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  • Open Access

Thermodynamics of readout devices and semiclassical gravity

Samuel Fedida1 and Adrian Kent1,2

  • 1Centre for Quantum Information and Foundations, DAMTP, Centre for Mathematical Sciences, University of Cambridge, Wilberforce Road, Cambridge CB3 0WA, United Kingdom
  • 2Perimeter Institute for Theoretical Physics, 31 Caroline Street North, Waterloo, Ontario N2L 2Y5, Canada

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Phys. Rev. A 113, 012214 – Published 12 January, 2026

DOI: https://doi.org/10.1103/bpwh-1pkf

Abstract

We analyze the common claim that nonlinear modifications of quantum theory necessarily violate the second law of thermodynamics. We focus on hypothetical extensions of quantum theory that contain readout devices. These black boxes provide a classical description of quantum states without perturbing them. They allow quantum state cloning, though in a way consistent with the relativistic no-signalling principle. We review the existence of such devices in the context of Møller-Rosenfeld semiclassical gravity, which postulates that the gravitational field remains classical and is sourced by the expectation value of a quantum energy-momentum tensor. We show that the definition of information in the models examined in this paper deviates from that given by von Neumann entropy, and that claims of second law violations based on the distinguishability of nonorthogonal states or on violations of uncertainty principles fail to hold in such theories.

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Phys. Rev. A 113, 012214– Published 12 January, 2026
  • Received 10 September 2025
  • Accepted 16 December 2025
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