Exciton-polariton condensates

TL;DR

This review discusses the emergence, properties, and phenomena of exciton-polariton condensates in semiconductor microcavities, highlighting their non-equilibrium nature and related quantum effects.

Contribution

It provides a comprehensive overview of physical phenomena, distinctions between related systems, and potential applications of exciton-polariton condensates.

Findings

Polariton condensates exhibit superfluidity and vortex formation.

Distinct behaviors between polariton BEC, polariton laser, and photon laser.

Engineered polariton structures have promising applications.

Abstract

Recently a new type of system exhibiting spontaneous coherence has emerged -- the exciton-polariton condensate. Exciton-polaritons (or polaritons for short) are bosonic quasiparticles that exist inside semiconductor microcavities, consisting of a superposition of an exciton and a cavity photon. Above a threshold density the polaritons macroscopically occupy the same quantum state, forming a condensate. The lifetime of the polaritons are typically comparable to or shorter than thermalization times, making them possess an inherently non-equilibrium nature. Nevertheless, they display many of the features that would be expected of equilibrium Bose-Einstein condensates (BECs). The non-equilibrium nature of the system raises fundamental questions of what it means for a system to be a BEC, and introduces new physics beyond that seen in other macroscopically coherent systems. In this review we focus upon several physical phenomena exhibited by exciton-polariton condensates. In particular we examine topics such as the difference between a polariton BEC, a polariton laser, and a photon laser, as well as physical phenomena such as superfluidity, vortex formation, BKT (Berezinskii-Kosterlitz-Thouless) and BCS (Bardeen-Cooper-Schrieffer) physics. We also discuss the physics and applications of engineered polariton structures.