Polariton BECs: Theory and Concepts

TL;DR

This chapter reviews theoretical concepts of polariton condensates, emphasizing their unique properties, formation, coherence, and dynamics, and challenges the emphasis on strong interactions in understanding their phenomenology.

Contribution

It highlights the undervalued role of linear and non-interacting effects in polariton physics and offers alternative explanations for observed phenomena.

Findings

Linear and non-interacting effects are significant in polariton phenomenology.

Coherence buildup can occur without strong interactions or quantum effects.

Polariton condensates differ from atomic condensates in formation and dynamics.

Abstract

Polaritons are a superposition of light and matter, that combine Strong Interferences (of light) with Weak Interactions (of excitons), making them WISI (Weakly-Interacting, Strongly-Interfering) particles. Their condensation is the main highlight of a field which occupies a unique position at the intersection of quantum optics, condensed matter physics and nonlinear dynamics of driven, dissipative systems. This chapter surveys selected theoretical concepts of polariton condensates' formation, coherence and dynamics, with an emphasis on their distinctions from their atomic counterparts and on points of ongoing controversy. We argue that linear and non-interacting effects are undervalued in polariton physics, and that a significant part of the phenomenology -- including bosonic correlations and coherence buildup -- can often be understood without invoking strong interactions or genuine quantum effects.