Dissipative time crystal in a strongly interacting Rydberg gas

The notion of spontaneous symmetry breaking describes classical and quantum phase transitions, but extensions to time can yield time crystals that spontaneously break time-translation symmetry. While continuous time crystals (CTCs) at equilibrium are precluded by no-go theorems, dissipation in open systems can circumvent these constraints. The authors report the experimental observation of dissipative time-crystalline order in a room-temperature atomic gas, where ground-state atoms are continuously driven to Rydberg states. The time crystal is revealed by persistent oscillations in photon transmission, originating from limit cycles driven by coexistence and competition between distinct Rydberg components. Nondecaying autocorrelation of the oscillations and robustness against temporal noise demonstrate true long-range temporal order and realization of a continuous time crystal.