Dipole-matter interactions governed by the asymmetry of Maxwell equations

TL;DR

This paper reveals that the asymmetry in Maxwell's equations causes an intrinsic asymmetry in dipole-matter interactions, affecting the directionality of both near-field and far-field radiation, with potential applications in nanophotonics.

Contribution

It uncovers the fundamental asymmetry in dipole-matter interactions caused by Maxwell's equations and demonstrates its impact on radiation directionality.

Findings

Dipole-matter interaction is inherently asymmetric due to Maxwell's equations.

Changing dipole position near an interface can reverse radiation directionality.

Asymmetry offers new ways to control radiation in nanophotonics.

Abstract

Directionally molding the near-field and far-field radiation lies at the heart of nanophotonics and is crucial for applications such as on-chip information processing and chiral quantum networks. The most fundamental model for radiating structures is a dipolar source located inside a homogeneous matter. However, the influence of matter on the directionality of dipolar radiation is oftentimes overlooked, especially for the near-field radiation. We show that the dipole-matter interaction is intrinsically asymmetric and does not fulfill the duality principle, originating from the inherent asymmetry of Maxwell equations, i.e., electric charge and current are ubiquitous but their magnetic counterparts are non-existent to elusive. Moreover, we find that the asymmetric dipole-matter interaction could offer an enticing route to reshape the directionality of not only the near-field radiation but also the far-field radiation. As an example, both the near-field and far-field radiation directionality of Huygens dipole (located close to a dielectric-metal interface) would be reversed, if the dipolar position is changed from the dielectric region to the metal region.