Direct measurement of polariton-polariton interaction strength in the Thomas-Fermi regime of exciton-polariton condensation

TL;DR

This paper reports the first direct measurement of exciton-polariton interaction strength in the Thomas-Fermi regime, achieved by creating a reservoir-separated condensate in a semiconductor system, reducing uncertainty significantly.

Contribution

It introduces a method to measure polariton interactions directly in a non-equilibrium system by utilizing a reservoir-separated condensate in the Thomas-Fermi regime.

Findings

Polariton-polariton interaction strength measured with reduced uncertainty.

Reservoir separation enables direct probing of interactions.

Thomas-Fermi regime demonstrated in a non-equilibrium exciton-polariton system.

Abstract

Bosonic condensates of exciton polaritons (light-matter quasiparticles in a semiconductor) provide a solid-state platform for studies of non-equilibrium quantum systems with a spontaneous macroscopic coherence. These driven, dissipative condensates typically coexist and interact with an incoherent reservoir, which undermines measurements of key parameters of the condensate. Here, we overcome this limitation by creating a high-density exciton-polariton condensate in an optically-induced "box" trap. In this so-called Thomas-Fermi regime, the condensate is fully separated from the reservoir and its behaviour is dominated by interparticle interactions. We use this regime to directly measure the polariton-polariton interaction strength, and reduce the existing uncertainty in its value from four orders of magnitude to within three times the theoretical prediction. The Thomas-Fermi regime has previously been demonstrated only in ultracold atomic gases in thermal equilibrium. In a non-equilibrium exciton-polariton system, this regime offers a novel opportunity to study interaction-driven effects unmasked by an incoherent reservoir.