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.
Highlights
As the first successful field theory Maxwell electrodynamics revolutionised our understanding of light and matter and its wide applicability has ensured its status as one of the pillars of modern physics
Since photons in the quantum theory are defined in terms of the operator-valued Maxwell fields, one can investigate the quantum versions of the classical radiation fields to determine whether or not these straightforward interpretations can be made
The implications of our analysis for quantum electrodynamics are largely independent of whether or not one deems this Poynting vector to be a true representation of radiated energy flux
Summary
As the first successful field theory Maxwell electrodynamics revolutionised our understanding of light and matter and its wide applicability has ensured its status as one of the pillars of modern physics. The photons involved in these energy non-conserving processes are interpreted as virtual and since for their existence they rely on the presence of the dipole, they are sometimes hypothesised as forming a localised cloud surrounding the ‘bare’ dipole [4, 20,21,22,23,24,25] In both classical and quantum theories electromagnetic energy is supposed to come in two varieties; energy permanently tied to the charged source and energy able to detach itself in the form of radiation. Since photons in the quantum theory are defined in terms of the operator-valued Maxwell fields, one can investigate the quantum versions of the classical radiation fields to determine whether or not these straightforward interpretations can be made. The implications of our analysis for quantum electrodynamics are largely independent of whether or not one deems this Poynting vector to be a true representation of radiated energy flux
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