Ratchet effect for cold atoms in an optical lattice

TL;DR

This paper investigates how quantum particles in an optical lattice can exhibit directed current (ratchet effect), showing that current direction depends on potential strength and a key ratio, with observable experimental implications.

Contribution

It introduces a quantum ratchet model in optical lattices, highlighting how potential strength and a specific frequency-to-potential ratio influence current direction and quantum effects.

Findings

Positive current at weak potentials dominated by quantum diffusion

Current reversal occurs at stronger potentials

A single parameter controls quantum effects and ratchet current feasibility

Abstract

The realization of a directed current for a quantum particle in a flashing asymmetric potential is studied. It is found that a positive current, i.e. in the direction expected for a conventional diffusive ratchet, can be attained at short times in the limit where the potential is weak and quantum diffusion dominates, while current reversal is obtained for stronger potentials. A single parameter, the ratio between the kicking frequency and the optical lattice potential strength, determines both the degree to which quantum effects dominate, and the possibility of obtaining a ratchet current. The effect should be readily observable in experiments.