Unveiling Material Determinants of Exciton Polariton Condensation: Coherent Dynamics Probed by Classical and Quantum Optical Methods

Understanding the material and photonic factors governing exciton-polariton quantum dynamics is critical for enabling low-threshold polariton condensation. Here, we explore the many-body interactions that drive such dynamics in different material architectures using coherent nonlinear optical probes and quantum optical methods. First, we study polariton dynamics in a two-dimensional metal-halide semiconductor, focusing on the many-body processes that impede condensation. Our findings reveal that the intricate scattering landscape between the exciton reservoir and polaritons restricts condensate formation in these materials. Second, we examine the ultrafast formation and decay dynamics of a condensate in an organic chromophore system using excitation correlation photoluminescence spectroscopy. The condensate population emerges on a timescale of hundreds of femtoseconds—longer than the polariton lifetime. Complementary transient absorption measurements attribute this behavior to a radiative pumping mechanism, where the lower polariton state is populated via exciton reservoir interactions. In both cases, reservoir dynamics dominate spectroscopic observables, complicating the estimation of polariton-polariton interactions. To overcome this, we introduce an alternative methodology that uses spectrally entangled biphoton states to probe many-body dynamics. In a proof-of-principle experiment, we transmit biphoton states through a strongly coupled microcavity, analyzing variations in their spectral correlations to estimate the polariton-polariton scattering. This approach offers a pathway to quantifying many-body interactions even near the single-photon excitation limit.