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  • Open Access

Quantum Thermal State Preparation for Near-Term Quantum Processors

Jerome Lloyd1 and Dmitry A. Abanin2,3,4

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Phys. Rev. X 16, 031053 – Published 28 August, 2026

DOI: https://doi.org/10.1103/cbrd-ssnm

Abstract

Preparation of quantum thermal states of many-body systems is a key computational challenge for quantum processors, with applications in physics, chemistry, and classical optimization. We provide a simple and efficient algorithm for thermal state preparation, combining engineered bath resetting and modulated system-bath coupling to derive a quantum channel approximately satisfying quantum detailed balance relations. We show that the fixed point σ^ of the channel approximates the Gibbs state as ∥σ^−σ^β∥∼θ2, where θ is the system-bath coupling and σ^β∝e−βH^S. We provide extensive numerics, for the example of the 2D quantum Ising model, confirming that the protocol successfully prepares the thermal state throughout the finite-temperature phase diagram, including near the quantum phase transition. Simulations for free-fermion systems provide further evidence for the accuracy of the protocol for large system sizes in the weak-coupling limit. Our algorithm provides a path to efficient quantum simulation of quantum-correlated states at finite temperature with current and near-term quantum processors.

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Popular Summary

Preparing quantum thermal states of many-body systems, especially at low temperatures where quantum effects are most significant, is a central challenge of quantum simulation. We address this difficulty by designing an efficient algorithm which combines engineered bath resetting with time-dependent system-bath coupling. The time-dependent coupling provides a simple way to approximately enforce detailed balance relations, and is particularly suited for near-term quantum processors. We demonstrate the accuracy of our protocol with numerical simulations of two-dimensional quantum magnetic systems and large-scale free-fermion chains, finding close agreement for key thermodynamic observables, including near quantum phase transitions. In the long term, our method provides a practical path toward simulating strongly correlated quantum matter at finite temperatures on near-term digital and analog quantum hardware.

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Phys. Rev. X 16, 031053– Published 28 August, 2026
  • Received 17 July 2025
  • Revised 17 March 2026
  • Accepted 8 July 2026
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