Spin-redirection Berry phase with planar rays

TL;DR

This paper reveals that the spin-redirection Berry phase can occur along planar rays in electromagnetic waves, expanding understanding of geometric phases and enabling new control mechanisms for light through spin-orbit interactions.

Contribution

It demonstrates that spin-redirection Berry phases can arise in planar rays, challenging the previous assumption that nonplanar rays are necessary, and introduces a new mechanism involving finite transverse spin.

Findings

Spin-redirection Berry phase can occur in planar rays.

The effect is demonstrated in a moving unmagnetized plasma.

This mechanism broadens the potential for controlling light via spin-orbit interactions.

Abstract

Geometric or Berry phases are fundamental manifestations that appear in many areas of physics. They arise from the geometry of the space describing the properties of multi-component wave fields. An important example for electromagnetic waves is the spin-redirection Berry phase associated with the evolution of the spin direction. Because this effect has traditionally been studied in isotropic media where the spin is aligned with the ray trajectory, it has become commonly assumed that this spin-redirection Berry phase requires nonplanar rays. Here we show that a spin-redirection phase can in fact arise along a planar ray if the spin evolves along the ray. We expose this effect through the singular example of a moving unmagnetized plasma, and demonstrate how this behavior can more generally arise from a finite transverse spin. In identifying this new spin-redirection mechanism our work not only provides the tools to discover additional manifestations of SOIs in nature, but also uncovers supplemental degrees of freedom to harness SOIs to control light.