Duality, decay rates and local-field models in macroscopic QED

TL;DR

This paper explores how including local-field effects in macroscopic QED restores the fundamental duality symmetry between electric and magnetic interactions, affecting decay rates and force calculations.

Contribution

It demonstrates that local-field effects can restore duality symmetry in macroscopic QED and provides a method to compute magnetic dipole decay rates with this symmetry.

Findings

Restoration of duality symmetry with local-field effects

Calculation of magnetic dipole decay rate in magneto-dielectric

Macroscopic QED can be dual symmetric at an operator level

Abstract

Any treatment of magnetic interactions between atoms, molecules and optical media must start at the form of the interaction energy. This forms the base on which predictions about any number of magnetic atom-light properties stands -- spontaneous decay rates and forces included. As is well-known, the Heaviside-Larmor duality symmetry of Maxwell's equations, where electric and magnetic quantities are exchanges, is broken by the usual form of the magnetic interaction energy. We argue that this symmetry can be restored by including general local-field effects, and that local fields should be treated as a necessity for correctly translating between the microscopic world of the dipole and the macroscopic world of the measured fields. This may additionally aid in resolving a long standing debate over the form of the force on a dipole in a medium. Finally, we compute the magnetic dipole decay rate in a magneto-dielectric with local-field effects taken into account, and show that macroscopic quantum electrodynamics can be made to be dual symmetric at an operator level, instead of only for expectation values.