Resonant ratcheting of a Bose-Einstein condensate

TL;DR

This paper investigates how quantum interactions affect resonant ratcheting in Bose-Einstein condensates, revealing that resonances persist but shift and induce instabilities leading to new nonlinear states with distinct transport behaviors.

Contribution

It demonstrates that quantum resonances in ratcheting are robust against interactions, but their properties change, and new nonlinear Floquet states emerge due to instabilities.

Findings

Resonances are not destroyed by interactions.

Resonance locations shift with increasing interaction strength.

Interactions induce instabilities leading to new nonlinear Floquet states.

Abstract

We study the rectification process of interacting quantum particles in a periodic potential exposed to the action of an external ac driving. The breaking of spatio-temporal symmetries leads to directed motion already in the absence of interactions. A hallmark of quantum ratcheting is the appearance of resonant enhancement of the current (Europhys. Lett. 79 (2007) 10007 and Phys. Rev. A 75 (2007) 063424). Here we study the fate of these resonances within a Gross-Pitaevskii equation which describes a mean field interaction between many particles. We find, that the resonance is i) not destroyed by interactions, ii) shifting its location with increasing interaction strength. We trace the Floquet states of the linear equations into the nonlinear domain, and show that the resonance gives rise to an instability and thus to the appearance of new nonlinear Floquet states, whose transport properties differ strongly as compared to the case of noninteracting particles.