Observation of a Prethermal U(1) Discrete Time Crystal

A time crystal is a novel state of periodically driven matter which breaks discrete time translation symmetry. Time crystals have been demonstrated experimentally in various programmable quantum simulators and exemplify how non-equilibrium, driven quantum systems can exhibit intriguing and robust properties absent in systems at equilibrium. These states are often stabilized by prethermalization, in which a periodically driven quantum system heats to infinite temperature exponentially slowly in the driving frequency. Recent theoretical work has developed the notion of prethermalization without temperature in order to explain time crystalline observations at (or near) infinite temperature. In this work, we utilize prethermalization without temperature to conclusively verify the emergence of a prethermal U(1) time crystalline state at infinite temperature. Here we show the existence of a long-lived prethermal regime whose lifetime is significantly enhanced by strengthening an emergent U(1) conservation law. In our solid-state NMR quantum simulator, we measure this enhancement through the global magnetization, and utilize on-site disorder to measure local observables and rule out the possibility of many-body localization. We thus conclusively verify the predictions for a time crystalline state of a high temperature spin ensemble. Additionally, we investigate the response of a novel short-range correlated initial state, the dipolar order, under time crystalline driving.