Abstract

In the last decade, there has been much debate about the possibility of observing states with spontaneous time oscillations that are robust to noise, including unavoidable quantum fluctuations. These states were first proposed as exotic equilibrium states of matter [1] and dubbed “time crystals” after regular crystals, which have analogous robustness in space. However, it was soon proven [2] that non-equilibrium conditions are necessary for such a goal, to which several workarounds followed. In particular, it has been suggested that time-crystalline order might arise in asymptotic states of driven-dissipative systems [3].

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