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Quantum measurements and equilibration: The emergence of objective outcomes via entropy maximization

Emanuel Schwarzhans1,2,*, Felix C. Binder3,†, Marcus Huber1,4,‡, and Maximilian P. E. Lock1,4,§

  • *Contact author: emanuel.schwarzhans@oeaw.ac.at
  • †Contact author: quantum@felix-binder.net
  • ‡Contact author: marcus.huber@tuwien.ac.at
  • §Contact author: maximilian.paul.lock@tuwien.ac.at
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Phys. Rev. Research 7, 043279 – Published 10 December, 2025

DOI: https://doi.org/10.1103/h2yj-25rn

Abstract

The measurement postulate of quantum theory stands in conflict with the laws of thermodynamics and has evoked debate regarding what actually constitutes a measurement. With the help of modern quantum statistical mechanics, we take the first step in formalizing the hypothesis that quantum measurements are driven by the natural tendency of closed systems to maximize entropy, a notion that we call the measurement-equilibration hypothesis. In this paradigm, we investigate how classical measurement outcomes can emerge within a purely unitary framework, and find that (1) the interactions used in standard measurement models fail to spontaneously encode information classically and (2) while ideal projective measurements are impossible, one can (for a given form of Hamiltonian) approximate them exponentially well as more physical systems are collected together into an “observer” system. We thus lay the groundwork for self-contained models of quantum measurement, proposing improvements to our simple scheme.

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Phys. Rev. Research 7, 043279– Published 10 December, 2025
  • Received 28 March 2023
  • Revised 26 June 2024
  • Accepted 8 November 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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