Topological exciton-polaritons with negative coupling.

Coupling between quantum or classical degrees of freedom underpins a wide range of physical phenomena, from condensed matter systems to engineered photonic lattices. While positive coupling arising naturally from evanescent interactions has been extensively studied and employed, negative coupling unlocks unique phenomena that are challenging to realize with positive coupling alone. Exciton-polariton micropillars, celebrated for enabling topological lasers, reservoir computing, and quantum simulations, have primarily relied on positive coupling. In this work, we experimentally demonstrate negative coupling between two micropillars using an additional larger micropillar. By combining positively and negatively coupled micropillars, we construct a Su-Schrieffer-Heeger (SSH) topological lattice with a significant topological gap of approximately 15 meV, where band inversion occurs at the center of the Brillouin zone (BZ), rather than at the edges as in conventional SSH lattices. Under non-resonant excitation, we achieve polariton condensation in the in-gap topological edge states at room temperature. Our study introduces a universal method to realize negative coupling in polariton systems, paving the way for novel polaritonic devices based on lattices with arbitrarily controlled coupling signs.