Kick-induced rectified current in symmetric nano-electromechanical shuttle

We have studied the rectified current in a geometrically symmetric nano-electromechanical shuttle with periodic kicks and sinusoidal ac bias voltages. The rectified current is exactly zero under the geometrical symmetry which is generated by the electrons transferred from source to drain electrodes through the movable shuttle. We investigate the nonzero rectified currents through the symmetric shuttle with regular motion of which the time-translational symmetry is broken. The motion of the shuttle, moreover, becomes chaotic with the same mechanism of the kicked rotor and generates the scattered current as increasing kick strength. We point out that the time-translational-symmetry breaking of the instantaneous current is an important role of manipulation of the rectified current.Comment: 6 pages, 5 figure

Complexity and instability of quantum motion near a quantum phase transition

We show that the number of harmonics of the Wigner function, recently proposed as a measure of quantum complexity, can be also used to characterize quantum phase transitions. The non-analytic behavior of this quantity in the neighborhood of a quantum phase transition is illustrated by means of the Dicke model and is compared to two well-known measures of the (in)stability of quantum motion, the quantum Loschmidt echo and the fidelity.Comment: 9 pages, 5 figure

Semiclassical Approach to Survival Probability at Quantum Phase Transitions

We study the decay of survival probability at quantum phase transitions (QPT). The semiclassical theory is found applicable in the vicinities of critical points with infinite degeneracy. The theory predicts a power law decay of the survival probability for relatively long times in systems with d=1 and an exponential decay in systems with sufficiently large d, where d is the degrees of freedom of the underlying classical dynamics. The semiclassical predictions are checked numerically in four models.Comment: 4 pages, 3 figures; published versio

Semiclassical approach to the quantum Loschmidt echo in deep quantum regions: from validity to breakdown

Semiclassical results are usually expected to be valid in the semiclassical regime. An interesting question is, in models in which appropriate effective Planck constants can be introduced, to what extent will a semiclassical prediction stay valid when the effective Planck constant is increased? In this paper, we numerically study this problem, focusing on semiclassical predictions for the decay of the quantum Loschmidt echo in deep quantum regions. Our numerical simulations, carried out in the chaotic regime in the sawtooth model and in the kicked rotator model and also in the critical region of a 1D Ising chain in transverse field, show that the semiclassical predictions may work even in deep quantum regions, in particularly, for perturbation strength in the so-called Fermi-Golden-rule regime.Comment: 8 pages, 10 figures. Published versio

Scaling behavior for a class of quantum phase transitions

We show that for quantum phase transitions with a single bosonic zero mode at the critical point, like the Dicke model and the Lipkin-Meshkov-Glick model, metric quantities such as fidelity, that is, the overlap between two ground states corresponding to two values $\lambda_1$ and $\lambda_2$ of the controlling parameter $\lambda$, only depend on the ratio $\eta=(\lambda_1-\lambda_c)/(\lambda_2-\lambda_c)$, where $\lambda=\lambda_c$ at the critical point. Such scaling property is valid also for time-dependent quantities such as the Loschmidt echo, provided time is measured in units of the inverse frequency of the critical mode.Comment: 7 pages, 3 figures, added new data and discussio

Role of chiral symmetry in a kicked Jaynes-Cummings model

We have studied the role of chiral symmetry in a periodically kicked Jaynes-Cummings (KJC) model by freezing an initial phase. We show that commensurate kicks (27rk periodicity with integer k) conserve the chiral symmetry in the KJC model under the resonant condition, while incommensurate kicks break the symmetry. The chiral symmetry preserves the phase of an initial state against phase fluctuations during the dynamical evolution, but broken chiral symmetry erases the initial phase. The frozen phase is preserved within a finite evolution time for slight deviations of the kick period from an integer multiple of 27r and small variations of detuning from the resonant condition. The chiral symmetry-protected phase information is noteworthy as it provides various uses in quantum computation and information.11Nsciescopu

Electronic current in a nano-mechanical kicked electron shuttle

We have studied the phase-space dynamics and rectified current of a nano-electromechanical shuttle with two types of time-periodic potentials. By applying only sinusoidal voltage with frequency at one lead, regular shuttle motion constructs Arnold’s tongues in parameter space, where the motion in each tongue has a period of ∕ or 2∕. The rectified current in each tongue is finite for the 2∕ period but zero for the ∕ period. We then apply discrete kicks, the periods of which modify the period of motion in the tongues. We find that it is important to the rectified current whether the integer of the lowest common multiple between the two periods is even or odd. Specifically, the rectified current is finite in the tongues when the lowest common multiple integer is even, while the current is zero when the integer is odd. © 2019 Elsevier B.V. All rights reserved.11sciescopu

Interacting ultracold atomic kicked rotors: Loss of dynamical localization

We study the fate of dynamical localization of two quantum kicked rotors with contact interaction, which relates to experimental realizations of the rotors with ultra-cold atomic gases. A single kicked rotor is known to exhibit dynamical localization, which takes place in momentum space. The contact interaction affects the evolution of the relative momentum k of a pair of interacting rotors in a non-analytic way. Consequently the evolution operator U is exciting large relative momenta with amplitudes which decay only as a power law 1/k 4. This is in contrast to the center-of-mass momentum K for which the amplitudes excited by U decay superexponentially fast with K. Therefore dynamical localization is preserved for the center-of-mass momentum, but destroyed for the relative momentum for any nonzero strength of interaction. © The Author(s) 20171