Dilute gas of ultracold two-level atoms inside a cavity; generalized Dicke model

TL;DR

This paper explores a generalized Dicke model for ultracold two-level atoms in a cavity, revealing new phase transition features due to atomic motion and cavity mode variations, including both first and second order transitions.

Contribution

It introduces a generalized Dicke model accounting for atomic motion and cavity mode shape, uncovering novel phase transition phenomena not seen in the standard model.

Findings

Existence of both first and second order phase transitions.

Atomic motion significantly alters phase diagrams.

Internal and external atomic degrees of freedom become highly correlated.

Abstract

We consider a gas of ultracold two-level atoms confined in a cavity, taking into account for atomic center-of-mass motion and cavity mode variations. We use the generalized Dicke model, and analyze separately the cases of a Gaussian, and a standing wave mode shape. Owing to the interplay between external motional energies of the atoms and internal atomic and field energies, the phase-diagrams exhibit novel features not encountered in the standard Dicke model, such as the existence of first and second order phase transitions between normal and superradiant phases. Due to the quantum description of atomic motion, internal and external atomic degrees of freedom are highly correlated leading to modified normal and superradiant phases.