title: Observation of a discrete time crystal.
abstract: Spontaneous symmetry breaking is a fundamental concept in many areas of physics, including cosmology, particle physics and condensed matter. An example is the breaking of spatial translational symmetry, which underlies the formation of crystals and the phase transition from liquid to solid. Using the analogy of crystals in space, the breaking of translational symmetry in time and the emergence of a 'time crystal' was recently proposed, but was later shown to be forbidden in thermal equilibrium. However, non-equilibrium Floquet systems, which are subject to a periodic drive, can exhibit persistent time correlations at an emergent subharmonic frequency. This new phase of matter has been dubbed a 'discrete time crystal'. Here we present the experimental observation of a discrete time crystal, in an interacting spin chain of trapped atomic ions. We apply a periodic Hamiltonian to the system under many-body localization conditions, and observe a subharmonic temporal response that is robust to external perturbations. The observation of such a time crystal opens the door to the study of systems with long-range spatio-temporal correlations and novel phases of matter that emerge under intrinsically non-equilibrium conditions.
authors.affiliation: Joint Quantum Institute, University of Maryland Department of Physics and National Institute of Standards and Technology, College Park, Maryland 20742, USA.
authors.forename: J
authors.initials: J
authors.lastname: Zhang
authors.affiliation: Joint Quantum Institute, University of Maryland Department of Physics and National Institute of Standards and Technology, College Park, Maryland 20742, USA.
authors.forename: P W
authors.initials: PW
authors.lastname: Hess
authors.affiliation: Joint Quantum Institute, University of Maryland Department of Physics and National Institute of Standards and Technology, College Park, Maryland 20742, USA.
authors.forename: A
authors.initials: A
authors.lastname: Kyprianidis
authors.affiliation: Joint Quantum Institute, University of Maryland Department of Physics and National Institute of Standards and Technology, College Park, Maryland 20742, USA.
authors.forename: P
authors.initials: P
authors.lastname: Becker
authors.affiliation: Joint Quantum Institute, University of Maryland Department of Physics and National Institute of Standards and Technology, College Park, Maryland 20742, USA.
authors.forename: A
authors.initials: A
authors.lastname: Lee
authors.affiliation: Joint Quantum Institute, University of Maryland Department of Physics and National Institute of Standards and Technology, College Park, Maryland 20742, USA.
authors.forename: J
authors.initials: J
authors.lastname: Smith
authors.affiliation: Joint Quantum Institute, University of Maryland Department of Physics and National Institute of Standards and Technology, College Park, Maryland 20742, USA.
authors.forename: G
authors.initials: G
authors.lastname: Pagano
authors.affiliation: Department of Physics, University of California Berkeley, Berkeley, California 94720, USA.
authors.forename: I-D
authors.initials: ID
authors.lastname: Potirniche
authors.affiliation: Department of Physics, University of Texas at Austin, Austin, Texas 78712, USA.
authors.forename: A C
authors.initials: AC
authors.lastname: Potter
authors.affiliation: Department of Physics, University of California Berkeley, Berkeley, California 94720, USA.|Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA.
authors.forename: A
authors.initials: A
authors.lastname: Vishwanath
authors.affiliation: Department of Physics, University of California Berkeley, Berkeley, California 94720, USA.
authors.forename: N Y
authors.initials: NY
authors.lastname: Yao
authors.affiliation: Joint Quantum Institute, University of Maryland Department of Physics and National Institute of Standards and Technology, College Park, Maryland 20742, USA.|IonQ, Inc., College Park, Maryland 20742, USA.
authors.forename: C
authors.initials: C
authors.lastname: Monroe