Long-Range Coherence Between Spatially Separated Polariton Condensates via External Coupling

Lattice arrays of exciton–polariton condensates are powerful platforms for simulating complex nonequilibrium many-body phenomena. However, physical implementations typically allow only nearest-neighbor coupling defined by the lattice geometry, limiting their scalability for analog spin and neuromorphic architectures. Achieving independently tunable, long-range interactions between distant condensates remains a major challenge. Here, we demonstrate an all-optical scheme that enables coherent coupling between spatially separated polariton condensates in a planar microcavity via light that leaves the cavity and comes back. Light emitted vertically from one condensate is imaged and reflected back to the sample to impinge on another condensate at an arbitrary distance, effectively creating a reconfigurable optical feedback loop. We verify long-range phase locking between two geometrically isolated condensates with suppressed planar coupling, confirmed by phase-resolved interferometry showing clear interference fringes and deterministic phase correlation. Analytical modeling reveals complementary mechanisms underpinning the robust coherence, consistent with experimental observations. Our mirror-based feedback scheme introduces no cameras, modulators, or electronic processing, allowing the condensate pair to function as a pure, high-bandwidth analog element. Because the coupling topology can be reprogrammed optically, this approach can be extended to dense condensate lattices via segmented micro-mirror arrays. The resulting platform allows independently tunable, nonlocal coupling between polariton condensates, paving the way toward scalable, energy-efficient, and reconfigurable polaritonic hardware for optimization, classification, and other neuromorphic computing tasks at the speed of light.