Harnessing highly efficient coherent polariton parametric emission in quantum confined perovskite microcavities

Microcavity exciton polaritons emerge as a versatile platform for nonlinear optical effects thanks to the unique dispersion which enables a manifold of energy and wavevector conserved processes. However, efficient generation of parametric emission while preserving coherence remains challenging mainly due to lack of strong parametric interactions compared to simultaneous interaction with relaxation channels. Herein, we report highly efficient parametric emission with sub-1-meV linewidth from quantum confined microcavities, enabling the first observation of strong phase coherence between the two parametric species. Quantum size effect enabled by surface disorder in confined systems acts as the microscopic mechanism for the observed anomalous enhancement of parametric emission, playing important role in triggering exotic parametric interactions for microcavity polaritons. Finally, we demonstrate the emergence of polariton supersolid phase at room temperature in a coherent parametric oscillator, characterized by periodic density modulation in real space that indicates the breaking of translational symmetry.