Berry phase, Berry Connection, and Chern Number for a Continuum Bianisotropic Material from a Classical Electromagnetics Perspective

TL;DR

This paper derives and explains photonic topological insulator quantities like Berry phase, connection, and Chern number purely from classical electromagnetics, avoiding quantum mechanics and enhancing engineering understanding.

Contribution

It provides a classical derivation of topological quantities for photonic systems, demonstrating their classical nature and broadening their conceptual foundation.

Findings

Berry phase can be acquired by electromagnetic modes without quantum mechanics

Classical Maxwell's equations suffice to describe topological properties

Examples include wave propagation in plasma and rotating emitters

Abstract

The properties that quantify photonic topological insulators (PTIs), Berry phase, Berry connection, and Chern number, are typically obtained by making analogies between classical Maxwell's equations and the quantum mechanical Schr\"{o}dinger equation, writing both in Hamiltonian form. However, the aforementioned quantities are not necessarily quantum in nature, and for photonic systems they can be explained using only classical concepts. Here we provide a derivation and description of PTI quantities using classical Maxwell's equations, we demonstrate how an electromagnetic mode can acquire Berry phase, and we discuss the ramifications of this effect. We consider several examples, including wave propagation in a biased plasma, and radiation by a rotating isotropic emitter. These concepts are discussed without invoking quantum mechanics, and can be easily understood from an engineering electromagnetics perspective.