In one minute

Stefan Buhmann and Stefan Scheel ask when the duality between electric and magnetic fields is a true symmetry of macroscopic quantum electrodynamics, the theory of quantum light in real materials. The question is timely: magnetic effects are much smaller in natural materials, but recent developments have drawn fresh interest to them. Without free charges, Maxwell's equations are duality invariant at the operator level, although Lorentz forces and atom-field couplings generally are not. They prove that Casimir forces, local-field corrected decay rates and van der Waals potentials stay unchanged under a global swap of electric and magnetic quantities. This exact symmetry lets researchers deduce the physics of new configurations from ones already worked out.

Macroscopic quantum electrodynamics and duality