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  • Open Access

Taking the temperature of quantum many-body scars

Phillip C. Burke1,2,* and Shane Dooley3,†

  • *Contact author: phillip.cussenburke@ucd.ie
  • †Contact author: dooleysh@stp.dias.ie
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Phys. Rev. Research 7, 043054 – Published 15 October, 2025

DOI: https://doi.org/10.1103/ytqp-jml7

Abstract

A quantum many-body scar is an eigenstate of a chaotic many-body Hamiltonian that exhibits two seemingly incongruous properties: Its energy eigenvalue corresponds to a high temperature, yet its entanglement structure resembles that of low-temperature eigenstates, such as ground states. Traditionally, a temperature is assigned to an energy eigenvalue through the textbook canonical temperature-energy relationship. However, in this work, we use the eigenstate subsystem temperature—a recently developed quantity that assigns a temperature to an energy eigenstate, based on the structure of its reduced density matrix. For a thermal state, the eigenstate subsystem temperature is approximately equal to its canonical temperature. Given that quantum many-body scars have a ground-state-like entanglement structure, it is not immediately clear that their eigenstate subsystem temperature would be close to their canonical temperature. Surprisingly, we find that this is the case: The quantum many-body scars retain local information about their position in the spectrum encoded within their state structure.

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Phys. Rev. Research 7, 043054– Published 15 October, 2025
  • Received 24 April 2025
  • Accepted 8 September 2025
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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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