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.

非厄米系统中的奇偶校验时间反转对称性（PT 对称性）实现了自发的对称性破缺，从而导致了违反直觉的现象。需要一个具有反对称增益/损耗分布的耦合系统来将 PT 对称性引入光子学。由于光子本质上是非交互的，因此不可避免地选择双光子组件来介导通过近场的间接耦合。值得注意的是，激子-极化子（激子和光子的混合性质）通过激子成分直接相互作用。然而，迄今为止尚未研究激子 - 极化子模式之间直接耦合的特征。在这里，我们证明了这种直接耦合可以将非厄米系统的传统光子平台改造成具有单个组件的极化子平台；从而提高耦合系统的集成和设计的自由度。我们专注于利用退化光子模式的六重对称微腔。通过采用直接耦合与损耗调制，我们观察到室温极化子 PT 对称性具有从完整到破裂的相变，尽管损失增加，但揭示了非厄米简并中极化子凝聚的最低阈值。