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

Bosonic condensates of exciton polaritons typically coexist and interact with an incoherent reservoir, which undermines measurements of key parameters of the condensate. Here, the authors overcome this limitation by creating a high-density polariton condensate in an optically induced box trap. In this interaction-dominated Thomas-Fermi regime, the condensate is fully separated from the reservoir, which enables a direct measurement of the polariton-polariton interaction strength. The results of the measurement are in agreement with theoretical predictions.