Light-matter interaction and Bose-Einstein condensation of light

TL;DR

This paper investigates the Dicke model's superradiant phase, revealing that photon Bose-Einstein condensation alters the fundamental nature of photons and introduces a new coherent transition process with significant transition probabilities.

Contribution

It demonstrates that in the superradiant phase, photons form a condensate with new excitations, and introduces a novel coherent transition process distinct from known emission mechanisms.

Findings

Photon as an elementary excitation ceases to exist in the condensate.

A new coherent transition process is identified with large transition probability.

Atom interacts with phase and intensity excitations of the condensate.

Abstract

The atom - electromagnetic field interaction is studied in the Dicke model, wherein a single field mode is interacting with a collection of two level atoms at thermal equilibrium. It is found that in the superradiant phase of the system, wherein the Bose-Einstein condensation of photons takes place, the notion of photon as an elementary electromagnetic excitation ceases to exist. The phase and intensity excitations of the condensate are found to be the true excitations of electromagnetic field. It is found that in this phase, the atom interacts with these excitations in a distinct coherent transition process, apart from the known stimulated emission/absorption and spontaneous emission processes. In the coherent transition it is found that while the atomic state changes in course of the transition process, the state of electromagnetic field remains unaffected. It is found that the transition probability of such coherent transition process is macroscopically large compared to other stimulated emission/absorption and spontaneous emission processes.