The most elementary heat to work conversion: work extraction from a completely passive state by a single photon

TL;DR

This paper demonstrates that a single photon can extract work from a passive two-level quantum system, showing heat-to-work conversion at the most elementary quantum level, with potential for experimental verification.

Contribution

It provides the first theoretical evidence that a single photon emitted spontaneously can extract work from a passive quantum system, expanding understanding of quantum thermodynamics.

Findings

Work can be extracted from a passive two-level system by a single photon.

The process is cyclic with the initial and final states of the system being identical.

The work corresponds to a change in the photon's color during reemission.

Abstract

The concepts of work and heat in the quantum domain, as well as their interconversion principles, are still an open debate. We have found theoretical evidence that a single photon packet is capable of extracting work from a single two-level system (TLS). More importantly, this effect is found for a photon as it is spontaneously emitted, therefore carrying only heat away from the emitter. This is the most elementary process in which heat is converted into work, requiring not more than two off-resonance atoms for that purpose. From a more practical point of view it is found that, surprisingly, work can be extracted from a TLS in a completely passive initial state. The process is cyclic in the sense that the TLS initial and final states are equal. The state of the TLS remains passive throughout the interaction time with the single-photon packet. The physical meaning of the work performed by the TLS is found to be a dynamical change in the color of the photon during the reemission process. All our predictions are, in principle, measurable within state-of-the-art experiments.