High entanglement regimes in the Weisskopf-Wigner theory for spontaneous decay

TL;DR

This paper reviews the Weisskopf-Wigner formalism for spontaneous emission, analyzing how atomic momentum uncertainty influences entanglement with emitted photons, revealing two distinct high entanglement regimes driven by recoil and Doppler effects.

Contribution

It introduces a detailed analysis of entanglement regimes in spontaneous emission considering atomic momentum uncertainty, highlighting recoil and Doppler effects as key factors.

Findings

Identifies recoil and Doppler regimes as high entanglement regimes.

Quantifies entanglement using purity calculations.

Provides thresholds for different entanglement regimes.

Abstract

In this work we review the Weisskopf-Wigner formalism for spontaneous emission considering the spatial modes of light as well as external atomic degrees of freedom which we introduce in the theory by modeling the atom as a wavepacket in momentum space with a given initial uncertainty. We perform a purity calculation in order to quantify the entanglement encoded in the momentum variables of the atom-photon system. Our purity calculations reveal two high entanglement regimes depending on the initial atomic momentum uncertainty: $1)$ the Recoil entanglement regime (which arises in the small momentum uncertainty region) where recoil effects dominate the mechanisms that originate entanglement, and $2)$ the Doppler entanglement regime (in the large momentum uncertainty region) where homogeneous Doppler shifts in the emitted photon's frequency play the fundamental part in the build up of quantum correlations in the system. Physical considerations are made to explain the nature of each entanglement regime as well as provide their respective thresholds.