Coherent room-temperature dipole synchronization in plasmonic nanocavities

Plasmonic nanocavities enable the synchronization of spatially distant emissive dipoles through strong near-field coupling in subnanometre gaps. Yet, it remains unclear how collective phase order can emerge in nanoscale optical systems where dissipation, disorder and ultrafast radiative loss normally suppress long-lived coherence. Here we report the formation of a room-temperature synchronized dipole state in locally ordered plasmonic nanogap two-dimensional arrays under non-resonant continuous-wave pumping. The system consists of methylene blue emitters confined in cucurbit[7]uril-defined subnanometre gaps between close-packed gold nanoparticles. Unlike lasers, photonic Bose-Einstein condensates or exciton-polariton condensates, this system exhibits spatial coherence across the dipoles, while rapid radiative emission suppresses temporal photon coherence. Increased coherence is observed with increasing pumping, marked by the spatial spread of g⁽¹⁾ coherence, but without spectral narrowing or directional emission. This driven-dissipative system exhibits fast temporal coherence formation within 10 fs and complex spatial correlations. Combining ultralow mode volumes and high Purcell enhancement, it offers a scalable platform for studying dipole synchronization at room temperature for photonic and quantum technologies.