Quantum optical dipole radiation fields

TL;DR

This paper introduces quantum optical dipole radiation fields, clarifies their spatial dependence, and discusses their implications for understanding radiated energy and the distinction between virtual and real photons.

Contribution

It defines quantum optical dipole radiation fields based on photon operators and analyzes their role in electromagnetic energy flux far from the source.

Findings

Radiated energy-flux includes virtual photon contributions.

Distinction between radiative and real photons depends on energy conservation.

Standard virtual photon cloud interpretation around atoms is challenged.

Abstract

We introduce quantum optical dipole radiation fields defined in terms of photon creation and annihilation operators. These fields are identified through their spatial dependence, as the components of the total fields that survive infinitely far from the dipole source. We use these radiation fields to perturbatively evaluate the electromagnetic radiated energy-flux of the excited dipole. Our results indicate that the standard interpretation of a bare atom surrounded by a localised virtual photon cloud, is difficult to sustain, because the radiated energy-flux surviving infinitely far from the source contains virtual contributions. It follows that there is a clear distinction to be made between a radiative photon defined in terms of the radiation fields, and a real photon, whose identification depends on whether or not a given process conserves the free energy. This free energy is represented by the difference between the total dipole-field Hamiltonian and its interaction component.