Time-crystalline behavior in an engineered spin chain

Understand

Time crystals appear when systems display a commensurate spontaneous breaking of the discrete time translational invariance imposed by an external periodic drive.

• No consensus on the definition has been reached as yet, but important aspects comprise robustness against small variations of the parameters and the initial quantum state.
• Often, disorder and interaction are thought to be essential ingredients for the occurrence of time crystals.
• We study a finite-length polarized XX spin chain engineered to display a spectrum of equidistant energy levels without drive and show that it keeps a spectrum of equidistant quasienergies in Floquet theory for a large variety of periodic driving schemes.