Exploring unresolved sideband, optomechanical strong coupling using a single atom coupled to a cavity

TL;DR

This paper investigates a regime in cavity QED where a single atom's motional degree of freedom strongly interacts with the cavity field, leading to novel quantum optomechanical phenomena such as entanglement and anomalous heating.

Contribution

It identifies and analyzes the single-photon optomechanical strong coupling regime in atom-cavity systems considering atomic motion, revealing new quantum effects.

Findings

Strong entanglement between atomic wave-function and photon scattering

Atomic motion can be significantly heated by single-photon scattering

Regime where zero-point motion shifts cavity frequency beyond linewidth

Abstract

A major trend within the field of cavity QED is to boost the interaction strength between the cavity field and the atomic internal degrees of freedom of the trapped atom by decreasing the mode volume of the cavity. In such systems, it is natural to achieve strong atom-cavity coupling, where the coherent interaction strength exceeds the cavity linewidth, while the linewidth exceeds the atomic trap frequency. While most work focuses on coupling of photons to the internal degrees of freedom, additional rich dynamics can occur by considering the atomic motional degree of freedom as well. In particular, we show that such a system is a natural candidate to explore an interesting regime of quantum optomechanics, where the zero-point atomic motion yields a cavity frequency shift larger than its linewidth (so-called single-photon optomechanical strong coupling), but simultaneously where the motional frequency cannot be resolved by the cavity. We show that this regime can result in a number of remarkable phenomena, such as strong entanglement between the atomic wave-function and the scattering properties of single incident photons, or an anomalous mechanism where the atomic motion can significantly heat up due to single-photon scattering, even if the atom is trapped tightly within the Lamb-Dicke limit.