Observation of a discrete time crystal

• Published in: Nature (London) 2017-03, Vol.543 (7644), p.217-220
• Main Authors: Zhang, J., Hess, P. W., Kyprianidis, A., Becker, P., Lee, A., Smith, J., Pagano, G., Potirniche, I.-D., Potter, A. C., Vishwanath, A., Yao, N. Y., Monroe, C.
• Format: Article
• Language: English
• Subjects: 140/125; 639/766/119/2795; 639/766/483/3926; 639/766/483/481; Crystals; Equilibrium; Humanities and Social Sciences; Lasers; letter; multidisciplinary; Phase transitions; Physics; Quantum physics; Science; Symmetry
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature21413

A time crystal is a state of matter that shows robust oscillations in time, and although forbidden in equilibrium, a discrete time crystal has now been observed in a periodically driven quantum system. Time crystals aren't forever Much like ordinary crystals, time crystals exhibit a high degree of structural order. But whereas ordinary crystals get their periodicity from the regular repetition of spatial elements, time crystals are an exotic, non-equilibrium state of matter in which the same structures repeat themselves in time. Predicted to exist a few years ago, time crystals have so far resisted experimental demonstration. Now, two groups offer evidence for experimental observation of this elusive form of matter. Jiehang Zhang et al . create a specific kind of time crystal—a discrete time crystal—in a chain of ten trapped ions under the influence of periodic driving. Mikhail Lukin and colleagues achieve a similar feat using approximately one million nitrogen–vacancy spin impurities in diamond as an experimental platform. In both cases, the time-crystalline order is shown to be robust to external perturbations. Such time crystals could potentially find applications in robust quantum memory. Spontaneous symmetry breaking is a fundamental concept in many areas of physics, including cosmology, particle physics and condensed matter 1 . 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 2 , 3 , but was later shown to be forbidden in thermal equilibrium 4 , 5 , 6 . However, non-equilibrium Floquet systems, which are subject to a periodic drive, can exhibit persistent time correlations at an emergent subharmonic frequency 7 , 8 , 9 , 10 . This new phase of matter has been dubbed a ‘discrete time crystal’ 10 . 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 7 .