Superfluids of Light: Bose–Einstein Condensation of Exciton–Polaritons*

Exciton-polaritons are composite bosonic quasiparticles that emerge from the strong coupling between cavity photons and semiconductor excitons. Owing to their extremely light effective mass, polaritons can undergo Bose–Einstein condensation at remarkably high temperatures. In this talk, I will discuss our recent studies on the thermalization and coherence of polaritons in GaAs/AlGaAs microcavities. At cryogenic temperatures, we observed spatially homogeneous polariton condensation in true thermal equilibrium. By measuring the coherent fraction over a wide density range—from the classical to the quantum-degenerate regime—we uncovered a universal power-law relationship between coherence and density. Extending these studies to room temperature, we directly measured the polariton dispersion in GaAs/AlGaAs microcavities, confirming that strong coupling and nonlinear behavior persist even at 300 K. These results open a path toward realizing high-performance, room-temperature polaritonic devices in GaAs-based materials.