Crossover from exciton-polariton to photon Bose-Einstein condensation

TL;DR

This paper demonstrates a dynamic phase transition between exciton-polariton and photon Bose-Einstein condensates in a single system, revealing coexistence and coherence changes under different excitation conditions.

Contribution

It shows the first observation of a crossover between polariton and photon BECs in the same microcavity system under varying optical excitations.

Findings

Both exciton-polariton and photon BECs can be achieved in the same system.

A phase transition occurs after a high-power pulse, switching between condensates.

Coexistence of photons and polaritons at the crossover reduces spatial coherence.

Abstract

BEC of exciton-polaritons and related effects such as superfluidity1,2, spontaneous symmetry breaking3,4 and quantised vortices5,6 open way to creation of novel light sources7 and optical logic elements8. Remarkable observations of exciton-polariton BEC in microcavities9-12 have been reported in the recent ten years. Very recently, thermalisation and subsequent condensation of cavity photons in a dye-filled microcavity have been observed13. Here we show that BEC of both exciton-polaritons and photons can be created in the same system under different optical excitation conditions. A dynamic phase transition between a photon and a polariton BEC takes place after a single high-power excitation pulse and we find both condensed states in thermal equilibrium with the excited states. At the crossover, photons and polaritons coexist, which results in a decrease in the long-range spatial coherence. Build-up and successive depinning of polarisation is observed at the threshold of both polariton and photon condensation.