Atom-Field Entanglement in Cavity QED: Nonlinearity and Saturation

TL;DR

This paper explores how atom-field entanglement in cavity QED depends on driving strength, nonlinearity, and saturation effects, revealing optimal entanglement conditions and phase transition phenomena.

Contribution

It provides new insights into the nonlinear and saturation effects on atom-field entanglement, including the role of multiphoton resonances and phase transitions.

Findings

Entanglement peaks at intermediate driving fields near atomic saturation.

Entanglement recurs at multiphoton resonances.

Phase transition in entanglement occurs at specific detuning and driving conditions.

Abstract

We investigate the degree of entanglement between an atom and a driven cavity mode, in the presence of dissipation. Previous work has shown that in the limit of weak driving fields, the steady state entanglement is proportional to the square of the driving intensity. This quadratic dependence is due to the generation of entanglement by the creation of pairs of photons/excitations. In this work we investigate the entanglement between an atom and a cavity in the presence of multiple photons. Nonlinearity of the atomic response is needed to generate entanglement, but as that nonlinearity saturates the entanglement vanishes. We posit that this is due to spontaneous emission, which puts the atom in the ground state and the atom-field state into a direct product state. An intermediate value of the driving field, near the field that saturates the atomic response, optimizes the atom-field entanglement. In a parameter regime for which multiphoton resonances occur, we find that entanglement recurs at those resonances. \cite{Shamailov-10} In this regime, we find that the entanglement decreases with increaing photon number. We also investigate, in the bimodal regime of Alsing et. al.\cite{Alsing-91-DressedState} \cite{Alsing-92-DSS}\cite{Carm-15-X}, the entanglement as a function of atom and/or cavity detuning. Here we find that there is evidence of a phase transition in the entanglement, which occurs at $2\epsilon/g \geq 1$.