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1

ccsd00002813, SR study of the quantum dynamics in the frustrated S = 3

;ned spinons, are still under debate [4]. Among all corner sharing highly frustrated magnets, onlyccsdÂ00002813, version 2 Â 13 Sep 2004 #22;SR study of the quantum dynamics in the frustrated S = 3 for the latter new results for p #21; 0:89. Quantum-dynamical low energy magnetic excitations are evidenced

2

Nuclear magnetometry studies of spin dynamics in quantum Hall systems

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

3

Nonadiabatic quantum molecular dynamics with hopping. I. General formalism and case study

NASA Astrophysics Data System (ADS)

An extension of the nonadiabatic quantum molecular dynamics approach is presented to account for electron-nuclear correlations in the dynamics of atomic many-body systems. The method combines electron dynamics described within time-dependent density-functional or Hartree-Fock theory with trajectory-surface-hopping dynamics for the nuclei, allowing us to take into account explicitly a possible external laser field. As a case study, a model system of H++H collisions is considered where full quantum-mechanical calculations are available for comparison. For this benchmark system the extended surface-hopping scheme exactly reproduces the full quantum results. Future applications are briefly outlined.

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

2014-07-01

4

Dynamical noncommutative quantum mechanics

NASA Astrophysics Data System (ADS)

We study some basic and interesting quantum mechanical systems in dynamical noncommutative spaces in which the space-space commutation relations are position dependent. It is observed that the fundamental objects in the dynamical noncommutative space introduced here are string-like. We show that the Stark effect can be employed to determine whether the noncommutativity of space is dynamical or non-dynamical. It appears that unlike a non-dynamical case there is a fundamental energy ??2/m in this dynamical space.

Alavi, S. A.; Abbaspour, S.

2014-01-01

5

Quantum molecular dynamics study of warm dense iron.

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

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

2014-02-01

6

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

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

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

1995-11-16

7

Excitons in a photosynthetic light-harvesting system: A combined molecular dynamics, quantum 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

Kosztin, Ioan

8

and finite tempera- tures [2, 3] and the (continuum) quantum-mechanical SG model [7, 9]. However, less is known about the quantum-mechanical properties of the discrete quantum FK (QFK) model, in particularQuantum dynamics in the highly discrete, commensurate Frenkel Kontorova model: A path

Mueser, Martin

9

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

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

2013-07-07

10

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

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

1990-01-01

11

We present a quantum dynamical study of exciton transfer across a torsional defect that locally breaks the pi-conjugation in an oligo-(p-phenylene vinylene) (OPV) fragment. A site-based vibronic coupling Hamiltonian is used which is formulated in a comparative fashion (i) for a Frenkel exciton basis, assuming localized electron-hole pairs whose superposition yields a delocalized exciton, and (ii) more accurately, for a Merrifield type exciton basis including spatially separated electron-hole pairs. Starting from a partially delocalized ("spectroscopic unit") initial condition, the observed transfer dynamics is found to involve two characteristic time scales: (i) a very rapid, coherent transient on a 10-100 femtosecond scale, largely determined by Rabi type oscillations modulated by bond-length-alternation modes, and (ii) a slower time scale involving the planarization of the torsional coordinates that determines the onset of a quasi-stationary exciton-polaron state, and in the process leads to a "healing" of the torsional defect within - 500 femtoseconds. The dynamics obtained from the full electron-hole basis vs. Frenkel basis are in good agreement. In the full electron-hole dynamics, the transients are found to involve a rapid expansion and subsequent contraction of the electron-hole coherence size. Quantum dynamical simulations for a minimal six-site model involving 36 states and 22 vibrational modes, were carried out using the multiconfiguration time dependent Hartree (MCTDH) method. PMID:24020204

Binder, R; Wahl, J; Römer, S; Burghardt, I

2013-01-01

12

NASA Astrophysics Data System (ADS)

This thesis presents extensive studies on the quantum dynamics of diatom-diatom systems using primarily the time-dependent(TD) wave packet approach. The theoretical investigations include the photofragmentation of tetraatomic molecules and bimolecular diatom-diatom chemical reaction. Specifically, the quantum mechanical study on direct photodissociation of H_20 _2 is carried out using a time-dependent golden rule wave packet method on an empirical potential energy surface. The calculation shows that the rotation distributions are Gaussian-like and two OH radicals are highly correlated in rotation. Both the time-dependent and time-independent golden rule methods are employed to compute the vibrational predissociation decay widths for weakly bound clusters including D_2HF, H_2HF, HD-HF, and HF-HF. These quantum mechanical calculations reveal that the vibrational predissociation processes are very stereospecific and state specific, that the lifetimes depend critically on the type of mode being excited and the nature of the vibrational coupling, and the theoretical results are very sensitive to details of the interaction potential energy surface including the repulse of the PES. The full-dimensional (6D) dynamics study for diatom -diatom chemical reactions is presented with the first initial state-selected total reaction probabilities, cross sections and thermal rate constants reported for H_2 + OH to H_2 O + H reaction. The effects of reagents rotation and vibration on reaction are examined in detail in this study. Our calculations reveal surprisingly sharp resonance -like features at low collision energies on the Schatz-Elgersma potential surface, and also demonstrate that the potential -averaged 5D (PA5D) treatment can produce reaction probabilities essentially indistinguishable from the full-dimensional (6D) treatment.

Zhang, Dong Hui

13

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

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

1993-12-01

14

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

NASA Astrophysics Data System (ADS)

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

León, A.; Pacheco, M.

2011-03-01

15

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

16

Rapid hydrogen production from water using aluminum nanoclusters: A quantum molecular dynamics Available online 31 December 2013 Keywords: Hydrogen production Water Aluminum nanoclusters Quantum hydrogen production from water using aluminum nanoclusters, Aln (n = 16, 17, and 18). We have found a low

Southern California, University of

17

Characterization of Majorization Monotone Quantum Dynamics

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

Yuan, Haidong

18

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

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

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

2014-04-14

19

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

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

20

Efficient Quantum Computing of Complex Dynamics

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

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

2001-01-01

21

Aqueous monoethanolamine (MEA) has been extensively studied as a solvent for CO2 capture, yet the underlying reaction mechanisms are still not fully understood. Combined ab initio and classical molecular dynamics simulations were performed to revisit and identify key elementary reactions and intermediates in 25-30 wt% aqueous MEA with CO2, by explicitly taking into account the structural and dynamic effects. Using static quantum chemical calculations, we also analyzed in more detail the fundamental interactions involved in the MEA-CO2 reaction. We find that both the CO2 capture by MEA and solvent regeneration follow a zwitterion-mediated two-step mechanism; from the zwitterionic intermediate, the relative probability between deprotonation (carbamate formation) and CO2 removal (MEA regeneration) tends to be determined largely by the interaction between the zwitterion and neighboring H2O molecules. In addition, our calculations clearly demonstrate that proton transfer in the MEA-CO2-H2O solution primarily occurs through H-bonded water bridges, and thus the availability and arrangement of H2O molecules also directly impacts the protonation and/or deprotonation of MEA and its derivatives. This improved understanding should contribute to developing more comprehensive kinetic models for use in modeling and optimizing the CO2 capture process. Moreover, this work highlights the importance of a detailed atomic-level description of the solution structure and dynamics in order to better understand molecular mechanisms underlying the reaction of CO2 with aqueous amines. PMID:25382097

Hwang, Gyeong S; Stowe, Haley M; Paek, Eunsu; Manogaran, Dhivya

2015-01-14

22

Ultrafast optical studies of coherent spin dynamics in magnetic quantum structures

NASA Astrophysics Data System (ADS)

Using femtosecond lasers and ultrafast optical techniques, we have investigated the time-evolution of the spins of electrons, holes, and excitons which are optically injected into magnetic semiconductor quantum wells. Here, the spins of the mobile electronic carriers can directly couple to the spins of the local magnetic moments (Mn2+) present in the quantum structure, leading to new channels for spin relaxation, decoherence, and angular momentum transfer. Timescales, strengths, and physical manifestations of these dynamic spin-spin interactions are measured in real-time with femtosecond resolution using a method of ultrafast Faraday rotation. Model systems in which to study the interaction of electronic spins with embedded local moments are realized in a new class of 'digital' magnetic heterostructures: II-VI ZnSe/ZnCdSe single quantum wells containing discrete mono- and submonolayer planes of MnSe. Strong coupling between excitons and local moments is observed, resulting in large effective exciton g-factors (g ~ 500) and enhanced Faraday rotation. The fractional planes of magnetic material can be considered nearly ideal 2-D spin distributions, and the statistics of Mn spin clustering in the 2D planes is studied through photoluminescence Zeeman shifts in high magnetic fields (30T). In longitudinal applied magnetic fields (Faraday geometry), the monotonic exciton spin relaxation is rapid (<5ps) and found to depend solely on the magnitude of the exciton Zeeman splitting, regardless of the particular digital magnetic environment. No longlived spin-dependent imprint on the magnetic sublattice is measured. By contrast, in transverse magnetic fields the electron spins are found to precess at THz frequencies, enabling measurement of the electron spin decoherence time separate from the spin relaxation of the holes. Furthermore, the data indicate that the embedded Mn2+ sublattice undergoes an ultrafast coherent rotation about the transient exchange field of the spin polarized holes. The perturbed Mn2+ spin ensemble subsequently undergoes a measurable free-induction decay, permitting all-optical time-domain electron paramagnetic resonance studies of fractional-monolayer magnetic planes.

Crooker, Scott A.

23

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

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

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

2014-10-23

24

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

There has been a substantial amount of theoretical investigations on the photodynamics of pyrrole, often relying on surface hopping techniques or, if fully quantal, confining the study to the lowest two or three singlet states. In this study we extend ab initio based quantum dynamical investigations to cover simultaneously the lowest five singlet states, two ?-?? and two ?-?? excited states. The underlying potential energy surfaces are obtained from large-scale MRCI ab initio computations. These are used to extract linear and quadratic vibronic coupling constants employing the corresponding coupling models. For the N-H stretching mode Q(24) an anharmonic treatment is necessary and also adopted. The results reveal a sub-picosecond internal conversion from the S(4) (?-??) state, corresponding to the strongly dipole-allowed transition, to the S(1) and S(2) (?-??) states and, hence, to the ground state of pyrrole. The significance of the various vibrational modes and coupling terms is assessed. Results are also presented for the dissociation probabilities on the three lowest electronic states. PMID:22029316

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

2011-10-21

25

Coarse Grained Quantum Dynamics

We consider coarse graining a quantum system divided between short distance and long distance degrees of freedom, which are coupled by the Hamiltonian. Observations using purely long distance observables can be described by the reduced density matrix that arises from tracing out the short-distance observables. The dynamics of this density matrix is that of an open quantum system, and is nonlocal in time, on the order of some short time scale. We describe these dynamics in a model system with a simple hierarchy of energy gaps $\\Delta E_{UV} > \\Delta E_{IR}$, in which the coupling between high-and low-energy degrees of freedom is treated to second order in perturbation theory. We then describe the equations of motion under suitable time averaging, reflecting the limited time resolution of actual experiments, and find an expansion of the master equation in powers of $\\Delta E_{IR}/\\Delta E_{UV}$, in which the failure of the system to be Hamiltonian or even Markovian appears at higher orders in this ratio. We compute the evolution of the density matrix in two specific examples -- coupled spins, and linearly coupled simple harmonic oscillators. Finally, we discuss the evolution of the density matrix using the path integral approach, computing the Feynman-Vernon influence functional for the IR degrees of freedom in perturbation theory, and argue that this influence functional is the correct analog of the Wilsonian effective action for this problem.

Cesar Agon; Vijay Balasubramanian; Skyler Kasko; Albion Lawrence

2014-12-09

26

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

27

Quantum emulation of classical dynamics

In statistical mechanics, it is well known that finite-state classical lattice models can be recast as quantum models, with distinct classical configurations identified with orthogonal basis states. This mapping makes classical statistical mechanics on a lattice a special case of quantum statistical mechanics, and classical combinatorial entropy a special case of quantum entropy. In a similar manner, finite-state classical dynamics can be recast as finite-energy quantum dynamics. This mapping translates continuous quantities, concepts and machinery of quantum mechanics into a simplified finite-state context in which they have a purely classical and combinatorial interpretation. For example, in this mapping quantum average energy becomes the classical update rate. Interpolation theory and communication theory help explain the truce achieved here between perfect classical determinism and quantum uncertainty, and between discrete and continuous dynamics.

Norman Margolus

2011-09-23

28

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

The ionic and electronic structures of warm dense silane at the densities of 1.795, 2.260, 3.382, and 3.844 g/cm^{3} have been studied with temperatures from 1000 K to 3 eV using quantum molecular dynamics simulations. At all densities, the structures are melted above 1000 K. The matter states are characterized as polymeric from 1000 to 4000 K and become dense plasma states with further increasing temperature to 1 eV. At two lower densities of 1.795 and 2.260 g/cm^{3}, silane first dissociates and then becomes the polymeric state via a chain state from the initial crystalline structure. At higher densities, however, no dissociation stage was found. These findings can help us understand how the warm dense matter forms. A rise is found for the direct current electric conductivity at T?1000 K, indicating the nonmetal-to-metal transition. The conductivity decreases slightly with the increase of temperature, which is due to the more disordered structures at higher temperatures. PMID:25353443

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

2014-02-01

29

Quantum dynamics in dual spaces

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

Sudarshan, E.C.G.

1993-12-31

30

Accurate 3 dimensional quantum dynamical study of the Ne+H2+-->NeH++H reaction

NASA Astrophysics Data System (ADS)

In this work a comprehensive, fully converged coupled states (CS) quantum mechanical (QM) study of the endothermic Ne+H2+ ion-molecule reaction is presented. The computed dynamical properties are compared with quasi-classical trajectory (QCT) and with the available experimental data. To this end, the analytical potential energy surface of Pendergast, Heck, Hayes, and Jacquet was employed. The two main features of the dynamical behavior for this system are: (1) the rich structure present in the state-selected integral cross section energy-dependent curves, which may be attributed to resonances surviving the partial wave summation; and (2) the large differences between the quantum and the QCT cross sections which are caused by the inability of classical mechanics to conserve the zero point energy. Also noteworthy are the strong enhancement of the reactivity due to higher vibrational states and the effect of the activated complex, formed during the reaction process, on the angular and the rotational distributions.

Gilibert, M.; Giménez, X.; Huarte-Larrañaga, F.; González, M.; Aguilar, A.; Last, I.; Baer, M.

1999-04-01

31

NASA Astrophysics Data System (ADS)

The mechanisms of radiationless decay involved in the photodissociation of formaldehyde into H2 and CO have been investigated using complete active space self-consistent field (CASSCF) calculations and direct dynamics variational multiconfiguration Gaussian (DD-vMCG) quantum dynamics in the S1, T1, and S0 states. A commonly accepted scheme involves Fermi Golden Rule internal conversion from S1 followed by dissociation of vibrationally hot H2CO in S0. We recently proposed a novel mechanism [M. Araujo et al., J. Phys. Chem. A 112, 7489 (2008)] whereby internal conversion and dissociation take place in concert through a seam of conical intersection between S1 and S0 after the system has passed through an S1 transition barrier. The relevance of this mechanism depends on the efficiency of tunneling in S1. At lower energy, an alternative scheme to internal conversion involves intersystem crossing via T1 to regenerate the reactant before the S0 barrier to dissociation. We propose here a previously unidentified mechanism leading directly to H2 and CO products via T1. This channel opens at medium energies, near or above the T1 barrier to dissociation and still lower than the S1 barrier, thus making T1 a possible shortcut to molecular dissociation.

Araújo, Marta; Lasorne, Benjamin; Magalhães, Alexandre L.; Worth, Graham A.; Bearpark, Michael J.; Robb, Michael A.

2009-10-01

32

Computable functions, quantum measurements, and quantum dynamics

We construct quantum mechanical observables and unitary operators which, if implemented in physical systems as measurements and dynamical evolutions, would contradict the Church-Turing thesis which lies at the foundation of computer science. We conclude that either the Church-Turing thesis needs revision, or that only restricted classes of observables may be realized, in principle, as measurements, and that only restricted classes of unitary operators may be realized, in principle, as dynamics.

M. A. Nielsen

1997-06-03

33

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

Sheldon Goldstein; Ward Struyve

2014-11-05

34

NASA Astrophysics Data System (ADS)

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

Goldstein, Sheldon; Struyve, Ward

2015-01-01

35

is the use of classical molecular dynamics simulations with molecular mechanical forcefields.7Hybrid 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

Hammes-Schiffer, Sharon

36

Zeno Dynamics in Quantum Statistical Mechanics

We study the quantum Zeno effect in quantum statistical mechanics within the operator algebraic framework. We formulate a condition for the appearance of the effect in W*-dynamical systems, in terms of the short-time behaviour of the dynamics. Examples of quantum spin systems show that this condition can be effectively applied to quantum statistical mechanical models. Further, we derive an explicit form of the Zeno generator, and use it to construct Gibbs equilibrium states for the Zeno dynamics. As a concrete example, we consider the X-Y model, for which we show that a frequent measurement at a microscopic level, e.g. a single lattice site, can produce a macroscopic effect in changing the global equilibrium.

Andreas U. Schmidt

2002-07-11

37

Dynamical evaporation of quantum horizons

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

Daniele Pranzetti

2012-11-12

38

Classical and Quantum Discrete Dynamical Systems

We study deterministic and quantum dynamics from a constructive "finite" point of view, since the introduction of a continuum, or other actual infinities in physics poses serious conceptual and technical difficulties, without any need for these concepts to physics as an empirical science. For a consistent description of the symmetries of dynamical systems at different times and the symmetries of the various parts of such systems, we introduce discrete analogs of the gauge connections. Gauge structures are particularly important to describe the quantum behavior. We show that quantum behavior is the result of a fundamental inability to trace the identity of indistinguishable objects in the process of evolution. Information is available only on invariant statements and values, relating to such objects. Using mathematical arguments of a general nature we can show that any quantum dynamics can be reduced to a sequence of permutations. Quantum interferences occur in the invariant subspaces of permutation representations of symmetry groups of dynamical systems. The observable values can be expressed in terms of permutation invariants. We also show that for the description of quantum phenomena, instead of a nonconstructive number system --- the field of complex numbers, it is enough to use cyclotomic fields --- the minimal extentions of natural numbers suitable for quantum mechanics. Finite groups of symmetries play a central role in this article. The interest in such groups has an additional motivation in physics. Numerous experiments and observations in particle physics point to an important role of finite groups of relatively low orders in a number of fundamental processes.

Vladimir V. Kornyak

2014-04-21

39

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

NASA Astrophysics Data System (ADS)

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

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

2007-03-01

40

Quantum regression theorem and non-Markovianity of quantum dynamics

NASA Astrophysics Data System (ADS)

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

Guarnieri, Giacomo; Smirne, Andrea; Vacchini, Bassano

2014-08-01

41

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

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

2013-10-28

42

Stochastic Quantum Gas Dynamics

NASA Astrophysics Data System (ADS)

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.

Proukakis, Nick P.; Cockburn, Stuart P.

2010-03-01

43

Dynamical Localization in Kicked Quantum Rotors

The periodically $\\delta$-kicked quantum linear rotor is known to experience non-classical bounded energy growth due to quantum dynamical localization in angular momentum space. We study the effect of random deviations of the kick period in simulations and experiments. This breaks the energy and angular momentum localization and increases the rotational alignment, which is the analog of the onset of Anderson localization in 1-D chains.

Kamalov, Andrei; Bucksbaum, Philip H

2015-01-01

44

Many electronic systems exhibit striking features in their dynamical response over a prominent range of experimental parameters. While there are empirical suggestions of particular increasing length scales that accompany such transitions, this identification is not universal. To better understand such behavior in quantum systems, we extend a known mapping (earlier studied in stochastic, or supersymmetric, quantum mechanics) between finite temperature classical Fokker-Planck systems and related quantum systems at zero temperature to include general non-equilibrium dynamics. Unlike Feynman mappings or stochastic quantization methods (or holographic type dualities), the classical systems that we consider and their quantum duals reside in the same number of space-time dimensions. The upshot of our exact result is that a Wick rotation relates (i) dynamics in general finite temperature classical dissipative systems to (ii) zero temperature dynamics in the corresponding dual many-body quantum systems. Using this cor...

Nussinov, Zohar; Graf, Matthias J; Balatsky, Alexander V

2013-01-01

45

NASA Astrophysics Data System (ADS)

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

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

1993-01-01

46

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

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

2014-01-01

47

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

48

Ab initio quantum dynamical study of photoinduced ring opening in furan

NASA Astrophysics Data System (ADS)

The nonadiabatic photoinduced ring opening occurring in the two lowest excited singlet states of furan is investigated theoretically, using wave-packet propagation techniques. The underlying multidimensional potential energy surfaces (PESs) are obtained from ab initio computations, using the equation-of-motion coupled cluster method restricted to single and double excitations (EOM-CCSD), reported in earlier recent work [E. V. Gromov, A. B. Trofimov, F. Gatti, and H. Köppel, J. Chem. Phys. 133, 164309 (2010), 10.1063/1.3493451]. Up to five nuclear degrees of freedom are considered in the quantum dynamical treatment. Four of them represent in-plane motion for which the electronic states in question (correlating with the valence 1B2(V) and Rydberg 1A2(3s) states at the C2v ground-state molecular configuration) have different symmetries, A' and A'', respectively. The fifth mode, representing out-of-plane bending of the oxygen atom against the carbon-atom plane, leads to an interaction of these states, as is crucial for the photoreaction. The nonadiabatic coupling and conical intersection cause an electronic population transfer on the order of ˜10 fs. Its main features, and that of the wave-packet motion, are interpreted in terms of properties of the PES. The lifetime due to the ring-opening process has been estimated to be around 2 ps. The dependence of this estimate on the nuclear degrees of freedom retained in the computations is discussed.

Gromov, E. V.; Lévêque, C.; Gatti, F.; Burghardt, I.; Köppel, H.

2011-10-01

49

Ab initio quantum dynamical study of photoinduced ring opening in furan.

The nonadiabatic photoinduced ring opening occurring in the two lowest excited singlet states of furan is investigated theoretically, using wave-packet propagation techniques. The underlying multidimensional potential energy surfaces (PESs) are obtained from ab initio computations, using the equation-of-motion coupled cluster method restricted to single and double excitations (EOM-CCSD), reported in earlier recent work [E. V. Gromov, A. B. Trofimov, F. Gatti, and H. Ko?ppel, J. Chem. Phys. 133, 164309 (2010)]. Up to five nuclear degrees of freedom are considered in the quantum dynamical treatment. Four of them represent in-plane motion for which the electronic states in question (correlating with the valence (1)B(2)(V) and Rydberg (1)A(2)(3s) states at the C(2v) ground-state molecular configuration) have different symmetries, A(') and A(''), respectively. The fifth mode, representing out-of-plane bending of the oxygen atom against the carbon-atom plane, leads to an interaction of these states, as is crucial for the photoreaction. The nonadiabatic coupling and conical intersection cause an electronic population transfer on the order of ?10 fs. Its main features, and that of the wave-packet motion, are interpreted in terms of properties of the PES. The lifetime due to the ring-opening process has been estimated to be around 2 ps. The dependence of this estimate on the nuclear degrees of freedom retained in the computations is discussed. PMID:22047237

Gromov, E V; Lévêque, C; Gatti, F; Burghardt, I; Köppel, H

2011-10-28

50

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

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

2013-04-01

51

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

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

2014-01-01

52

We have calculated the equation of states, 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 is accordant with underground nuclear explosive and high power laser experimental results up to $\\sim$ 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 presents the relationship between the viscosity and self-diffusion coefficients, is found to hold fairly well in the strong coupling regime. The Lorenz number, which is the ratio between thermal and electrical conductivities, is computed via Kubo-Greenwood formula and compared to the well-known Wiedemann-Franz law in the warm dense region.

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

2013-01-01

53

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

54

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

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

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

1995-05-15

55

Efficient quantum computing of complex dynamics.

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

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

2001-11-26

56

Computation and Dynamics: Classical and Quantum

NASA Astrophysics Data System (ADS)

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

Kisil, Vladimir V.

2010-05-01

57

NASA Astrophysics Data System (ADS)

In this dissertation, the optical and electrical properties of semiconductor heterostructures are studied both theoretically and experimentally. Photoluminescence spectra were measured as a function of temperature and excitation intensity, in multiple narrow asymmetric coupled quantum well structures. The lineshape linewidths are deduced by fitting the low energy sides to Gaussian functions. The excellent fits indicate dominant inhomogeneous broadening. We have determined the scattering rates of the acoustic and optical phonons, of the impurities, and of the inhomogeneous broadening. Above 215 K, the photoluminescence depends linearly on high pump laser intensity and quadratically on low pump laser intensity. This is due to the competition between radiative recombination, and nonradiative recombination of carriers at excitation intensity saturable deep traps. Below 215 K the trapping becomes negligible; radiative recombination dominates. The nonradiative decay time and the quantum efficiency have also been determined. The dependence of the photoluminescence on laser intensity, is affected by the trap saturation and the dominant nonradiative recombination. In order to examine the trap saturation, we have calculated the dependence of the effective nonradiative decay time on the laser intensity. In addition, the laser-intensity dependences of the trapping efficiency and of the ratio of the electron and hole nonradiative decay times, have been determined for different ratios of the trapping and nonradiative recombination rates. The enhancement of the acoustic phonon limited intersubband transition rate, through impurity scattering, has been investigated in double asymmetric coupled quantum wells. The acoustic phonon rate dependence on the barrier thickness and the effect of a delta -doped region on the impurity rate, have been treated rigorously. This allows for the design of intersubband lasers, in which population inversion between acoustic phonon limited discrete conduction band states is achieved by impurity scattering and control of barrier thickness. Room temperature electroabsorption modulation was observed in narrow rm Ga_{0.47 }In_{0.53}As/Al_{0.48 }In_{0.52}As multiple quantum well p-i-n diodes, grown lattice matched to InP substrates by molecular beam epitaxy. The diodes exhibit a 6% modulation depth at the 1.27 ?m broad excitonic resonance and a 10% band-edge modulation depth at 1.3 mum. They correspond to absorption coefficient changes of 450 and 254 cm^{ -1} respectively.

Veliadis, John-Victor Dimitrios

58

Quantum fluctuations and quantum dynamics of small Josephson junctions

NASA Astrophysics Data System (ADS)

The quantum properties of small Josephson junctions with both linear Ohmic and quasiparticle (“cosine”) dissipation are investigated by means of a real-time path-integral technique. Quantum diffusion of the quasicharge and quantum corrections to the classical conductivity are analyzed. The current-voltage characteristics and the effect of voltage steps are studied. It is shown that coherent voltage oscillations may exist not only for small, but also for large values of the junction tunneling conductivity. For not very small values of the quasiparticle conductivity of the junction the frequency of these oscillations is twice the Bloch oscillation frequency. The quantum dynamics of the phase difference across the junction is studied for a wide region of parameters. It is shown that linear and “cosine” dissipation mechanisms cause the presence of two dissipative phase transitions, which are qualitatively different from each other in many aspects.

Panyukov, S. V.; Zaikin, A. D.

1988-10-01

59

Anomalies in non-Markovian quantum dynamics

NASA Astrophysics Data System (ADS)

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

Giraldi, Filippo; Petruccione, Francesco

2015-02-01

60

The dynamics of pigment-pigment and pigment-protein interactions in light-harvesting complexes is studied with a novel approach which combines molecular dynamics (MD) simulations with quantum chemistry (QC) calculations. The MD simulations of an LH-II complex, solvated and embedded in a lipid bilayer at physiological conditions (with total system size of 87,055 atoms) revealed a pathway of a water molecule into the B800 binding site, as well as increased dimerization within the B850 BChl ring, as compared to the dimerization found for the crystal structure. The fluctuations of pigment (B850 BChl) excitation energies, as a function of time, were determined via ab initio QC calculations based on the geometries that emerged from the MD simulations. From the results of these calculations we constructed a time-dependent Hamiltonian of the B850 exciton system from which we determined the linear absorption spectrum. Finally, a polaron model is introduced to describe quantum mechanically both the excitonic and vibrat...

Damjanovic, A; Schulten, K; Damjanovic, Ana; Kosztin, Ioan; Schulten, Klaus

2001-01-01

61

Many electronic systems exhibit striking features in their dynamical response over a prominent range of experimental parameters. While there are empirical suggestions of particular increasing length scales that accompany such transitions, this identification is not universal. To better understand such behavior in quantum systems, we extend a known mapping (earlier studied in stochastic, or supersymmetric, quantum mechanics) between finite temperature classical Fokker-Planck systems and related quantum systems at zero temperature to include general non-equilibrium dynamics. Unlike Feynman mappings or stochastic quantization methods (or holographic type dualities), the classical systems that we consider and their quantum duals reside in the same number of space-time dimensions. The upshot of our exact result is that a Wick rotation relates (i) dynamics in general finite temperature classical dissipative systems to (ii) zero temperature dynamics in the corresponding dual many-body quantum systems. Using this correspondence, we illustrate that, even in the absence of imposed disorder, many continuum quantum fluid systems (and possible lattice counterparts) may exhibit a zero-point "quantum dynamical heterogeneity" wherein the dynamics, at a given instant, is spatially non-uniform. While the static length scales accompanying this phenomenon do not exhibit a clear divergence in standard correlation functions, the length scale of the dynamical heterogeneities can increase dramatically. We study "quantum jamming" and illustrate how a hard core bosonic system may undergo a zero temperature quantum critical metal-to-insulator-type transition with an extremely large effective dynamical exponent z>4 consistent with length scales that increase far more slowly than the relaxation time as a putative critical transition is approached. We suggest ways to analyze experimental data.

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

2013-04-15

62

Theory of controlled quantum dynamics

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

Salvatore De Martino; Silvio De Siena; Fabrizio Illuminati

1997-01-01

63

NASA Astrophysics Data System (ADS)

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.

Ghatee, Mohammad Hadi; Sedghamiz, Tahereh

2014-12-01

64

NASA Astrophysics Data System (ADS)

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

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

2005-03-01

65

This article highlights some physical studies on the relaxation dynamics and Förster resonance energy transfer (FRET) of semiconductor quantum dots (QDs) and the way these phenomena change with size, shape, and composition of the QDs. The understanding of the excited-state dynamics of photoexcited QDs is essential for technological applications such as efficient solar energy conversion, light-emitting diodes, and photovoltaic cells. Here, our emphasis is directed at describing the influence of size, shape, and composition of the QDs on their different relaxation processes, that is, radiative relaxation rate, nonradiative relaxation rate, and number of trap states. A stochastic model of carrier relaxation dynamics in semiconductor QDs was proposed to correlate with the experimental results. Many recent studies reveal that the energy transfer between the QDs and a dye is a FRET process, as established from 1/d(6) distance dependence. QD-based energy-transfer processes have been used in applications such as luminescence tagging, imaging, sensors, and light harvesting. Thus, the understanding of the interaction between the excited state of the QD and the dye molecule and quantitative estimation of the number of dye molecules attached to the surface of the QD by using a kinetic model is important. Here, we highlight the influence of size, shape, and composition of QDs on the kinetics of energy transfer. Interesting findings reveal that QD-based energy-transfer processes offer exciting opportunities for future applications. Finally, a tentative outlook on future developments in this research field is given. PMID:23804322

Sadhu, Suparna; Patra, Amitava

2013-08-26

66

Quantum Computation and Quantum Spin Dynamics

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

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

2001-01-01

67

Experimental realization of quantum zeno dynamics.

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

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

2014-01-01

68

Experimental realization of quantum zeno dynamics

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

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

2014-01-01

69

Quantum approach to coupling classical and quantum dynamics

We present a consistent framework of coupled classical and quantum dynamics. Our result allows us to overcome severe limitations of previous phenomenological approaches, such as evolutions that do not preserve the positivity of quantum states or that allow one to activate quantum nonlocality for superluminal signaling. A ``hybrid'' quantum-classical density is introduced, and its evolution equation derived. The implications and

Lajos Diósi; Nicolas Gisin; Walter T. Strunz

2000-01-01

70

Quantum Information Processing with Quantum Zeno Many-Body Dynamics

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

Alex Monras; Oriol Romero-Isart

2008-01-01

71

On fractional time quantum dynamics

Application of the fractional calculus to quantum processes is presented. In particular, the quantum dynamics is considered in the framework of the fractional time Schr\\"odinger equation (SE), which differs from the standard SE by the fractional time derivative: $\\frac{\\prt}{\\prt t}\\to \\frac{\\prt^{\\alpha}}{\\prt t^{\\alpha}}$. It is shown that for $\\alpha =1/2$ the fractional SE is isospectral to a comb model. An analytical expression for the Green functions of the systems are obtained. The semiclassical limit is discussed.

Iomin, Alexander

2009-01-01

72

On fractional time quantum dynamics

Application of the fractional calculus to quantum processes is presented. In particular, the quantum dynamics is considered in the framework of the fractional time Schr\\"odinger equation (SE), which differs from the standard SE by the fractional time derivative: $\\frac{\\prt}{\\prt t}\\to \\frac{\\prt^{\\alpha}}{\\prt t^{\\alpha}}$. It is shown that for $\\alpha =1/2$ the fractional SE is isospectral to a comb model. An analytical expression for the Green functions of the systems are obtained. The semiclassical limit is discussed.

Alexander Iomin

2009-09-07

73

Orbits of hybrid systems as qualitative indicators of quantum dynamics

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

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

2014-03-03

74

Quantum dynamics in open quantum-classical systems.

Often quantum systems are not isolated and interactions with their environments must be taken into account. In such open quantum systems these environmental interactions can lead to decoherence and dissipation, which have a marked influence on the properties of the quantum system. In many instances the environment is well-approximated by classical mechanics, so that one is led to consider the dynamics of open quantum-classical systems. Since a full quantum dynamical description of large many-body systems is not currently feasible, mixed quantum-classical methods can provide accurate and computationally tractable ways to follow the dynamics of both the system and its environment. This review focuses on quantum-classical Liouville dynamics, one of several quantum-classical descriptions, and discusses the problems that arise when one attempts to combine quantum and classical mechanics, coherence and decoherence in quantum-classical systems, nonadiabatic dynamics, surface-hopping and mean-field theories and their relation to quantum-classical Liouville dynamics, as well as methods for simulating the dynamics. PMID:25634784

Kapral, Raymond

2015-02-25

75

Theory of controlled quantum dynamics

We introduce a general formalism, based on the stochastic formulation of quantum mechanics, to obtain localized quasi-classical wave packets as dynamically controlled systems, for arbitrary anharmonic potentials. The control is in general linear, and it amounts to introduce additional quadratic and linear time-dependent terms to the given potential. In this way one can construct for general systems either coherent packets moving with constant dispersion, or dynamically squeezed packets whose spreading remains bounded for all times. In the standard operatorial framework our scheme corresponds to a suitable generalization of the displacement and scaling operators that generate the coherent and squeezed states of the harmonic oscillator.

Salvatore De Martino; Silvio De Siena; Fabrizio Illuminati

1997-02-20

76

The notion of “active sites” is fundamental to heterogeneous catalysis. However, the exact nature of the active sites, and hence the mechanism by which they act, are still largely a matter of speculation. In this study, we have presented a systematic quantum chemical molecular dynamics (QCMD) calculations for the interaction of hydrogen on different step and terrace sites of the

Farouq Ahmed; Ryo Nagumo; Ryuji Miura; Suzuki Ai; Hideyuki Tsuboi; Nozomu Hatakeyama; Akira Endou; Hiromitsu Takaba; Momoji Kubo; Akira Miyamoto

2011-01-01

77

Non-Markovian dynamics of quantum discord

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

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

2010-05-15

78

Quantum nature of the big bang: Improved dynamics

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

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

2006-10-15

79

NASA Astrophysics Data System (ADS)

Accurate full dimensional quantum dynamics calculations studying the photodissociation of CH3I@resorc[4]arene on an ab initio based potential energy surface (PES) model are reported. The converged 189D quantum dynamics calculations are facilitated by the multilayer multi-configurational time-dependent Hartree (ML-MCTDH) approach combined with the correlation discrete variable representation (CDVR) for the evaluation of potential energy matrix elements. The potential employed combines an established ab initio PES describing the photodissociation of methyl iodide in the A band with a harmonic description of the resorc[4]arene host and a bilinear modeling of the host-guest interaction. All potential parameters required in the description of the vibrations of the host molecule and the host-guest interaction are derived from ab initio calculations on the host-guest complex. Absorption spectra at 0 K and 300 K are calculated and the electronic population dynamics during the bond breaking process occurring in the first 20-30 fs after the photoexcitation is investigated. Weak but significant effects resulting from the host-guest interaction on this time scale are found and interpreted. The present study demonstrates that accurate fully quantum mechanical dynamics calculations can be preformed for systems consisting of more than 50 atoms using the ML-MCTDH/CDVR approach. Utilizing an efficient statistical approach for the construction of the ensemble of initial wavepackets, these calculations are not restricted to zero temperature but can also study the dynamics at 300 K.

Westermann, Till; Brodbeck, Ralf; Rozhenko, Alexander B.; Schoeller, Wolfgang; Manthe, Uwe

2011-11-01

80

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

Ibrahim, Mahmoud A A

2011-10-24

81

Radiation from quantum weakly dynamical horizons in loop quantum gravity.

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

Pranzetti, Daniele

2012-07-01

82

Why quantum dynamics is linear

NASA Astrophysics Data System (ADS)

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

Jordan, Thomas F.

2009-11-01

83

Transient dynamics of linear quantum amplifiers

The transient dynamics of a quantum linear amplifier during the transition from damping to amplification regime is studied. The master equation for the quantized mode of the field is solved, and the solution is used to describe the statistics of the output field. The conditions under which a nonclassical input field may retain nonclassical features at the output of the amplifier are analyzed and compared to the results of earlier theories. As an application we give a dynamical description of the departure of the system from thermal equilibrium.

S. Maniscalco; J. Piilo; N. Vitanov; S. Stenholm

2006-01-13

84

Separability and dynamical symmetry of Quantum Dots

The separability and Runge–Lenz-type dynamical symmetry of the internal dynamics of certain two-electron Quantum Dots, found by Simonovi? et al. (2003), are traced back to that of the perturbed Kepler problem. A large class of axially symmetric perturbing potentials which allow for separation in parabolic coordinates can easily be found. Apart from the 2:1 anisotropic harmonic trapping potential considered in Simonovi? and Nazmitdinov (2013), they include a constant electric field parallel to the magnetic field (Stark effect), the ring-shaped Hartmann potential, etc. The harmonic case is studied in detail. -- Highlights: • The separability of Quantum Dots is derived from that of the perturbed Kepler problem. • Harmonic perturbation with 2:1 anisotropy is separable in parabolic coordinates. • The system has a conserved Runge–Lenz type quantity.

Zhang, P.-M., E-mail: zhpm@impcas.ac.cn [Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou (China); Zou, L.-P., E-mail: zoulp@impcas.ac.cn [Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou (China); Horvathy, P.A., E-mail: horvathy@lmpt.univ-tours.fr [Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou (China); Laboratoire de Mathématiques et de Physique Théorique, Tours University (France); Gibbons, G.W., E-mail: G.W.Gibbons@damtp.cam.ac.uk [Department of Applied Mathematics and Theoretical Physics, Cambridge University, Cambridge (United Kingdom)

2014-02-15

85

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

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

2014-02-25

86

Transmission through a Quantum Dynamical Delta Barrier

. Exactly solvable models for the interaction of photons or phonons with electrons in quantum dots [1 subsequently been used as a model for scattering in quasi-one-dimensional quantum wires by Bagwell and Lake [3Transmission through a Quantum Dynamical Delta Barrier T. Brandes1 Ã? and J. Robinson Department

Levi, Anthony F. J.

87

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

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

2011-10-07

88

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

Yang, Tianxiao; Bursten, Bruce E

2006-07-10

89

Carboxylesterases (CEs) are a family of ubiquitous enzymes with broad substrate specificity, and their inhibition may have important implications in pharmaceutical and agrochemical fields. One of the most potent inhibitors both for mammalian and insect CEs are trifluoromethyl ketones (TFMKs), but the mechanism of action of these chemicals is not completely understood. This study examines the balance between reactivity versus steric effects in modulating the activity against human carboxylesterase 1. The intrinsic reactivity of the ketone moiety is determined from quantum mechanical computations, which combine gas phase B3LYP calculations with hydration free energies estimated with the IEF/MST model. In addition, docking and molecular dynamics simulations are used to explore the binding mode of the inhibitors along the deep gorge that delineates the binding site. The results point out that the activity largely depends on the nature of the fluorinated ketone, since the activity is modulated by the balance between the intrinsic electrophilicity of the carbonyl carbon atom and the ratio between keto and hydrate forms. However, the results also suggest that the correct alignment of the alkyl chain in the binding site can exert a large influence on the inhibitory activity, as this effect seems to override the intrinsic reactivity features of the fluorinated ketone. Overall, the results sustain a subtle balance between reactivity and steric effects in modulating the inhibitory activity of TFMK inhibitors. PMID:20676708

Rayo, Josep; Muñoz, Lourdes; Rosell, Gloria; Hammock, Bruce D; Guerrero, Angel; Luque, F Javier; Pouplana, Ramon

2010-11-01

90

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

A. Murayama; K. Seo; K. Nishibayashi; I. Souma; Y. Oka

2006-01-01

91

Dynamics of Spin(1)\\/(2) Quantum Plasmas

The fully nonlinear governing equations for spin-(1)\\/(2) quantum plasmas are presented. Starting from the Pauli equation, the relevant plasma equations are derived, and it is shown that nontrivial quantum spin couplings arise, enabling studies of the combined collective and spin dynamics. The linear response of the quantum plasma in an electron-ion system is obtained and analyzed. Applications of the theory

Mattias Marklund; Gert Brodin

2007-01-01

92

Dynamics of spin 1/2 quantum plasmas

The fully nonlinear governing equations for spin 1/2 quantum plasmas are presented. Starting from the Pauli equation, the relevant plasma equations are derived, and it is shown that nontrivial quantum spin couplings arise, enabling studies of the combined collective and spin dynamics. The linear response of the quantum plasma in an electron--ion system is obtained and analyzed. Applications of the theory to solid state and astrophysical systems as well as dusty plasmas are pointed out.

M. Marklund; G. Brodin

2006-12-06

93

Selective dynamical decoupling for quantum state transfer

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

94

Quantum Computation as a Dynamical Process

In this paper, we discuss the dynamical issues of quantum computation. We demonstrate that fast wave function oscillations can affect the performance of Shor's quantum algorithm by destroying required quantum interference. We also show that this destructive effect can be routinely avoided by using resonant-pulse techniques. We discuss the dynamics of resonant pulse implementations of quantum logic gates in Ising spin systems. We also discuss the influence of non-resonant excitations. We calculate the range of parameters where undesirable non-resonant effects can be minimized. Finally, we describe the ``$2\\pi k$-method'' which avoids the detrimental deflection of non-resonant qubits.

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

1999-04-29

95

Quantum critical dynamics of S = 1/2 antiferromagnetic heisenberg chains studied in CuPzN by ESR

NASA Astrophysics Data System (ADS)

We found the dramatic crossover of the quantum critical dynamics of the chain antiferromagnet CuPzN which manifests itself in a change of symmetry properties of the ESR lineshape at low temperatures. We argue that such a crossover reveals the subtle interplay of two different perturbations of the isotropic Heisenberg model: i) the exchange anisotropy and ii) the staggered magnetic field induced by alternating g-factors of nonequivalent Cu sites of the unit cell of this compound. We estimate the magnitude of these perturbations, which drive the system from the ideal Tomonaga-Luttinger-Liquid state to the state with the field-induced gapped spin excitation spectrum.

Validov, A. A.; Lavrentyeva, E. M.; Ozerov, M.; Zvyagin, S. A.; Turnbull, M. M.; Landee, C. P.; Teitel'baum, G. B.

2010-01-01

96

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

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

2014-12-01

97

Dynamical triangulations, a gateway to quantum gravity?

NASA Astrophysics Data System (ADS)

We show how it is possible to formulate Euclidean two-dimensional quantum gravity as the scaling limit of an ordinary statistical system by means of dynamical triangulations, which can be viewed as a discretization in the space of equivalence classes of metrics. Scaling relations exist and the critical exponents have simple geometric interpretations. Hartle-Hawking wave functionals as well as reparametrization invariant correlation functions which depend on the geodesic distance can be calculated. The discretized approach makes sense even in higher-dimensional space-time. Although analytic solutions are still missing in the higher-dimensional case, numerical studies reveal an interesting structure and allow the identification of a fixed point where we can hope to define a genuine non-perturbative theory of four-dimensional quantum gravity.

Ambjørn, J.; Jurkiewicz, J.; Watabiki, Y.

1995-11-01

98

Direct characterization of quantum dynamics: General theory

The characterization of the dynamics of quantum systems is a task of both fundamental and practical importance. A general class of methods which have been developed in quantum information theory to accomplish this task is known as quantum process tomography (QPT). In an earlier paper [M. Mohseni and D. A. Lidar Phys. Rev. Lett. 97, 170501 (2006)] we presented an algorithm for direct characterization of quantum dynamics (DCQD) of two-level quantum systems. Here we provide a generalization by developing a theory for direct and complete characterization of the dynamics of arbitrary quantum systems. In contrast to other QPT schemes, DCQD relies on quantum error-detection techniques and does not require any quantum state tomography. We demonstrate that for the full characterization of the dynamics of n d-level quantum systems (with d prime), the minimal number of required experimental configurations is reduced quadratically from d{sup 4n} in separable QPT schemes to d{sup 2n} in DCQD.

Mohseni, M. [Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford St., Cambridge, Massachusetts 012138 (United States); Department of Chemistry, University of Southern California, Los Angeles, California 90089 (United States); Lidar, D. A. [Department of Chemistry, University of Southern California, Los Angeles, California 90089 (United States); Departments of Electrical Engineering and Physics, University of Southern California, Los Angeles, California 90089 (United States)

2007-06-15

99

Generalized dynamic scaling for quantum critical relaxation in imaginary time.

We study the imaginary-time relaxation critical dynamics of a quantum system with a vanishing initial correlation length and an arbitrary initial order parameter M0. We find that in quantum critical dynamics, the behavior of M0 under scale transformations deviates from a simple power law, which was proposed for very small M0 previously. A universal characteristic function is then suggested to describe the rescaled initial magnetization, similar to classical critical dynamics. This characteristic function is shown to be able to describe the quantum critical dynamics in both short- and long-time stages of the evolution. The one-dimensional transverse-field Ising model is employed to numerically determine the specific form of the characteristic function. We demonstrate that it is applicable as long as the system is in the vicinity of the quantum critical point. The universality of the characteristic function is confirmed by numerical simulations of models belonging to the same universality class. PMID:25375435

Zhang, Shuyi; Yin, Shuai; Zhong, Fan

2014-10-01

100

Generalized dynamic scaling for quantum critical relaxation in imaginary time

NASA Astrophysics Data System (ADS)

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

Zhang, Shuyi; Yin, Shuai; Zhong, Fan

2014-10-01

101

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

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

Jarrod R. McClean; Alán Aspuru-Guzik

2014-10-07

102

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

NASA Astrophysics Data System (ADS)

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

McClean, Jarrod R.; Aspuru-Guzik, Alán

2015-01-01

103

Non-equilibrium dynamics of an unstable quantum pendulum

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

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

2012-05-09

104

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

Dardi, P.S.

1984-11-01

105

NASA Astrophysics Data System (ADS)

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

Canaval, Lorenz R.; Rode, Bernd M.

2015-01-01

106

Angiotensin-converting enzyme (ACE) is an important zinc-dependent hydrolase responsible for converting the inactive angiotensin I to the vasoconstrictor angiotensin II and for inactivating the vasodilator bradykinin. However, the substrate binding mode of ACE has not been completely understood. In this work, we propose a model for an ACE Michaelis complex based on two known X-ray structures of inhibitor-enzyme complexes. Specifically, the human testis angiotensin-converting enzyme (tACE) complexed with two clinic drugs were first investigated using a combined quantum mechanical and molecular mechanical (QM/MM) approach. The structural parameters obtained from the 550 ps molecular dynamics simulations are in excellent agreement with the X-ray structures, validating the QM/MM approach. Based on these structures, a model for the Michaelis complex was proposed and simulated using the same computational protocol. Implications to ACE catalysis are discussed. PMID:21520937

Wang, Xuemei; Wu, Shanshan; Xu, Dingguo; Xie, Daiqian; Guo, Hua

2011-05-23

107

Fault-tolerant quantum dynamical decoupling.

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

Khodjasteh, K; Lidar, D A

2005-10-28

108

Dynamical regimes of dissipative quantum systems

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

109

Dynamics of nuclear spin measurement in a mesoscopic solid-state quantum computer

We study numerically the process of nuclear spin measurement in a solid-state quantum computer of the type proposed by Kane, by calculating the quantum dynamics of two coupled nuclear spins on 31 P donors implanted in 28 Si. We estimate the time of the `quantum swap operation' - the minimum measurement time required for the reliable transfer of quantum information

Gennady P. Berman; David K. Campbell; Gary D. Doolen; Kirill E. Nagaev

2000-01-01

110

Simulating quantum dynamics on a quantum computer

NASA Astrophysics Data System (ADS)

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

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

2011-11-01

111

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

Lorenza Viola; David Tannor

2011-01-01

112

Dynamical Localization in Disordered Quantum Spin Systems

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

Eman Hamza; Robert Sims; Günter Stolz

2011-08-18

113

Quantum quenches, dynamical transitions, and off-equilibrium quantum criticality

NASA Astrophysics Data System (ADS)

Several mean-field computations have revealed the existence of an out-of-equilibrium dynamical transition induced by quantum-quenching an isolated system starting from its symmetry-broken phase. In this work we focus on the quantum ?4 N-component field theory. By taking into account dynamical fluctuations at the Hartree-Fock level, corresponding to the leading order of the 1/N expansion, we derive the critical properties of the dynamical transition beyond mean-field theory (including at finite temperature). We find diverging time and length scales, dynamic scaling, and aging. Finally, we unveil a relationship with critical coarsening, an off-equilibrium regime that can be induced by quenching from the symmetric toward the symmetry-broken phase.

Sciolla, Bruno; Biroli, Giulio

2013-11-01

114

Quantum dynamics in classical thermal baths

NASA Astrophysics Data System (ADS)

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

Dlamini, Nkosinathi; Sergi, Alessandro

2013-11-01

115

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

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

2014-05-19

116

Quantum spin dynamics as a model for quantum computer operation

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

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

2002-01-01

117

Quantum fluctuations in beam dynamics.

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

Kim, K.-J.

1998-06-04

118

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

119

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

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

120

Efficient Quantum State Estimation by Continuous Weak Measurement and Dynamical Control

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

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

2006-06-13

121

Hydration dynamics in water clusters via quantum molecular dynamics simulations

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

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

2014-05-28

122

Nuclear quantum dynamics in dense hydrogen

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

123

Quantum theory of dynamic nuclear polarization in quantum dots

NASA Astrophysics Data System (ADS)

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

Economou, Sophia; Barnes, Edwin

2013-03-01

124

Stochastic solution to quantum dynamics

NASA Technical Reports Server (NTRS)

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

John, Sarah; Wilson, John W.

1994-01-01

125

Quantum dynamics via adiabatic ab initio centroid molecular dynamics

NASA Astrophysics Data System (ADS)

The ab initio path integral simulation method is combined with centroid molecular dynamics. This unification, and thus extension of these basic techniques, allows for the investigation of the real-time quantum dynamics in chemically complex many-body systems. The theory underlying the proposed ab initio centroid molecular dynamics (AICMD) technique is presented in detail. The real-time propagation of the nuclei is obtained in the quasiclassical approximation within the framework of centroid path integrals. Concurrently, the forces acting on the nuclei are computed from "on the fly" electronic structure calculations based on first-principle techniques such as, e.g., Hohenberg—Kohn—Sham density functional theory. AICMD can be considered as a quasiclassical generalization of standard Car—Parrinello ab initio molecular dynamics. At the same time, AICMD preserves the virtues of the ab initio path integral technique to generate exact time-independent quantum equilibrium averages. AICMD is well suited to investigate, in a quasiclassical sense, the real-time evolution of molecular quantum systems with complex interactions which cannot be satisfactorily represented by simple model potentials. In particular, the method permits the simulation of the dynamics of chemical reactions including quantum effects. AICMD is applicable to isolated systems in the gas phase such as molecules, clusters or complexes as well as to condensed matter, i.e. molecular liquids or solids.

Marx, Dominik; Tuckerman, Mark E.; Martyna, Glenn J.

1999-05-01

126

Phase space representation of quantum dynamics

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

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

2010-08-15

127

Optimal Measurement and Control in Quantum Dynamical Systems.

', February 1979 Abstract A Markovian model for a quantum automata, i.e. an open quantum dynamical system containing quantum channels. Due to fundamental limitations of quantum-mechanical measurement a speci c prob, and the time development of the discrete models of quantum open systems for commu- nication and control became

Belavkin, Viacheslav P.

128

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

129

Effective Evolution Equations from Quantum Dynamics

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

Niels Benedikter; Marcello Porta; Benjamin Schlein

2015-02-09

130

Instability of quantum equilibrium in Bohm's dynamics.

We consider Bohm's second-order dynamics for arbitrary initial conditions in phase space. In principle, Bohm's dynamics allows for 'extended' non-equilibrium, with initial momenta not equal to the gradient of phase of the wave function (as well as initial positions whose distribution departs from the Born rule). We show that extended non-equilibrium does not relax in general and is in fact unstable. This is in sharp contrast with de Broglie's first-order dynamics, for which non-standard momenta are not allowed and which shows an efficient relaxation to the Born rule for positions. On this basis, we argue that, while de Broglie's dynamics is a tenable physical theory, Bohm's dynamics is not. In a world governed by Bohm's dynamics, there would be no reason to expect to see an effective quantum theory today (even approximately), in contradiction with observation. PMID:25383020

Colin, Samuel; Valentini, Antony

2014-11-01

131

A quantum molecular dynamics study of the properties of NO+(H2O)n clusters

NASA Astrophysics Data System (ADS)

The structures and dynamics of NO+(H2O)n, with n=1,2,3, have been studied using first principles Born-Oppenheimer molecular dynamics (BOMD) performed in the framework of density functional theory (DFT) with a generalized gradient approximation (GGA). The ground-state structure of NO+(H2O), in which a relatively weak bond connects NO+ and H2O, is shown to be floppy along certain degrees of freedom. When a second water molecule is added, a new solvation shell is formed via a hydrogen bond. Our investigations indicate that a third water molecule attaches to the first water molecule and completes the second solvation shell. The hydration energies are found to be 1.31, 0.87, and 0.77 eV for n=1,2,3, respectively. The vibrational spectra at room temperature are calculated for NO+, and all three hydrated clusters. Compared to an isolated NO+ ion, a redshift of 120-200 cm-1 is observed for the N-O vibrational mode in NO+(H2O)n. For n=2, new peaks, identified as O-H stretches of the first H2O molecule, appear below the O-H stretch in the second H2O molecule. The spectrum of NO+(H2O)3, which maintains the most important features in NO+(H2O)2, indicates the presence of a complete solvation shell. Our studies suggest that the BOMD method is an efficient method for finding the optimal geometry of NO+(H2O)n clusters. More importantly, BOMD simulations allow for studies of dynamical and thermodynamical properties of these clusters at finite temperature, which mimics the physical conditions in which these clusters are found in nature and in the laboratory.

Ye, Ling; Cheng, Hai-Ping

1998-02-01

132

Dynamics and conductivity near quantum criticality

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

133

NASA Astrophysics Data System (ADS)

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

Marvian, Iman; Spekkens, Robert W.

2014-12-01

134

Quantum dynamics in the thermodynamic limit

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

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

2008-08-01

135

Lévy flights and nonlocal quantum dynamics

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

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

2013-07-15

136

Smooth Quantum Dynamics of Mixmaster Universe

We present a quantum version of the vacuum Bianchi IX model by implementing affine coherent state quantization combined with a Born-Oppenheimer-like adiabatic approximation. The analytical treatment is carried out on both quantum and semiclassical levels. The resolution of the classical singularity occurs by means of a repulsive potential generated by our quantization procedure. The quantization of the oscillatory degrees of freedom produces a radiation energy density term in the semiclassical constraint equation. The Friedmann-like lowest energy eigenstates of the system are found to be dynamically stable.

Bergeron, Hervé; Gazeau, Jean Pierre; Ma?kiewicz, Przemys?aw; Piechocki, W?odzimierz

2015-01-01

137

NASA Astrophysics Data System (ADS)

We show that the hybrid quantum mechanical/effective fragment potential (QM/EFP) can be a very effective and practical quantum mechanical molecular dynamics method, when it is properly combined with well-developed traditional molecular dynamics (MD) techniques. QM/EFP-MD simulations on intra-molecular proton transfer of glycine with 290 EFP waters yielded accurate free energy change and reaction barrier of the zwitterion ? neutral form conversion. Water rearrangements turned out to be the main driving force of the proton transfer.

Choi, Cheol Ho; Re, Suyong; Feig, Michael; Sugita, Yuji

2012-06-01

138

Quantum molecular Dynamics Ronnie Kosloff

demolition if Monotonic Energy Change #12;#12;#12;#12;#12;40 :Chirp Pulses Husimi Plot Frequency Transform #12;#12;#12;#12;#12;#12;#12;#12;#12;#12;#12;#12;#12;#12;#12;Li2 nuclear dynamics on the E state #12

Kosloff, Ronnie

139

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

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

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

2010-11-15

140

We present a mixed quantum-classical molecular dynamics study of the nonequilibrium hydrogen-bond dynamics following vibrational energy relaxation of the hydroxyl stretch in a 10 mol % methanol/carbon tetrachloride mixture and pure methanol. The ground and first-excited energy levels and wave functions are identified with the eigenvalues and eigenfunctions of the hydroxyl's adiabatic Hamiltonian and as such depend parametrically on the configuration of the remaining, classically treated, degrees of freedom. The dynamics of the classical degrees of freedom are in turn governed by forces obtained by taking the expectation value of the force with respect to the ground or excited vibrational wave functions. Polarizable force fields and nonlinear mapping relations between the hydroxyl transition frequencies and dipole moments and the electric field along the hydroxyl bond are used, which were previously shown to quantitatively reproduce the experimental infrared steady-state absorption spectra and excited state lifetime [Kwac, K.; Geva, E. J. Phys. Chem. B 2011, 115, 9184; 2012, 116, 2856]. The relaxation from the first-excited state to the ground state is treated as a nonadiabatic transition. Within the mixed quantum-classical treatment, relaxation from the excited state to the ground state is accompanied by a momentum-jump in the classical degrees of freedom, which is in turn dictated by the nonadiabatic coupling vector. We find that the momentum jump leads to breaking of hydrogen bonds involving the relaxing hydroxyl, thereby blue-shifting the transition frequency by more than the Stokes shift between the steady-state emission and absorption spectra. The subsequent nonequilibrium relaxation toward equilibrium on the ground state potential energy surface is thereby accompanied by red shifting of the transition frequency. The signature of this nonequilibrium relaxation process on the pump-probe spectrum is analyzed in detail. The calculated pump-probe spectrum is found to be in reasonable agreement with experiment, thereby providing further credibility to the underlying force fields and mixed quantum-classical methodology. PMID:23713405

Kwac, Kijeong; Geva, Eitan

2013-06-27

141

Dynamics of the Measurement of Nuclear Spins in a Solid-State Quantum Computer

We study numerically the process of nuclear spin measurement in a solid-state quantum computer of the type proposed by Kane by modeling the quantum dynamics of two coupled nuclear spins on $^{31}$P donors implanted in silicon. We estimate the minimum measurement time necessary for the reliable transfer of quantum information from the nuclear spin subsystem to the electronic subsystem. We

Gennady P. Berman; David K. Campbell; Gary D. Doolen; Kirill E. Nagaev

1999-01-01

142

Relativistic Quantum Metrology in Open System Dynamics

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

Tian, Zehua; Fan, Heng; Jing, Jiliang

2015-01-01

143

Universal quench dynamics of interacting quantum impurity systems

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

144

QUANTUM FLUCTUATIONS IN BEAM DYNAMICS KWANG-JE KIM

QUANTUM FLUCTUATIONS IN BEAM DYNAMICS KWANG-JE KIM Accelerator Systems Division, Advanced Photon@aps.anl.gov Quantum e ects could become important for particle and photon beams used in high-luminosityand high spot size x. 1 LSLLS-271 Presented at the 15th ICFA Advanced Beam Dynamics Workshop on Quantum Aspects

Kemner, Ken

145

Information geometry, dynamics and discrete quantum mechanics

NASA Astrophysics Data System (ADS)

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

Reginatto, Marcel; Hall, Michael J. W.

2013-08-01

146

Dynamics of quantum wave packets

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

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

1998-11-01

147

Quantum Processes and Dynamic Networks in Physical and Biological Systems.

NASA Astrophysics Data System (ADS)

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

Dudziak, Martin Joseph

148

Quantum Gibbs distribution from dynamical thermalization in classical nonlinear lattices

NASA Astrophysics Data System (ADS)

We study numerically time evolution in classical lattices with weak or moderate nonlinearity which leads to interactions between linear modes. Our results show that in a certain strength range a moderate nonlinearity generates a dynamical thermalization process which drives the system to the quantum Gibbs distribution of probabilities, or average oscillation amplitudes. The effective dynamical temperature of the lattice varies from large positive to large negative values depending on the energy of the initially excited modes. This quantum Gibbs distribution is drastically different from the usually expected energy equipartition over linear modes corresponding to a regime of classical thermalization. Possible experimental observations of this dynamical thermalization are discussed for cold atoms in optical lattices, nonlinear photonic lattices and optical fiber arrays.

Ermann, Leonardo; Shepelyansky, Dima L.

2013-12-01

149

Quantum dynamical framework for Brownian heat engines

NASA Astrophysics Data System (ADS)

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

Agarwal, G. S.; Chaturvedi, S.

2013-07-01

150

NASA Astrophysics Data System (ADS)

The notion of "active sites" is fundamental to heterogeneous catalysis. However, the exact nature of the active sites, and hence the mechanism by which they act, are still largely a matter of speculation. In this study, we have presented a systematic quantum chemical molecular dynamics (QCMD) calculations for the interaction of hydrogen on different step and terrace sites of the Pd (3 3 2) surface. Finally the dissociative adsorption of hydrogen on step and terrace as well as the influence of surface hydrogen vacancy for the dissociative adsorption of hydrogen has been investigated through QCMD. This is a state-of-the-art method for calculating the interaction of atoms and molecules with metal surfaces. It is found that fully hydrogen covered (saturated) step sites can dissociate hydrogen moderately and that a monovacancy surface is suitable for significant dissociative adsorption of hydrogen. However in terrace site of the surface we have found that dissociation of hydrogen takes place only on Pd sites where the metal atom is not bound to any pre-adsorbed hydrogen atoms. Furthermore, from the molecular dynamics and electronic structure calculations, we identify a number of consequences for the interpretation and modeling of diffusion experiments demonstrating the coverage and directional dependence of atomic hydrogen diffusion on stepped palladium surface.

Ahmed, Farouq; Nagumo, Ryo; Miura, Ryuji; Ai, Suzuki; Tsuboi, Hideyuki; Hatakeyama, Nozomu; Endou, Akira; Takaba, Hiromitsu; Kubo, Momoji; Miyamoto, Akira

2011-10-01

151

Quantum effects in unimolecular reaction dynamics

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

Gezelter, J.D.

1995-12-01

152

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

Fu, Bina; Zhang, Dong H

2015-02-14

153

NASA Astrophysics Data System (ADS)

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

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

2006-05-01

154

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

NASA Astrophysics Data System (ADS)

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

Madsen, K. H.; Lodahl, P.

2013-02-01

155

Quantum soliton dynamics in vibrational chains: Comparison of fully correlated, mean field in polymer chains. The motivation beyond studying solitons is that they can have several interesting a chromophore on one side with a strong oscillation, injecting a soliton, which then propagates undisturbed

Baer, Roi

156

Automated synthesis of dynamically corrected quantum gates

NASA Astrophysics Data System (ADS)

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

Khodjasteh, Kaveh; Bluhm, Hendrik; Viola, Lorenza

2012-10-01

157

Quantum Process Tomography Quantifies Coherence Transfer Dynamics in Vibrational Exciton

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

Chuntonov, Lev; Ma, Jianqiang

2013-01-01

158

Quantum Gravity, Dynamical Phase Space and String Theory

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

Laurent Freidel; Robert G. Leigh; Djordje Minic

2014-05-15

159

Quantum gravity, dynamical phase-space and string theory

NASA Astrophysics Data System (ADS)

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

Freidel, Laurent; Leigh, Robert G.; Minic, Djordje

2014-08-01

160

Optical Nonlinearities and Ultrafast Carrier Dynamics in Semiconductor Quantum Dots

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

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

1998-08-10

161

Dynamics of Quantum Adiabatic Evolution Algorithm for Number Partitioning

NASA Technical Reports Server (NTRS)

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

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

2002-01-01

162

Chaos and Nonlinear Dynamics in a Quantum Artificial Economy

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

Carlos Pedro Gonçalves

2012-02-29

163

Relativistic Quantum Metrology in Open System Dynamics

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

Zehua Tian; Jieci Wang; Heng Fan; Jiliang Jing

2015-01-27

164

Relativistic Quantum Metrology in Open System Dynamics

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

165

Relativistic Quantum Metrology in Open System Dynamics

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

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

2015-01-01

166

Relativistic quantum metrology in open system dynamics.

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

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

2015-01-01

167

Nonclassical dynamics induced by a quantum meter

Conventionally, the effect of measurements on a quantum system is assumed to introduce decoherence, which renders the system classical-like. We consider here a microscopic meter, that is, an auxiliary essentially quantum system whose state is measured repeatedly, and show that it can be employed to induce transitions from classical states into inherently quantumlike states. The meter state is assumed to be lost in the environment and we derive a non-Markovian master equation for the dynamic system in the case of nondemolition coupling to the meter; this equation can be cast in the form of an (N{sub a})th-order differential equation in time, where N{sub a} is the dimension of the meter basis. We apply the approach to a harmonic oscillator coupled to a spin-(1/2) meter and demonstrate how it can be used to engineer effective Hamiltonian evolution, subject to decoherence induced by the projective meter measurements.

Clausen, J.; Akulin, V. M. [Laboratoire Aime Cotton, Universite Paris-Sud, 91405 Orsay Cedex (France); Salo, J. [Laser Physics and Quantum Optics, Royal Institute of Technology (KTH), 10691 Stockholm (Sweden); Materials Physics Laboratory, Helsinki University of Technology, 02015 HUT (Finland); Stenholm, S. [Laser Physics and Quantum Optics, Royal Institute of Technology (KTH), 10691 Stockholm (Sweden)

2005-12-15

168

Quantum corrections to inflaton and curvaton dynamics

NASA Astrophysics Data System (ADS)

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

Markkanen, Tommi; Tranberg, Anders

2012-11-01

169

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 ...

170

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

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

H. P. Buchler; G. Blatter

2003-12-19

171

Dynamical Causal Modeling from a Quantum Dynamical Perspective

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

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

2010-09-30

172

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

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

Sangchul Oh; Sabre Kais

2014-06-27

173

Quantum dynamics of supergravity on R3 × S1

NASA Astrophysics Data System (ADS)

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

Tong, David; Turner, Carl

2014-12-01

174

Hidden Symmetries of Dynamics in Classical and Quantum Physics

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

Marco Cariglia

2014-11-05

175

Hidden symmetries of dynamics in classical and quantum physics

NASA Astrophysics Data System (ADS)

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

Cariglia, Marco

2014-10-01

176

Quantum ice: a quantum Monte Carlo study.

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

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

2012-02-10

177

Quantum dynamics of a plane pendulum

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

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

2009-07-15

178

Quantum dynamics of a plane pendulum

NASA Astrophysics Data System (ADS)

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.

Leibscher, Monika; Schmidt, Burkhard

2009-07-01

179

Excitonic optical nonlinearity and exciton dynamics in semiconductor quantum dots

Two salient features of the excitonic state in semiconductor quantum dots are theoretically clarified. One is the enhanced excitonic optical nonlinearity arising from the state filling of discrete levels due to the quantum size effect. The calculated third-order nonlinear susceptibility explains successfully the recent experimental results. The other feature is the exciton dynamics in semiconductor quantum dots. A comprehensive interpretation

T. Takagahara

1987-01-01

180

NASA Astrophysics Data System (ADS)

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

Benatti, Fabio; Floreanini, Roberto; Scholes, Greg

2012-08-01

181

Modeling quantum fluid dynamics at nonzero temperatures

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

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

2014-01-01

182

Quantum dynamics with two Planck constants and the semiclassical limit

The mathematical possibility of coupling two quantum dynamic systems having two different Planck constants, respectively, is investigated. It turns out that such canonical dynamics are always irreversible. Semiclassical dynamics is obtained by letting one of the two Planck constants go to zero. This semiclassical dynamics will preserve positivity, as expected, so an improvement of the earlier proposals by Aleksandrov and

Lajos Diosi

1995-01-01

183

Exponential rise of dynamical complexity in quantum computing through projections

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

184

NASA Technical Reports Server (NTRS)

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

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

1993-01-01

185

Loop quantum cosmology of Bianchi IX: Effective dynamics

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

Alejandro Corichi; Edison Montoya

2015-02-09

186

Summary form only given. Far-field femtosecond spectroscopic studies provide direct insight into the dephasing, scattering and energy relaxation of free carrier and excitons in semiconductors. In general, however, such studies give less direct information on the ballistic and diffusive real-space transfer of photogenerated carriers or their trapping into low-dimensional nanostructures, processes that involve the real-space motion of carriers on length

V. Emiliani; T. Guenther; C. Lienau; T. Elsaesser; R. Notrel; K. H. Plong

2000-01-01

187

Thermal Rates of Hydrogen Exchange of Methane with Zeolite: A Direct ab Initio Dynamics Study ab initio dynamics study on the kinetics of the hydrogen exchange of methane with a zeolite model, particularly tunneling, were found to be significant even at the room temperature. Zeolites are important

Truong, Thanh N.

188

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

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

2009-01-01

189

Open Quantum System Stochastic Dynamics and the Rotating Wave Approximation

We study the stochastic dynamics of a two-level quantum system interacting with a stochastic magnetic field, and a single frequency electromagnetic 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, making the RWA modifies the stochastic terms in the Hamiltonian. Modification of the decay terms is also required in a master equation approach (i.e., the Liouville--von Neumann density matrix equation) for describing the dynamics. For isotropic Gaussian white noise, the RWA dynamics remains Markovian, although the Lindblad terms in the master equation for the density matrix become time-dependent when the non-commutation of the RWA transformation and the noise Hamiltonian is properly accounted for. We also treat Ornstein--Uhlenbeck noise, and find, in contra-distinction to the white noise case, a significant difference in the dynamics calculated with the RWA when the non-commutation of the RWA transformation and the noise Hamiltonian is taken into account. These findings are applicable to the modeling of any open quantum system coupled to an electromagentic field.

Y. B. Band

2014-12-22

190

. \\u000a Evolution of the helium atom in a strong time-dependent (TD) magnetic field\\u000a (B) of strength up to 1011 G is investigated through a quantum fluid\\u000a dynamics (QFD) based current-density functional theory (CDFT). The\\u000a TD-QFD-CDFT computations are performed through numerical solution of a\\u000a single generalized nonlinear Schrödinger equation employing vector\\u000a exchange-correlation potentials and scalar exchange-correlation density\\u000a functionals that depend both on

2011-01-01

191

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

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

192

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

A classical limit of quantum dynamics can be defined by compensation of the quantum potential in the time-dependent Schrödinger equation. The quantum potential is a non-local quantity, defined in the trajectory-based form of the Schrödinger equation, due to Madelung, de Broglie, and Bohm, which formally generates the quantum-mechanical features in dynamics. Selective inclusion of the quantum potential for the degrees of freedom deemed "quantum," defines a hybrid quantum/classical dynamics, appropriate for molecular systems comprised of light and heavy nuclei. The wavefunction is associated with all of the nuclei, and the Ehrenfest, or mean-field, averaging of the force acting on the classical degrees of freedom, typical of the mixed quantum/classical methods, is avoided. The hybrid approach is used to examine evolution of light/heavy systems in the harmonic and double-well potentials, using conventional grid-based and approximate quantum-trajectory time propagation. The approximate quantum force is defined on spatial domains, which removes unphysical coupling of the wavefunction fragments corresponding to distinct classical channels or configurations. The quantum potential, associated with the quantum particle, generates forces acting on both quantum and classical particles to describe the backreaction. PMID:25527919

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

2014-12-21

193

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

NASA Technical Reports Server (NTRS)

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

Wang, Dunyou; Kwak, Dochan (Technical Monitor)

2002-01-01

194

New methods for quantum mechanical reaction dynamics

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

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

1996-12-01

195

Royal Road to Coupling Classical and Quantum Dynamics

We present a consistent framework of coupled classical and quantum dynamics. Our result allows us to overcome severe limitations of previous phenomenological approaches, like evolutions that do not preserve the positivity of quantum states or that allow to activate quantum nonlocality for superluminal signaling. A `hybrid' quantum-classical density is introduced and its evolution equation derived. The implications and applications of our result are numerous: it incorporates the back-reaction of quantum on classical variables, it resolves fundamental problems encountered in standard mean field theories, and remarkably, also the quantum measurement process, i.e. the most controversial example of quantum-classical interaction is consistently described within our approach, leading to a theory of dynamical collapse.

Diósi, L; Strunz, W T; Diosi, Lajos; Gisin, Nicolas; Strunz, Walter T.

2000-01-01

196

Royal Road to Coupling Classical and Quantum Dynamics

We present a consistent framework of coupled classical and quantum dynamics. Our result allows us to overcome severe limitations of previous phenomenological approaches, like evolutions that do not preserve the positivity of quantum states or that allow to activate quantum nonlocality for superluminal signaling. A `hybrid' quantum-classical density is introduced and its evolution equation derived. The implications and applications of our result are numerous: it incorporates the back-reaction of quantum on classical variables, it resolves fundamental problems encountered in standard mean field theories, and remarkably, also the quantum measurement process, i.e. the most controversial example of quantum-classical interaction is consistently described within our approach, leading to a theory of dynamical collapse.

Lajos Diosi; Nicolas Gisin; Walter T. Strunz

1999-02-22

197

Ab initio UMP2, RMP2, DFT/UB3LYP, and CBS-QB3 calculations have shown that the adiabatic potential energy surface (PES) of the 1,2,3-trifluorobenzene radical anion is a pseudorotation surface formed by nonplanar stationary structures. The low (approximately 2-4 kcal/mol) energy barriers in the path of pseudorotation imply manifestations of spectral exchange in the ESR spectra of this radical anion. The optically detected ESR of radical ion pairs was used to obtain the ESR spectrum of 1,2,3-trifluorobenzene radical anion in liquid squalane solution and to study temperature variations in the spectrum over the range of 243-325 K. The spectrum is a doublet of triplets with hfc constants of a(F(2)) = 29 mT and a(2F(1,3)) = 7.6 mT at T = 243 K. The experimental hfc constants are temperature-dependent. Calculations of the temperature dependence of hfc constants in the framework of the model of classical nuclei motion along the pseudorotation coordinate reproduce well the experimental data. PMID:16833771

Barlukova, Maria M; Beregovaya, Irina V; Vysotsky, Victor P; Shchegoleva, Lyudmila N; Bagryansky, Victor A; Molin, Yuri N

2005-05-19

198

Dynamic homotopy and landscape dynamical set topology in quantum control

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

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

2012-08-15

199

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

200

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

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

Yuri Ozhigov

2007-11-01

201

Relativistic Quantum Dynamics in Intense Laser Fields

NASA Astrophysics Data System (ADS)

We investigate the relativistic dynamics of electrons in intense laser fields. Examples of both free and bound electron dynamics are discussed using the approach appropriate for each particular case, i.e., either classical relativistic mechanics or relativistic quantum mechanics. The algorithm for numerically solving the Dirac equation is explained in detail before showing results that were obtained for both free and bound electronic wave packets in interaction with laser fields. In the case of the former, we discuss Volkov wave packets and point out features such as Lorentz contraction, spin and non-dipole effects. A sevenfold charged oxygen ion in a counterpropagating beam illustrates the latter and demonstrates a method for generating high-energy electron—nucleus collisions. Furthermore, we briefly outline the procedure for solving the classical equations of motion in arbitrary electromagnetic fields. A special field configuration (that of a radially polarized laser beam) is considered as an example. We discuss the fields that result from solving Maxwell's equations and calculate the energy that may be gained by a single electron in interaction with this particular configuration.

Mocken, Guido R.; Salamin, Yousef I.; Keitel, Christoph H.

202

Vortex quantum dynamics of two dimensional lattice bosons

NASA Astrophysics Data System (ADS)

We study hard core lattice bosons in a magnetic field near half fillingootnotetextSee: arXiv:0810.2604. The strong periodic potential scatters the vortices by units of reciprocal lattice momenta, enhancing their mobility and modifying their effective Magnus field. The bare vortex hopping rate on the dual lattice is extracted by exact diagonalizations of square clusters. We deduce quantum melting of the vortex lattice above vortex density of 6.5x10-3 per lattice site. The Hall conductivity, which reflects the vortex Magnus dynamics, reverses sign abruptly at half filling. The characteristic temperature scale of the Hall conductivity vanishes at the transition point. We prove that at half filling, each vortex carries a spin half quantum number (`v-spin'). Experimental implications of these results are relevant for diverse systems of current interest, e.g. cold atoms on rotating optical lattices, arrays of Josephson junctions and underdoped cuprate superconductors.

Lindner, Netanel; Auerbach, Assa; Arovas, Daniel P.

2009-03-01

203

Quantum dynamics of a molecular matter-wave amplifier

We study the quantum dynamics of a model of molecular matter-wave amplifier proposed by Search and Meystre [Phys. Rev. Lett. 93, 140405 (2004)], which employs a strongly damped optical cavity to convert an atomic Bose-Einstein condensate into vibrational ground-state molecules. By using the Monte Carlo wave-function method, we calculate the quantum evolution of the atomic and molecular matter waves. We find that the system always evolves into a pure ground-state molecular matter wave even if initially there was no ground-state molecules. Statistical properties of these atomic and molecular matter waves are also investigated. The final state of the molecular field is sub-Poissonian. Two-mode correlation functions exhibit anticorrelated properties.

Cheng, Jing [School of Physical Science and Technology, South China University of Technology, Guangzhou 510640 (China); Yan, YiJing [Department of Chemistry, Hong Kong University of Science and Technology, Kowloon (Hong Kong)

2007-03-15

204

Dynamically Disordered Quantum Walk as a Maximal Entanglement Generator

NASA Astrophysics Data System (ADS)

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

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

2013-11-01

205

Quantum tomography meets dynamical systems and bifurcations theory

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

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

2014-06-15

206

Dynamical stability of the quantum Lifshitz theory in 2+1 dimensions

NASA Astrophysics Data System (ADS)

The roles of magnetic and electric perturbations in the quantum Lifshitz model in 2+1 dimensions are examined in this paper. The quantum Lifshitz model is an effective field theory for quantum multicritical systems, which include generalized two-dimensional (2D) quantum dimer models in bipartite lattices and their generalizations. It describes a class of quantum phase transitions between ordered and topological phases in 2+1 dimensions. Magnetic perturbations break the dimer conservation law. Electric excitations, the condensation of which leads to ordered phases, have been studied extensively both in the classical three-dimensional model and in the quantum 2D model. The role of magnetic vortex excitations, the condensation of which drives these systems into a Z2 topological phase, has been largely ignored. Recent numerical studies claim that the quantum theory has a peculiar feature: the dynamical exponent z flows continuously and the quantum theory is hence unstable to magnetic vortices. To study the interplay of both excitations, we perform a perturbative renormalization group study to one-loop order and study the stability of the theory away from quantum multicriticality. This is done by generalizing the operator-product expansion to anisotropic models. It is found that the dynamical exponent does not appear to flow, in contrast to the classical Monte Carlo study. Possible reasons for this difference are discussed at length.

Hsu, Benjamin; Fradkin, Eduardo

2013-02-01

207

Real-time nonequilibrium dynamics of quantum glassy systems

NASA Astrophysics Data System (ADS)

We develop a systematic analytic approach to aging effects in quantum disordered systems in contact with an environment. Within the closed-time path-integral formalism we include dissipation by coupling the system to a set of independent harmonic oscillators that mimic a quantum thermal bath. After integrating over the bath variables and averaging over disorder we obtain an effective action that determines the real-time dynamics of the system. The classical limit yields the Martin-Siggia-Rose generating functional associated to a colored noise. We apply this general formalism to a prototype model related to the p spin glass. We show that the model has a dynamic phase transition separating the paramagnetic from the spin-glass phase and that quantum fluctuations depress the transition temperature until a quantum critical point is reached. We show that the dynamics in the paramagnetic phase is stationary but presents an interesting crossover from a region controlled by the classical critical point to another one controlled by the quantum critical point. The most characteristic property of the dynamics in a glassy phase, namely, aging, survives the quantum fluctuations. In the subcritical region the quantum fluctuation-dissipation theorem is modified in a way that is consistent with the notion of effective temperatures introduced for the classical case. We discuss these results in connection with recent experiments in dipolar quantum spin glasses and the relevance of the effective temperatures with respect to the understanding of the low-temperature dynamics.

Cugliandolo, Leticia F.; Lozano, Gustavo

1999-01-01

208

Confined quantum Zeno dynamics of a watched atomic arrow

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

209

NASA Astrophysics Data System (ADS)

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

Keshavamurthy, S.

2009-03-01

210

Quantum molecular dynamic simulations of warm dense carbon monoxide.

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

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

2011-08-14

211

Dynamic characteristics of photonic crystal quantum dot lasers.

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

Banihashemi, Mehdi; Ahmadi, Vahid

2014-04-20

212

Density and temperature dependence of carrier dynamics in self-organized InGaAs quantum dots

We have used two- and three-pulse femtosecond differential transmission spectroscopy to study the dependence of quantum dot carrier dynamics on temperature. At low temperatures and densities, the rates for relaxation between the quantum dot confined states and for capture from the barrier region into the various dot levels could be directly determined. For electron-hole pairs generated directly in the quantum

T. B. Norris; K. Kim; J. Urayama; Z. K. Wu; J. Singh; P. K. Bhattacharya

2005-01-01

213

Carrier and spin dynamics in charged quantum dots

Carrier and spin dynamics are measured in meutral, positively and negatively charged quantum dots using polarization-sensitive time-resolved photoluminescence. Carrier capture rates are observed to be strongly enhanced in charged quantum dots, suggesting that electron-hole scattering dominates this process. For positive quantum dots, the enhanced spin-polarized electron capture rate eliminates loss of electron spin information in the GaAs barriers prior to

Kimberley C. Hall; Kenan Gundogdu; Thomas F. Boggess; Oleg B. Shchekin; Dennis G. Deppe

2004-01-01

214

Complexity of controlling quantum many-body dynamics

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

Caneva, T.

215

Effect of dynamical instability on timing jitter in passively mode-locked quantum-dot lasers.

We study the effect of noise on the dynamics of passively mode-locked semiconductor lasers both experimentally and theoretically. A method combining analytical and numerical approaches for estimation of pulse timing jitter is proposed. We investigate how the presence of dynamical features such as wavelength bistability in a quantum-dot laser affects timing jitter. PMID:25503004

Pimenov, A; Habruseva, T; Rachinskii, D; Hegarty, S P; Huyet, G; Vladimirov, A G

2014-12-15

216

Quantum many-body dynamics of coupled double-well superlattices Peter Barmettler,1

Quantum many-body dynamics of coupled double-well superlattices Peter Barmettler,1 Ana Maria Rey,2 in opti- cal lattices 10Â12 . Here we generalize these approaches to study the many-body dynamics of a simple iterative swap- ping procedure, performed by controlling the double-well barrier height see Fig. 1

Demler, Eugene

217

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

NASA Astrophysics Data System (ADS)

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

Poon, Gary K.

218

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

We present simulation studies of the formation and dynamics of dark solitons and vortices in quantum electron plasmas. The electron dynamics in the latter is governed by a pair of equations comprising the nonlinear Schrödinger and Poisson system of equations, which conserves the number of electrons as well as their momentum and energy. The present governing equations in one spatial

P. K. Shukla; B. Eliasson

2006-01-01

219

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

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

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

2010-04-15

220

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

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

Queensland, University of

221

Loop quantum cosmology of Bianchi IX: Effective dynamics

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

Corichi, Alejandro

2015-01-01

222

Dynamics of tripartite geometric quantifiers of correlations in a quantum spin system

NASA Astrophysics Data System (ADS)

We derive an exact formula of geometric measure of quantum discord (GMQD) for an arbitrary 3-qubit state. The dynamics of GMQD in a quantum spin system coupled to a thermal bath is studied by simulation and analytical approximation. It is found that tripartite quantum discord has distinct time behaviors within two different eigenspaces. Further, we extend the square norm distance to define tripartite geometric quantifiers of total and classical correlations. We obtain their explicit expressions and discuss the possibility of having a closed additive relation among various kinds of correlations during the dynamical evolution.

Zhou, Jiang; Guo, Hong

2013-06-01

223

Quantum dynamics with two Planck constants and the semiclassical limit

The mathematical possibility of coupling two quantum dynamic systems having two different Planck constants, respectively, is investigated. It turns out that such canonical dynamics are always irreversible. Semiclassical dynamics is obtained by letting one of the two Planck constants go to zero. This semiclassical dynamics will preserve positivity, as expected, so an improvement of the earlier proposals by Aleksandrov and by Boucher and Traschen is achieved. Coupling of quantized matter to gravity is illustrated by a simplistic example.

Lajos Diosi

1995-03-28

224

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

225

Scaling in quantum chaos: A study of quantum dots

NASA Astrophysics Data System (ADS)

We study the level statistics of the quantum spectrum of a harmonic oscillator with biquadratic corrections. The distribution of interlevel spacings along the lines of constant scaled energy, whose values determine the classical dynamics, is obtained numerically. A transition from the Poisson to the Wigner character of the distribution is observed with the increase of the scaled energy. Using a quasi- classical approximation and assuming ergodic chaos we derive the level correlation function along the lines of constant scaled energy by employing the trace formula and keeping only the diagonal term. Our calculation yields a smoothed out tail of a Gaussian ensemble and is based on the exact cancellation of two ratios: the ratio of the mean level density along the line of constant scaled energy to that at a fixed bi- quadratic coupling and the ratio of the action to the period of a long periodic orbit. We further argue that the Wigner distribution will be found along any smooth line crossing the spectrum in the region of classical chaos. Applicability of our findings to quantum-dot structures at semiconductor interfaces is discussed.

Zeng, Y. H.; Serota, R. A.

1994-07-01

226

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

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

2007-06-21

227

Spin decoherence from Hamiltonian dynamics in quantum dots

The dynamics of a spin-1/2 particle coupled to a nuclear spin bath through an isotropic Heisenberg interaction is studied as a model for the spin decoherence in quantum dots. The time-dependent polarization of the central spin is calculated as a function of the bath-spin distribution and the polarizations of the initial bath state. For short times, the polarization of the central spin shows a Gaussian decay, and at later times it is revived displaying nonmonotonic time dependence. The decoherence time scale depends on moments of the bath-spin distribution, and also on the polarization strengths in various bath-spin channels. The bath polarizations have a tendency to increase the decoherence time scale. The effective dynamics of the central spin polarization is shown to be described by a master equation with non-Markovian features.

Bhaktavatsala Rao, D. D.; Ravishankar, V.; Subrahmanyam, V. [Department of Physics, Indian Institute of Technology, Kanpur-208016 (India)

2006-08-15

228

NASA Astrophysics Data System (ADS)

Fully rigorous optical Bloch equations based on exciton states in a quantum well are presented for the study of coherent terahertz radiative dynamics from ultrafast optical excitation. The new formalism includes valence-band mixing, the angular-momentum dependence of exciton states, and heavy-hole-light-hole exciton quantum beats in single quantum wells. Both time-domain and frequency-domain solutions of the optical Bloch equations from ultrafast excitation are presented. The theoretical model shows good agreement with the single-quantum-well terahertz generation experiment of Planken et al. [Phys. Rev. Lett. 69, 3800 (1992)]. .

Chansungsan, Chaiyuth

1996-12-01

229

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

NASA Astrophysics Data System (ADS)

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

Cazalilla, M. A.; Rigol, M.

2010-05-01

230

Analyzing Big Data with Dynamic Quantum Clustering

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...

Weinstein, M; Hume, A; Sciau, Ph; Shaked, G; Hofstetter, R; Persi, E; Mehta, A; Horn, D

2013-01-01

231

Constructing quantum dynamics from mixed quantum-classical descriptions

quantum bath corrections in calculation of the non-adiabatic transition rate is presented. Ã? 2003 Elsevier in the context of non- adiabatic (NA) transitions in condensed phase envi- ronments with the emphasis on the role of quantum corrections in calculation of NA transition rates and evaluation of pure dephasing within a mixed

Barsegov, Valeri

232

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

233

Quantum molecular dynamics simulations of hydrogen production and solar cells

NASA Astrophysics Data System (ADS)

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

Mou, Weiwei

234

Quantum and classical dynamics in adiabatic computation

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

235

Dynamical Behavior of Interacting Dark Energy in Loop Quantum Cosmology

NASA Astrophysics Data System (ADS)

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

Xiao, Kui; Zhu, Jian-Yang

236

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

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

2011-09-21

237

NASA Astrophysics Data System (ADS)

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

Dattani, Nikesh S.

2013-06-01

238

A mathematical study of Quantum Revivals and Quantum Fidelity

A mathematical study of Quantum Revivals and Quantum Fidelity Monique Combescure Laboratoire de(t) := | , U(t, 0) | When the Hamiltonian ^H(t) (possibly time-dependent) is assumed to be perturbed ^Hg(t) := ^H(t) + gV , then we can compare the evolutions generated by ^H(t) and ^Hg(t) respectively, acting

Boyer, Edmond

239

Correlated Single Quantum Dot Blinking and Interfacial Electron Transfer Dynamics

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

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

2011-01-01

240

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

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

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

2011-09-15

241

Arbitrarily accurate dynamical control in open quantum systems.

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

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

2010-03-01

242

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

Ingo Kamleitner

2010-09-22

243

Fisher-Shannon product and quantum revivals in wavepacket dynamics

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.

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

2014-09-19

244

Asymptotic Dynamics of Coined Quantum Walks on Percolation Graphs

NASA Astrophysics Data System (ADS)

Quantum walks obey unitary dynamics: they form closed quantum systems. The system becomes open if the walk suffers from imperfections represented as missing links on the underlying basic graph structure, described by dynamical percolation. Openness of the system’s dynamics creates decoherence, leading to strong mixing. We present a method to analytically solve the asymptotic dynamics of coined, percolated quantum walks for a general graph structure. For the case of a circle and a linear graph we derive the explicit form of the asymptotic states. We find that a rich variety of asymptotic evolutions occur: not only the fully mixed state, but other stationary states; stable periodic and quasiperiodic oscillations can emerge, depending on the coin operator, the initial state, and the topology of the underlying graph.

Kollár, B.; Kiss, T.; Novotný, J.; Jex, I.

2012-06-01

245

. INTRODUCTION THE development of semiconductor quantum dot (QD) lasers and amplifiers has brought about devices982 IEEE JOURNAL OF QUANTUM ELECTRONICS, VOL. 43, NO. 11, NOVEMBER 2007 Carrier Dynamics of Quantum-Dot, Quantum-Dash, and Quantum-Well Semiconductor Optical Amplifiers Operating at 1.55 m Aaron J. Zilkie

Mojahedi, Mohammad

246

A Measure of Non-Markovianity for Unital Quantum Dynamical Maps

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.

S. Haseli; S. Salimi; A. S. Khorashad

2014-11-18

247

Programmable quantum simulation by dynamic Hamiltonian engineering

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

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

2014-06-18

248

Vibrational Spectra Including Critical Nuclear Quantum Effects Isaiah Sumner and Srinivasan S. Iyengar to study vibrational spectroscopy in clusters inclusive of critical nuclear quantum effects. This approach the vibrational density of states of [Cl-H-Cl]- , inclusive of critical quantum nuclear effects, and our results

Iyengar, Srinivasan S.

249

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

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

Jang, Seogjoo, 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

250

Entanglement dynamics in a quantum–classical hybrid of two q-bits and one oscillator

NASA Astrophysics Data System (ADS)

We investigate new features, especially of entanglement dynamics, which arise in a quantum–classical hybrid. As a model, we study the coupling between two quantum mechanical two-level systems, i.e., two q-bits and a classical harmonic oscillator. Their interaction is described by a hybrid coupling, in accordance with a recently developed quantum–classical hybrid theory. We discuss various situations in which entanglement of the q-bits does (not) evolve. Furthermore, we point out an experimental application in a hybrid cooling scheme and indicate topics for future study.

Fratino, L.; Lampo, A.; Elze, H.-T.

2014-12-01

251

Entanglement dynamics in a quantum-classical hybrid of two q-bits and one oscillator

We investigate new features, especially of entanglement dynamics, which arise in a quantum-classical hybrid. As a model, we study the coupling between two quantum mechanical two-level systems, i.e. two q-bits, and a classical harmonic oscillator. Their interaction is described by a hybrid coupling, in accordance with a recently developed quantum-classical hybrid theory. We discuss various situations in which entanglement of the q-bits does (not) evolve. Furthermore, we point out an experimental application in a hybrid cooling scheme and indicate topics for future study.

L. Fratino; A. Lampo; H. -T. Elze

2014-08-05

252

Lectures on Dynamical Models for Quantum Measurements

NASA Astrophysics Data System (ADS)

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

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

2015-10-01

253

Ornithine cyclodeaminase (OCD) is an NAD+-dependent deaminase that is found in bacterial species such as Pseudomonas putida. Importantly, it catalyzes the direct conversion of the amino acid L-ornithine to L-proline. Using molecular dynamics (MD) and a hybrid quantum mechanics/molecular mechanics (QM/MM) method in the ONIOM formalism, the catalytic mechanism of OCD has been examined. The rate limiting step is calculated to be the initial step in the overall mechanism: hydride transfer from the L-ornithine’s C?–H group to the NAD+ cofactor with concomitant formation of a C?=NH2 + Schiff base with a barrier of 90.6 kJ mol?1. Importantly, no water is observed within the active site during the MD simulations suitably positioned to hydrolyze the C?=NH2 + intermediate to form the corresponding carbonyl. Instead, the reaction proceeds via a non-hydrolytic mechanism involving direct nucleophilic attack of the ?-amine at the C?-position. This is then followed by cleavage and loss of the ?-NH2 group to give the ?1-pyrroline-2-carboxylate that is subsequently reduced to L-proline. PMID:23202934

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

2012-01-01

254

On the quantum dynamics of the rigid rotor

NASA Astrophysics Data System (ADS)

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.

Kowalski, K.; Rembieli?ski, J.; Zawadzki, J.

2015-01-01

255

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

Quantum criticality arises when a macroscopic phase of matter undergoes a continuous transformation at zero temperature. While the collective fluctuations at quantum-critical points are being increasingly recognized as playing an important role in a wide range of quantum materials, the nature of the underlying quantum-critical excitations remains poorly understood. Here we report in-depth measurements of the Hall effect in the heavy-fermion metal YbRh2Si2, a prototypical system for quantum criticality. We isolate a rapid crossover of the isothermal Hall coefficient clearly connected to the quantum-critical point from a smooth background contribution; the latter exists away from the quantum-critical point and is detectable through our studies only over a wide range of magnetic field. Importantly, the width of the critical crossover is proportional to temperature, which violates the predictions of conventional theory and is instead consistent with an energy over temperature, E/T, scaling of the quantum-critical single-electron fluctuation spectrum. Our results provide evidence that the quantum-dynamical scaling and a critical Kondo breakdown simultaneously operate in the same material. Correspondingly, we infer that macroscopic scale-invariant fluctuations emerge from the microscopic many-body excitations associated with a collapsing Fermi-surface. This insight is expected to be relevant to the unconventional finite-temperature behavior in a broad range of strongly correlated quantum systems. PMID:20668246

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

2010-01-01

256

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

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

257

Quantum Dynamics of a Bose Superfluid Vortex

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

Thompson, Lara

258

Electron Spin Dynamics in Semiconductor Quantum Dots

An electron spin confined to a semiconductor quantum dot is not subject to the classical spin relaxation mechanisms known for free carriers but it strongly interacts with the nuclear spin system via the hyperfine interaction. We show in time resolved photoluminescence spectroscopy experiments on ensembles of self assembled InAs quantum dots in GaAs that this interaction leads to strong electron spin dephasing.

Marie, X.; Belhadj, T.; Urbaszek, B.; Amand, T. [Universite de Toulouse, LPCNO, INSA-CNRS-UPS, 135 avenue de Rangueil, 31077 Toulouse (France); Krebs, O.; Lemaitre, A.; Voisin, P. [Laboratoire de Photonique et Nanostructures, route de Nozay, 91460 Marcoussis (France)

2011-07-15

259

NASA Astrophysics Data System (ADS)

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

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

260

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

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

261

Complex scattering dynamics and the quantum Hall effects

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

Trugman, S.A.

1994-12-16

262

Noise-resilient quantum evolution steered by dynamical decoupling

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

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

2013-01-01

263

Quantum correlation dynamics in photosynthetic processes assisted by molecular vibrations

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

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

2015-01-30

264

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

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

Peter Leifer

2008-04-11

265

Theoretical studies of chemical reaction dynamics

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

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

1993-12-01

266

Study of correlations in molecular motion by multiple quantum NMR

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

Tang, J.H.

1981-11-01

267

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

NASA Astrophysics Data System (ADS)

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

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

2011-03-01

268

Formation and dynamics of dark solitons and vortices in quantum electron plasmas.

We present simulation studies of the formation and dynamics of dark solitons and vortices in quantum electron plasmas. The electron dynamics in the latter is governed by a pair of equations comprising the nonlinear Schrödinger and Poisson system of equations, which conserves the number of electrons as well as their momentum and energy. The present governing equations in one spatial dimension admit stationary solutions in the form a dark envelope soliton. The dynamics of the latter reveals its robustness. Furthermore, we numerically demonstrate the existence of cylindrically symmetric two-dimensional quantum electron vortices, which survive during collisions. The nonlinear structures presented here may serve the purpose of transporting information at quantum scales in ultracold micromechanical systems and dense plasmas, such as those created during intense laser-matter interactions. PMID:16907249

Shukla, P K; Eliasson, B

2006-06-23

269

Controlling the quantum dynamics of a mesoscopic spin bath in diamond

Understanding and mitigating decoherence is a key challenge for quantum science and technology. The main source of decoherence for solid-state spin systems is the uncontrolled spin bath environment. Here, we demonstrate quantum control of a mesoscopic spin bath in diamond at room temperature that is composed of electron spins of substitutional nitrogen impurities. The resulting spin bath dynamics are probed using a single nitrogen-vacancy (NV) centre electron spin as a magnetic field sensor. We exploit the spin bath control to dynamically suppress dephasing of the NV spin by the spin bath. Furthermore, by combining spin bath control with dynamical decoupling, we directly measure the coherence and temporal correlations of different groups of bath spins. These results uncover a new arena for fundamental studies on decoherence and enable novel avenues for spin-based magnetometry and quantum information processing. PMID:22536480

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

2012-01-01

270

Optimized dynamical decoupling in a model quantum memory.

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

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

2009-04-23

271

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

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

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

2012-05-29

272

NASA Astrophysics Data System (ADS)

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

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

2011-03-01

273

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

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

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

2014-06-11

274

Theory of dynamic nuclear polarization and feedback in quantum dots

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

Sophia E. Economou; Edwin Barnes

2014-04-06

275

Theory of dynamic nuclear polarization and feedback in quantum dots

NASA Astrophysics Data System (ADS)

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

Economou, Sophia E.; Barnes, Edwin

2014-04-01

276

Theory of fast quantum control of exciton dynamics in semiconductor quantum dots

Optical techniques for the quantum control of the dynamics of multiexciton\\u000astates in a semiconductor quantum dot are explored in theory. Composite\\u000abichromatic phase-locked pulses are shown to reduce the time of elementary\\u000aquantum operations on excitons and biexcitons by an order of magnitude or more.\\u000aAnalytic and numerical methods of designing the pulse sequences are\\u000ainvestigated. Fidelity of the

C. Piermarocchi; Pochung Chen; Y. S. Dale; L. J. Sham

2002-01-01

277

Structural dynamics verification facility study

NASA Technical Reports Server (NTRS)

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

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

1981-01-01

278

NASA Astrophysics Data System (ADS)

In the context of group field theory condensate cosmology, we clarify the extraction of cosmological variables from the microscopic quantum gravity degrees of freedom. We show that an important implication of the second quantized formalism is the dependence of cosmological variables and equations on the quantum gravitational atomic number N (number of spin network vertices/elementary simplices). We clarify the relation of the effective cosmological equations with loop quantum cosmology, understood as an effective (hydrodynamic-like) approximation of a more fundamental quantum gravity theory. By doing so, we provide a fundamental basis to the idea of lattice refinement, showing the dependence of the effective cosmological connection on N, and hence indirectly on the scale factor. Our results open a new arena for exploring effective cosmological dynamics, as this depends crucially on the new observable N, which is entirely of quantum gravitational origin.

Gielen, Steffen; Oriti, Daniele

2014-12-01

279

From nonequilibrium quantum Brownian motion to impurity dynamics in one-dimensional quantum liquids

NASA Astrophysics Data System (ADS)

Impurity motion in one-dimensional ultracold quantum liquids confined in an optical trap has attracted much interest recently. As a step towards its full understanding, we construct a generating functional from which we derive the position nonequilibrium correlation function of a quantum Brownian particle with general Gaussian nonfactorizing initial conditions. We investigate the slow dynamics of a particle confined in a harmonic potential after a position measurement; the rapid relaxation of a particle trapped in a harmonic potential after a quantum quench realized as a sudden change in the potential parameters; and the evolution of an impurity in contact with a one-dimensional bosonic quantum gas. We argue that such an impurity-Luttinger-liquid system, which has been recently realized experimentally, admits a simple modeling as quantum Brownian motion in a super-Ohmic bath.

Bonart, Julius; Cugliandolo, Leticia F.

2012-08-01

280

Quantum teleportation of dynamics and effective interactions between remote systems.

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

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

2013-07-12

281

Nonadiabatic quantum state engineering driven by fast quench dynamics

There are a number of tasks in quantum information science that exploit non-transitional 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.

Marcela Herrera; Marcelo S. Sarandy; Eduardo I. Duzzioni; Roberto M. Serra

2014-03-03

282

"Almost" Quotient Space, Non-dynamical Decoherence and Quantum Measurement

An alternative approach to decoherence, named non-dynamical decoherence is developed and used to resolve the quantum measurement problem. According to decoherence, the observed system is open to a macroscopic apparatus(together with a possible added environment) in a quantum measurement process. We show that this open system can be well described by an "almost" quotient Hilbert space formed phenomenally according to some stability conditions. A group of random phase unitary operators is introduced further to obtain an exact quotient space for the observed system. In this quotient space, a density matrix can be constructed to give the Born's probability rule, realizing a (non-dynamical) decoherence. The concept of the ("almost") quotient space can also be used to explain the classical properties of a macroscopic system. We show further that the definite outcomes in a quantum measurement are mainly caused by the "almost" quotient space of the macroscopic apparatus.

Yu-Lei Feng; Yi-Xin Chen

2014-09-25

283

Interacting distributed approximating functions for real-time quantum dynamics

The distributed approximating function (DAF) approach to quantum real-time dynamics is generalized to include the effects of the potential. The ‘‘interacting’’ DAF (IDAF) is introduced as the identity for a certain class of functions that can be chosen to approximate as closely as desired any wave packet of interest. Free propagation of the IDAF yields the free propagator for the

David K. Hoffman; Mark Arnold; Wei Zhu; Donald J. Kouri

1993-01-01

284

Open System Dynamics with Non-Markovian Quantum Trajectories

A non-Markovian stochastic Schrödinger equation for a quantum system coupled to an environment of harmonic oscillators is presented. The ensemble average recovers the reduced density matrix without approximation and hence it allows one to determine open system dynamics with strong and non-Markovian environmental effects in a very efficient way. We demonstrate the power of our approach with several illustrative examples.

Walter T. Strunz; Lajos Diósi; Nicolas Gisin

1999-01-01

285

Multiconfigurational molecular dynamics with quantum transitions: Multiple proton transfer reactions

multiple proton transfer reactions. MC-MDQT is a mixed quantum/classical molecular dynamics method on the surface hopping method MDQT, which has already been applied to single proton transfer reactions mechanically. The direct extension of MDQT to multiple proton transfer reactions, where many hydrogen atoms

Hammes-Schiffer, Sharon

286

Quantum Molecular Dynamics Simulations of Nanotube Tip Assisted Reactions

NASA Technical Reports Server (NTRS)

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

Menon, Madhu

1998-01-01

287

Quantum Dynamics and a Semiclassical Description of the Photon.

ERIC Educational Resources Information Center

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

Henderson, Giles

1980-01-01

288

Spin and dynamics in relativistic quantum W. N. Polyzou,

Spin and dynamics in relativistic quantum theories W. N. Polyzou, Department of Physics in defining the spin and orbital angular momentum content of hadronic systems is discussed. 1 Introduction There is a great deal of interest in the distribution of spin and orbital angular momentum in hadronic systems

Polyzou, Wayne

289

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

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

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

2006-02-15

290

Quantum Yang-Mills-Weyl Dynamics in the Schrödinger paradigm

NASA Astrophysics Data System (ADS)

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

Dynin, A.

2014-04-01

291

Exploring the control landscape for nonlinear quantum dynamics

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

292

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

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

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

2011-03-21

293

A True Equation to Couple Classical and Quantum Dynamics

Starting from the Schr\\"odinger-equation of a composite system, we derive unified dynamics of a classical harmonic system coupled to an arbitrary quantized system. The classical subsystem is described by random phase-space coordinates entangled with the quantized variables of the complementary subsystem. Our semiclassical equation is {\\it true} in a sense that its predictions are identical to those of the fully quantized composite dynamics. This exact method applies to a broad class of theories, including e.g. the relativistic quantum-electrodynamics and the electron-fonon dynamics.

Lajos Diosi

1995-10-26

294

Optical realization of quantum Kerr medium dynamics.

We use the propagation of a conveniently shaped Gaussian beam in a GRIN media to mimic a quantum cavity filled with a Kerr medium. This is attained by introducing a second-order correction to the paraxial propagation of the beam. An additional result is that a Gaussian beam propagating in GRIN media may split into two Gaussian beams, corresponding to the generation of superposition of coherent states (Schrödinger cat states) in the cavity filled with the Kerr medium. PMID:25361303

Soto-Eguibar, F; Arrizon, V; Zúñiga-Segundo, A; Moya-Cessa, H M

2014-11-01

295

Quantum Signatures of Solar System Dynamics

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

Arkady L. Kholodenko

2007-07-26

296

Molecular dynamics study of Cu-Pd ordered alloys

Purpose: The goal of the paper is to study the molecular dynamics of Cu-Pd ordered alloys. Design\\/methodology\\/approach: The thermal and mechanical properties of Cu, Pd pure metals and their ordered intermetallic alloys of Cu3Pd(L12) and CuPd3(L12) are studied by using the molecular dynamics simulation. The melting behavior of the metals considered in this work is studied by utilizing quantum Sutton-Chen

S. Özdemir Kart; A. Erbay; H. Kiliç; T. Cagin; M. Tomak

2008-01-01

297

On model reduction for quantum dynamics: symmetries and invariant subspaces

NASA Astrophysics Data System (ADS)

Simulation of quantum dynamics is a grand challenge of computational physics. In this work we investigate methods for reducing the demands of such simulation by identifying reduced-order models for dynamics generated by parameterized quantum Hamiltonians. In particular, we first formulate an algebraic condition that certifies the existence of invariant subspaces for a model defined by a parameterized Hamiltonian and an initial state. Following this we develop and analyze two methods to explicitly construct a reduced-order model, if one exists. In addition to general results characterizing invariant subspaces of arbitrary finite dimensional Hamiltonians, by exploiting properties of the generalized Pauli group we develop practical tools to speed up simulation of dynamics generated by certain spin Hamiltonians. To illustrate the methods developed we apply them to several paradigmatic spin models.

Kumar, Akshat; Sarovar, Mohan

2015-01-01

298

Quantum vortex dynamics in two-dimensional neutral superfluids

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

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

2010-01-15

299

Self-sustaining dynamical nuclear polarization oscillations in quantum dots.

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. PMID:23473181

Rudner, M S; Levitov, L S

2013-02-22

300

Quantum Monte Carlo study of quantum dots in magnetic fields

NASA Astrophysics Data System (ADS)

We have studied the ground state energies and quantum numbers of confined two-dimensional (2D) electrons in weak and intermediate magnetic field strengths using quantum Monte Carlo methods. These 2D quantum dots are of theoretical interest, because it is possible to go from a weakly to a strongly correlated system by tuning the relative strength of the external potential to the electron-electron interaction. The accuracy of current spin density functional theory, and of the variational and diffusion Monte Carlo methods using single and multi configuration wave functions, is studied by comparison with results obtained by exact diagonalization. Using optimized trial wave functions, we calculate pair correlation functions as a function of the magnetic field and confinement strength. (Supported by the DOE and NSF)

Geist, Wolfgang; Zeng, Lang; Chou, Mei-Yin

2004-03-01

301

Quantum mechanical studies of lincosamides.

Lincosamides are a class of antibiotics used both in clinical and veterinary practice for a wide range of pathogens. This group of drugs inhibits the activity of the bacterial ribosome by binding to the 23S RNA of the large ribosomal subunit and blocking protein synthesis. Currently, three X-ray structures of the ribosome in complex with clindamycin are available in the Protein Data Bank, which reveal that there are two distinct conformations of the pyrrolidinyl propyl group of the bound clindamycin. In this work, we used quantum mechanical methods to investigate the probable conformations of clindamycin in order to explain the two binding modes in the ribosomal 23S RNA. We studied three lincosamide antibiotics: clindamycin, lincomycin, and pirlimycin at the B3LYP level with the 6-31G** basis set. The focus of our work was to connect the conformational landscape and electron densities of the two clindamycin conformers found experimentally with their physicochemical properties. For both functional conformers, we applied natural bond orbital (NBO) analysis and the atoms in molecules (AIM) theory, and calculated the NMR parameters. Based on the results obtained, we were able to show that the structure with the intramolecular hydrogen bond C=O…H-O is the most stable conformer of clindamycin. The charge transfer between the pyrrolidine-derivative ring and the six-atom sugar (methylthiolincosamide), which are linked via an amide bond, was found to be the dominant factor influencing the high stability of this conformer. PMID:22116607

Kulczycka-Mierzejewska, Katarzyna; Trylska, Joanna; Sadlej, Joanna

2012-06-01

302

Nonperturbative quantum dynamics of a new inflation model

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

Boyanovsky, D. [Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, Pennsylvania 15260 (United States)] [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

303

Spatio-temporal dynamics and fluctuations in quantum dot lasers: mesoscopic theory and modeling

We present a mesoscopic theory for the spatio-temporal carrier- and light field dynamics in quantum dot lasers based on spatially resolved semiconductor Bloch equations describing the dynamics of electrons and holes in each quantum dot. The Bloch equations are dynamically coupled to spatially resolved wave equations for the counterpropagating light fields and to a diffusion equation describing the carrier dynamics

Edeltraud Gehrig; Ortwin G. Hess

2002-01-01

304

NASA Astrophysics Data System (ADS)

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

Viola, Lorenza; Tannor, David

2011-08-01

305

Hierarchy of stochastic pure states for open quantum system dynamics.

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

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

2014-10-10

306

Massive Quantum Memories by Periodically Inverted Dynamic Evolutions

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

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

2005-06-27

307

Hierarchy of Stochastic Pure States for Open Quantum System Dynamics

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

308

NASA Technical Reports Server (NTRS)

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

Xiong, Fugin

2003-01-01

309

Thermo Field Dynamics and quantum algebras

The algebraic structure of Thermo Field Dynamics lies in the $q$-deformation of the algebra of creation and annihilation operators. Doubling of the degrees of freedom, tilde-conjugation rules, and Bogoliubov transformation for bosons and fermions are recognized as algebraic properties of $h_{q}(1)$ and of $h_{q}(1|1)$, respectively.

E. Celeghini; S. De Martino; S. De Siena; A. Iorio; M. Rasetti; G. Vitiello

1998-01-07

310

quantum dynamical description of the inter-

of ultrafast laser pulse driven dynamics in specific molecular nanostructures called light-harvesting antennae: Photosynthetic Antenna Complexes The storage of solar energy in energetically rich organic compounds is supplied by light- harvesting antennae, which surround the reaction center to enlarge the cross section

RÃ¶der, Beate

311

Dynamics of symmetry breaking during quantum real-time evolution in a minimal model system.

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

Heyl, Markus; Vojta, Matthias

2014-10-31

312

Theoretical and computational studies of non-RRKM unimolecular dynamics.

A survey is presented of theoretical models and computational studies for unimolecular reaction dynamics. Intrinsic RRKM and non-RRKM dynamics are described, and properties of the unimolecular reactant's classical phase space giving rise to these dynamics are discussed. Quantum dynamical calculations of isolated resonances and state-specific decomposition are reviewed, and the resulting possible mode-specific or statistical state-specific decomposition is delineated. The relationship between the latter and RRKM theory is described. Computational studies give the probability that a molecule dissociates in a time interval of t --> t + dt, that is, the lifetime distribution P(t), and determining unimolecular rate constants versus pressure, energy, and temperature from P(t) is outlined. Non-RRKM behavior evident in P(t) is not always present in the rate constants. The need to include anharmonicity and the proper treatment of the K quantum number, in calculating the RRKM unimolecular rate constant, is explained. The possibility of observing "steps" in unimolecular rate constants is considered. The extensive experimental non-RRKM dynamics found for several classes of chemical reactions are surveyed. The direct coupling of chemical dynamics with electronic structure theory, that is, direct dynamics, has allowed one to study the atomic-level dynamics for numerous unimolecular reactions, and extensive non-RRKM and nonintrinsic reaction coordinate (IRC) dynamics have been discovered. These dynamics for OH(-) + CH(3)F and F(-) + CH(3)OOH are reviewed. PMID:19243125

Lourderaj, Upakarasamy; Hase, William L

2009-03-19

313

We study the nonequilibrium dynamics of a coherently split one-dimensional Bose gas by measuring the full probability distribution functions of matter-wave interference. Observing the system on different length scales allows us to probe the dynamics of excitations on different energy scales, revealing two distinct length-scale-dependent regimes of relaxation. We measure the crossover length scale separating these two regimes and identify it with the prethermalized phase-correlation length of the system. Our approach enables a direct observation of the multimode dynamics characterizing one-dimensional quantum systems. PMID:23496695

Kuhnert, M; Geiger, R; Langen, T; Gring, M; Rauer, B; Kitagawa, T; Demler, E; Adu Smith, D; Schmiedmayer, J

2013-03-01

314

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

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

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

2010-12-15

315

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

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

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

2014-03-25

316

Comparative study of the performance of quantum annealing and simulated annealing

NASA Astrophysics Data System (ADS)

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

Nishimori, Hidetoshi; Tsuda, Junichi; Knysh, Sergey

2015-01-01

317

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

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

Alexis Diaz-Torres; David Hinde; Mahananda Dasgupta; Gerard Milburn; Jeff Tostevin

2008-11-11

318

Optimally combining dynamical decoupling and quantum error correction

Quantum control and fault-tolerant quantum computing (FTQC) are two of the cornerstones on which the hope of realizing a large-scale quantum computer is pinned, yet only preliminary steps have been taken towards formalizing the interplay between them. Here we explore this interplay using the powerful strategy of dynamical decoupling (DD), and show how it can be seamlessly and optimally integrated with FTQC. To this end we show how to find the optimal decoupling generator set (DGS) for various subspaces relevant to FTQC, and how to simultaneously decouple them. We focus on stabilizer codes, which represent the largest contribution to the size of the DGS, showing that the intuitive choice comprising the stabilizers and logical operators of the code is in fact optimal, i.e., minimizes a natural cost function associated with the length of DD sequences. Our work brings hybrid DD-FTQC schemes, and their potentially considerable advantages, closer to realization. PMID:23559088

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

2013-01-01

319

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

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

2007-08-15

320

Full-dimensional quantum dynamics of vibrationally highly excited NHD2

NASA Astrophysics Data System (ADS)

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

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

2010-11-01

321

sampling techniques and quantum wave packet dynamics to study both the inhomogeneous structural effects consider control of the vibrational dynamics on an excited electronic state of I2 that has been embedded a measure of how its effectiveness falls off with time in comparison with the parallel gas-phase case

Apkarian, V. Ara

322

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

323

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

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

324

Method for discovering relationships in data by dynamic quantum clustering

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

Weinstein, Marvin; Horn, David

2014-10-28

325

Quantum dynamics of ultrasmall tunnel junctions: Real-time analysis

We present a real-time path-integral analysis of the quantum dynamics of an ultrasmall tunnel junction interacting with an arbitrary external impedance. For a normal junction, we derive a quasiclassical Langevin equation for the phase variable and calculate the I-V curve beyond perturbation theory for the junction conductance. In the superconducting case, we develop a nonperturbative calculation of the time-dependent expectation

D. S. Golubev; A. D. Zaikin

1992-01-01

326

Non-relativistic Gravity in Entropic Quantum Dynamics

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

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

2011-03-14

327

On quantum dynamics and statistics of vectors

NASA Astrophysics Data System (ADS)

Given a sequence of vectors in a Hilbert space, we propose to use the spectrum of the associated Gram matrix as a tool for extracting statistical information on the sequence. We examine two simple models in some detail: the fractional shift where the sequence is generated by a deterministic unitary dynamics and random normalized vectors in a high-dimensional space chosen at a given density. In both cases, the limiting eigenvalue distribution of the Gram matrix is explicitly found. We relate our results to the notion of growth entropy and recover in the stochastic case the eigenvalue distribution of the Wishart matrices.

DeCock, M.; Fannes, M.; Spincemaille, P.

1999-09-01

328

Quantum groups and thermo field dynamics

The algebraic structure of Thermo Field Dynamics for bosons can be fully incorporated in the q-deformation of the Weyl-Heisenberg algebra h{sub q}. The doubling of the degrees of freedom, the set of the tilde-conjugation rules, the Bogoliubov transformation and its generator have a direct and simple interpretation in terms of operators and of properties of h{sub q}. The notion of ``thermal degree of freedom`` introduced by Umezawa also finds a more specific formalization since the corresponding ``thermal conjugate momentum`` can be formally introduced, thus providing one with a set of canonical ``thermal`` values.

De Martino, S.; De Siena, S.; Vitiello, G. [Universita di Salerno (Italy). Dipt. di Fisica]|[INFN, Salerno (Italy)

1996-06-30

329

Phase-ordering dynamics in itinerant quantum ferromagnets

NASA Astrophysics Data System (ADS)

Phase ordering following a rapid quench from the disordered phase to the ordered phase occurs via growth of domains that arise from spontaneous fluctuations. The linear size L of these domains grow as a power law function of time for late times: L(t) t^1/z, with z a dynamical exponent[1]. Until now this description of phase ordering dynamics has been applied to classical systems only. We apply this theory to describe domain growth in both clean and dirty itinerant quantum ferromagnets. The fluctuation effects that invalidate Hertz's theory of the quantum phase transition[2] also affect the phase ordering. For a quench into the ordered phase a transient regime appears, where the dynamical exponent differs from the classical case, and for asymptotically long times the prefactor of the growth law has an anomalous magnetization dependence[3]. A quench to the quantum critical point results in a growth law which is not a power-law function of time.[1] A.J. Bray, Adv. in Phys. 43, 357 (1994). [2] D. Belitz, T.R. Kirkpatrick, and T. Vojta, Rev. Mod. Phys. 77, 579 (2005). [3] D. Belitz, T. R. Kirkpatrick, and Ronojoy Saha, cond-mat/0610650.

Saha, R.; Belitz, D.; Kirkpatrick, T. R.

2007-03-01

330

Dynamical quantum Hall effect in the parameter space

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

Gritsev, V.; Polkovnikov, A.

2012-01-01

331

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

NASA Astrophysics Data System (ADS)

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

Wang, Chen; Chen, Qing-Hu

2013-10-01

332

Canonical versus noncanonical equilibration dynamics of open quantum systems.

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

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

2014-08-01

333

NASA Astrophysics Data System (ADS)

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.

Teixidor, Marc Moix; Varandas, António J. C.

2015-01-01

334

Quantum scattering calculations of the O((3)P)+OH((2)?)?O2((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. PMID:25573563

Teixidor, Marc Moix; Varandas, António J C

2015-01-01

335

Dynamics of quantum turbulence of different spectra

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

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

2014-01-01

336

Quantum dynamics of the avian compass

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

Zachary B. Walters

2012-08-13

337

Quantum dynamics of the avian compass.

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

Walters, Zachary B

2014-10-01

338

Regular and chaotic quantum dynamics in atom-diatom reactive collisions

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

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

2008-05-15

339

Quantum Dynamics in Solid Helium 2009 NHMFL Science Highlight for NSF

"supersolid" phases have been postulated. The experiments measure the nuclear spin dynamics of helium threeQuantum Dynamics in Solid Helium 2009 NHMFL Science Highlight for NSF DMR-Award 0654118 High B at low temperatures to expose the quantum dynamics of solid helium four in the region where new

Weston, Ken

340

Efficient Quantum Monte Carlo Energies for Molecular Dynamics Simulations Jeffrey C. Grossman

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

Mitas, Lubos

341

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

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

2014-10-15

342

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

343

Dynamics of quantum liquids at high momentum

NASA Astrophysics Data System (ADS)

The dynamic form factor S(Q,?) in liquid 3He and 4He is evaluated in the wave-vector transfer range 3<=Q<=15 Å-1. The input is the pair interatomic potential, developed by Aziz et al. The S(Q,?) is calculated within the random-phase approximation (RPA) which becomes valid when ?Q is much larger than the average momentum in the liquid. A T-matrix approximation represents the interaction appearing in the RPA. The aim is to explore how well S(Q,?) can be described for 3<=Q<=15 Å-1 from first principles. In 3He, we find S(Q,?) is a broad, nearly Gaussian function, centered just below the recoil frequency having a width and shape that agrees well with experiment. It does, however, have tails at high frequency which make important contributions to its moments. In 4He, S(Q,?) is a more sharply peaked function which also agrees quite well with experiment. We are able to reproduce the oscillations in the peak position and in the width of S(Q,?) with Q in liquid 4He observed by Martel et al. In the present model, these oscillations originate from oscillations in the magnitude of the T-matrix interaction with Q. The corresponding oscillations are predicted to be very small and probably unobservable in liquid 3He.

Tanatar, B.; Talbot, E. F.; Glyde, H. R.

1987-12-01

344

i t = H A Multi-Stage Ab-initio Quantum Wavepacket Dynamics Formalism for Electronic Structure University, Bloomington, IN 47405 Outline Â· Multi-Stage quantum Wavepacket Ab-initio Dynamical (MS- tive/regenerative behavior . Â· Multiple stages allows for computational simplicity and accuracy

Iyengar, Srinivasan S.

345

NASA Astrophysics Data System (ADS)

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

Sheu, Yae-lin; Hsu, Liang-Yan; Wu, Hau-tieng; Li, Peng-Cheng; Chu, Shih-I.

2014-11-01

346

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

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

2014-01-01

347

Localization and Glassy Dynamics Of Many-Body Quantum Systems

When classical systems fail to explore their entire configurational space, intriguing macroscopic phenomena like aging and glass formation may emerge. Also closed quanto-mechanical systems may stop wandering freely around the whole Hilbert space, even if they are initially prepared into a macroscopically large combination of eigenstates. Here, we report numerical evidences that the dynamics of strongly interacting lattice bosons driven sufficiently far from equilibrium can be trapped into extremely long-lived inhomogeneous metastable states. The slowing down of incoherent density excitations above a threshold energy, much reminiscent of a dynamical arrest on the verge of a glass transition, is identified as the key feature of this phenomenon. We argue that the resulting long-lived inhomogeneities are responsible for the lack of thermalization observed in large systems. Such a rich phenomenology could be experimentally uncovered upon probing the out-of-equilibrium dynamics of conveniently prepared quantum states of trapped cold atoms which we hereby suggest. PMID:22355756

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

2012-01-01

348

Entanglement amplification in the nonperturbative dynamics of modular quantum systems

NASA Astrophysics Data System (ADS)

We analyze the conditions for entanglement amplification between distant and not directly interacting quantum objects by their common coupling to media with static modular structure and subject to a local (single-bond) quenched dynamics. We show that in the nonperturbative regime of the dynamics the initial end-to-end entanglement is strongly amplified and, moreover, can be distributed efficiently between distant objects. Due to its intrinsic local and nonperturbative nature the dynamics is fast and robust against thermal fluctuations, and its control is undemanding. We show that the origin of entanglement amplification lies in the interference of the ground state and at most one of the low-lying energy eigenstates. The scheme can be generalized to provide a fast and efficient router for generating entanglement between simultaneous multiple users.

Bayat, A.; Giampaolo, S. M.; Illuminati, F.; Plenio, M. B.

2013-08-01

349

Quantum Dynamics of a d-wave Josephson Junction

NASA Astrophysics Data System (ADS)

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

Bauch, Thilo

2007-03-01

350

Dynamics of quantum liquids at high momentum

The dynamic form factor S(Q,..omega..) in liquid /sup 3/He and /sup 4/He is evaluated in the wave-vector transfer range 3less than or equal toQless than or equal to15 A/sup -1/. The input is the pair interatomic potential, developed by Aziz et al. The S(Q,..omega..) is calculated within the random-phase approximation (RPA) which becomes valid when h-dash-barQ is much larger than the average momentum in the liquid. A T-matrix approximation represents the interaction appearing in the RPA. The aim is to explore how well S(Q,..omega..) can be described for 3less than or equal toQless than or equal to15 A/sup -1/ from first principles. In /sup 3/He, we find S(Q,..omega..) is a broad, nearly Gaussian function, centered just below the recoil frequency having a width and shape that agrees well with experiment. It does, however, have tails at high frequency which make important contributions to its moments. In /sup 4/He, S(Q,..omega..) is a more sharply peaked function which also agrees quite well with experiment. We are able to reproduce the oscillations in the peak position and in the width of S(Q,..omega..) with Q in liquid /sup 4/He observed by Martel et al. In the present model, these oscillations originate from oscillations in the magnitude of the T-matrix interaction with Q. The corresponding oscillations are predicted to be very small and probably unobservable in liquid /sup 3/He.

Tanatar, B.; Talbot, E.F.; Glyde, H.R.

1987-12-01

351

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

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

Nguyen, Minh Tho

352

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

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

2012-01-01

353

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

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

354

Stroboscopic observation of quantum many-body dynamics

Recent experiments have demonstrated single-site resolved observation of cold atoms in optical lattices. Thus, in the future it may be possible to take repeated snapshots of an interacting quantum many-body system during the course of its evolution. Here we address the impact of the resulting Quantum (anti-)Zeno physics on the many-body dynamics. We use time-dependent DMRG to obtain the time evolution of the full many-body wave function that is then periodically projected in order to simulate realizations of stroboscopic measurements. For the example of a 1-D lattice of spin-polarized fermions with nearest-neighbor interactions, we find regimes for which many-particle configurations are stabilized and destabilized depending on the interaction strength and the time between observations.

Kessler, Stefan; McCulloch, Ian P; von Delft, Jan; Marquardt, Florian

2011-01-01

355

Stroboscopic observation of quantum many-body dynamics

Recent experiments have demonstrated single-site resolved observation of cold atoms in optical lattices. Thus, in the future it may be possible to take repeated snapshots of an interacting quantum many-body system during the course of its evolution. Here we address the impact of the resulting Quantum (anti-)Zeno physics on the many-body dynamics. We use the time-dependent density-matrix renormalization group to obtain the time evolution of the full many-body wave function, which is then periodically projected in order to simulate realizations of stroboscopic measurements. For the example of a one-dimensional lattice of spin-polarized fermions with nearest-neighbor interactions, we find regimes for which many-particle configurations are stabilized and destabilized depending on the interaction strength and the time between observations.

Stefan Kessler; Andreas Holzner; Ian P. McCulloch; Jan von Delft; Florian Marquardt

2012-01-12

356

Quantum dynamics of ultrasmall tunnel junctions: Real-time analysis

NASA Astrophysics Data System (ADS)

We present a real-time path-integral analysis of the quantum dynamics of an ultrasmall tunnel junction interacting with an arbitrary external impedance. For a normal junction, we derive a quasiclassical Langevin equation for the phase variable and calculate the I-V curve beyond perturbation theory for the junction conductance. In the superconducting case, we develop a nonperturbative calculation of the time-dependent expectation value of the voltage operator and voltage-voltage correlation functions. Provided that dissipation is small enough, both of these quantities show damped oscillations and a power-law decay in the low-temperature limit. We also analyze the effect of resonant voltage steps on the I-V curve of an ac-driven tunnel junction and evaluate the linewidth of Bloch oscillations in the quantum limit.

Golubev, D. S.; Zaikin, A. D.

1992-11-01

357

Monte Carlo techniques for real-time quantum dynamics

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

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

2005-07-01

358

High-performance dynamic quantum clustering on graphics processors

NASA Astrophysics Data System (ADS)

Clustering methods in machine learning may benefit from borrowing metaphors from physics. Dynamic quantum clustering associates a Gaussian wave packet with the multidimensional data points and regards them as eigenfunctions of the Schrödinger equation. The clustering structure emerges by letting the system evolve and the visual nature of the algorithm has been shown to be useful in a range of applications. Furthermore, the method only uses matrix operations, which readily lend themselves to parallelization. In this paper, we develop an implementation on graphics hardware and investigate how this approach can accelerate the computations. We achieve a speedup of up to two magnitudes over a multicore CPU implementation, which proves that quantum-like methods and acceleration by graphics processing units have a great relevance to machine learning.

Wittek, Peter

2013-01-01

359

High-performance dynamic quantum clustering on graphics processors

Clustering methods in machine learning may benefit from borrowing metaphors from physics. Dynamic quantum clustering associates a Gaussian wave packet with the multidimensional data points and regards them as eigenfunctions of the Schroedinger equation. The clustering structure emerges by letting the system evolve and the visual nature of the algorithm has been shown to be useful in a range of applications. Furthermore, the method only uses matrix operations, which readily lend themselves to parallelization. In this paper, we develop an implementation on graphics hardware and investigate how this approach can accelerate the computations. We achieve a speedup of up to two magnitudes over a multicore CPU implementation, which proves that quantum-like methods and acceleration by graphics processing units have a great relevance to machine learning.

Wittek, Peter, E-mail: peterwittek@acm.org [Swedish School of Library and Information Science, University of Boras, Boras (Sweden)] [Swedish School of Library and Information Science, University of Boras, Boras (Sweden)

2013-01-15

360

Dynamic phase diagram for the quantum phase model

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

361

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

Jiao Wang; Anders S. Mouritzen; Jiangbin Gong

2008-03-27

362

Quantum dynamics in continuum for proton transport—Generalized correlation

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

Chen, Duan; Wei, Guo-Wei

2012-01-01

363

Quantum dynamics in continuum for proton transport—Generalized correlation

NASA Astrophysics Data System (ADS)

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.

Chen, Duan; Wei, Guo-Wei

2012-04-01

364

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

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

Chen, Duan; Wei, Guo-Wei

2012-04-01

365

Influence of external magnetic field on dynamics of open quantum systems

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

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

2007-03-15

366

Dynamics of spin injection has been studied in double quantum wells (DQWs) composed of diluted magnetic and non-magnetic semiconductors. Picosecond-transient photoluminescence (PL) of excitons in the DQWs has been measured in magnetic field. In the Cd1?xMnxTe-based DQWs, the PL intensity of the magnetic well (MW) excitons decays faster with decreasing barrier width from 12 to 2nm. This provides the evidence

K. Kayanuma; K. Seo; K. Nishibayashi; A. Murayama; Y. Oka; I. A. Buyanova; W. M. Chen

2006-01-01

367

Quantum dynamics of the phase in Josephson tunnel junctions at millikelvin temperatures

We experimentally study the dynamics of the phase difference in a small current-biased Josephson tunnel junction at low temperatures. The experiments are performed using a high resolution measurement of the junctions switching current by a timing technique. The measured switching current distributions indicate the macroscopic quantum tunneling of the phase below a cross-over temperature of T* = 250 mK. At

A. Wallraff; C. Coqui; T. Duty; A. V. Ustinov; A. Lukashenko; M. V. Fistul

2002-01-01

368

Dynamics of the Measurement of Nuclear Spins in a Solid-State Quantum Computer

We study numerically the process of nuclear spin measurement in a solid-state\\u000aquantum computer of the type proposed by Kane by modeling the quantum dynamics\\u000aof two coupled nuclear spins on $^{31}$P donors implanted in silicon. We\\u000aestimate the minimum measurement time necessary for the reliable transfer of\\u000aquantum information from the nuclear spin subsystem to the electronic\\u000asubsystem. We

Gennady P. Berman; David K. Campbell; Gary D. Doolen; Kirill E. Nagaev

1999-01-01

369

Interacting distributed approximating functions for real-time quantum dynamics

NASA Astrophysics Data System (ADS)

The distributed approximating function (DAF) approach to quantum real-time dynamics is generalized to include the effects of the potential. The ``interacting'' DAF (IDAF) is introduced as the identity for a certain class of functions that can be chosen to approximate as closely as desired any wave packet of interest. Free propagation of the IDAF yields the free propagator for the IDAF class in the coordinate representation, and substitution of this result into the Trotter form for the short-time full propagator, G(x,x'??), yields the IDAF class full propagator, G(x,x';{p}??), in the coordinate representation. Here {p} denotes the set of parameters that determine the IDAF class. The IDAF class full propagator can be used to develop discretized path integral-based algorithms for real-time quantum dynamics. Use of G(x,x';{p}??) in the Feynman path integral formalism leads to a new result with interesting features compared to the standard path integral. Specifically, the IDAF class full propagator incorporates the classical force, and (1) automatically biases the dynamics toward the neighborhood of classical trajectories (but without relying on destructive and constructive interferences in that no recourse is made to stationary phase arguments), (2) automatically concentrates the wave packet in highly classical regions and attenuates the wave packet in highly nonclassical regions. Of the many possible IDAF-based algorithms two are presented as examples. One illustrates a Monte Carlo approach and the other a discretized matrix multiplication approach.

Hoffman, David K.; Arnold, Mark; Zhu, Wei; Kouri, Donald J.

1993-07-01

370

Ultrafast carrier dynamics in CuInS{sub 2} quantum dots

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.

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

371

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

372

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

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

Zied Ammari; Marco Falconi; Boris Pawilowski

2014-11-23

373

Quantum dynamics of non-relativistic particles and isometric embeddings

It is considered, in the framework of constrained systems, the quantum dynamics of non-relativistic particles moving on a d-dimensional Riemannian manifold M isometrically embedded in $R^{d+n}$. This generalizes recent investigations where M has been assumed to be a hypersurface of $R^{d+1}$. We show, contrary to recent claims, that constrained systems theory does not contribute to the elimination of the ambiguities present in the canonical and path integral formulations of the problem. These discrepancies with recent works are discussed.

Alberto Saa

1996-11-08

374

Dynamic quantum secret sharing protocol based on GHZ state

NASA Astrophysics Data System (ADS)

This work proposes a new dynamic quantum secret sharing (DQSS) protocol using the measurement property of Greenberger-Horne-Zeilinger state and the controlled-NOT gate. In the proposed DQSS protocol, an agent can obtain a shadow of the secret key by simply performing a measurement on single photons. In comparison with the existing DQSS protocols, it provides better qubit efficiency and has an easy way to add a new agent. The proposed protocol is also free from the eavesdropping attack, the collusion attack, and can have an honesty check on a revoked agent.

Liao, Ci-Hong; Yang, Chun-Wei; Hwang, Tzonelish

2014-08-01

375

Theoretical studies of combustion dynamics

The basic objectives of this research program are to develop and apply theoretical techniques to fundamental dynamical processes of importance in gas-phase combustion. There are two major areas currently supported by this grant. One is reactive scattering of diatom-diatom systems, and the other is the dynamics of complex formation and decay based on L{sup 2} methods. In all of these studies, the authors focus on systems that are of interest experimentally, and for which potential energy surfaces based, at least in part, on ab initio calculations are available.

Bowman, J.M. [Emory Univ., Atlanta, GA (United States)

1993-12-01

376

One-step implementation of the 1->3 orbital state quantum cloning machine via quantum Zeno dynamics

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.

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

377

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

NASA Astrophysics Data System (ADS)

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

Rivas, Angel; Martin-Delgado, Miguel A.

2013-03-01

378

NASA Astrophysics Data System (ADS)

The effect of proton exchange on the measurement of 1H- 1H, 1H- 2H, and 2H- 2H residual dipolar interactions in water molecules in bovine Achilles tendons was investigated using double-quantum-filtered (DQF) NMR and new pulse sequences based on heteronuclear and homonuclear multiple-quantum filtering (MQF). Derivation of theoretical expressions for these techniques allowed evaluation of the 1H- 1H and 1H- 2H residual dipolar interactions and the proton exchange rate at a temperature of 24°C and above, where no dipolar splitting is evident. The values obtained for these parameters at 24°C were 300 and 50 Hz and 3000 s -1, respectively. The results for the residual dipolar interactions were verified by repeating the above measurements at a temperature of 1.5°C, where the spectra of the H 2O molecules were well resolved, so that the 1H- 1H dipolar interaction could be determined directly from the observed splitting. Analysis of the MQF experiments at 1.5°C, where the proton exchange was in the intermediate regime for the 1H- 2H dipolar interaction, confirmed the result obtained at 24°C for this interaction. A strong dependence of the intensities of the MQF signals on the proton exchange rate, in the intermediate and the fast exchange regimes, was observed and theoretically interpreted. This leads to the conclusion that the MQF techniques are mostly useful for tissues where the residual dipolar interaction is not significantly smaller than the proton exchange rate. Dependence of the relaxation times and signal intensities of the MQF experiments on the orientation of the tendon with respect to the magnetic field was observed and analyzed. One of the results of the theoretical analysis is that, in the fast exchange regime, the signal decay rates in the MQF experiments as well as in the spin echo or CPMG pulse sequences ( T2) depend on the orientation as the square of the second-rank Legendre polynomial.

Eliav, Uzi; Navon, Gil

1999-04-01

379

Dynamics of Quantum Vorticity in a Random Potential

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

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

2009-04-03

380

Dynamics of Crowd Behaviors: From Complex Plane to Quantum Random Fields

NASA Astrophysics Data System (ADS)

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

Ivancevic, Vladimir G.; Reid, Darryn J.

2015-11-01

381

Ultrafast dynamics of type-II GaSb/GaAs quantum dots

NASA Astrophysics Data System (ADS)

In this paper, room temperature two-colour pump-probe spectroscopy is employed to study ultrafast carrier dynamics in type-II GaSb/GaAs quantum dots. Our results demonstrate a strong dependency of carrier capture/escape processes on applied reverse bias voltage, probing wavelength and number of injected carriers. The extracted timescales as a function of both forward and reverse bias may provide important information for the design of efficient solar cells and quantum dot memories based on this material. The first few picoseconds of the dynamics reveal a complex behaviour with an interesting feature, which does not appear in devices based on type-I materials, and hence is linked to the unique carrier capture/escape processes possible in type-II structures.

Komolibus, K.; Piwonski, T.; Gradkowski, K.; Reyner, C. J.; Liang, B.; Huyet, G.; Huffaker, D. L.; Houlihan, J.

2015-01-01

382

Picosecond dynamics and stimulated emissions of excitons in Zn1-xCdxSe\\/ZnSe quantum wells

The dynamics and stimulated emission processes of the exciton luminescence are studied in quantum wells (QWs) of the Zn1-xCdxSe\\/ZnSe system. A multiquantum well (MQW) structure shows an exciton lifetime of 150-280 ps and a stimulated emission effect due to exciton-exciton scattering as well as due to electron-hole plasma recombination. A combined-QW structure in which a single quantum well (SQW) is

Takeham Tsutsumi; Jen Y. Jen; Izuru Souma; Yasuo Oka

1994-01-01

383

Carrier dynamics in self-organized quantum dots have been studied using temperature-dependent differential transmission spectroscopy and room temperature high-frequency electrical impedance measurements on quantum dot lasers. These results suggest the existence of a long relaxation time (?100ps) for the excited state carriers at higher temperatures with the dominant scattering mechanism being electron–hole scattering. The long relaxation time is exploited to realize

Pallab Bhattacharya; Sanjay Krishna; Jamie Phillips; Patrick J. McCann; Khosrow Namjou

2001-01-01

384

Competing quantum effects in the dynamics of a flexible water model

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

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

2010-11-04

385

Vortex Quantum Dynamics of Two Dimensional Lattice Bosons

NASA Astrophysics Data System (ADS)

We study hard-core lattice bosons in a magnetic field near half filling. The bare vortex hopping rate is extracted from exact diagonalizations of square clusters. We deduce a quantum melting of the vortex lattice above vortex density of 6.5×10-3 per lattice site. The Hall conductivity reverses sign abruptly as the density crosses half filling, where its characteristic temperature scale vanishes. We prove that at precisely half filling, each vortex carries a spin-1/2 quantum number (“v spin”). Experimental implications of these results are discussed.

Lindner, Netanel H.; Auerbach, Assa; Arovas, Daniel P.

2009-02-01

386

Cold atom dynamics in a quantum optical lattice potential

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

Christoph Maschler; Helmut Ritsch

2006-02-27

387

1H spin-lattice relaxation times and second moments were determined for polycrystalline (CH3NH3)3Sb2Br9 sample in a wide range of temperature (5-200 K) at 24.6 and 55.2 MHz. 2H NMR spectra of (CD3NH3)3Sb2Br9 were recorded between 5 K and room temperature. The relaxation time is interpreted as a result of motion of two different non-equivalent types of monomethylammonium cations occurring at the 2:1 proportion in a unit cell. Below 30 K, the relaxation processes via tunneling are suggested to dominate. Above 30 K, only classical behaviour of methylammonium cations is detected. Two monomethylammonium cations relax with the classical correlated C3 reorientation and the rotational tunnelling mechanism, while the third cation exhibits only the classical correlated reorientation. The dynamic parameters of these motions have been determined. PMID:10499659

Medycki, W

1999-09-01

388

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

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

2008-03-28

389

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...

390

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

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

Devoret, Michel H.

391

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

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

Shepelyansky, Dima

392

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

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

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

2007-01-01

393

In the second part of this paper on micro-canonical ensemble a new numerical approach for consideration of quantum dynamics and calculations of the average values of quantum operators and time correlation functions in the Wigner representation of quantum statistical mechanics has been developed. The time correlation functions have been presented in the form of the integral of the Weyl's symbol

V. S. Filinov; Yu E. Lozovik; A. V. Filinov; I. E. Zacharov; Alexei M. Oparin

1998-01-01

394

In the second part of this paper on micro-canonical ensemble a new numerical approach for consideration of quantum dynamics and calculations of the average values of quantum operators and time correlation functions in the Wigner representation of quantum statistical mechanics has been developed. The time correlation functions have been presented in the form of the integral of the Weyl’s symbol

V. S. Filinov; Yu E Lozovik; A V Filinov; I E Zacharov; Alexei M Oparin

1998-01-01

395

Electron-nuclear spin dynamics in a mesoscopic solid-state quantum computer

We numerically simulate the process of nuclear spin measurement in Kane's quantum computer. For this purpose, we model the quantum dynamics of two coupled nuclear spins on 31P donors implanted in Si. We estimate the minimum time of measurement necessary for the reliable transfer of quantum information from the nuclear spin subsystem to the electronic subsystem. We also calculate the

Gennady P. Berman; David K. Campbell; Gary D. Doolen; Kirill E. Nagaev

1999-01-01

396

The time-evolution of multiparty quantum correlations as quantified by monogamy scores and bipartition collections of quantum correlations is investigated for light-harvesting complexes modelled by the fully connected and the Fenna-Mathews-Olson networks. The dynamics consists of a coherent term as well as dissipative, dephasing, and sink operator terms. The multiparty quantum correlation reveals important information regarding the sharability of quantum correlations in the networks. In particular, we show that the relative values of the ingredients of multiparty quantum correlation measures in the time dynamics clearly indicate the route of energy transfer from the antenna to the bacterial reaction center in the Fenna-Mathews-Olson complex.

Titas Chanda; Utkarsh Mishra; Aditi Sen De; Ujjwal Sen

2014-12-19

397

Nonadiabatic molecular dynamics simulation: An approach based on quantum measurement picture

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.

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

398

Exact Time-Local Quantum-State-Diffusion Equation for Multilevel Quantum Dynamics

An open quantum system with multiple levels coupled to a bosonic environment at zero temperature is investigated systematically using the non-Markovian quantum state diffusion (QSD) method [W. T. Strunz, L.Di\\'osi and N. Gisin, Phys. Rev. Lett. {\\bf 82}, 1801 (1999)]. For the first time, we have established exact time-local QSD equations for a set of interesting multilevel open systems including the high-spin systems, multiple transition atom models, and multilevel atom models driven by time-dependent external fields. These exact QSD equations have paved a way to evaluate the dynamics of the open multilevel atomic systems in the general non-Markovian regimes without any approximation.

Jing, Jun; You, J Q; Yu, Ting

2012-01-01

399

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

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

2014-01-01

400

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

Density-dependent carrier dynamics in a quantum dots-in-a-well heterostructure R. P. Prasankumar,1 transmission spectroscopy to temporally and spectrally resolve density-dependent carrier dynamics in a quantum levels at low densities, while at high densities we observe an anomalous induced absorption

Krishna, Sanjay

401

We present a general time-dependent approach for efficient and accurate treatment of high-resolution spectrocopy and quantum dynamics. The procedure is applied to an ab initio time-dependent study of three-dimensional ...

Tong, Xiao-Min; Chu, Shih-I

2000-02-01

402

A quantum dynamical approach to matrix Khrushchev's formulas

Khrushchev's formula is the cornerstone of the so called Khrushchev theory, a body of results which has revolutionized the theory of orthogonal polynomials on the unit circle. This formula can be understood as a factorization of the Schur function for an orthogonal polynomial modification of a measure on the unit circle. No such formula is known in the case of matrix-valued measures. This constitutes the main obstacle to generalize Khrushchev theory to the matrix-valued setting which we overcome in this paper. It was recently discovered that orthogonal polynomials on the unit circle and their matrix-valued versions play a significant role in the study of quantum walks, the quantum mechanical analogue of random walks. In particular, Schur functions turn out to be the mathematical tool which best codify the return properties of a discrete time quantum system, a topic in which Khrushchev's formula has profound and surprising implications. We will show that this connection between Schur functions and quantum walks is behind a simple proof of Khrushchev's formula via `quantum' diagrammatic techniques for CMV matrices. This does not merely give a quantum meaning to a known mathematical result, since the diagrammatic proof also works for matrix-valued measures. Actually, this path counting approach is so fruitful that it provides different matrix generalizations of Khrushchev's formula, some of them new even in the case of scalar measures. Furthermore, the path counting approach allows us to identify the properties of CMV matrices which are responsible for Khrushchev's formula. On the one hand, this helps to formalize and unify the diagrammatic proofs using simple operator theory tools. On the other hand, this is the origin of our main result which extends Khrushchev's formula beyond the CMV case, as a factorization rule for Schur functions related to general unitary operators.

C. Cedzich; F. A. Grünbaum; L. Velázquez; A. H. Werner; R. F. Werner

2014-05-05

403

A study on quantum discord in Gaussian states

NASA Astrophysics Data System (ADS)

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.

Yang, Xiong; Huang, Guo Hui; Fang, Mao Fa

2015-04-01

404

Efficient semiclassical quantum nuclear effects for shock compression studies

NASA Astrophysics Data System (ADS)

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

Reed, Evan

2013-03-01

405

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

406

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

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

2011-05-15

407

NASA Astrophysics Data System (ADS)

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

Zhu, Lili; Liu, Hao; Shi, Qiang

2013-09-01

408

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

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

2009-01-01

409

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

NASA Astrophysics Data System (ADS)

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

Rosales-Zárate, L.; Opanchuk, B.; Drummond, P. D.; Reid, M. D.

2014-08-01

410

Quantum Dynamical Behaviour in Complex Systems - A Semiclassical Approach

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

Gliebe, Cheryn E; Ananth, Nandini

2008-05-22

411

Dynamical quantum phase transitions in systems with broken-symmetry phases

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.

Markus Heyl

2014-11-21

412

A combined quantum-classical dynamics method for calculating thermal rate constants of chemical February 1992) We present a combined quantum-classical-stochastic dynamics method based on the flux to combine classical and quantum dynamics have been pro- posed and have shown some encouraging results

Truong, Thanh N.

413

Hot electron dynamics at semiconductor surfaces: Implications for quantum dot photovoltaics

NASA Astrophysics Data System (ADS)

Finding a viable supply of clean, renewable energy is one of the most daunting challenges facing the world today. Solar cells have had limited impact in meeting this challenge because of their high cost and low power conversion efficiencies. Semiconductor nanocrystals, or quantum dots, are promising materials for use in novel solar cells because they can be processed with potentially inexpensive solution-based techniques and because they are predicted to have novel optoelectronic properties that could enable the realization of ultra-efficient solar power converters. However, there is a lack of fundamental understanding regarding the behavior of highly-excited, or "hot," charge carriers near quantum-dot and semiconductor interfaces, which is of paramount importance to the rational design of high-efficiency devices. The elucidation of these ultrafast hot electron dynamics is the central aim of this Dissertation. I present a theoretical framework for treating the electronic interactions between quantum dots and bulk semiconductor surfaces and propose a novel experimental technique, time-resolved surface second harmonic generation (TR-SHG), for probing these interactions. I then describe a series of experimental investigations into hot electron dynamics in specific quantum-dot/semiconductor systems. A two-photon photoelectron spectroscopy (2PPE) study of the technologically-relevant ZnO(1010) surface reveals ultrafast (sub-30fs) cooling of hot electrons in the bulk conduction band, which is due to strong electron-phonon coupling in this highly polar material. The presence of a continuum of defect states near the conduction band edge results in Fermi-level pinning and upward (n-type) band-bending at the (1010) surface and provides an alternate route for electronic relaxation. In monolayer films of colloidal PbSe quantum dots, chemical treatment with either hydrazine or 1,2-ethanedithiol results in strong and tunable electronic coupling between neighboring quantum dots. A TR-SHG study of these electronically-coupled quantum-dot films reveals temperature-activated cooling of hot charge carriers and coherent excitation of a previously-unidentified surface optical phonon. Finally, I report the first experimental observation of ultrafast electron transfer from the higher excited states of a colloidal quantum dot (PbSe) to delocalized conduction band states of a widely-used electron acceptor (TiO2). The electric field resulting from ultrafast (<50fs) separation of charge carriers across the PbSe/TiO2(110) interface excites coherent vibration of the TiO2 surface atoms, whose collective motions can be followed in real time.

Tisdale, William A., III

414

to the dynamical properties of low dimensionality semiconductor lasers. We concentrate on quantum dash lasers but many of the properties hold, with very few changes, to quantum dot lasers. We formulate a self of quantum dot (QD) and quantum dash (QDash) which have the properties of quantum wires [1]) lasers [2

Eisenstein, Gadi

415

proven to be a valuable tool. Few- electron ground states and the corresponding charging ener- gies can,4 Instead of a highly doped 3D GaAs layer however, a 2DEG is used as a back contact.5,9,10 The QDs. The dot density of the sample is about 8.3 109 cm-2 , determined by atomic force micros- copy studies

Lorke, Axel

416

The title isotope exchange reaction was studied by converged time-dependent wave packet calculations, where an efficient 4th order split operator was applied to propagate the initial wave packet. State-to-state differential and integral cross sections up to the collision energy of 0.35 eV were obtained with (32)O2 in the hypothetical j0 = 0 state. It is discovered that the differential cross sections are largely forward biased in the studied collision energy range, due to the fact that there is a considerable part of the reaction occurring with large impact parameter and short lifetime relative to the rotational period of the intermediate complex. The oscillations of the forward scattering amplitude as a function of collision energy, which result from coherent contribution of adjacent resonances, may be a sensitive probe for examining the quality of the underlying potential energy surface. A good agreement between the theoretical and recent experimental integral and differential cross sections at collision energy of 7.3 kcal/mol is obtained. However, the theoretical results predict slightly too much forward scattering and colder rotational distributions than the experimental observations at collision energy of 5.7 kcal/mol. PMID:25681907

Xie, Wenbo; Liu, Lan; Sun, Zhigang; Guo, Hua; Dawes, Richard

2015-02-14

417

Ab Initio Time-Domain Study of Phonon-Assisted Relaxation of Charge Carriers in a PbSe Quantum Dot

of inorganic semiconductors, known as artificial atoms or quantum dots (QD), exhibit a variety of uniqueAb Initio Time-Domain Study of Phonon-Assisted Relaxation of Charge Carriers in a PbSe Quantum Dot The phonon-induced relaxation dynamics of charge carriers in a PbSe quantum dot is studied for the first time

418

Vortex Quantum Dynamics of Two Dimensional Lattice Bosons

We study hard-core lattice bosons in a magnetic field near half filling. The bare vortex hopping rate is extracted from exact diagonalizations of square clusters. We deduce a quantum melting of the vortex lattice above vortex density of 6.5×10-3 per lattice site. The Hall conductivity reverses sign abruptly as the density crosses half filling, where its characteristic temperature scale vanishes.

Netanel H. Lindner; Assa Auerbach; Daniel P. Arovas

2009-01-01

419

Vortex Quantum Dynamics of Two Dimensional Lattice Bosons

We study hard-core lattice bosons in a magnetic field near half filling. The bare vortex hopping rate is extracted from exact diagonalizations of square clusters. We deduce a quantum melting of the vortex lattice above vortex density of 6.5x10³ per lattice site. The Hall conductivity reverses sign abruptly as the density crosses half filling, where its characteristic temperature scale vanishes.

Netanel H. Lindner; Assa Auerbach; Daniel P. Arovas

2009-01-01

420

Vortex quantum dynamics of two dimensional lattice bosons

We study hard core lattice bosons in a magnetic field near half filling ootnotetextSee: arXiv:0810.2604. The strong periodic potential scatters the vortices by units of reciprocal lattice momenta, enhancing their mobility and modifying their effective Magnus field. The bare vortex hopping rate on the dual lattice is extracted by exact diagonalizations of square clusters. We deduce quantum melting of the

Netanel H. Lindner; Assa Auerbach; Daniel P. Arovas

2009-01-01

421

NASA Astrophysics Data System (ADS)

Solid inclusion complex of the non-steroidal anti-inflammatory drug Ibuprofen (IBP, (2-[4-(2-methylpropyl)phenyl]-propanoic acid) with (2,6-dimethyl)-?-cyclodextrin (diME-?-CD) has been investigated by Fourier transform infrared spectroscopy in attenuated total reflectance geometry (FTIR-ATR spectroscopy) and numerical simulation. The complexation-induced changes in the FTIR-ATR spectrum of IBP have been interpreted by comparison with the theoretical vibrational wavenumbers and IR intensities of dimeric structures of IBP, derived from symmetric hydrogen bonding of the two carboxylic groups, computed by using Density Functional Theory (DFT) calculations. From temperature-dependent studies, the enthalpy change ?H associated with the binding of IBP with diME-?-CD for 1:1 stoichiometry, in solid phase, has been estimated.

Crupi, V.; Guella, G.; Majolino, D.; Mancini, I.; Rossi, B.; Stancanelli, R.; Venuti, V.; Verrocchio, P.; Viliani, G.

2010-05-01

422

Generalized uncertainty relations and entanglement dynamics in quantum Brownian motion models

We study entanglement dynamics in quantum Brownian motion (QBM) models. Our main tool is the Wigner function propagator. Time evolution in the Wigner picture is physically intuitive and it leads to a simple derivation of a master equation for any number of system harmonic oscillators and spectral density of the environment. It also provides generalized uncertainty relations, valid for any initial state, that allow a characterization of the environment in terms of the modifications it causes to the system's dynamics. In particular, the uncertainty relations are very informative about the entanglement dynamics of Gaussian states, and to a lesser extent for other families of states. For concreteness, we apply these techniques to a bipartite QBM model, describing the processes of entanglement creation, disentanglement, and decoherence at all temperatures and time scales.

Anastopoulos, C.; Kechribaris, S.; Mylonas, D. [Department of Physics, University of Patras, GR-26500 Patras (Greece)

2010-10-15

423

Imaging mGluR5 dynamics in astrocytes using quantum dots.

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

Arizono, Misa; Bannai, Hiroko; Mikoshiba, Katsuhiko

2014-01-01

424

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

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

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

2010-09-14

425

Dissipationless directed transport in rocked single-band quantum dynamics

Using matter waves that are trapped in a deep optical lattice, dissipationless directed transport is demonstrated to occur if the single-band quantum dynamics is periodically tilted on one half of the lattice by a monochromatic field. Most importantly, the directed transport can exist for almost all system parameters, even after averaged over a broad range of single-band initial states. The directed transport is theoretically explained within ac-scattering theory. Total reflection phenomena associated with the matter waves traveling from a tilting-free region to a tilted region are emphasized. The results are of relevance to ultracold physics and solid-state physics, and may lead to powerful means of selective, coherent, and directed transport of cold particles in optical lattices.

Gong, Jiangbin; Poletti, Dario [Department of Physics and Center for Computational Science and Engineering, National University of Singapore, 117542 (Singapore); Hanggi, Peter [Theoretische Physik I, Institut fuer Physik, Universitaet Augsburg, D-86135 Augsburg (Germany); Department of Physics and Center for Computational Science and Engineering, National University of Singapore, 117542 (Singapore)

2007-03-15

426

Common Axioms for Inferring Classical Ensemble Dynamics and Quantum Theory

The same set of physically motivated axioms can be used to construct both the classical ensemble Hamilton-Jacobi equation and Schroedingers equation. Crucial roles are played by the assumptions of universality and simplicity (Occam's Razor) which restrict the number and type of of arbitrary constants that appear in the equations of motion. In this approach, non-relativistic quantum theory is seen as the unique single parameter extension of the classical ensemble dynamics. The method is contrasted with other related constructions in the literature and some consequences of relaxing the axioms are also discussed: for example, the appearance of nonlinear higher-derivative corrections possibly related to gravity and spacetime fluctuations. Finally, some open research problems within this approach are highlighted.

Parwani, Rajesh R. [Department of Physics, National University of Singapore, Kent Ridge (Singapore); University Scholars Programme, National University of Singapore, Kent Ridge (Singapore)

2006-01-04

427

Dynamic-local-field approximation for the quantum solids

NASA Technical Reports Server (NTRS)

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

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

1974-01-01

428

Dynamics of a Two-Dimensional System of Quantum Dipoles

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.

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

429

Exact quantum dynamics calculations using a symmetrized Gaussian basis

NASA Astrophysics Data System (ADS)

In a series of earlier articles, a new method was introduced for performing exact quantum dynamics calculations. The method uses a ``weylet'' basis set (orthogonalized Weyl-Heisenberg wavelets), combined with phase space truncation, to defeat the exponential scaling of CPU effort with system dimensionality that has long plagued such calculations. Here, we present results obtained using a basis of momentum-symmetrized Gaussians. Despite being non-orthogonal, symmetrized Gaussians do exhibit collectively locality, allowing for effective phase space truncation. Application to both isotropic uncoupled harmonic oscillators and coupled anharmonic oscillators are discussed. Results for uncoupled systems up to 15 dimensions are compared with previous weylet calculations and found to be essentially just as efficient. A ``universal'' code has been written, which is dimensionally independent, and which also exploits massively parallel algorithms. Using the new codes, calculations up to 27 dimensions have been achieved. Lastly, symmetrized Gaussian calculations for coupled anharmonic oscillators are analyzed, and compared to first order degenerate perturbation theory.

Halverson, Thomas; Poirier, Bill

2012-10-01

430

THz-driven nonlinear intersubband dynamics in quantum wells.

In this work, we demonstrate the direct observation of non-equilibrium intersubband dynamics in a modulation-doped multiple quantum well sample induced by intense terahertz pulses. The transmission spectra show a clear dependence on the incident THz field strength, which gives rise to a multitude of nonlinear optical effects that go beyond the standard textbook two-level description of light-matter interaction. Of special interest is thereby the multiple octave spanning bandwidth of the used single-cycle THz pulses, which allows the phase-locked coupling of adjacent intersubband transitions. Examples of this interaction include the efficient, coherent population transfer, the THz induced undressing of collective excitations, and the THz Stark effect. PMID:23188269

Dietze, D; Darmo, J; Unterrainer, K

2012-10-01

431

State-to-state ArHBr photodissociation quantum dynamics

NASA Astrophysics Data System (ADS)

We report quantum dynamical calculations on the photodissociation process: ArHBr+hnu[right arrow]H+ArBr or Ar+Br+H. Jacobi coordinates associated with the product arrangement H+ArBr have been used as well as a pseudospectral wave packet propagation method. The radial singularity at the origin is either analytically lifted with a discrete Bessel transform approach, or treated within a sine transform strategy. The relative fraction of a bound ArBr product state is high (of the order of 50%) and decreases with energy. Product vibrational populations decrease with vibrational energies. Rotational distributions show oscillatory patterns characteristic of rotational rainbows, whereas angular distributions have maxima at rainbow angles.

Lepetit, Bruno; Lemoine, Didier

2002-11-01

432

Analytical investigation of the dynamics behaviors of quantum cascade laser

NASA Astrophysics Data System (ADS)

In this paper, we investigate analytically and numerically the transient dynamics of the mid-infrared quantum cascade laser operating in a single mode. The approach is based on using adiabatic elimination in the rate equations model. Analytical solutions are derived for steady-state and time-dependent number of electrons in the various levels, population inversion and number of photons in the cavity. In addition, the equation that allows for the determination of time for steady-state establishment is derived within the premises of our analytical model in the most general case. The results are compared with numerical calculations. The dependence of the buildup time on current injection is also examined and compared with our other existing model.

Hamadou, A.

2015-01-01

433

Quantum-Chemical Studies on TATB Processes

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

R. S. Patil; S. Radhakrishnan; P. M. Jadhav; V. D. Ghule; T. Soman

2010-01-01

434

Two dimensional kicked quantum Ising model: dynamical phase transitions

NASA Astrophysics Data System (ADS)

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.

Pineda, C.; Prosen, T.; Villaseñor, E.

2014-12-01

435

Dynamical Gaussian state transfer with quantum-error-correcting architecture

NASA Astrophysics Data System (ADS)

Transferring a quantum state of a light field to a memory is of particular importance. However, this transfer is usually hampered because the memory system is subjected to some noise and this can limit the performance of the state transfer greatly. In this paper, we consider the transfer of a Gaussian state of light to a linear medium memory such as an optomechanical oscillator and propose a dynamical feedback controller that suppresses the noise in the memory system. To protect an unknown state, the feedback scheme employs the specific configuration of the quantum error correction; that is, a three-mode Gaussian state having appropriate syndromes is taken as the input. Correspondingly, the memory consists of three independent linear systems. The syndrome errors are estimated continuously in time through the measurement of the output field, and the results are then fed back to control the system. Because the input is Gaussian and the systems are all linear, it is possible to formulate the problem using the framework of the celebrated classical Kalman filtering and linear quadratic Gaussian control. A numerical simulation demonstrates the effectiveness of the control scheme.

Tajimi, Go; Yamamoto, Naoki

2012-02-01

436

A Simplified Hierarchical Dynamic Quantum Secret Sharing Protocol with Added Features

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

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

2014-09-06

437

Numerical study of dynamical mass generation in QED3

NASA Astrophysics Data System (ADS)

We carry out a numerical study of dynamical generation of fermion masses by solving the Schwinger-Dyson equation for the fermion propagator in three-dimensional quenched Quantum