Demonstration of Discrete Time Crystals in a Quantum system

Synopsis

Time crystals are novel quantum phases in which the evolution of matter violates the intrinsic time-translation symmetry of the system. This phenomenon can be stimulated by any weak perturbation and hence is called spontaneous breaking of time-translation symmetry. After Frank Wilczek published his seminal article about time crystals in 2012, many research groups started to search for them. Later, it was shown that it is impossible for any equilibrium state to form a time crystal. When a system is driven out of equilibrium by a periodic perturbation, however, it can sustain subharmonic oscillations that break the original discrete time-translation symmetry. In this presentation, I will discuss spontaneous breaking of discrete time-translation symmetry in a model of atoms bouncing on an oscillating mirror. In the model, interacting atoms fall under gravity on a vibrating mirror. Simulation shows that atomic cloud bounces up and down with a smaller frequency than that of the mirror, which demonstrates a discrete time crystal.