Observation of ultra-strong spin-motion coupling for cold atoms in optical microtraps

TL;DR

This paper demonstrates an ultra-strong spin-motion coupling in cold atoms trapped optically, creating a mechanical analogue of the Dicke model, with tunable coupling strength, opening avenues for quantum protocols exploiting extreme coupling regimes.

Contribution

The authors experimentally realize and control ultra-strong spin-motion coupling in cold atoms, establishing a direct analogy to the Dicke model with tunable interaction strength.

Findings

Achieved ultra-strong coupling regime with significant fraction of trap frequency.

Demonstrated in-situ tuning of the coupling strength.

Established a fundamental mapping between cold atom physics and the Dicke model.

Abstract

We realize a mechanical analogue of the Dicke model, achieved by coupling the spin of individual neutral atoms to their quantized motion in an optical trapping potential. The atomic spin states play the role of the electronic states of the atomic ensemble considered in the Dicke model, and the in-trap motional states of the atoms correspond to the states of the electromagnetic field mode. The coupling between spin and motion is induced by an inherent polarization gradient of the trapping light fields, which leads to a spatially varying vector light shift. We experimentally show that our system reaches the ultra-strong coupling regime, i.e., we obtain a coupling strength which is a significant fraction of the trap frequency. Moreover, with the help of an additional light field, we demonstrate the in-situ tuning of the coupling strength. Beyond its fundamental interest, the demonstrated one-to-one mapping between the physics of optically trapped cold atoms and the Dicke model paves the way for implementing protocols and applications that exploit extreme coupling strengths.