USTC observes higher-order and fractional DTCs in floquet-driven Rydberg atomic gases

A team led by Prof. DING Dongsheng from the University of Science and Technology of China (USTC) of the Chinese Academy of Sciences experimentally observed higher-order and fractional discrete time crystals (DTCs) in periodically driven Rydberg atomic dissipative systems. Their study was published in Nature Communications.

Spontaneous symmetry breaking is a key mechanism for explaining phase transitions in matter and is responsible for the formation of ordered structures such as spatial crystals. Time crystals have made considerable progress in theory and experiment since they were proposed by Nobel Prize winner Professor Frank Wilczek. On the theoretical front, researchers have introduced DTCs and demonstrated their emergence in periodically driven systems. Experimentally, DTCs have been observed in various quantum platforms, such as trapped ions, ultracold atoms, solid-state spin systems, and superconducting qubits.

In this work, Prof. Ding's team constructed an experimental platform combining a quantum many-body system with periodic Floquet driving. The many-body system consists of interacting cesium atoms excited to high-energy Rydberg states. By employing a three-photon electromagnetically induced transparency (EIT) scheme, they prepared and measured the Rydberg atom populations. At the same time, a periodic pulsed RF field was applied to modulate the Rydberg energy levels and drive the system out of equilibrium.

Based on their experimental setup, the team observed higher-order DTCs, where the system's response exhibited integer multiples of the driving period. These DTCs demonstrated robustness against the perturbations, persisting within a small range of experimental conditions. Additionally, the team identified phase transitions between adjacent integer DTCs. The team further discovered fractional DTCs, where the system exhibited periodic responses at fractional multiples of the driving period. These fractional DTCs, which arise from symmetry breaking into fractional temporal structures, exhibited stability against perturbations.

This research represents a breakthrough in the study of time crystals, expanding the understanding of both higher-order and fractional DTCs. The work paves the way for future exploration of intricate temporal symmetries and non-equilibrium phenomena in driven quantum systems.