Time Crystals (Experimental Realization)

First experimental realizations of discrete time crystals, reported simultaneously in 2017 by two independent groups using different platforms: Zhang et al. (trapped ytterbium ions, Nature 543, 217, primary landmark here) and Choi et al. (nitrogen-vacancy centers in diamond, Nature 543, 221, OpenAlex W2540688686). Both realize a periodically-driven (Floquet) discrete time crystal, not Wilczek's original continuous-time-translation-breaking proposal, which was later shown (Nature 2015, "Absence of Quantum Time Crystals," OpenAlex W1652183760) not to be realizable in equilibrium -- the 2017 experiments are of a genuinely different, driven variant.