Long-range Synchronization of Nanomechanical Oscillators with Light

We experimentally demonstrate mutual synchronization of two free-running nanomechanical oscillators separated by an effective distance of 30 meters and coupled through light. Due to the finite speed of light, the large separation introduces a significant coupling delay of 139 nanoseconds, approximately four and a half times the mechanical oscillation time period. We reveal multiple stable states of synchronized oscillations, enabled by delayed coupling, with distinct synchronization frequency in the coupled system. These states are accessed by tuning independently the directional coupling strengths. Our results demonstrate rich dynamics and could enable applications in reconfigurable radio-frequency networks and novel computing concepts.