Time crystals are classified as discrete or continuous depending on whether they spontaneously break discrete or continuous time translation symmetry. Although discrete time crystals have been extensively studied in periodically driven systems, the experimental realization of a continuous time crystal is still pending. We report the observation of a limit cycle phase in a continuously pumped dissipative atom-cavity system that is characterized by emergent oscillations in the intracavity photon number. The phase of the oscillation was found to be random for different realizations, and hence, this dynamical many-body state breaks continuous time translation symmetry spontaneously. Furthermore, the observed limit cycles are robust against temporal perturbations and therefore demonstrate the realization of a continuous time crystal.

中文翻译：

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观察一个连续的时间晶体。

时间晶体根据它们是否自发地破坏离散或连续时间平移对称性而分为离散或连续。尽管离散时间晶体已在周期性驱动系统中得到广泛研究，但连续时间晶体的实验实现仍有待实现。我们报告了在连续泵浦耗散原子腔系统中对极限循环阶段的观察，该系统的特点是腔内光子数的出现振荡。发现振荡的相位对于不同的实现是随机的，因此，这种动态多体状态自发地打破了连续时间平移对称性。此外，观察到的极限环对时间扰动具有鲁棒性，因此证明了连续时间晶体的实现。