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  • Letter
  • Open Access

Photon condensation from thermal sources and the limits of heat engines

Luísa Toledo Tude1,2, Emily Haughton1, and Paul R. Eastham1

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Phys. Rev. A 113, L010201 – Published 2 January, 2026

DOI: https://doi.org/10.1103/6lyv-trfj

Abstract

The trapping and cooling of photon gases in microcavities has been used to create Bose-Einstein condensates. We investigate the conditions required for condensation in dye-filled microcavities, with photon populations created either by driving a transition of the dye, or by coupling the cavity modes to a thermal photon reservoir such as sunlight. We find that the threshold pump temperature, above which condensation appears, is determined by the second law of thermodynamics. The minimum achievable threshold is that of a reversible three-level heat engine, which we show arises in the dye-pumped case, and for pumping of the modes of a two-level cavity. For a many-level cavity condensation occurs at a similar but higher temperature. Our results show that photon condensates can be produced by pumping with incoherent thermal sources, opening possibilities for coherent light generation, energy harvesting, and experimental studies of quantum heat engines.

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Phys. Rev. A 113, L010201– Published 2 January, 2026
  • Received 25 July 2025
  • Accepted 10 December 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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