| URL | https://arxiv.org/abs/1901.09362 |
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| 摘要 | The quantum motion of N coupled kicked rotors is mapped to an interacting N-particle Anderson-Aubry-André tight-binding problem supporting many-body localised (MBL) phases. Interactions in configuration space are known to be insufficient for destroying Anderson localisation in a system in the MBL phase. The mapping we establish here predicts that a similar effect takes place in momentum space and determines the quantum dynamics of the coupled kicked rotors. Due to the boundedness of the Floquet quasi-energy spectrum there exists limitations on the interacting lattice models that can be mapped to quantum kicked rotors; in particular, no extensive observable can be mapped in the thermodynamic limit. |
| URL | https://journals.aps.org/prl/pdf/10.1103/PhysRevLett.120.013601 |
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| 摘要 | We realize a spin-orbit interaction between the collective spin precession and center-of-mass motion of a trapped ultracold atomic gas, mediated by spin- and position-dependent dispersive coupling to a driven optical cavity. The collective spin, precessing near its highest-energy state in an applied magnetic field, can be approximated as a negative-mass harmonic oscillator. When the Larmor precession and mechanical motion are nearly resonant, cavity mediated coupling leads to a negative-mass instability, driving exponential growth of a correlated mode of the hybrid system. We observe this growth imprinted on modulations of the cavity field and estimate the full covariance of the resulting two-mode state by observing its transient decay during subsequent free evolution. |
| URL | https://journals.aps.org/prb/abstract/10.1103/PhysRevB.86.144521 |
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| 摘要 | We study a linear ramp of the nearest-neighbor tunneling rate in the Bose-Hubbard model driving the system from the Mott insulator state into the superfluid phase. We employ the truncated Wigner approximation to simulate linear quenches of a uniform system in one, two, and three dimensions, and in a harmonic trap, in three dimensions. In all these setups, the excitation energy decays like one over third root of the quench time. The -1/3 scaling arises from an impulse-adiabatic approximation—a variant of the Kibble-Zurek mechanism—describing a crossover from nonadiabatic to adiabatic evolution when the system begins to keep pace with the increasing tunneling rate. |
| URL | https://journals.aps.org/pra/abstract/10.1103/PhysRevA.83.043607 |
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| 摘要 | We consider a theoretical model of a four-mode Bose-Hubbard model consisting of two pairs of wells coupled via two processes with two different rates. The model is naturally divided into two subsystems with strong intrasystem coupling and much weaker coupling between the two subsystems and has previously been introduced as a model for Josephson heat oscillations by Strzys and Anglin [Phys. Rev. A 81, 043616 (2010)]. We examine the quantum dynamics of this model for a range of different initial conditions, in terms of both the number distribution among the wells and the quantum statistics. We find that the time evolution is different to that predicted by a mean-field model and that this system exhibits a wide range of interesting behaviours. We find that the system equilibrates to a maximum entropy state and is thus a useful model for quantum thermalisation. As our model may be realized to a good approximation in the laboratory, it becomes a candidate for experimental investigation. |
| URL | https://journals.aps.org/prb/abstract/10.1103/PhysRevB.99.094301 |
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| 摘要 | We investigate the nonequilibrium behavior of a fully connected (or all-to-all coupled) Bose-Hubbard model after a Mott to superfluid quench, in the limit of large boson densities and for an arbitrary number V of lattice sites, with potential relevance in experiments ranging from cold atoms to superconducting qubits. By means of the truncated Wigner approximation, we predict that crossing a critical quench strength the system undergoes a dynamical phase transition between two regimes that are characterized at long times either by an inhomogeneous population of the lattice (i.e., macroscopical self-trapping) or by the tendency of the mean-field bosonic variables to split into two groups with phase difference π, that we refer to as π-synchronization. We show the latter process to be intimately connected to the presence, only for V≥4, of a manifold of infinitely many fixed points of the dynamical equations. Finally, we show that no fine-tuning of the model parameters is needed for the emergence of such π-synchronization, that is in fact found to vanish smoothly in presence of an increasing site-dependent disorder, in what we call a synchronization crossover. |
| URL | http://www3.ntu.edu.sg/home/zhaoyang/AJ11700_resub.pdf |
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| 摘要 | A nonperturbative treatment, the Dirac-Frenkel time-dependent variation is employed to examine dynamics of the Landau-Zener model with both diagonal and off-diagonal qubit-bath coupling using the multiple Davydov trial states. It is shown that steady-state transition probabilities agree with analytical predictions at long times. Landau-Zener dynamics at intermediate times is little affected by diagonal coupling, and is found to be determined by off-diagonal coupling and tunneling between two diabatic states. We investigate effects of bath spectral densities, coupling strengths, and interaction angles on Laudau-Zener dynamics. Thanks to the multiple Davydov trial states, detailed boson dynamics can also be analyzed in Landau-Zener transitions. The results presented here may help provide guiding principles to manipulate the Laudau-Zener transitions in circuit QED architectures by tuning off-diagonal coupling and tunneling strength. |
| URL | https://aip.scitation.org/doi/full/10.1063/1.4792502 |
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| 摘要 | The Dirac-Frenkel time-dependent variation is employed to probe the dynamics of the zero temperature sub-Ohmic spin-boson model with strong friction utilizing the Davydov D1 ansatz. It is shown that initial conditions of the phonon bath have considerable influence on the dynamics. Counterintuitively, even in the very strong coupling regime, quantum coherence features still manage to survive under the polarized bath initial condition, while such features are absent under the factorized bath initial condition. In addition, a coherent-incoherent transition is found at a critical coupling strength α ≈ 0.1 for s = 0.25 under the factorized bath initial condition. We quantify how faithfully our ansatz follows the Schrödinger equation, finding that the time-dependent variational approach is robust for strong dissipation and deep sub-Ohmic baths (s ≪ 1). |
| URL | https://aip.scitation.org/doi/10.1063/1.1703954 |
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| 摘要 | The individual spins of the Ising model are assumed to interact with an external agency (e.g., a heat reservoir) which causes them to change their states randomly with time. Coupling between the spins is introduced through the assumption that the transition probabilities for any one spin depend on the values of the neighboring spins. This dependence is determined, in part, by the detailed balancing condition obeyed by the equilibrium state of the model. The Markoff process which describes the spin functions is analyzed in detail for the case of a closed N‐member chain. The expectation values of the individual spins and of the products of pairs of spins, each of the pair evaluated at a different time, are found explicitly. The influence of a uniform, time‐varying magnetic field upon the model is discussed, and the frequency‐dependent magnetic susceptibility is found in the weak‐field limit. Some fluctuation‐dissipation theorems are derived which relate the susceptibility to the Fourier transform of the time‐dependent correlation function of the magnetization at equilibrium. |
| URL | https://journals.aps.org/pra/abstract/10.1103/PhysRevA.72.022113 |
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| 摘要 | We analyze a model system of fermions in a harmonic oscillator potential under the influence of a dissipative environment: The fermions are subject to a fluctuating force deriving from a bath of harmonic oscillators. This represents an extension of the well-known Caldeira-Leggett model to the case of many fermions. Using the method of bosonization, we calculate one- and two-particle Green’s functions of the fermions. We discuss the relaxation of a single extra particle added above the Fermi sea, considering also dephasing of a particle added in a coherent superposition of states. The consequences of the separation of center-of-mass and relative motion, the Pauli principle, and the bath-induced effective interaction are discussed. Finally, we extend our analysis to a more generic coupling between system and bath, which results in complete thermalization of the system. |
| URL | http://www.wuli.ac.cn/CN/abstract/abstract31813.shtml |
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| 摘要 | 文章基于作者在2005年纪念爱因斯坦奇迹年的香山会议上的综述报告，扼要叙述了从布朗运动到统计涨落场论的发展历程，特别提及了与中国物理学家有关的贡献. |
| URL | https://link.springer.com/article/10.1023/B:JOSS.0000033245.43421.14 |
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| 摘要 | While many papers in the last few years have dealt with various equations euphemistically called “ratchets,” the original Feyman two-temperature setup has been left largely unchallenged. We present here a look at the details of how this famous engine actually generates motion from a temperature difference. |
| URL | https://journals.aps.org/prx/abstract/10.1103/PhysRevX.7.021002 |
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| 摘要 | A growing number of biological, soft, and active matter systems are observed to exhibit normal diffusive dynamics with a linear growth of the mean-squared displacement, yet with a non-Gaussian distribution of increments. Based on the Chubinsky-Slater idea of a diffusing diffusivity, we here establish and analyze a minimal model framework of diffusion processes with fluctuating diffusivity. In particular, we demonstrate the equivalence of the diffusing diffusivity process with a superstatistical approach with a distribution of diffusivities, at times shorter than the diffusivity correlation time. At longer times, a crossover to a Gaussian distribution with an effective diffusivity emerges. Specifically, we establish a subordination picture of Brownian but non-Gaussian diffusion processes, which can be used for a wide class of diffusivity fluctuation statistics. Our results are shown to be in excellent agreement with simulations and numerical evaluations. |
| URL | https://journals.aps.org/prb/abstract/10.1103/PhysRevB.67.144303 |
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| 摘要 | We study the influence of a fast noise on Landau-Zener transitions. We demonstrate that a fast colored noise much weaker than the conventional white noise can produce transitions itself or can change substantially the Landau-Zener transition probabilities. In the limit of fast colored or strong white noise we derive asymptotically exact formulas for transition probabilities and study the time evolution of a spin coupled to the noise and a sweeping magnetic field. |
| URL | https://www.sciencedirect.com/science/article/pii/S0167278906000443 |
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| 摘要 | We present a model for a thermal Brownian motor based on Feynman’s famous ratchet and pawl device. Its main feature is that the ratchet and the pawl are in different thermal baths and connected by a harmonic spring. We simulate its dynamics, explore its main features and also derive an approximate analytical solution for the mean velocity as a function of the external torque applied and the temperatures of the baths. Such theoretical predictions and results from numerical simulations agree within the ranges of the approximations performed. |
| URL | https://journals.aps.org/pra/abstract/10.1103/PhysRevA.90.023633 |
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| 摘要 | We develop a quantum model for nonequilibrium Bose-Einstein condensation of photons and polaritons in planar microcavity devices. The model builds on laser theory and includes the spatial dynamics of the cavity field, a saturation mechanism, and some frequency dependence of the gain: quantum Langevin equations are written for a cavity field coupled to a continuous distribution of externally pumped two-level emitters with a well-defined frequency. As an example of application, the method is used to study the linearized quantum fluctuations around a steady-state condensed state. In the good-cavity regime, an effective equation for the cavity field only is proposed in terms of a stochastic Gross-Pitaevskii equation. Perspectives in view of a full quantum simulation of the nonequilibrium condensation process are finally sketched. |
| URL | https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.114.113601 |
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| 摘要 | Because of their low energy content, microwave signals at the single-photon level are extremely challenging to measure. Guided by recent progress in single-photon optomechanics and hybrid optomechanical systems, we propose a multimode optomechanical transducer that can detect intensities significantly below the single-photon level via adiabatic transfer of the microwave signal to the optical frequency domain where the measurement is then performed. The influence of intrinsic quantum and thermal fluctuations is also discussed. |
| URL | https://iopscience.iop.org/article/10.1088/1361-6544/ab2a2c |
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| 摘要 | In many problems of classical mechanics and theoretical physics dynamics can be described as a slow evolution of periodic or quasi-periodic processes. Adiabatic invariants are approximate first integrals for such dynamics. The existence of adiabatic invariants makes dynamics close to regular. Destruction of adiabatic invariance leads to chaotic dynamics. We present a review of some mechanisms of destruction of adiabatic invariance in slow–fast Hamiltonian systems with examples from charged particle dynamics. |
| URL | https://journals.aps.org/prb/abstract/10.1103/PhysRevB.69.174407 |
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| 摘要 | The phase diagram and the critical behavior of the planar rotator model on square lattice with fourfold and on triangular lattice with sixfold symmetry-breaking field is obtained by Monte Carlo simulation. On the basis of a renormalization-group analysis the planar model with a fourfold symmetry-breaking field is expected to undergo a continuous phase transition with unconventional field dependent critical exponents, while the same model with sixfold symmetry-breaking field is expected to exhibit two phase transitions: a ferromagnetic–BKT ~Berezinskii-Kosterlitz-Thouless! one at low temperature followed by a BKT–paramagnetic phase transition at high temperature. Both these expectations are confirmed by Monte Carlo simulations. |
| URL | https://journals.aps.org/prb/abstract/10.1103/PhysRevB.106.024204 |
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| 摘要 | In the presence of quasiperiodic potentials, the celebrated Kitaev chain presents an intriguing phase diagram with ergodic, localized, and multifractal states. In this work, we generalize these results by studying the localization properties of the Aubry-André-Harper model in the presence of long-range hopping and superconducting pairing amplitudes. These amplitudes decay with power-law exponents ξ and α, respectively. To this end, we review and compare a toolbox of global and local characterization methods in order to investigate different types of transitions between ergodic, localized, and multifractal states. We report energy-dependent transitions from ergodic to multifractal states for pairing terms with α < 1 and energy-dependent transitions from ergodic to localized states with an intermediate multifractal region for α > 1 . The size of the intermediate multifractal region depends not only on the value of the superconducting pairing term Δ , but also on the energy band. The transitions are not described by a mobility edge, but instead we report hybridization of bands with different types of localization properties. This leads to coexisting multifractal regimes where fractal dimensions follow different distributions |
| URL | https://arxiv.org/abs/1703.02750 |
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| 摘要 | In this paper, we investigate vortex dynamics in a two-dimensional Bose-Hubbard model coupled with a weak artificial magnetic field, a random white noise and a dissipation. Origin of the noise and dissipation is considered as thermal fluctuations of atoms that do not participate the Bose-Einstein condensation (BEC). Solving a stochastic Gross-Pitaevskii equation to this system, we show that the interplay of the magnetic field and the white noise generates vortices in the bulk of the BEC and stable steady states of vortices form after a transition period. We calculate the incompressible part of the kinetic-energy spectrum of the BEC. In the transition period, a Kolmogorov k−5/3 spectrum appears in the infrared regime with the wave number k, k<ζ−1, where ζ is the healing length, whereas in the ultraviolet region, k>ζ−1, the spectrum behaves as k−3. On the other hand in the steady states, another scaling low appears. We find a relationship between the above mentioned kinetic-energy spectra and the velocity of vortices. By an inverse cascade, the large velocity of a few created vortices develops the Kolmogorov k−5/3 spectrum. |
| URL | https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.82.648 |
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| 摘要 | We generalize the Kuramoto model of coupled oscillators to allow time-delayed interactions. New phenomena include bistability between synchronized and incoherent states, and unsteady solutions with time-dependent order parameters. We derive exact formulas for the stability boundaries of the incoherent and synchronized states, as a function of the delay, in the special case where the oscillators are identical. The experimental implications of the model are discussed for populations of chirping crickets, where the finite speed of sound causes communication delays, and for physical systems such as coupled phase-locked loops or lasers. |