Universal condensation threshold dependence on pump beam size for exciton-polaritons

Exciton-polariton Bose-Einstein condensates (BECs) in semiconductor microcavities represent a peculiar example of a quantum coherent state on macroscopic lengths scales created by all-optical excitation. Current studies and applications of polariton BECs include quantum simulators, topology, coherent light sources engineering, information processing, and controllable energy transferring. However, many fundamental aspects of condensation are still not comprehensively understood. Here, we perform experimental and theoretical studies of probably the most popular setup -- condensation due to a single Gaussian incoherent laser pumping profile. We have shown that the pumping intensity threshold, a crucial condensation characteristic, is explicitly related to the polariton spectral line properties. The latter are dependent only on several combinations of the respective microstructure parameters. This study paves the way toward controllable condensate creation and utilization. It also provides insights into the characterization of out-of-equilibrium quantum light-matter coherent states.