A team led by Academician Guo Guangcan from the University of Science and Technology of China, including Professor Shi Baosen and Professor Ding Dongsheng, in collaboration with Professor Li Weibin from the University of Nottingham, Associate Researcher Bai Zhengyang from East China Normal University, and Professor Charles S. Adams from Durham University, UK, have observed the phenomenon of ergodicity breaking in open Rydberg atom systems. Their findings were recently published in "Science Advances".
In physical systems, ergodicity typically allows for relaxation to an equilibrium state, where observables no longer change over time, quickly seeking new fixed points in phase space. However, exceptions exist, such as in integrable and many-body localized systems, where broken ergodicity can suppress system equilibration and thermalization. Studying ergodicity breaking offers insights and references for understanding market collapses and recoveries in financial networks, epileptic seizures in neural networks, and early warnings of critical transitions in complex systems. Rydberg atoms, known for their long-range interactions, serve as an ideal system for studying non-ergodic dynamical behavior. In driven-dissipative Rydberg atom systems, non-equilibrium long-lived oscillatory phases emerge due to the clustering of Rydberg atoms.
Ding Dongsheng and colleagues have observed non-ergodic many-body dynamical phenomena in a strongly interacting Rydberg atom gas via two-photon excitation of Rydberg atoms at room temperature. This phenomenon results from the combined effects of laser coherence driving, Rydberg atom interactions, and dissipation. By tuning the laser parameters, they observed a non-equilibrium phase transition, featuring a bifurcation between ergodic and weak non-ergodic phases. In the ergodic phase, atoms are uniformly distributed, whereas in the weak non-ergodic phase, the number of Rydberg state particles exhibits non-trivial oscillations. They observed sustained millisecond-long many-body collective oscillations, far exceeding the time scale of related dissipations. Analysis indicates that this ergodicity breaking is due to the clustering of strongly interacting Rydberg atoms in free space.
For more details on the paper, visit: https://doi.org/10.1126/sciadv.adl5893
