Dipole light-matter interactions in the bispinor formalism

TL;DR

This paper introduces a bispinor formalism to unify and simplify the analysis of dipole light-matter interactions, revealing fundamental symmetry-based relationships and inequalities.

Contribution

It develops a general bispinor framework that consolidates power absorption, optical forces, and torques, highlighting symmetry-breaking effects and fundamental bounds.

Findings

Unified expressions for force, torque, and power absorption in terms of broken symmetries.

Derived inequalities that dipolar particles' cross-sections must satisfy.

Clarified the dependence of optical forces on symmetry-breaking and helicity cross sections.

Abstract

The conventional formulation of power absorption, optical forces, and torques on dipolar particles involve lenghty and cumbersome expressions that obscure their shared physical origin. We apply a bispinor formalism that unifies these disparate phenomena in a very general case including chiral and nonreciprocal particles. This reveals that force, torque, absorbed power, and absorbed helicity rate can all be concisely expressed in terms of broken symmetries, and leads to the fundamental inequalities that dipolar particles' cross-sections must satisfy. This framework uncovers profound connections normally hidden behind complex algebra -- for instance, pressure forces depend exclusively on the difference in linear momenta of different light components and the corresponding breaking of symmetry by a particle, and optical recoil forces depend exclusively on helicity cross sections -- providing clarity, conciseness, and a powerful predictive tool for arbitrary dipole interactions.