Spin Josephson effects of spin-orbit-coupled Bose-Einstein condensates in a non-Hermitian double well

TL;DR

This paper explores the spin and tunneling dynamics of spin-orbit-coupled Bose-Einstein condensates in a non-Hermitian double well, revealing PT-symmetry breaking, spin current generation, and potential applications in spintronics.

Contribution

It provides analytical and numerical insights into Floquet quasienergies, PT-phase transitions, and spin current control in non-Hermitian driven systems with spin-orbit coupling.

Findings

PT-breaking phase transition occurs at small non-Hermitian parameters for half-integer spin-orbit coupling.

Net spin current exists in broken PT-symmetric regions without atomic current.

Stable spin current can be generated in non-PT-symmetric systems through periodic driving.

Abstract

In this paper, we investigate the spin and tunneling dynamics of a spin-orbit-coupled noninteracting Bose-Einstein condensate in a periodically driven non-Hermitian double-well potential. Under high-frequency driving, we obtain the effective time-averaged Hamiltonian by using the standard time-averaging method, and analytically calculate the Floquet quasienergies, revealing that the parity-time (PT)-breaking phase transition appears even for arbitrarily small non-Hermitian parameters when the spin-orbit coupling strength takes half-integer value, irrespective of the values of other parameters used. When the system is PT-symmetric with balanced gain and loss, we find numerically and analytically that in the broken PT-symmetric regions, there will exist the net spin current together with a vanishing atomic current, if we drop the contribution of the exponential growth of the norm to the current behaviors. When the system is non-PT-symmetric, though the quasienergies are partial complex, a stable net spin current can be generated by controlling the periodic driving field, which is accompanied by a spatial localization of the condensate in the well with gain. The results deepen the understanding of non-Hermitian physics and could be useful for engineering a variety of devices for spintronics.