Sub-classical fields and polarization in electrodynamics

TL;DR

This paper explores how classical electromagnetic phenomena emerge from quantum electrodynamics by analyzing expectation values, polarization, and decoherence of the photon field using a space-time resolution approach.

Contribution

It introduces a framework for deriving classical electromagnetic features from QED, including radiation fields and polarizability, using the Closed Time Path formalism.

Findings

Derivation of the radiation field as a retarded solution from an action principle

Systematic calculation of charge system polarizability

Establishment of photon field decoherence and consistency

Abstract

Expectation values of the electromagnetic field and the electric current are introduced at space-time resolution which belongs to the quantum domain. These allow us to approach some key features of classical electrodynamics from the underlying QED. One is the emergence of the radiation field in the retarded solution of the Maxwell equation, derived from an action principle. Another question discussed is the systematic derivation of the polarizability of a charge system. Furthermore, the decoherence and the consistency of the photon field is established by a perturbative calculation of the reduced density matrix for the electromagnetic field within the Closed Time Path formalism.