Floquet time-crystals as sensors of AC fields

We discuss the performance of discrete time crystals (DTC) as quantum sensors. The long-range spatial and time ordering displayed by DTC, leads to an exponentially slow heating, turning DTC into advantageous sensors. Specifically, their performance (determined by the quantum Fisher information) to estimate AC fields, can overcome the shot-noise limit while allowing for long-time sensing protocols. Since the collective interactions stabilize their dynamics against noise, these sensors become robust to imperfections in the protocol. The performance of such a sensor can also be used in a dual role to probe the presence or absence of a many-body localized phase.