Iyengar, Srinivasan S.
Quantum wave packet ab initio molecular dynamics: An approach to study quantum dynamics in large and Toeplitz representation for the discrete free propagator, in conjunction with ab initio molecular dynamics of the methodology, namely, quantum dynamics and ab initio molecular dynamics, are harnessed together using a time
Quantum dynamics study for Dâ + OH reaction
Yici Zhang; Desheng Zhang; Wei Li; Qinggang Zhang; Dunyou Wang; Dong H. Zhang; John Z. H. Zhang
1995-01-01
A PA5D (potential averaged 5D) TD (time-dependent) quantum wave-packet calculation is reported for the reaction Dâ + OH â D + DOH on the Schatz-Elgersma potential energy surface. The dynamics calculation is carried out on a workstation with a modest memory, which is made possible by using a normalized angular quadrature scheme to minimize the requirement for computer memory during
A detailed quantum mechanical and quasiclassical trajectory study on the dynamics of the H+
Honvault, Pascal
The comparison of the recorded rotational22 and angular distributions20,21 with qua- siclassical trajectory QCTA detailed quantum mechanical and quasiclassical trajectory study on the dynamics of the H+ +H2\\H2 quantum mechanical, approximate quantum wave packet, statistical quantum, and quasiclassical trajectory
The use of artificial intelligence methods in studying quantum intramolecular vibrational dynamics
NASA Astrophysics Data System (ADS)
Lederman, Steven M.; Marcus, R. A.
1988-05-01
Artificial intelligence methods are used to treat the time evolution in intramolecular quantum dynamics. Comparison is made of several AI search algorithms and evaluation functions in an application to the study of quantum intramolecular vibrational redistribution. A combination of a beam search and a best-first search is used, in conjunction with an accumulated evaluation function which encourages both searching and ultimately satisfying the uncertainty principle. The methods developed are applied to an 11-coordinate heavy central mass problem and used to treat both quantum beats and 'dissipative' intramolecular energy transfer. Good agreement is obtained with the 'exact' quantum dynamics.
Quantum molecular dynamics study of warm dense iron
NASA Astrophysics Data System (ADS)
Wang, Cong; Wang, Zhe-Bin; Chen, Qi-Feng; Zhang, Ping
2014-02-01
The equation of state, the self-diffusion coefficient and viscosity of fluid iron in the warm dense regime at densities from 12.5 to 25.0g/cm3, and temperatures from 0.5 to 15.0 eV have been calculated via quantum molecular dynamics simulations. The principal Hugoniot is in good agreement with nuclear explosive experiments up to ˜50Mbar but predicts lower pressures compared with high intensity laser results. The self-diffusion coefficient and viscosity have been simulated and have been compared with the one-component plasma model. The Stokes-Einstein relationship, defined by connections between the viscosity and the self-diffusion coefficient, has been determined and has been found to be fairly well described by classical predictions.
Experimental Study of Quantum Dynamics in a Regime of Classical Anomalous Diffusion
R EVIEW L ETTERS; B. G. Klappauf; W. H. Oskay; D. A. Steck
1998-01-01
The correspondence between a quantum system and the underlying classical dynamics is a topic of fundamental im- portance. The paradigm system for the study of this corre- spondence is the kicked rotor, because of the simplicity of its equations of motion and the wealth of knowledge avail- able on the classical system. One particularly interesting aspect of the kicked rotor
Chong, Frederic T.
.t@gatech.edu, ken.brown@chemistry.gatech.edu, chong@cs.ucsb.edu ABSTRACT Work in quantum computer architecture hasTo appear in the 2013 International Symposium on Computer Architecture Quantum Rotations: A Case Study in Static and Dynamic Machine-Code Generation for Quantum Computers Daniel Kudrow , Kenneth Bier
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
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.
James Sherwood Smith
2009-01-01
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
J. Miller; K. Miaskiewicz; R. Osman
1993-01-01
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
Habib, S; Doherty, A; Greenbaum, B; Hopkins, A; Jacobs, K; Mabuchi, H; Schwab, K; Shizume, K; Steck, D; Sundaram, B; Habib, Salman; Bhattacharya, Tanmoy; Doherty, Andrew; Greenbaum, Benjamin; Hopkins, Asa; Jacobs, Kurt; Mabuchi, Hideo; Schwab, Keith; Shizume, Kosuke; Steck, Daniel; Sundaram, Bala
2005-01-01
The vast majority of the literature dealing with quantum dynamics is concerned with linear evolution of the wave function or the density matrix. A complete dynamical description requires a full understanding of the evolution of measured quantum systems, necessary to explain actual experimental results. The dynamics of such systems is intrinsically nonlinear even at the level of distribution functions, both classically as well as quantum mechanically. Aside from being physically more complete, this treatment reveals the existence of dynamical regimes, such as chaos, that have no counterpart in the linear case. Here, we present a short introductory review of some of these aspects, with a few illustrative results and examples.
Salman Habib; Tanmoy Bhattacharya; Andrew Doherty; Benjamin Greenbaum; Asa Hopkins; Kurt Jacobs; Hideo Mabuchi; Keith Schwab; Kosuke Shizume; Daniel Steck; Bala Sundaram
2005-05-07
The vast majority of the literature dealing with quantum dynamics is concerned with linear evolution of the wave function or the density matrix. A complete dynamical description requires a full understanding of the evolution of measured quantum systems, necessary to explain actual experimental results. The dynamics of such systems is intrinsically nonlinear even at the level of distribution functions, both classically as well as quantum mechanically. Aside from being physically more complete, this treatment reveals the existence of dynamical regimes, such as chaos, that have no counterpart in the linear case. Here, we present a short introductory review of some of these aspects, with a few illustrative results and examples.
Response of solid Ne upon photoexcitation of a NO impurity: a quantum dynamics study.
Uranga-Piña, Ll; Meier, C; Rubayo-Soneira, J
2011-10-28
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
Salman Habib; Tanmoy Bhattacharya; Andrew Doherty; Benjamin Greenbaum; Asa Hopkins; Kurt Jacobs; Hideo Mabuchi; Keith Schwab; Kosuke Shizume; Daniel Steck; Bala Sundaram
2006-01-01
The vast majority of the literature dealing with quantum dynamics is concerned with linear evolution of the wave function\\u000a or the density matrix. A complete dynamical description requires a full understanding of the evolution of measured quantum\\u000a systems, necessary to explain actual experimental results. The dynamics of such systems is intrinsically nonlinear even at\\u000a the level of distribution functions, both
Kosztin, Ioan
that combines molecular dynamics simulations with quantum chemistry calculations and a polaron model analysis quantum chemistry calculations on geometries that emerged from the molecular dynamical simulations from the molecular dynamics and quantum chemistry simulations. The model predicts that excitons
Southern California, University of
Rapid hydrogen production from water using aluminum nanoclusters: A quantum molecular dynamics Available online 31 December 2013 Keywords: Hydrogen production Water Aluminum nanoclusters Quantum molecular dynamics simulation It is hoped that a hydrogen-on-demand generator may one day start with just
Particle Dynamics in Kicked Quantum Networks
NASA Astrophysics Data System (ADS)
Eshniyozov, Valijon; Yusupov, Jambul; Matrasulov, Davron; Ibragimov, Inomjon
Particle dynamics in a periodically driven quantum network is studied by considering delta-kicked quantum star graph is studied. Quantum dynamics is treated by solving Schrodinger equation with time-dependent boundary conditions given on graphs. Time-dependence of the average kinetic energy is analyzed. Space-time evolution of the Gaussian wave packet is treated.
Statistical properties of energy levels in quantum reaction dynamics: a case study
NASA Astrophysics Data System (ADS)
Peroncelli, Leonardo; Grossi, Gaia; Aquilanti, Vincenzo
2004-01-01
An account is presented of recent approaches to the characterization of the statistical properties of the energy level sequences of interest in quantum reaction dynamics. The case study of the quantum eigenvalues of the reactive process F+ H2? HF+ H as a function of the hyperradius (a measure of the total inertia of the three-body system) is illustrated. Previous work is extended by examining different angular momentum projection values for two recently proposed potential energy surfaces. We study spectral properties such as the standard deviation ? of the level spacings and the shape of the nearest-neighbour spacing distribution (NNSD), evaluating the q parameters of the Brody and Berry-Robnik distributions, which are alternative interpolations between the Poisson and the Wigner distributions. We also apply statistical tools, such as the ?3(L) of Dyson and Mehta) and the correlation coefficient C(r). This analysis, which is typical of current investigations on the topic of 'quantum chaos', gives insight into the nature of the reactive event and may be useful for the development of statistical theories in molecular dynamics.
Quantum molecular Dynamics Ronnie Kosloff
Kosloff, Ronnie
Quantum molecular Dynamics Ronnie Kosloff The Fritz Haber Center for Molecular Dynamics Hebrew University, Jerusalem Israel. · Lecture 6: · Time dependent Quantum Molecular Dynamics #12;#12;State #12;Quantum molecular Dynamics Ronnie Kosloff The Fritz Haber Center for Molecular Dynamics Hebrew
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
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.
Quantum dynamics of N-methylacetamide studied by the vibrational configuration interaction method
NASA Astrophysics Data System (ADS)
Fujisaki, Hiroshi; Yagi, Kiyoshi; Hirao, Kimihiko; Straub, John E.
2007-07-01
Vibrational energy transfer of the amide I mode of N-methylacetamide (NMA) is studied theoretically using the vibrational configuration interaction method. A quartic force field of NMA is constructed at the B3LYP/6-31G+(d) level of theory and its accuracy is checked by comparing the resulting anharmonic frequencies with available theoretical and experimental values. Quantum dynamics calculations for the amide I mode excitation clarify the dominant energy transfer pathways, which sensitively depend on the anharmonic couplings among vibrational modes. A ratio of the anharmonic coupling to the frequency mismatch is employed to predict and interpret the dominant energy flow pathways.
Study of the dynamic behavior of quantum cellular automata in graphane nanoclusters
NASA Astrophysics Data System (ADS)
León, A.; Pacheco, M.
2011-03-01
The possible creation of architectures of quantum cellular automata formed by simple molecules opens a very promising and interesting area of research due to the possibility of going beyond the current limits of miniaturization and integration of devices. In this research we theoretically study the electronic properties of a quan- tum dot array in graphene nanoribbons and in an array of molecules with graphane structures. The role of quantum dots in the ribbons and in the mole- cules is played by oxide reduction centers that can trap or release electrons. With the knowledge about these properties we design cellular automata archi- tectures with nanoribbons and molecular arrays, with this it will be feasible to store and process logic information at room temperature. The stability of the proposed graphene structures are studied using quan- tum methods of geometric optimization [1]. The electronic properties of the nanoribbons are obtained from first-principle calculations based on pseudo- potentials by using the generalized gradient approximation (GGA) of Perdew- Burke-Ernzerhof [2-3]. With the parameters obtained from the study of the electronic properties of the cells that make up the automata, we can make a simulation of the dynamical response of the system. To do this, we use a set of accelerated algorithms for discrete systems [4] based on the Glauber dynamic [5]. Our results show that the studied system can be scaled so that the propagation of digital information throughout the automata is possible at room temperature.
Ortiz-Sanchez, Juan Manuel; Gelabert, Ricard; Moreno, Miquel; Lluch, Jose M. [Departament de Quimica, Universitat Autonoma de Barcelona, 08193 Bellaterra, Barcelona (Spain)
2008-12-07
The ultrafast proton transfer dynamics of salicylideneaniline has been theoretically analyzed in the ground and first singlet excited electronic states using density functional theory (DFT) and time-dependent DFT calculations, which predict a ({pi},{pi}*) barrierless excited state intramolecular proton transfer (ESIPT). In addition to this, the photochemistry of salicylideneaniline is experimentally known to present fast depopulation processes of the photoexcited species before and after the proton transfer reaction. Such processes are explained by means of conical intersections between the ground and first singlet ({pi},{pi}*) excited electronic states. The electronic energies obtained by the time-dependent density functional theory formalism have been fitted to a monodimensional potential energy surface in order to perform quantum dynamics study of the processes. Our results show that the proton transfer and deactivation of the photoexcited species before the ESIPT processes are completed within 49.6 and 37.7 fs, respectively, which is in remarkable good agreement with experiments.
Ana Damjanovic; Ioan Kosztin; Ulrich Kleinekathöfer; Klaus Schulten
2002-01-01
The dynamics of pigment-pigment and pigment-protein interactions in light-harvesting complexes is studied with an approach that combines molecular dynamics simulations with quantum chemistry calculations and a polaron model analysis. The molecular dynamics simulation of light-harvesting (LH) complexes was performed on an 87 055 atom system comprised of a LH-II complex of Rhodospirillum molischianum embedded in a lipid bilayer and surrounded
Six-dimensional quantum dynamics study for the dissociative adsorption of DCl on Au(111) surface
NASA Astrophysics Data System (ADS)
Liu, Tianhui; Fu, Bina; Zhang, Dong H.
2014-04-01
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.
Six-dimensional quantum dynamics study for the dissociative adsorption of DCl on Au(111) surface.
Liu, Tianhui; Fu, Bina; Zhang, Dong H
2014-04-14
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. PMID:24735307
Six-dimensional quantum dynamics study for the dissociative adsorption of DCl on Au(111) surface
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
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.
Information dynamics in quantum theory
Piotr Garbaczewski
2006-12-18
Shannon entropy and Fisher information functionals are known to quantify certain information-theoretic properties of continuous probability distributions of various origins. We carry out a systematic study of these functionals, while assuming that the pertinent probability density has a quantum mechanical appearance $\\rho \\doteq |\\psi |^2$, with $\\psi \\in L^2(R)$. Their behavior in time, due to the quantum Schr\\"{o}dinger picture evolution-induced dynamics of $\\rho (x,t)$ is investigated as well, with an emphasis on thermodynamical features of quantum motion.
Quantum molecular Dynamics Ronnie Kosloff
Kosloff, Ronnie
Quantum molecular Dynamics Ronnie Kosloff The Fritz Haber Center for Molecular Dynamics Hebrew.mpg #12;#12;#12;#12;Quantum molecular Dynamics Ronnie Kosloff The Fritz Haber Center for Molecular Dynamics Hebrew University, Jerusalem Israel. ·Lecture 10: Coherent Control & Summary #12;Coherent Control
Quantum Behaviors and Dynamic Horizons
James Lindesay
2009-04-27
Geometries with horizons offer insights into relationships between general relativity and quantum physics. Quantum mechanics constrains relationships between kinematic parameters and the coordinates describing the dynamics. Example quantum behaviors on space-times with dynamic horizons will be demonstrated, with an emphasis on examining co-gravitating quantum systems. Finally, the large scale causal structure of a multi-fluid cosmology that can describe dynamic coherent aspects of the universe as a whole will be presented.
Kim, Myung Soo
Construction of an accurate potential energy surface by interpolation for quantum dynamics studies, Seoul 151-742, Korea Received 15 June 1999; accepted 28 June 1999 A method to construct an accurate were nearly indistinguishable. An accurate analytic PES can be constructed with the ab initio results
Kroes, G J; Pijper, E; Salin, A
2007-10-28
Six-dimensional quantum dynamical and quasiclassical trajectory (QCT) calculations are reported for the reaction and vibrationally inelastic scattering of (v = 0,1,j = 0) H(2) scattering from Cu(110), and for the reaction and rovibrationally elastic and inelastic scattering of (v = 1,j = 1) H(2) scattering from Cu(110). The dynamics results were obtained using a potential energy surface obtained with density functional theory using the PW91 functional. The reaction probabilities computed with quantum dynamics for (v = 0,1,j = 0) were in excellent agreement with the QCT results obtained earlier for these states, thereby validating the QCT approach to sticking of hydrogen on Cu(110). The vibrational de-excitation probability P(v=1,j = 0 --> v = 0) computed with the QCT method is in remarkably good agreement with the quantum dynamical results for normal incidence energies E(n) between 0.2 and 0.6 eV. The QCT result for the vibrational excitation probability P(v = 0,j = 0 --> v = 1) is likewise accurate for E(n) between 0.8 and 1 eV, but the QCT method overestimates vibrational excitation for lower E(n). The QCT method gives probabilities for rovibrationally (in)elastic scattering, P(v = 1,j = 1 --> v('),j(')), which are in remarkably good agreement with quantum dynamical results. The rotationally averaged, initial vibrational state-selective reaction probability obtained with QCT agrees well with the initial vibrational state-selective reaction probability extracted from molecular beam experiments for v = 1, for the range of collision energies for which the v=1 contribution to the measured total sticking probability dominates. The quantum dynamical probabilities for rovibrationally elastic scattering of (v = 1,j = 1) H(2) from Cu(110) are in good agreement with experiment for E(n) between 0.08 and 0.25 eV. PMID:17979386
Three-dimensional quantum time-dependent study of the photodissociation dynamics of Na FH=D
Zeiri, Yehuda
Three-dimensional quantum time-dependent study of the photodissociation dynamics of Na Á Á Á FH of the photodissociation of the van der Waals Na Á Á Á FH molecule was performed for total J ¼ 0. A very low probability]. This idea is behind the experimental study of the photodissociation of the Na Á Á Á FH [2], Li Á Á Á FH [3
Dynamical origin of quantum probabilities
NASA Astrophysics Data System (ADS)
Valentini, Antony; Westman, Hans
2005-01-01
We study the origin of the Born probability rule ? = |?|2 in the de Broglie-Bohm pilot-wave formulation of quantum theory. It is argued that quantum probabilities arise dynamically, and have a status similar to thermal probabilities in ordinary statistical mechanics. This is illustrated by numerical simulations for a two-dimensional system. We show that a simple initial ensemble, with a non-standard distribution ? ? |?|2 of particle positions, evolves towards the quantum distribution to high accuracy. The relaxation process ? ? |?|2 is quantified in terms of a coarse-grained H-function (equal to minus the relative entropy of ? with respect to |?|2), which is found to decrease approximately exponentially over time, with a time constant that accords with a simple theoretical estimate.
Potential energy surface and quantum dynamics study of rovibrational states for HO(3) (X (2)A'').
Braams, Bastiaan J; Yu, Hua-Gen
2008-06-01
An analytic potential energy surface has been constructed by fitting to about 28 thousand energy points for the electronic ground-state (X (2)A'') of HO(3). The energy points are calculated using a hybrid density functional HCTH and a large basis set aug-cc-pVTZ, i.e., a HCTH/aug-cc-pVTZ density functional theory (DFT) method. The DFT calculations show that the trans-HO(3) isomer is the global minimum with a potential well depth of 9.94 kcal mol(-1) with respect to the OH + O(2) asymptote. The equilibrium geometry of the cis-HO(3) conformer is located 1.08 kcal mol(-1) above that of the trans-HO(3) one with an isomerization barrier of 2.41 kcal mol(-1) from trans- to cis-HO(3). By using this surface, a rigorous quantum dynamics (QD) study has been carried out for computing the rovibrational energy levels of HO(3). The calculated results determine a dissociation energy of 6.15 kcal mol(-1), which is in excellent agreement with the experimental value of Lester et al. [J. Phys. Chem. A, 2007, 111, 4727.]. PMID:18688380
Quantum molecular dynamics study on the structures and dc conductivity of warm dense silane
NASA Astrophysics Data System (ADS)
Sun, Huayang; Kang, Dongdong; Dai, Jiayu; Zeng, Jiaolong; Yuan, Jianmin
2014-02-01
The ionic and electronic structures of warm dense silane at the densities of 1.795, 2.260, 3.382, and 3.844 g/cm3 have been studied with temperatures from 1000 K to 3 eV using quantum molecular dynamics simulations. At all densities, the structures are melted above 1000 K. The matter states are characterized as polymeric from 1000 to 4000 K and become dense plasma states with further increasing temperature to 1 eV. At two lower densities of 1.795 and 2.260 g/cm3, silane first dissociates and then becomes the polymeric state via a chain state from the initial crystalline structure. At higher densities, however, no dissociation stage was found. These findings can help us understand how the warm dense matter forms. A rise is found for the direct current electric conductivity at T ˜1000 K, indicating the nonmetal-to-metal transition. The conductivity decreases slightly with the increase of temperature, which is due to the more disordered structures at higher temperatures.
A molecular dynamics study of nuclear quantum effect on the diffusion of hydrogen in condensed phase
NASA Astrophysics Data System (ADS)
Nagashima, Hiroki; Tsuda, Shin-ichi; Tsuboi, Nobuyuki; Koshi, Mitsuo; Hayashie, A. Koichi; Tokumasu, Takashi
2014-10-01
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.
Zeno dynamics in quantum open systems
Zhang, Yu-Ran; Fan, Heng
2015-01-01
Quantum Zeno effect shows that frequent observations can slow down or even stop the unitary time evolution of an unstable quantum system. This effect can also be regarded as a physical consequence of the statistical indistinguishability of neighboring quantum states. The accessibility of quantum Zeno dynamics under unitary time evolution can be quantitatively estimated by quantum Zeno time in terms of Fisher information. In this work, we investigate the accessibility of quantum Zeno dynamics in quantum open systems by calculating noisy Fisher information when a trace preserving and completely positive map is assumed. We firstly study the consequences of non-Markovian noise on quantum Zeno effect and give the exact forms of the dissipative Fisher information and the quantum Zeno time. Then, for the operator-sum representation, an achievable upper bound of the quantum Zeno time is given with the help of the results in noisy quantum metrology. It is of significance that the noise reducing the accuracy in the entanglement-enhanced parameter estimation can conversely be favorable for the accessibility of quantum Zeno dynamics of entangled states. PMID:26099840
Universal simulation of Markovian quantum dynamics
Dave Bacon; Andrew M. Childs; Isaac L. Chuang; Julia Kempe; Debbie W. Leung; Xinlan Zhou
2001-06-18
Although the conditions for performing arbitrary unitary operations to simulate the dynamics of a closed quantum system are well understood, the same is not true of the more general class of quantum operations (also known as superoperators) corresponding to the dynamics of open quantum systems. We propose a framework for the generation of Markovian quantum dynamics and study the resources needed for universality. For the case of a single qubit, we show that a single nonunitary process is necessary and sufficient to generate all unital Markovian quantum dynamics, whereas a set of processes parametrized by one continuous parameter is needed in general. We also obtain preliminary results for the unital case in higher dimensions.
Quantum emitters dynamically coupled to a quantum field
Acevedo, O. L.; Quiroga, L.; Rodríguez, F. J. [Departamento de Física, Universidad de los Andes, A.A. 4976, Bogotá (Colombia); Johnson, N. F. [Department of Physics, University of Miami, Coral Gables, Miami, FL 33124 (United States)
2013-12-04
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.
Quantum dynamics in dual spaces
Sudarshan, E.C.G.
1993-12-31
Quantum mechanics gives us information about spectra of dynamical variables and transition rates including scattering cross sections. They can be exhibited as spectral information in analytically continued spaces and their duals. Quantum mechanics formulated in these generalized spaces is used to study scattering and time evolution. It is shown that the usual asymptotic condition is inadequate to deal with scattering of composite or unstable particles. Scattering theory needs amendment when the interacting system is not isospectral with the free Hamiltonian, and the amendment is formulated. Perturbation theory in generalized spaces is developed and used to study the deletion and augmentation of the spectrum of the Hamiltonian. A complete set of algebraically independent constants for an interacting system is obtained. The question of the breaking of time symmetry is discussed.
Shielding quantum discord through continuous dynamical decoupling
Felipe F. Fanchini; Emanuel F. de Lima; Leonardo K. Castelano
2012-11-06
This work investigates the use of dynamical decoupling to shield quantum discord from errors introduced by the environment. Specifically, a two-qubits system interacting with independent baths of bosons is considered. The initial conditions of the system were chosen as pure and mixed states, while the dynamical decoupling has been achieved by means of continuous fields. The effects of the temperature on the shielding of quantum discord is also studied. It is shown that although the quantum discord for particular initial states may be perfectly preserved over some finite time window in the absence of any protective field, the effectiveness of the dynamical decoupling with continuous fields depends essentially on the timescale required to preserve quantum discord. It is also shown that for these particular initial states the time for which the shielding of the quantum discord becomes effective decreases as the temperature increases.
Dynamics of quantum discord in a quantum critical environment
NASA Astrophysics Data System (ADS)
Xi, Zhengjun; Lu, Xiao-Ming; Sun, Zhe; Li, Yongming
2011-11-01
We study the dynamics of quantum discord (QD) of two qubits independently coupled to an Ising spin chain in a transverse field, which exhibits a quantum phase transition. For this model, we drive the corresponding Kraus operators, obtain the analytic results of QD and compare the dynamics of QD with the dynamics of relative entropy of entanglement nearby the critical point. It is shown that the impact of the quantum criticality environment on QD can be concentrated in a very narrow region nearby the critical point, so it supplies an efficient way to detect the critical points. In the vicinity of the critical point, the evolution of QD is shown to be more complicated than that of entanglement. Furthermore, we find that separable states can also be used to reflect the quantum criticality of the environment.
Consciousness and Quantum Brain Dynamics
NASA Astrophysics Data System (ADS)
Globus, Gordon
The opposition to quantum brain theory is "deconstructed". The quantum brain theory originated by Umezawa and coworkers is elaborated as a unimode quantum brain dynamics (QBD), a Hermitean dual-mode QBD and a non-Hermitean dual-mode QBD. The non-Hermitean version is applied to mathematics, where the Riemann hypothesis is seen in a fresh way. The philosophical implications of this approach turn out to be "monadological".
Hammes-Schiffer, Sharon
Hybrid approach for including electronic and nuclear quantum effects in molecular dynamics profiles. The dynamical effects are studied with the molecular dynamics with quantum transitions MDQT is the use of classical molecular dynamics simulations with molecular mechanical forcefields.7
Six-dimensional quantum dynamics study for the dissociative adsorption of HCl on Au(111) surface
Liu, Tianhui; Fu, Bina; Zhang, Dong H., E-mail: zhangdh@dicp.ac.cn [State Key Laboratory of Molecular Reaction Dynamics and Center for Theoretical Computational Chemistry, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023 (China)
2013-11-14
The six-dimensional quantum dynamics calculations for the dissociative chemisorption of HCl on Au(111) are carried out using the time-dependent wave-packet approach, based on an accurate PES which was recently developed by neural network fitting to density functional theory energy points. The influence of vibrational excitation and rotational orientation of HCl on the reactivity is investigated by calculating the exact six-dimensional dissociation probabilities, as well as the four-dimensional fixed-site dissociation probabilities. The vibrational excitation of HCl enhances the reactivity and the helicopter orientation yields higher dissociation probability than the cartwheel orientation. A new interesting site-averaged effect is found for the title molecule-surface system that one can essentially reproduce the six-dimensional dissociation probability by averaging the four-dimensional dissociation probabilities over 25 fixed sites.
Six-dimensional quantum dynamics study for the dissociative adsorption of HCl on Au(111) surface
NASA Astrophysics Data System (ADS)
Liu, Tianhui; Fu, Bina; Zhang, Dong H.
2013-11-01
The six-dimensional quantum dynamics calculations for the dissociative chemisorption of HCl on Au(111) are carried out using the time-dependent wave-packet approach, based on an accurate PES which was recently developed by neural network fitting to density functional theory energy points. The influence of vibrational excitation and rotational orientation of HCl on the reactivity is investigated by calculating the exact six-dimensional dissociation probabilities, as well as the four-dimensional fixed-site dissociation probabilities. The vibrational excitation of HCl enhances the reactivity and the helicopter orientation yields higher dissociation probability than the cartwheel orientation. A new interesting site-averaged effect is found for the title molecule-surface system that one can essentially reproduce the six-dimensional dissociation probability by averaging the four-dimensional dissociation probabilities over 25 fixed sites.
Six-dimensional quantum dynamics study for the dissociative adsorption of HCl on Au(111) surface.
Liu, Tianhui; Fu, Bina; Zhang, Dong H
2013-11-14
The six-dimensional quantum dynamics calculations for the dissociative chemisorption of HCl on Au(111) are carried out using the time-dependent wave-packet approach, based on an accurate PES which was recently developed by neural network fitting to density functional theory energy points. The influence of vibrational excitation and rotational orientation of HCl on the reactivity is investigated by calculating the exact six-dimensional dissociation probabilities, as well as the four-dimensional fixed-site dissociation probabilities. The vibrational excitation of HCl enhances the reactivity and the helicopter orientation yields higher dissociation probability than the cartwheel orientation. A new interesting site-averaged effect is found for the title molecule-surface system that one can essentially reproduce the six-dimensional dissociation probability by averaging the four-dimensional dissociation probabilities over 25 fixed sites. PMID:24320289
Sheldon Goldstein; Ward Struyve
2014-11-05
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.
NASA Astrophysics Data System (ADS)
Azzouz, H.; Borgis, D.
1993-05-01
A molecular-dynamics study of a model for AH-B?A--H+B reactions in liquid chloromethane is presented. The parameters of the model are fitted to those of typical OH-N proton-transfer complexes. The rate constant is computed at a quantum level for complexes of various H-bond strength and A-B equilibrium distance. The influence of the properties of the complex on the proton-transfer mechanism is outlined. Also the static and dynamical role of the solvent, the tunneling contribution to the rate, and the associated kinetic isotope effect are discussed. The rate calculations are based on two independent methods. First a curve-crossing, transition-state rate formula which, although related to standard charge-transfer theories, presents some original features and allows the determination of the rate at very low computational cost is developed. The curve-crossing results are compared to those of a path-integral, quantum transition-state calculation. The overall agreement between the two methods is satisfactory, although there is a discrepancy in the adiabatic reaction regime; a rigorous estimation of the transmission coefficients would be needed then. Finally, it is shown that zero-point energy and parabolic barrier tunneling factors added to the classical transition-state-theory rate constant are unable to describe properly the quantum effects in the present case.
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
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.
Saieswari Amaran; Ronnie Kosloff; Micha? Tomza; Wojciech Skomorowski; Filip Pawlowski; Robert Moszynski; Leonid Rybak; Liat Levin; Zohar Amitay; J. Martin Berglund; Daniel M. Reich; Christiane P. Koch
2013-10-31
Two-photon photoassociation of hot magnesium atoms by femtosecond laser pulses, creating electronically excited magnesium dimer molecules, is studied from first principles, combining \\textit{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 \\textit{et al.}, Phys. Rev. Lett. {\\bf 107}, 273001 (2011)]. Random phase thermal wave functions 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.
Quantifying spatial correlations of general quantum dynamics
NASA Astrophysics Data System (ADS)
Rivas, Ángel; Müller, Markus
2015-06-01
Understanding the role of correlations in quantum systems is both a fundamental challenge as well as of high practical relevance for the control of multi-particle quantum systems. Whereas a lot of research has been devoted to study the various types of correlations that can be present in the states of quantum systems, in this work we introduce a general and rigorous method to quantify the amount of correlations in the dynamics of quantum systems. Using a resource-theoretical approach, we introduce a suitable quantifier and characterize the properties of correlated dynamics. Furthermore, we benchmark our method by applying it to the paradigmatic case of two atoms weakly coupled to the electromagnetic radiation field, and illustrate its potential use to detect and assess spatial noise correlations in quantum computing architectures.
Quantum discord dynamics in structured reservoirs
Z. -K. Su; S. -J. Jiang
2011-05-25
The non-Markovian master equations are derived to study quantum discord dynamics of two qubits coupled to a common reservoir and two independent reservoirs, respectively. We compare the dynamics under different parameters, such as reservoir spectra and resonant parameters, at high temperature and at zero temperature. The results indicate that the dynamics at these two extreme temperatures share similar characters, as well as differences.
Asshoff, P.; Loeffler, W.; Fluegge, H.; Zimmer, J.; Mueller, J.; Westenfelder, B.; Hu, D. Z.; Schaadt, D. M.; Kalt, H.; Hetterich, M. [Institut fuer Angewandte Physik and DFG Center for Functional Nanostructures (CFN), Universitaet Karlsruhe, 76131 Karlsruhe (Germany)
2010-01-04
We present time-resolved studies of the spin polarization dynamics during and after initialization through pulsed electrical spin injection into InGaAs quantum dots embedded in a p-i-n-type spin-injection light-emitting diode. Experiments are performed with pulse widths in the nanosecond range and a time-resolved single photon counting setup is used to detect the subsequent electroluminescence. We find evidence that the achieved spin polarization shows an unexpected temporal behavior, attributed mainly to many-carrier and non-equilibrium effects in the device.
NASA Astrophysics Data System (ADS)
Lévêque, Camille; Köppel, Horst; Taïeb, Richard
2014-05-01
We present an ab initio quantum study of the photoelectron spectra of sulfur dioxide, based on wavepacket propagations on manifolds of ionic, and excited/Rydberg states. We obtain excellent agreement for two different cases. First, the one photon ionization case where we can reproduce all details of the experimental spectrum and demonstrate the influence of the conical intersection between two of the ionic states. Then the multiphoton ionization regime, in which the dynamics of the wave packet on the two lowest singlet states is directly mapped in the spectra via a pump-probe scheme, as proposed in the experimental companion paper [I. Wilkinson et al., J. Chem. Phys. 140, 204301 (2014)].
Quaternionic Quantum Dynamics on Complex Hilbert Spaces
Matthew A. Graydon
2011-03-18
We consider a quaternionic quantum formalism for the description of quantum states and quantum dynamics. We prove that generalized quantum measurements on physical systems in quaternionic quantum theory can be simulated by usual quantum measurements with positive operator valued measures on complex Hilbert spaces. Furthermore, we prove that quaternionic quantum channels can be simulated by completely positive trace preserving maps on complex matrices. These novel results map all quaternionic quantum processes to algorithms in usual quantum information theory.
Quantum nature of the big bang: Improved dynamics
Abhay Ashtekar; Tomasz Pawlowski; Parampreet Singh
2006-01-01
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
NASA Astrophysics Data System (ADS)
Völl, Annika; Wessel, Stefan
2015-04-01
We study thermodynamic properties as well as the dynamical spin and quadrupolar structure factors of the O(3)-symmetric spin-1 Heisenberg model with bilinear-biquadratic exchange interactions on the triangular lattice. Based on a sign-problem-free quantum Monte Carlo approach, we access both the ferromagnetic and the ferroquadrupolar ordered spin nematic phase as well as the SU(3)-symmetric point that separates these phases. Signatures of Goldstone soft modes in the dynamical spin and the quadrupolar structure factors are identified, and the properties of the low-energy excitations are compared to the thermodynamic behavior observed at finite temperatures as well as to Schwinger-boson flavor-wave theory.
Stochastic Quantum Gas Dynamics
NASA Astrophysics Data System (ADS)
Proukakis, Nick P.; Cockburn, Stuart P.
2010-03-01
We study the dynamics of weakly-interacting finite temperature Bose gases via the Stochastic Gross-Pitaevskii equation (SGPE). As a first step, we demonstrate [jointly with A. Negretti (Ulm, Germany) and C. Henkel (Potsdam, Germany)] that the SGPE provides a significantly better method for generating an equilibrium state than the number-conserving Bogoliubov method (except for low temperatures and small atom numbers). We then study [jointly with H. Nistazakis and D.J. Frantzeskakis (University of Athens, Greece), P.G.Kevrekidis (University of Massachusetts) and T.P. Horikis (University of Ioannina, Greece)] the dynamics of dark solitons in elongated finite temperature condensates. We demonstrate numerical shot-to-shot variations in soliton trajectories (S.P. Cockburn et al., arXiv:0909.1660.), finding individual long-lived trajectories as in experiments. In our simulations, these variations arise from fluctuations in the phase and density of the underlying medium. We provide a detailed statistical analysis, proposing regimes for the controlled experimental demonstration of this effect; we also discuss the extent to which simpler models can be used to mimic the features of ensemble-averaged stochastic trajectories.
Studies of dynamical localization in a finite-dimensional model of the quantum kicked rotator
Thanos Manos; Marko Robnik
2015-04-12
We review our recent works on the dynamical localization in the quantum kicked rotator (QKR) and the related properties of the classical kicked rotator (the standard map, SM). We introduce the Izrailev $N$-dimensional model of the QKR and analyze the localization properties of the Floquet eigenstates [{\\em Phys. Rev. E} {\\bf 87}, 062905 (2013)], and the statistical properties of the quasienergy spectra. We survey normal and anomalous diffusion in the SM, and the related accelerator modes [{\\em Phys. Rev. E} {\\bf 89}, 022905 (2014)]. We analyze the statistical properties [{\\em Phys. Rev. E} {\\bf 91},042904 (2015)] of the localization measure, and show that the reciprocal localization length has an almost Gaussian distribution which has a finite variance even in the limit of the infinitely dimensional model of the QKR, $N\\rightarrow \\infty$. This sheds new light on the relation between the QKR and the Anderson localization phenomenon in the one-dimensional tight-binding model. It explains the so far mysterious strong fluctuations in the scaling properties of the QKR. The reason is that the finite bandwidth approximation of the underlying Hamilton dynamical system in the Shepelyansky picture [{\\em Phys. Rev. Lett.} {\\bf 56}, 677 (1986)] does not apply rigorously. These results call for a more refined theory of the localization length in the QKR and in similar Floquet systems, where we must predict not only the mean value of the inverse of the localization length but also its (Gaussian) distribution. We also numerically analyze the related behavior of finite time Lyapunov exponents in the SM and of the $2\\times2$ transfer matrix formalism.
Control by quantum dynamics on graphs
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
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.
Quantum dynamics study of the reaction HD+OH{r_arrow}H+DOH, D+HOH
Zhang, D.H.; Zhang, J.Z.H. [Department of Chemistry, New York University, New York, New York 10003 (United States)] [Department of Chemistry, New York University, New York, New York 10003 (United States); Zhang, Y.; Wang, D.; Zhang, Q. [Department of Physics, Shandong Teacher`s University, Jinan, Shandong (China)] [Department of Physics, Shandong Teacher`s University, Jinan, Shandong (China)
1995-05-15
Accurate time-dependent (TD) quantum wavepacket calculations are reported for the combustion reaction HD+OH. Due to the lack of symmetry, the HD+OH reaction has roughly twice the number of channels of the corresponding H{sub 2}+OH reaction and produces two distinguishable products--HOH and HOD. In order to make the TD calculation possible on workstations with limited memories, we employed a normalized quadrature scheme in the wavepacket propagation by the split-operator propagator. The normalized quadrature scheme eliminates the need to store large matrices during the wavepacket propagation while preserving the unitarity of the split-operator propagator and producing numerically stable results. This approach made TD dynamics calculations possible on small-memory workstations for the title reaction and for other polyatomic reactions. Reaction probabilities, cross sections, rate constants, and reaction branching ratios are reported in this paper for the title reaction. The observed strong dependence of the reaction probabilities on the reactive HD rotation and the relative weak dependence on the nonreactive OH rotation are explained in terms of a steric effect. The isotope effect in the branching ratio is examined and physical explanation is given for the observed branching ratio at low and high kinetic energies.
Wang, Cong; Long, Yao; Tian, Ming-Feng; He, Xian-Tu; Zhang, Ping
2013-04-01
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
Li, Dafang; Liu, Haitao; Zeng, Siliang; Wang, Cong; Wu, Zeqing; Zhang, Ping; Yan, Jun
2014-01-01
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
Dynamical evaporation of quantum horizons
NASA Astrophysics Data System (ADS)
Pranzetti, Daniele
2013-08-01
We describe the black hole evaporation process driven by the dynamical evolution of the quantum gravitational degrees of freedom resident at the horizon, as identified by the loop quantum gravity kinematics. Using a parallel with the Brownian motion, we interpret the first law of the quantum-dynamical horizon in terms of a fluctuation-dissipation relation applied to this fundamental discrete structure. In this way, the horizon evolution is described in terms of relaxation to an equilibrium state balanced by the excitation of Planck scale constituents of the horizon. We investigate the final stage of the evaporation process and show how, from this setting, the emergence of several conservative scenarios for the information paradox can be microscopically derived. Namely, the leakage of part of the horizon quantum geometry information prior to the Planckian phase and the stabilization of the hole surface shrinkage forming a massive remnant, which can eventually decay, are described.
Dynamical evaporation of quantum horizons
Pranzetti, Daniele
2013-01-01
We describe the black hole evaporation process driven by the dynamical evolution of the quantum gravitational degrees of freedom resident at the horizon, as identified by the Loop Quantum Gravity kinematics. Using a parallel with the Brownian motion, we interpret the first law of quantum dynamical horizon in terms of a fluctuation-dissipation relation applied to this fundamental discrete structure. In this way, the horizon evolution is described in terms of relaxation to an equilibrium state balanced by the excitation of Planck scale constituents of the horizon. We investigate the final stage of the evaporation process and show how, from this setting, the emergence of several conservative scenarios for the information paradox can be microscopically derived. Namely, the leakage of part of the horizon quantum geometry information prior to the Planckian phase and the stabilization of the hole surface shrinkage forming a massive remnant, which can eventually decay, are described.
Dynamical Correspondence in a Generalized Quantum Theory
Gerd Niestegge
2015-03-06
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 Lueders-von Neumann quantum measurement process, and third-order interference is a property of the conditional probabilities which was discovered by R. Sorkin in 1994 and which is ruled out by quantum mechanics. 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.
Reynolds, J.
1997-10-08
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.
NASA Astrophysics Data System (ADS)
Ghatee, Mohammad Hadi; Sedghamiz, Tahereh
2014-12-01
Enantiomeric recognition of Propranolol by complexation with ?-Cyclodextrin was studied by PM3 method and molecular dynamics (MD) simulation. Gas phase results show that the R-enantiomer complex is more stable than the S-enantiomer complex by 8.54 kJ/mol (Hartree-Fock energy). Using polarized continuum model, solution phase of R-enantiomer complex was found to be more stable than S-enantiomer complex by 25.95 kJ/mol. Both complexes hardly occur at room temperature free-energy-wise, though, complexation with R-enantiomer is more favorable than with S-enantiomer enthalpy-wise. Also, complexes were studied by molecular dynamics simulation in gas and solution phases. More stability of R-enantiomer complex in gas phase is confirmed by MD van der Waals energy (5.04 kJ/mol) and closely by the counterpart PM3 binding energy (8.54 kJ/mol). Simulation in solution phase indicates more stability of R-enantiomer complex. Finally, simulated transport property provides insight into the high anisotropic atoms motion according to which S-Propranolol found possessing significantly higher dynamics.
Nonlocal interactions and quantum dynamics
Renat Kh. Gainutdinov
2001-06-19
The problem is considered of describing the dynamics of quantum systems generated by a nonlocal in time interaction. It is shown that the use of the Feynman approach to quantum theory in combination with the canonical approach allows one to extend quantum dynamics to describe the time evolution in the case of such interactions. In this way, using only the current concepts of quantum theory, a generalized equation of motion for state vectors is derived. In the case, where the fundamental interaction generating the dynamics in a system is local in time, this equation is equivalent to the Schr{\\"o}dinger equation. Explicit examples are given for an exactly solvable model. The proposed formalism is shown to provide a new insight into the problem of the description of nonlocal interactions in quantum field theory. It is shown that such a property of the equation of motion as nonlocality in time may be important for describing hadron-hadron interactions at low and intermediate energies.
Experimental Study of Quantum Dynamics in a Regime of Classical Anomalous Diffusion
B. G. Klappauf; W. H. Oskay; D. A. Steck; M. G. Raizen
1998-01-01
We measure the momentum of cold cesium atoms in a periodically pulsed standing wave of light. This system is an experimental realization of the quantum kicked rotor. The momentum diffusion in the (chaotic) classical analog of this system is typically suppressed by quantum localization. We find, however, that for certain pulse amplitudes where the classical system exhibits anomalous diffusion, our
Quantum Fluctuations and Dynamical Chaos
Matinyan, S.G.; Mueller, B. [Department of Physics, Duke University, Durham, North Carolina 27708-0305 (United States)] [Department of Physics, Duke University, Durham, North Carolina 27708-0305 (United States); Matinyan, S.G. [Yerevan Physics Institute, Yerevan (Armenia)] [Yerevan Physics Institute, Yerevan (Armenia)
1997-03-01
We discuss the intimate connection between the chaotic dynamics of a classical field theory and the instability of the one-loop effective action of the associated quantum field theory. Using massless scalar electrodynamics as an example, we show how the radiatively induced spontaneous symmetry breaking stabilizes the vacuum state against chaos. {copyright} {ital 1997} {ital The American Physical Society}
Theory of controlled quantum dynamics
Salvatore De Martino; Silvio De Siena; Fabrizio Illuminati
1997-01-01
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
Distance Bounds on Quantum Dynamics
D. A. Lidar; P. Zanardi; K. Khodjasteh
2008-03-29
We derive rigorous upper bounds on the distance between quantum states in an open system setting, in terms of the operator norm between the Hamiltonians describing their evolution. We illustrate our results with an example taken from protection against decoherence using dynamical decoupling.
Nonequilibrium quench dynamics in quantum quasicrystals
Ferenc Igloi; Gergo Roosz; Yu-Cheng Lin
2013-02-18
We study the nonequilibrium dynamics of a quasiperiodic quantum Ising chain after a sudden change in the strength of the transverse field at zero temperature. In particular we consider the dynamics of the entanglement entropy and the relaxation of the magnetization. The entanglement entropy increases with time as a power-law, and the magnetization is found to exhibit stretched-exponential relaxation. These behaviors are explained in terms of anomalously diffusing quasiparticles, which are studied in a wave packet approach. The nonequilibrium magnetization is shown to have a dynamical phase transition.
Lévêque, Camille; Köppel, Horst; Taïeb, Richard
2014-05-28
We present an ab initio quantum study of the photoelectron spectra of sulfur dioxide, based on wavepacket propagations on manifolds of ionic, and excited/Rydberg states. We obtain excellent agreement for two different cases. First, the one photon ionization case where we can reproduce all details of the experimental spectrum and demonstrate the influence of the conical intersection between two of the ionic states. Then the multiphoton ionization regime, in which the dynamics of the wave packet on the two lowest singlet states is directly mapped in the spectra via a pump-probe scheme, as proposed in the experimental companion paper [I. Wilkinson et al., J. Chem. Phys. 140, 204301 (2014)]. PMID:24880276
Experimental realization of quantum zeno dynamics.
Schäfer, F; Herrera, I; Cherukattil, S; Lovecchio, C; Cataliotti, F S; Caruso, F; Smerzi, A
2014-01-01
It is generally impossible to probe a quantum system without disturbing it. However, it is possible to exploit the back action of quantum measurements and strong couplings to tailor and protect the coherent evolution of a quantum system. This is a profound and counterintuitive phenomenon known as quantum Zeno dynamics. Here we demonstrate quantum Zeno dynamics with a rubidium Bose-Einstein condensate in a five-level Hilbert space. We harness measurements and strong couplings to dynamically disconnect different groups of quantum states and constrain the atoms to coherently evolve inside a two-level subregion. In parallel to the foundational importance due to the realization of a dynamical superselection rule and the theory of quantum measurements, this is an important step forward in protecting and controlling quantum dynamics and, broadly speaking, quantum information processing. PMID:24476716
Fractional-time quantum dynamics.
Iomin, Alexander
2009-08-01
Application of the fractional calculus to quantum processes is presented. In particular, the quantum dynamics is considered in the framework of the fractional time Schrödinger equation (SE), which differs from the standard SE by the fractional time derivative: partial differential/partial differentialt --> partial differential(alpha)/partial differentialt(alpha). It is shown that for alpha=1/2 the fractional SE is isospectral to a comb model. An analytical expression for the Green's functions of the systems are obtained. The semiclassical limit is discussed. PMID:19792181
Yamada, Atsushi; Kojima, Hidekazu; Okazaki, Susumu
2014-08-28
In order to investigate proton transfer reaction in solution, mixed quantum-classical molecular dynamics calculations have been carried out based on our previously proposed quantum equation of motion for the reacting system [A. Yamada and S. Okazaki, J. Chem. Phys. 128, 044507 (2008)]. Surface hopping method was applied to describe forces acting on the solvent classical degrees of freedom. In a series of our studies, quantum and solvent effects on the reaction dynamics in solutions have been analysed in detail. Here, we report our mixed quantum-classical molecular dynamics calculations for intramolecular proton transfer of malonaldehyde in water. Thermally activated proton transfer process, i.e., vibrational excitation in the reactant state followed by transition to the product state and vibrational relaxation in the product state, as well as tunneling reaction can be described by solving the equation of motion. Zero point energy is, of course, included, too. The quantum simulation in water has been compared with the fully classical one and the wave packet calculation in vacuum. The calculated quantum reaction rate in water was 0.70 ps(-1), which is about 2.5 times faster than that in vacuum, 0.27 ps(-1). This indicates that the solvent water accelerates the reaction. Further, the quantum calculation resulted in the reaction rate about 2 times faster than the fully classical calculation, which indicates that quantum effect enhances the reaction rate, too. Contribution from three reaction mechanisms, i.e., tunneling, thermal activation, and barrier vanishing reactions, is 33:46:21 in the mixed quantum-classical calculations. This clearly shows that the tunneling effect is important in the reaction. PMID:25173023
Quantum dynamical semigroups generated by noncommutative unbounded elliptic operators
C. Bahn; C. K. Ko; Y. M. Park
2005-05-09
We study quantum dynamical semigroups generated by noncommutative unbounded elliptic operators which can be written as Lindblad type unbounded generators. Under appropriate conditions, we first construct the minimal quantum dynamical semigroups for the generators and then use Chebotarev and Fagnola's sufficient conditions for conservativity to show that the semigroups are conservative.
Understanding quantum entanglement by thermo field dynamics
NASA Astrophysics Data System (ADS)
Hashizume, Yoichiro; Suzuki, Masuo
2013-09-01
We propose a new method to understand quantum entanglement using the thermo field dynamics (TFD) described by a double Hilbert space. The entanglement states show a quantum-mechanically complicated behavior. Our new method using TFD makes it easy to understand the entanglement states, because the states in the tilde space in TFD play a role of tracer of the initial states. For our new treatment, we define an extended density matrix on the double Hilbert space. From this study, we make a general formulation of this extended density matrix and examine some simple cases using this formulation. Consequently, we have found that we can distinguish intrinsic quantum entanglement from the thermal fluctuations included in the definition of the ordinary quantum entanglement at finite temperatures. Through the above examination, our method using TFD can be applied not only to equilibrium states but also to non-equilibrium states. This is shown using some simple finite systems in the present paper.
Quench dynamics across quantum critical points
Sengupta, K.; Powell, Stephen; Sachdev, Subir [Department of Physics, Yale University, P.O. Box 208120, New Haven, Connecticut 06520-8120 (United States)
2004-05-01
We study the quantum dynamics of a number of model systems as their coupling constants are changed rapidly across a quantum critical point. The primary motivation is provided by the recent experiments of Greiner et al. [Nature (London) 415, 39 (2002)] who studied the response of a Mott insulator of ultracold atoms in an optical lattice to a strong potential gradient. In a previous work, it had been argued that the resonant response observed at a critical potential gradient could be understood by proximity to an Ising quantum critical point describing the onset of density wave order. Here we obtain numerical results on the evolution of the density wave order as the potential gradient is scanned across the quantum critical point. This is supplemented by studies of the integrable quantum Ising spin chain in a transverse field, where we obtain exact results for the evolution of the Ising order correlations under a time-dependent transverse field. We also study the evolution of transverse superfluid order in the three-dimensional case. In all cases, the order parameter is best enhanced in the vicinity of the quantum critical point.
Quantum dynamics of human decision-making
Jerome R. Busemeyer; Zheng Wang; James T. Townsend
2006-01-01
A quantum dynamic model of decision-making is presented, and it is compared with a previously established Markov model. Both the quantum and the Markov models are formulated as random walk decision processes, but the probabilistic principles differ between the two approaches. Quantum dynamics describe the evolution of complex valued probability amplitudes over time, whereas Markov models describe the evolution of
Quantum Discord: A Dynamic Approach in Geometric Picture
Mingjun Shi; Fengjian Jiang; Jiangfeng Du
2011-07-22
We present a dynamic approach to study the quantum discord and classical correlation. By local filtering operation, the evaluation of quantum discord is closely related to quantum channel and channel capacity. As a consequence, the traditional optimization over horizontal-or-vertical von Neumann measurements is replaced by that over horizontal-and-vertical three-element POVM measurement, from which more rigorous results of quantum discord are obtained.
Ibrahim, Mahmoud A A
2011-10-24
The performance of semiempirical molecular-orbital methods--MNDO, MNDO-d, AM1, RM1, PM3 and PM6--in describing halogen bonding was evaluated, and the results were compared with molecular mechanical (MM) and quantum mechanical (QM) data. Three types of performance were assessed: (1) geometrical optimizations and binding energy calculations for 27 halogen-containing molecules complexed with various Lewis bases (Two of the tested methods, AM1 and RM1, gave results that agree with the QM data.); (2) charge distribution calculations for halobenzene molecules, determined by calculating the solvation free energies of the molecules relative to benzene in explicit and implicit generalized Born (GB) solvents (None of the methods gave results that agree with the experimental data.); and (3) appropriateness of the semiempirical methods in the hybrid quantum-mechanical/molecular-mechanical (QM/MM) scheme, investigated by studying the molecular inhibition of CK2 protein by eight halobenzimidazole and -benzotriazole derivatives using hybrid QM/MM molecular-dynamics (MD) simulations with the inhibitor described at the QM level by the AM1 method and the rest of the system described at the MM level. The pure MM approach with inclusion of an extra point of positive charge on the halogen atom approach gave better results than the hybrid QM/MM approach involving the AM1 method. Also, in comparison with the pure MM-GBSA (generalized Born surface area) binding energies and experimental data, the calculated QM/MM-GBSA binding energies of the inhibitors were improved by replacing the G(GB,QM/MM) solvation term with the corresponding G(GB,MM) term. PMID:21942911
Quantum Spin Dynamics and Quantum Computation
H. De Raedt; A. H. Hams; K. Michielsen; S. Miyashita; K. Saito
2000-01-14
We describe a simulation method for a quantum spin model of a generic, general purpose quantum computer. The use of this quantum computer simulator is illustrated through several implementations of Grover's database search algorithm. Some preliminary results on the stability of quantum algorithms are presented.
Quantum nature of the big bang: Improved dynamics
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
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.
Quantum dynamical study of the O((1)D) + CH4 ? CH3 + OH atmospheric reaction.
Ben Bouchrit, R; Jorfi, M; Ben Abdallah, D; Jaidane, N; González, M; Bussery-Honvault, B; Honvault, P
2014-06-28
Time independent quantum mechanical (TIQM) scattering calculations have been carried out for the O((1)D) + CH4(X(1)A1) ? CH3(X(2)A2?) + OH(X(2)?) atmospheric reaction, using an ab initio ground potential energy surface where the CH3 group is described as a pseudo-atom. Total and state-to-state reaction probabilities for a total angular momentum J = 0 have been determined for collision energies up to 0.5 eV. The vibrational and rotational state OH product distributions show no specific behavior. The rate coefficient has been calculated by means of the J-shifting approach in the 10-500 K temperature range and slightly depends on T at ordinary temperatures (as expected for a barrierless reaction). Quantum effects do not influence the vibrational populations and rate coefficient in an important way, and a rather good agreement has been found between the TIQM results and the quasiclassical trajectory and experimental ones. This reinforces somewhat the reliability of the pseudo-triatomic approach under the reaction conditions explored. PMID:24985646
Carrier Dynamics in Colloidal Graphene Quantum Dots
Cheng Sun; Xin Yan; Liang-Shi Li; John A. McGuire
2011-01-01
We describe carrier dynamics for single and multiple excitons in colloidal graphene quantum dots (GQDs). Strong confinement and corresponding size-tunable electronic structure make GQDs potentially useful sensitizers in photovoltaic devices. We have studied the optical response of GQDs consisting of 132 and 168 sp^2 hybridized carbon atoms dissolved in toluene with HOMO-LUMO transitions of 1.4-1.6 eV. From measurements of ultrafast
Quantum dynamics as a physical resource
Michael A. Nielsen; Christopher M. Dawson; Jennifer L. Dodd; Alexei Gilchrist; Duncan Mortimer; Tobias J. Osborne; Michael J. Bremner; Aram W. Harrow; Andrew Hines
2003-01-13
How useful is a quantum dynamical operation for quantum information processing? Motivated by this question we investigate several strength measures quantifying the resources intrinsic to a quantum operation. We develop a general theory of such strength measures, based on axiomatic considerations independent of state-based resources. The power of this theory is demonstrated with applications to quantum communication complexity, quantum computational complexity, and entanglement generation by unitary operations.
Joseph Patrick Reynolds
1997-01-01
Using high-accuracy numerical methods we investigate 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, we numerically solve the time-dependent Schrodinger equation. In the case of ideal periodic superlattice potentials, we
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
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
Xijia Miao
2011-11-22
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.
NASA Astrophysics Data System (ADS)
Ishizaki, Akihito; Fleming, Graham R.
2009-06-01
The observation of long-lived electronic coherence in photosynthetic excitation energy transfer (EET) by Engel et al. [Nature (London) 446, 782 (2007)] raises questions about the role of the protein environment in protecting this coherence and the significance of the quantum coherence in light harvesting efficiency. In this paper we explore the applicability of the Redfield equation in its full form, in the secular approximation and with neglect of the imaginary part of the relaxation terms for the study of these phenomena. We find that none of the methods can give a reliable picture of the role of the environment in photosynthetic EET. In particular the popular secular approximation (or the corresponding Lindblad equation) produces anomalous behavior in the incoherent transfer region leading to overestimation of the contribution of environment-assisted transfer. The full Redfield expression on the other hand produces environment-independent dynamics in the large reorganization energy region. A companion paper presents an improved approach, which corrects these deficiencies [A. Ishizaki and G. R. Fleming, J. Chem. Phys. 130, 234111 (2009)].
Why quantum dynamics is linear
NASA Astrophysics Data System (ADS)
Jordan, Thomas F.
2009-11-01
A seed George planted 45 years ago is still producing fruit now. In 1961, George set out the fundamental proposition that quantum dynamics is described most generally by linear maps of density matrices. Since the first sprout from George's seed appeared in 1962, we have known that George's fundamental proposition can be used to derive the linear Schrodinger equation in cases where it can be expected to apply. Now we have a proof of George's proposition that density matrices are mapped linearly to density matrices, that there can be no nonlinear generalization of this. That completes the derivation of the linear Schrodinger equation. The proof of George's proposition replaces Wigner's theorem that a symmetry transformation is represented by a linear or antilinear operator. The assumption needed to prove George's proposition is just that the dynamics does not depend on anything outside the system but must allow the system to be described as part of a larger system. This replaces the physically less compelling assumption of Wigner's theorem that absolute values of inner products are preserved. The history of this question is reviewed. Nonlinear generalizations of quantum mechanics have been proposed. They predict small but clear nonlinear effects, which very accurate experiments have not seen. This begs the question. Is there a reason in principle why nonlinearity is not found? Is it impossible? Does quantum dynamics have to be linear? Attempts to prove this have not been decisive, because either their assumptions are not compelling or their arguments are not conclusive. The question has been left unsettled. The simple answer, based on a simple assumption, was found in two steps separated by 44 years.
NASA Astrophysics Data System (ADS)
Cavelier, German; Amzel, L. Mario
2006-08-01
Quinone Reductase is a cytosolic FAD-containing enzyme that carries out the obligatory two-electron reduction of quinones to hydroquinones. The first step in the mechanism consists of the reduction of the FAD by NAD(P)H via direct a hydride transfer. Combined QM/MM calculations show that the protein accelerates this step by a combination of effects that include charge stabilization and distortion. The calculations also show that dynamic effects play an important role in QR catalysis: the distance between the donor and the acceptor atoms of the hydride transfer, which is too long for transfer in the static structure, becomes shorter than 3 Å 25% of the time due to motions of the protein and the cofactors.
Volume dynamics and quantum gravity
NASA Astrophysics Data System (ADS)
Haggard, Hal
2012-03-01
Polyhedral grains of space can be given a dynamical structure. In recent work it was shown that Bohr-Sommerfeld quantization of the volume of a tetrahedral grain of space results in a spectrum in excellent agreement with loop gravity. Here we present preliminary investigations of the volume of a 5-faced convex polyhedron. We give for the first time a constructive method for finding these polyhedra given their face areas and normals to the faces and find an explicit formula for the volume. In particular, we are interested in discovering whether the evolution generated by this volume is chaotic or integrable which has important consequences for loop gravity: If the classical volume generates a chaotic flow then the corresponding quantum spectrum will generically be non-degenerate and the volume eigenvalue continues to act as a good label for spin network states. On the other hand, if the volume flow is classically integrable then the degeneracy of the corresponding quantum spectrum will have to be lifted by another observable. We report on progress distinguishing these two cases. Either of these outcomes will impact the direction of future research into volume operators in quantum gravity.
A Theory of Accelerated Quantum Dynamics
Lynch, Morgan H
2015-01-01
The role of acceleration in particle physics can provide an alternative method for probing the properties of quantum gravity. To analyze acceleration-induced processes one utilizes the formalism of quantum field theory in curved spacetime. This quantum theory of fields in classical general relativistic backgrounds has already provided the first insights into the quantum effects of general relativity. By utilizing this formalism to compute acceleration-induced particle physics processes, we can better establish how the dynamics of elementary particles change in non-Minkowskian spacetimes. To analyze these processes, we present a theory of Accelerated Quantum Dynamics (AQD) along with certain observables predicted by the theory.
Modeling quantum fluid dynamics at nonzero temperatures
Modeling quantum fluid dynamics at nonzero temperatures Natalia G. Berloffa,b,1 , Marc Brachetc (received for review July 15, 2013) The detailed understanding of the intricate dynamics of quantum fluids in such systems. The Landau two-fluid model is the most successful hydrodynamical theory of superfluid helium
Silver, R.N.; Gubernatis, J.E.; Sivia, D.S. (Los Alamos National Lab., NM (USA)); Jarrell, M. (Ohio State Univ., Columbus, OH (USA). Dept. of Physics)
1990-01-01
In this article we describe the results of a new method for calculating the dynamical properties of the Anderson model. QMC generates data about the Matsubara Green's functions in imaginary time. To obtain dynamical properties, one must analytically continue these data to real time. This is an extremely ill-posed inverse problem similar to the inversion of a Laplace transform from incomplete and noisy data. Our method is a general one, applicable to the calculation of dynamical properties from a wide variety of quantum simulations. We use Bayesian methods of statistical inference to determine the dynamical properties based on both the QMC data and any prior information we may have such as sum rules, symmetry, high frequency limits, etc. This provides a natural means of combining perturbation theory and numerical simulations in order to understand dynamical many-body problems. Specifically we use the well-established maximum entropy (ME) method for image reconstruction. We obtain the spectral density and transport coefficients over the entire range of model parameters accessible by QMC, with data having much larger statistical error than required by other proposed analytic continuation methods.
Universality in dynamical formation of entanglement for quantum chaos
Kubotani, Hiroto; Toda, Mikito; Adachi, Satoshi [Institute of Physics, Faculty of Engineering, Kanagawa University, Yokohama 221-8686 (Japan); Department of Physics, Faculty of Science, Nara Women's University, Nara 630-8506 (Japan); Department of Physics, Faculty of Science, Tokyo Institute of Technology, Meguro 152-8550 (Japan)
2006-09-15
Dynamical formation of entanglement is studied for quantum chaotic biparticle systems. We find that statistical properties of the Schmidt eigenvalues for strong chaos are well described by the random matrix theory of the Laguerre unitary ensemble. This implies that entanglement formation for quantum chaos has universal properties, and does not depend on specific aspects of the systems.
Kessler, Ji?í; Dra?ínský, Martin; Bou?, Petr
2015-05-28
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
Structure and dynamics of acrolein in 1,3(?,? *) excited electronic states: A quantum-chemical study
NASA Astrophysics Data System (ADS)
Bokareva, O. S.; Bataev, V. A.; Pupyshev, V. I.; Godunov, I. A.
2009-08-01
The geometrical structure, conformer energy differences, and conformational and vibrational dynamics of acrolein in 1,3(?,? *) electronic states were investigated using a number of single- and multi-reference quantum-chemical methods. Peculiarities of acrolein in the 1(?,? *) state were described with both conformers being significantly non-planar. A Valence Focal-Point Analysis of the conformer energy difference in the 3(?,? *) state was performed. The coupling of the internal rotation about C sbnd C and C dbnd C bonds with large amplitude molecular motions, such as non-planar distortions of carbonyl, methylene, and methyne fragments was also investigated. The corresponding two-dimensional PES sections were constructed.
Quantum Geometry and Quantum Dynamics at the Planck Scale
Bojowald, Martin [Institute for Gravitation and the Cosmos, The Pennsylvania State University, 104 Davey Lab, University Park, PA 16802 (United States)
2009-12-15
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.
Effective quantum dynamics of interacting systems with inhomogeneous coupling
Lopez, C. E.; Retamal, J. C. [Departamento de Fisica, Universidad de Santiago de Chile, Casilla 307 Correo 2, Santiago (Chile); Christ, H. [Max-Planck-Institut fuer Quantenoptik, Hans-Kopfermann-Strasse 1, D-85748 Garching (Germany); Solano, E. [Max-Planck-Institut fuer Quantenoptik, Hans-Kopfermann-Strasse 1, D-85748 Garching (Germany); Physics Department, ASC, and CeNS, Ludwig-Maximilians-Universitaet, Theresienstrasse 37, 80333 Munich (Germany); Departamento de Ciencias, Seccion Fisica, Pontificia Universidad Catolica del Peru, Apartado 1761, Lima (Peru)
2007-03-15
We study the quantum dynamics of a single mode (particle) interacting inhomogeneously with a large number of particles and introduce an effective approach to find the accessible Hilbert space, where the dynamics takes place. Two relevant examples are given: the inhomogeneous Tavis-Cummings model (e.g., N atomic qubits coupled to a single cavity mode, or to a motional mode in trapped ions) and the inhomogeneous coupling of an electron spin to N nuclear spins in a quantum dot.
Quantum Speed Limits in Open System Dynamics
NASA Astrophysics Data System (ADS)
del Campo, A.; Egusquiza, I. L.; Plenio, M. B.; Huelga, S. F.
2013-02-01
Bounds to the speed of evolution of a quantum system are of fundamental interest in quantum metrology, quantum chemical dynamics, and quantum computation. We derive a time-energy uncertainty relation for open quantum systems undergoing a general, completely positive, and trace preserving evolution which provides a bound to the quantum speed limit. When the evolution is of the Lindblad form, the bound is analogous to the Mandelstam-Tamm relation which applies in the unitary case, with the role of the Hamiltonian being played by the adjoint of the generator of the dynamical semigroup. The utility of the new bound is exemplified in different scenarios, ranging from the estimation of the passage time to the determination of precision limits for quantum metrology in the presence of dephasing noise.
Combinatorial dynamics in quantum gravity
Stuart Kauffman; Lee Smolin
1998-09-22
We describe the application of methods from the study of discrete dynanmical systems to the problem of the continuum limit of evolving spin networks. These have been found to describe the small scale structure of quantum general relativity and extensions of them have been conjectured to give background independent formulations of string theory. We explain why the the usual equilibrium critical phenomena may not be relevant for the problem of the continuum limit of such theories and why, instead, the continuum limits of such theories are likely to be governed by non-equilibrium critical phenomena such as directed percolation. The fact that such non-equilibrium critical phenomena can be self-organized implies the possibility that the classical limit of quantum theories of gravity may exist without fine tuning of parameters.
Large nonadiabatic quantum molecular dynamics simulations on parallel computers
NASA Astrophysics Data System (ADS)
Shimojo, Fuyuki; Ohmura, Satoshi; Mou, Weiwei; Kalia, Rajiv K.; Nakano, Aiichiro; Vashishta, Priya
2013-01-01
We have implemented a quantum molecular dynamics simulation incorporating nonadiabatic electronic transitions on massively parallel computers to study photoexcitation dynamics of electrons and ions. The nonadiabatic quantum molecular dynamics (NAQMD) simulation is based on Casida's linear response time-dependent density functional theory to describe electronic excited states and Tully's fewest-switches surface hopping approach to describe nonadiabatic electron-ion dynamics. To enable large NAQMD simulations, a series of techniques are employed for efficiently calculating long-range exact exchange correction and excited-state forces. The simulation program is parallelized using hybrid spatial and band decomposition, and is tested for various materials.
Non-equilibrium dynamics of an unstable quantum pendulum
C. S. Gerving; T. M. Hoang; B. J. Land; M. Anquez; C. D. Hamley; M. S. Chapman
2012-05-09
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.
Compressing measurements in quantum dynamic parameter estimation
Magesan, Easwar
We present methods that can provide an exponential savings in the resources required to perform dynamic parameter estimation using quantum systems. The key idea is to merge classical compressive sensing techniques with ...
Employing feedback in adiabatic quantum dynamics
Armen E. Allahverdyan; Guenter Mahler
2008-04-10
We study quantum adiabatic dynamics, where the slowly moving field is influenced by system's state (feedback). The information for the feedback is gained from non-disturbating measurements done on an ensemble of identical non-interacting systems. The situation without feedback is governed by the adiabatic theorem: adiabatic energy level populations stay constant, while the adiabatic eigenvectors get a specific phase contribution (Berry phase). However, under feedback the adiabatic theorem does not hold: the adiabatic populations satisfy a closed equation of motion that coincides with the replicator dynamics well-known by its applications in evolutionary game theory. The feedback generates a new gauge-invariant adiabatic phase, which is free of the constraints on the Berry phase (e.g., the new phase is non-zero even for real adiabatic eigenfunctions).
NASA Astrophysics Data System (ADS)
Murayama, A.; Seo, K.; Nishibayashi, K.; Souma, I.; Oka, Y.
2006-06-01
Exciton spin dynamics is studied in a diluted magnetic semiconductor quantum well of Cd0.95Mn0.05Te by pump-probe absorption spectroscopy under magnetic fields. The time dependences of the saturated absorbance for the higher- and lower-energy spin states of heavy-hole (hh) excitons clarify the following exciton-spin relaxation process in magnetic fields: ultrafast hh-spin relaxation with the formation of dark excitons and subsequent electron-spin relaxation. The electron-spin relaxation due to the s-d exchange mechanism involving Mn spins is suppressed in a high magnetic field by field-induced pinning of the Mn spins.
Obanayama, Kazuya; Kobayashi, Hiroaki; Fukushima, Kentaro; Sakurai, Minoru
2008-01-01
BLUF (blue-light sensing using FAD) domains constitute a new family of flavin-based blue light photoreceptors. The photocycle of BLUF is unique in the sense that a few hydrogen bond rearrangements are accompanied by only slight structural changes in the bound chromophore. The hydrogen bond rearrangements upon illumination have been inferred from spectral changes in the chromophore: approximately 10 nm redshift of the absorption maximum and approximately 16 cm(-1) downshift of the C4=O stretching frequency. However, the exact features of the hydrogen bond network around the active site are still the subject of some controversy. In particular, the orientation of a conserved Gln (Gln63 in AppA) is presently one of the most questioned topics in the field. Here we perform molecular dynamics simulations for the wild-type AppA, AppA1-124C20S, BlrB and T110078 and furthermore quantum chemical calculations to investigate their spectroscopic properties in the dark and signaling states. On the basis of these results, we reveal the dynamic aspect of hydrogen bonding networks at the active site and propose theoretically reasonable models for the dark and signaling states of the BLUF domains. PMID:18435699
Chiranjeeb Roy
2010-01-01
We study the population and disentanglement dynamics of two identical quantum dots placed inside the structured electromagnetic reservoir of a photonic crystal and coupled to an independent bath of thermal phonons. A formalism based on the method of generalized-Laplace transforms is developed to study the population and disentanglement dynamics. The effect of resonant dipole dipole interaction between the two quantum
Quantum dynamics of bio-molecular systems in noisy environments
M. B. Plenio; S. F. Huelga
2012-02-05
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.
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
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.
Optimal dynamic discrimination of similar quantum systems
NASA Astrophysics Data System (ADS)
Li, Baiqing
2005-07-01
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.
Lorenza Viola; David Tannor
2011-01-01
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
Quantum Simulation for Open-System Dynamics
NASA Astrophysics Data System (ADS)
Wang, Dong-Sheng; de Oliveira, Marcos Cesar; Berry, Dominic; Sanders, Barry
2013-03-01
Simulations are essential for predicting and explaining properties of physical and mathematical systems yet so far have been restricted to classical and closed quantum systems. Although forays have been made into open-system quantum simulation, the strict algorithmic aspect has not been explored yet is necessary to account fully for resource consumption to deliver bounded-error answers to computational questions. An open-system quantum simulator would encompass classical and closed-system simulation and also solve outstanding problems concerning, e.g. dynamical phase transitions in non-equilibrium systems, establishing long-range order via dissipation, verifying the simulatability of open-system dynamics on a quantum Turing machine. We construct an efficient autonomous algorithm for designing an efficient quantum circuit to simulate many-body open-system dynamics described by a local Hamiltonian plus decoherence due to separate baths for each particle. The execution time and number of gates for the quantum simulator both scale polynomially with the system size. Simulations are essential for predicting and explaining properties of physical and mathematical systems yet so far have been restricted to classical and closed quantum systems. Although forays have been made into open-system quantum simulation, the strict algorithmic aspect has not been explored yet is necessary to account fully for resource consumption to deliver bounded-error answers to computational questions. An open-system quantum simulator would encompass classical and closed-system simulation and also solve outstanding problems concerning, e.g. dynamical phase transitions in non-equilibrium systems, establishing long-range order via dissipation, verifying the simulatability of open-system dynamics on a quantum Turing machine. We construct an efficient autonomous algorithm for designing an efficient quantum circuit to simulate many-body open-system dynamics described by a local Hamiltonian plus decoherence due to separate baths for each particle. The execution time and number of gates for the quantum simulator both scale polynomially with the system size. DSW funded by USARO. MCO funded by AITF and Brazilian agencies CNPq and FAPESP through Instituto Nacional de Ciencia e Tecnologia-Informacao Quantica (INCT-IQ). DWB funded by ARC Future Fellowship (FT100100761). BCS funded by AITF, CIFAR, NSERC and USARO.
Simulating quantum dynamics on a quantum computer
NASA Astrophysics Data System (ADS)
Wiebe, Nathan; Berry, Dominic W.; Høyer, Peter; Sanders, Barry C.
2011-11-01
We explicitly show how to simulate time-dependent sparse Hamiltonian evolution on a quantum computer, with complexity that is close to linear in the evolution time. The complexity also depends on the magnitude of the derivatives of the Hamiltonian. We propose a range of techniques to simulate Hamiltonians with badly behaved derivatives. These include using adaptive time steps, adapting the order of the integrators, and omitting regions about discontinuities. The complexity of the algorithm is quantified by calls to an oracle, which yields information about the Hamiltonian, and accounts for all computational resources. We explicitly determine the number of bits of output that this oracle needs to provide, and show how to efficiently perform the required 1-sparse unitary operations using these bits. We also account for discretization error in the time, as well as accounting for Hamiltonians that are a sum of terms that are sparse in different bases.
NASA Astrophysics Data System (ADS)
Distasio, Robert A., Jr.; Santra, Biswajit; Ko, Hsin-Yu; Car, Roberto
2014-03-01
In this work, we report highly accurate ab initio path-integral molecular dynamics (AI-PIMD) simulations on liquid water at ambient conditions utilizing the recently developed PBE0+vdW(SC) exchange-correlation functional, which accounts for exact exchange and a self-consistent pairwise treatment of van der Waals (vdW) or dispersion interactions, combined with nuclear quantum effects (via the colored-noise generalized Langevin equation). The importance of each of these effects in the theoretical prediction of the structure of liquid water will be demonstrated by a detailed comparative analysis of the predicted and experimental oxygen-oxygen (O-O), oxygen-hydrogen (O-H), and hydrogen-hydrogen (H-H) radial distribution functions as well as other structural properties. In addition, we will discuss the theoretically obtained proton momentum distribution, computed using the recently developed Feynman path formulation, in light of the experimental deep inelastic neutron scattering (DINS) measurements. DOE: DE-SC0008626, DOE: DE-SC0005180.
NASA Technical Reports Server (NTRS)
Wang, Dunyou
2003-01-01
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.
Quantum dynamics in regions of quaternionic curvature
Brumby, S P
1994-01-01
The complex unit appearing in the equations of quantum mechanics is generalised to a quaternionic structure on spacetime, leading to the consideration of complex quantum mechanical particles whose dynamical behaviour is governed by inhomogeneous Dirac and Schr\\"{o}dinger equations. Mixing of hyper-complex components of wavefunctions occurs through their interaction with potentials dissipative into the extra quaternionic degrees of freedom. An interferometric experiment is analysed to illustrate the effect.
Quantum Dynamics in Regions of Quaternionic Curvature
S. P. Brumby; G. C. Joshi
1994-06-29
The complex unit appearing in the equations of quantum mechanics is generalised to a quaternionic structure on spacetime, leading to the consideration of complex quantum mechanical particles whose dynamical behaviour is governed by inhomogeneous Dirac and Schr\\"{o}dinger equations. Mixing of hyper-complex components of wavefunctions occurs through their interaction with potentials dissipative into the extra quaternionic degrees of freedom. An interferometric experiment is analysed to illustrate the effect.
Dynamical quantum phase transitions: scaling and universality
Markus Heyl
2015-05-10
Dynamical quantum phase transitions (DQPTs) at critical times appear as non-analyticities during nonequilibrium quantum real-time evolution. Although there is evidence for a close relationship between DQPTs and equilibrium phase transitions, a major challenge is still to connect to fundamental concepts such as scaling and universality. In this work, renormalization group transformations in complex parameter space are formulated for quantum quenches in Ising models showing that the DQPTs are critical points associated with unstable fixed points of equilibrium Ising models. Therefore, these DQPTs obey scaling and universality. On the basis of numerical simulations, signatures of these DQPTs in the dynamical buildup of spin correlations are found with an associated power-law scaling determined solely by the fixed point's universality class. An outlook is given on how to explore this dynamical scaling experimentally in systems of trapped ions.
Origin of Dynamical Quantum Non-locality
NASA Astrophysics Data System (ADS)
Pachon, Cesar E.; Pachon, Leonardo A.
2014-03-01
Non-locality is one of the hallmarks of quantum mechanics and is responsible for paradigmatic features such as entanglement and the Aharonov-Bohm effect. Non-locality comes in two ``flavours'': a kinematic non-locality- arising from the structure of the Hilbert space- and a dynamical non-locality- arising from the quantum equations of motion-. Kinematic non-locality is unable to induce any change in the probability distributions, so that the ``action-at-a-distance'' cannot manifest. Conversely, dynamical non-locality does create explicit changes in probability, though in a ``causality-preserving'' manner. The origin of non-locality of quantum measurements and its relations to the fundamental postulates of quantum mechanics, such as the uncertainty principle, have been only recently elucidated. Here we trace the origin of dynamical non-locality to the superposition principle. This relation allows us to establish and identify how the uncertainty and the superposition principles determine the non-local character of the outcome of a quantum measurement. Being based on group theoretical and path integral formulations, our formulation admits immediate generalizations and extensions to to, e.g., quantum field theory. This work was supported by the Departamento Administrativo de Ciencia, Tecnologia e Innovacion -COLCIENCIAS- of Colombia under the grant number 111556934912.
Controlling quantum critical dynamics of isolated systems
NASA Astrophysics Data System (ADS)
del Campo, A.; Sengupta, K.
2015-02-01
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.
An instability of unitary quantum dynamics
Jasper van Wezel
2015-02-26
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.
Exploring the capabilities of quantum optimal dynamic discrimination
NASA Astrophysics Data System (ADS)
Beltrani, Vincent; Ghosh, Pritha; Rabitz, Herschel
2009-04-01
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.
Combining dynamical decoupling with fault-tolerant quantum computation
Hui Khoon Ng; Daniel A. Lidar; John Preskill
2011-07-18
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.
Efficient Quantum-State Estimation by Continuous Weak Measurement and Dynamical Control
Smith, Greg A.; Jessen, Poul S. [College of Optical Sciences, University of Arizona, Tucson, Arizona 85721 (United States); Silberfarb, Andrew; Deutsch, Ivan H. [Department of Physics and Astronomy, University of New Mexico, Albuquerque, New Mexico 87131 (United States)
2006-11-03
We demonstrate a fast, robust, and nondestructive 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 test bed and successfully reconstructs a range of trial states with fidelities of {approx}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.
Nuclear quantum dynamics in dense hydrogen
Kang, Dongdong; Sun, Huayang; Dai, Jiayu; Chen, Wenbo; Zhao, Zengxiu; Hou, Yong; Zeng, Jiaolong; Yuan, Jianmin
2014-01-01
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
Dissipative quantum dynamics in a boson bath
NASA Astrophysics Data System (ADS)
Chen, Y.-C.; Lebowitz, J. L.; Liverani, C.
1989-09-01
We investigate the dynamics of a quantum particle coupled to a boson heat bath. Using a real-time path-integral formalism, we obtain the Wigner distribution of the particle in the form of a power series in the strength of the anharmonicity V0. This series is shown to converge for all V0 when t is fixed and for small V0 uniformly in t. The latter proves the convergence to equilibrium for small anharmonicities. The effects of initial conditions on the evolution are studied by explicitly considering two types of initial states: product states and mixed Gibbs states. We show that in certain cases the evolution of the mixed states which avoid many pathologies of the product states, arising from the removal of the cutoff on the frequency distribution of the bath, can be related to that of product states when the latter are started at t=-?. We also solve exactly a simple stationary nonequilibrium model, a harmonic system in contact with two thermal baths, and derive an alternative criterion for a practically useful quasiclassical approximation. Finally, some connections to the Josephson junction are discussed. These include (a) the Green-Kubo-Einstein relation between the mobility and the diffusion constant of the washboard potential and (b) the time evolution of a rf superconducting quantum interference device.
Dynamical correlations after a quantum quench.
Essler, Fabian H L; Evangelisti, Stefano; Fagotti, Maurizio
2012-12-14
We consider dynamic (non-equal-time) correlation functions of local observables after a quantum quench. We show that, in the absence of long-range interactions in the final Hamiltonian, the dynamics is determined by the same ensemble that describes static (equal-time) correlations. For many integrable models, static correlation functions of local observables after a quantum quench relax to stationary values, which are described by a generalized Gibbs ensemble. The same generalized Gibbs ensemble then determines dynamic correlation functions, and the basic form of the fluctuation dissipation theorem holds, although the absorption and emission spectra are not simply related as in the thermal case. For quenches in the transverse field Ising chain, we derive explicit expressions for the time evolution of dynamic order parameter correlators after a quench. PMID:23368374
Quantum Dynamics of Nonlinear Cavity Systems
Paul D. Nation
2010-09-16
We investigate the quantum dynamics of three different configurations of nonlinear cavity systems. To begin, we carry out a quantum analysis of a dc superconducting quantum interference device (SQUID) mechanical displacement detector comprised of a SQUID with a mechanically compliant loop segment. The SQUID is approximated by a nonlinear current-dependent inductor, inducing a flux tunable nonlinear Duffing term in the cavity equation of motion. Expressions are derived for the detector signal and noise response where it is found that a soft-spring Duffing self-interaction enables a closer approach to the displacement detection standard quantum limit, as well as cooling closer to the ground state. Next, we make use of a superconducting transmission line formed from an array of dc-SQUIDs for investigating analogue Hawking radiation. Biasing the array with a space-time varying flux modifies the propagation velocity of the transmission line, leading to an effective metric with a horizon. This setup allows for quantum effects such as backreaction and analogue space-time fluctuations on the Hawking process. Finally, we look at a quantum parametric amplifier with dynamical pump mode, viewed as a zero-dimensional model of Hawking radiation from an evaporating black hole. The conditions are derived under which the spectrum of particles generated from vacuum fluctuations deviates from the thermal spectrum predicted for the conventional parametric amplifier. We find that significant deviation occurs once the pump mode (black hole) has released nearly half of its initial energy in the signal (Hawking radiation) and idler (in-falling particle) modes. As a model of black hole dynamics, this finding lends support to the view that late-time Hawking radiation contains information about the quantum state of the black hole and is entangled with the black hole's quantum gravitational degrees of freedom.
Stochastic solution to quantum dynamics
NASA Technical Reports Server (NTRS)
John, Sarah; Wilson, John W.
1994-01-01
The quantum Liouville equation in the Wigner representation is solved numerically by using Monte Carlo methods. For incremental time steps, the propagation is implemented as a classical evolution in phase space modified by a quantum correction. The correction, which is a momentum jump function, is simulated in the quasi-classical approximation via a stochastic process. The technique, which is developed and validated in two- and three- dimensional momentum space, extends an earlier one-dimensional work. Also, by developing a new algorithm, the application to bound state motion in an anharmonic quartic potential shows better agreement with exact solutions in two-dimensional phase space.
Ultra-cold Atom CollisionsUltra-cold Atom Collisions and Quantum Dynamics atand Quantum Dynamics at
Band, Yehuda B.
Ultra-cold Atom CollisionsUltra-cold Atom Collisions and Quantum Dynamics atand Quantum Dynamics are available at Ben-Gurion University to carry out research in ultra-cold atomic and molecular physics
Quantum Scaling Laws in the Onset of Dynamical Delocalization
Chabe, Julien; Lignier, Hans; Cavalcante, Hugo; Szriftgiser, Pascal; Garreau, Jean Claude [Laboratoire de Physique des Lasers, Atomes et Molecules, Universite des Sciences et Technologies de Lille, Centre d'Etudes et Recherches Lasers et Applications, F-59655 Villeneuve d'Ascq Cedex (France); Delande, Dominique [Laboratoire Kastler-Brossel, Case 74, UPMC, 4 Place Jussieu, F-75252 Paris Cedex 05 (France)
2006-12-31
We study the destruction of dynamical localization experimentally observed in an atomic realization of the kicked rotor by a deterministic Hamiltonian perturbation, with a temporal periodicity incommensurate with the principal driving. We show that the destruction is gradual, with well-defined scaling laws for the various classical and quantum parameters, in sharp contrast to predictions based on the analogy with Anderson localization.
Effective Evolution Equations from Quantum Dynamics
Niels Benedikter; Marcello Porta; Benjamin Schlein
2015-02-09
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.
Quantum Potential and Random Phase - Space Dynamics
R. Czopnik; P. Garbaczewski
2002-06-17
We analyze limitations upon any kinetic theory inspired derivation of a probabilistic counterpart of the Schr\\"{o}dinger picture quantum dynamics. Neither dissipative nor non-dissipative stochastic phase-space processes based on the white-noise (Brownian motion) kinetics are valid candidates unless additional constraints (a suitable form of the energy conservation law) are properly incorporated in the formalism.
Tomaru Ogawa; Masayuki Miyano; Yasuhiro Suzuki; Ai Suzuki; Hideyuki Tsuboi; Nozomu Hatakeyama; Akira Endou; Hiromitsu Takaba; Momoji Kubo; Akira Miyamoto
2010-01-01
Initial processes of Li-ion transport at the electrolyte\\/cathode interface of a Li-ion battery were investigated using an ultra-accelerated quantum chemical molecular dynamics (UA-QCMD) simulator. This simulator was based on our in-house tight-binding quantum chemical (TB-QC) simulator and MD simulator. The parameterization for LiCoO2 crystal and ethylene carbonate (EC) molecule in UA-QCMD was first carried out to show the fine agreement
Dynamics of a complex quantum magnet.
Landry, James W.; Coppersmith, S. N. (University of Wisconsin, Madison, WI)
2003-01-01
We have computed the low energy quantum states and low frequency dynamical susceptibility of complex quantum spin systems in the limit of strong interactions, obtaining exact results for system sizes enormously larger than accessible previously. The ground state is a complex superposition of a substantial fraction of all the classical ground states, and yet the dynamical susceptibility exhibits sharp resonances reminiscent of the behavior of single spins. These results show that strongly interacting quantum systems can organize to generate coherent excitations and shed light on recent experiments demonstrating that coherent excitations are present in a disordered spin liquid. The dependence of the energy spectra on system size differs qualitatively from that of the energy spectra of random undirected bipartite graphs with similar statistics, implying that strong interactions are giving rise to these unusual spectral properties.
Quantum Dynamics of Nonlinear Cavity Systems
Nation, Paul D
2010-01-01
We investigate the quantum dynamics of three different configurations of nonlinear cavity systems. To begin, we carry out a quantum analysis of a dc superconducting quantum interference device (SQUID) mechanical displacement detector comprised of a SQUID with a mechanically compliant loop segment. The SQUID is approximated by a nonlinear current-dependent inductor, inducing a flux tunable nonlinear Duffing term in the cavity equation of motion. Expressions are derived for the detector signal and noise response where it is found that a soft-spring Duffing self-interaction enables a closer approach to the displacement detection standard quantum limit, as well as cooling closer to the ground state. Next, we make use of a superconducting transmission line formed from an array of dc-SQUIDs for investigating analogue Hawking radiation. Biasing the array with a space-time varying flux modifies the propagation velocity of the transmission line, leading to an effective metric with a horizon. This setup allows for quan...
Johannes Schachenmayer; Alexander Pikovski; Ana Maria Rey
2015-06-15
Interacting quantum spin models are remarkably useful for describing different types of physical, chemical, and biological systems. Significant understanding of their equilibrium properties has been achieved to date, especially for the case of spin models with short-range couplings. However, progress towards the development of a comparable understanding in long-range interacting models, in particular out-of-equilibrium, remains limited. In a recent work, we proposed a semiclassical numerical method to study spin models, the discrete truncated Wigner approximation (DTWA), and demonstrated its capability to correctly capture the dynamics of one- and two-point correlations in one dimensional (1D) systems. Here we go one step forward and use the DTWA method to study the dynamics of correlations in 2D systems with many spins and different types of long-range couplings, in regimes where other numerical methods are generally unreliable. We compute spatial and time-dependent correlations for spin-couplings that decay with distance as a power-law and determine the velocity at which correlations propagate through the system. Sharp changes in the behavior of those velocities are found as a function of the power-law decay exponent. Our predictions are relevant for a broad range of systems including solid state materials, atom-photon systems and ultracold gases of polar molecules, trapped ions, Rydberg, and magnetic atoms. We validate the DTWA predictions for small 2D systems and 1D systems, but ultimately, in the spirt of quantum simulation, experiments will be needed to confirm our predictions for large 2D systems.
NASA Astrophysics Data System (ADS)
Schachenmayer, J.; Pikovski, A.; Rey, A. M.
2015-06-01
Interacting quantum spin models are remarkably useful for describing different types of physical, chemical, and biological systems. Significant understanding of their equilibrium properties has been achieved to date, especially for the case of spin models with short-range couplings. However, progress toward the development of a comparable understanding in long-range interacting models, in particular out-of-equilibrium, remains limited. In a recent work, we proposed a semiclassical numerical method to study spin models, the discrete truncated Wigner approximation (DTWA), and demonstrated its capability to correctly capture the dynamics of one- and two-point correlations in one-dimensional (1D) systems. Here we go one step forward and use the DTWA method to study the dynamics of correlations in two-dimensional (2D) systems with many spins and different types of long-range couplings, in regimes where other numerical methods are generally unreliable. We compute spatial and time-dependent correlations for spin-couplings that decay with distance as a power-law and determine the velocity at which correlations propagate through the system. Sharp changes in the behavior of those velocities are found as a function of the power-law decay exponent. Our predictions are relevant for a broad range of systems including solid state materials, atom–photon systems and ultracold gases of polar molecules, trapped ions, Rydberg, and magnetic atoms. We validate the DTWA predictions for small 2D systems and 1D systems, but ultimately, in the spirt of quantum simulation, experiments will be needed to confirm our predictions for large 2D systems.
Unified dynamics of quantum vortices
Uri Ben-Ya'Acov
1992-01-01
A unified model for quantum vortices (including cosmic strings and superfluid vortices as particular cases) is presented. Using the so-called ``analyticity condition'', we find the exact equations of motion of any general vortex system described by this model. A short-ranged attractive force is found to act on all types of vortices. Its inclusion leads to a total finite self-interaction. The
NASA Astrophysics Data System (ADS)
Bursulaya, Badry D.; Jeon, Jonggu; Zichi, Dominic A.; Kim, Hyung J.
1998-02-01
By employing the truncated adiabatic basis set (TAB) description developed in the preceding article [B. D. Bursulaya and H. J. Kim, J. Chem. Phys. 108, 3277 (1998), preceding paper], solvent water under an ambient condition is studied via a molecular dynamics (MD) computer simulation method. The evolving charge distribution of each water molecule is described by the mixing of the TAB functions, which fluctuates with its local environment. The parametrization of these basis functions is couched in terms of the complete active space self-consistent field (CASSCF) ab initio calculations in vacuum. By using an interaction site representation for the diagonal and overlap charge distributions of the basis functions, electronic polarizability both in and out of the water molecular plane is accounted for. The ground-state charge distribution for the entire solvent system is determined at the self-consistent field (SCF) level with a numerical iteration method. Two different models, TAB/10 and TAB/10D, are studied. The average water dipole moment in liquid is found to be 2.58 D for the former and 2.65 D for the latter, while it is 1.85 D in vacuum for both models. The solution-phase electronic polarizability distributions, characterized by a narrow but finite width, show that nonlinear hyperpolarizability makes a non-negligible contribution to instantaneous electronic response of water even though its average response mainly falls in a linear regime. It is found that the TAB water predictions for structural, dynamic, spectroscopic, dielectric, and transport properties are in good agreement with corresponding experimental results.
Dynamical competition between quantum Hall and quantum spin Hall effects
NASA Astrophysics Data System (ADS)
Quelle, A.; Morais Smith, C.
2014-11-01
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.
NASA Astrophysics Data System (ADS)
Marvian, Iman; Spekkens, Robert W.
2014-12-01
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.
Quantum algorithm for simulating the dynamics of an open quantum system
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
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.
Role of controllability in optimizing quantum dynamics
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
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.
NASA Astrophysics Data System (ADS)
Feng, Hai-Ran; Meng, Xiang-Jia; Li, Peng; Zheng, Yu-Jun
2014-07-01
The dynamical correlation between quantum entanglement and intramolecular energy in realistic molecular vibrations is explored using the Lie algebraic approach. The explicit expression of entanglement measurement can be achieved using algebraic operations. The common and different characteristics of dynamical entanglement in different molecular vibrations are also provided. The dynamical study of quantum entanglement and intramolecular energy in small molecular vibrations can be helpful for controlling the entanglement and further understanding the intramolecular dynamics.
Lévy flights and nonlocal quantum dynamics
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
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.
Many-body dynamics of a Bose-Einstein condensate collapsing by quantum tunneling
NASA Astrophysics Data System (ADS)
Saito, Hiroki
2014-02-01
The dynamics of a Bose-Einstein condensate of atoms having attractive interactions is studied using quantum many-body simulations. The collapse of the condensate by quantum tunneling is numerically demonstrated, and the tunneling rate is calculated. The correlation properties of the quantum many-body state are investigated.
Modular Dynamical Semigroups for Quantum Dissipative Systems
David Taj; Hans Christian Öttinger
2015-03-10
We introduce a class of Markovian quantum master equations, able to describe the dissipative dynamics of a quantum system weakly coupled to one or several heat baths. The dissipative structure is driven by an entropic operator, the so called modular Hamiltonian, which makes it nonlinear. The generated Modular Dynamical Semigroup (MDS) is not, in general, a Quantum Dynamical Semigroup (QDS), whose dynamics is of the popular Lindblad type. The MDS has a robust thermodynamic structure, which guarantees for the positivity of the time evolved state, the correct steady state properties, the positivity of the entropy production, a positive Onsager matrix and Onsager symmetry relations (arising from Green-Kubo formulas). We show that the celebrated Davies generator, obtained through the Born and the secular approximations, generates a MDS. By unravelling the modular structure of the former, we provide a different and genuinely nonlinear MDS, not of QDS type, which is free from the severe spectral restrictions of the Davies generator, while still being supported by a weak coupling limit argument. With respect to the latter, the present work is a substantial extension of \\cite{Ottinger2011_GEO,Ottinger2010_TLS_DHO}
Reflections on Quantum Computing Quantum Computing Based on Fixed Point Dynamics
Svozil, Karl
Reflections on Quantum Computing Quantum Computing Based on Fixed Point Dynamics WHEN ARE QUANTUM SPEEDUPS POSSIBLE? T his section discusses the possibility that speedups in quantum computing can the computational complexity class UP [2]. Typical examples are Shor's quantum algorithm for prime factoring [3
Exact Quantum Dynamics of a Bosonic Josephson Junction
NASA Astrophysics Data System (ADS)
Sakmann, Kaspar; Streltsov, Alexej I.; Alon, Ofir E.; Cederbaum, Lorenz S.
2009-11-01
The quantum dynamics of a one-dimensional bosonic Josephson junction is studied by solving the time-dependent many-boson Schrödinger equation numerically exactly. Already for weak interparticle interactions and on short time scales, the commonly employed mean-field and many-body methods are found to deviate substantially from the exact dynamics. The system exhibits rich many-body dynamics such as enhanced tunneling and a novel equilibration phenomenon of the junction depending on the interaction, which is attributed to a quick loss of coherence.
Ilya A. Shkrob; William J. Glover; Ross E. Larsen; Benjamin J. Schwartz
2006-01-01
Adiabatic mixed quantum\\/classical molecular dynamics simulations were used to generate snapshots of the hydrated electron (e-) in liquid water at 300 K. Water cluster anions that include two complete solvation shells centered on the e- were extracted from these simulations and embedded in a matrix of fractional point charges designed to represent the rest of the solvent. Density functional theory
Quantum simulation of molecular interaction and dynamics at surfaces
NASA Astrophysics Data System (ADS)
Ding, Zi-Jing; Jiao, Yang; Meng, Sheng
2011-09-01
The interaction between molecules and solid surfaces plays important roles in various applications, including catalysis, sensors, nanoelectronics, and solar cells. Surprisingly, a full understanding of molecule-surface interaction at the quantum mechanical level has not been achieved even for very simple molecules, such as water. In this mini-review, we report recent progresses and current status of studies on interaction between representative molecules and surfaces. Taking water/metal, DNA bases/carbon nanotube, and organic dye molecule/oxide as examples, we focus on the understanding on the microstructure, electronic property, and electron-ion dynamics involved in these systems obtained from first-principles quantum mechanical calculations. We find that a quantum mechanical description of molecule-surface interaction is essential for understanding interface phenomenon at the microscopic level, such as wetting. New theoretical developments, including van der Waals density functional and quantum nuclei treatment, improve further our understanding of surface interactions.
Akihito Ishizaki; Graham R. Fleming
2009-01-01
The observation of long-lived electronic coherence in photosynthetic excitation energy transfer (EET) by Engel et al. [Nature (London) 446, 782 (2007)] raises questions about the role of the protein environment in protecting this coherence and the significance of the quantum coherence in light harvesting efficiency. In this paper we explore the applicability of the Redfield equation in its full form,
Avoiding irreversible dynamics in quantum systems
NASA Astrophysics Data System (ADS)
Karasik, Raisa Iosifovna
2009-10-01
Devices that exploit laws of quantum physics offer revolutionary advances in computation and communication. However, building such devices presents an enormous challenge, since it would require technologies that go far beyond current capabilities. One of the main obstacles to building a quantum computer and devices needed for quantum communication is decoherence or noise that originates from the interaction between a quantum system and its environment, and which leads to the destruction of the fragile quantum information. Encoding into decoherence-free subspaces (DFS) provides an important strategy for combating decoherence effects in quantum systems and constitutes the focus of my dissertation. The theory of DFS relies on the existence of certain symmetries in the decoherence process, which allow some states of a quantum system to be completely decoupled from the environment and thus to experience no decoherence. In this thesis I describe various approaches to DFS that are developed in the current literature. Although the general idea behind various approaches to DFS is the same, I show that different mathematical definitions of DFS actually have different physical meaning. I provide a rigorous definition of DFS for every approach, explaining its physical meaning and relation to other definitions. I also examine the theory of DFS for Markovian systems. These are systems for which the environment has no memory, i.e., any change in the environment affects the quantum system instantaneously. Examples of such systems include many systems in quantum optics that have been proposed for implementation of a quantum computer, such as atomic and molecular gases, trapped ions, and quantum dots. Here I develop a rigorous theory that provides necessary and sufficient conditions for the existence of DFS. This theory allows us to identify a special new class of DFS that was not known before. Under particular circumstances, dynamics of a quantum system can connive together with the interactions between the system and its environment in a special way to reduce decoherence. This property is used to discover new DFS that rely on rather counterintuitive phenomenon, which I call an "incoherent generation of coherences." I also provide examples of physical systems that support such states. These DFS can be used to suppress & coherence, but may not be sufficient for performing full quantum computation. I also explore the possibility of physically generating the DFS that are useful for quantum computation. For quantum computation we need to preserve at least two quantum states to encode the quantum analogue of classical bits. Here I aim to generate DFS in a system composed from a large collection of atoms or molecules and I need to determine how one should position atoms or molecules in 3D space so that the overall system possesses a DFS with at least two states (i.e., non-trivial DFS). I show that for many Markovian systems, non-trivial DFS can exist only when particles are located in exactly the same position in space. This, of course, is not possible in the real world. For these systems, I also show that states in DFS are states with infinite lifetime. However, for all practical applications we just need long-lived states. Thus in reality, we do just need to bring quantum particles close together to generate an imperfect DFS, i.e. a collection of long-lived states. This can be achieved, for example, for atoms within a single molecule.
Dynamical and thermodynamical control of Open Quantum Walks
NASA Astrophysics Data System (ADS)
Petruccione, Francesco; Sinayskiy, Ilya
2014-03-01
Over the last few years dynamical properties and limit distributions of Open Quantum Walks (OQWs), quantum walks driven by dissipation, have been intensely studied [S. Attal et. al. J. Stat. Phys. 147, Issue 4, 832 (2012)]. For some particular cases of OQWs central limit theorems have been proven [S. Attal, N. Guillotin, C. Sabot, ``Central Limit Theorems for Open Quantum Random Walks,'' to appear in Annales Henri Poincaré]. However, only recently the connection between the rich dynamical behavior of OQWs and the corresponding microscopic system-environment models has been established. The microscopic derivation of an OQW as a reduced system dynamics on a 2-nodes graph [I. Sinayskiy, F. Petruccione, Open Syst. Inf. Dyn. 20, 1340007 (2013)] and its generalization to arbitrary graphs allow to explain the dependance of the dynamical behavior of the OQW on the temperature and coupling to the environment. For thermal environments we observe Gaussian behaviour, whereas at zero temperature population trapping and ``soliton''-like behaviour are possible. Physical realizations of OQWs in quantum optical setups will be also presented. This work is based on research supported by the South African Research Chair Initiative of the Department of Science and Technology and National Research Foundation.
Fu, Bina; Zhang, Dong H
2015-02-14
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. PMID:25681913
NASA Astrophysics Data System (ADS)
Fu, Bina; Zhang, Dong H.
2015-02-01
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.
Studies in quantum information theory
NASA Astrophysics Data System (ADS)
Menicucci, Nicolas C.
Quantum information theory started as the backdrop for quantum computing and is often considered only in relation to this technology, which is still in its infancy. But quantum information theory is only partly about quantum computing. While much of the interest in this field is spurred by the possible use of quantum computers for code breaking using fast factoring algorithms, to a physicist interested in deeper issues, it presents an entirely new set of questions based on an entirely different way of looking at the quantum world. This thesis is an exploration of several topics in quantum information theory. But it is also more than this. This thesis explores the new paradigm brought about by quantum information theory---that of physics as the flow of information. The thesis consists of three main parts. The first part describes my work on continuous-variable cluster states, a new platform for quantum computation. This begins with background material discussing classical and quantum computation and emphasizing the physical underpinnings of each, followed by a discussion of two recent unorthodox models of quantum computation. These models are combined into an original proposal for quantum computation using continuous-variable cluster states, including a proposed optical implementation. These are followed by a mathematical result radically simplifying the optical construction. Subsequent work simplifies this connection even further and provides a constructive proposal for scalable generation of large-scale cluster states---necessary if there is to be any hope of using this method in practical quantum computation. Experimental implementation is currently underway by my collaborators at The University of Virginia. The second part describes my work related to the physics of trapped ions, starting with an overview of the basic theory of linear ion traps. Although ion traps are often discussed in terms of their potential use for quantum computation, my work looks at their potential for use as generic quantum systems over which the experimenter has exquisite control and which can be used to simulate other quantum systems and also study generic quantum phenomena. This is followed by a proposal for using a trapped ion as a time-dependent harmonic oscillator---a quantum system that is common in theoretical literature but of which few laboratory examples are known. A second project studies the way that quantum fluctuations in the vibrational state of a chain of ions influence correlations in optical measurements made on the ions. The final part looks at quantum information theory in a relativistic setting. An introduction discusses the interface between quantum information theory and relativity in general, including the nonclassical notion of entanglement and the peculiar features of curved-space quantum field theory. An original gedankenexperiment combines these ideas and examines whether entanglement---a quantum information-theoretic concept and physical resource---can be used to distinguish universes of different curvature in a situation where local measurements would show no difference. These three parts are followed by a personal (and possibly controversial) conclusion, which describes my fascination with---and ultimately my reason for pursuing---studies in quantum information theory.
Chandar, Nellore Bhanu; Lo, Rabindranath; Ganguly, Bishwajit
2014-09-01
Dimethyl(pyridin-2-yl)sulfonium based oxime has been designed to reverse the aging process of organophosphorus inhibited AChE and to reactivate the aged-AChE adduct. We have employed DFT M05-2X/6-31G(?) level of theory in aqueous phase with polarizable continuum solvation model (PCM) for the methylation of phosphonate ester monoanion of the soman-aged adduct. The calculated free energy of activation for the methyl transfer process from designed dimethyl(phenyl)sulfonium (1) to aged AChE-OP adduct occurs with a barrier of 31.4kcal/mol at M05-2X/6-31G(?) level of theory, which is 6.4kcal/mol lower compared to the aging process signifies the preferential reversal process to recover the aged AChE-OP adduct. The pyridine ring containing alkylated sulfonium species, dimethyl(pyridin-2-yl)sulfonium (2), reduced the free energy of activation by 4.4kcal/mol compared to the previously reported alkylating agent N-methyl-2-methoxypyridinium species (A) for the alkylation of aged AChE-OP adduct. The free enzyme can be liberated from the inhibited acetylcholinesterase with the sulfonium compound decorated with an oxime group to avoid the administration of oxime drugs separately. The calculated potential energy surfaces show that the oxime based sulfonium compound (3) can effectively methylate the aged phosphonate ester monoanion of soman aged-adduct. The calculated global reactivity descriptors of the oxime 3 also shed light on this observation. To gain better understanding for protein drug interaction as well as the unbinding and conformational changes of the drug candidate in the active site of cholinesterase, steered molecular dynamics (SMD) simulation with 3 has been performed. Through a protein-drug interaction parameters (rupture force profiles, hydrogen bonds, hydrophobic interactions), geometrical and the orientation of drug-like candidate, the oxime 3 suggests to orchestrate the better reactivation process. The docking studies have been performed with 3 in the aged AChE and BChE to obtain the initial geometry of the SMD studies. The docking methods adopted in this study have been verified with the available crystal geometry of 1-methyl-2-(pentafluorobenzyloxyimino)pyridinium compound in aged soman inhibited human BChE (PDB code: 4B0P). The computational study suggests that the newly designed oxime is a potential candidate to reactivate the aged-AChE adduct. PMID:25218671
NASA Astrophysics Data System (ADS)
Zhang, Yu; Yam, ChiYung; Chen, GuanHua
2015-04-01
A time-dependent inelastic electron transport theory for strong electron-phonon interaction is established via the equations of motion method combined with the small polaron transformation. In this work, the dissipation via electron-phonon coupling is taken into account in the strong coupling regime, which validates the small polaron transformation. The corresponding equations of motion are developed, which are used to study the quantum interference effect and phonon-induced decoherence dynamics in molecular junctions. Numerical studies show clearly quantum interference effect of the transport electrons through two quasi-degenerate states with different couplings to the leads. We also found that the quantum interference can be suppressed by the electron-phonon interaction where the phase coherence is destroyed by phonon scattering. This indicates the importance of electron-phonon interaction in systems with prominent quantum interference effect.
Dynamics in many-body localized quantum systems without disorder
NASA Astrophysics Data System (ADS)
Schiulaz, Mauro; Silva, Alessandro; Müller, Markus
2015-05-01
We study the relaxation dynamics of strongly interacting quantum systems that display a kind of many-body localization in spite of their translation-invariant Hamiltonian. We show that dynamics starting from a random initial configuration is nonperturbatively slow in the hopping strength, and potentially genuinely nonergodic in the thermodynamic limit. In finite systems with periodic boundary conditions, density relaxation takes place in two stages, which are separated by a long out-of-equilibrium plateau whose duration diverges exponentially with the system size. We estimate the phase boundary of this quantum glass phase, and discuss the role of local resonant configurations. We suggest experimental realizations and methods to observe the discussed nonergodic dynamics.
Hydrodynamic scaling from the dynamics of relativistic quantum field theory
Luis M. A. Bettencourt; Fred Cooper; Karen Pao
2001-09-19
Hydrodynamic behavior is a general feature of interacting systems with many degrees of freedom constrained by conservation laws. To date hydrodynamic scaling in relativistic quantum systems has been observed in many high energy settings, from cosmic ray detections to accelerators, with large particle multiplicity final states. Here we show first evidence for the emergence of hydrodynamic scaling in the dynamics of a relativistic quantum field theory. We consider a simple scalar $\\lambda \\phi^4$ model in 1+1 dimensions in the Hartree approximation and study the dynamics of two colliding kinks at relativistic speeds as well as the decay of a localized high energy density region. The evolution of the energy-momentum tensor determines the dynamical local equation of state and allows the measurement of the speed of sound. Hydrodynamic scaling emerges at high local energy densities.
NASA Technical Reports Server (NTRS)
Fleck, R. L.
1970-01-01
The use of the dynamic EKG study as a part of periodic health examination is considered to be a valuable complement to other forms of stress testing with its ability to detect abnormal heart responses to stress stimuli. It is believed that statistical correlations of dynamic EKG findings with physical examination results contribute greatly to the understanding of cardiac abnormalities.
Quantum dynamics of Kaluza-Klein theories
Thomas Appelquist; Alan Chodos
1983-01-01
Some of the quantum properties of Kaluza-Klein theories are studied. The classical features of these theories are reviewed, and the quantization of the gravitational field in an arbitrary number of dimensions is described. These results are then applied to a detailed analysis of the five-dimensional Kaluza-Klein model. The fifth dimension is taken to be compact and a quantum effective potential,
Upper bounds in quantum dynamics
NASA Astrophysics Data System (ADS)
Damanik, David; Tcheremchantsev, Serguei
2007-07-01
We develop a general method to bound the spreading of an entire wavepacket under Schroedinger dynamics from above. This method derives upper bounds on time-averaged moments of the position operator from lower bounds on norms of transfer matrices at complex energies. This general result is applied to the Fibonacci operator. We find that at sufficiently large coupling, all transport exponents take values strictly between zero and one. This is the first rigorous result on anomalous transport. For quasi-periodic potentials associated with trigonometric polynomials, we prove that all lower transport exponents and, under a weak assumption on the frequency, all upper transport exponents vanish for all phases if the Lyapunov exponent is uniformly bounded away from zero. By a well-known result of Herman, this assumption always holds at sufficiently large coupling. For the particular case of the almost Mathieu operator, our result applies for coupling greater than two.
A dynamical point of view of Quantum Information: Wigner measures
A. Baraviera; C. F. Lardizabal; A. O. Lopes; M. Terra Cunha
2011-04-14
We analyze a known version of the discrete Wigner function and some connections with Quantum Iterated Funcion Systems. This paper is a follow up of "A dynamical point of view of Quantum Information: entropy and pressure" by the same authors.
A dynamical point of view of Quantum Information: Wigner measures
Baraviera, A; Lopes, A O; Cunha, M Terra
2011-01-01
We analyze a known version of the discrete Wigner function and some connections with Quantum Iterated Funcion Systems. This paper is a follow up of "A dynamical point of view of Quantum Information: entropy and pressure" by the same authors.
Observation-assisted optimal control of quantum dynamics
Feng Shuang; Alexander Pechen; Tak-San Ho; Herschel Rabitz
2007-05-31
This paper explores the utility of instantaneous and continuous observations in the optimal control of quantum dynamics. Simulations of the processes are performed on several multilevel quantum systems with the goal of population transfer. Optimal control fields are shown to be capable of cooperating or fighting with observations to achieve a good yield, and the nature of the observations may be optimized to more effectively control the quantum dynamics. Quantum observations also can break dynamical symmetries to increase the controllability of a quantum system. The quantum Zeno and anti-Zeno effects induced by observations are the key operating principles in these processes. The results indicate that quantum observations can be effective tools in the control of quantum dynamics.
Technology Transfer Automated Retrieval System (TEKTRAN)
In the crystal structure of cellulose Ibeta, disordered hydrogen (H) bonding can be represented by the average of two mutually exclusive H bonding schemes that have been designated A and B. An unanswered question is whether A and B interconvert dynamically, or whether they are static but present in ...
Signatures of discrete breathers in coherent state quantum dynamics
Igumenshchev, Kirill; Ovchinnikov, Misha; Prezhdo, Oleg [Department of Chemistry, University of Rochester, Rochester, New York 14627 (United States); Maniadis, Panagiotis [Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)
2013-02-07
In classical mechanics, discrete breathers (DBs) - a spatial time-periodic localization of energy - are predicted in a large variety of nonlinear systems. Motivated by a conceptual bridging of the DB phenomena in classical and quantum mechanical representations, we study their signatures in the dynamics of a quantum equivalent of a classical mechanical point in phase space - a coherent state. In contrast to the classical point that exhibits either delocalized or localized motion, the coherent state shows signatures of both localized and delocalized behavior. The transition from normal to local modes have different characteristics in quantum and classical perspectives. Here, we get an insight into the connection between classical and quantum perspectives by analyzing the decomposition of the coherent state into system's eigenstates, and analyzing the spacial distribution of the wave-function density within these eigenstates. We find that the delocalized and localized eigenvalue components of the coherent state are separated by a mixed region, where both kinds of behavior can be observed. Further analysis leads to the following observations. Considered as a function of coupling, energy eigenstates go through avoided crossings between tunneling and non-tunneling modes. The dominance of tunneling modes in the high nonlinearity region is compromised by the appearance of new types of modes - high order tunneling modes - that are similar to the tunneling modes but have attributes of non-tunneling modes. Certain types of excitations preferentially excite higher order tunneling modes, allowing one to study their properties. Since auto-correlation functions decrease quickly in highly nonlinear systems, short-time dynamics are sufficient for modeling quantum DBs. This work provides a foundation for implementing modern semi-classical methods to model quantum DBs, bridging classical and quantum mechanical signatures of DBs, and understanding spectroscopic experiments that involve a coherent state.
Dynamical Objectivity in Quantum Brownian Motion
J. Tuziemski; J. K. Korbicz
2015-01-05
We analyze one of the fundamental models of decoherence and quantum-to-classical transition---Quantum Brownian Motion, and show formation of a, so called, spectrum broadcast structure. As recently shown, this is a specific structure of multi-partite quantum states responsible for appearance of classical objective features in quantum mechanics. Working in the limit of a very massive central system and in a weak-coupling regime, we derive a surprising time-evolving, rather than time-asymptotic, spectrum broadcast structure, leading to perceived objectivity of a state of motion. We do it for realistic, noisy random environment, modeled as a thermal bath, and present some generalization to arbitrary single-mode Gaussian states. We study numerically the formation of the spectrum broadcast structure as a function of the temperature, showing its certain noise-robustness.
Open quantum reaction-diffusion dynamics: Absorbing states and relaxation.
van Horssen, Merlijn; Garrahan, Juan P
2015-03-01
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
Quantum Process Tomography Quantifies Coherence Transfer Dynamics in Vibrational Exciton
Chuntonov, Lev; Ma, Jianqiang
2013-01-01
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
Open quantum reaction-diffusion dynamics: Absorbing states and relaxation
NASA Astrophysics Data System (ADS)
van Horssen, Merlijn; Garrahan, Juan P.
2015-03-01
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
Coupled Dynamics of a Nanomechanical Resonator and Superconducting Quantum Circuits
NASA Astrophysics Data System (ADS)
Suh, Junho
The coupled dynamics of a nanomechanical resonator and superconducting quantum circuits are studied in three experiments, in the context of studying the quantum limit for force detection and quantum physics of macroscopic objects. In the first experiment, the dispersive mechanical resonance shift from the interaction with a Cooper-pair box qubit is studied. The measured coupling strength is large enough to satisfy one of the conditions required to perform many of the proposed quantum nanomechanical measurements. The resonance shift also probes the microwave-driven response of the qubit, showing Rabi oscillation and Landau-Zener tunneling, proving the coherent dynamics of the qubit. Second, the parametric excitation of nanomechanical motion is studied via experiments with a driven qubit. Degenerate parametric amplification and oscillation are demonstrated, with a new observation of nonlinear dissipation. The squeezing of the back-action noise from the detection amplifier is also observed, up to 4dB. It is the first demonstration using a qubit as an auxiliary system to modify the nanomechanical dynamics, showing a possible route for generation of nanomechanical quantum states. Finally, back-action cooling of nanomechanical motion has been investigated, which is implemented by capacitively coupling a high-Q coplanar waveguide microwave resonator to a nanomechanical resonator. The thermal state with 7.5 mechanical quanta on average is reached, a result that is ultimately limited due to increased bath heating with microwave power. The heating is consistent with a model based on two-level systems resonantly coupled to the nanomechanical mode. This additional heating suggests future efforts to improve coupling and for reducing two-level system density in materials employed to reach the motional ground state via back-action cooling.
Full quantum dynamics of the electronic coupling between photosynthetic pigments
Oviedo, María Belén
2015-01-01
From studying the time evolution of the single electron density matrix within a density functional tight-binding formalism we study in a fully atomistic picture the electronic excitation transfer between two photosynthetic pigments in real time. This time-dependent quantum dynamics is based on fully atomistic structural models of the photosynthetic pigment. We analyze the dependence of the electronic excitation transfer with distance and orientation between photosynthetic pigments. We compare the results obtained from full quantum dynamics with analytical ones, based on a two level system model were the interaction between the pigments is dipolar. We observed that even when the distance of the photosynthetic pigment is about $30$ \\AA\\ the deviation of the dipolarity is of about $15$ percent.
Dynamical Yang-Baxter Equation and Quantum Vector Bundles
J. Donin; A. Mudrov
2005-01-01
We develop a categorical approach to the dynamical Yang-Baxter equation (DYBE) for arbitrary Hopf algebras. In particular, we introduce the notion of a dynamical extension of a monoidal category, which provides a natural environment for quantum dynamical R-matrices, dynamical twists, etc. In this context, we define dynamical associative algebras and show that such algebras give quantizations of vector bundles on
Chaos and Nonlinear Dynamics in a Quantum Artificial Economy
Carlos Pedro Gonçalves
2012-02-29
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.
Quantum mechanics and low energy nucleon dynamics
Renat Kh. Gainutdinov; Aigul A. Mutygullina
2004-08-25
We discuss the problem of consistency of quantum mechanics as applied to low energy nucleon dynamics with the symmetries of QCD. It is shown that the dynamics consistent with these symmetries is not governed by the Schrodinger equation. We present a new way to formulate the effective theory of nuclear forces as an inevitable consequence of the basic principles of quantum mechanics and the symmetries of strong interactions. We show that being formulated in this way the effective theory of nuclear forces can be put on the same firm theoretical grounds as the quantum mechanics of atomic phenomena. In this case the effective theory allows one to describe with a given accuracy not only two-nucleon scattering, but also the evolution of nucleon systems, and places the constraints on the off-shell behavior of the two-nucleon interaction. In this way we predict the off-shell behavior of the S wave two-nucleon T-matrix at very low energies when the pionless theory is applicable. Further extensions and applications of this approach are discussed.
Simulation of chemical reaction dynamics on an NMR quantum computer
Lu, Dawei; Xu, Ruixue; Chen, Hongwei; Gong, Jiangbin; Peng, Xinhua; Du, Jiangfeng
2011-01-01
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.
NASA Astrophysics Data System (ADS)
Bokareva, O. S.; Bataev, V. A.; Godunov, I. A.
2009-01-01
The geometric parameters (including vibrationally averaged parameters), energy differences (? E) between the s-cis and s-trans conformers, and barrier to internal rotation ( V t ) were calculated for the acrolein molecule CH2=CHCHO by various quantum-chemical methods (MP2, DFT, CASSCF, QCISD, CCSD(T), and MR-AQCC). The MP2 and B3LYP methods were used to calculate internal rotation potential functions and vibrational frequencies; the calculations were performed in various anharmonic approximations. To refine the ? E and V t values, two-dimensional (using a basis set of atomic orbitals) VFPA extrapolation procedure was applied, which allowed the results to be estimated in the FCI/CBS approximation taking into account nonadiabaticity, core correlation effects, and changes in the difference between zero point energies.
Dynamic characteristics of double tunneling-injection quantum dot lasers
NASA Astrophysics Data System (ADS)
Asryan, Levon V.
2015-03-01
Dynamic characteristics of double tunneling-injection (DTI) quantum dot (QD) lasers are studied. To reveal the potential of such lasers for high-speed direct modulation of their optical output by pump current, fast carrier injection into QDs and no carrier leakage from QDs are assumed. The small-signal analysis of rate equations is applied. The modulation bandwidth is calculated as a function of the dc component of the injection current density and parameters of the laser structure.
Ilya A. Shkrob; William J. Glover; Ross E. Larsen; Benjamin J. Schwartz
2007-01-01
Adiabatic mixed quantum\\/classical molecular dynamics simulations were used to\\u000agenerate snapshots of the hydrated electron (e-) in liquid water at 300 K.\\u000aWater cluster anions that include two complete solvation shells centered on the\\u000ae- were extracted from these simulations and embedded in a matrix of fractional\\u000apoint charges designed to represent the rest of the solvent. Density functional\\u000atheory
Vertex-IRF transformations, dynamical quantum groups and harmonic analysis
Jasper V. Stokman
2003-05-23
It is shown that a dynamical quantum group arising from a vertex-IRF transformation has a second realization with untwisted dynamical multiplication but nontrivial bigrading. Applied to the $\\hbox{SL}(2;\\mathbb{C})$ dynamical quantum group, the second realization is naturally described in terms of Koornwinder's twisted primitive elements. This leads to an intrinsic explanation why harmonic analysis on the ``classical'' $\\hbox{SL}(2;\\mathbb{C})$ quantum group with respect to twisted primitive elements, as initiated by Koornwinder, is the same as harmonic analysis on the $\\hbox{SL}(2;\\mathbb{C})$ dynamical quantum group.
NASA Technical Reports Server (NTRS)
Mcnider, Richard T.; Christy, John R.; Cox, Gregory N.
1993-01-01
In order to better understand the dynamics of the global atmosphere, a data set of precision temperature measurements was developed using the NASA built Microwave Sounding Unit. Modeling research was carried out to validate global model outputs using various satellite data. Idealized flows in a rotating annulus were studied and applied to the general circulation of the atmosphere. Dynamic stratospheric ozone fluctuations were investigated. An extensive bibliography and several reprints are appended.
Dynamical Causal Modeling from a Quantum Dynamical Perspective
NASA Astrophysics Data System (ADS)
Demiralp, Emre; Demiralp, Metin
2010-09-01
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.
Dynamical Causal Modeling from a Quantum Dynamical Perspective
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
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.
Quantum corrections to inflaton and curvaton dynamics
Markkanen, Tommi [Helsinki Institute of Physics and Department of Physics, University of Helsinki, P.O. Box 64, FI-00014, Helsinki (Finland); Tranberg, Anders, E-mail: tommi.markkanen@helsinki.fi, E-mail: anders.tranberg@nbi.dk [Niels Bohr International Academy and Discovery Center, Niels Bohr Institute, Blegdamsvej 17, 2100 Copenhagen (Denmark)
2012-11-01
We compute the fully renormalized one-loop effective action for two interacting and self-interacting scalar fields in FRW space-time. We then derive and solve the quantum corrected equations of motion both for fields that dominate the energy density (such as an inflaton) and fields that do not (such as a subdominant curvaton). In particular, we introduce quantum corrected Friedmann equations that determine the evolution of the scale factor. We find that in general, gravitational corrections are negligible for the field dynamics. For the curvaton-type fields this leaves only the effect of the flat-space Coleman-Weinberg-type effective potential, and we find that these can be significant. For the inflaton case, both the corrections to the potential and the Friedmann equations can lead to behaviour very different from the classical evolution. Even to the point that inflation, although present at tree level, can be absent at one-loop order.
Experimental Study of Quantum Chaos with Cesium Atoms
B. G. Klappauf; D. A. Steck; W. H. Oskay; M. G. Raizen
1998-01-01
Ultra-cold atoms in a pulsed, far-detuned standing wave of light constitute an experimental realization of the delta-kicked rotor, a paradigm for classical and quantum chaos. A key prediction in this system is the phenomenon of dynamical localization, a quantum suppression of diffusion in a classically chaotic regime. Previous work in our group centered on the study of dynamical localization with
Symmetry examples in open quantum dynamics
Thomas F. Jordan; San Ha Seo
2014-08-19
Dependent symmetries, a new kind of symmetry of the open quantum dynamics of a subsystem, symmetries that depend on the situation of the subsystem in a larger closed system, are explored by looking at simple examples. Each symmetry implies a particular form for the results of the open dynamics. The forms exhibit the symmetries very simply. It is shown directly, without assuming anything about the symmetry, that the dynamics produces the form, but knowing the symmetry and the form it implies can reduce what needs to be done to work out the dynamics; pieces can be deduced from the symmetry rather that calculated from the dynamics. Symmetries can be related to constants of the motion in new ways. A quantity might be a dependent constant of the motion, constant only for particular situations of the subsystem in the larger system. In particular, a generator of dependent symmetries could represent a quantity that is a dependent constant of the motion for the same situations as for the symmetries. The examples present a variety of possibilities. Sometimes a generator of dependent symmetries does represent a dependent constant of the motion. Sometimes it does not. Sometimes no quantity is a dependent constant of the motion. Sometimes every quantity is.
Non-Markovian dynamics in open quantum systems
Heinz-Peter Breuer; Elsi-Mari Laine; Jyrki Piilo; Bassano Vacchini
2015-05-06
The dynamical behavior of open quantum systems plays a key role in many applications of quantum mechanics, examples ranging from fundamental problems, such as the environment-induced decay of quantum coherence and relaxation in many-body systems, to applications in condensed matter theory, quantum transport, quantum chemistry and quantum information. In close analogy to a classical Markov process, the interaction of an open quantum system with a noisy environment is often modelled by a dynamical semigroup with a generator in Lindblad form, which describes a memoryless dynamics leading to an irreversible loss of characteristic quantum features. However, in many applications open systems exhibit pronounced memory effects and a revival of genuine quantum properties such as quantum coherence and correlations. Here, recent results on the rich non-Markovian quantum dynamics of open systems are discussed, paying particular attention to the rigorous mathematical definition, to the physical interpretation and classification, as well as to the quantification of memory effects. The general theory is illustrated by a series of examples. The analysis reveals that memory effects of the open system dynamics reflect characteristic features of the environment which opens a new perspective for applications, namely to exploit a small open system as a quantum probe signifying nontrivial features of the environment it is interacting with. This article further explores the various physical sources of non-Markovian quantum dynamics, such as structured spectral densities, nonlocal correlations between environmental degrees of freedom and correlations in the initial system-environment state, in addition to developing schemes for their local detection. Recent experiments on the detection, quantification and control of non-Markovian quantum dynamics are also discussed.
Cheng, Yuan-Chung, Ph. D. Massachusetts Institute of Technology
2006-01-01
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 ...
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
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.
Quantum dynamics of a plane pendulum
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
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.
Quantum dynamics of a plane pendulum
NASA Astrophysics Data System (ADS)
Leibscher, Monika; Schmidt, Burkhard
2009-07-01
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 Schrödinger 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.
Fourth Meeting on Constrained Dynamics and Quantum Gravity
Mariano Cadoni; Marco Cavaglia; Jeanette E Nelson
2006-01-01
The formulation of a quantum theory of gravity seems to be the unavoidable endpoint of modern theoretical physics. Yet the quantum description of the gravitational field remains elusive. The year 2005 marks the tenth anniversary of the First Meeting on Constrained Dynamics and Quantum Gravity, held in Dubna (Russia) due to the efforts of Alexandre T. Filippov (JINR, Dubna) and
Spatiotemporal dynamics in Rayleigh band of photonic quantum ring laser
D. K. Kim; O'Dae Kwon
2006-01-01
Spatiotemporal dynamic analysis is used to analyze the carrier-field interactions on photonic quantum ring laser devices in a three dimensional toroidal whispering gallery cavity. We observe quantum wires-like carrier re-distributions instantly and naturally formed in the quantum well plane within the Rayleigh cavity.
Quantum Information, Thermofield Dynamics and Thermalized Bosonic Oscillator
NASA Astrophysics Data System (ADS)
Trindade, M. A. S.; Silva Filho, L. M.; Santos, L. C.; Martins, M. Graças R.; Vianna, J. D. M.
2013-09-01
We show through Thermofield Dynamics approach that the action of the thermalized quantum logic gate on the thermalized state is equivalent to thermalization of the state that arise from the application of the nonthermalized quantum logic gate. In particular, we study the effect of temperature on a mixed state associated to a system capable of implementing a controlled-NOT (CNOT) quantum logic gate. According to a proposal in the literature, a way of implementing such a logic gate is by using a representation of the qubit states as elements of the Fock space of a bosonic system. We consider such a proposal and use the Thermofield Dynamics to determine the thermalized qubit states. The temperature acts as a quantum noise on pure states, making them a statistical mixture. In this context, we analyze the fidelity as a function of the temperature and using the Mandel parameter, we determine temperature ranges for which the statistics of the system becomes subpoissonian, poissonian and superpoissonian. Finally, we calculate the Wigner function, allowing an analysis of the thermal state in phase space, and we obtain that the increase of temperature decreases nonclassical properties of the system. The temperature range where one has a subpoissonian statistics and high fidelity is determined.
Quantum dynamics of the abstraction reaction of H with cyclopropane.
Shan, Xiao; Clary, David C
2014-10-30
The dynamics of the abstraction reaction of H atoms with the cyclopropane molecule is studied using quantum mechanical scattering theory. The quantum scattering calculations are performed in hyperspherical coordinates with a two-dimensional (2D) potential energy surface. The ab initio energy calculations are carried out with CCSD(T)-F12a/cc-pVTZ-F12 level of theory with the geometry and frequency calculations at the MP2/cc-pVTZ level. The contribution to the potential energy surface from the spectator modes is included as the projected zero-point energy correction to the ab initio energy. The 2D surface is fitted with a 29-parameter double Morse potential. An R-matrix propagation scheme is carried out to solve the close-coupled equations. The adiabatic energy barrier and reaction enthalpy are compared with high level computational calculations as well as experimental data. The calculated reaction rate constants shows very good agreement when compared with the experimental data, especially at lower temperature highlighting the importance of quantum tunnelling. The reaction probabilities are also presented and discussed. The special features of performing quantum dynamics calculation on the chemical reaction of a cyclic molecule are discussed. PMID:25271568
Quantum Theory of Chemical Reaction Dynamics.
NASA Astrophysics Data System (ADS)
Zhao, Meishan
The generalized Newton variational principle is extended to treat chemical reactions with nonzero total angular momentum J, and it is applied to various chemical reactions with J = 0 to 20. Chapter 1 reviews the basic theory and discusses the evaluation of nonzero-J matrix elements. Chapters 2-5 report extensive quantum mechanical calculations on the reaction H + p-H_2 to o-H_2 + H. Chapter 2 reports vibrational branching ratios. Chapter 3 reports probabilities and partial cross sections, which are compared to corresponding quantities calculated by the quasiclassical trajectory method. Chapter 4 presents converged quantum mechanical state-to-state cross sections. The converged vibrational branching ratio is in good agreement with recent experiments but the rotational distribution is not. Chapter 5 reports converged quantum mechanical calculations of resonances and time delays for total angular momentum 0, 1, and 4. Chapter 4 compares the results of classical simulations to accurate quantum studies for the reaction D + H _2 to HD + H. Chapter 7 presents accurate state-to-state transition probabilities and delay times for this reaction. Chapter 8 reports fully converged quantum mechanical transition probabilities for the F + H_2 to HF + H reaction. Chapter 9 presents calculations of state-to-state partial reaction cross sections in H + D_2 to HD + D collisions. The results are compared to quasiclassical trajectory calculations to test the classical simulation method. In chapter 10 a new method for constructing efficient basis functions for {cal L}^2 variational calculations of quantum mechanical rearrangements is presented and tested.
Honvault, Pascal
Trajectory Study L. Ban~ares* and F. J. Aoiz Departamento de Qui´mica Fi´sica Facultad de Qui´mica, Uni at a collision energy of 2.24 kcal/mol. Additionally, quasiclassical trajectory (QCT) calculations have been at total angular momentum J ) 0 as a function of collision energy within the range 0-11.5 kcal
Dynamics of open bosonic quantum systems in coherent state representation
Dalvit, D. A. R.; Berman, G. P. [Theoretical Division, MS B213, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Vishik, M. [Department of Mathematics, University of Texas at Austin, Austin, Texas 78712-1082 (United States)
2006-01-15
We consider the problem of decoherence and relaxation of open bosonic quantum systems from a perspective alternative to the standard master equation or quantum trajectories approaches. Our method is based on the dynamics of expectation values of observables evaluated in a coherent state representation. We examine a model of a quantum nonlinear oscillator with a density-density interaction with a collection of environmental oscillators at finite temperature. We derive the exact solution for dynamics of observables and demonstrate a consistent perturbation approach.
Decoherence dynamics of two charge qubits in vertically coupled quantum dots
Ben Chouikha, W.; Bennaceur, R. [Laboratoire de Physique de la Matiere Condensee, Departement de Physique, Faculte des Sciences de Tunis, 1060 Tunis (Tunisia); Jaziri, S. [Departement de Physique, Faculte des Sciences de Bizerte, Jarzouna 7021 Bizerte (Tunisia)
2007-12-15
The decoherence dynamics of two charge qubits in a double quantum dot is investigated theoretically. We consider the quantum dynamics of two interacting electrons in a vertically coupled quantum dot driven by an external electric field. We derive the equations of motion for the density matrix, in which the presence of an electron confined in the double dot represents one qubit. A Markovian approach to the dynamical evolution of the reduced density matrix is adopted. We evaluate the concurrence of two qubits in order to study the effect of acoustic phonons on the entanglement. We also show that the disentanglement effect depends on the double dot parameters and increases with the temperature.
Exponential rise of dynamical complexity in quantum computing through projections
Burgarth, Daniel Klaus; Facchi, Paolo; Giovannetti, Vittorio; Nakazato, Hiromichi; Pascazio, Saverio; Yuasa, Kazuya
2014-01-01
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
Tingli Sun; Yudong Wang; Chenxi Zhang; Xiaomin Sun; Wenxing Wang
2011-01-01
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 O3 has been studied using high level molecular orbital theory. A detailed description of the possible ozonolysis mechanism in the presence of H2O
Loop quantum cosmology of Bianchi IX: Effective dynamics
Alejandro Corichi; Edison Montoya
2015-02-09
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.
A Time-Dependent Quantum Dynamics Study of the H2 + CH3 yields H + CH4 Reaction
NASA Technical Reports Server (NTRS)
Wang, Dunyou; Kwak, Dochan (Technical Monitor)
2002-01-01
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.
Singh, Tanya; Adekoya, Olayiwola Adedotun; Jayaram, B
2015-04-01
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
Quantum dynamics in a camel-back potential of a dc SQUID E. Hoskinson1
Paris-Sud XI, UniversitÃ© de
Quantum dynamics in a camel-back potential of a dc SQUID E. Hoskinson1 , F. Lecocq1 , N. Didier2 Josephson junctions (dc SQUID), with near-zero current bias and flux bias near half a flux quantum. We SQUID and the rf SQUID phase qubit have been extensively studied [2Â6]. In each of these devices
Quantum Phase Transition and Universal Dynamics in the Rabi model
Myung-Joong Hwang; Ricardo Puebla; Martin B. Plenio
2015-03-10
We consider the Rabi Hamiltonian which exhibits a quantum phase transition (QPT) despite consisting only of a single-mode cavity field and a two-level atom. We prove QPT by deriving an exact solution in the limit where the atomic transition frequency in unit of the cavity frequency tends to infinity. The effect of a finite transition frequency is studied by analytically calculating finite-frequency scaling exponents as well as performing a numerically exact diagonalization. Going beyond this equilibrium QPT setting, we prove that the dynamics under slow quenches in the vicinity of the critical point is universal, that is, the dynamics is completely characterized by critical exponents. Our analysis demonstrates that the Kibble-Zurek mechanism can precisely predict the universal scaling of residual energy for a model without spatial degrees of freedom. Moreover, we find that the onset of the universal dynamics can be observed even with a finite transition frequency.
NASA Astrophysics Data System (ADS)
Kim, Jungho
2012-12-01
We theoretically investigate the effect of multichannel pump injection on the ultrafast gain and phase recovery dynamics of quantum-dot (QD) semiconductor optical amplifiers (SOAs) by solving 10880 coupled rate equations. The ultrafast gain and phase recovery responses induced by three-channel pump injection are calculated compared with the single-channel pump injection. The gain and phase recovery response caused by three-channel pump injection is different from the summation of the three gain and phase recovery responses induced by separate single-channel pump injection. We identify the physical mechanism of the distinct gain and phase recovery responses due to different pump wavelength by considering the interplay between the Lorentzian line shape function and the spectral spacing between the pump and probe beams. The calculation results help to understand the gain and phase recovery dynamics of QD SOAs for multichannel amplification in coarse wavelength division multiplexing (CWDM) applications.
NASA Astrophysics Data System (ADS)
Hele, Timothy J. H.; Willatt, Michael J.; Muolo, Andrea; Althorpe, Stuart C.
2015-05-01
We recently obtained a quantum-Boltzmann-conserving classical dynamics by making a single change to the derivation of the "Classical Wigner" approximation. Here, we show that the further approximation of this "Matsubara dynamics" gives rise to two popular heuristic methods for treating quantum Boltzmann time-correlation functions: centroid molecular dynamics (CMD) and ring-polymer molecular dynamics (RPMD). We show that CMD is a mean-field approximation to Matsubara dynamics, obtained by discarding (classical) fluctuations around the centroid, and that RPMD is the result of discarding a term in the Matsubara Liouvillian which shifts the frequencies of these fluctuations. These findings are consistent with previous numerical results and give explicit formulae for the terms that CMD and RPMD leave out.
Hele, Timothy J H; Willatt, Michael J; Muolo, Andrea; Althorpe, Stuart C
2015-05-21
We recently obtained a quantum-Boltzmann-conserving classical dynamics by making a single change to the derivation of the "Classical Wigner" approximation. Here, we show that the further approximation of this "Matsubara dynamics" gives rise to two popular heuristic methods for treating quantum Boltzmann time-correlation functions: centroid molecular dynamics (CMD) and ring-polymer molecular dynamics (RPMD). We show that CMD is a mean-field approximation to Matsubara dynamics, obtained by discarding (classical) fluctuations around the centroid, and that RPMD is the result of discarding a term in the Matsubara Liouvillian which shifts the frequencies of these fluctuations. These findings are consistent with previous numerical results and give explicit formulae for the terms that CMD and RPMD leave out. PMID:26001438
Geometry and Dynamics of Quantum State Diffusion
Nikola Buric
2007-04-11
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.
Switching quantum dynamics for fast stabilization
NASA Astrophysics Data System (ADS)
Scaramuzza, Pierre; Ticozzi, Francesco
2015-06-01
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 problem 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 nonswitching methods, but can be designed so that they retain robustness with respect to initialization, as long as the target is a pure state or a subspace.
Liu, Tianhui; Fu, Bina; Zhang, Dong H
2014-11-21
A new finding of the site-averaging approximation was recently reported on the dissociative chemisorption of the HCl/DCl+Au(111) surface reaction [T. Liu, B. Fu, and D. H. Zhang, J. Chem. Phys. 139, 184705 (2013); T. Liu, B. Fu, and D. H. Zhang, J. Chem. Phys. 140, 144701 (2014)]. Here, in order to investigate the dependence of new site-averaging approximation on the initial vibrational state of H2 as well as the PES for the dissociative chemisorption of H2 on Cu(111) surface at normal incidence, we carried out six-dimensional quantum dynamics calculations using the initial state-selected time-dependent wave packet approach, with H2 initially in its ground vibrational state and the first vibrational excited state. The corresponding four-dimensional site-specific dissociation probabilities are also calculated with H2 fixed at bridge, center, and top sites. These calculations are all performed based on two different potential energy surfaces (PESs). It is found that the site-averaging dissociation probability over 15 fixed sites obtained from four-dimensional quantum dynamics calculations can accurately reproduce the six-dimensional dissociation probability for H2 (v = 0) and (v = 1) on the two PESs. PMID:25416886
NASA Astrophysics Data System (ADS)
Nikshych, Dmitri Alexandrovich
2001-08-01
Finite quantum groupoids (weak Hopf algebras) were recently introduced by G. Böhm and K. Szlachányi as a generalization of usual Hopf algebras and groupoid algebras. A weak Hopf algebra is a vector space that has both algebra and coalgebra structures related to each other in a certain self-dual fashion and possesses an analogue of the linearized inverse map. The main difference between weak and ordinary Hopf algebras comes from the fact that the comultiplication of the latter is no longer required to preserve the unit (equivalently, the counit is not required to be a homomorphism) and results in the existence of two canonical subalgebras playing the role of ``non-commutative bases''. Weak Hopf algebras provide a suitable algebraic framework for studying various non-commutative phenomena that cannot be otherwise described by means of Hopf algebras, such as, e.g., finite depth subfactors with non-integer index and semisimple monoidal categories with non-integer quantum dimensions. We describe the foundations of the theory of weak Hopf algebras and illustrate it by motivating examples. We develop the theory of monoidal categories of representations of weak Hopf algebras and show that their additional symmetry properties, such as braiding, ribbon and modular structures, can be used for constructing Reshetikhin-Turaev type invariants of links and 3- manifolds. We investigate the relation between weak Hopf algebras and dynamical quantum groups and show that the result of a dynamical twisting of an ordinary finite-dimensional Hopf algebra is a weak Hopf algebra. We use this observation to introduce and study dynamical quantum groups at roots of unity. Finally, we study the algebraic structure of weak Hopf C*-algebras and explain how they characterize finite index depth 2 inclusions of II 1 factors. We prove a Galois correspondence for arbitrary finite depth subfactors that allows to describe them as certain ``quotients'' of weak Hopf C*-algebra crossed products.
Fundamental significance of tests that quantum dynamics is linear
Jordan, Thomas F. [Department of Physics, University of Minnesota, Duluth, Minnesota 55812 (United States)
2010-09-15
Experiments that look for nonlinear quantum dynamics test the fundamental premise of physics that one of two separate systems can influence the physical behavior of the other only if there is a force between them, an interaction that involves momentum and energy. The premise is tested because it is the assumption of a proof that quantum dynamics must be linear. Here, variations of a familiar example are used to show how results of nonlinear dynamics in one system can depend on correlations with the other. Effects of one system on the other, influence without interaction between separate systems, not previously considered possible, would be expected with nonlinear quantum dynamics. Whether it is possible or not is subject to experimental tests together with the linearity of quantum dynamics. Concluding comments and questions consider directions our thinking might take in response to this surprising unprecedented situation.
Rong-Chun Ge; Stephen Hughes
2015-05-08
We study the quantum dynamics of two quantum dots (QDs) or artificial atoms electromagnetically coupled through the localized plasmon of a single gold nanorod. We derive an intuitive and efficient time-local master equation, in which the effect of the gold nanorod is taken into consideration self-consistently using a quasinormal mode (QNM) expansion technique of the photon Green function. We then present a study of the quantum dynamics and photoluminescence spectra of the two plasmon coupled QDs. We first explore the non-Markovian regime, which is found to be important on the time scale of the lifetime of the plasmon mode which is about 40$\\,$fs. For the free evolution case of excited QDs in homogeneous dielectric background, we show how spatially separated QDs can be effectively coupled through the plasmon and we demonstrate that frequencies away from the plasmon resonance are more effective for coherently coupling the QDs. Despite the strong inherent dissipation of gold, we show that qubit entanglements as large as 0.7 can be achieved from an initially separate state, which has been limited to less than 0.5 in previous work for weakly coupled reservoirs. We also study the superradiance and subradiance decay dynamics of the QD pair. Finally, we investigate the dynamics of QDs that are incoherently pumped, and study the polarization dependent behaviour of the emitted photoluminescence spectrum where a double-resonance structure is observed due to the strong photon exchange interactions. Our formalism can easily be extended to include multiple QDs interacting through the QNMs of metallic resonator structures.
Genetic simulation of quantum dynamics by the principle of quantum state selection
Yuri Ozhigov
2008-01-24
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.
NASA Astrophysics Data System (ADS)
Yang, Yu-Guang; Xu, Peng; Tian, Ju; Zhang, Hua
2014-09-01
We investigate the dynamic watermarking scheme for quantum images using quantum wavelet transform (QWT) proposed by Song et al. (Quantum Inf Process 12(12):3689-3706, 2013). It is aimed to embed the watermark image into the wavelet coefficients of the quantum carrier image. However, in our opinion, the key procedures of the protocol are wrong. At last, a possible improvement strategy is presented.
Neutral modes' edge state dynamics through quantum point contacts
NASA Astrophysics Data System (ADS)
Ferraro, D.; Braggio, A.; Magnoli, N.; Sassetti, M.
2010-01-01
The dynamics of neutral modes for fractional quantum Hall states is investigated for a quantum point contact geometry in the weak-backscattering regime. The effective field theory introduced by Fradkin-Lopez for edge states in the Jain sequence is generalized to the case of propagating neutral modes. The dominant tunnelling processes are identified also in the presence of non-universal phenomena induced by interactions. The crossover regime in the backscattering current between tunnelling of single-quasiparticles and of agglomerates of p-quasiparticles is analysed. We demonstrate that higher-order cumulants of the backscattering current fluctuations are a unique resource to study quantitatively the competition between different carrier charges. We find that propagating neutral modes are a necessary ingredient in order to explain this crossover phenomenon.
Conditions for strictly purity-decreasing quantum Markovian dynamics
D. A. Lidar; A. Shabani; R. Alicki
2005-02-03
The purity, Tr(rho^2), measures how pure or mixed a quantum state rho is. It is well known that quantum dynamical semigroups that preserve the identity operator (which we refer to as unital) are strictly purity-decreasing transformations. Here we provide an almost complete characterization of the class of strictly purity-decreasing quantum dynamical semigroups. We show that in the case of finite-dimensional Hilbert spaces a dynamical semigroup is strictly purity-decreasing if and only if it is unital, while in the infinite dimensional case, unitality is only sufficient.
Quantum molecular dynamic simulations of warm dense carbon monoxide.
Zhang, Yujuan; Wang, Cong; Li, Dafang; Zhang, Ping
2011-08-14
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
Quantitative study of amplitude noise effects on dynamical localization
Daniel A. Steck; Valery Milner; Windell H. Oskay; Mark G. Raizen
2000-01-01
We study the motion of cold atoms in a pulsed standing wave of light, which constitutes an experimental realization of the quantum kicked rotor. This system exhibits dynamical localization, where quantum effects suppress classical momentum diffusion. As we introduce amplitude noise, the coherences that lead to local- ization are destroyed, resulting in restored diffusion. For high levels of noise, we
Quantitative study of amplitude noise effects on dynamical localization
Daniel A. Steck; Valery Milner; Windell H. Oskay; Mark G. Raizen
2000-01-01
We study the motion of cold atoms in a pulsed standing wave of light, which constitutes an experimental realization of the quantum kicked rotor. This system exhibits dynamical localization, where quantum effects suppress classical momentum diffusion. As we introduce amplitude noise, the coherences that lead to localization are destroyed, resulting in restored diffusion. For high levels of noise, we find
Relative unitary implementability of perturbed quantum field dynamics on de Sitter space
Poon, Gary Kaiman [Department of Physics, SUNY at Buffalo, Amherst, New York 14260 (United States)
2010-04-15
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.
Lindblad- and non-Lindblad-type dynamics of a quantum Brownian particle
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
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.
Loop quantum cosmology of Bianchi IX: Effective dynamics
Corichi, Alejandro
2015-01-01
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...
Algebraic and geometric aspects of generalized quantum dynamics
Adler, S.L. (Institute for Advanced Study, Princeton, New Jersey 08540 (United States)); Wu, Y. (Department of Physics, University of Utah, Salt Lake City, Utah 84112 (United States))
1994-06-15
We briefly discuss some algebraic and geometric aspects of the generalized Poisson bracket and noncommutative phase space for generalized quantum dynamics, which are analogous to properties of the classical Poisson bracket and ordinary symplectic structure.
On the phase space description of quantum nonlinear dynamics
NASA Astrophysics Data System (ADS)
Atakishiyev, N. M.; Chumakov, S. M.; Rivera, A. L.; Wolf, K. B.
1996-02-01
We analyze the difference between classical dynamics (geometric optics) and quantum dynamics (wave optics) by calculating the time history of the Wigner function for the simplest nonlinear Hamiltonians which are fourth-degree polynomials in p and q. It is shown that the moments of the Wigner function carry important information about the state of a system and can be used to distinguish between quasiclassical and quantum evolution.
Editorial: Focus on Dynamics and Thermalization in Isolated Quantum Many-Body Systems
NASA Astrophysics Data System (ADS)
Cazalilla, M. A.; Rigol, M.
2010-05-01
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
NASA Astrophysics Data System (ADS)
Andreani, C.; Romanelli, G.; Senesi, R.
2013-12-01
We report new results of a combined analysis of previous Inelastic Neutron Scattering (INS) and Deep Inelastic Neutron Scattering (DINS) experiments on ice at T = 271 K and water at T = 285 K and T = 673 K. Proton quantum dynamics is discussed in terms of the total mean kinetic energy,
Dynamics of multiphoton excitation and quantum diffusion in Rydberg atoms
NASA Astrophysics Data System (ADS)
Wang, Kwanghsi; Chu, Shih-I.
1989-02-01
We present a detailed two-dimensional (2D) quantal study of the dynamical evolution of microwave-driven Rydberg H atoms. We examine the range of validity of the conventional one-dimensional (1D) models and explore the frequency- and intensity-dependent excitation and ionization mechanisms. The main findings of this paper can be summarized as follows: (i) The excitation spectra of Rydberg H atoms are strongly frequency dependent and can be roughly grouped into three characteristically different regions, each with a different excitation mechanism. In this paper, we emphasize the study of the two major excitation mechanisms: quantum diffusion and multiphoton resonant excitation. The region dominated by quantum diffusion lies in the frequency range ?cquantum number of the initial state); ?c, the classical chaotic threshold; and ?d, the quantum delocalization border. In this region, quasienergy levels are strongly perturbed and mixed and excitation is efficient, leading to the so-called underthreshold photoelectric ionization phenomenon. On the other hand, we found a series of frequency regions (in ?0>?d) where the ionization is mainly due to multiphoton resonant excitation through the more isolated quasienergy avoided crossing points. (ii) The excitation pathways (1D versus 2D) are strongly intensity dependent. For microwave (rescaled) field strength ?0 (??n40) in the range ?cquantum delocalization threshold), large discrepancies exist between 1D and 2D results. It is found that the 1D model seriously underestimates the ionization probabilities and, more importantly, the dominant channels for Rydberg atom excitation and ionization proceed through n2>0 ladders rather than the n2=0 ladder, as often assumed in the 1D model. As field strength increases above ?q, however, the 1D model improves significantly. (iii) The quantum localization phenomenon is observed in the classically chaotic region (?cquantum delocalization can appear when ?0>?q. (iv) The stability of quantum diffusive motion is analyzed in terms of the quantal phase-space diagram and the autocorrelation function. The results lend support to the view that quantum mechanics can impose limitations on classical chaotic motion. (v) The way of turning on the field (sin?t or cos?t) does not affect significantly the dynamical evolution of the system. (vi) Finally, a computationally powerful new technique, invoking the use of artificial intelligence algorithms as well as the generalized Van Vleck perturbation theory for effectively reducing the dimensionality of the Floquet matrix, is introduced to facilitate the study of multiphoton resonant excitation of Rydberg atoms.
Analyzing Big Data with Dynamic Quantum Clustering
Weinstein, M; Hume, A; Sciau, Ph; Shaked, G; Hofstetter, R; Persi, E; Mehta, A; Horn, D
2013-01-01
How does one search for a needle in a multi-dimensional haystack without knowing what a needle is and without knowing if there is one in the haystack? This kind of problem requires a paradigm shift - away from hypothesis driven searches of the data - towards a methodology that lets the data speak for itself. Dynamic Quantum Clustering (DQC) is such a methodology. DQC is a powerful visual method that works with big, high-dimensional data. It exploits variations of the density of the data (in feature space) and unearths subsets of the data that exhibit correlations among all the measured variables. The outcome of a DQC analysis is a movie that shows how and why sets of data-points are eventually classified as members of simple clusters or as members of - what we call - extended structures. This allows DQC to be successfully used in a non-conventional exploratory mode where one searches data for unexpected information without the need to model the data. We show how this works for big, complex, real-world dataset...
Theoretical studies on bimolecular reaction dynamics
Clary, David C.
2008-01-01
This perspective discusses progress in the theory of bimolecular reaction dynamics in the gas phase. The examples selected show that definitive quantum dynamical computations are providing insights into the detailed mechanisms of chemical reactions. PMID:18626015
Quantum dynamics in the bosonic Josephson junction
Chuchem, Maya; Cohen, Doron [Department of Physics, Ben-Gurion University of the Negev, P.O.B. 653, Beer-Sheva 84105 (Israel); Smith-Mannschott, Katrina [Department of Physics, Wesleyan University, Middletown, Connecticut 06459 (United States); MPI for Dynamics and Self-Organization, Bunsenstrasse 10, D-37073 Goettingen (Germany); Hiller, Moritz [Physikalisches Institut, Albert-Ludwigs-Universitaet, Hermann-Herder-Strasse 3, D-79104 Freiburg (Germany); Kottos, Tsampikos [Department of Physics, Wesleyan University, Middletown, Connecticut 06459 (United States); Vardi, Amichay [Department of Chemistry, Ben-Gurion University of the Negev, P.O.B. 653, Beer-Sheva 84105 (Israel); Institute for Theoretical Atomic, Molecular and Optical Physics, Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts 02138 (United States)
2010-11-15
We employ a semiclassical picture to study dynamics in a bosonic Josephson junction with various initial conditions. Phase diffusion of coherent preparations in the Josephson regime is shown to depend on the initial relative phase between the two condensates. For initially incoherent condensates, we find a universal value for the buildup of coherence in the Josephson regime. In addition, we contrast two seemingly similar on-separatrix coherent preparations, finding striking differences in their convergence to classicality as the number of particles increases.
Dynamical Yang-Baxter Equation and Quantum Vector Bundles
NASA Astrophysics Data System (ADS)
Donin, J.; Mudrov, A.
2005-03-01
We develop a categorical approach to the dynamical Yang-Baxter equation (DYBE) for arbitrary Hopf algebras. In particular, we introduce the notion of a dynamical extension of a monoidal category, which provides a natural environment for quantum dynamical R-matrices, dynamical twists, etc. In this context, we define dynamical associative algebras and show that such algebras give quantizations of vector bundles on coadjoint orbits. We build a dynamical twist for any pair of a reductive Lie algebra and its Levi subalgebra. Using this twist, we obtain an equivariant star product quantization of vector bundles on semisimple coadjoint orbits of reductive Lie groups.
Quantum dynamics of Kaluza-Klein theories
Appelquist, T.; Chodos, A.
1983-08-15
Some of the quantum properties of Kaluza-Klein theories are studied. The classical features of these theories are reviewed, and the quantization of the gravitational field in an arbitrary number of dimensions is described. These results are then applied to a detailed analysis of the five-dimensional Kaluza-Klein model. The fifth dimension is taken to be compact and a quantum effective potential, as a function of the five-five component of the metric, is constructed. It is argued that the one-loop computation is reliable as long as the distance around the fifth dimension is large compared to the Planck length. The effective potential separates into two pieces: an induced cosmological constant, independent of the size of the fifth dimension, and a distance-dependent ''Casimir'' energy. The cosmological term is subtracted, leaving an attractive Casimir potential which will contract the fifth dimension to a size on the order of the Planck length. Consequences of this result are discussed and some of the ways in which it can be generalized are outlined.
Quantum dynamics of a plasmonic metamolecule with a time-dependent driving
Daniel A. Uken; Alessandro Sergi
2015-06-18
We simulate the dynamics of a quantum dot coupled to the single resonating mode of a metal nano-particle. Systems like this are known as metamolecules. In this study, we consider a time-dependent driving field acting onto the metamolecule. We use the Heisenberg equations of motion for the entire system, while representing the resonating mode in Wigner phase space. A time-dependent basis is adopted for the quantum dot. We integrate the dynamics of the metamolecule for a range of coupling strengths between the quantum dot and the driving field, while restricting the coupling between the quantum dot and the resonant mode to weak values. By monitoring the average of the time variation of the energy of the metamolecule model, as well as the coherence and the population difference of the quantum dot, we observe distinct non-linear behavior in the case of strong coupling to the driving field.
Continuous-Representation Theory. II. Generalized Relation between Quantum and Classical Dynamics
John R. Klauder
1963-01-01
This paper discusses an application to the study of dynamics of the typical overcomplete, non-independent sets of unit vectors that characterize continuous-representation theory. It is shown in particular that the conventional, classical Hamiltonian dynamical formalism arises from an analysis of quantum dynamics restricted to an overcomplete, nonindependent set of vectors which lie in one-to-one correspondence with, and are labeled by,
Investigations of quantum pendulum dynamics in a spin-1 BEC
NASA Astrophysics Data System (ADS)
Hoang, Thai; Gerving, Corey; Land, Ben; Anquez, Martin; Hamley, Chris; Chapman, Michael
2013-05-01
We investigate the quantum spin dynamics of a spin-1 BEC initialized to an unstable critical point of the dynamical phase space. The subsequent evolution of the collective states of the system is analogous to an inverted simple pendulum in the quantum limit and yields non-classical states with quantum correlations. For short evolution times in the low depletion limit, we observe squeezed states and for longer times beyond the low depletion limit we observe highly non-Gaussian distributions. We investigate the quantum spin dynamics of a spin-1 BEC initialized to an unstable critical point of the dynamical phase space. The subsequent evolution of the collective states of the system is analogous to an inverted simple pendulum in the quantum limit and yields non-classical states with quantum correlations. For short evolution times in the low depletion limit, we observe squeezed states and for longer times beyond the low depletion limit we observe highly non-Gaussian distributions. C.D. Hamley, C.S. Gerving, T.M. Hoang, E.M. Bookjans, and M.S. Chapman, ``Spin-Nematic Squeezed Vacuum in a Quantum Gas,'' Nature Physics 8, 305-308 (2012).
Quantum processes, space-time representation and brain dynamics
Sisir Roy; Menas Kafatos
2003-05-07
The recent controversy of applicability of quantum formalism to brain dynamics has been critically analysed. The prerequisites for any type of quantum formalism or quantum field theory is to investigate whether the anatomical structure of brain permits any kind of smooth geometric notion like Hilbert structure or four dimensional Minkowskian structure for quantum field theory. The present understanding of brain function clearly denies any kind of space-time representation in Minkowskian sense. However, three dimensional space and one time can be assigned to the neuromanifold and the concept of probabilistic geometry is shown to be appropriate framework to understand the brain dynamics. The possibility of quantum structure is also discussed in this framework.
A study on neuromorphic quantum computation
Shigeo Sato; Mitsunaga Kinjo; Osamu Takahashi; Yuuki Nakamiya; Koji Nakajima
2004-01-01
A quantum computer employing a single quantum as a qubit executes real parallel computation. Several algorithms have been proposed for quantum computation. However, these algorithms are applicable only to a limited number of applications. Therefore, a general purpose algorithm should be studied and developed for practical use in the near future. We focus on the adiabatic evolution algorithm in order
Quantum dynamics of tunneling dominated reactions at low temperatures
NASA Astrophysics Data System (ADS)
Hazra, Jisha; Balakrishnan, N.
2015-05-01
We report a quantum dynamics study of the Li + HF ? LiF + H reaction at low temperatures of interest to cooling and trapping experiments. Contributions from non-zero partial waves are analyzed and results show narrow resonances in the energy dependence of the cross section that survive partial wave summation. The computations are performed using the ABC code and a simple modification of the ABC code that enables separate energy cutoffs for the reactant and product rovibrational energy levels is found to dramatically reduce the basis set size and computational expense. Results obtained using two ab initio electronic potential energy surfaces for the LiHF system show strong sensitivity to the choice of the potential. In particular, small differences in the barrier heights of the two potential surfaces are found to dramatically influence the reaction cross sections at low energies. Comparison with recent measurements of the reaction cross section (Bobbenkamp et al 2011 J. Chem. Phys. 135 204306) shows similar energy dependence in the threshold regime and an overall good agreement with experimental data compared to previous theoretical results. Also, usefulness of a recently introduced method for ultracold reactions that employ the quantum close-coupling method at short-range and the multichannel quantum defect theory at long-range, is demonstrated in accurately evaluating product state-resolved cross sections for D + H2 and H + D2 reactions.
Derivation of the Euler Equations from Quantum Dynamics
Bruno Nachtergaele; Horng-Tzer Yau
2003-07-14
We derive the Euler equations from quantum dynamics for a class of fermionic many-body systems. We make two types of assumptions. The first type are physical assumptions on the solution of the Euler equations for the given initial data. The second type are a number of reasonable conjectures on the statistical mechanics and dynamics of the Fermion Hamiltonian.
Quantum Gravity, Dynamical Energy-Momentum Space and Vacuum Energy
Lay Nam Chang; Djordje Minic; Tatsu Takeuchi
2010-04-23
We argue that the combination of the principles of quantum theory and general relativity allow for a dynamical energy-momentum space. We discuss the freezing of vacuum energy in such a dynamical energy-momentum space and present a phenomenologically viable seesaw formula for the cosmological constant in this context.
Correlated Single Quantum Dot Blinking and Interfacial Electron Transfer Dynamics
Jin, Shengye; Hsiang, Jung-Cheng; Zhu, Haiming; Song, Nianhui; Dickson, Robert M.; Lian, Tianquan
2011-01-01
The electron transfer (ET) dynamics from core/multi-shell (CdSe/CdS3MLZnCdS2MLZnS2ML) quantum dots (QDs) to adsorbed Fluorescein (F27) molecules have been studied by single particle spectroscopy to probe the relationship between single QD interfacial electron transfer and blinking dynamics. Electron transfer from the QD to F27 and the subsequent recombination were directly observed by ensemble-averaged transient absorption spectroscopy. Single QD-F27 complexes show correlated fluctuation of fluorescence intensity and lifetime, similar to those observed in free QDs. With increasing ET rate (controlled by F27-to-QD ratio), the lifetime of on states decreases and relative contribution of off states increases. It was shown that ET is active for QDs in on states, the excited state lifetime of which reflects the ET rate, whereas in the off state QD excitons decay by Auger relaxation and ET is not a competitive quenching pathway. Thus, the blinking dynamics of single QDs modulate their interfacial ET activity. Furthermore, interfacial ET provides an additional pathway for generating off states, leading to correlated single QD interfacial ET and blinking dynamics in QD-acceptor complexes. Because blinking is a general phenomenon of single QDs, it appears that the correlated interfacial ET and blinking and the resulting intermittent ET activity are general phenomena for single QDs. PMID:21915369
NASA Astrophysics Data System (ADS)
Dattani, Nikesh S.
2013-06-01
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.
Quantum Molecular Dynamics calculation of electrical and thermal transport properties
NASA Astrophysics Data System (ADS)
Desjarlais, Michael
2011-10-01
Dense, strongly-coupled plasmas, with degenerate or partially degenerate electrons--ubiquitous in high energy density physics, inertial fusion, planetary science, and warm dense matter--are very difficult to describe accurately with traditional theoretical approaches. Over the last decade, density functional based molecular dynamics, also know as quantum molecular dynamics (QMD), has emerged as a powerful tool for the study of dense quantum plasmas, providing accurate equation of state, structural, and transport properties. This talk will focus on the QMD calculation of electrical and thermal conductivities with a much higher degree of accuracy than was possible with earlier methods. Within the density functional approach, electrical and thermal conductivities are extracted directly from the electronic orbitals using the Kubo-Greenwood and Chester-Thellung formalisms, circumventing the need to define the ionization states and collision cross sections. These transport calculations have now been used to generate several wide-range transport models for use in large-scale simulation codes, allowing unprecedented simulations of complex experiments. Sandia National Laboratories is a multi program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.
A study of Quantum Correlation for Three Qubit States under the effect of Quantum Noisy Channels
Pratik K. Sarangi; Indranil Chakrabarty
2014-11-27
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.
Quantum heat bath for spin-lattice dynamics
NASA Astrophysics Data System (ADS)
Woo, C. H.; Wen, Haohua; Semenov, A. A.; Dudarev, S. L.; Ma, Pui-Wai
2015-03-01
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.
Quantum properties and dynamics of X states
Nicolás Quesada; Asma Al-Qasimi; Daniel F. V. James
2012-07-16
X states are a broad class of two-qubit density matrices that generalize many states of interest in the literature. In this work, we give a comprehensive account of various quantum properties of these states, such as entanglement, negativity, quantum discord and other related quantities. Moreover, we discuss the transformations that preserve their structure both in terms of continuous time evolution and discrete quantum processes.
Fisher-Shannon product and quantum revivals in wavepacket dynamics
T. García; F. de los Santos; E. Romera
2014-09-19
We show the usefulness of the Fisher-Shannon information product in the study of the sequence of collapses and revivals that take place along the time evolution of quantum wavepackets. This fact is illustrated in two models, the quantum bouncer and a graphene quantum ring.
Acceleration of adiabatic quantum dynamics in electromagnetic fields
Masuda, Shumpei [Department of Physics, Tohoku University, Sendai 980 (Japan); Nakamura, Katsuhiro [Faculty of Physics, National University of Uzbekistan, Vuzgorodok, Tashkent 100174 (Uzbekistan); Department of Applied Physics, Osaka City University, Sumiyoshi-ku, Osaka 558-8585 (Japan)
2011-10-15
We show a method to accelerate quantum adiabatic dynamics of wave functions under electromagnetic field (EMF) by developing the preceding theory [Masuda and Nakamura, Proc. R. Soc. London Ser. A 466, 1135 (2010)]. Treating the orbital dynamics of a charged particle in EMF, we derive the driving field which accelerates quantum adiabatic dynamics in order to obtain the final adiabatic states in any desired short time. The scheme is consolidated by describing a way to overcome possible singularities in both the additional phase and driving potential due to nodes proper to wave functions under EMF. As explicit examples, we exhibit the fast forward of adiabatic squeezing and transport of excited Landau states with nonzero angular momentum, obtaining the result consistent with the transitionless quantum driving applied to the orbital dynamics in EMF.
A Measure of Non-Markovianity for Unital Quantum Dynamical Maps
S. Haseli; S. Salimi; A. S. Khorashad
2014-11-18
One of the most important topics in the study of the dynamics of open quantum system is information exchange between system and environment. Based on the features of a back-flow information from an environment to a system, an approach is provided to detect non-Markovianity for unital dynamical maps. The method takes advantage of non-contractive property of the von Neumann entropy under completely positive and trace preserving unital maps. Accordingly, for the dynamics of a single qubit as an open quantum system, the sign of the time-derivative of the density matrix eigenvalues of the system determines the non-Markovianity of unital quantum dynamical maps. The main characteristics of the measure is to make the corresponding calculations and optimization procedure simpler.
Beenken, Wichard; Maes, Wouter; Kruk, Mikalai; Martínez, Todd; Presselt, Martin
2015-07-01
Free-base corroles exist as individual NH-tautomers that may differ in their spectral and chemical properties. The present paper focuses on the origin of the basicity difference between two AB2-pyrimidinylcorrole NH-tautomers, which has been tentatively attributed to differences in the weak out-of-plane distortions of the pyrrolenic ring between two NH-tautomers. Using DFT-geometry optimizations, we show that the pyrroles involved in the NH-tautomerization process are approximately in-plane, whereas the other two pyrroles are tilted out-of-plane in opposite directions. Alternative out-of-plane distortion patterns play a minor role, as revealed by ab initio molecular dynamics simulations. Given that the protonated corrole is a unique species, the energy difference between the two NH-tautomers equals the difference in protonation driving force between them. This energy difference increases with improved theoretical level of accounting for intermolecular interactions and dielectric screening of surface charges. The different charge distributions of the two NH-tautomers result in electrostatic potential distributions that effect a larger proton attraction in the case of the T1 tautomer than in the case of the T2 tautomer. In summary, our quantum chemical results show clearly a higher basicity of the T1 tautomer as compared to the T2 tautomer: The previously assumed pronounced out-of-plane tilt of the T1-nonprotonated nitrogen is verified by ab initio molecular dynamics simulations. Together with analysis of the electrostatic potential distribution we show that the nonprotonated nitrogen is not only tilted stronger but also significantly more accessible for protons in the case of T1 as compared to T2. Additionally, the thermodynamic basicity is higher for T1 than for T2. PMID:26052732
Quantum Dynamical Semigroups involving Separable and Entangled States
Ajit Iqbal Singh
2015-04-22
Power symmetric matrices defned and studied by R. Sinkhorn (1981) and their generalization by R.B. Bapat, S.K. Jain and K. Manjunatha Prasad (1999) have been utilized to give positive block matrices with trace one possessing positive partial transpose, the so-called PPT states. Another method to construct such PPT states is given, it uses the form of a matrix unitarily equivalent to its transpose obtained by S.R. Garcia and J.E. Tener (2012). Evolvement or suppression of separability or entanglement of various levels for a quantum dynamical semigroup of completely positive maps has been studied using Choi-Jamiolkowsky matrix of such maps and the famous Horodecki's criteria (1996). A Trichotomy Theorem has been proved, and examples have been given that depend mainly on generalized Choi maps and clearly distinguish the levels of entanglement breaking.
Josephson bifurcation amplifier: Amplifying quantum signals using a dynamical bifurcation
NASA Astrophysics Data System (ADS)
Vijayaraghavan, Rajamani
Quantum measurements of solid-state systems, such as the readout of superconducting quantum bits challenge conventional low-noise amplification techniques. Ideally, the amplifier for a quantum measurement should minimally perturb the measured system while maintaining sufficient sensitivity to overcome the noise of subsequent elements in the amplification chain. Additionally, the drift of materials properties in solid-state systems mandates a fast acquisition rate to permit measurements in rapid succession. In this thesis, we describe the Josephson Bifurcation Amplifier (JBA) which was developed to meet these requirements. The JBA exploits the sensitivity of a dynamical system - a non-linear oscillator tuned near a bifurcation point. In this new scheme, all available degrees of freedom in the dynamical system participate in information transfer and none contribute to unnecessary dissipation resulting in excess noise. We have used a superconducting tunnel junction, also known as a Josephson junction to construct our non-linear oscillator. The Josephson junction is the only electronic circuit element which remains non-linear and non-dissipative at arbitrarily low temperatures. This thesis will describe the theory and experiments demonstrating bifurcation amplification in the JBA and its application to the measurement of superconducting quantum bits. By describing the JBA as a parametrically driven oscillator, we will demonstrate that the ultimate sensitivity of the JBA is limited only by quantum fluctuations. Using this treatment, we will identify the connection between the four main aspects of working with a dynamical bifurcation: parametric amplification, squeezing, quantum activation and the Dynamical Casimir Effect.
Ion, Bogdan F; Bushnell, Eric A C; Luna, Phil De; Gauld, James W
2012-01-01
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(?)=NH(2)+ 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(?)=NH(2)+ 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 ?-NH(2) 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
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
Liu, Jianbo; Miller, William H.; Fanourgakis, G. S.; Xantheas, Sotiris S.; Imoto, Sho; Saito, Shinji
2011-12-28
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.
Shkrob, I A; Larsen, R E; Schwartz, B J; Glover, William J.; Larsen, Ross E.; Schwartz, Benjamin J.; Shkrob, Ilya A.
2006-01-01
Adiabatic mixed quantum/classical molecular dynamics simulations were used to generate snapshots of the hydrated electron (e-) in liquid water at 300 K. Water cluster anions that include two complete solvation shells centered on the e- were extracted from these simulations and embedded in a matrix of fractional point charges designed to represent the rest of the solvent. Density functional theory and single-excitation configuration interaction methods were then applied to these embedded clusters. The salient feature of these hybrid calculations is significant transfer (ca. 0.18) of the excess electron's charge density into the O 2p orbitals in OH groups forming the solvation cavity. We used the results of these calculations to examine the structure of the molecular orbitals, the density of states, the absorption spectra in the visible and ultraviolet, the hyperfine coupling (hfc) tensors, and the IR and Raman spectra of the e-. The calculated hfc tensors were used to compute the EPR and ESEEM spectra for the ...
Can the ring polymer molecular dynamics method be interpreted as real time quantum dynamics?
Jang, Seogjoo, E-mail: sjang@qc.cuny.edu [Department of Chemistry and Biochemistry, Queens College and the Graduate Center, City University of New York, 65-30 Kissena Boulevard, Flushing, New York 11367 (United States)] [Department of Chemistry and Biochemistry, Queens College and the Graduate Center, City University of New York, 65-30 Kissena Boulevard, Flushing, New York 11367 (United States); Sinitskiy, Anton V.; Voth, Gregory A., E-mail: gavoth@uchicago.edu [Department of Chemistry, James Franck Institute, Institute for Biophysical Dynamics and Computation Institute, University of Chicago, 5735 S. Ellis Avenue, Chicago, Illinois 60637 (United States)
2014-04-21
The ring polymer molecular dynamics (RPMD) method has gained popularity in recent years as a simple approximation for calculating real time quantum correlation functions in condensed media. However, the extent to which RPMD captures real dynamical quantum effects and why it fails under certain situations have not been clearly understood. Addressing this issue has been difficult in the absence of a genuine justification for the RPMD algorithm starting from the quantum Liouville equation. To this end, a new and exact path integral formalism for the calculation of real time quantum correlation functions is presented in this work, which can serve as a rigorous foundation for the analysis of the RPMD method as well as providing an alternative derivation of the well established centroid molecular dynamics method. The new formalism utilizes the cyclic symmetry of the imaginary time path integral in the most general sense and enables the expression of Kubo-transformed quantum time correlation functions as that of physical observables pre-averaged over the imaginary time path. Upon filtering with a centroid constraint function, the formulation results in the centroid dynamics formalism. Upon filtering with the position representation of the imaginary time path integral, we obtain an exact quantum dynamics formalism involving the same variables as the RPMD method. The analysis of the RPMD approximation based on this approach clarifies that an explicit quantum dynamical justification does not exist for the use of the ring polymer harmonic potential term (imaginary time kinetic energy) as implemented in the RPMD method. It is analyzed why this can cause substantial errors in nonlinear correlation functions of harmonic oscillators. Such errors can be significant for general correlation functions of anharmonic systems. We also demonstrate that the short time accuracy of the exact path integral limit of RPMD is of lower order than those for finite discretization of path. The present quantum dynamics formulation also serves as the basis for developing new quantum dynamical methods that utilize the cyclic nature of the imaginary time path integral.
Batalhão, Tiago B; Souza, Alexandre M; Mazzola, Laura; Auccaise, Ruben; Sarthour, Roberto S; Oliveira, Ivan S; Goold, John; De Chiara, Gabriele; Paternostro, Mauro; Serra, Roberto M
2014-10-01
We report the experimental reconstruction of the nonequilibrium work probability distribution in a closed quantum system, and the study of the corresponding quantum fluctuation relations. The experiment uses a liquid-state nuclear magnetic resonance platform that offers full control on the preparation and dynamics of the system. Our endeavors enable the characterization of the out-of-equilibrium dynamics of a quantum spin from a finite-time thermodynamics viewpoint. PMID:25325627
Simulation of Complete Many-Body Quantum Dynamics Using Controlled Quantum-Semiclassical Hybrids
NASA Astrophysics Data System (ADS)
Deuar, P.
2009-09-01
A controlled hybridization between full quantum dynamics and semiclassical approaches (mean-field and truncated Wigner) is implemented for interacting many-boson systems. It is then demonstrated how simulating the resulting hybrid evolution equations allows one to obtain the full quantum dynamics for much longer times than is possible using an exact treatment directly. A collision of sodium BECs with 1.5×105atoms is simulated, in a regime that is difficult to describe semiclassically. The uncertainty of physical quantities depends on the statistics of the full quantum prediction. Cutoffs are minimized to a discretization of the Hamiltonian. The technique presented is quite general and extension to other systems is considered.
Structural dynamics verification facility study
NASA Technical Reports Server (NTRS)
Kiraly, L. J.; Hirchbein, M. S.; Mcaleese, J. M.; Fleming, D. P.
1981-01-01
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.
Truong, Thanh N.
-flux correlation function for calculating the thermal rate constants of chemical reactions in solution in this study would provide a complete tool for studying the quantum dynamics of chemical reactions the thermal chemical reaction rate constants. Furthermore, we also employ an efficient and accurate quantum
Quantum Dynamics, Minkowski-Hilbert space, and A Quantum Stochastic Duhamel Principle
Matthew F. Brown
2014-07-10
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.
Study of correlations in molecular motion by multiple quantum NMR
Tang, J.H.
1981-11-01
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.
Decoherence and quantum-classical master equation dynamics
Robbie Grunwald; Raymond Kapral
2007-01-01
The conditions under which quantum-classical Liouville dynamics may be reduced to a master equation are investigated. Systems that can be partitioned into a quantum-classical subsystem interacting with a classical bath are considered. Starting with an exact non-Markovian equation for the diagonal elements of the density matrix, an evolution equation for the subsystem density matrix is derived. One contribution to this
Decoherence and Quantum-Classical Master Equation Dynamics
Robbie Grunwald; Raymond Kapral
2006-01-01
The conditions under which quantum-classical Liouville dynamics may be\\u000areduced to a master equation are investigated. Systems that can be partitioned\\u000ainto a quantum-classical subsystem interacting with a classical bath are\\u000aconsidered. Starting with an exact non-Markovian equation for the diagonal\\u000aelements of the density matrix, an evolution equation for the subsystem density\\u000amatrix is derived. One contribution to this
On the quantum dynamics of the rigid rotor
NASA Astrophysics Data System (ADS)
Kowalski, K.; Rembieli?ski, J.; Zawadzki, J.
2015-01-01
The dynamics is investigated of a free particle on a sphere (rigid rotor or rotator) that is initially in a coherent state. The instability of coherent states with respect to the free evolution leads to nontrivial temporal development of averages of observables representing the position of a particle on a sphere that can be interpreted as quantum beats of the rotor. The beats are related to occuring quantum coherent state wave packet revivals on a sphere.
Quantum modeling of nonlinear dynamics of stock prices: Bohmian approach
NASA Astrophysics Data System (ADS)
Choustova, O.
2007-08-01
We use quantum mechanical methods to model the price dynamics in the financial market mathematically. We propose describing behavioral financial factors using the pilot-wave (Bohmian) model of quantum mechanics. The real price trajectories are determined (via the financial analogue of the second Newton law) by two financial potentials: the classical-like potential V (q) (“hard” market conditions) and the quantumlike potential U(q) (behavioral market conditions).
Quantized recurrence time in iterated open quantum dynamics
P. Sinkovicz; Z. Kurucz; T. Kiss; J. K. Asbóth
2014-11-03
The expected return time to the original state is a key concept characterizing systems obeying both classical or quantum dynamics. We consider iterated open quantum dynamical systems in finite dimensional Hilbert spaces, a broad class of systems that includes classical Markov chains and unitary discrete time quantum walks on networks. Starting from a pure state, the time evolution is induced by repeated applications of a general quantum channel, in each timestep followed by a measurement to detect whether the system has returned to the original state. We prove that if the superoperator is unital in the relevant Hilbert space (the part of the Hilbert space explored by the system), then the expectation value of the return time is an integer, equal to the dimension of this relevant Hilbert space. We illustrate our results on partially coherent quantum walks on finite graphs. Our work connects the previously known quantization of the expected return time for bistochastic Markov chains and for unitary quantum walks, and shows that these are special cases of a more general statement. The expected return time is thus a quantitative measure of the size of the part of the Hilbert space available to the system when the dynamics is started from a certain state.
Dynamical quantum noise in Bose-Einstein condensates
M. J. Steel; M. K. Olsen; L. I. Plimak; P. D. Drummond; S. M. Tan; M. J. Collett; D. F. Walls; R. Graham
1998-07-27
We introduce the study of dynamical quantum noise in Bose-Einstein condensates through numerical simulation of stochastic partial differential equations obtained using phase space representations. We derive evolution equations for a single trapped condensate in both the positive-$P$ and Wigner representations, and perform simulations to compare the predictions of the two methods. The positive-$P$ approach is found to be highly susceptible to the stability problems that have been observed in other strongly nonlinear, weakly damped systems. Using the Wigner representation, we examine the evolution of several quantities of interest using from a variety of choices of initial state for the condensate, and compare results to those for single-mode models.
Optimal approach to quantum communication using dynamic programming.
Jiang, Liang; Taylor, Jacob M; Khaneja, Navin; Lukin, Mikhail D
2007-10-30
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
Optimal approach to quantum communication using dynamic programming
Jiang, Liang; Khaneja, Navin; Lukin, Mikhail D
2007-01-01
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.
Optimal approach to quantum communication using dynamic programming
Liang Jiang; Jacob M. Taylor; Navin Khaneja; Mikhail D. Lukin
2007-10-31
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.
Long-Distance Quantum Transport Dynamics in Macromolecules
E. Schneider; P. Faccioli
2014-03-20
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 purpose, we apply this method to investigate intelastic electornic hole transport in a long homo-DNA chain.
Efficient measurement of quantum dynamics via compressive sensing.
Shabani, A; Kosut, R L; Mohseni, M; Rabitz, H; Broome, M A; Almeida, M P; Fedrizzi, A; White, A G
2011-03-11
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
Dynamics of a driven quantum gas: Non-hermiticity, pseudo-spectra and phase transitions
NASA Astrophysics Data System (ADS)
Makris, Konstantinos; Kulkarni, Manas; Tureci, Hakan
2015-03-01
System of an optically driven quantum gas coupled to a single mode of a leaky cavity offers a unique platform to study open quantum systems. This system displays two exceptional points and a quantum critical point when the drive strength (equivalently, the light-matter coupling) is tuned. Here, we study the non-normal properties of this system especially near these special points. Adapting the rich mathematics behind the theory of pseudo-spectra, we characterize the open quantum phase transitions in this system by studying the fluctuations. Our method offers a novel way to understand physics near criticality beyond the traditional approach of arriving at a phase diagram using the semi-classical solutions arising from a mean field approach. We further show that the quench dynamics of a driven dissipative quantum gas displays a non-Markovian dynamics featuring substantial transient amplification of the photon flux near the critical point. We also investigate the non-Hermitian physics behind two-operator products thereby shining light on higher order quantum correlations in an open quantum system.
How virtual particles generate quantum dynamics
Alberto C. de la Torre
2015-06-07
In support of the quantum field theory interpretation of quantum mechanics it is shown that two types of virtual particles $A$ and $B$ with an asymmetric interaction such that $A$ rejects (hates) $B$ and $B$ attracts (loves) $A$ have a combined distribution that satisfies Schr\\"odinger's equation. It is also shown how four virtual particles drifting, creating and destroying themselves have a combined distribution that satisfies Dirac's equation.
Quantum dynamics and state-dependent affine gauge fields on CP(N-1)
Peter Leifer
2008-04-11
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.
Noise-resilient quantum evolution steered by dynamical decoupling
Liu, Gang-Qin; Po, Hoi Chun; Du, Jiangfeng; Liu, Ren-Bao; Pan, Xin-Yu
2013-01-01
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
Optimal dynamics for quantum-state and entanglement transfer through homogeneous quantum systems
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
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.
da Silva, Robson; Hoff, Diego A; Rego, Luis G C
2015-04-10
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
NASA Astrophysics Data System (ADS)
da Silva, Robson; Hoff, Diego A.; Rego, Luis G. C.
2015-04-01
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.
Superadiabatic transition histories in quantum molecular dynamics
Volker Betz; Benjamin D. Goddard; Stefan Teufel
2009-02-03
We study the dynamics of a molecule's nuclear wave-function near an avoided crossing of two electronic energy levels, for one nuclear degree of freedom. We derive the general form of the Schroedinger equation in the n-th superadiabatic representation for all n, and give some partial results about the asymptotics for large n. Using these results, we obtain closed formulas for the time development of the component of the wave function in an initially unoccupied energy subspace, when a wave packet crosses the transition region. In the optimal superadiabatic representation, which we define, this component builds up monontonically. Finally, we give an explicit formula for the transition wave function away from the crossing, which is in excellent agreement with high precision numerical calculations.
Dokainish, Hisham M; Gauld, James W
2013-03-12
The catalytic mechanism of MsrA in Mycobacterium tuberculosis, in which S-methionine sulfoxide (Met-O) is reduced to methionine (Met), has been investigated using docking, molecular dynamics (MD) simulations, and ONIOM (quantum mechanics/molecular mechanics) methods. In addition, the roles of specific active site residues, including an aspartyl (Asp87) near the recycling cysteine, tyrosyls (Tyr44 and Tyr92), and glutamyl (Glu52), have been examined, as well as the general effects of the protein and active site on the nature and properties of mechanistic intermediates. The mechanism is initiated by the transfer of a proton from the catalytic cysteine's thiol (Cys13SH) via a bridging water to the R group carboxylate of Glu52. The now anionic sulfur of Cys13 nucleophilically attacks the substrate's sulfur with concomitant transfer of a proton from Glu52 to the sulfoxide oxygen, generating a sulfurane. The active site enhances the proton affinity of the sulfurane oxygen, which can readily accept a proton from the phenolic hydroxyls of Tyr44 or Tyr92 to give a sulfonium cation. Subsequently, Asp87 and the recycling cysteine (Cys154) can facilitate nucleophilic attack of a solvent water at the Cys13S center of the sulfonium to give a sulfenic acid (Cys13SOH) and Met. For the subsequent reduction of Cys13SOH with intramolecular disulfide bond formation, Asp87 can help facilitate nucleophilic attack of Cys154S at the sulfur of Cys13SOH by deprotonating its thiol. This reduction is found likely to occur readily upon suitable positioning of the active site hydrogen bond network and the sulfur centers of both Cys13 and Cys154. The calculated rate-limiting barrier is in good agreement with experiment. PMID:23418817
Quantum correlation dynamics in photosynthetic processes assisted by molecular vibrations
G. L. Giorgi; M. Roncaglia; F. A. Raffa; M. Genovese
2015-01-30
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.
Dynamic Stabilization of a Quantum Many-Body Spin System
NASA Astrophysics Data System (ADS)
Hoang, T. M.; Gerving, C. S.; Land, B. J.; Anquez, M.; Hamley, C. D.; Chapman, M. S.
2013-08-01
We demonstrate dynamic stabilization of a strongly interacting quantum spin system realized in a spin-1 atomic Bose-Einstein condensate. The spinor Bose-Einstein condensate is initialized to an unstable fixed point of the spin-nematic phase space, where subsequent free evolution gives rise to squeezing and quantum spin mixing. To stabilize the system, periodic microwave pulses are applied that rotate the spin-nematic many-body fluctuations and limit their growth. The stability diagram for the range of pulse periods and phase shifts that stabilize the dynamics is measured and compares well with a stability analysis.
Quantum diffusion dynamics in nonlinear systems: A modified kicked-rotor model
Gong Jiangbin [Department of Physics and Centre of Computational Science and Engineering, National University of Singapore, 117542 (Singapore); Wang Jiao [Temasek Laboratories and Beijing-Hong Kong-Singapore Joint Center for Nonlinear and Complex Systems (Singapore), National University of Singapore, 117542 (Singapore)
2007-09-15
Using a simple method analogous to a quantum rephasing technique, a simple modification to a paradigm of classical and quantum chaos is proposed. The interesting quantum maps thus obtained display remarkably rich quantum dynamics. Emphasis is placed on the destruction of dynamical localization without breaking periodicity, unbounded quantum anomalous diffusion in integrable systems, and transient dynamical localization. Experimental realizations of this work are also discussed.
Lu, Dawei; Xu, Nanyang; Xu, Boruo; Li, Zhaokai; Chen, Hongwei; Peng, Xinhua; Xu, Ruixue; Du, Jiangfeng
2012-10-13
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
Controlling the quantum dynamics of a mesoscopic spin bath in diamond
NASA Astrophysics Data System (ADS)
de Lange, Gijs; van der Sar, Toeno; Blok, Machiel; Wang, Zhi-Hui; Dobrovitski, Viatcheslav; Hanson, Ronald
2012-04-01
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.
Kim, Nam-Chol; Ko, Myong-Chol; So, Guang Hyok; Kim, Il-Guang
2015-01-01
We studied theoretically the population dynamics and the absorption spectrum of hybrid nanosystem consisted of a matal nanoparticle (MNP) and a semiconductor quantum dot(SQD). We investigated the exciton-plasmon coupling effects on the population dynamics and the absorption properties of the nanostructure. Our results show that the nonlinear optical response of the hybrid nanosystem can be greatly enhanced or depressed due to the exciton-plasmon couplings. The results obtained here may have the potential applications of nanoscale optical devices such as optical switches and quantum devices such as a single photon transistor.
Dynamically self-regular quantum harmonic black holes
NASA Astrophysics Data System (ADS)
Spallucci, Euro; Smailagic, Anais
2015-04-01
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.
NASA Astrophysics Data System (ADS)
Sumner, Isaiah; Iyengar, Srinivasan S.
2008-08-01
We discuss hybrid quantum-mechanics/molecular-mechanics (QM/MM) and quantum mechanics/quantum mechanics (QM/QM) generalizations to our recently developed quantum wavepacket ab initio molecular dynamics methodology for simultaneous dynamics of electrons and nuclei. The approach is a synergy between a quantum wavepacket dynamics, ab initio molecular dynamics, and the ONIOM scheme. We utilize this method to include nuclear quantum effects arising from a portion of the system along with a simultaneous description of the electronic structure. The generalizations provided here make the approach a potentially viable alternative for large systems. The quantum wavepacket dynamics is performed on a grid using a banded, sparse, and Toeplitz representation of the discrete free propagator, known as the ``distributed approximating functional.'' Grid-based potential surfaces for wavepacket dynamics are constructed using an empirical valence bond generalization of ONIOM and further computational gains are achieved through the use of our recently introduced time-dependent deterministic sampling technique. The ab initio molecular dynamics is achieved using Born-Oppenheimer dynamics. All components of the methodology, namely, quantum dynamics and ONIOM molecular dynamics, are harnessed together using a time-dependent Hartree-like procedure. We benchmark the approach through the study of structural and vibrational properties of molecular, hydrogen bonded clusters inclusive of electronic, dynamical, temperature, and critical quantum nuclear effects. The vibrational properties are constructed through a velocity/flux correlation function formalism introduced by us in an earlier publication.
Teki, Yoshio; Matsumoto, Takafumi
2011-04-01
The mechanism of the unique dynamic electron polarization of the quartet (S = 3/2) high-spin state via a doublet-quartet quantum-mixed state and detail theoretical calculations of the population transfer are reported. By the photo-induced electron transfer, the quantum-mixed charge-separate state is generated in acceptor-donor-radical triad (A-D-R). This mechanism explains well the unique dynamic electron polarization of the quartet state of A-D-R. The generation of the selectively populated quantum-mixed state and its transfer to the strongly coupled pure quartet and doublet states have been treated both by a perturbation approach and by exact numerical calculations. The analytical solutions show that generation of the quantum-mixed states with the selective populations after de-coherence and/or accompanying the (complete) dephasing during the charge-recombination are essential for the unique dynamic electron polarization. Thus, the elimination of the quantum coherence (loss of the quantum information) is the key process for the population transfer from the quantum-mixed state to the quartet state. The generation of high-field polarization on the strongly coupled quartet state by the charge-recombination process can be explained by a polarization transfer from the quantum-mixed charge-separate state. Typical time-resolved ESR patterns of the quantum-mixed state and of the strongly coupled quartet state are simulated based on the generation mechanism of the dynamic electron polarization. The dependence of the spectral pattern of the quartet high-spin state has been clarified for the fine-structure tensor and the exchange interaction of the quantum-mixed state. The spectral pattern of the quartet state is not sensitive towards the fine-structure tensor of the quantum-mixed state, because this tensor contributes only as a perturbation in the population transfer to the spin-sublevels of the quartet state. Based on the stochastic Liouville equation, it is also discussed why the selective population in the quantum-mixed state is generated for the "finite field" spin-sublevels. The numerical calculations of the elimination of the quantum coherence (de-coherence and/or dephasing) are demonstrated. A new possibility of the enhanced intersystem crossing pathway in solution is also proposed. PMID:21321715
Optimized dynamical decoupling in a model quantum memory.
Biercuk, Michael J; Uys, Hermann; VanDevender, Aaron P; Shiga, Nobuyasu; Itano, Wayne M; Bollinger, John J
2009-04-23
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
Quantum dissipation and neural net dynamics
Eliano Pessa; Giuseppe Vitiello
1999-12-14
Inspired by the dissipative quantum model of brain, we model the states of neural nets in terms of collective modes by the help of the formalism of Quantum Field Theory. We exhibit an explicit neural net model which allows to memorize a sequence of several informations without reciprocal destructive interference, namely we solve the overprinting problem in such a way last registered information does not destroy the ones previously registered. Moreover, the net is able to recall not only the last registered information in the sequence, but also anyone of those previously registered.
NASA Astrophysics Data System (ADS)
Vagov, A.; Croitoru, M. D.; Glässl, M.; Axt, V. M.; Kuhn, T.
2011-03-01
Based on a representation of the functional integral as the time evolution of the augmented density matrix we have worked out an implementation of the real-time path integral approach that is applicable to the dynamics of quantum dissipative systems with superohmic coupling to the environment. As a prototype for such a system we consider a laser-driven strongly confined semiconductor quantum dot coupled to acoustic phonons. First applications of this approach to quantum dot systems have already been published. Here, we provide a detailed description of the implementation, including a discussion of numerical issues and extend the formalism from two-level quantum dot models with a pure-dephasing type carrier-phonon coupling to the case of multiple electronic levels. The method allows for numerically exact calculations of the dot dynamics at strong dot-phonon and dot-laser coupling and at long times, usually inaccessible by other approaches.
Proton transfer in solution: Molecular dynamics with quantum transitions
NASA Astrophysics Data System (ADS)
Hammes-Schiffer, Sharon; Tully, John C.
1994-09-01
We apply ``molecular dynamics with quantum transitions'' (MDQT), a surface-hopping method previously used only for electronic transitions, to proton transfer in solution, where the quantum particle is an atom. We use full classical mechanical molecular dynamics for the heavy atom degrees of freedom, including the solvent molecules, and treat the hydrogen motion quantum mechanically. We identify new obstacles that arise in this application of MDQT and present methods for overcoming them. We implement these new methods to demonstrate that application of MDQT to proton transfer in solution is computationally feasible and appears capable of accurately incorporating quantum mechanical phenomena such as tunneling and isotope effects. As an initial application of the method, we employ a model used previously by Azzouz and Borgis to represent the proton transfer reaction AH-B?A--H+B in liquid methyl chloride, where the AH-B complex corresponds to a typical phenol-amine complex. We have chosen this model, in part, because it exhibits both adiabatic and diabatic behavior, thereby offering a stringent test of the theory. MDQT proves capable of treating both limits, as well as the intermediate regime. Up to four quantum states were included in this simulation, and the method can easily be extended to include additional excited states, so it can be applied to a wide range of processes, such as photoassisted tunneling. In addition, this method is not perturbative, so trajectories can be continued after the barrier is crossed to follow the subsequent dynamics.
Non-Markovian dynamics without using a quantum trajectory
Wu Chengjun; Li Yang; Zhu Mingyi; Guo Hong [CREAM Group, State Key Laboratory of Advanced Optical Communication Systems and Networks, Peking University, School of Electronics Engineering and Computer Science, Peking University, Beijing 100871 (China)
2011-05-15
Open quantum systems interacting with structured environments is important and manifests non-Markovian behavior, which was conventionally studied using a quantum trajectory stochastic method. In this paper, by dividing the effects of the environment into two parts, we propose a deterministic method without using a quantum trajectory. This method is more efficient and accurate than the stochastic method in most Markovian and non-Markovian cases. We also extend this method to the generalized Lindblad master equation.
Non-Markovian dynamics without using quantum trajectory
Chengjun Wu; Yang Li; Mingyi Zhu; Hong Guo
2011-01-23
Open quantum system interacting with structured environment is important and manifests non- Markovian behavior, which was conventionally studied using quantum trajectory stochastic method. In this paper, by dividing the effects of the environment into two parts, we propose a deterministic method without using quantum trajectory. This method is more efficient and accurate than stochastic method in most Markovian and non-Markovian cases. We also extend this method to the generalized Lindblad master equation.
Quantum-like dynamics of decision-making
NASA Astrophysics Data System (ADS)
Asano, Masanari; Basieva, Irina; Khrennikov, Andrei; Ohya, Masanori; Tanaka, Yoshiharu
2012-03-01
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.
Entropy for Quantum Pure States and Its Dynamical Relaxation
Xizhi Han; Biao Wu
2015-03-09
We construct a complete set of Wannier functions which are localized at both given positions and momenta. This allows us to introduce the quantum phase space, onto which a quantum pure state can be mapped unitarily. Using its probability distribution in quantum phase space, we define an entropy for a quantum pure state. We prove an inequality regarding the long time behavior of our entropy's fluctuation. For a typical initial state, this inequality indicates that our entropy can relax dynamically to a maximized value and stay there most of time with small fluctuations. This result echoes the quantum H-theorem proved by von Neumann in [Zeitschrift f\\"ur Physik {\\bf 57}, 30 (1929)]. Our entropy is different from the standard von Neumann entropy, which is always zero for quantum pure states. According to our definition, a system always has bigger entropy than its subsystem even when the system is described by a pure state. As the construction of the Wannier basis can be implemented numerically, the dynamical evolution of our entropy is illustrated with an example.
Christopher G. Jesudason
2009-01-01
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
William D. Mattson; Radhakrishnan Balu; Betsy M. Rice; Jennifer A. Ciezak
We present a combined experimental and theoretical study on carbon nanodiamonds using Raman and DAC experimentation and ab initio calculations. Our calculations confirm the surface reconstruction to a fullerene-like structure, and indicate compression of the diamond core, producing an estimated internal pressure of 50 GPa. Quantum molecular dynamics simulations of hypervelocity collisions of NDs show that upon collision shock-induced amorphization
Hot-electron relaxation dynamics in quantum wires
V. Mitin; Michael A. Stroscio; Gerald J. Iafrate; H. L. Grubin
1994-01-01
Monte Carlo simulations of hot nonequilibrium electron relaxation in rectangular GaAs quantum wires of different cross sections are carried out. The simulations demonstrate that the initial stage of hot-electron cooling dynamics is determined by cascade emission of optical phonons and exhibits strong dependence on the excitation energy. The second (slow) relaxation stage is controlled by strongly inelastic electron interactions with
Hot-electron relaxation dynamics in quantum wires
R. Gaska; R. Mickevicius; V. Mitin; M. A. Stroscio; G. J. Iafrate; H. L. Grubin
1994-01-01
Monte Carlo simulations of hot nonequilibrium electron relaxation in rectangualr GaAs quantum wires of different cross sections are carried out. The simulations demonstrate that the initial stage of hot-electron cooling dynamics is determined by cascade emission of optical phonons and exhibits strong dependence on the excitation energy. The second (slow) relaxation stage is controlled by strongly inelastic electron interactions with
Theoretical method for analyzing quantum dynamics of correlated photons
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
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.
Functional treatment of quantum scattering via the dynamical principle
Edouard Berg Manoukian; Seckson Sukkhasena
2007-09-27
A careful functional treatment of quantum scattering is given using Schwinger's dynamical principle which involves a functional differentiation operation applied to a generating functional written in closed form. For long range interactions, such as for the Coulomb one, it is shown that this expression may be used to obtain explicitly the asymptotic "free" modified Green function near the energy shell.
Simulation of quantum dynamical processes in condensed phase
Zvi Kotler
1989-01-01
The aim was to develop an approximation system to enable quantum and classical mechanics to be applied to systems of many degrees of freedom. The usually appropriate Time Dependent Self Consistent Field (TDSCF) approximation is shown to be inappropriate for dynamical processes involving a few electronic potential surfaces; a Multi-Configuration TDSCF (MCTDSCF) formalism, suitable for such cases, was developed, tested,
Quantum dynamics of chemical reactions by converged algebraic variational calculations
Donald G. Truhlar; David W. Schwenke; Donald J. Kouri
1990-01-01
This paper describes recent progress in using algebraic variational methods and LÂ² basis sets for converged quantum mechanical calculations of chemical reaction dynamics of the H + Hâ, O + Hâ, H + HBr, and F + Hâ reactions and the isotopically substituted reactions D + Hâ and O + HD and some of the reverse reactions. The paper emphasizes
Quantum Potential and Random Phase-Space Dynamics
Piotr Garbaczewski
We analyze limitations upon any kinetic theory inspired derivation of a probabilistic coun- terpart of the Schrodinger picture quantum dynamics. Neither dissipative nor non-dissipative stochastic phase-space processes based on the white-noise (Brownian motion) kinetics are valid candidates unless additional constraints (a suitable form of the energy conservation law) are prop- erly incorporated in the formalism.
Quantum potential and random phase-space dynamics
Radoslaw Czopnik; Piotr Garbaczewski
2002-01-01
We analyze limitations upon any kinetic theory inspired derivation of a probabilistic counterpart of the Schrödinger picture quantum dynamics. Neither dissipative nor non-dissipative stochastic phase space processes based on the white-noise (Brownian motion) kinetics are valid candidates unless additional constraints (a suitable form of the energy conservation law) are properly incorporated in the formalism.
Quantum potential and random phase-space dynamics
NASA Astrophysics Data System (ADS)
Czopnik, Rados?aw; Garbaczewski, Piotr
2002-07-01
We analyze limitations upon any kinetic theory inspired derivation of a probabilistic counterpart of the Schrödinger picture quantum dynamics. Neither dissipative nor non-dissipative stochastic phase space processes based on the white-noise (Brownian motion) kinetics are valid candidates unless additional constraints (a suitable form of the energy conservation law) are properly incorporated in the formalism.
Quantum molecular dynamics and particle production in heavy ion collisions
S. W. Huang; A. Faessler; G. Q. Li; D. T. Khoa; E. Lehmann; M. A. Matin; N. Ohtsuka; R. K. Puri
1993-01-01
The production of photons, kaons, antikaons and antiprotons in heavy-ion collisions is calculated in the framework of ``quantum'' molecular dynamics (QMD). The Skyrme potentials, with parameters chosen to generate the soft and hard nuclear equations of state(EOS), are used in the propagation of nucleons within QMD. The sensitivity of the production of each type of particle to the EOS is
Nonadiabatic quantum state engineering driven by fast quench dynamics
NASA Astrophysics Data System (ADS)
Herrera, Marcela; Sarandy, Marcelo S.; Duzzioni, Eduardo I.; Serra, Roberto M.
2014-02-01
There are a number of tasks in quantum information science that exploit nontransitional adiabatic dynamics. Such a dynamics is bounded by the adiabatic theorem, which naturally imposes a speed limit in the evolution of quantum systems. Here, we investigate an approach for quantum state engineering exploiting a shortcut to the adiabatic evolution, which is based on rapid quenches in a continuous-time Hamiltonian evolution. In particular, this procedure is able to provide state preparation faster than the adiabatic brachistochrone. Remarkably, the evolution time in this approach is shown to be ultimately limited by its "thermodynamical cost," provided in terms of the average work rate (average power) of the quench process. We illustrate this result in a scenario that can be experimentally implemented in a nuclear magnetic resonance setup.
Open quantum system stochastic dynamics with and without the RWA
NASA Astrophysics Data System (ADS)
Band, Y. B.
2015-02-01
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.
Dynamic Charge Carrier Trapping in Quantum Dot Field Effect Transistors.
Zhang, Yingjie; Chen, Qian; Alivisatos, A Paul; Salmeron, Miquel
2015-07-01
Noncrystalline semiconductor materials often exhibit hysteresis in charge transport measurements whose mechanism is largely unknown. Here we study the dynamics of charge injection and transport in PbS quantum dot (QD) monolayers in a field effect transistor (FET). Using Kelvin probe force microscopy, we measured the temporal response of the QDs as the channel material in a FET following step function changes of gate bias. The measurements reveal an exponential decay of mobile carrier density with time constants of 3-5 s for holes and ?10 s for electrons. An Ohmic behavior, with uniform carrier density, was observed along the channel during the injection and transport processes. These slow, uniform carrier trapping processes are reversible, with time constants that depend critically on the gas environment. We propose that the underlying mechanism is some reversible electrochemical process involving dissociation and diffusion of water and/or oxygen related species. These trapping processes are dynamically activated by the injected charges, in contrast with static electronic traps whose presence is independent of the charge state. Understanding and controlling these processes is important for improving the performance of electronic, optoelectronic, and memory devices based on disordered semiconductors. PMID:26099508
Dynamics of quantum tomography in an open system
NASA Astrophysics Data System (ADS)
Uchiyama, Chikako
2015-06-01
In this study, we provide a way to describe the dynamics of quantum tomography in an open system with a generalized master equation, considering a case where the relevant system under tomographic measurement is influenced by the environment. We apply this to spin tomography because such situations typically occur in ?SR (muon spin rotation/relaxation/resonance) experiments where microscopic features of the material are investigated by injecting muons as probes. As a typical example to describe the interaction between muons and a sample material, we use a spin-boson model where the relevant spin interacts with a bosonic environment. We describe the dynamics of a spin tomogram using a time-convolutionless type of generalized master equation that enables us to describe short time scales and/or low-temperature regions. Through numerical evaluation for the case of Ohmic spectral density with an exponential cutoff, a clear interdependency is found between the time evolution of elements of the density operator and a spin tomogram. The formulation in this paper may provide important fundamental information for the analysis of results from, for example, ?SR experiments on short time scales and/or in low-temperature regions using spin tomography.
Torsion as a dynamic degree of freedom of quantum gravity
Sang-Woo Kim; D. G. Pak
2008-03-05
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.
Quantum Yang-Mills-Weyl Dynamics in the Schrödinger paradigm
NASA Astrophysics Data System (ADS)
Dynin, A.
2014-04-01
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.
Quantum Communication through Spin Chain Dynamics: an Introductory Overview
Bose, Sougato
2008-01-01
We present an introductory overview of the use of spin chains as quantum wires, which has recently developed into a topic of lively interest. The principal motivation is in connecting quantum registers without resorting to optics. A spin chain is a permanently coupled 1D system of spins. When one places a quantum state on one end of it, the state will be dynamically transmitted to the other end with some efficiency if the spins are coupled by an exchange interaction. No external modulations or measurements on the body of the chain, except perhaps at the very ends, is required for this purpose. For the simplest (uniformly coupled) chain and the simplest encoding (single qubit encoding), however, dispersion reduces the quality of transfer. We present a variety of alternatives proposed by various groups to achieve perfect quantum state transfer through spin chains. We conclude with a brief discussion of the various directions in which the topic is developing.
Quantum Communication through Spin Chain Dynamics: an Introductory Overview
Sougato Bose
2008-02-08
We present an introductory overview of the use of spin chains as quantum wires, which has recently developed into a topic of lively interest. The principal motivation is in connecting quantum registers without resorting to optics. A spin chain is a permanently coupled 1D system of spins. When one places a quantum state on one end of it, the state will be dynamically transmitted to the other end with some efficiency if the spins are coupled by an exchange interaction. No external modulations or measurements on the body of the chain, except perhaps at the very ends, is required for this purpose. For the simplest (uniformly coupled) chain and the simplest encoding (single qubit encoding), however, dispersion reduces the quality of transfer. We present a variety of alternatives proposed by various groups to achieve perfect quantum state transfer through spin chains. We conclude with a brief discussion of the various directions in which the topic is developing.
Simulation of Quantum Dynamics Based on the Quantum Stochastic Differential Equation
2013-01-01
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
Adiabatic tracking of quantum many-body dynamics
Hamed Saberi; Tomáš Opatrný; Klaus Mølmer; Adolfo del Campo
2014-12-05
The nonadiabatic dynamics of a many-body system driven through a quantum critical point can be controlled using counterdiabatic driving, where the formation of excitations is suppressed by assisting the dynamics with auxiliary multiple-body nonlocal interactions. We propose an alternative scheme which circumvents practical challenges to realize shortcuts to adiabaticity in mesoscopic systems by tailoring the functional form of the auxiliary counterdiabatic interactions. A driving scheme resorting in few-body short-range interactions is shown to generate an effectively adiabatic dynamics.
Operational dynamic modeling transcending quantum and classical mechanics.
Bondar, Denys I; Cabrera, Renan; Lompay, Robert R; Ivanov, Misha Yu; Rabitz, Herschel A
2012-11-01
We introduce a general and systematic theoretical framework for operational dynamic modeling (ODM) by combining a kinematic description of a model with the evolution of the dynamical average values. The kinematics includes the algebra of the observables and their defined averages. The evolution of the average values is drawn in the form of Ehrenfest-like theorems. We show that ODM is capable of encompassing wide-ranging dynamics from classical non-relativistic mechanics to quantum field theory. The generality of ODM should provide a basis for formulating novel theories. PMID:23215365
Operational Dynamic Modeling Transcending Quantum and Classical Mechanics
NASA Astrophysics Data System (ADS)
Bondar, Denys I.; Cabrera, Renan; Lompay, Robert R.; Ivanov, Misha Yu.; Rabitz, Herschel A.
2012-11-01
We introduce a general and systematic theoretical framework for operational dynamic modeling (ODM) by combining a kinematic description of a model with the evolution of the dynamical average values. The kinematics includes the algebra of the observables and their defined averages. The evolution of the average values is drawn in the form of Ehrenfest-like theorems. We show that ODM is capable of encompassing wide-ranging dynamics from classical non-relativistic mechanics to quantum field theory. The generality of ODM should provide a basis for formulating novel theories.
Self-Sustaining Dynamical Nuclear Polarization Oscillations in Quantum Dots
NASA Astrophysics Data System (ADS)
Rudner, M. S.; Levitov, L. S.
2013-02-01
Early experiments on spin-blockaded double quantum dots revealed robust, large-amplitude current oscillations in the presence of a static (dc) source-drain bias. Despite experimental evidence implicating dynamical nuclear polarization, the mechanism has remained a mystery. Here we introduce a minimal albeit realistic model of coupled electron and nuclear spin dynamics which supports self-sustained oscillations. Our mechanism relies on a nuclear spin analog of the tunneling magnetoresistance phenomenon (spin-dependent tunneling rates in the presence of an inhomogeneous Overhauser field) and nuclear spin diffusion, which governs dynamics of the spatial profile of nuclear polarization. The proposed framework naturally explains the differences in phenomenology between vertical and lateral quantum dot structures as well as the extremely long oscillation periods.
Quantum vortex dynamics in two-dimensional neutral superfluids
NASA Astrophysics Data System (ADS)
Wang, C.-C. Joseph; Duine, R. A.; MacDonald, A. H.
2010-01-01
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 ?. 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.
NASA Astrophysics Data System (ADS)
Sumner, Isaiah
A methodology, Quantum Wavepacket Ab Initio Molecular Dynamics (QWAIMD), for the efficient, simultaneous dynamics of electrons and nuclei is presented. This approach allows for the quantum-dynamical treatment of a subset of nuclei in complex, molecular systems while treating the remaining nuclei and electrons within in the ab initio molecular dynamics (AIMD) paradigm. Developments of QWAIMD discussed within include: (a) a novel sampling algorithm dubbed Time-Dependent Deterministic Sampling (TDDS), which increases the computational efficiency by several orders of magnitude; (b) generalizations to hybrid QM/QM and QM/MM electronic structure methods via a combination of the ONIOM and empirical valence bond approaches, which may allow for the accurate simulation of large molecules; and (c) a novel velocity-flux autocorrelation function to calculate the vibrational density-of-states of quantum-classical systems. These techniques are benchmarked on calculations of small, hydrogen-bound clusters. Furthermore, since many chemical processes occur over time-scales inaccessible to computation, a scheme is discussed and benchmarked here which can bias both QWAIMD and classical-AIMD dynamics to sample these long time-scale events, like proton transfer in enzyme catalysis. Finally, hydrogen tunneling in an enzyme, soybean lipoxygenase-1 (SLO-1) is examined by calculating the orbitals (eigenstates) of the transferring proton along the reaction coordinate. This orbital analysis is then supplemented by using quantum measurement theory to reexamine the transfer.
NASA Astrophysics Data System (ADS)
Yang, Xu-qiu; Zhai, Peng-cheng; Liu, Li-sheng; Chen, Gang; Zhang, Qing-jie
2014-06-01
Molecular dynamics simulations have been performed to investigate the effect of nanometer-size pores on the phonon conductivity of single-crystal bulk CoSb3. The cylindrical pores are uniformly distributed along two vertical principal crystallographic directions of a square lattice. Because pore diameter and porosity are two key factors that could affect the performance of the materials, they were varied individually in the ranges a 0-6 a 0 and 0.1-5%, respectively, where a 0 is the lattice constant of CoSb3. The simulation results indicate that the phonon conductivity of nanoporous CoSb3 is significantly lower than that of no-pore CoSb3. The reduction of phonon conductivity in this simulation was consistent with the ballistic-diffusive microscopic effective medium model, demonstrating the ballistic character of phonon transport when the phonon mean-free-path is comparable with or larger than the pore size. Reducing pore diameter or increasing porosity are alternative means of effective reduction of the thermal conductivity of CoSb3. These results are expected to provide a useful basis for the design of high-performance skutterudites.
Nonperturbative quantum dynamics of a new inflation model
Boyanovsky, D. [Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, Pennsylvania 15260 (United States)] [Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, Pennsylvania 15260 (United States); Cormier, D.; Holman, R.; Kumar, S.P. [Department of Physics, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213 (United States)] [Department of Physics, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213 (United States); de Vega, H.J. [LPTHE, Universite Pierre et Marie Curie (Paris VI) et Denis Diderot (Paris VII), Tour 16, 1er. etage, 4, Place Jussieu75252Paris, Cedex 05 (France)] [LPTHE, Universite Pierre et Marie Curie (Paris VI) et Denis Diderot (Paris VII), Tour 16, 1er. etage, 4, Place Jussieu75252Paris, Cedex 05 (France)
1998-02-01
We consider an O(N) model coupled self-consistently to gravity in the semiclassical approximation, where the field is subject to {open_quotes}new inflation{close_quotes} type initial conditions. We study the dynamics self-consistently and non-perturbatively with non-equilibrium field theory methods in the large N limit. We find that spinodal instabilities drive the growth of non-perturbatively large quantum fluctuations which shut off the inflationary growth of the scale factor. We find that a very specific combination of these large fluctuations plus the inflaton zero mode assemble into a new effective field. This new field behaves classically and it is the object which actually rolls down. We show how this reinterpretation saves the standard picture of how metric perturbations are generated during inflation and that the spinodal growth of fluctuations dominates the time dependence of the Bardeen variable for superhorizon modes during inflation. We compute the amplitude and index for the spectrum of scalar density and tensor perturbations and argue that in all models of this type the spinodal instabilities are responsible for a {open_quotes}red{close_quotes} spectrum of primordial scalar density perturbations. A criterion for the validity of these models is provided and contact with the reconstruction program is established validating some of the results within a non-perturbative framework. The decoherence aspects and the quantum to classical transition through inflation are studied in detail by following the full evolution of the density matrix and relating the classicality of cosmological perturbations to that of long-wavelength matter fluctuations. {copyright} {ital 1998} {ital The American Physical Society}
Dynamical decoupling based quantum sensing: Floquet spectroscopy
J. E. Lang; Ren-Bao Liu; T. S. Monteiro
2015-03-26
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 than the frequencies of either the static problem or of average Hamiltonian models. This approach is fully general for any temporally periodic protocol and sensor, but is here tested on NV centres and systems for which the quantization axis varies as a function of applied magnetic field; for instance, electron donors in silicon, such as arsenic and bismuth, exhibit regimes of high sensitivity of decoherence with respect to magnetic fields, so represent promising potential sensors.
Dynamical quantum filtering in hydrogen surface reactions
NASA Astrophysics Data System (ADS)
Diño, Wilson Agerico; Kasai, Hideaki; Okiji, Ayao
1998-11-01
We report on how surfaces that adsorb hydrogen could act as rotational quantum state filters and cause, for example, D 2 molecules desorbing in the vibrational ground state from Cu(111) to exhibit strong rotational alignment. For low final translational energies, we found that desorbing D 2 molecules have rotational alignment factor values corresponding to cartwheel-type rotational preference. As the final translational energy increases, the corresponding alignment factor increases initially to values corresponding to helicopter-type rotational preference and then, eventually, decreases to values almost compatible with a spatially isotropic distribution, as the translational energy increases further.
Quantum Brownian motion of multipartite systems and their entanglement dynamics
C. H. Fleming; Albert Roura; B. L. Hu
2011-06-28
We solve the model of N quantum Brownian oscillators linearly coupled to an environment of quantum oscillators at finite temperature, with no extra assumptions about the structure of the system-environment coupling. Using a compact phase-space formalism, we give a rather quick and direct derivation of the master equation and its solutions for general spectral functions and arbitrary temperatures. Since our framework is intrinsically nonperturbative, we are able to analyze the entanglement dynamics of two oscillators coupled to a common scalar field in previously unexplored regimes, such as off resonance and strong coupling.
Massive Quantum Memories by Periodically Inverted Dynamic Evolutions
S. M. Giampaolo; F. Illuminati; A. Di Lisi; G. Mazzarella
2005-06-27
We introduce a general scheme to realize perfect quantum state reconstruction and storage in systems of interacting qubits. This novel approach is based on the idea of controlling the residual interactions by suitable external controls that, acting on the inter-qubit couplings, yield time-periodic inversions in the dynamical evolution, thus cancelling exactly the effects of quantum state diffusion. We illustrate the method for spin systems on closed rings with XY residual interactions, showing that it enables the massive storage of arbitrarily large numbers of local states, and we demonstrate its robustness against several realistic sources of noise and imperfections.
Hierarchy of Stochastic Pure States for Open Quantum System Dynamics
NASA Astrophysics Data System (ADS)
Suess, D.; Eisfeld, A.; Strunz, W. T.
2014-10-01
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.
Comparative study of the performance of quantum annealing and simulated annealing
NASA Astrophysics Data System (ADS)
Nishimori, Hidetoshi; Tsuda, Junichi; Knysh, Sergey
2015-01-01
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.
NASA Astrophysics Data System (ADS)
Glezakou, V. A.; McGrail, P.; Dang, L. X.
2009-12-01
Because of the rapidly increasing interest in technologies for capturing and permanently sequestering CO2 as part of a climate change mitigation strategy, understanding the interaction of CO2 with materials that comprise a sequestration system (steels, cements, silicate minerals, etc.) is of fundamental importance. The majority of models for corrosion of metals involve water-mediated processes, with CO2 dissolved in the aqueous phase playing a minor role in the process. In contrast, recent experiments with mild steels have shown that much greater corrosivity actually occurs in the dense CO2 phase, provided sufficient molecular water is present in the CO2 phase to catalyse certain reactions. In our study, we use DFT-based dynamics to study the internal structure of the the super-critical CO2/(H2O)n system, with n=0-4. While water does not disturb the super-critical CO2 phase, it also gives rise to short-lived CO2...H2O bonds which are likely to facilitate the activation of CO2 on the surface, but otherwise maintains its molecular form. We also use DFT methods to probe the fundamental interactions of CO2 or SO2 and H2O with clean or doped iron surfaces and determine the reactive pathways that lead to CO2 chemisorption, dissociation and further formation of corrosion products in the form of carbonates or sulfites. DFT-based molecular dynamics are employed to sample the configurational space of reactants and products more efficiently. CO2 adsorbs readily on the surface assuming a bent geometry, indicative of charge transfer from the surface to CO2, which closely resembles a CO2- moiety. Once CO2 is adsorbed, it can decompose to adsorbed O+CO, which further reacts with CO2 or SO2 to form corrosion products. Molecularly adsorbed water acts as catalyst to lower these reaction barriers. Clearly, the reactive pathways on the surface are quite different than those in aqueous solution. Battelle operates Pacific Northwest National Laboratory for the US Department of Energy.
Quantum dissipative dynamics of two-level atoms in hyperbolic metamaterials
NASA Astrophysics Data System (ADS)
Cortes, Cristian; Jacob, Zubin
2015-04-01
Hyperbolic metamaterials (HMMs) represent a class of artificial nanostructured media that have garnered a lot of attention over the past few years due their broadband singularity in the photonic density of states. This unique property has led to many research directions ranging from subwavelength light manipulation to the control of radiative decay rates of quantum emitters in HMMs. Here, we apply a second quantization approach, first developed by Dekker (1975), to study the quantum dissipative dynamics of a two-level atom coupled to a hyperbolic medium. The Dekker quantization approach provides a framework that allows for non-Hermitian Hamiltonians whose imaginary part represents the dissipation of the quantum system. We calculate the resonance fluorescence spectrum and steady-state dynamics of a two-level atom in an HMM. Our results take into account non-idealities of the medium such as loss and finite unit-cell size and should be experimentally observable using current nanofabrication technology.
A separable, dynamically local ontological model of quantum mechanics
Jacques Pienaar
2015-05-19
A model of reality is called separable if the state of a composite system is equal to the union of the states of its parts, located in different regions of space. Spekkens has argued that it is trivial to reproduce the predictions of quantum mechanics using a separable ontological model, provided one allows for arbitrary violations of `dynamical locality'. However, since dynamical locality is strictly weaker than local causality, this leaves open the question of whether an ontological model for quantum mechanics can be both separable and dynamically local. We answer this question in the affirmative, using an ontological model based on previous work by Deutsch and Hayden. Although the original formulation of the model avoids Bell's theorem by denying that measurements result in single, definite outcomes, we show that the model can alternatively be cast in the framework of ontological models, where Bell's theorem does apply. We find that the resulting model violates local causality, but satisfies both separability and dynamical locality, making it a candidate for the `most local' ontological model of quantum mechanics.
Dynamically self-regular quantum harmonic black holes
Spallucci, Euro
2015-01-01
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 cut-off. We propose a quantisation 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-establish the classical black hole description. F...
Collision Microscope to Study Many-Body Quantum Entanglement
NASA Astrophysics Data System (ADS)
Price, Craig; Liu, Qi; Gemelke, Nathan
2014-05-01
Quantum entanglement over long length scales is present in both quantum critical and quantum ordered many-body systems and can often be used as a fingerprint for underlying dynamics or ground-state structure. Limited quantum measurement and thermal back-action via controlled collisions of cold atoms and subsequent optical detection can be used to probe long-range entanglement. Entanglement Entropy has recently arisen as a quantitative vehicle to describe entanglement in thermodynamic systems, and its scaling with area can reveal detailed character of the system. We present progress in constructing an apparatus to experimentally extract Entanglement Entropy through pair-wise entanglement of cold fermionic potassium and bosonic cesium gases. The measurement will be made by translating localized probe atoms through a portion of a strongly entangled sample, then recording the heating effect of back-action after optical detection of probe atoms. To do so, precise independent control over the atoms will be maintained in a bichromatic lattice formed with a monolithic, common-mode optical setup imbedded in a quantum gas microscope. Other applications are discussed, including cooling of a Mott-Insulator and study of non-equilibrium quantum systems.
Conditional quantum dynamics with several observers
Dziarmaga, Jacek [Los Alamos National Laboratory, Theoretical Division, MS-B213, Los Alamos, New Mexico 87545 (United States); Instytut Fizyki Uniwersytetu Jagiellonskiego, Ulnicka Reymonta 4, 30-059 Cracow (Poland); Dalvit, Diego A.R.; Zurek, Wojciech H. [Los Alamos National Laboratory, Theoretical Division, MS-B213, Los Alamos, New Mexico 87545 (United States)
2004-02-01
We consider several observers who monitor different parts of the environment of a single quantum system and use their data to deduce its state. We derive a set of conditional stochastic master equations that describe the evolution of the density matrices each observer ascribes to the system under the Markov approximation, and show that this problem can be reduced to the case of a single 'superobserver', who has access to all the acquired data. The key problem - consistency of the sets of data acquired by different observers - is then reduced to the probability that a given combination of data sets will be ever detected by the superobserver. The resulting conditional master equations are applied to several physical examples: homodyne detection of phonons in quantum Brownian motion, photodetection and homodyne detection of resonance fluorescence from a two-level atom. We introduce relative purity to quantify the correlations between the information about the system gathered by different observers from their measurements of the environment. We find that observers gain the most information about the state of the system and they agree the most about it when they measure the environment observables with eigenstates most closely correlated with the optimally predictable pointer basis of the system.
Shortcuts to adiabaticity in quantum many-body systems: a quantum dynamical microscope
NASA Astrophysics Data System (ADS)
Del Campo, Adolfo
2014-03-01
The evolution of a quantum system induced by a shortcut to adiabaticity mimics the adiabatic dynamics without the requirement of slow driving. Engineering it involves diagonalizing the instantaneous Hamiltonian of the system and results in the need of auxiliary non-local interactions for matter-waves. Here experimentally realizable driving protocols are found for a large class of single-particle, many-body, and non-linear systems without demanding the spectral properties as an input. The method is applied to the expansion of a trapped ultracold gas which spatially scales up the size of the cloud while conserving the quantum correlations of the initial many-body state. This shortcut to adiabatic expansions acts as a quantum dynamical microscope.
NASA Astrophysics Data System (ADS)
Inoue, Jun-Ichi
2011-03-01
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. We were financially supported by Grant-in-Aid for Scientific Research (C) of Japan Society for the Promotion of Science, No. 22500195.
Boltzmann-conserving classical dynamics in quantum time-correlation functions: "Matsubara dynamics"
NASA Astrophysics Data System (ADS)
Hele, Timothy J. H.; Willatt, Michael J.; Muolo, Andrea; Althorpe, Stuart C.
2015-04-01
We show that a single change in the derivation of the linearized semiclassical-initial value representation (LSC-IVR or "classical Wigner approximation") results in a classical dynamics which conserves the quantum Boltzmann distribution. We rederive the (standard) LSC-IVR approach by writing the (exact) quantum time-correlation function in terms of the normal modes of a free ring-polymer (i.e., a discrete imaginary-time Feynman path), taking the limit that the number of polymer beads N ? ?, such that the lowest normal-mode frequencies take their "Matsubara" values. The change we propose is to truncate the quantum Liouvillian, not explicitly in powers of ?2 at ?0 (which gives back the standard LSC-IVR approximation), but in the normal-mode derivatives corresponding to the lowest Matsubara frequencies. The resulting "Matsubara" dynamics is inherently classical (since all terms O ( ? 2 ) disappear from the Matsubara Liouvillian in the limit N ? ?) and conserves the quantum Boltzmann distribution because the Matsubara Hamiltonian is symmetric with respect to imaginary-time translation. Numerical tests show that the Matsubara approximation to the quantum time-correlation function converges with respect to the number of modes and gives better agreement than LSC-IVR with the exact quantum result. Matsubara dynamics is too computationally expensive to be applied to complex systems, but its further approximation may lead to practical methods.
Boltzmann-conserving classical dynamics in quantum time-correlation functions: "Matsubara dynamics".
Hele, Timothy J H; Willatt, Michael J; Muolo, Andrea; Althorpe, Stuart C
2015-04-01
We show that a single change in the derivation of the linearized semiclassical-initial value representation (LSC-IVR or "classical Wigner approximation") results in a classical dynamics which conserves the quantum Boltzmann distribution. We rederive the (standard) LSC-IVR approach by writing the (exact) quantum time-correlation function in terms of the normal modes of a free ring-polymer (i.e., a discrete imaginary-time Feynman path), taking the limit that the number of polymer beads N ? ?, such that the lowest normal-mode frequencies take their "Matsubara" values. The change we propose is to truncate the quantum Liouvillian, not explicitly in powers of ?(2) at ?(0) (which gives back the standard LSC-IVR approximation), but in the normal-mode derivatives corresponding to the lowest Matsubara frequencies. The resulting "Matsubara" dynamics is inherently classical (since all terms O(?(2)) disappear from the Matsubara Liouvillian in the limit N ? ?) and conserves the quantum Boltzmann distribution because the Matsubara Hamiltonian is symmetric with respect to imaginary-time translation. Numerical tests show that the Matsubara approximation to the quantum time-correlation function converges with respect to the number of modes and gives better agreement than LSC-IVR with the exact quantum result. Matsubara dynamics is too computationally expensive to be applied to complex systems, but its further approximation may lead to practical methods. PMID:25854224
Dynamical mean-field theory study of Nagaoka ferromagnetism
Hyowon Park; K. Haule; C. A. Marianetti; G. Kotliar
2008-01-01
We revisit Nagaoka ferromagnetism in the U=? Hubbard model within the dynamical mean-field theory (DMFT) using the recently developed continuous time quantum Monte Carlo method as the impurity solver. The stability of Nagaoka ferromagnetism is studied as a function of the temperature, the doping level, and the next-nearest-neighbor lattice hopping t' . We found that the nature of the phase
Quantum Dynamics in Continuum for Proton Transport I: Basic Formulation
Chen, Duan; Wei, Guo-Wei
2012-01-01
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
Andreev reflection, a tool to investigate vortex dynamics and quantum turbulence in 3He-B
Fisher, Shaun Neil; Jackson, Martin James; Sergeev, Yuri A.; Tsepelin, Viktor
2014-01-01
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
Jain, P. [School of Chemical and Physical Sciences, Victoria University of Wellington (New Zealand); Jack Dodd and Dan Walls Centre for Photonics and Ultra Cold Atoms, University of Otago (New Zealand); Bradley, A. S. [ARC Centre of Excellence for Quantum-Atom Optics, Department of Physics, University of Queensland, Brisbane, QLD 4072 (Australia); Gardiner, C. W. [Jack Dodd and Dan Walls Centre for Photonics and Ultra Cold Atoms, University of Otago (New Zealand)
2007-08-15
We study an experimentally realizable system containing stable black hole-white hole acoustic horizons in toroidally trapped Bose-Einstein condensates--the quantum de Laval nozzle. We numerically obtain stationary flow configurations and assess their stability using Bogoliubov theory, finding both in hydrodynamic and nonhydrodynamic regimes there exist dynamically unstable regions associated with the creation of positive and negative energy quasiparticle pairs in analogy with the gravitational Hawking effect. The dynamical instability takes the form of a two mode squeezing interaction between resonant pairs of Bogoliubov modes. We study the evolution of dynamically unstable flows using the truncated Wigner method, which confirms the two mode squeezed state picture of the analogue Hawking effect for low winding number.
Open quantum system parameters from molecular dynamics
Wang, Xiaoqing; Wüster, Sebastian; Eisfeld, Alexander
2015-01-01
We extract the site energies and spectral densities of the Fenna-Matthews-Olson (FMO) pigment protein complex of green sulphur bacteria from simulations of molecular dynamics combined with energy gap calculations. Comparing four different combinations of methods, we investigate the origin of quantitative differences regarding site energies and spectral densities obtained previously in the literature. We find that different forcefields for molecular dynamics and varying local energy minima found by the structure relaxation yield significantly different results. Nevertheless, a picture averaged over these variations is in good agreement with experiments and some other theory results. Throughout, we discuss how vibrations external- or internal to the pigment molecules enter the extracted quantities differently and can be distinguished. Our results offer some guidance to set up more computationally intensive calculations for a precise determination of spectral densities in the future. These are required to determ...
Tomas Zimmermann; Jiri Vanicek
2011-12-01
We propose to measure nonadiabaticity of molecular quantum dynamics rigorously with the quantum fidelity between the Born-Oppenheimer and fully nonadiabatic dynamics. It is shown that this measure of nonadiabaticity applies in situations where other criteria, such as the energy gap criterion or the extent of population transfer, fail. We further propose to estimate this quantum fidelity efficiently with a generalization of the dephasing representation to multiple surfaces. Two variants of the multiple-surface dephasing representation (MSDR) are introduced, in which the nuclei are propagated either with the fewest-switches surface hopping (FSSH) or with the locally mean field dynamics (LMFD). The LMFD can be interpreted as the Ehrenfest dynamics of an ensemble of nuclear trajectories, and has been used previously in the nonadiabatic semiclassical initial value representation. In addition to propagating an ensemble of classical trajectories, the MSDR requires evaluating nonadiabatic couplings and solving the Schr\\"{o}dinger (or more generally, the quantum Liouville-von Neumann) equation for a single discrete degree of freedom. The MSDR can be also used to measure the importance of other terms present in the molecular Hamiltonian, such as diabatic couplings, spin-orbit couplings, or couplings to external fields, and to evaluate the accuracy of quantum dynamics with an approximate nonadiabatic Hamiltonian. The method is tested on three model problems introduced by Tully, on a two-surface model of dissociation of NaI, and a three-surface model including spin-orbit interactions. An example is presented that demonstrates the importance of often-neglected second-order nonadiabatic couplings.
Bell states and entanglement dynamics on two coupled quantum molecules
NASA Astrophysics Data System (ADS)
Oliveira, P. A.; Sanz, L.
2015-05-01
This work provides a complete description of entanglement properties between electrons inside coupled quantum molecules, nanoestructures which consist of two quantum dots. Each electron can tunnel between the two quantum dots inside the molecule, being also coupled by Coulomb interaction. First, it is shown that Bell states act as a natural basis for the description of this physical system, defining the characteristics of the energy spectrum and the eigenstates. Then, the entanglement properties of the eigenstates are discussed, shedding light on the roles of each physical parameters on experimental setup. Finally, a detailed analysis of the dynamics shows the path to generate states with a high degree of entanglement, as well as physical conditions associated with coherent oscillations between separable and Bell states.
Optimally combining dynamical decoupling and quantum error correction
Paz-Silva, Gerardo A.; Lidar, D. A.
2013-01-01
Quantum control and fault-tolerant quantum computing (FTQC) are two of the cornerstones on which the hope of realizing a large-scale quantum computer is pinned, yet only preliminary steps have been taken towards formalizing the interplay between them. Here we explore this interplay using the powerful strategy of dynamical decoupling (DD), and show how it can be seamlessly and optimally integrated with FTQC. To this end we show how to find the optimal decoupling generator set (DGS) for various subspaces relevant to FTQC, and how to simultaneously decouple them. We focus on stabilizer codes, which represent the largest contribution to the size of the DGS, showing that the intuitive choice comprising the stabilizers and logical operators of the code is in fact optimal, i.e., minimizes a natural cost function associated with the length of DD sequences. Our work brings hybrid DD-FTQC schemes, and their potentially considerable advantages, closer to realization. PMID:23559088
Dynamic control of plasmon generation by an individual quantum system.
Große, Christoph; Kabakchiev, Alexander; Lutz, Theresa; Froidevaux, Romain; Schramm, Frank; Ruben, Mario; Etzkorn, Markus; Schlickum, Uta; Kuhnke, Klaus; Kern, Klaus
2014-10-01
Controlling light on the nanoscale in a similar way as electric currents has the potential to revolutionize the exchange and processing of information. Although light can be guided on this scale by coupling it to plasmons, that is, collective electron oscillations in metals, their local electronic control remains a challenge. Here, we demonstrate that an individual quantum system is able to dynamically gate the electrical plasmon generation. Using a single molecule in a double tunnel barrier between two electrodes we show that this gating can be exploited to monitor fast changes of the quantum system itself and to realize a single-molecule plasmon-generating field-effect transistor operable in the gigahertz range. This opens new avenues toward atomic scale quantum interfaces bridging nanoelectronics and nanophotonics. PMID:25181332
Bell states and entanglement dynamics on two coupled quantum molecules
P. A. Oliveira; L. Sanz
2015-03-06
This work provides a complete description of entanglement properties between electrons inside coupled quantum molecules, nanoestructures which consist of two quantum dots. Each electron can tunnel between the two quantum dots inside the molecule, being also coupled by Coulomb interaction. First, it is shown that Bell states act as a natural basis for the description of this physical system, defining the characteristics of the energy spectrum and the eigenstates. Then, the entanglement properties of the eigenstates are discussed, shedding light on the roles of each physical parameters on experimental setup. Finally, a detailed analysis of the dynamics shows the path to generate states with a high degree of entanglement, as well as physical conditions associated with coherent oscillations between separable and Bell states.
Loop quantum cosmology: From pre-inflationary dynamics to observations
Abhay Ashtekar; Aurelien Barrau
2015-04-28
The Planck collaboration has provided us rich information about the early universe, and a host of new observational missions will soon shed further light on the `anomalies' that appear to exist on the largest angular scales. From a quantum gravity perspective, it is natural to inquire if one can trace back the origin of such puzzling features to Planck scale physics. Loop quantum cosmology provides a promising avenue to explore this issue because of its natural resolution of the big bang singularity. Thanks to advances over the last decade, the theory has matured sufficiently to allow concrete calculations of the phenomenological consequences of its pre-inflationary dynamics. In this article we summarize the current status of the ensuing two-way dialog between quantum gravity and observations.
Gigahertz dynamics of a strongly driven single quantum spin.
Fuchs, G D; Dobrovitski, V V; Toyli, D M; Heremans, F J; Awschalom, D D
2009-12-11
Two-level systems are at the core of numerous real-world technologies such as magnetic resonance imaging and atomic clocks. Coherent control of the state is achieved with an oscillating field that drives dynamics at a rate determined by its amplitude. As the strength of the field is increased, a different regime emerges where linear scaling of the manipulation rate breaks down and complex dynamics are expected. By calibrating the spin rotation with an adiabatic passage, we have measured the room-temperature "strong-driving" dynamics of a single nitrogen vacancy center in diamond. With an adiabatic passage to calibrate the spin rotation, we observed dynamics on sub-nanosecond time scales. Contrary to conventional thinking, this breakdown of the rotating wave approximation provides opportunities for time-optimal quantum control of a single spin. PMID:19965386
Dynamical decoupling efficiency versus quantum non-Markovianity
Carole Addis; Francesco Ciccarello; Michele Cascio; G. Massimo Palma; Sabrina Maniscalco
2015-02-09
We investigate the relationship between non-Markovianity and the effectiveness of a dynamical decoupling protocol for qubits undergoing pure dephasing. We consider an exact model in which dephasing arises due to a bosonic environment with a spectral density of the Ohmic class. This is parametrised by an Ohmicity parameter by changing which we can model both Markovian and non-Markovian environments. Interestingly, we find that engineering a non-Markovian environment is detrimental to the efficiency of the dynamical decoupling scheme, leading to a worse coherence preservation. We show that each dynamical decoupling pulse reverses the flow of quantum information and, on this basis, we investigate the connection between dynamical decoupling efficiency and the reservoir spectral density. Finally, in the spirit of reservoir engineering, we investigate the optimum system-reservoir parameters for achieving maximum stationary coherences.
NASA Astrophysics Data System (ADS)
Teixidor, Marc Moix; Varandas, António J. C.
2015-01-01
Quantum scattering calculations of the O ( 3 P ) + OH ( 2 ? ) ? O 2 ( 3 ?g - ) + H ( 2 S ) reactions are presented using the combined-hyperbolic-inverse-power-representation potential energy surface [A. J. C. Varandas, J. Chem. Phys. 138, 134117 (2013)], which employs a realistic, ab initio-based, description of both the valence and long-range interactions. The calculations have been performed with the ABC time-independent quantum reactive scattering computer program based on hyperspherical coordinates. The reactivity of both arrangements has been investigated, with particular attention paid to the effects of vibrational excitation. By using the J-shifting approximation, rate constants are also reported for both the title reactions.
Dynamics, synchronization, and quantum phase transitions of two dissipative spins
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
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.
Multidimensional classical Liouville dynamics with quantum initial conditions
NASA Astrophysics Data System (ADS)
Horenko, Illia; Schmidt, Burkhard; Schutte, Christof
2002-09-01
A simple and numerically efficient approach to Wigner transforms and classical Liouville dynamics in phase space is presented. (1) The Wigner transform can be obtained with a given accuracy by optimal decomposition of an initial quantum-mechanical wave function in terms of a minimal set of Gaussian wave packets. (2) The solution of the classical Liouville equation within the locally quadratic approximation of the potential energy function requires a representation of the density in terms of an ensemble of narrow Gaussian phase-space packets. The corresponding equations of motion can be efficiently solved by a modified leap-frog integrator. For both problems the use of Monte Carlo based techniques allows numerical calculation in multidimensional cases where grid-based methods such as fast Fourier transforms are prohibitive. In total, the proposed strategy provides a practical and efficient tool for classical Liouville dynamics with quantum-mechanical initial states.
Extended space expectation values in quantum dynamical system evolutions
Demiralp, Metin [Istanbul Technical University, Informatics Institute, Maslak, 34469, Istanbul (Turkey)
2014-10-06
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 operators and are somehow pseudo expectation values.
Universal short-time quantum critical dynamics in imaginary time
NASA Astrophysics Data System (ADS)
Yin, Shuai; Mai, Peizhi; Zhong, Fan
2014-04-01
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.
Fingerprints of Classical Instability in Open Quantum Dynamics
Paul A. Miller; Sarben Sarkar
1998-07-03
The dynamics near a hyperbolic point in phase space is modelled by an inverted harmonic oscillator. We investigate the effect of the classical instability on the open quantum dynamics of the oscillator, introduced through the interaction with a thermal bath, using both the survival probability function and the rate of von Neumann entropy increase, for large times. In this parameter range we prove, using influence functional techniques, that the survival probability function decreases exponentially at a rate, K', depending not only on the measure of instability in the model but also on the strength of interaction with the environment. We also show that K' determines the rate of von Neumann entropy increase and that this result is independent of the temperature of the environment. This generalises earlier results which are valid in the limit of vanishing dissipation. The validity of inferring similar rates of survival probability decrease and entropy increase for quantum chaotic systems is also discussed.
Signatures of chaos in the dynamics of quantum discord.
Madhok, Vaibhav; Gupta, Vibhu; Trottier, Denis-Alexandre; Ghose, Shohini
2015-03-01
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. PMID:25871171
Method for discovering relationships in data by dynamic quantum clustering
Weinstein, Marvin; Horn, David
2014-10-28
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.
Characterizing quantum dynamics with initial system-environment correlations
Martin Ringbauer; Christopher J. Wood; Kavan Modi; Alexei Gilchrist; Andrew G. White; Alessandro Fedrizzi
2014-10-21
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.
Quantum dynamics from the Brownian recoil principle
NASA Astrophysics Data System (ADS)
Garbaczewski, Piotr; Vigier, Jean-Pierre
1992-10-01
We formulate a theory of the Brownian motion for particle ensembles, whose diffusive evolution is entirely generated by the surrounding random environment. By demanding the validity of the momentum conservation law on all conceivable scales adopted for the investigation of individual particle scattering (collisions) on the medium constituents, we are forced to incorporate the environmental recoil effects in the formalism. The Brownian recoil principle elevates the individually negligible phenomena to the momentum conservation law on the ensemble average. The resultant dynamics of the statistical ensemble is governed by the Schrödinger equation, once the diffusion constant D is identified with ?/2m.
QCD (Quantum Chromo-Dynamics) with dynamical fermions on the connection machine
Baillie, C.F.; Brickner, R.G.; Gupta, R.; Johnsson, L. (California Inst. of Tech., Pasadena, CA (USA). Concurrent Computation Project; Los Alamos National Lab., NM (USA); Thinking Machines Corp., Cambridge, MA (USA))
1989-01-01
We have implemented Quantum Chromo-Dynamics (QCD) on the massively parallel Connection Machine in *Lisp. The code uses dynamical Wilson fermions and the Hybrid Monte Carlo Algorithm (HMCA) to update the lattice. We describe our program and give performance measurements for it. With no tuning or optimization, the code runs at approximately 500 to 1000 MFLOPS on a 64-K Connection Machine, model CM-2, depending on the VP ratio.
Kijeong Kwac; Chewook Lee; Yousung Jung; Jaebeom Han; Kyungwon Kwak; Junrong Zheng; M. D. Fayer; Minhaeng Cho
2006-01-01
Molecular dynamics (MD) simulations and quantum mechanical electronic structure calculations are used to investigate the nature and dynamics of the phenol-benzene complex in the mixed solvent, benzene?CCl4. Under thermal equilibrium conditions, the complexes are continuously dissociating and forming. The MD simulations are used to calculate the experimental observables related to the phenol hydroxyl stretching mode, i.e., the two dimensional infrared
Dynamical decoupling based quantum sensing: Floquet spectroscopy
J. E. Lang; Ren-Bao Liu; T. S. Monteiro
2015-06-05
Sensing the internal dynamics of individual nuclear spins or clusters of nuclear spins has recently become possible by observing the coherence decay of a nearby electronic spin: the weak magnetic noise is amplified by a periodic, multi-pulse decoupling sequence. However, it remains challenging to robustly infer underlying atomic-scale structure from decoherence traces in all but the simplest cases. We introduce Floquet spectroscopy as a versatile paradigm for analysis of these experiments, and argue it offers a number of general advantages. In particular, this technique generalises to more complex situations, offering physical insight in regimes of many-body dynamics, strong coupling and pulses of finite duration. As there is no requirement for resonant driving, the proposed spectroscopic approach permits physical interpretation of striking, but overlooked, coherence decay features in terms of the form of the avoided crossings of the underlying quasienergy eigenspectrum. This is exemplified by a set of "diamond" shaped features arising for transverse-field scans in the case of single-spin sensing by NV-centers in diamond. We investigate also applications for donors in silicon showing that the resulting tunable interaction strengths offer highly promising future sensors.
Canonical versus noncanonical equilibration dynamics of open quantum systems
Chun-Jie Yang; Jun-Hong An; Hong-Gang Luo; Yading Li; C. H. Oh
2014-08-24
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.
Dynamical quantum Hall effect in the parameter space.
Gritsev, V; Polkovnikov, A
2012-04-24
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
Dynamical quantum Hall effect in the parameter space
Gritsev, V.; Polkovnikov, A.
2012-01-01
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
Including Quantum Effects in the Dynamics of Complex (i.e., Large)Molecular Systems
Miller, William H.
2006-04-27
The development in the 1950's and 60's of crossed molecular beam methods for studying chemical reactions at the single-collision molecular level stimulated the need and desire for theoretical methods to describe these and other dynamical processes in molecular systems. Chemical dynamics theory has made great strides in the ensuing decades, so that methods are now available for treating the quantum dynamics of small molecular systems essentially completely. For the large molecular systems that are of so much interest nowadays (e.g. chemical reactions in solution, in clusters, in nano-structures, in biological systems, etc.), however, the only generally available theoretical approach is classical molecular dynamics (MD) simulations. Much effort is currently being devoted to the development of approaches for describing the quantum dynamics of these complex systems. This paper reviews some of these approaches, especially the use of semiclassical approximations for adding quantum effects to classical MD simulations, also showing some new versions that should make these semiclassical approaches even more practical and accurate.
A centroid molecular dynamics study of liquid para-hydrogen and ortho-deuterium.
Hone, Tyler D; Voth, Gregory A
2004-10-01
Centroid molecular dynamics (CMD) is applied to the study of collective and single-particle dynamics in liquid para-hydrogen at two state points and liquid ortho-deuterium at one state point. The CMD results are compared with the results of classical molecular dynamics, quantum mode coupling theory, a maximum entropy analytic continuation approach, pair-product forward- backward semiclassical dynamics, and available experimental results. The self-diffusion constants are in excellent agreement with the experimental measurements for all systems studied. Furthermore, it is shown that the method is able to adequately describe both the single-particle and collective dynamics of quantum liquids. PMID:15446940
From Coulomb-blockade to nonlinear quantum dynamics in a superconducting circuit with a resonator.
Gramich, Vera; Kubala, Björn; Rohrer, Selina; Ankerhold, Joachim
2013-12-13
Motivated by recent experiments on superconducting circuits consisting of a dc-voltage-biased Josephson junction in series with a resonator, quantum properties of these devices far from equilibrium are studied. This includes a crossover from a domain of incoherent to a domain of coherent Cooper pair tunneling, where the circuit realizes a driven nonlinear oscillator. Equivalently, weak photon-charge coupling turns into strong correlations captured by a single degree of freedom. Radiated photons offer a new tool to monitor charge flow and current noise gives access to nonlinear dynamics, which allows us to analyze quantum-classical boundaries. PMID:24483693
Quantum dynamics of 16O + 36O2 and 18O + 32O2 exchange reactions
NASA Astrophysics Data System (ADS)
Rajagopala Rao, T.; Guillon, G.; Mahapatra, S.; Honvault, P.
2015-05-01
We present quantum dynamical investigations of 16O + 36O2 and 18O + 32O2 exchange reactions using a time-independent quantum mechanical method and an accurate global potential energy surface of ozone [Dawes et al., J. Chem. Phys. 135, 081102 (2011)]. Initial state-selected integral cross sections, rate constants, and Boltzmann averaged thermal rate constants are obtained and compared with earlier experimental and theoretical results. The computed thermal rate constants for the oxygen exchange reactions exhibit a negative temperature dependence, as found experimentally. They are in better agreement with the experiments than the previous studies on the same reactions.
Relaxation Dynamics and Pre-thermalization in an isolated Quantum System
NASA Astrophysics Data System (ADS)
Schmiedmayer, Jörg
2012-02-01
Understanding non-equilibrium dynamics of many-body quantum systems is crucial for understanding many fundamental and applied physics problems ranging from decoherence and equilibration to the development of future quantum technologies such as quantum computers which are inherently non-equilibrium quantum systems. One of the biggest challenges is that there is no general approach to characterize the resulting quantum states. In this talk I will present how to use the full distribution functions of a quantum observable to study the relaxation dynamics in one-dimensional quantum systems and to characterize the underlying many body states. Interfering two 1 dimensional quantum gases allows to study how the coherence created between the two many body systems by the splitting process [1] slowly dies by coupling to the many internal degrees of freedom available [2]. To reveal the nature of the quantum states behind this de-coherence we analyze the interference of the two evolving quantum systems. The full distribution function of the shot to shot variations of the interference patterns [3,4], especially its higher moments, allows characterizing the underlying physical processes [5]. Two distinct regimes are clearly visible in the experiment: for short length scales the system is characterized by spin diffusion, for long length scales by spin decay [6]. After a rapid evolution the distributions approach a steady state which can be characterized by thermal distribution functions. Interestingly, its (effective) temperature is over five times lower than the kinetic temperature of the initial system. Our system, being a weakly-interacting Bosons in one dimension, is nearly integrable and the dynamics is constrained by constants of motion which leads to the establishment of a generalized Gibbs ensemble and pre-thermalization. We therefore interpret our observations as an illustration of the fast relaxation of a nearly integrable many-body system to a quasi-steady state through de-phasing. The observation of an effective temperature significant different from the expected kinetic temperature supports the observation of the generalized Gibbs state [6]. [4pt] [1] T. Schumm et al. Nature Physics, 1, 57 (2005).[0pt] [2] S. Hofferberth et al. Nature 449, 324 (2007).[0pt] [3] A. Polkovnikov, et al. Proc. Natl. Acad. Sci. 103, 6125 (2006); V. Gritsev, et al., Nature Phys. 2, 705 (2006); [0pt] [4] S. Hofferberth et al. Nature Physics 4, 489 (2008); [0pt] [5] T. Kitagawa, et al., Phys. Rev. Lett. 104, 255302 (2010); New Journal of Physcs, 13 073018 (2011)[0pt] [6] Gring et al., to be published
Quantum dynamics of the avian compass
Zachary B. Walters
2014-09-19
The ability of migratory birds to orient relative to the Earth's magnetic field is believed to involve a coherent superposition of two spin states of a radical electron pair. However, the mechanism by which this coherence can be maintained in the face of strong interactions with the cellular environment has remained unclear. This Letter addresses the problem of decoherence between two electron spins due to hyperfine interaction with a bath of spin 1/2 nuclei. Dynamics of the radical pair density matrix are derived and shown to yield a simple mechanism for sensing magnetic field orientation. Rates of dephasing and decoherence are calculated ab initio and found to yield millisecond coherence times, consistent with behavioral experiments.
Danel, J.-F.; Blottiau, P.; Kazandjian, L.; Piron, R.; Torrent, M. [CEA, DAM, DIF, 91297 Arpajon (France)
2014-10-15
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.
NASA Astrophysics Data System (ADS)
Gerving, C. S.; Hoang, T. M.; Land, B. J.; Anquez, M.; Hamley, C. D.; Chapman, M. S.
2012-11-01
A pendulum prepared perfectly inverted and motionless is a prototype of unstable equilibrium and corresponds to an unstable hyperbolic fixed point in the dynamical phase space. Here, we measure the non-equilibrium dynamics of a spin-1 Bose-Einstein condensate initialized as a minimum uncertainty spin-nematic state to a hyperbolic fixed point of the phase space. Quantum fluctuations lead to non-linear spin evolution along a separatrix and non-Gaussian probability distributions that are measured to be in good agreement with exact quantum calculations up to 0.25s. At longer times, atomic loss due to the finite lifetime of the condensate leads to larger spin oscillation amplitudes, as orbits depart from the separatrix. This demonstrates how decoherence of a many-body system can result in apparent coherent behaviour. This experiment provides new avenues for studying macroscopic spin systems in the quantum limit and for investigations of important topics in non-equilibrium quantum dynamics.
Quantum dynamical study of the O({sup 1}D) + CH{sub 4} ? CH{sub 3} + OH atmospheric reaction
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
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.
LIE GROUP DYNAMICAL FORMALISM AND THE RELATION BETWEEN QUANTUM MECHANICS AND CLASSICAL MECHANICS
Thomas Jordan; E. C. G. Sudarshan
1961-01-01
General structural features of dynamical theories can be exhibited in ; relations between classical and quantum mechanics; the essential structure is a ; Lie algebra of basic dynamical-variable fanctions providing transformationgroup ; infinitesimal generators. It is shown that the particular representation chosen ; is not important for the dynamical structure analysis by considering ; possibilities of transcribing classical and quantum
Efficient Quantum Monte Carlo Energies for Molecular Dynamics Simulations Jeffrey C. Grossman
Mitas, Lubos
Efficient Quantum Monte Carlo Energies for Molecular Dynamics Simulations Jeffrey C. Grossman methods has prevented their application to molecular dynamics simulations in which a typical trajectory the many-body quantum Monte Carlo (QMC) approach ``on-the-fly'' throughout a molecular dynamics (MD
Phase space theory of quantum–classical systems with nonlinear and stochastic dynamics
Buri?, Nikola, E-mail: buric@ipb.ac.rs; Popovi?, Duška B.; Radonji?, Milan; Prvanovi?, Slobodan
2014-04-15
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.
Chin-Yi. Tsai
1995-01-01
Theoretical models are presented to study the physical processes of particle dynamics and energy transfer between electrons, holes, photons, LO phonons, and acoustic phonons in high-speed semiconductor quantum well lasers. We simultaneously study the effects of spectral hole burning, carrier heating, and carrier diffusion-capture-escape on the modulation response of the quantum well laser. Our theoretical results indicate that the degradation
Kinetic Analyses Combining Quantum Chemical and Quantum Statistical Methods: Some Case Studies
Nguyen, Minh Tho
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
Creating exotic condensates via quantum-phase-revival dynamics in engineered lattice potentials
Buchhold, Michael; Bissbort, Ulf; Hofstetter, Walter [Institut fuer Theoretische Physik, Johann Wolfgang Goethe-Universitaet, D-60438 Frankfurt/Main (Germany); Will, Sebastian [Fakultaet fuer Physik, Ludwig-Maximilians-Universitaet, D-80799 Muenchen (Germany); Max-Planck-Institut fuer Quantenoptik, D-85748 Garching (Germany)
2011-08-15
In the field of ultracold atoms in optical lattices a plethora of phenomena governed by the hopping energy J and the interaction energy U have been studied in recent years. However, the trapping potential typically present in these systems sets another energy scale and the effects of the corresponding time scale on the quantum dynamics have rarely been considered. Here we study the quantum collapse and revival of a lattice Bose-Einstein condensate (BEC) in an arbitrary spatial potential, focusing on the special case of harmonic confinement. Analyzing the time evolution of the single-particle density matrix, we show that the physics arising at the (temporally) recurrent quantum phase revivals is essentially captured by an effective single-particle theory. This opens the possibility of preparing exotic nonequilibrium condensate states with a large degree of freedom by engineering the underlying spatial lattice potential.
Localization and Glassy Dynamics Of Many-Body Quantum Systems
Carleo, Giuseppe; Becca, Federico; Schiró, Marco; Fabrizio, Michele
2012-01-01
When classical systems fail to explore their entire configurational space, intriguing macroscopic phenomena like aging and glass formation may emerge. Also closed quanto-mechanical systems may stop wandering freely around the whole Hilbert space, even if they are initially prepared into a macroscopically large combination of eigenstates. Here, we report numerical evidences that the dynamics of strongly interacting lattice bosons driven sufficiently far from equilibrium can be trapped into extremely long-lived inhomogeneous metastable states. The slowing down of incoherent density excitations above a threshold energy, much reminiscent of a dynamical arrest on the verge of a glass transition, is identified as the key feature of this phenomenon. We argue that the resulting long-lived inhomogeneities are responsible for the lack of thermalization observed in large systems. Such a rich phenomenology could be experimentally uncovered upon probing the out-of-equilibrium dynamics of conveniently prepared quantum states of trapped cold atoms which we hereby suggest. PMID:22355756
Asymptotically Decreasing Lieb-Robinson Velocity for a Class of Dissipative Quantum Dynamics
Benoît Descamps
2013-08-07
We study the velocity of the propagation of information for a class of local dissipative quantum dynamics. This finite velocity is expressed by the so-called Lieb-Robinson bound. Besides the properties of the already studied dynamics, we consider an additional relation that expresses the propagation of certain subspaces. The previously derived bounds did not reflect the dissipative character of the dynamics and yielded the same result as for the reversible case. In this article, we show that for this class the velocity of propagation of information is time dependent and decays in time towards a smaller velocity. In some cases the velocity becomes zero. At the end of the article, the exponential clustering theorem of general frustration free local Markovian dynamics is revisited.
NASA Astrophysics Data System (ADS)
Kelly, Aaron; Brackbill, Nora; Markland, Thomas E.
2015-03-01
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.
Quantum control and long-range quantum correlations in dynamical Casimir arrays
Roberto Stassi; Simone De Liberato; Luigi Garziano; Bernardo Spagnolo; Salvatore Savasta
2015-01-29
The recent observation of the dynamical Casimir effect in a modulated superconducting waveguide, coronating thirty years of world-wide research, empowered the quantum technology community with a powerful tool to create entangled photons on-chip. In this work we show how, going beyond the single waveguide paradigm using a scalable array, it is possible to create multipartite nonclassical states, with the possibility to control the long-range quantum correlations of the emitted photons. In particular, our finite-temperature theory shows how maximally entangled $NOON$ states can be engineered in a realistic setup. The results here presented open the way to new kinds of quantum fluids of light, arising from modulated vacuum fluctuations in linear systems.
Effect of carrier dynamics and temperature on two-state lasing in semiconductor quantum dot lasers
Korenev, V. V., E-mail: korenev@spbau.ru; Savelyev, A. V.; Zhukov, A. E.; Omelchenko, A. V.; Maximov, M. V. [Saint Petersburg Academic University-Nanotechnology Research and Education Center (Russian Federation)] [Saint Petersburg Academic University-Nanotechnology Research and Education Center (Russian Federation)
2013-10-15
It is analytically shown that the both the charge carrier dynamics in quantum dots and their capture into the quantum dots from the matrix material have a significant effect on two-state lasing phenomenon in quantum dot lasers. In particular, the consideration of desynchronization in electron and hole capture into quantum dots allows one to describe the quenching of ground-state lasing observed at high injection currents both qualitatevely and quantitatively. At the same time, an analysis of the charge carrier dynamics in a single quantum dot allowed us to describe the temperature dependences of the emission power via the ground- and excited-state optical transitions of quantum dots.
Quantum chaotic scattering in graphene systems in the absence of invariant classical dynamics.
Wang, Guang-Lei; Ying, Lei; Lai, Ying-Cheng; Grebogi, Celso
2013-05-01
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
Spatiotemporal Dynamics of Quantum Computing Solid Dipole-Dipole Block Systems
Hideaki Matsueda
1998-01-01
This paper enstimates the stability of dipole-dipole interaction in quantum dot array, and proposes a novel solid state quantum\\u000a CCN (controlled controlled not) gate having a block structure, which is effective to maintain quantum mechanical coherence\\u000a and reduce both the bit error and the phase error. The spatiotemporal dynamics of quantum computation process involving the\\u000a quantum entangled pure states is
Elio Conte; Gianpaolo Pierri; Leonardo Mendolicchio; Andrei Yu. Khrennikov; Joseph P. Zbilut
2006-08-24
In the first part of the present paper we give an analysis of the ontic nature of quantum states to be intended as potentialities and of the central role of spin to be considered as the basic essence of quantum mechanical reality: using an algebraic quantum like structure we give mathematical proof on the transition from potentiality to actualization : we recall here what was recently given by us in arXiv quant-ph/0607196. However, as may be expected, it is not so easy to introduce examples containing an adequate description of ontic potentialities through detailed models of systems. The central aim of this paper is to attempt to reach this objective giving direct cases of systems in which ontic potentialities act jointly to actualization. Our aim is to provide evidence for the possible importance of potential states in the sphere of the biological dynamics giving detailed examples of interest for biological studies. We outline the possible implications of potentialities at the level of linear and non linear biological dynamics.
Jiao Wang; Anders S. Mouritzen; Jiangbin Gong
2008-03-27
Controlling the translational motion of cold atoms using optical lattice potentials is of both theoretical and experimental interest. By designing two on-resonance time sequences of kicking optical lattice potentials, a novel connection between two paradigms of nonlinear mapping systems, i.e., the kicked rotor model and the kicked Harper model, is established. In particular, it is shown that Hofstadter's butterfly quasi-energy spectrum in periodically driven quantum systems may soon be realized experimentally, with the effective Planck constant tunable by varying the time delay between two sequences of control fields. Extensions of this study are also discussed. The results are intended to open up a new generation of cold-atom experiments of quantum nonlinear dynamics
Wells, J.C.; Oberacker, V.E.; Umar, A.S. [Oak Ridge National Lab., TN (United States)]|[Vanderbilt Univ., Nashville, TN (United States). Dept. of Physics and Astronomy; Bottcher, C.; Strayer, M.R.; Drake, J.; Flanery, R. [Oak Ridge National Lab., TN (United States)
1993-09-01
We describe the numerical methods used to solve the time-dependent Dirac equation on a three-dimensional Cartesian lattice. Efficient algorithms are required for computationally intensive studies of nonperturbative relativistic quantum dynamics. Discretization is achieved through the lattice basis-spline collocation method, in which quantum-state vectors and coordinate-space operators are expressed in terms of basis-spline functions on a spatial lattice. All numerical procedures reduce to a series of matrix-vector operations which we perform on the Intel iPSC/860 hypercube, making full use of parallelism. We discuss our solutions to the problems of limited node memory and node-to-node communication overhead inherent in using distributed-memory, multiple-instruction, multiple-data stream parallel computers.
Wells, J.C.; Oberacker, V.E.; Umar, A.S. [Oak Ridge National Lab., TN (United States). Physics Division; [Vanderbilt Univ., Nashville, TN (United States). Dept. of Physics and Astronomy; Bottcher, C.; Strayer, M.R.; Drake, J.; Flanery, R. [Oak Ridge National Lab., TN (United States)
1993-12-31
The authors describe the numerical methods used to solve the time-dependent Dirac equation on a three-dimensional Cartesian lattice. Efficient algorithms are required for computationally intensive studies of nonperturbative relativistic quantum dynamics. Discretization is achieved through the lattice basis-spline collocation method, in which quantum-state vectors and coordinate-space operators are expressed in terms of basis-spline functions on a spatial lattice. All numerical procedures reduce to a series of matrix-vector operations which they perform on the Intel iPSC/860 hypercube, making full use of parallelism. They discuss their solutions to the problems of limited node memory and node-to-node communication overhead inherent in using distributed-memory, multiple-instruction, multiple-data stream parallel computers.
Quantum dynamics in continuum for proton transport--generalized correlation.
Chen, Duan; Wei, Guo-Wei
2012-04-01
As a key process of many biological reactions such as biological energy transduction or human sensory systems, proton transport has attracted much research attention in biological, biophysical, and mathematical fields. A quantum dynamics in continuum framework has been proposed to study proton permeation through membrane proteins in our earlier work and the present work focuses on the generalized correlation of protons with their environment. Being complementary to electrostatic potentials, generalized correlations consist of proton-proton, proton-ion, proton-protein, and proton-water interactions. In our approach, protons are treated as quantum particles while other components of generalized correlations are described classically and in different levels of approximations upon simulation feasibility and difficulty. Specifically, the membrane protein is modeled as a group of discrete atoms, while ion densities are approximated by Boltzmann distributions, and water molecules are represented as a dielectric continuum. These proton-environment interactions are formulated as convolutions between number densities of species and their corresponding interaction kernels, in which parameters are obtained from experimental data. In the present formulation, generalized correlations are important components in the total Hamiltonian of protons, and thus is seamlessly embedded in the multiscale/multiphysics total variational model of the system. It takes care of non-electrostatic interactions, including the finite size effect, the geometry confinement induced channel barriers, dehydration and hydrogen bond effects, etc. The variational principle or the Euler-Lagrange equation is utilized to minimize the total energy functional, which includes the total Hamiltonian of protons, and obtain a new version of generalized Laplace-Beltrami equation, generalized Poisson-Boltzmann equation and generalized Kohn-Sham equation. A set of numerical algorithms, such as the matched interface and boundary method, the Dirichlet to Neumann mapping, Gummel iteration, and Krylov space techniques, is employed to improve the accuracy, efficiency, and robustness of model simulations. Finally, comparisons between the present model predictions and experimental data of current-voltage curves, as well as current-concentration curves of the Gramicidin A channel, verify our new model. PMID:22482542
Dynamics of elastic and inelastic energy transfer between quantum dots in a microcavity
NASA Astrophysics Data System (ADS)
Xu, K. J.; Piermarocchi, C.
2011-09-01
We develop a theory of exciton energy transfer dynamics between two quantum dots in a planar microcavity. We study the dynamics of quantum dot excitons in three different cases: (i) a single dot coupled only to cavity modes, (ii) two dots coupled to cavity modes, and (iii) two dots coupled to cavity modes and to acoustic phonons. In the latter case, we focus on the process of phonon-assisted inelastic exciton energy transfer between the quantum dots. We take into account phonon effects by introducing a light-matter Hamiltonian with operators describing the exciton-photon-phonon coupling and we truncate the Hilbert space by assuming that at most one excitation is present in the system. Using this approach we simulate the exciton dynamics with realistic parameters in the zero temperature limit. From the dynamics we extract the dependence of the characteristic energy transfer rate as a function of the interdot separation. This theoretical approach can be used to optimize exciton energy transfer by designing structures with engineered photon and phonon density of states.
Quantum trajectory dynamics in imaginary time with the momentum-dependent quantum potential
Garashchuk, Sophya [Department of Chemistry and Biochemistry, University of South Carolina, Columbia, South Carolina 29208 (United States)
2010-01-07
The quantum trajectory dynamics is extended to the wave function evolution in imaginary time. For a nodeless wave function a simple exponential form leads to the classical-like equations of motion of trajectories, representing the wave function, in the presence of the momentum-dependent quantum potential in addition to the external potential. For a Gaussian wave function this quantum potential is a time-dependent constant, generating zero quantum force yet contributing to the total energy. For anharmonic potentials the momentum-dependent quantum potential is cheaply estimated from the global Least-squares Fit to the trajectory momenta in the Taylor basis. Wave functions with nodes are described in the mixed coordinate space/trajectory representation at little additional computational cost. The nodeless wave function, represented by the trajectory ensemble, decays to the ground state. The mixed representation wave functions, with lower energy contributions projected out at each time step, decay to the excited energy states. The approach, illustrated by computing energy levels for anharmonic oscillators and energy level splitting for the double-well potential, can be used for the Boltzmann operator evolution.
Dynamically Corrected Quantum Gates for Two-Electron Spin Qubits
NASA Astrophysics Data System (ADS)
Cerfontaine, Pascal; Loebl, Matthias; Bluhm, Hendrik
2014-03-01
Two-electron spin qubits in double quantum dots offer the possibility of fast and fully electrical manipulation via the exchange interaction. Arbitrary single-qubit gates have been demonstrated while maintaining a magnetic field gradient. However, simple gate constructions are extremely sensitive to noise in the Hamiltonian and thus incur considerable decoherence. Dynamically corrected gates are first-order insensitive to disturbances and present an appealing solution if slow noise sources are dominant. Using a numerical model that reflects the experimentally important imperfections and hardware constraints, we find control pulses for singlet-triplet qubits in GaAs double quantum dots which decouple in both the electrical control and the hyperfine magnetic field gradient. Additionally, dephasing effects from fast noise sources are minimized by favoring operating points close to a sweet spot. For experimentally determined noise levels the resulting gates feature fidelities as high as 99.9% and are mainly limited by high-frequency noise and nonlinearities.
Quantum dynamics as an analog of conditional probability
NASA Astrophysics Data System (ADS)
Leifer, M. S.
2006-10-01
Quantum theory can be regarded as a noncommutative generalization of classical probability. From this point of view, one expects quantum dynamics to be analogous to classical conditional probabilities. In this paper, a variant of the well-known isomorphism between completely positive maps and bipartite density operators is derived, which makes this connection much more explicit. This isomorphism is given an operational interpretation in terms of statistical correlations between ensemble preparation procedures and outcomes of measurements. Finally, the isomorphism is applied to elucidate the connection between no-cloning and no-broadcasting theorems and the monogamy of entanglement, and a simplified proof of the no-broadcasting theorem is obtained as a by-product.
Dynamical symmetry approach to path integrals of quantum spin systems
NASA Astrophysics Data System (ADS)
Ringel, Matouš; Gritsev, Vladimir
2013-12-01
We develop a dynamical symmetry approach to path integrals for general interacting quantum spin systems. The time-ordered exponential obtained after the Hubbard-Stratonovich transformation can be disentangled into the product of a finite number of the usual exponentials. This procedure leads to a set of stochastic differential equations on the group manifold, which can be further formulated in terms of the supersymmetric effective action. This action has the form of the Witten topological field theory in the continuum limit. As a consequence, we show how it can be used to obtain the exact results for a specific quantum many-body system which can be otherwise solved only by the Bethe ansatz. This represents an example of a many-body system treated exactly using the path-integral formulation. Moreover, our method can deal with time-dependent parameters, which we demonstrate explicitly.
Marginal picture of quantum dynamics related to intrinsic arrival times
Torres-Vega, Gabino [Physics Department, Cinvestav, Apartado Postal 14-740, 07000 Mexico City, Distrito Federal (Mexico)
2007-09-15
We introduce a marginal picture of the evolution of quantum systems, in which the representation vectors are the quantities that evolve and operators and wave packets remain static. The representation vectors can be seen as probe functions that are the evolution of a {delta} function with initial support on q=X in coordinate space. This picture of the dynamics is suited for the determination of intrinsic arrival distributions for quantum systems, providing a clear physical meaning to the 'time eigenstates' used in these calculations. We also analyze Galapon et al.'s 'confined time eigenstates' [Phys. Rev. Lett. 93, 180406 (2004)] from this point of view, and propose alternative probe functions for confined systems without the need of a quantized time.
Monte Carlo techniques for real-time quantum dynamics
Mark R. Dowling; Matthew J. Davis; Peter D. Drummond; Joel F. Corney
2005-07-01
The stochastic-gauge representation is a method of mapping the equation of motion for the quantum mechanical density operator onto a set of equivalent stochastic differential equations. One of the stochastic variables is termed the "weight", and its magnitude is related to the importance of the stochastic trajectory. We investigate the use of Monte Carlo algorithms to improve the sampling of the weighted trajectories and thus reduce sampling error in a simulation of quantum dynamics. The method can be applied to calculations in real time, as well as imaginary time for which Monte Carlo algorithms are more-commonly used. The method is applicable when the weight is guaranteed to be real, and we demonstrate how to ensure this is the case. Examples are given for the anharmonic oscillator, where large improvements over stochastic sampling are observed.
Entanglement and quantum discord dynamics of two atoms under practical feedback control
Yang Li; Bin Luo; Hong Guo
2011-04-08
We study the dynamics of two identical atoms resonantly coupled to a single-mode cavity under practical feedback control, and focus on the detection inefficiency. The entanglement is induced to vanish in finite time by the inefficiency of detection. Counterintuitively, the asymptotic entanglement and quantum discord can be increased by the inefficiency of detection. The noise of detection triggers control field to create entanglement and discord when no photon are emitted from the atoms. Furthermore, sudden change happens to the dynamics of entanglement.
Entanglement and quantum discord dynamics of two atoms under practical feedback control
Li Yang; Luo Bin; Guo Hong [CREAM Group, State Key Laboratory of Advanced Optical Communication Systems and Networks, School of Electronics Engineering and Computer Science, and Center for Computational Science and Engineering (CCSE), Peking University, Beijing 100871 (China)
2011-07-15
We study the dynamics of two identical atoms resonantly coupled to a single-mode cavity under practical feedback control, and focus on the detection inefficiency. The entanglement is induced to vanish in finite time by the inefficiency of detection. Counterintuitively, the asymptotic entanglement and quantum discord can be increased by the inefficiency of detection. The noise of detection triggers the control field to create entanglement and discord when no photons are emitted from the atoms. Furthermore, sudden change happens to the dynamics of entanglement.
Ultrafast carrier dynamics in CuInS{sub 2} quantum dots
Sun, Jianhui [Institute of Physics, University of Tsukuba, Tsukuba 305-8571 (Japan); State Key Laboratory of Luminescence and Applications, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun 130033 (China); University of Chinese Academy of Sciences, Beijing 100039 (China); Zhu, Dehua [College of Mechanical and Electrical Engineering, Wenzhou University, Wenzhou 325035 (China); Zhao, Jialong, E-mail: zhaojl@ciomp.ac.cn [State Key Laboratory of Luminescence and Applications, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun 130033 (China); College of Mechanical and Electrical Engineering, Wenzhou University, Wenzhou 325035 (China); Ikezawa, Michio; Masumoto, Yasuaki, E-mail: masumoto@physics.px.tsukuba.ac.jp [Institute of Physics, University of Tsukuba, Tsukuba 305-8571 (Japan); Wang, Xiuying [State Key Laboratory of Luminescence and Applications, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun 130033 (China)
2014-01-13
The ultrafast carrier dynamics in CuInS{sub 2} (CIS) quantum dots (QDs) was studied by means of femtosecond transient absorption (TA) spectroscopy. The size-dependent 1S transition energy determined from bleaching spectra is in agreement with that calculated on the finite-depth-well model in the effective mass approximation. The TA bleaching comes from filling of electron quantized levels, allowing us to know the dynamics of the 1S electron in CIS QDs. The sub-100-ps electron trapping at surface defects in bare QDs accelerates with decreasing QD size, while is effectively suppressed in well-passivated CIS/ZnS core/shell QDs.
NASA Astrophysics Data System (ADS)
Green, D. G.; Harvey, C. N.
2015-07-01
We present the Fortran program SIMLA, which is designed for the study of charged particle dynamics in laser and other background fields. The dynamics can be determined classically via the Lorentz force and Landau-Lifshitz equations or, alternatively, via the simulation of photon emission events determined by strong-field quantum-electrodynamics amplitudes and implemented using Monte-Carlo routines. Multiple background fields can be included in the simulation and, where applicable, the propagation direction, field type (plane wave, focussed paraxial, constant crossed, or constant magnetic), and time envelope of each can be independently specified.
Linear dynamics subject to thermal fluctuations and non-Gaussian noise: from classical to quantum
NASA Astrophysics Data System (ADS)
Köpke, M.; Ankerhold, J.
2013-04-01
The dynamics of a linear system embedded in a heat bath environment and subject to white non-Gaussian noise is studied. Classical higher-order cumulants in coordinate space are derived for Poissonian noise and their impact on the dynamics and on asymptotic steady-state distributions is analyzed. In the quantum regime, non-Gaussian properties are present in reduced density in coordinate representation, but in energy representation they exist on a transient time scale only, due to symmetry. Within an exactly solvable model, our results provide insight into mechanisms of linear detectors as sensors for non-Gaussian noise at high and low temperatures.
NASA Astrophysics Data System (ADS)
Gupta, Manish K.; Navarro, Erik J.; Moulder, Todd A.; Mueller, Jason D.; Balouchi, Ashkan; Brown, Katherine L.; Lee, Hwang; Dowling, Jonathan P.
2015-03-01
The implementation of polarization-based quantum communication is limited by signal loss and decoherence caused by the birefringence of a single-mode fiber. We investigate the Knill dynamical decoupling scheme, implemented using half-wave plates, to minimize decoherence and show that a fidelity greater than 99% can be achieved in absence of rotation error and fidelity greater than 96% can be achieved in presence of rotation error. Such a scheme can be used to preserve any quantum state with high fidelity and has potential application for constructing all optical quantum delay line, quantum memory, and quantum repeater.
NASA Astrophysics Data System (ADS)
Gupta, Manish K.; Navarro, Erik J.; Moulder, Todd A.; Mueller, Jason D.; Balouchi, Ashkan; Brown, Katherine L.; Lee, Hwang; Dowling, Jonathan P.
2015-03-01
The implementation of polarization-based quantum communication is limited by signal loss and decoherence caused by the birefringence of a single-mode fiber. We investigate the Knill dynamical decoupling scheme, implemented using half-wave plates, to minimize decoherence and show that a fidelity greater than 99 % can be achieved in the absence of rotation error and a fidelity greater than 96 % can be achieved in the presence of rotation error. Such a scheme can be used to preserve any quantum state with high fidelity and has potential application for constructing all optical quantum delay lines, quantum memory, and quantum repeaters.
On the rate of convergence for the mean field approximation of many-body quantum dynamics
Zied Ammari; Marco Falconi; Boris Pawilowski
2014-11-23
We consider the time evolution of quantum states by many-body Schr\\"odinger dynamics and study the rate of convergence of their reduced density matrices in the mean field limit. If the prepared state at initial time is of coherent or factorized type and the number of particles $n$ is large enough then it is known that $1/n$ is the correct rate of convergence at any time. We show in the simple case of bounded pair potentials that the previous rate of convergence holds in more general situations with possibly correlated prepared states. In particular, it turns out that the coherent structure at initial time is unessential and the important fact is rather the speed of convergence of all reduced density matrices of the prepared states. We illustrate our result with several numerical simulations and examples of multi-partite entangled quantum states borrowed from quantum information.
Noise Induced Dissipation in Discrete-Time Classical and Quantum Dynamical Systems
Lech Wolowski
2004-06-26
We introduce a new characteristics of chaoticity of classical and quantum dynamical systems by defining the notion of the dissipation time which enables us to test how the system responds to the noise and in particular to measure the speed at which an initially closed, conservative system converges to the equilibrium when subjected to noisy (stochastic) perturbations. We prove fast dissipation result for classical Anosov systems and general exponentially mixing maps. Slow dissipation result is proved for regular systems including non-weakly mixing maps. In quantum setting we study simultaneous semiclassical and small noise asymptotics of the dissipation time of quantized toral symplectomorphisms (generalized cat maps) and derive sharp bounds for semiclassical regime in which quantum-classical correspondence of dissipation times holds.
Wu, C.-H.; Lee, D.-S. [Department of Physics, National Dong-Hwa University, Hualien, Taiwan (China)
2005-06-15
We employ the Schwinger-Keldysh formalism to study the nonequilibrium dynamics of the mirror with perfect reflection moving in a quantum field. In the case where the mirror undergoes the small displacement, the coarse-grained effective action is obtained by integrating out the quantum field with the method of influence functional. The semiclassical Langevin equation is derived, and is found to involve two levels of backreaction effects on the dynamics of mirrors: radiation reaction induced by the motion of the mirror and backreaction dissipation arising from fluctuations in quantum field via a fluctuation-dissipation relation. Although the corresponding theorem of fluctuation and dissipation for the case with the small mirror's displacement is of model independence, the study from the first principles derivation shows that the theorem is also independent of the regulators introduced to deal with short-distance divergences from the quantum field. Thus, when the method of regularization is introduced to compute the dissipation and fluctuation effects, this theorem must be fulfilled as the results are obtained by taking the short-distance limit in the end of calculations. The backreaction effects from vacuum fluctuations on moving mirrors are found to be hardly detected while those effects from thermal fluctuations may be detectable.
Quantum control of orbital and spin dynamics in diamond using ultrafast optical pulses
NASA Astrophysics Data System (ADS)
Heremans, F. Joseph
2015-03-01
Optically addressable spin defects in solid-state materials have shown great potential for applications ranging from metrology to quantum information processing. Many of these experiments require a detailed understanding of the full Hamiltonian dynamics in order to develop precise quantum control. Here we use picosecond resonant optical pulses to investigate the coherent orbital and spin dynamics of the nitrogen-vacancy (NV) center in diamond, over timescales spanning six orders of magnitude. We implement an ultrafast optical pump-probe technique to study the NV center's orbital-doublet, spin-triplet excited state at cryogenic temperatures (T < 20 K), where the excited state becomes stable and optically coherent with the ground state. This technique, coupled with optical polarization selection rules, allows us to probe the coherent orbital dynamics of the NV center's excited state. These experiments reveal dynamics on femtosecond to nanosecond timescales due to the interplay between the ground and excited state orbital levels. This all-optical technique also provides a method to dynamically control the spin state of the NV center by harnessing the excited state structure. Through studying the spin dynamics of the NV center with coherent pulses of light, we are able to rotate the spin state on sub-nanosecond timescales. Furthermore, by tuning the excited-state spin Hamiltonian with an external magnetic field, we demonstrate arbitrary-axis spin rotations through controlled unitary evolution of the spin state. Extending this to the full excited-state manifold, we develop a time-domain quantum tomography technique to precisely map the NV center's excited state Hamiltonian. These techniques generalize to other systems and can be a powerful tool in characterizing and controlling qubits in other optically addressable spin systems. This work is supported by the AFOSR and NSF.
Quantum Mechanics Studies of Cellobiose Conformations
Technology Transfer Automated Retrieval System (TEKTRAN)
Three regions of the Phi,Psi space of cellobiose were analyzed with quantum mechanics. A central region, in which most crystal structures are found, was covered by a 9 x 9 grid of 20° increments of Phi and Psi. Besides these 81 constrained minimizations, we studied two central sub-regions and two re...
Dynamical eigenfunctions and critical density in loop quantum cosmology
David A. Craig
2012-12-31
We offer a new, physically transparent argument for the existence of the critical, universal maximum matter density in loop quantum cosmology for the case of a flat Friedmann-Lemaitre-Robertson-Walker cosmology with scalar matter. The argument is based on the existence of a sharp exponential ultraviolet cutoff in momentum space on the eigenfunctions of the quantum cosmological dynamical evolution operator (the gravitational part of the Hamiltonian constraint), attributable to the fundamental discreteness of spatial volume in loop quantum cosmology. The existence of the cutoff is proved directly from recently found exact solutions for the eigenfunctions for this model. As a consequence, the operators corresponding to the momentum of the scalar field and the spatial volume approximately commute. The ultraviolet cutoff then implies that the scalar momentum, though not a bounded operator, is in effect bounded on subspaces of constant volume, leading to the upper bound on the expectation value of the matter density. The maximum matter density is universal (i.e. independent of the quantum state) because of the linear scaling of the cutoff with volume. These heuristic arguments are supplemented by a new proof in the volume representation of the existence of the maximum matter density. The techniques employed to demonstrate the existence of the cutoff also allow us to extract the large volume limit of the exact eigenfunctions, confirming earlier numerical and analytical work showing that the eigenfunctions approach superpositions of the eigenfunctions of the Wheeler-DeWitt quantization of the same model. We argue that generic (not just semiclassical) quantum states approach symmetric superpositions of expanding and contracting universes.
Three Dimensional Characterization of Quantum Vortex Dynamics in Superfluid Helium
NASA Astrophysics Data System (ADS)
Meichle, David; Lathrop, Daniel
2015-03-01
Vorticity is constrained to line-like topological defects in quantum superfluids, such as liquid Helium below the Lambda transition. We have invented a novel method to disperse fluorescent nanoparticles directly into the superfluid which become trapped on the vortex cores, providing optical tracers. Using a newly constructed multi-camera stereographic microscope, we present data dynamically characterizing vortex reconnections and the subsequent emission of Kelvin waves fully in three dimensions. Statistics of thermally driven counterflow will be compared in 3D to previous measurements in projection.
Magnetooptics and dynamics of a magnetic polaron in semimagnetic CdSe\\/ZnMnSe quantum dots
S. V. Zaitsev; H. Schömig; A. Forchel; G. Bacher
2007-01-01
The magnetooptics and picosecond dynamics of the radiative recombination of excitons in self-assembled semimagnetic CdSe\\/ZnMnSe\\u000a quantum dots is studied at low temperatures. The behavior of individual quantum dots in a magnetic field and with an increase\\u000a in temperature is indicative of a strong exchange interaction of excitons and magnetic Mn ions giving rise to a quasi-zero-dimensional\\u000a exciton magnetic polaron. When
Dynamics of Entropy in Quantum-like Model of Decision Making
NASA Astrophysics Data System (ADS)
Basieva, Irina; Khrennikov, Andrei; Asano, Masanari; Ohya, Masanori; Tanaka, Yoshiharu
2011-03-01
We present a quantum-like model of decision making in games of the Prisoner's Dilemma type. By this model the brain processes information by using representation of mental states in complex Hilbert space. Driven by the master equation the mental state of a player, say Alice, approaches an equilibrium point in the space of density matrices. By using this equilibrium point Alice determines her mixed (i.e., probabilistic) strategy with respect to Bob. Thus our model is a model of thinking through decoherence of initially pure mental state. Decoherence is induced by interaction with memory and external environment. In this paper we study (numerically) dynamics of quantum entropy of Alice's state in the process of decision making. Our analysis demonstrates that this dynamics depends nontrivially on the initial state of Alice's mind on her own actions and her prediction state (for possible actions of Bob.)
Dynamics of Crowd Behaviors: From Complex Plane to Quantum Random Fields
NASA Astrophysics Data System (ADS)
Ivancevic, Vladimir G.; Reid, Darryn J.
2015-11-01
The following sections are included: * Complex Plane Dynamics of Crowds and Groups * Introduction * Complex-Valued Dynamics of Crowd and Group Behaviors * Kähler Geometry of Crowd and Group Dynamics * Computer Simulations of Crowds and Croups Dynamics * Braids of Agents' Behaviors in the Complex Plane * Hilbert-Space Control of Crowds and Groups Dynamics * Quantum Random Fields: A Unique Framework for Simulation, Optimization, Control and Learning * Introduction * Adaptive Quantum Oscillator * Optimization and Learning on Banach and Hilbert Spaces * Appendix * Complex-Valued Image Processing * Linear Integral Equations * Riemann-Liouville Fractional Calculus * Rigorous Geometric Quantization * Supervised Machine-Learning Methods * First-Order Logic and Quantum Random Fields
One-step implementation of the 1->3 orbital state quantum cloning machine via quantum Zeno dynamics
Shao Xiaoqiang; Wang Hongfu; Zhang Shou [Center for the Condensed-Matter Science and Technology, Department of Physics, Harbin Institute of Technology, Harbin, Heilongjiang 150001 (China); Department of Physics, College of Science, Yanbian University, Yanji, Jilin 133002 (China); Chen Li [Department of Physics, College of Science, Yanbian University, Yanji, Jilin 133002 (China); Zhao Yongfang [Center for the Condensed-Matter Science and Technology, Department of Physics, Harbin Institute of Technology, Harbin, Heilongjiang 150001 (China); Yeon, Kyu-Hwang [BK21 Program Physics and Department of Physics, College of Natural Science, Chungbuk National University, Cheonju, Chungbuk 361-763 (Korea, Republic of)
2009-12-15
We present an approach for implementation of a 1->3 orbital state quantum cloning machine based on the quantum Zeno dynamics via manipulating three rf superconducting quantum interference device (SQUID) qubits to resonantly interact with a superconducting cavity assisted by classical fields. Through appropriate modulation of the coupling constants between rf SQUIDs and classical fields, the quantum cloning machine can be realized within one step. We also discuss the effects of decoherence such as spontaneous emission and the loss of cavity in virtue of master equation. The numerical simulation result reveals that the quantum cloning machine is especially robust against the cavity decay, since all qubits evolve in the decoherence-free subspace with respect to cavity decay due to the quantum Zeno dynamics.
Entropic Dynamics: from Entropy and Information Geometry to Hamiltonians and Quantum Mechanics
Ariel Caticha; Daniel Bartolomeo; Marcel Reginatto
2014-12-17
Entropic Dynamics is a framework in which quantum theory is derived as an application of entropic methods of inference. There is no underlying action principle. Instead, the dynamics is driven by entropy subject to the appropriate constraints. In this paper we show how a Hamiltonian dynamics arises as a type of non-dissipative entropic dynamics. We also show that the particular form of the "quantum potential" that leads to the Schroedinger equation follows naturally from information geometry.
Instability and dynamics of two nonlinearly coupled intense laser beams in a quantum plasma
Wang Yunliang [International Centre for Advanced Studies in Physical Sciences and Institute for Theoretical Physics, Faculty of Physics and Astronomy, Ruhr University Bochum, D-44780 Bochum (Germany); Department of Physics, School of Mathematics and Physics, University of Science and Technology Beijing, Beijing 100083 (China); Shukla, P. K. [International Centre for Advanced Studies in Physical Sciences and Institute for Theoretical Physics, Faculty of Physics and Astronomy, Ruhr University Bochum, D-44780 Bochum (Germany); Department of Mechanical and Aerospace Engineering and Center for Energy Research, University of California San Diego, La Jolla, California 92093 (United States); School of Chemistry and Physics, KwaZulu-Natal University, Durban 4000 (South Africa); Eliasson, B. [International Centre for Advanced Studies in Physical Sciences and Institute for Theoretical Physics, Faculty of Physics and Astronomy, Ruhr University Bochum, D-44780 Bochum (Germany)
2013-01-15
We consider nonlinear interactions between two relativistically strong laser beams and a quantum plasma composed of degenerate electron fluids and immobile ions. The collective behavior of degenerate electrons is modeled by quantum hydrodynamic equations composed of the electron continuity, quantum electron momentum (QEM) equation, as well as the Poisson and Maxwell equations. The QEM equation accounts the quantum statistical electron pressure, the quantum electron recoil due to electron tunneling through the quantum Bohm potential, electron-exchange, and electron-correlation effects caused by electron spin, and relativistic ponderomotive forces (RPFs) of two circularly polarized electromagnetic (CPEM) beams. The dynamics of the latter are governed by nonlinear wave equations that include nonlinear currents arising from the relativistic electron mass increase in the CPEM wave fields, as well as from the beating of the electron quiver velocity and electron density variations reinforced by the RPFs of the two CPEM waves. Furthermore, nonlinear electron density variations associated with the driven (by the RPFs) quantum electron plasma oscillations obey a coupled nonlinear Schroedinger and Poisson equations. The nonlinearly coupled equations for our purposes are then used to obtain a general dispersion relation (GDR) for studying the parametric instabilities and the localization of CPEM wave packets in a quantum plasma. Numerical analyses of the GDR reveal that the growth rate of a fastest growing parametrically unstable mode is in agreement with the result that has been deduced from numerical simulations of the governing nonlinear equations. Explicit numerical results for two-dimensional (2D) localized CPEM wave packets at nanoscales are also presented. Possible applications of our investigation to intense laser-solid density compressed plasma experiments are highlighted.
Trajectory-guided configuration interaction simulations of multidimensional quantum dynamics
Habershon, Scott [Centre for Computational Chemistry, School of Chemistry, University of Bristol, Bristol BS8 1TS (United Kingdom)
2012-02-07
We propose an approach to modelling multidimensional quantum systems which uses direct-dynamics trajectories to guide wavefunction propagation. First, trajectory simulations are used to generate a sample of dynamically relevant configurations on the potential energy surface (PES). Second, the sampled configurations are used to construct an n-mode representation of the PES using a greedy algorithm. Finally, the time-dependent Schroedinger equation is solved using a configuration interaction expansion of the wavefunction, with individual basis functions derived directly from the 1-mode contributions to the n-mode PES. This approach is successfully demonstrated by application to a 20-dimensional benchmark problem describing tunnelling in the presence of coupled degrees of freedom.
Dynamical invariants and nonadiabatic geometric phases in open quantum systems
Sarandy, M. S. [Departamento de Ciencias Exatas, Polo Universitario de Volta Redonda, Universidade Federal Fluminense, Avenida dos Trabalhadores 420, Volta Redonda, 27255-125 Rio de Janeiro (Brazil); Duzzioni, E. I. [Centro de Ciencias Naturais e Humanas, Universidade Federal do ABC, R. Santa Adelia 166, Santo Andre 09210-170, Sao Paulo (Brazil); Moussa, M. H. Y. [Instituto de Fisica de Sao Carlos, Universidade de Sao Paulo, Caixa Postal 369, Sao Carlos, 13560-970, Sao Paulo (Brazil)
2007-11-15
We introduce an operational framework to analyze nonadiabatic Abelian and non-Abelian, cyclic and noncyclic, geometric phases in open quantum systems. In order to remove the adiabaticity condition, we generalize the theory of dynamical invariants to the context of open systems evolving under arbitrary convolutionless master equations. Geometric phases are then defined through the Jordan canonical form of the dynamical invariant associated with the superoperator that governs the master equation. As a by-product, we provide a sufficient condition for the robustness of the phase against a given decohering process. We illustrate our results by considering a two-level system in a Markovian interaction with the environment, where we show that the nonadiabatic geometric phase acquired by the system can be constructed in such a way that it is robust against both dephasing and spontaneous emission.
Spinor Bose gases: Symmetries, magnetism, and quantum dynamics
NASA Astrophysics Data System (ADS)
Stamper-Kurn, Dan M.; Ueda, Masahito
2013-07-01
Spinor Bose gases form a family of quantum fluids manifesting both magnetic order and superfluidity. This article reviews experimental and theoretical progress in understanding the static and dynamic properties of these fluids. The connection between system properties and the rotational symmetry properties of the atomic states and their interactions are investigated. Following a review of the experimental techniques used for characterizing spinor gases, their mean-field and many-body ground states, both in isolation and under the application of symmetry-breaking external fields, are discussed. These states serve as the starting point for understanding low-energy dynamics, spin textures, and topological defects, effects of magnetic-dipole interactions, and various nonequilibrium collective spin-mixing phenomena. The paper aims to form connections and establish coherence among the vast range of works on spinor Bose gases, so as to point to open questions and future research opportunities.
Protection of quantum systems by nested dynamical decoupling
Wang Zhenyu; Liu Renbao [Department of Physics, Chinese University of Hong Hong, Shatin, N. T. (Hong Kong)
2011-02-15
Based on a theorem we establish on dynamical decoupling of time-dependent systems, we present a scheme of nested Uhrig dynamical decoupling (NUDD) to protect multiqubit systems in generic quantum baths to arbitrary decoupling orders, using only single-qubit operations. The number of control pulses in NUDD increases polynomially with the decoupling order. For general multilevel systems, this scheme can preserve a set of unitary Hermitian system operators which mutually either commute or anticommute, and hence all operators in the Lie algebra generated from this set of operators, generating an effective symmetry group for the system up to a given order of precision. NUDD can be implemented with pulses of finite amplitude, up to an error in the second order of the pulse durations.
Kojima, H; Yamada, A; Okazaki, S
2015-05-01
The intramolecular proton transfer reaction of malonaldehyde in neon solvent has been investigated by mixed quantum-classical molecular dynamics (QCMD) calculations and fully classical molecular dynamics (FCMD) calculations. Comparing these calculated results with those for malonaldehyde in water reported in Part I [A. Yamada, H. Kojima, and S. Okazaki, J. Chem. Phys. 141, 084509 (2014)], the solvent dependence of the reaction rate, the reaction mechanism involved, and the quantum effect therein have been investigated. With FCMD, the reaction rate in weakly interacting neon is lower than that in strongly interacting water. However, with QCMD, the order of the reaction rates is reversed. To investigate the mechanisms in detail, the reactions were categorized into three mechanisms: tunneling, thermal activation, and barrier vanishing. Then, the quantum and solvent effects were analyzed from the viewpoint of the reaction mechanism focusing on the shape of potential energy curve and its fluctuations. The higher reaction rate that was found for neon in QCMD compared with that found for water solvent arises from the tunneling reactions because of the nearly symmetric double-well shape of the potential curve in neon. The thermal activation and barrier vanishing reactions were also accelerated by the zero-point energy. The number of reactions based on these two mechanisms in water was greater than that in neon in both QCMD and FCMD because these reactions are dominated by the strength of solute-solvent interactions. PMID:25956108
NASA Astrophysics Data System (ADS)
Kojima, H.; Yamada, A.; Okazaki, S.
2015-05-01
The intramolecular proton transfer reaction of malonaldehyde in neon solvent has been investigated by mixed quantum-classical molecular dynamics (QCMD) calculations and fully classical molecular dynamics (FCMD) calculations. Comparing these calculated results with those for malonaldehyde in water reported in Part I [A. Yamada, H. Kojima, and S. Okazaki, J. Chem. Phys. 141, 084509 (2014)], the solvent dependence of the reaction rate, the reaction mechanism involved, and the quantum effect therein have been investigated. With FCMD, the reaction rate in weakly interacting neon is lower than that in strongly interacting water. However, with QCMD, the order of the reaction rates is reversed. To investigate the mechanisms in detail, the reactions were categorized into three mechanisms: tunneling, thermal activation, and barrier vanishing. Then, the quantum and solvent effects were analyzed from the viewpoint of the reaction mechanism focusing on the shape of potential energy curve and its fluctuations. The higher reaction rate that was found for neon in QCMD compared with that found for water solvent arises from the tunneling reactions because of the nearly symmetric double-well shape of the potential curve in neon. The thermal activation and barrier vanishing reactions were also accelerated by the zero-point energy. The number of reactions based on these two mechanisms in water was greater than that in neon in both QCMD and FCMD because these reactions are dominated by the strength of solute-solvent interactions.
Cold atom dynamics in a quantum optical lattice potential
Christoph Maschler; Helmut Ritsch
2006-02-27
We study a generalized cold atom Bose Hubbard model, where the periodic optical potential is formed by a cavity field with quantum properties. On the one hand the common coupling of all atoms to the same mode introduces cavity mediated long range atom-atom interactions and on the other hand atomic backaction on the field introduces atom-field entanglement. This modifies the properties of the associated quantum phase transitions and allows for new correlated atom-field states including superposition of different atomic quantum phases. After deriving an approximative Hamiltonian including the new long range interaction terms we exhibit central physical phenomena at generic configurations of few atoms in few wells. We find strong modifications of population fluctuations and next-nearest neighbor correlations near the phase transition point.
A study on quantum discord in Gaussian states
NASA Astrophysics Data System (ADS)
Yang, Xiong; Huang, Guo Hui; Fang, Mao Fa
2015-04-01
We consider analytically the dynamic behaviors of quantum correlation measured by a quantum discord between two mode Gaussian states coupled to a common squeezed thermal reservoir. We derive the conditions to produce and enlarge quantum discord. If the two modes are initially in factorized squeezed states, we reveal that the thermal bath can not only produce but also amplify the two-mode quantum discord provided that initial squeezing parameters can control properly. Whereas two-modes are initially in a two-mode squeezed vacuum state, whether quantum discord is increased or reduced has a strong relationship with the difference between the squeezing parameters of thermal bath and of considered state.
Density-dependent carrier dynamics in a quantum dots-in-a-well heterostructure
Krishna, Sanjay
The incorporation of semiconductor quantum dots into different heterostructures for applications in nanoscale lasingDensity-dependent carrier dynamics in a quantum dots-in-a-well heterostructure R. P. Prasankumar,1 dots-in-a-well DWELL heterostructure. We observe excitation-dependent shifts of the quantum dot energy
Quantum Mechanics as a Generalization of Nambu Dynamics to the Weyl-Wigner Formalism *, **
Morrison, Philip J.,
, j Quantum Mechanics as a Generalization of Nambu Dynamics to the Weyl-Wigner Formalism *, ** Iwo obtain the phase-space formulation of quantum mechanics. The noncanonical bracket for the Wigner function-72072 Tiibingen #12;I I, 10 I. Bialynicki-Birula and P.1. Morrison . Quantum Mechanics
Mixed quantum-classical molecular dynamics: Aspects of the multithreads algorithm
Schofield, Jeremy
Mixed quantum-classical molecular dynamics: Aspects of the multithreads algorithm Chun-Cheng Wan. In addition, most semi- classical methods do not take advantage of the fact that the quantum interactions. In contrast, the mixed quantum-classical molecular ap- proach to nonadiabatic systems separates the full
Quantum decoherence and the isotope effect in condensed phase nonadiabatic molecular dynamics of this isotope dependence of the nonadiabatic transition rate on changes in the quantum decoherence time to simulate the physics and chemistry of interest by treating a few select degrees of freedom quantum mechani
The influence of laser field noise on controlled quantum dynamics.
Sola, Ignacio R; Rabitz, Herschel
2004-05-15
The influence of laser noise on the dynamics of simple quantum systems is analyzed. An anharmonic ladder is chosen for illustration and several pulses are obtained that optimize the yield of a quantum transition by constraining the laser parameters. The following models of laser noise are introduced: Amplitude white noise, phase white noise, frequency white noise and shot-to-shot static noise in the different pulse parameters. It is shown that the optimal pulses are robust to white amplitude noise, since the system acts as a dynamical filter. White phase noise affects the optimal pulses in a similar way by reducing the pulse area. This effect can be easily compensated for by pulse amplitude rescaling, up to a high level of noise. White frequency noise reduces the pulse area and induces spectral broadening, more strongly affecting the high frequency components. It can be partially compensated for by amplitude rescaling. The effects of static noise in the parameters cannot be easily corrected. It is shown that optimal pulses that drive n-photon transitions become more sensitive to noise in the amplitude and less sensitive to noise in the frequency as n increases. The effects of noise in the relative phase rapidly become constant for a large number of interfering pathways. PMID:15267836
NASA Astrophysics Data System (ADS)
Guo, You-Neng; Fang, Mao-Fa; Yang, Bai-Yuan; Zou, Hong-Mei; Liu, Xiang
2015-03-01
In this paper, the dynamics and protection of quantum discord for two uncoupled qubits driven by classical phase noisy laser(CPNL) is investigated. The results show that, the dynamics of quantum discord depends on the ratio of CPNL rate and the system-environment coupling strength. The quantum discord can be well protected by increasing the ratio in the Markovian classical noise region or by decreasing the ratio in the non-Markovian classical noise region. Besides, we explain the revivals of the quantum discord by means of the increase of parameter used to quantify non-Markovianty of the single qubit dynamics in the non-Markovian classical noise region.
Nonadiabatic molecular dynamics simulation: An approach based on quantum measurement picture
Feng, Wei; Xu, Luting [Department of Physics, Beijing Normal University, Beijing 100875 (China); Li, Xin-Qi, E-mail: lixinqi@bnu.edu.cn [Department of Physics, Beijing Normal University, Beijing 100875 (China); Key Laboratory of Theoretical and Computational Photochemistry of Ministry of Education, Beijing Normal University, Beijing 100875 (China); Fang, Weihai [Key Laboratory of Theoretical and Computational Photochemistry of Ministry of Education, Beijing Normal University, Beijing 100875 (China); Department of Chemistry, Beijing Normal University, Beijing 100875 (China); Yan, YiJing [Department of Chemistry, Hong Kong University of Science and Technology, Kowloon (Hong Kong)
2014-07-15
Mixed-quantum-classical molecular dynamics simulation implies an effective quantum measurement on the electronic states by the classical motion of atoms. Based on this insight, we propose a quantum trajectory mean-field approach for nonadiabatic molecular dynamics simulations. The new protocol provides a natural interface between the separate quantum and classical treatments, without invoking artificial surface hopping algorithm. Moreover, it also bridges two widely adopted nonadiabatic dynamics methods, the Ehrenfest mean-field theory and the trajectory surface-hopping method. Excellent agreement with the exact results is illustrated with representative model systems, including the challenging ones for traditional methods.
Longhi, Stefano, E-mail: stefano.longhi@fisi.polimi.it
2014-06-15
Quantum recurrence and dynamic localization are investigated in a class of ac-driven tight-binding Hamiltonians, the Krawtchouk quantum chain, which in the undriven case provides a paradigmatic Hamiltonian model that realizes perfect quantum state transfer and mirror inversion. The equivalence between the ac-driven single-particle Krawtchouk Hamiltonian H{sup -hat} (t) and the non-interacting ac-driven bosonic junction Hamiltonian enables to determine in a closed form the quasi energy spectrum of H{sup -hat} (t) and the conditions for exact wave packet reconstruction (dynamic localization). In particular, we show that quantum recurrence, which is predicted by the general quantum recurrence theorem, is exact for the Krawtchouk quantum chain in a dense range of the driving amplitude. Exact quantum recurrence provides perfect wave packet reconstruction at a frequency which is fractional than the driving frequency, a phenomenon that can be referred to as fractional dynamic localization.
Probability Theories with Dynamic Causal Structure: A New Framework for Quantum Gravity
Lucien Hardy; Ontario N
2005-01-01
Quantum theory is a probabilistic theory with fixed causal structure. General relativity is a deterministic theory but where the causal structure is dynamic. It is reasonable to expect that quantum gravity will be a probabilistic theory with dynamic causal structure. The purpose of this paper is to present a framework for such a probability calculus. We define an operational notion
Quantum Field Theory of Classically Unstable Hamiltonian Dynamics
Yossi Strauss; Lawrence P. Horwitz; Jacob Levitan; Asher Yahalom
2014-07-20
We study a class of dynamical systems for which the motions can be described in terms of geodesics on a manifold (ordinary potential models can be cast into this form by means of a conformal map). It is rigorously proven that the geodesic deviation equation of Jacobi, constructed with a second covariant derivative, is unitarily equivalent to that of a parametric harmonic oscillator, and we study the second quatization of this oscillator. The excitations of the Fock space modes correspond to the emission and absorption of quanta into the dynamical medium, thus associating unstable behavior of the dynamical system with calculable fluctuations in an ensamble with possible thermodynamic consequences.
Wavefunction dynamics in a quantum-dot electron pump under a high magnetic field
NASA Astrophysics Data System (ADS)
Ryu, Sungguen; Kataoka, Masaya; Sim, Heung-Sun
2015-03-01
A quantum-dot electron pump, formed and operated by applying time-dependent potential barriers to a two dimensional electron gas system, provides a promising redefinition of ampere. The pump operation consists of capturing an electron from a reservoir into a quantum dot and ejecting it to another reservoir. The capturing process has been theoretically understood by a semi-classical treatment of the tunneling between the dot and reservoir. But the dynamics of the wavefunction of the captured electron in the ejection process has not been theoretically addressed, although it is useful for enhancing pump accuracy and for utilizing the pump as a single-electron source for mesoscopic quantum electron devices. We study the dynamics under a strong magnetic field that leads to magnetic confinement of the captured electron, which dominates over the electrostatic confinement of the dot. We find that the wave packet of the captured electron has the Gaussian form with the width determined by the strength of the magnetic field, and that the time evolution of the packet follows the classical drift motion, with maintaining the Gaussian form. We discuss the possible signatures of the wave packet dynamics in experiments.
Quantum State Resolved Photodissociation Dynamics of the Formyl Radical.
NASA Astrophysics Data System (ADS)
Neyer, David William
The photodissociation dynamics of the formyl (HCO) radical have been investigated both experimentally and theoretically. HCO molecules, produced in a molecular beam by the laser photolysis of acetaldehyde, were excited to metastable levels with quantum state resolution. The rotational and vibrational states of the CO products from the dissociation of these levels were probed by laser-induced fluorescence using a tunable vacuum ultraviolet laser. Measurement of detailed state-to-state dissociation cross sections and theoretical modeling of these dynamics have provided valuable information about the potential energy surface of the ground electronic state (X) of the HCO system. HCO was excited to predissociative levels of the first electronic state (A) characterized by their vibrational and K-rotational quantum numbers, and the rotational and vibrational populations of the CO products were measured. While the K-state excited in the HCO has little effect on the CO products, the vibrational character of the parent causes specific changes in the product state distributions. Addition of bending or C-H stretching quanta to the HCO parent leads to increased rotational excitation in the CO(nu =O) products. Adding C-O stretch to the parent state produces increased vibrational excitation in the CO products, The dynamics of this dissociation process, which involves Renner-Teller coupling between the X and A states, was modeled using classical trajectories calculated on a global X-state potential energy surface. Stimulated emission pumping (SEP) was used to prepare HCO in metastable resonances on the X state of HCO with vibrational and rotational resolution. The energies and linewidths of these resonances were measured, and the rotational and vibrational distributions of the CO products were determined. The linewidths and product state distributions show highly non-statistical behavior which depends on the vibrational character of the HCO resonance. The rotational distributions of the product CO molecules also show a marked dependence on the rotational state of the parent. The results are analyzed within the context of transition state wavefunctions using a modified Franck-Condon model and are compared to other detailed quantum mechanical dynamics calculations for HCO.
From classical to quantum non-equilibrium dynamics of Rydberg excitations in optical lattices
Marco Mattioli; Alexander W. Glaetzle; Wolfgang Lechner
2015-06-02
The glass phase and its quantum analog are prominent challenges of current non-equilibrium statistical mechanics and condensed matter physics. As a model system to study the transition from classical to quantum glassy dynamics, we propose a setup of laser driven three-level atoms trapped in an optical lattice. Tuning the strength of the laser driving to the intermediate level allows one to study the transition from a classical Kinetically Constrained Model to the coherent regime. For strong driving, Rydberg excitations evolve analogously to defects in the One-Spin Facilitated Model, a minimal model known to exhibit glassy dynamics. In our setup, the constraints result from the interplay between Rydberg interactions and the laser detuning from the Rydberg state. The emerging heterogeneous relaxation timescales are tuneable over several orders of magnitudes. In the opposite limit of weak driving of the intermediate level, we find an effective cluster model which describes the dynamics in a reduced subspace of the allowed number and positions of Rydberg excitations. This subspace is uniquely determined by the initial state and is characterized by a fixed number of clusters of Rydberg excitations. In addition, we investigate the influence of random fields on the classical relaxation. We find that the glassy dynamics can relax faster in the presence of weak random fields.
Quantum dynamics of ultrafast charge transfer at an oligothiophene-fullerene heterojunction
NASA Astrophysics Data System (ADS)
Tamura, Hiroyuki; Martinazzo, Rocco; Ruckenbauer, Matthias; Burghardt, Irene
2012-12-01
Following up on our recent study of ultrafast charge separation at oligothiophene-fullerene interfaces [H. Tamura, I. Burghardt, and M. Tsukada, J. Phys. Chem. C 115, 10205 (2011), 10.1021/jp203174e], we present here a detailed quantum dynamical perspective on the charge transfer process. To this end, electron-phonon coupling is included non-perturbatively, by an explicit quantum dynamical treatment using the multi-configuration time-dependent Hartree (MCTDH) method. Based upon a distribution of electron-phonon couplings determined from electronic structure studies, a spectral density is constructed and employed to parametrize a linear vibronic coupling Hamiltonian. The diabatic coupling is found to depend noticeably on the inter-fragment distance, whose effect on the dynamics is here investigated. MCTDH calculations of the nonadiabatic transfer dynamics are carried out for the two most relevant electronic states and 60 phonon modes. The electron transfer process is found to be ultrafast and mediated by electronic coherence, resulting in characteristic oscillatory features during a period of about 100 fs.
Quantum dynamics of solid Ne upon photo-excitation of a NO impurity: A Gaussian wave packet approach
NASA Astrophysics Data System (ADS)
Unn-Toc, W.; Uranga-Piña, Ll.; Meier, C.; Halberstadt, N.; Rubayo-Soneira, J.
2012-08-01
A high-dimensional quantum wave packet approach based on Gaussian wave packets in Cartesian coordinates is presented. In this method, the high-dimensional wave packet is expressed as a product of time-dependent complex Gaussian functions, which describe the motion of individual atoms. It is applied to the ultrafast geometrical rearrangement dynamics of NO doped cryogenic Ne matrices after femtosecond laser pulse excitation. The static deformation of the solid due to the impurity as well as the dynamical response after femtosecond excitation are analyzed and compared to reduced dimensionality studies. The advantages and limitations of this method are analyzed in the perspective of future applications to other quantum solids.
Prasankumar, Rohit P [Los Alamos National Laboratory; Taylor, Antoinette J [Los Alamos National Laboratory; Chow, W W [SNL; Attaluri, R S [UNM; Shenoi, R [UNM
2009-01-01
Semiconductor heterostructures incorporating multiple degrees of spatial confinement have recently attracted substantial interest for photonic applications. One example is the quantum dots-in-a-well (DWELL) heterostructure, consisting of zero-dimensional quantum dots embedded in a two-dimensional quantum well and surrounded by three-dimensional bulk material. This structure offers several advantages over conventional photonic devices while providing a model system for the study of light-matter interactions across multiple spatial dimensions. Here, we use ultrafast differential transmission spectroscopy2 to temporally and spectrally resolve density-dependent carrier dynamics in a DWELL heterostructure. We observe excitation-dependent shifts of the quantum dot energy levels at low densities, while at high densities we observe an anomalous induced absorption at the quantum dot excited state that is correlated to quantum well population dynamics. These studies of density-dependent light-matter interactions across multiple coupled spatial dimensions provide clues to the underlying physics governing quantum dot properties, with important implications for DWELL-based photonic devices.
Tacconi, M.; Gianturco, F. A.; Yurtsever, E.; Caruso, D. [Department of Chemistry, ''Sapienza'', University of Rome, Piazzale Aldo Moro 5, I-00185 Rome (Italy); Department of Chemistry, Koc University, Rumelifeneriyalu, Sariyer, TR-34450 Instabul (Turkey); Department of Chemistry, ''Sapienza,'' The University of Rome, Piazzale Aldo Moro 5, I-00185 Rome (Italy)
2011-07-15
The quantum dynamics of the rotational quenching of the {sup 24}MgH{sup +}(X {sup 1}{Sigma}{sup +}) molecular cation interacting with {sup 4}He({sup 1}S) as a buffer gas, at relative temperatures ranging from 1 K down to millikelvins, is described by accurate close coupling scattering calculations on an ab initio potential energy surface. The efficiency of the process is quantitatively analyzed by employing the ab initio quenching rates and cross sections and effective decay rate values are obtained from simple unimolecular kinetics over a broad range of trap conditions.
Car, R.; Parrinello, M.
1988-01-18
An amorphous silicon structure is obtained with a computer simulation based on a new molecular-dynamics technique in which the interatomic potential is derived from a parameter-free quantum mechanical method. Our results for the atomic structure, the phonon spectrum, and the electronic properties are in excellent agreement with experiment. In addition we study details of the microscopic dynamics which are not directly accessible to experiment. We find in particular that structural defects are associated with weak bonds. These may give rise to low-frequency vibrational modes.
Dynamical Quantum Phase Transitions in Systems with Broken-Symmetry Phases
NASA Astrophysics Data System (ADS)
Heyl, M.
2014-11-01
In this Letter it is shown that dynamical quantum phase transitions in Loschmidt echos control the nonequilibrium dynamics of the order parameter after particular quantum quenches in systems with broken-symmetry phases. A direct connection between Loschmidt echos and the order parameter dynamics is established which links nonequilibrium microscopic probabilities to the system's macroscopic dynamical properties. These concepts are illustrated numerically using exact diagonalization for quantum quenches in the X X Z chain with initial Néel states. An outlook is given on how to explore these predictions experimentally with ultracold gases in optical lattices.
Dynamical quantum phase transitions in systems with broken-symmetry phases
Markus Heyl
2014-11-21
In this work it is shown that dynamical quantum phase transitions in Loschmidt echos control the nonequilibrium dynamics of the order parameter after particular quantum quenches in systems with broken-symmetry phases. A direct connection between Loschmidt echos and the order parameter dynamics is established which links nonequilibrium microscopic probabilities to the system's macroscopic dynamical properties. These concepts are illustrated numerically using exact diagonalization for quantum quenches in the XXZ chain with initial N\\'eel states. An outlook is given how to explore these predictions experimentally with ultra-cold gases in optical lattices.
Quantum-Chemical Studies on TATB Processes
R. S. Patil; S. Radhakrishnan; P. M. Jadhav; V. D. Ghule; T. Soman
2010-01-01
Quantum chemical studies have gained paramount importance in screening of thermodynamically feasible chemical processes. The current investigation attempts to select an appropriate process for the synthesis of 1,3,5-triamino-2,4,6-trinitro benzene (TATB), a reasonably powerful insensitive high explosive (IHE) through density functional theory (DFT) calculations. Although, 1,3,5-trichlorobenzene (TCB) and 1,3,5-trihydroxybenzene (THB) routes for synthesis of TATB have been well established, this article
Quantum Dynamics of Many-body Spin Chains Using Atomic Ions
NASA Astrophysics Data System (ADS)
Senko, Crystal
2014-05-01
Quantum simulation, a field in which well-controlled quantum systems are used to study many-body physics that would otherwise be challenging to model, has undergone a great deal of progress in recent years. In particular, trapped ions have proven an excellent platform for simulating quantum magnetism, with their long-lived coherence times, tunable spin-spin interactions mediated by optical dipole forces, and ease of individual readout. The manipulation of more than 10 spins is now routine and has allowed the study of dynamics that will be difficult to simulate classically in larger systems, such as spectroscopy of excitation energies (arXiv:1401.5751) and the spread of spin correlations in a system with long-range interactions (arXiv:1401.5088). In the near future, we expect to apply these techniques to the study of a variety of phenomena such as prethermalization in an isolated quantum system, and to upgrade the apparatus so as to handle many tens of spins, a system size well beyond what is classically calculable. This work is supported by grants from the U.S. Army Research Office with funding from the DARPA OLE program, IARPA, and the MURI program; and the NSF Physics Frontier Center at JQI.
Rigol, Marcos [Physics Department, University of California, Davis, California 95616 (United States); Dunjko, Vanja; Olshanii, Maxim [Department of Physics and Astronomy, University of Southern California, Los Angeles, California 90089 (United States); Institute for Theoretical Atomic and Molecular Physics, Cambridge, Massachusetts 02138 (United States); Yurovsky, Vladimir [School of Chemistry, Tel Aviv University, Tel Aviv 69978 (Israel)
2007-02-02
In this Letter we pose the question of whether a many-body quantum system with a full set of conserved quantities can relax to an equilibrium state, and, if it can, what the properties of such a state are. We confirm the relaxation hypothesis through an ab initio numerical investigation of the dynamics of hard-core bosons on a one-dimensional lattice. Further, a natural extension of the Gibbs ensemble to integrable systems results in a theory that is able to predict the mean values of physical observables after relaxation. Finally, we show that our generalized equilibrium carries more memory of the initial conditions than the usual thermodynamic one. This effect may have many experimental consequences, some of which have already been observed in the recent experiment on the nonequilibrium dynamics of one-dimensional hard-core bosons in a harmonic potential [T. Kinoshita et al., Nature (London) 440, 900 (2006)].
NASA Astrophysics Data System (ADS)
Rigol, Marcos; Dunjko, Vanja; Yurovsky, Vladimir; Olshanii, Maxim
2007-02-01
In this Letter we pose the question of whether a many-body quantum system with a full set of conserved quantities can relax to an equilibrium state, and, if it can, what the properties of such a state are. We confirm the relaxation hypothesis through an ab initio numerical investigation of the dynamics of hard-core bosons on a one-dimensional lattice. Further, a natural extension of the Gibbs ensemble to integrable systems results in a theory that is able to predict the mean values of physical observables after relaxation. Finally, we show that our generalized equilibrium carries more memory of the initial conditions than the usual thermodynamic one. This effect may have many experimental consequences, some of which have already been observed in the recent experiment on the nonequilibrium dynamics of one-dimensional hard-core bosons in a harmonic potential [T. Kinoshita et al., Nature (London) 440, 900 (2006)NATUAS0028-083610.1038/nature04693].
Exhaust oxygen sensor dynamic study
Da Yu Wang; Eric Detwiler
2006-01-01
We used transfer function approach to investigate the dynamics of oxygen sensors in engine exhaust environment, operated in both Lambda and wide range sensing modes. We measured the sensor transfer functions of the sensor responses and compared with the model. All the dynamic mechanisms involved were identified. The dynamic contributions are from the louver-shield, the protection coating-layer, the sensing electrode
Cooperman, Joshua H
2014-01-01
The causal dynamical triangulations approach aims to construct a quantum theory of gravity as the continuum limit of a lattice-regularized model of dynamical geometry. A renormalization group scheme--in concert with finite size scaling analysis--is essential to this aim. Formulating and implementing such a scheme in the present context raises novel and notable conceptual and technical problems. I explored these problems, and, building on standard techniques, suggested potential solutions in the first paper of this two-part series. As an application of these solutions, I now propose a renormalization group scheme for causal dynamical triangulations. This scheme differs significantly from that studied recently by Ambjorn, Gorlich, Jurkiewicz, Kreienbuehl, and Loll.
Imaging mGluR5 dynamics in astrocytes using quantum dots.
Arizono, Misa; Bannai, Hiroko; Mikoshiba, Katsuhiko
2014-01-01
This unit describes the method that we have developed to clarify endogenous mGluR5 (metabotropic glutamate receptors 5) dynamics in astrocytes by single-particle tracking using quantum dots (QD-SPT). QD-SPT has been a powerful tool to examine the contribution of neurotransmitter receptor dynamics to synaptic plasticity. Neurotransmitter receptors are also expressed in astrocytes, the most abundant form of glial cell in the brain. mGluR5s, which evoke intracellular Ca(2+) signals upon receiving glutamate, contribute to the modulation of synaptic transmission efficacy and local blood flow by astrocytes. QD-SPT has previously revealed that the regulation of the lateral diffusion of mGluR5 on the plasma membrane is important for local Ca(2+) signaling in astrocytes. Determining how mGluR5 dynamics are regulated in response to neuronal input would enable a better understanding of neuron-astrocyte communication in future studies. PMID:24510777
Quantum dynamics of a kicked system with position-dependent effective mass
NASA Astrophysics Data System (ADS)
Vubangsi, M.; Tchoffo, M.; Fai, L. C.
2014-06-01
The quantum dynamics of a complexified position-dependent effective-mass system is considered within the framework of the ?-function kicking perturbation. The absorptive/dissipative dynamics of the system exhibits energy crossing subject to different parametrization of space deformation upon time evolution, which is reminiscent of chaotic behavior in quantum systems. It is also observed a cross-over from ballistic dissipation to dynamic localization for decreasing perturbation strengths.
NASA Astrophysics Data System (ADS)
Gat, Omri
2007-09-01
The leading nonclassical term in the quantum dynamics of nonlinear oscillators is calculated in the Moyal quasi-trajectory representation. The irreducibility of the quantum dynamics to phase-space trajectories is quantified by the discrepancy of the canonical quasi-flow and the quasi-flow of a general observable. This discrepancy is shown to imply the breakdown of classical realism that can give rise to a dynamical violation of Bell's inequalities.
Zheng Shi; Jiujun Zhang; Zhong-Sheng Liu; Haijiang Wang; David P. Wilkinson
2006-01-01
Recent progress in the ab initio quantum chemistry study of cathode oxygen reduction on fuel cell catalysts is reviewed with emphasis on density functional theory and ab initio molecular dynamics methods. The capabilities of these methods are illustrated using examples of oxygen adsorption on transition metals and alloys, and the reduction mechanism. Ab initio studies can calculate adsorption geometry, energy,
Boltzmann-conserving classical dynamics in quantum time-correlation functions: Matsubara dynamics
Hele, Timothy J H; Muolo, Andrea; Althorpe, Stuart C
2015-01-01
We show that a single change in the derivation of the linearized semiclassical-initial value representation (LSC-IVR or classical Wigner approximation) results in a classical dynamics which conserves the quantum Boltzmann distribution. We rederive the (standard) LSC-IVR approach by writing the (exact) quantum time-correlation function in terms of the normal modes of a free ring-polymer (i.e. a discrete imaginary-time Feynman path), taking the limit that the number of polymer beads $N \\to \\infty$, such that the lowest normal-mode frequencies take their Matsubara values. The change we propose is to truncate the quantum Liouvillian, not explicitly in powers of $\\hbar^2$ at $\\hbar^0$ (which gives back the standard LSC-IVR approximation), but in the normal-mode derivatives corresponding to the lowest Matsubara frequencies. The resulting Matsubara dynamics is inherently classical (since all terms $\\mathcal{O}\\left(\\hbar^{2}\\right)$ disappear from the Matsubara Liouvillian in the limit $N \\to \\infty$), and conserves...
New applications of quantum algebraically integrable systems in fluid dynamics
NASA Astrophysics Data System (ADS)
Boutet de Monvel, Anne; Loutsenko, Igor; Yermolayeva, Oksana
2013-09-01
Rational quantum algebraically integrable systems are non-trivial generalizations of Laplacian operators to the case of elliptic operators with variable coefficients. We study corresponding extensions of Laplacian growth connected with algebraically integrable systems, describing viscous free-boundary flows in non-homogenous media. We introduce a class of planar flows related with application of Adler-Moser polynomials and construct solutions for higher-dimensional cases, where the conformal mapping technique is unavailable.
Studies of Quantum Chromodynamics at the LHC
Carli, Tancredi; Schumann, Steffen
2015-01-01
A successful description of hadron-hadron collision data demands a profound understanding of quantum chromodynamics. Inevitably, the complexity of strong-interaction phenomena requires the use of a large variety of theoretical techniques -- from perturbative cross-section calculations up to the modelling of exclusive hadronic final states. Together with the unprecedented precision of the data provided by the experiments in the first running period of the LHC, a solid foundation of hadron-hadron collision physics at the TeV scale could be established that allowed the discovery of the Higgs boson and that is vital for estimating the background in searches for new phenomena. This chapter on studies of quantum chromodynamics at the LHC is part of a recent book on the results of LHC Run 1 and presents the advances in theoretical methods side-by-side with related key measurements in an integrated approach.
Unitary Dynamics and Quantum Circuits Robert B. Griffiths
Griffiths, Robert B.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 2.2 One qubit gates.4 Other two-qubit gates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.5 More = Consistent Quantum Theory by Griffiths (Cambridge, 2002), Ch. 7. QCQI = Quantum Computation and Quantum
Dynamic-local-field approximation for the quantum solids
NASA Technical Reports Server (NTRS)
Etters, R. D.; Danilowicz, R. L.
1974-01-01
A local-molecular-field description for the ground-state properties of the quantum solids is presented. The dynamical behavior of atoms contributing to the local field, which acts on an arbitrary pair of test particles, is incorporated by decoupling the pair correlations between these field atoms. The energy, pressure, compressibility, single-particle-distribution function, and the rms atomic deviations about the equilibrium lattice sites are calculated for H2, He-3, and He-4 over the volume range from 5 to 24.5 cu cm/mole. The results are in close agreement with existing Monte Carlo calculations wherever comparisons are possible. At very high pressure, the results agree with simplified descriptions which depend on negligible overlap of the system wave function between neighboring lattice sites.
Dynamics of a Two-Dimensional System of Quantum Dipoles
Mazzanti, F.; Astrakharchik, G. E.; Boronat, J. [Departament de Fisica i Enginyeria Nuclear, Campus Nord B4-B5, Universitat Politecnica de Catalunya, E-08034 Barcelona (Spain); Zillich, R. E. [Institut fuer Theoretische Physik, Johannes-Kepler Universitaet, Altenbergerstr. 69, 4040 Linz (Austria)
2009-03-20
A detailed microscopic analysis of the dynamic structure function S(k,{omega}) of a two-dimensional Bose system of dipoles polarized along the direction perpendicular to the plane is presented and discussed. Starting from ground-state quantities obtained using a quantum diffusion Monte Carlo algorithm, the density-density response is evaluated in the context of the correlated basis functions (CBF) theory. CBF predicts a sharp peak and a multiexcitation component at higher energies produced by the decay of excitations. We discuss the structure of the phonon-roton peak and show that the Feynman and Bogoliubov predictions depart from the CBF result already at low densities. We finally discuss the emergence of a roton in the spectrum, but find the roton energy not low enough to make the system unstable under density fluctuations up to the highest density considered that is close to the freezing point.
Chapter 5: Quantum Dynamics in Dissipative Molecular Systems
NASA Astrophysics Data System (ADS)
Zhang, Hou-Dao; Xu, J.; Xu, Rui-Xue; Yan, Y. J.
2014-04-01
The following sections are included: * Introduction * HEOM versus Path Integral Formalism: Background * Generic form and terminology of HEOM * Statistical mechanics description of bath influence * Feynman-Vernon influence functional formalism * General comments * Memory-Frequency Decomposition of Bath Correlation Functions * PSD of Bose function * Brownian oscillators decomposition of bath spectral density function * Optimized HEOM Theory With Accuracy Control * Construction of HEOM via path integral formalism * Accuracy control on white-noise residue ansatz * Efficient HEOM propagator: Numerical filtering and indexing algorithm * HEOM in Quantum Mechanics for Open Systems * The HEOM space and the Schrödinger picture * HEOM in the Heisenberg picture * Mixed Heisenberg-Schrödinger block-matrix dynamics in nonlinear optical response functions * Two-Dimensional Spectroscopy: Model Calculations * Concluding Remarks * Acknowledgments * References
Quantum statistics and dynamics of nonlinear couplers with nonlinear exchange
Abdalla, M Sebawe; Perina, J
2011-01-01
In this paper we derive the quantum statistical and dynamical properties of nonlinear optical couplers composed of two nonlinear waveguides operating by the second subharmonic generation, which are coupled linearly through evanescent waves and nonlinearly through nondegenerate optical parametric interaction. Main attention is paid to generation and transmission of nonclassical light, based on a discussion of squeezing phenomenon, normalized second-order correlation function, and quasiprobability distribution functions. Initially coherent, number and thermal states of optical beams are considered. In particular, results are discussed in dependence on the strength of the nonlinear coupling relatively to the linear coupling. We show that if the Fock state $|1>$ enters the first waveguide and the vacuum state $|0>$ enters the second waveguide, the coupler can serve as a generator of squeezed vacuum state governed by the coupler parameters. Further, if thermal fields enter initially the waveguides the coupler play...
Nonlinear dynamics of quantum cascade lasers with optical feedback
NASA Astrophysics Data System (ADS)
Jumpertz, L.; Ferré, S.; Schires, K.; Carras, M.; Grillot, F.
2015-01-01
Quantum Cascade (QC) lasers are widely used in optical communications, high-resolution spectroscopy, imaging, and remote sensing due to their wide spectral range, going from mid-infrared to the terahertz regime. The dynamics of QClasers are dominated by their ultrafast carrier lifetime, typically of the order of a few picoseconds. The combination of optical nonlinearities and ultrafast dynamics is an interesting feature of QC-lasers, and investigating the dynamical properties of such lasers gives unprecedented insights into the underlying physics of the components, which is of interest for the next generation of QC devices. A particular feature of QC-lasers is the absence of relaxation oscillations, which is the consequence of the relatively short carrier lifetime compared to photon lifetime. Optical feedback (i.e. self-injection) is known to be a robust technique for stabilizing or synchronizing a free-running laser, however its effect on QC-lasers remains mostly unexplored. This work aims at discussing the dynamical properties of QC-lasers operating under optical feedback by employing a novel set of rate equations taking into account the upper and lower lasing levels, the bottom state as well as the gain stage's cascading. This work analyzes the static laser properties subject to optical feedback and provides a comparison with experiments. Spectral analysis reveals that QC-lasers undergo distinct feedback regimes depending on the phase and amplitude of the reinjected field, and that the coherence-collapse regime only appears in a very narrow range of operation, making such lasers much more stable than their interband counterparts.
Two dimensional kicked quantum Ising model: dynamical phase transitions
NASA Astrophysics Data System (ADS)
Pineda, C.; Prosen, T.; Villaseñor, E.
2014-12-01
Using an efficient one and two qubit gate simulator operating on graphical processing units, we investigate ergodic properties of a quantum Ising spin 1/2 model on a two-dimensional lattice, which is periodically driven by a ?-pulsed transverse magnetic field. We consider three different dynamical properties: (i) level density, (ii) level spacing distribution of the Floquet quasienergy spectrum, and (iii) time-averaged autocorrelation function of magnetization components. Varying the parameters of the model, we found transitions between ordered (non-ergodic) and quantum chaotic (ergodic) phases, but the transitions between flat and non-flat spectral density do not correspond to transitions between ergodic and non-ergodic local observables. Even more surprisingly, we found good agreement of level spacing distribution with the Wigner surmise of random matrix theory for almost all values of parameters except where the model is essentially non-interacting, even in regions where local observables are not ergodic or where spectral density is non-flat. These findings question the versatility of the interpretation of level spacing distribution in many-body systems and stress the importance of the concept of locality.
Inclusion of quantum fluctuations in wave packet dynamics
Ohnishi, A. [Department of Physics, Faculty of Science, Hokkaido University, Sapporo 060 (Japan)] [Department of Physics, Faculty of Science, Hokkaido University, Sapporo 060 (Japan); Randrup, J. [Nuclear Science Division, Lawrence Berkeley Laboratory, University of California, Berkeley, California 94720 (United States)] [Nuclear Science Division, Lawrence Berkeley Laboratory, University of California, Berkeley, California 94720 (United States)
1997-01-01
We discuss a method by which quantum fluctuations can be included in microscopic transport models based on wave packets that are not energy eigenstates. By including the next-to-leading order term in the cumulant expansion of the statistical weight, which corresponds to the wave packets having Poisson energy distributions, we obtain a much improved global description of the quantum statistical properties of the many-body system. In the case of atomic nuclei, exemplified by {sup 12}C and {sup 40}Ca, the standard liquid-drop results are reproduced at low temperatures and a phase transformation to a fragment gas occurs as the temperature is raised. The treatment can be extended to dynamical scenarios by means of a Langevin force emulating the transitions between the wave packets. The general form of the associated transport coefficients is derived and it is shown that the appropriate microcanonical equilibrium distribution is achieved in the course of the time evolution. Finally, invoking Fermi{close_quote}s golden rule, we derive specific expressions for the transport coefficients and verify that they satisfy the fluctuation-dissipation theorem. {copyright} 1997 Academic Press, Inc.
Real-time quantum electron-phonon dynamics
NASA Astrophysics Data System (ADS)
Rizzi, Valerio; Todorov, Tchavdar; Kohanoff, Jorge; Correa, Alfredo
2015-03-01
Electrons and atomic motion out of equilibrium exchange energy and momentum. Physical problems that involve this exchange include Joule heating, inelastic electron tunneling, and thermalization of hot electrons in an irradiated material. An explicit dynamical treatment of both subsystems is essential to model such non-adiabatic phenomena and requires the ability to describe the interaction of the coupled electrons and nuclei without enforcing equilibration a priori. Therefore, being able to describe an electronic system in real time together with the underlying ionic system is a key feature for first-principles electron-phonon methods. We have developed an approach for real-time phonon-assisted electron transfer in nanowires, explicitly tracking out-of-equilibrium systems that exchange energy. Our model is fully quantum mechanical: it overcomes the limitations of the Ehrenfest (quantum-classical) approximation and doesn't require thermostats, or the treatment of either subsystem as a bath. We can probe a range of timescales: from attoseconds (electronic timescale) to picoseconds (typical of atomic vibrations). The comparison with exact simulations of systems with a single phonon and a single electron have proved an invaluable validation tool for our method. We are able to describe the population inversion of an excited electronic system coupled to phonons and phonon-assisted conduction in systems with Anderson localization. Leverhulme Trust
Borgis, D.; Tarjus, G.; Azzouz, H. [Universite Pierre et Marie Curie, Paris (France)
1992-04-16
By using an adiabatic dynamical simulation method, this report attempts to study a mixed classical-quantum model of strongly H-bonded complexes in polar solvents. The influence of the solvent on the proton-transfer rate constant and adiabatic proton dynamics is discussed. 21 refs., 3 figs.
The quantum dynamics of electronically nonadiabatic chemical reactions
NASA Technical Reports Server (NTRS)
Truhlar, Donald G.
1993-01-01
Considerable progress was achieved on the quantum mechanical treatment of electronically nonadiabatic collisions involving energy transfer and chemical reaction in the collision of an electronically excited atom with a molecule. In the first step, a new diabatic representation for the coupled potential energy surfaces was created. A two-state diabatic representation was developed which was designed to realistically reproduce the two lowest adiabatic states of the valence bond model and also to have the following three desirable features: (1) it is more economical to evaluate; (2) it is more portable; and (3) all spline fits are replaced by analytic functions. The new representation consists of a set of two coupled diabatic potential energy surfaces plus a coupling surface. It is suitable for dynamics calculations on both the electronic quenching and reaction processes in collisions of Na(3p2p) with H2. The new two-state representation was obtained by a three-step process from a modified eight-state diatomics-in-molecules (DIM) representation of Blais. The second step required the development of new dynamical methods. A formalism was developed for treating reactions with very general basis functions including electronically excited states. Our formalism is based on the generalized Newton, scattered wave, and outgoing wave variational principles that were used previously for reactive collisions on a single potential energy surface, and it incorporates three new features: (1) the basis functions include electronic degrees of freedom, as required to treat reactions involving electronic excitation and two or more coupled potential energy surfaces; (2) the primitive electronic basis is assumed to be diabatic, and it is not assumed that it diagonalizes the electronic Hamiltonian even asymptotically; and (3) contracted basis functions for vibrational-rotational-orbital degrees of freedom are included in a very general way, similar to previous prescriptions for locally adiabatic functions in various quantum scattering algorithms.
Manfred Requardt; Saeed Rastgoo
2015-06-12
Starting from the working hypothesis that both physics and the corresponding mathematics and in particular geometry have to be described by means of discrete concepts on the Planck-scale, one of the many problems one has to face in this enterprise is to find the discrete protoforms of the building blocks of our ordinary continuum physics and mathematics living on a smooth background, and perhaps more importantly find a way how this continuum limit emerges from the mentioned discrete structure. We model this underlying substratum as a structurally dynamic cellular network (basically a generalisation of a cellular automaton). We regard these continuum concepts and continuum spacetime in particular as being emergent, coarse-grained and derived relative to this underlying erratic and disordered microscopic substratum, which we would like to call quantum geometry and which is expected to play by quite different rules, namely generalized cellular automaton rules. A central role in our analysis is played by a geometric renormalization group which creates (among other things) a kind of sparse translocal network of correlations between the points in classical continuous space-time and underlies, in our view, such mysterious phenomena as holography and the black hole entropy-area law. The same point of view holds for quantum theory which we also regard as a low-energy, coarse-grained continuum theory, being emergent from something more fundamental. In this paper we review our approach and compare it to the quantum graphity framework.
Liu, Jian; Miller, William H
2011-03-14
We have reformulated and generalized our recent work [J. Liu and W. H. Miller, J. Chem. Phys. 126, 234110 (2007)] into an approach for generating a family of trajectory-based dynamics methods in the phase space formulation of quantum mechanics. The approach (equilibrium Liouville dynamics) is in the spirit of Liouville's theorem in classical mechanics. The trajectory-based dynamics is able to conserve the quantum canonical distribution for the thermal equilibrium system and approaches classical dynamics in the classical (? ? 0), high temperature (? ? 0), and harmonic limits. Equilibrium Liouville dynamics provides the framework for the development of novel theoretical?computational tools for studying quantum dynamical effects in large?complex molecular systems. PMID:21405150
Quantum confined Stark effect in Gaussian quantum wells: A tight-binding study
Ramírez-Morales, A.; Martínez-Orozco, J. C.; Rodríguez-Vargas, I. [Unidad Académica de Física, Universidad Autónoma de Zacatecas, Calzada Solidaridad Esquina Con Paseo La Bufa S/N, 98060 Zacatecas, Zac. (Mexico)
2014-05-15
The main characteristics of the quantum confined Stark effect (QCSE) are studied theoretically in quantum wells of Gaussian profile. The semi-empirical tight-binding model and the Green function formalism are applied in the numerical calculations. A comparison of the QCSE in quantum wells with different kinds of confining potential is presented.
Mechanism and dynamics of biexciton formation from a long-lived dark exciton in a CdTe quantum dot
NASA Astrophysics Data System (ADS)
Smole?ski, T.; Kazimierczuk, T.; Goryca, M.; Wojnar, P.; Kossacki, P.
2015-04-01
We study the biexciton formation process in a single CdTe/ZnTe quantum dot. Consistently with previous studies, we find subquadratic dependence of the biexciton photoluminescence intensity on the excitation power. We quantitatively explain this dependence in terms of the interplay between two alternative biexciton formation mechanisms, including the formation from a long-lived dark exciton residing in the quantum dot. This mechanism is demonstrated to be a dominant one for a wide range of excitation intensities. Our study is complemented by determination of a characteristic biexciton formation time, which is shown to be governed by the spin relaxation dynamics of an excited electron pair.
T. N. Palmer
2013-05-20
A realistic measurement-free theory for the quantum physics of multiple qubits is proposed. This theory is based on a symbolic representation of a fractal state-space geometry which is invariant under the action of deterministic and locally causal dynamics. This symbolic representation is constructed from self-similar families of quaternionic operators. Using number-theoretic properties of the cosine function, the statistical properties of the symbolic representation of the invariant set are shown to be consistent with the contextual requirements of the Kochen-Specker theorem, are not constrained by Bell inequalities, and mirror the statistics of entangled qubits. These number-theoretic properties in turn reflect the sparseness of the invariant set in state space, and relate to the metaphysical notion of counterfactual incompleteness. Using the concept of probability, the complex Hilbert Space can be considered the completion of this symbolic representation into the state space continuum. As a result, it is proposed that the complex Hilbert Space should merely be considered a computational convenience in the light of the algorithmic intractability of the invariant set geometry, and consequently the superposed state should not be considered a fundamental aspect of physical theory. The physical basis for the proposed theory is relativistic gravity; for example the symbols used to describe the invariant set themselves label gravitationally distinct cosmological space-times. This implies that the very notion of a `quantum theory of gravity' may be profoundly misguided - erroneously putting the quantum cart before the gravitational horse. Here some elements of an alternative `gravitational theory of the quantum' are proposed, based on a deterministic and locally causal theory of gravity which extends general relativity by being geometric in both space-time and state space.