This work investigates nonequilibrium phase transitions in a Rydberg atomic system under collective dissipation. By combining mean-field theory and Liouvillian spectral analysis, we reveal novel nonequilibrium phases induced by collective dissipation and compare the results from both approaches. Our findings indicate that collective dissipation not only generates interatomic correlations but also sustains persistent periodic oscillations and a unique bistable form, in which the system may evolve to a steady state or sustain self-consistent oscillatory dynamics. This study highlights the rich nonequilibrium phenomena present in quantum many-body systems and provides an extensible spectral framework for exploring dissipative phases in Rydberg and related systems.

Recent experiments have reported persistent oscillations in thermal Rydberg atomic ensembles, yet the theoretical consensus on their origin remains elusive. Motivated by these observations, we introduce a collective dissipation mechanism and employ both mean-field approximations and the Liouvillian spectrum method to systematically explore nonequilibrium phase transitions. Our results show that the collective dissipation effectively induces interatomic correlations and sustains persistent periodic oscillations, in which under the same parameters, independent dissipation leads the system to relax to a stationary state. Furthermore, the nonlinear effects arising from collective dissipation give rise to a novel type of bistability, in which the system can converge to a fixed point or maintain self-consistent periodic oscillations. This mechanism is clearly different from the traditional bistability induced by Rydberg interactions, which involves two steady states. Moreover, the Liouvillian spectral method, based on the quantum master equation, successfully captures the features of nonequilibrium phase transitions even in finite-dimensional systems, and the results accord well with those obtained from mean-field approximation in the thermodynamic limit.

Our work not only provides a theoretical explanation for recently observed oscillatory phenomena but also predicts novel bistable states and rich nonequilibrium phase structures. It further verifies the effectiveness of the Liouvillian spectroscopic method in studying quantum many-body systems, making significant contributions to understanding the microscopic mechanisms underlying nonequilibrium phase transitions.