Dynamics of spin-orbit-coupled cold atomic gases in a Floquet lattice with an impurity

TL;DR

This paper investigates spin-dependent quantum tunneling in a Floquet lattice with an impurity, revealing two distinct second-order tunneling mechanisms and their spectral signatures, with implications for quantum transport control.

Contribution

It uncovers two types of spin-dependent second-order tunneling processes in a Floquet lattice with an impurity, characterized by different mechanisms and spectral features.

Findings

Identification of two distinct second-order tunneling processes.

Resonant tunneling distinguishes spin-flip and non-spin-flip processes.

Analytical confirmation using effective models and perturbation methods.

Abstract

In this study, we have studied the quantum tunneling of a single spin-orbit-coupled atom held in a periodically modulated optical lattice with an impurity. At the pseudocollapse points of quasienergy bands, where the dynamical localization takes place globally, two types of local second-order tunneling processes appear beyond expectation between the two nearest-neighbor sites of the impurity with the spin unchanged and with impurity site population negligible all the time, when the impurity potential is far off-resonant with the driving field. Though tunneling behaviors of the two types seem to be the same, they are believed to involve two distinct mechanisms: one is related to spin-independent process, while the other is to spin-dependent tunneling process. The two types of second-order processes can be identified by means of resonant tunneling with or without spin-flipping by tuning the impurity potential to be in resonance with the driving field. In the Floquet picture, the second-order processes are manifested as subtle and fine avoided crossings of quasienergy spectrums near the pseudocollapse region. These results are confirmed analytically on the basis of effective three-site model and multiple-time-scale asymptotic perturbative method, and may be exploited for engineering the spin-dependent quantum transport in realistic experiments.