Observation of a discrete time crystal
The authors experimentally realize a discrete (Floquet) time crystal using a chain of trapped atomic ions driven periodically into a many-body-localized regime. The system spontaneously breaks the discrete time-translation symmetry of the drive, exhibiting a subharmonic oscillation at a period that is a rational multiple of the drive period. This rigid, period-doubled response persists despite perturbations to the drive, confirming the predicted time-crystalline phase.