How to Create a Time Crystal
Figure 1:Yao et al. have developed a blueprint for creating a time crystal and a method for detecting it.
[image courtesy APS/Alan Stonebraker/Phil Richerme]
The story of time crystals - whose lowest-energy configurations are periodic in time rather than space - epitomizes the creative ideas, controversy, and vigorous discussion that lie at the core of the scientific process. Originally theorized by Frank Wilczek in 2012, time crystals were met with widespread attention, but also a healthy dose of skepticism. This ignited a debate in the literature, culminating in a proof that time crystals cannot exist in thermal equilibrium, as originally imagined by Wilczek. But the tale did not end there. It was later argued that time crystals might still be possible in periodically driven systems, which can never reach thermal equilibrium. Three recent papers have now completed the story, one proposing a roadmap for creating a nonequilibrium time crystal in the lab , and two describing subsequent experimental demonstrations in systems of trapped ions  and spin impurities in diamond  (both posted on the physics arXiv preprint server). [Prof. Ashvin Vishwanath is a coauthor on the first two, Profs. Eugene Demler and Mikhail Lukin, on the third.]
Read a "Viewpoint" article by Phil Richerme, Harvard Physics alumnus (PhD 2012) in APS Physics: P. Richerme, "How to Create a Time Crystal," Physics 10, 5 (Jan 18, 2017) http://physics.aps.org/articles/v10/5.
Also read the original papers:1. N.Y. Yao, A.C. Potter, I.-D. Potirniche, and A. Vishwanath, "Discrete Time Crystals: Rigidity, Criticality, and Realizations," Phys. Rev. Lett. 118, 030401 (Jan 18, 2017) DOI: http://dx.doi.org/10.1103/PhysRevLett.118.030401 doi.org/10.1103/PhysRevLett.118.030401.
2. J. Zhang, P.W. Hess, A. Kyprianidis, P. Becker, A. Lee, J. Smith, G. Pagano, I.-D. Potirniche, A. C. Potter, A. Vishwanath, N. Y. Yao, C. Monroe, "Observation of a Discrete Time Crystal," arXiv:1609.08684 (27 Sep 2016).
3. S. Choi, J. Choi, R.e Landig, G. Kucsko, H. Zhou, J. Isoya, F. Jelezko, S. Onoda, H. Sumiya, V. Khemani, C. von Keyserlingk, N.Y. Yao, E. Demler, M.D. Lukin, “Observation of Discrete Time-Crystalline Order in a Disordered Dipolar Many-Body System,”) arXiv:1610.08057 (25 Oct 2016).