Quantum work by a single photon

TL;DR

This paper demonstrates that a single-photon electromagnetic pulse can perform work on a quantum dipole by inducing a Stark shift, expanding understanding of energy transfer at the quantum level.

Contribution

It introduces a method to quantify quantum work and heat for a single-photon interaction with a quantum dipole, linking these concepts to out-of-equilibrium photon processes.

Findings

Single-photon pulses can perform work on quantum dipoles via Stark shifts.

Quantum work is identified as the energy used to induce the Stark shift.

Generalized quantum heat corresponds to out-of-equilibrium photon absorption and emission.

Abstract

The work performed by a classical electromagnetic field on a quantum dipole is well known in quantum optics. The absorbed power linearly depends on the time derivative of the average dipole moment, in that case. The following problem, however, still lacks an answer: can the most elementary electromagnetic pulse, consisting of a single-photon state, perform work on a quantum dipole? As a matter of fact, the average quantum dipole moment exactly vanishes in such a scenario. In this paper, we present a method that positively answers to this question, by combining techniques from the fields of quantum machines and open quantum systems. Quantum work here is defined as the unitary contribution to the energy variation of the quantum dipole. We show that this quantum work corresponds to the energy spent by the photon pulse to dynamically Stark shift the dipole. The non-unitary contribution to the dipole energy is defined here as a generalized quantum heat. We show that this generalized quantum heat is the energy corresponding to out-of-equilibrium photon absorption and emission. Finally, we reveal connexions between the quantum work and the generalized quantum heat transferred by a single photon and those by a low-intensity coherent field.