Experimental control of transport resonances in a coherent quantum rocking ratchet

TL;DR

This study demonstrates controlled quantum transport of ultra-cold atoms in a rocking ratchet, revealing resonance effects and the influence of interactions among Floquet states, with potential applications in quantum devices.

Contribution

It introduces a method to control and observe transport resonances in a coherent quantum ratchet using a Bose-Einstein condensate in a biharmonic optical potential.

Findings

Resonance enhancement of atom transport due to avoided crossings in Floquet spectrum.

Bifurcation of a single resonance into a doublet by tuning modulation strength.

Interactions among Floquet eigenstates affect quantum ratchet transport.

Abstract

The ratchet phenomenon is a means to get directed transport without net forces. Originally conceived to rectify stochastic motion and describe operational principles of biological motors, the ratchet effect can be used to achieve controllable coherent quantum transport. This transport is an ingredient of several perspective quantum devices including atomic chips. Here we examine coherent transport of ultra-cold atoms in a rocking quantum ratchet. This is realized by loading a rubidium atomic Bose-Einstein condensate into a periodic optical potential subjected to a biharmonic temporal drive. The achieved long-time coherence allows us to resolve resonance enhancement of the atom transport induced by avoided crossings in the Floquet spectrum of the system. By tuning the strength of the temporal modulations, we observe a bifurcation of a single resonance into a doublet. Our measurements reveal the role of interactions among Floquet eigenstates for quantum ratchet transport.