Phase Synchronization between Two Superradiant Lasers

Abstract: We experimentally demonstrate synchronization between two distinct ensembles of cold atoms undergoing steady state superradiance within a single longitudinal and transverse mode of the same optical cavity. The synchronization process is studied first in terms of the time dynamics of re-synchronization when the phase alignment of the two oscillators is abruptly broken. We also observe the steady state behavior of the lasers as their relative frequency is continuously varied. This system has the potential to realize a non-equilibrium quantum phase transition and could inform future implementations of milliHertz linewidth lasers.