Photon condensation from thermal sources and the limits of heat engines

TL;DR

This paper explores the conditions under which photon Bose-Einstein condensation can occur using thermal sources, revealing thermodynamic limits and potential applications in energy and quantum heat engine research.

Contribution

It demonstrates that photon condensation can be achieved with incoherent thermal pumping, establishing the thermodynamic threshold and limits for such processes.

Findings

Condensation threshold is set by the second law of thermodynamics.

Reversible three-level heat engine sets the minimum pump temperature.

Photon condensates can be generated using thermal sources, enabling new applications.

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.