophysics Data System (ADS)

Inspired by F. Wilczek's QCD Lite, quantum Yang-Mills-Weyl Dynamics (YMWD) describes quantum interaction between gauge bosons (associated with a simple gauge group ) and larks (massless chiral fields charged by an irreducible unitary representation of ). Schrödinger representation of this quantum Yang-Mills-Weyl theory is based on a sesqui-holomorphic operator calculus of infinite-dimensional operators with variational derivatives. The spectrum of quantum YMWD in a compact bag is a sequence of eigenvalues convergent to +?. The eigenvalues have finite multiplicities with respect to a von Neumann algebra with a regular trace. The spectrum is inversely proportional to the square of the running coupling constant. The rigorous mathematical theory is nonperturbative with a running coupling constant as the only ad hoc parameter. The application of the first mathematical principles is based on the properties of the compact simple Lie group.

Dynin, A.

2014-04-01

339

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

340

Recovering classical dynamics from coupled quantum systems through continuous measurement

We study the role of continuous measurement in the quantum to classical transition for a system with coupled internal (spin) and external (motional) degrees of freedom. Even when the measured motional degree of freedom can be treated classically, entanglement between spin and motion causes strong measurement back action on the quantum spin subsystem so that classical trajectories are not recovered in this mixed quantum-classical regime. The measurement can extract localized quantum trajectories that behave classically only when the internal action also becomes large relative to ({Dirac_h}/2{pi})

Ghose, Shohini; Alsing, Paul; Deutsch, Ivan; Bhattacharya, Tanmoy; Habib, Salman; Jacobs, Kurt [Department of Physics and Astronomy, University of New Mexico, Albuquerque, New Mexico 87131 (United States); T-8 Theoretical Division, MS B285, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

2003-05-01

341

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

Christopher G. Jesudason

2009-01-01

342

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

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

343

Structural dynamics verification facility study

NASA Technical Reports Server (NTRS)

The need for a structural dynamics verification facility to support structures programs was studied. Most of the industry operated facilities are used for highly focused research, component development, and problem solving, and are not used for the generic understanding of the coupled dynamic response of major engine subsystems. Capabilities for the proposed facility include: the ability to both excite and measure coupled structural dynamic response of elastic blades on elastic shafting, the mechanical simulation of various dynamical loadings representative of those seen in operating engines, and the measurement of engine dynamic deflections and interface forces caused by alternative engine mounting configurations and compliances.

Kiraly, L. J.; Hirchbein, M. S.; Mcaleese, J. M.; Fleming, D. P.

1981-01-01

344

Quantum dynamics and electronic spectroscopy within the framework of wavelets

NASA Astrophysics Data System (ADS)

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

Toutounji, Mohamad

2013-03-01

345

Open quantum system stochastic dynamics with and without the RWA

NASA Astrophysics Data System (ADS)

We study the dynamics of a two-level quantum system interacting with a single frequency electromagnetic field and a stochastic magnetic field, with and without making the rotating wave approximation (RWA). The transformation to the rotating frame does not commute with the stochastic Hamiltonian if the stochastic field has nonvanishing components in the transverse direction, hence, applying the RWA requires transformation of the stochastic terms in the Hamiltonian. For Gaussian white noise, the master equation is derived from the stochastic Schrödinger–Langevin equations, with and without the RWA. With the RWA, the master equation for the density matrix has Lindblad terms with coefficients that are time-dependent (i.e., the master equation is time-local). An approximate analytic expression for the density matrix is obtained with the RWA. For Ornstein–Uhlenbeck noise, as well as other types of colored noise, in contradistinction to the Gaussian white noise case, the non-commutation of the RWA transformation and the noise Hamiltonian can significantly affect the RWA dynamics when ? {{? }corr} 1, where ? is the electromagnetic field frequency and {{? }corr} is the stochastic magnetic field correlation time.

Band, Y. B.

2015-02-01

346

Spatiotemporal dynamics of quantum-well excitons

We investigate the lateral transport of excitons in ZnSe quantum wells by using time-resolved micro-photoluminescence enhanced by the introduction of a solid immersion lens. The spatial and temporal resolutions are 200 nm and 5 ps, respectively. Strong deviation from classical diffusion is observed up to 400 ps. This feature is attributed to the hot-exciton effects, consistent with previous experiments under

Hui Zhao; B. dal Don; S. Moehl; H. Kalt; K. Ohkawa; D. Hommel

2003-01-01

347

Quantum Signatures of Solar System Dynamics

Let w(i) be a period of rotation of the i-th planet around the Sun (or w(j;i) be a period of rotation of j-th satellite around the i-th planet). From empirical observations it is known that the sum of n(i)w(i)=0 (or the sum of n(j)w(j;i)=0) for some integers n(i) (or n(j)), different for different satellite systems. These conditions, known as resonance conditions, make uses of theories such as KAM difficult to implement. The resonances in Solar System are similar to those encountered in old quantum mechanics where applications of methods of celestial mechanics to atomic and molecular physics were highly sucsessful. With such a success, the birth of new quantum mechanics is difficult to understand. In short, the rationale for its birth lies in simplicity with which the same type of calculations are done using new methods capable of taking care of resonances. The solution of quantization puzzle was found by Heisenberg. In this paper new uses of Heisenberg's ideas are found. When superimposed with the equivalence principle of general relativity, they lead to quantum mechanical tratment of observed resonances in Solar System. To test correctness of our theoretical predictions the number of allowed stable orbits for planets and for equatorial stable orbits of satellites of heavy planets is calculated resulting in good agreement with observational data. In addition, the paper briefly discusses quantum mechanical nature of rings of heavy planets and potential usefulness of the obtained results for cosmology.

Arkady L. Kholodenko

2008-10-17

348

Quantum Dynamics of Biological Plasma in the External Coulomb Field

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

349

Quantum-to-classical transition in a system with mixed classical dynamics.

We study how decoherence rules the quantum-classical transition of the kicked harmonic oscillator. The system presents classical dynamics that ranges from regular to strong chaotic behavior depending on the amplitude of the kicks. We show that for regular and mixed classical dynamics, and in the presence of noise, the distance between the classical and quantum phase space distributions is proportional to a single parameter chi identical to K Planck's (eff)(2)/4D(3/2) , which relates the effective Planck constant, Planck's (eff), to the kicking strength, K, and the diffusion constant, D. This relation between classical and quantum distributions is valid when chi<1 , a case that is always attainable in the semiclassical regime, independent of the value of the strength of noise given by D. Our results extend a recent study performed in the chaotic regime. PMID:17279985

Toscano, Fabricio; Wisniacki, Diego A

2006-11-01

350

Quantum vortex dynamics in two-dimensional neutral superfluids

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

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

2010-01-15

351

NASA Astrophysics Data System (ADS)

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

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

2001-04-01

352

Dynamic Langmuir Probe Studies

The effects of circuit parameters, probe configuration, current delays, ; and displacement-current spikes on the results obtained using dynamic Langmuir ; probe methods are outlined. The analysis of these effects is carried out in the ; positive column of a d-c discharge, using pulsedprobe, high-frequency-probe, ; resonance-probe, and fixedprobe--time-varying-plasma measuring methods. (T.F.H.);

R. W. Carlson; T. Okuda; H. J. Oskam

1962-01-01

353

Dynamical decoupling based quantum sensing: Floquet spectroscopy

It is possible to sense the internal dynamics of individual clusters of nuclear spins by observing the coherence decay of a nearby electronic spin: the weak magnetic noise is amplified by a dynamical decoupling sequence of microwave pulses, though it remains challenging to relate experimental traces to underlying atomic-scale structure. For periodic dynamical decoupling control, we show that the Floquet eigenphases and eigenstates of the system provide the most natural framework for data analysis and fingerprinting of complex spin environments, offering more accuracy and insight than the frequencies of the static problem or current alternative models. This approach is fully general but is here tested on sensor spins for which the quantization axis varies as a function of an external parameter; in particular, electron donors in silicon, such as arsenic and bismuth, with regimes of high sensitivity of the decoherence with respect to magnetic fields offer excellent possibilities for sensing.

J. E. Lang; Ren-Bao Liu; T. S. Monteiro

2015-02-27

354

NASA Technical Reports Server (NTRS)

One half of Professor Xiong's effort will investigate robust timing synchronization schemes for dynamically varying characteristics of aviation communication channels. The other half of his time will focus on efficient modulation and coding study for the emerging quantum communications.

Xiong, Fugin

2003-01-01

355

Vibrational Spectra Including Critical Nuclear Quantum Effects Isaiah Sumner and Srinivasan S. Iyengar to study vibrational spectroscopy in clusters inclusive of critical nuclear quantum effects. This approach function, where the wavepacket flux from the quantized particle is combined with classical nuclear

Iyengar, Srinivasan S.

356

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

357

Generalized entanglement in static and dynamic quantum phase transitions

We investigate a class of one-dimensional, exactly solvable anisotropic XY spin-1/2 models in an alternating transverse magnetic field from an entanglement perspective. We find that a physically motivated Lie-algebraic generalized entanglement measure faithfully portraits the static phase diagram -- including second- and fourth-order quantum phase transitions belonging to distinct universality classes. In the simplest time-dependent scenario of a slow quench across a quantum critical point, we identify parameter regimes where entanglement exhibits universal dynamical scaling relative to the static limit.

Shusa Deng; Gerardo Ortiz; Lorenza Viola

2008-02-27

358

Hierarchy of stochastic pure states for open quantum system dynamics.

We derive a hierarchy of stochastic evolution equations for pure states (quantum trajectories) for open quantum system dynamics with non-Markovian structured environments. This hierarchy of pure states (HOPS) is generally applicable and provides the exact reduced density operator as an ensemble average over normalized states. The corresponding nonlinear equations are presented. We demonstrate that HOPS provides an efficient theoretical tool and apply it to the spin-boson model, the calculation of absorption spectra of molecular aggregates, and energy transfer in a photosynthetic pigment-protein complex. PMID:25375694

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

2014-10-10

359

Quantum effects in the dynamics of deeply supercooled water

NASA Astrophysics Data System (ADS)

Despite its simple chemical structure, water remains one of the most puzzling liquids with many anomalies at low temperatures. Combining neutron scattering and dielectric relaxation spectroscopy, we show that quantum fluctuations are not negligible in deeply supercooled water. Our dielectric measurements reveal the anomalously weak temperature dependence of structural relaxation in vapor-deposited water close to the glass transition temperature Tg˜136 K . We demonstrate that this anomalous behavior can be explained well by quantum effects. These results have significant implications for our understanding of water dynamics.

Agapov, A. L.; Kolesnikov, A. I.; Novikov, V. N.; Richert, R.; Sokolov, A. P.

2015-02-01

360

Long-time correlated quantum dynamics of phonon cooling

We investigate the steady-state cooling dynamics of vibrational degrees of freedom related to a nanomechanical oscillator coupled with a laser-pumped quantum dot in an optical resonator. Correlations between phonon-cooling and quantum-dot photon emission processes occur respectively when a photon laser absorption together with a vibrational phonon absorption is followed by photon emission in the optical resonator. Therefore, the detection of photons generated in the cavity mode concomitantly contribute to phonon cooling detection of the nanomechanical resonator.

Sergiu Carlig; Mihai A. Macovei

2014-05-05

361

Dynamic properties of quantum dot distributed feedback lasers

NASA Astrophysics Data System (ADS)

Semiconductor quantum dots (QDs) are nano-structures with three-dimensional spatial confinement of electrons and holes, representing the ultimate case of the application of the size quantization concept to semiconductor hetero-structures. The knowledge about the dynamic properties of QD semiconductor diode lasers is essential to improve the device performance and understand the physics of the QDs. In this dissertation, the dynamic properties of QD distributed feedback lasers (DFBs) are studied. The response function of QD DFBs under external modulation is characterized and the gain compression with photon density is identified to be the limiting factor of the modulation bandwidth. The enhancement of the gain compression by the gain saturation with the carrier density in QDs is analyzed for the first time with suggestions to improve the high speed performance of the devices by increasing the maximum gain of the QD medium. The linewidth of the QD DFBs are found to be more than one order of magnitude narrower than that of conventional quantum well (QW) DFBs at comparable output powers. The figure of merit for the narrow linewidth is identified by the comparison between different semiconductor materials, including bulk, QWs and QDs. Linewidth rebroadening and the effects of gain offset are also investigated. The effects of external feedback on the QD DFBs are compared to QW DFBs. Higher external feedback resistance is found in QD DFBs with an 8-dB improvement in terms of the coherence collapse of the devices and 20-dB improvement in terms of the degradation of the signal-to-noise ratio under 2.5 Gbps modulation. This result enables the isolator-free operation of the QD DFBs in real communication systems based on the IEEE 802.3ae Ethernet standard. Finally, the chirp of QD DFBs is studied by time-resolved-chirp measurements. The wavelength chirping of the QD DFBs under 2.5 Gbps modulation is characterized. The above-threshold behavior of the linewidth enhancement factor in QDs is studied, in contrast to the below-threshold ones in most of the published data to-date. The strong dependence of the linewidth enhancement factor on the photon density is explained by the enhancement of gain compression by the gain saturation with the carrier density, which is related to the inhomogeneous broadening and spectral hole burning in QDs.

Su, Hui

362

Dynamical properties of a nonequilibrium quantum dot close to a dissipative quantum phase transition

NASA Astrophysics Data System (ADS)

The dynamical decoherence rate and charge susceptibility of a nonequilibrium quantum dot close to a dissipative quantum phase transition are calculated. The setup concerns a resonance-level quantum dot coupled to two spinless fermionic baths with a finite bias voltage and an ohmic bosonic bath representing a dissipative environment. The system is equivalent to an anisotropic Kondo model. As dissipation strength increases, the system at zero temperature and zero bias exhibits a quantum phase transition of the Kosterlitz-Thouless (KT) type between a conducting delocalized phase and an insulating localized phase. Within the nonequilibrium frequency-dependent renormalization group (RG) approach, the finite bias crossover in dynamical decoherence rate and charge susceptibility close to the transition are addressed. The dynamical decoherence rate is found to increase with increasing frequency. In the delocalized phase, it shows a singularity at frequencies equal to positive or negative bias voltage. As the system cross overs to the localized phase, the decoherence rate at low frequencies gets progressively smaller and the singular feature is gradually smeared out, leading to a single linear frequency dependence. The dynamical charge susceptibility at low frequencies shows a dip-to-peak crossover across the transition. Relevance of these results to the experiments is discussed.

Chung, Chung-Hou

2011-03-01

363

This investigation presents the characterization of structural and dynamical properties of uranyl tricarbonate in aqueous solution employing an extended hybrid quantum mechanical/molecular mechanical (QM/MM) approach. It is shown that the inclusion of explicit solvent molecules in the quantum chemical treatment is essential to mimic the complex interaction occurring in an aqueous environment. Thus, in contrast to gas phase cluster calculations on a quantum chemical level proposing a 6-fold coordination of the three carbonates, the QMCF MD simulation proposes a 5-fold coordination. An extensive comparison of the simulation results to structural and dynamical data available in the literature was found to be in excellent agreement. Furthermore, this work is the first theoretical study on a quantum chemical level of theory able to observe the conversion of carbonate (CO?²?) to bicarbonate (HCO??) in the equatorial coordination sphere of the uranyl ion. From a comparison of the free energy ?G values for the unprotonated educt [UO?(CO?)?]?? and the protonated [UO?(CO?)?(HCO?)]³?, it could be concluded that the reaction equilibrium is strongly shifted toward the product state confirming the benignity for the observed protonation reaction. Structural properties and the three-dimensional arrangement of carbonate ligands were analyzed via pair-, three-body, and angular distributions, the dynamical properties were evaluated by hydrogen-bond correlation functions and vibrational power spectra. PMID:25157847

Tirler, Andreas O; Hofer, Thomas S

2014-11-13

364

Quantum Dynamics of Spin Wave Propagation Through

in a continuous medium. Such structure can be created or annihilated by some external action [1]. The manipulation pictures (a,b,c,d): Spin configurations at time t/ = 0; Right pictures (e,f,g): Dynamically stable spin picture (h): Spin configuration at time t/ = 100 for the Heisenberg model ( = 1), illustrating

365

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

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

2013-12-04

366

Indicators of quantum coherence in light-harvesting dynamics

NASA Astrophysics Data System (ADS)

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

Olaya-Castro, Alexandra

2011-03-01

367

Exact quantum dynamics of spin systems using the positive-P representation

NASA Astrophysics Data System (ADS)

We discuss a scheme for simulating the exact real time quantum dynamics of interacting quantum spin systems within the positive-P formalism. As model systems we study the transverse field Ising model as well as the Heisenberg model undergoing a quench away from the classical ferromagnetic ordered state. In using the positive-P representation (PPR), the dynamics of the interacting quantum spin system is mapped onto a set of stochastic differential equations (SDEs). The number of which scales linearly with the number of spins, N, compared to an exact solution through diagonalization that in the case of the Heisenberg model would require matrices exponentially large in N. This mapping is exact and can in principle be extended to higher dimensional interacting systems as well as to systems with an explicit coupling to the environment. We compare the results from using a PPR approach based on both the optical coherent states as well as SU(2) Radcliff coherent states.

Ng, Ray; Sorensen, Erik

2011-03-01

368

Summary A new method for the calculation of partial cross sections in the time-dependent quantum theory of molecular reactive scattering processes is discussed. Preliminary calculations are presented which clearly illustrate the power of the method. They show how all the partial cross sections associated with a single initial quantum state may be computed over a very wide energy range from

C. Clay Marston; Gabriel G. Balint-Kurti; Richard N. Dixon

1991-01-01

369

In the recent years, ultracold atoms in optical lattices have proven their great value as quantum simulators for studying strongly-correlated phases and complex phenomena in solid-state systems. Here we reveal their potential as quantum simulators for molecular physics and propose a technique to image the three-dimensional molecular orbitals with high resolution. The outstanding tunability of ultracold atoms in terms of potential and interaction offer fully-adjustable model systems for gaining deep insight into the electronic structure of molecules. We study the orbitals of an artificial benzene molecule and discuss the effect of tunable interactions in its conjugated pi electron system with special regard to localization and spin order. The dynamical timescale of ultracold atom simulators are on the order milliseconds which allow for the time-resolved monitoring of a broad range of dynamical processes. As an example, we compute the hole dynamics in the conjugated pi system of the artificial benzene molecule.

Lühmann, Dirk-Sören; Sengstock, Klaus

2015-01-01

370

Comparative study of the performance of quantum annealing and simulated annealing.

Relations of simulated annealing and quantum annealing are studied by a mapping from the transition matrix of classical Markovian dynamics of the Ising model to a quantum Hamiltonian and vice versa. It is shown that these two operators, the transition matrix and the Hamiltonian, share the eigenvalue spectrum. Thus, if simulated annealing with slow temperature change does not encounter a difficulty caused by an exponentially long relaxation time at a first-order phase transition, the same is true for the corresponding process of quantum annealing in the adiabatic limit. One of the important differences between the classical-to-quantum mapping and the converse quantum-to-classical mapping is that the Markovian dynamics of a short-range Ising model is mapped to a short-range quantum system, but the converse mapping from a short-range quantum system to a classical one results in long-range interactions. This leads to a difference in efficiencies that simulated annealing can be efficiently simulated by quantum annealing but the converse is not necessarily true. We conclude that quantum annealing is easier to implement and is more flexible than simulated annealing. We also point out that the present mapping can be extended to accommodate explicit time dependence of temperature, which is used to justify the quantum-mechanical analysis of simulated annealing by Somma, Batista, and Ortiz. Additionally, an alternative method to solve the nonequilibrium dynamics of the one-dimensional Ising model is provided through the classical-to-quantum mapping. PMID:25679567

Nishimori, Hidetoshi; Tsuda, Junichi; Knysh, Sergey

2015-01-01

371

Comparative study of the performance of quantum annealing and simulated annealing

NASA Astrophysics Data System (ADS)

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

Nishimori, Hidetoshi; Tsuda, Junichi; Knysh, Sergey

2015-01-01

372

Quantum Dynamics in Continuum for Proton Transport I: Basic Formulation

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

2012-01-01

373

Quantized Hamilton dynamics describes quantum discrete breathers in a simple way

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

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

2011-08-15

374

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

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. PMID:24704872

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

2014-01-01

375

A dynamic macroscopic quantum oscillator at room temperature

We demonstrate a dynamic macroscopic quantum oscillator of a light--matter hybrid state in high-density plasmas created in an optically induced confining potential in a semiconductor microcavity at room temperature. One major advancement is the visualization of quantum oscillator states in a micrometer-scale optical potential at quantized energies up to 4 meV, an order of magnitude higher than that previously observed in spatially confined polariton condensates at cryogenic temperatures. Another advancement is the ability to characterize the time evolution and optical spin polarization of the quantum oscillator states directly from the consequent pulse radiation. The ability to control the macroscopic coherent state of plasma polaritons enables ultrafast multiple pulse lasing in a semiconductor microcavity.

Xie, Wei; Lee, Yi-Shan; Lin, Sheng-Di; Lai, Chih-Wei

2015-01-01

376

Coupling Dynamical Quantum Diffeomorphisms to Matter Degrees of Freedom

NASA Astrophysics Data System (ADS)

We introduce matter degrees of freedom into a recently proposed 2D quantum gravity model based on the Virasoro group. Quantum diffeomorphisms have dynamical content in this model, thus spoiling their classical gauge nature. The algebra of observables is enlarged now with the inclusion of an ensemble of new operators closing the affine Kac-Moody algebra of the (non-compact) semi-simple group SL(2, R), and constituting the modes of a set of scalar fields. The gravity effect on those new fields is accomplished by the natural semi-direct action of the Virasoro group on the new subalgebra. While the model is rather entangled at the severe quantum regime, at the semi-classical level we recover the action of the scalar fields modified with an added gravitational interaction term...

Aldaya, V.; Jaramillo, J. L.

2002-12-01

377

Dynamical Horizon Entropy Bound Conjecture in Loop Quantum Cosmology

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

Li-Fang Li; Jian-Yang Zhu

2010-06-28

378

Cold and ultracold molecular ions: Quantum dynamics and interactions

NASA Astrophysics Data System (ADS)

The availability of MgH^+ Coulomb Crystals (CC) and the ability of obtaining large sample of ultracold Rb atoms gas have suggested the present computational study in which we investigate the behaviour of the MgH^+(X1^1&+circ;) molecular ion interacting with Rb(^2S) as an amenable system for experimenting in cold chemistry. From our computational analysis of the MgH^+-Rb system we found that there is a number of different ways in which this system can chemically evolve in a experimental setup in which a cloud of ultracold laser-cooled Rb atoms is superimposed onto a MgH^+ CC. Our findings suggest the most likely pathways for either the formation of a new CC of Rb ions or the combination of cold Mg^+, MgH^+, RbMgH^+ and Rb^+ mixtures. We also have focused our attention on two anionic molecules: OH^-(X^1&+circ;) and LiH^-(X^2&+circ;) interacting with Rb(^2S) and He respectively. An anion can offer some advantages over the neutral counterpart since the presence of an extra electron on the molecular target can mitigate the probability of unwanted charge exchange processes in which an electron is transferred from the Alkali atom to the molecule. We present the case of OH^-(X^1&+circ;)-Rb for which both rotational and vibrational quenching quantum dynamics has been studied. In the case of LiH^-(X^2&+circ;)-He we have focused on the rotational quenching dynamics and on the role played by the fine structure of the rotational levels.

Gianturco, Franco; Tacconi, Mario

2010-03-01

379

Dynamically self-regular quantum harmonic black holes

NASA Astrophysics Data System (ADS)

The recently proposed UV self-complete quantum gravity program is a new and very interesting way to envision Planckian/trans-Planckian physics. In this new framework, high energy scattering is dominated by the creation of micro black holes, and it is experimentally impossible to probe distances shorter than the horizon radius. In this letter we present a model which realizes this idea through the creation of self-regular quantum black holes admitting a minimal size extremal configuration. Their radius provides a dynamically generated minimal length acting as a universal short-distance cutoff. We propose a quantization scheme for this new kind of microscopic objects based on a Bohr-like approach, which does not require a detailed knowledge of quantum gravity. The resulting black hole quantum picture resembles the energy spectrum of a quantum harmonic oscillator. The mass of the extremal configuration plays the role of zero-point energy. Large quantum number re-establishes the classical black hole description. Finally, we also formulate a "quantum hoop conjecture" which is satisfied by all the mass eigenstates and sustains the existence of quantum black holes sourced by Gaussian matter distributions. "regularity", i.e. absence of curvature singularities; extremal configuration corresponding to a minimal size near l0. Regularity is an immediate consequence of the presence of l0 in the space-time geometry, while the existence of a minimal mass, extremal configuration, is a surprising property, at least from the point of view of the BH textbook solutions.In the first part of this letter we present the regular Schwarzschild solution that exhibits extremal configuration with radius r0 =l0. This is what one expects in a theory where distances below l0 have no physical meaning.All up to date experiments indicate that l0 <10-17 cm, which means that minimal BHs created in a Planckian collision, will be certainly quantum objects. Thus, neither classical nor semi-classical description is satisfactory and one should quantize BHs themselves.In the absence of a proper quantum mechanical description of BHs, we propose a quantization scheme based on the analogy with the quantum harmonic oscillator. This quantization scheme is discussed in Section 3, where we also provide a new formulation of QHC. Finally, in Section 4 we summarize the main results obtained.

Spallucci, Euro; Smailagic, Anais

2015-04-01

380

NON-EQUILIBRIUM DYNAMICS OF MANY-BODY QUANTUM SYSTEMS: FUNDAMENTALS AND NEW FRONTIER

Rapid progress in nanotechnology and naofabrication techniques has ushered in a new era of quantum transport experiments. This has in turn heightened the interest in theoretical understanding of nonequilibrium dynamics of strongly correlated quantum systems. This project has advanced the frontiers of understanding in this area along several fronts. For example, we showed that under certain conditions, quantum impurities out of equilibrium can be reformulated in terms of an effective equilibrium theory; this makes it possible to use the gamut of tools available for quantum systems in equilibrium. On a different front, we demonstrated that the elastic power of a transmitted microwave photon in circuit QED systems can exhibit a many-body Kondo resonance. We also showed that under many circumstances, bipartite fluctuations of particle number provide an effective tool for studying many-body physics—particularly the entanglement properties of a many-body system. This implies that it should be possible to measure many-body entanglement in relatively simple and tractable quantum systems. In addition, we studied charge relaxation in quantum RC circuits with a large number of conducting channels, and elucidated its relation to Kondo models in various regimes. We also extended our earlier work on the dynamics of driven and dissipative quantum spin-boson impurity systems, deriving a new formalism that makes it possible to compute the full spin density matrix and spin-spin correlation functions beyond the weak coupling limit. Finally, we provided a comprehensive analysis of the nonequilibrium transport near a quantum phase transition in the case of a spinless dissipative resonant-level model. This project supported the research of two Ph.D. students and two postdoctoral researchers, whose training will allow them to further advance the field in coming years.

DeMille, David; LeHur, Karyn

2013-11-27

381

Physics Reports 355 (2001) 235334 Quantum phase transitions and vortex dynamics in

of motion 287 3.2. Ballistic vortex motion 293 3.3. E ective single vortex action 296 3.4. Quantum vorticesPhysics Reports 355 (2001) 235Â334 Quantum phase transitions and vortex dynamics in superconducting-dimensional arrays 277 2.8. Field-tuned transitions 282 3. Quantum vortex dynamics 286 3.1. Classical equation

382

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

383

Quantum quench dynamics in analytically solvable one-dimensional models

NASA Astrophysics Data System (ADS)

In connection with experiments in cold atomic systems, we consider the non-equilibrium dynamics of some analytically solvable one-dimensional systems which undergo a quantum quench. In this quench one or several of the parameters of the Hamiltonian of an interacting quantum system are changed over a very short time scale. In particular, we concentrate on the Luttinger model and the sine-Gordon model in the Luther-Emery point. For the latter, we show that the order parameter and the two-point correlation function relax in the long time limit to the values determined by a generalized Gibbs ensemble first discussed by J. T. Jaynes [Phys. Rev. 106, 620 (1957); 108, 171 (1957)], and recently conjectured by M. Rigol et.al. [Phys. Rev. Lett. 98, 050405 (2007)] to apply to the non-equilibrium dynamics of integrable systems.

Iucci, Anibal; Cazalilla, Miguel A.; Giamarchi, Thierry

2008-03-01

384

Extended space expectation values in quantum dynamical system evolutions

NASA Astrophysics Data System (ADS)

The time variant power series expansion for the expectation value of a given quantum dynamical operator is well-known and well-investigated issue in quantum dynamics. However, depending on the operator and Hamiltonian singularities this expansion either may not exist or may not converge for all time instances except the beginning of the evolution. This work focuses on this issue and seeks certain cures for the negativities. We work in the extended space obtained by adding all images of the initial wave function under the system Hamiltonian's positive integer powers. This requires the introduction of certain appropriately defined weight operators. The resulting better convergence in the temporal power series urges us to call the new defined entities "extended space expectation values" even though they are constructed over certain weight oparetors and are somehow pseudo expectation values.

Demiralp, Metin

2014-10-01

385

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

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

386

Signatures of chaos in the dynamics of quantum discord

NASA Astrophysics Data System (ADS)

We identify signatures of chaos in the dynamics of discord in a multiqubit system collectively modelled as a quantum kicked top. The evolution of discord between any two qubits is quasiperiodic in regular regions, while in chaotic regions the quasiperiodicity is lost. As the initial wave function is varied from the regular regions to the chaotic sea, a contour plot of the time-averaged discord remarkably reproduces the structures of the classical stroboscopic map. We also find surprisingly opposite behavior of two-qubit discord versus entanglement of the two qubits as measured by the concurrence. Our results provide evidence of signatures of chaos in dynamically generated discord.

Madhok, Vaibhav; Gupta, Vibhu; Trottier, Denis-Alexandre; Ghose, Shohini

2015-03-01

387

Method for discovering relationships in data by dynamic quantum clustering

Data clustering is provided according to a dynamical framework based on quantum mechanical time evolution of states corresponding to data points. To expedite computations, we can approximate the time-dependent Hamiltonian formalism by a truncated calculation within a set of Gaussian wave-functions (coherent states) centered around the original points. This allows for analytic evaluation of the time evolution of all such states, opening up the possibility of exploration of relationships among data-points through observation of varying dynamical-distances among points and convergence of points into clusters. This formalism may be further supplemented by preprocessing, such as dimensional reduction through singular value decomposition and/or feature filtering.

Weinstein, Marvin; Horn, David

2014-10-28

388

Characterizing quantum dynamics with initial system-environment correlations

We fully characterize the reduced dynamics of an open quantum system initially correlated with its environment. Using a photonic qubit coupled to a simulated environment we tomographically reconstruct a superchannel---a generalised channel that treats preparation procedures as inputs---from measurement of the system alone, despite its coupling to the environment. We introduce novel quantitative measures for determining the strength of initial correlations, and to allow an experiment to be optimised in regards to its environment.

Martin Ringbauer; Christopher J. Wood; Kavan Modi; Alexei Gilchrist; Andrew G. White; Alessandro Fedrizzi

2014-10-21

389

Non-relativistic Gravity in Entropic Quantum Dynamics

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

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

2011-03-14

390

Characterizing quantum dynamics with initial system-environment correlations.

We fully characterize the reduced dynamics of an open quantum system initially correlated with its environment. Using a photonic qubit coupled to a simulated environment, we tomographically reconstruct a superchannel-a generalized channel that treats preparation procedures as inputs-from measurement of the system alone. We introduce novel quantitative measures for determining the strength of initial correlations, and to allow an experiment to be optimized in regard to its environment. PMID:25793785

Ringbauer, M; Wood, C J; Modi, K; Gilchrist, A; White, A G; Fedrizzi, A

2015-03-01

391

Recombination dynamics in InGaN quantum wells

NASA Astrophysics Data System (ADS)

Transient photoluminescence measurements are reported on a thin InGaN single quantum well, encompassing the high injection regime. The radiative processes that dominate the recombination dynamics, especially at low temperatures, show the impact of localized electronic states that are distributed over a large energy range (˜100 meV). We suggest that these states originate from microstructural disorder in the InGaN/GaN system.

Jeon, E. S.; Kozlov, V.; Song, Y.-K.; Vertikov, A.; Kuball, M.; Nurmikko, A. V.; Liu, H.; Chen, C.; Kern, R. S.; Kuo, C. P.; Craford, M. G.

1996-12-01

392

Characterizing Quantum Dynamics with Initial System-Environment Correlations

NASA Astrophysics Data System (ADS)

We fully characterize the reduced dynamics of an open quantum system initially correlated with its environment. Using a photonic qubit coupled to a simulated environment, we tomographically reconstruct a superchannel—a generalized channel that treats preparation procedures as inputs—from measurement of the system alone. We introduce novel quantitative measures for determining the strength of initial correlations, and to allow an experiment to be optimized in regard to its environment.

Ringbauer, M.; Wood, C. J.; Modi, K.; Gilchrist, A.; White, A. G.; Fedrizzi, A.

2015-03-01

393

Use of dynamical coupling for improved quantum state transfer

NASA Astrophysics Data System (ADS)

We propose a method to improve quantum state transfer in transmission lines. The idea is to localize the information on the last qubit of a transmission line by dynamically varying the coupling constants between the first and the last pair of qubits. The fidelity of state transfer is higher then in a chain with fixed coupling constants. The effect is stable against small fluctuations in the system parameters.

Lyakhov, A. O.; Bruder, C.

2006-12-01

394

Quantum Geometry of a Configuration Space in a Covariant Dynamical Theory

A quantum version of the action principle in a simple covariant dynamical theory of two relativistic particles is formulated. The central object of this new formulation of quantum theory is a stationary eigenvalue of the quantum action. This quantity defines a quantum geometry in a configuration space. In the presence of "probe" fields it plays the role of a generation function of observables.

N. Gorobey; A. Lukyanenko; I. Lukyanenko

2009-09-10

395

Accelerated monotonic convergence of optimal control over quantum dynamics

NASA Astrophysics Data System (ADS)

The control of quantum dynamics is often concerned with finding time-dependent optimal control fields that can take a system from an initial state to a final state to attain the desired value of an observable. This paper presents a general method for formulating monotonically convergent algorithms to iteratively improve control fields. The formulation is based on a two-point boundary-value quantum control paradigm (TBQCP) expressed as a nonlinear integral equation of the first kind arising from dynamical invariant tracking control. TBQCP is shown to be related to various existing techniques, including local control theory, the Krotov method, and optimal control theory. Several accelerated monotonic convergence schemes for iteratively computing control fields are derived based on TBQCP. Numerical simulations are compared with the Krotov method showing that the new TBQCP schemes are efficient and remain monotonically convergent over a wide range of the iteration step parameters and the control pulse lengths, which is attributable to the trap-free character of the transition probability quantum dynamics control landscape.

Ho, Tak-San; Rabitz, Herschel

2010-08-01

396

Accelerated monotonic convergence of optimal control over quantum dynamics.

The control of quantum dynamics is often concerned with finding time-dependent optimal control fields that can take a system from an initial state to a final state to attain the desired value of an observable. This paper presents a general method for formulating monotonically convergent algorithms to iteratively improve control fields. The formulation is based on a two-point boundary-value quantum control paradigm (TBQCP) expressed as a nonlinear integral equation of the first kind arising from dynamical invariant tracking control. TBQCP is shown to be related to various existing techniques, including local control theory, the Krotov method, and optimal control theory. Several accelerated monotonic convergence schemes for iteratively computing control fields are derived based on TBQCP. Numerical simulations are compared with the Krotov method showing that the new TBQCP schemes are efficient and remain monotonically convergent over a wide range of the iteration step parameters and the control pulse lengths, which is attributable to the trap-free character of the transition probability quantum dynamics control landscape. PMID:20866936

Ho, Tak-San; Rabitz, Herschel

2010-08-01

397

Quantum effects in the dynamics of biological systems

The performance of biological sensory systems is shown to reach the quantum limits to measurement, this being true in spite of the high levels of thermal noise associated with operation at phisiological temperatures. Theoretical issues associated with quantum-limited measurement at high temperatures are addressed and strategies for such measurements which make use of active filtering are formulated. Experimental and theoretical evidence supporting the existence of active filters in the sensors of the inner ear is discussed. Simple model Hamiltonians are formulated which seem to describe the dynamics of biological molecules and field-theoretic techniques are developed to solve these Hamiltonians in a variety of parameter regimes. Conditions for non-trivial quantum effects in these models are compared with experiments on the primary events of photosynthesis and the low-temperature behavior of heme proteins. Predicted quantum effects are observed and independent observations support the assignment of parameters outside the regime where semi-classical approximations are valid. In each case considered, theoretical analysis demonstrates that quantum effects in biology are significant if not dominant, and this leads to fundamentally new interpretations of several biological processes. Detailed experiments are proposed which will provide quantitative tests of these new interpretations.

Bialek, W.S.

1983-09-01

398

Dynamical quantum Hall effect in the parameter space

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

Gritsev, V.; Polkovnikov, A.

2012-01-01

399

Density-potential mappings in quantum dynamics

NASA Astrophysics Data System (ADS)

In a recent paper [Europhys. Lett.EULEEJ0295-507510.1209/0295-5075/95/13001 95, 13001 (2011)] the question of whether the density of a time-dependent quantum system determines its external potential was reformulated as a fixed-point problem. This idea was used to generalize the existence and uniqueness theorems underlying time-dependent density-functional theory. In this work we extend this proof to allow for more general norms and provide a numerical implementation of the fixed-point iteration scheme. We focus on the one-dimensional case because it allows for a more in-depth analysis using singular Sturm-Liouville theory and at the same time provides an easy visualization of the numerical applications in space and time. We give an explicit relation between the boundary conditions on the density and the convergence properties of the fixed-point procedure via the spectral properties of the associated Sturm-Liouville operator. We show precisely under which conditions discrete and continuous spectra arise and give explicit examples. These conditions are then used to show that, in the most physically relevant cases, the fixed-point procedure converges. This is further demonstrated with an example.

Ruggenthaler, M.; Giesbertz, K. J. H.; Penz, M.; van Leeuwen, R.

2012-05-01

400

Exciton inter- and intra-actions in a GaAs\\/AlGaAs quantum well (QW) and quantum dot (QD) ensemble are studied using optical two-dimensional Fourier transform spectroscopy. We measure population dynamics for times up to 300 ps and temperatures up to 50 K and observe biexponential decay for both QW and QD excitons, strong QW --> QD relaxation, and weak QD --> QW activation.

G. Moody; M. E. Siemens; A. D. Bristow; X. Dai; A. S. Bracker; D. Gammon; S. T. Cundiff

2011-01-01

401

Dynamical quantum phase transitions in the axial next-nearest-neighbor Ising chain

NASA Astrophysics Data System (ADS)

We investigate sudden quenches across the critical point in the transverse field Ising chain with a perturbing nonintegrable next-nearest-neighbor interaction. Expressions for the return (Loschmidt) amplitude and associated rate function are derived to linear order in the next-nearest-neighbor coupling. In the thermodynamic limit these quantities exhibit nonanalytic behavior at a set of critical times, a phenomenon referred to as a dynamical quantum phase transition. We quantify the effect of the integrability breaking perturbation on the location and shape of these nonanalyticities. Our results agree with those of earlier numerical studies and offer further support for the assertion that the dynamical quantum phase transitions exhibited by this model are a generic feature of its postquench dynamics and are robust with respect to the inclusion of nonintegrable perturbations.

Kriel, J. N.; Karrasch, C.; Kehrein, S.

2014-09-01

402

Canonical versus noncanonical equilibration dynamics of open quantum systems.

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

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

2014-08-01

403

Canonical versus noncanonical equilibration dynamics of open quantum systems

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

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

2014-08-24

404

Quantum dynamics in a tiered non-Markovian environment

We introduce a new analytical method for studying the open quantum systems problem of a discrete system weakly coupled to an environment of harmonic oscillators. Our approach is based on a phase space representation of the density matrix for a system coupled to a two-tiered environment. The dynamics of the system and its immediate environment are resolved in a non-Markovian way, and the environmental modes of the inner environment can themselves be damped by a wider `universe'. Applying our approach to the canonical cases of the Rabi and spin-boson models we obtain new analytical expressions for an effective thermalisation temperature and corrections to the environmental response functions as direct consequences of considering such a tiered environment. A comparison with exact numerical simulations confirms that our approximate expressions are remarkably accurate, while their analytic nature offers the prospect of deeper understanding of the physics which they describe. A unique advantage of our method is that it permits the simultaneous inclusion of a continuous bath as well as discrete environmental modes, leading to wide and versatile applicability.

Amir Fruchtman; Brendon W. Lovett; Simon C. Benjamin; Erik M. Gauger

2015-02-26

405

Quantum dynamics in a tiered non-Markovian environment

NASA Astrophysics Data System (ADS)

We introduce a new analytical method for studying the open quantum systems problem of a discrete system weakly coupled to an environment of harmonic oscillators. Our approach is based on a phase space representation of the density matrix for a system coupled to a two-tiered environment. The dynamics of the system and its immediate environment are resolved in a non-Markovian way, and the environmental modes of the inner environment can themselves be damped by a wider ‘universe’. Applying our approach to the canonical cases of the Rabi and spin-boson models we obtain new analytical expressions for an effective thermalization temperature and corrections to the environmental response functions as direct consequences of considering such a tiered environment. A comparison with exact numerical simulations confirms that our approximate expressions are remarkably accurate, while their analytic nature offers the prospect of deeper understanding of the physics which they describe. A unique advantage of our method is that it permits the simultaneous inclusion of a continuous bath as well as discrete environmental modes, leading to wide and versatile applicability.

Fruchtman, Amir; Lovett, Brendon W.; Benjamin, Simon C.; Gauger, Erik M.

2015-02-01

406

Quantum-gravity induced Lorentz violation and dynamical mass generation

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

407

Exciton dynamics in ZnCdSe\\/ZnSe quantum-well structures

Exciton dynamics in ZnCdSe\\/ZnSe quantum-well structures have been studied from luminescence spectra obtained at T=2 K. The energy and phase relaxation times of localized exciton states have been determined from a study of the destruction\\u000a of exciton optical alignment by an external magnetic field and direct measurements of the polarized-radiation decay kinetics\\u000a in the picosecond range. The exciton polarization lifetimes

S. A. Permogorov; A. N. Reznitskii; L. N. Tenishev; A. V. Kornievskii; S. Yu. Verbin; S. V. Ivanov; S. V. Sorokin; W. von der Osten; H. Stolz; M. Jütte

1998-01-01

408

We have investigated intersubband relaxation in GaN\\/AlN multiple quantum wells using a two-color pump-probe technique in a wide energy range around 800meV (1.55mum) . We have observed not only absorption bleaching signals but also, for the first time, induced absorption signals with an ultrafast and a slow component. Absorption bleaching signals are attributed to a phase space filling of the

J. Hamazaki; H. Kunugita; K. Ema; A. Kikuchi; K. Kishino

2005-01-01

409

Quantum dynamics of the avian compass

NASA Astrophysics Data System (ADS)

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

Walters, Zachary B.

2014-10-01

410

Quantum dynamics of the avian compass.

The ability of migratory birds to orient relative to the Earth's magnetic field is believed to involve a coherent superposition of two spin states of a radical electron pair. However, the mechanism by which this coherence can be maintained in the face of strong interactions with the cellular environment has remained unclear. This paper addresses the problem of decoherence between two electron spins due to hyperfine interaction with a bath of spin-1/2 nuclei. Dynamics of the radical pair density matrix are derived and shown to yield a simple mechanism for sensing magnetic field orientation. Rates of dephasing and decoherence are calculated ab initio and found to yield millisecond coherence times, consistent with behavioral experiments. PMID:25375526

Walters, Zachary B

2014-10-01

411

Dynamics of quantum turbulence of different spectra

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

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

2014-01-01

412

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

413

NASA Astrophysics Data System (ADS)

We investigate the hydrodynamic theory of metals, offering systematic studies of the linear-response dynamics for an inhomogeneous electron gas. We include the quantum functional terms of the Thomas-Fermi kinetic energy, the von Weizsäcker kinetic energy, and the exchange-correlation Coulomb energies under the local density approximation. The advantages, limitations, and possible improvements of the hydrodynamic theory are transparently demonstrated. The roles of various parameters in the theory are identified. We anticipate that the hydrodynamic theory can be applied to investigate the linear response of complex metallic nanostructures, including quantum effects, by adjusting theory parameters appropriately.

Yan, Wei

2015-03-01

414

Phase space theory of quantum–classical systems with nonlinear and stochastic dynamics

A novel theory of hybrid quantum–classical systems is developed, utilizing the mathematical framework of constrained dynamical systems on the quantum–classical phase space. Both, the quantum and classical descriptions of the respective parts of the hybrid system are treated as fundamental. Therefore, the description of the quantum–classical interaction has to be postulated, and includes the effects of neglected degrees of freedom. Dynamical law of the theory is given in terms of nonlinear stochastic differential equations with Hamiltonian and gradient terms. The theory provides a successful dynamical description of the collapse during quantum measurement. -- Highlights: •A novel theory of quantum–classical systems is developed. •Framework of quantum constrained dynamical systems is used. •A dynamical description of the measurement induced collapse is obtained.

Buri?, Nikola, E-mail: buric@ipb.ac.rs; Popovi?, Duška B.; Radonji?, Milan; Prvanovi?, Slobodan

2014-04-15

415

potential with a steep repulsion wall will support compression solitary waves. A simple reasoning is based correlated quantum mechanical calculation is compared with a time dependent mean field approach TDSCF and with a classical simulation. The dynamics were all generated from the same Hamiltonian. The TDSCF and classical

Baer, Roi

416

Kinetic Analyses Combining Quantum Chemical and Quantum Statistical Methods: Some Case Studies

Kinetic Analyses Combining Quantum Chemical and Quantum Statistical Methods: Some Case Studies Minh quantum chemical calculations with a quantum statistical treatment of rate constants. We first briefly methods employed. We then discuss a sampling of the studies recently carried out in the Laboratory

Nguyen, Minh Tho

417

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

Danel, J.-F.; Blottiau, P.; Kazandjian, L.; Piron, R.; Torrent, M. [CEA, DAM, DIF, 91297 Arpajon (France)

2014-10-15

418

Spatial mode dynamics in wide-aperture quantum-dot lasers

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

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

2009-05-15

419

On the non-Gaussian corrections in the self dynamics of semi-quantum fluids

NASA Astrophysics Data System (ADS)

This paper is devoted to the study of the limits of the well-known Gaussian approximation in the self dynamics of quantum systems. After introducing the basic formalism and shortly reviewing the methods used in classical systems to apply corrections to the Gaussian approximation, an extension to quantum fluids is devised, with a particular interest in the so-called semi-quantum fluids, i.e. those in which the single particle momentum distribution approximately retains its Maxwellian form (but not its classical width). In this case a detailed correction scheme for both the short- and the long-time behaviors of the intermediate scattering function is proposed. Subsequently, a practical test of this approach is performed on a high resolution neutron scattering spectrum derived from liquid parahydrogen at T = 14.1 K. Extracting the spectral deviations from the Gaussian approximation with the help of an accurate centroid molecular dynamics simulation, we are able to describe them precisely and to derive the first two correction coefficients in this system by means of a simple fitting procedure. These experimental findings confirm the validity of our approach and show that a description of the self dynamics beyond the Gaussian approximation is necessary even in simple liquids affected by mild quantum effects.

Colognesi, D.; Bafile, U.; Celli, M.; Neumann, M.

2015-01-01

420

We investigate the influence of the electron-phonon interaction on the decay dynamics of a quantum dot coupled to an optical microcavity. We show that the electron-phonon interaction has important consequences on the dynamics, especially when the quantum dot and cavity are tuned out of resonance, in which case the phonons may add or remove energy leading to an effective non-resonant coupling between quantum dot and cavity. The system is investigated using two different theoretical approaches: (i) a second-order expansion in the bare phonon coupling constant, and (ii) an expansion in a polaron-photon coupling constant, arising from the polaron transformation which allows an accurate description at high temperatures. In the low temperature regime we find excellent agreement between the two approaches. An extensive study of the quantum dot decay dynamics is performed, where important parameter dependencies are covered. We find that in general the electron-phonon interaction gives rise to a greatly increased band...

Kaer, P; Lodahl, P; Jauho, A -P; Mork, J

2012-01-01

421

NASA Astrophysics Data System (ADS)

In this article, we show how Ehrenfest mean field theory can be made both a more accurate and efficient method to treat nonadiabatic quantum dynamics by combining it with the generalized quantum master equation framework. The resulting mean field generalized quantum master equation (MF-GQME) approach is a non-perturbative and non-Markovian theory to treat open quantum systems without any restrictions on the form of the Hamiltonian that it can be applied to. By studying relaxation dynamics in a wide range of dynamical regimes, typical of charge and energy transfer, we show that MF-GQME provides a much higher accuracy than a direct application of mean field theory. In addition, these increases in accuracy are accompanied by computational speed-ups of between one and two orders of magnitude that become larger as the system becomes more nonadiabatic. This combination of quantum-classical theory and master equation techniques thus makes it possible to obtain the accuracy of much more computationally expensive approaches at a cost lower than even mean field dynamics, providing the ability to treat the quantum dynamics of atomistic condensed phase systems for long times.

Kelly, Aaron; Brackbill, Nora; Markland, Thomas E.

2015-03-01

422

In this article, we show how Ehrenfest mean field theory can be made both a more accurate and efficient method to treat nonadiabatic quantum dynamics by combining it with the generalized quantum master equation framework. The resulting mean field generalized quantum master equation (MF-GQME) approach is a non-perturbative and non-Markovian theory to treat open quantum systems without any restrictions on the form of the Hamiltonian that it can be applied to. By studying relaxation dynamics in a wide range of dynamical regimes, typical of charge and energy transfer, we show that MF-GQME provides a much higher accuracy than a direct application of mean field theory. In addition, these increases in accuracy are accompanied by computational speed-ups of between one and two orders of magnitude that become larger as the system becomes more nonadiabatic. This combination of quantum-classical theory and master equation techniques thus makes it possible to obtain the accuracy of much more computationally expensive approaches at a cost lower than even mean field dynamics, providing the ability to treat the quantum dynamics of atomistic condensed phase systems for long times. PMID:25747064

Kelly, Aaron; Brackbill, Nora; Markland, Thomas E

2015-03-01

423

Quantum dynamical study of the O({sup 1}D) + CH{sub 4} ? CH{sub 3} + OH atmospheric reaction

Time independent quantum mechanical (TIQM) scattering calculations have been carried out for the O({sup 1}D) + CH{sub 4}(X{sup 1}A{sub 1}) ? CH{sub 3}(X{sup 2}A{sub 2}?) + OH(X{sup 2}?) atmospheric reaction, using an ab initio ground potential energy surface where the CH{sub 3} group is described as a pseudo-atom. Total and state-to-state reaction probabilities for a total angular momentum J = 0 have been determined for collision energies up to 0.5 eV. The vibrational and rotational state OH product distributions show no specific behavior. The rate coefficient has been calculated by means of the J-shifting approach in the 10–500 K temperature range and slightly depends on T at ordinary temperatures (as expected for a barrierless reaction). Quantum effects do not influence the vibrational populations and rate coefficient in an important way, and a rather good agreement has been found between the TIQM results and the quasiclassical trajectory and experimental ones. This reinforces somewhat the reliability of the pseudo-triatomic approach under the reaction conditions explored.

Ben Bouchrit, R.; Ben Abdallah, D.; Jaidane, N. [Laboratoire de Physique Atomique et Moléculaire et Applications, Département de Physique, Faculté des Sciences, Université Tunis-El Manar, 1060 Tunis (Tunisia); Jorfi, M. [Institut de Chimie des Milieux et des Matériaux de Poitiers, UMR CNRS 6503, Université de Poitiers, 86022 Poitiers Cedex (France); González, M. [Departament de Química Física and IQTC, Universitat de Barcelona, C/Martí i Franqués 1, 08028 Barcelona (Spain); Bussery-Honvault, B. [Laboratoire Interdisciplinaire Carnot de Bourgogne, UMR CNRS 6303, Université de Bourgogne, 21078 Dijon Cedex (France); Honvault, P., E-mail: pascal.honvault@univ-fcomte.fr [Laboratoire Interdisciplinaire Carnot de Bourgogne, UMR CNRS 6303, Université de Bourgogne, 21078 Dijon Cedex (France); UFR Sciences et Techniques, Université de Franche-Comté, 25030 Besançon Cedex (France)

2014-06-28

424

Non-Markovian dynamics is studied for two interacting quibts strongly coupled to a dissipative bosonic environment. For the first time, we have derived the non-Markovian quantum state diffusion (QSD) equation for the coupled two-qubit system without any approximations, and in particular, without the Markov approximation. As an application and illustration of our derived time-local QSD equation, we investigate the temporal behavior of quantum coherence dynamics. In particular, we find a strongly non-Markovian regime where entanglement generation is significantly modulated by the environmental memory. Additionally, we studied the residual entanglement in the steady state by analyzing the steady state solution of the QSD equation. Finally, we have discussed an approximate QSD equation.

Xinyu Zhao; Jun Jing; Brittany Corn; Ting Yu

2011-09-06

425

Quantum chaotic scattering in graphene systems in the absence of invariant classical dynamics.

Quantum chaotic scattering is referred to as the study of quantum behaviors of open Hamiltonian systems that exhibit transient chaos in the classical limit. Traditionally a central issue in this field is how the elements of the scattering matrix or their functions fluctuate as a system parameter, e.g., the electron Fermi energy, is changed. A tacit hypothesis underlying previous works was that the underlying classical phase-space structure remains invariant as the parameter varies, so semiclassical theory can be used to explain various phenomena in quantum chaotic scattering. There are, however, experimental situations where the corresponding classical chaotic dynamics can change characteristically with some physical parameter. Multiple-terminal quantum dots are one such example where, when a magnetic field is present, the classical chaotic-scattering dynamics can change between being nonhyperbolic and being hyperbolic as the Fermi energy is changed continuously. For such systems semiclassical theory is inadequate to account for the characteristics of conductance fluctuations with the Fermi energy. To develop a general framework for quantum chaotic scattering associated with variable classical dynamics, we use multi-terminal graphene quantum-dot systems as a prototypical model. We find that significant conductance fluctuations occur with the Fermi energy even for fixed magnetic field strength, and the characteristics of the fluctuation patterns depend on the energy. We propose and validate that the statistical behaviors of the conductance-fluctuation patterns can be understood by the complex eigenvalue spectrum of the generalized, complex Hamiltonian of the system which includes self-energies resulted from the interactions between the device and the semi-infinite leads. As the Fermi energy is increased, complex eigenvalues with extremely smaller imaginary parts emerge, leading to sharp resonances in the conductance. PMID:23767599

Wang, Guang-Lei; Ying, Lei; Lai, Ying-Cheng; Grebogi, Celso

2013-05-01

426

Quantum chaotic scattering in graphene systems in the absence of invariant classical dynamics

NASA Astrophysics Data System (ADS)

Quantum chaotic scattering is referred to as the study of quantum behaviors of open Hamiltonian systems that exhibit transient chaos in the classical limit. Traditionally a central issue in this field is how the elements of the scattering matrix or their functions fluctuate as a system parameter, e.g., the electron Fermi energy, is changed. A tacit hypothesis underlying previous works was that the underlying classical phase-space structure remains invariant as the parameter varies, so semiclassical theory can be used to explain various phenomena in quantum chaotic scattering. There are, however, experimental situations where the corresponding classical chaotic dynamics can change characteristically with some physical parameter. Multiple-terminal quantum dots are one such example where, when a magnetic field is present, the classical chaotic-scattering dynamics can change between being nonhyperbolic and being hyperbolic as the