Bose-Einstein Condensation of Long-Lifetime Polaritons in Thermal Equilibrium

TL;DR

This paper demonstrates Bose-Einstein condensation of long-lifetime polaritons in thermal equilibrium within a semiconductor microcavity, confirming theoretical phase diagrams and distribution predictions.

Contribution

It introduces a polariton system with extended lifetime allowing thermal equilibrium, enabling direct observation of the phase diagram for Bose-Einstein condensation.

Findings

Polaritons reach thermal equilibrium in a confining trap.

Energy distributions fit Bose-Einstein statistics across densities.

Phase boundary follows predicted power law.

Abstract

Exciton-polaritons in semiconductor microcavities have been used to demonstrate quantum effects such as Bose-Einstein condensation, superfluity, and quantized vortices. However, in these experiments, the polaritons have not reached thermal equilibrium when they undergo the transition to a coherent state. This has prevented the verification of one of the canonical predictions for condensation, namely the phase diagram. In this work, we have created a polariton gas in a semiconductor microcavity in which the quasiparticles have a lifetime much longer than their thermalization time. This allows them to reach thermal equilibrium in a laser-generated confining trap. Their energy distributions are well fit by equilibrium Bose-Einstein distributions over a broad range of densities and temperatures from very low densities all the way up to the threshold for Bose-Einstein condensation. The good fits of the Bose-Einstein distribution over a broad range of density and temperature imply that the particles obey the predicted power law for the phase boundary of Bose-Einstein condensation.