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

Luca Capizzi1,* and Riccardo Travaglino2

  • *Contact author: luca.capizzi1701@gmail.com
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Phys. Rev. B 114, 094302 – Published 20 August, 2026

DOI: https://doi.org/10.1103/vnlm-3wys

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 an analytical explanation for this unexpected behavior.

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Phys. Rev. B 114, 094302– Published 20 August, 2026
  • Received 12 January 2026
  • Accepted 22 July 2026
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

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