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Restoring thermalization in long-range quantum magnets with staggered magnetic fields

Lucas Winter*, Pietro Brighi, and Andreas Nunnenkamp

  • *Contact author: lucas.winter@univie.ac.at
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Phys. Rev. Research 8, 023112 – Published 4 May, 2026

DOI: https://doi.org/10.1103/8nqf-xjnh

Abstract

Quantum systems with strong long-range interactions are thought to robustly resist thermalization because their energy spectra organize into a discrete number of multiplets. We show that this nonthermal behavior is surprisingly fragile to an experimentally ubiquitous perturbation: a staggered magnetic field. Using self-consistent mean-field theory and exact diagonalization, we reveal that the energy spectrum, while composed of discrete subspaces or multiplets, collectively forms a dense spectrum. The equilibration time is independent of system size and depends only on the fluctuations in the initial state. For initial states at low to intermediate energies, the long-time average aligns with the Sz sector-weighted microcanonical ensemble. However, for states in the middle of the spectrum, the long-time average depends on the initial state due to quantum scarlike eigenstates localized at unstable points in classical phase space. Our results can be readily tested on a range of experimental platforms, including Rydberg atoms or optical cavities.

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Phys. Rev. Research 8, 023112– Published 4 May, 2026
  • Received 4 April 2025
  • Revised 28 October 2025
  • Accepted 25 February 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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