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Many-Body Cages: Disorder-Free Glassiness from Flat Bands in Fock Space and Many-Body Rabi Oscillations

Tom Ben-Ami1,2, Markus Heyl1,3, and Roderich Moessner2

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Phys. Rev. Lett. 137, 100401 – Published 1 September, 2026

DOI: https://doi.org/10.1103/gmw6-x94c

Abstract

We introduce many-body caging as a novel mechanism for nonthermal behavior in quantum matter. We define many-body cages as eigenstates that, through quantum interference, become localized on a subgraph of the many-body state graph. These many-body cages can lead to the formation of flat bands in the many-body spectrum at characteristic, system-independent energies. These flat bands can realize a novel type of glassy eigenspectrum order in the absence of disorder, which we quantify by a band-overlap order parameter with an intricate, possibly fractal, distribution over the many-body state graph. We further show that these many-body cages exhibit distinctive signatures in experimentally accessible quantities, such as through a nonvanishing long-time memory of the initial condition, and many-body Rabi oscillations set by the characteristic flat-band energies. While our predictions in principle apply to any constrained quantum system, we demonstrate them here for 2D lattice gauge theories and models relevant for current experiments in Rydberg atoms. We expect that these many-body cages offer a promising route to realize nonequilibrium quantum states with novel properties.

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Phys. Rev. Lett. 137, 100401– Published 1 September, 2026
  • Received 2 June 2025
  • Revised 9 June 2026
  • Accepted 30 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. Open access publication funded by the Max Planck Society.

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