Observation of a Discrete Time Crystal

TL;DR

This paper reports the first experimental observation of a discrete time crystal in a trapped ion system, demonstrating a new phase of matter with persistent sub-harmonic oscillations under non-equilibrium conditions.

Contribution

It provides the first experimental evidence of a discrete time crystal in an interacting spin chain with many-body localization.

Findings

Observation of sub-harmonic temporal response

Robustness of the time crystal to external perturbations

Demonstration of long-range spatial-temporal correlations

Abstract

Spontaneous symmetry breaking is a fundamental concept in many areas of physics, ranging from cosmology and particle physics to condensed matter. A prime example is the breaking of spatial translation symmetry, which underlies the formation of crystals and the phase transition from liquid to solid. Analogous to crystals in space, the breaking of translation symmetry in time and the emergence of a "time crystal" was recently proposed, but later shown to be forbidden in thermal equilibrium. However, non-equilibrium Floquet systems subject to a periodic drive can exhibit persistent time-correlations at an emergent sub-harmonic frequency. This new phase of matter has been dubbed a "discrete time crystal" (DTC). Here, we present the first 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 (MBL) conditions, and observe a sub-harmonic temporal response that is robust to external perturbations. Such a time crystal opens the door for studying systems with long-range spatial-temporal correlations and novel phases of matter that emerge under intrinsically non-equilibrium conditions.