Long-Range Synchronization of Remote NV Color-Center Ensembles via an Active Microwave Cavity

For scalable quantum networks and distributed quantum sensing, remote NV color-center spin ensembles require controllable long-range coherent connections. However, the magnetic dipole coupling between NV centers decays rapidly with distance, making direct stable coherent exchange difficult to achieve. Here, we propose an active-microwave-cavity-assisted scheme for long-range synchronization, in which traveling microwave photons establish a remote cavity–spin coupling channel, while saturable gain compensates cavity loss and propagation attenuation. The results show that the system exhibits collective superradiant emission under gain-off and forms a hysteretic synchronized state controlled by the propagation phase, separation distance, and optical cooling rate under gain-on. Moreover, the active cavity can mediate long-range phase synchronization between two remote NV ensembles, with local optical cooling enabling switching between in-phase and out-of-phase synchronized states. This scheme provides a theoretical route toward room-temperature, optically reconfigurable spin networks.