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High-Temperature Fermionic Gibbs States Are Mixtures of Gaussian States

Akshar Ramkumar1,2, Yiyi Cai1,3, Yu Tong4,5,6, and Jiaqing Jiang1,7,8,*

  • *Contact author: jiaqingjiang95@gmail.com
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Phys. Rev. Lett. 137, 020601 – Published 7 July, 2026

DOI: https://doi.org/10.1103/qprk-k7wn

Abstract

Efficient simulation of a quantum system generally relies on structural properties of the quantum state. Motivated by the recent results by Bakshi et al. on the sudden death of entanglement in high-temperature Gibbs states of quantum spin systems, we study the high-temperature Gibbs states of bounded-degree local fermionic Hamiltonians, which include the special case of geometrically local fermionic systems. We prove that, at a sufficiently high temperature that is independent of the system size, the Gibbs state is a probabilistic mixture of fermionic Gaussian states. This forms the basis of an efficient classical algorithm to prepare the Gibbs state by sampling from a distribution of fermionic Gaussian states.

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Information

Phys. Rev. Lett. 137, 020601– Published 7 July, 2026
  • Received 19 July 2025
  • Revised 12 May 2026
  • Accepted 1 June 2026
Article part of CHORUS
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