Perturbative analysis of coherent quantum ratchets in cold atom systems

TL;DR

This paper investigates how cold atoms in optical lattices respond to weak asymmetric periodic drives, revealing that interference effects produce long-lasting ratchet currents, well-described by a simplified three-level model.

Contribution

It introduces a perturbative framework to analyze quantum ratchets in cold atom systems, highlighting the role of interference and resonant frequencies in generating sustained currents.

Findings

Ratchet currents arise from interference between first and second order processes.

A three-level model accurately predicts the dynamics under weak to moderate driving.

Long-lasting currents are observed at specific resonant frequencies.

Abstract

We present a perturbative study of the response of cold atoms in an optical lattice to a weak time- and space-asymmetric periodic driving signal. In the noninteracting limit, and for a finite set of resonant frequencies, we show how a coherent, long lasting ratchet current results from the interference between first and second order processes. In those cases, a suitable three-level model can account for the entire dynamics, yielding surprisingly good agreement with numerically exact results for weak and moderately strong driving.