Room-temperature polaritonic non-Hermitian system with single microcavity

Parity–time reversal symmetry (PT symmetry) in non-Hermitian systems realizes spontaneous symmetry breaking, thereby leading to counterintuitive phenomena. A coupled system with antisymmetric gain/loss profiles is required to introduce PT symmetry into photonics. As photons are intrinsically non-interactive, selection of two-photonic components is inevitable to mediate indirect coupling via near-fields. Remarkably, exciton–polaritons (the hybrid nature of excitons and photons) are directly interactive via excitonic components; however, the features of direct coupling between exciton–polariton modes have not been investigated so far. Here we demonstrate that such direct coupling can remodel conventional photonic platforms of non-Hermitian systems into polaritonic platforms with a single component; thus improving the degrees of freedom of both integration and design for the coupled system. We focused on the sixfold-symmetric microcavity to exploit degenerated photonic modes. By employing direct coupling with loss modulation, we observed room-temperature polaritonic PT symmetry with a phase transition from unbroken to broken, revealing the lowest threshold of polariton condensates in non-Hermitian degeneracies despite increasing loss.