Phase Transitions without gap closing in monitored quantum mean-field systems

TL;DR

This paper explores the dynamics of monitored quantum mean-field systems, revealing new stationary states that emerge in the thermodynamic limit without gap closing, challenging conventional understanding of phase transitions.

Contribution

It introduces a framework for analyzing monitored mean-field quantum systems and uncovers novel stationary states independent of Lindbladian gap closing.

Findings

Discovery of new stationary states in monitored mean-field systems

Stationary states are distinct from infinite-temperature states

Phenomenon occurs without Lindbladian gap closing

Abstract

We investigate the monitored dynamics of many-body quantum systems in which projective measurements of extensive operators are alternated with unitary evolution. Focusing on mean-field models characterized by all-to-all interactions, we develop a general framework that captures the thermodynamic limit, where a semiclassical description naturally emerges. Remarkably, we uncover novel stationary states, distinct from the conventional infinite-temperature state, that arise upon taking the infinite-volume limit. Counterintuitively, this phenomenon is not linked to the closing of the Lindbladian gap in that limit. We provide analytical explanation for this unexpected behavior.