From Canonical to Tunable Phase Diagrams in Open Quantum Long-Range Systems

This paper investigates how the dissipative dynamics of a generalized Lipkin-Meshkov-Glick (LMG) model—a long-range interacting quantum spin system—respond to different environmental coupling protocols. Specifically, the authors ask whether the system's stationary state can be controlled or modified by moving beyond standard linear dissipation models.

The researchers model the system's interaction with a thermal bath using the Lindblad master equation. They first analyze the system under standard linear Lindblad dynamics, where jump processes are thermally balanced. They then introduce a nonlinear generalization of the Lindblad equation by incorporating 'jump-retention parameters,' which represent imperfect quantum-jump processes. By deriving mean-field rate equations for the magnetization, they compare the resulting stationary states to those of the canonical equilibrium model.

The study establishes that standard linear Lindblad dynamics naturally reproduce the canonical equilibrium phase diagram of the generalized LMG model. However, the introduction of jump-retention parameters fundamentally changes the system's behavior. These parameters act as 'tunable knobs' that drive the system toward a genuine nonequilibrium stationary state (NESS). This NESS exhibits phase boundaries that shift based on the retention parameters and can even change the nature of phase transitions—for instance, converting a continuous transition into a first-order one. This demonstrates that controlled dissipation is a viable mechanism for engineering collective quantum phases.

This work provides a theoretical framework for using dissipation as a design tool in quantum technologies. By showing that nonequilibrium phases can be engineered through the precise control of quantum jump events, the authors offer a new perspective on how to stabilize or manipulate quantum states in open systems, moving beyond the limitations of equilibrium statistical mechanics.