Fluctuation-induced forces on an atom near a photonic topological material

TL;DR

This paper develops a theoretical framework to analyze Casimir-Polder forces on atoms near nonreciprocal, topological materials, revealing how nonreciprocity and surface plasmons influence nanoscale light-matter interactions.

Contribution

It introduces explicit formulas for optical forces in complex electromagnetic environments, including nonreciprocal media, and explores their implications for controlling atom-surface interactions.

Findings

Nonreciprocity enables exotic light-matter interactions.

Surface plasmons significantly influence fluctuation-induced forces.

Analytical expressions for forces near gyrotropic materials are derived.

Abstract

We theoretically study the Casimir-Polder force on an atom in a arbitrary initial state in a rather general electromagnetic environment wherein the materials may have a nonreciprocal bianisotropic dispersive response. It is shown that under the Markov approximation the force has resonant and nonresonant contributions. We obtain explicit expressions for the optical force both in terms of the system Green function and of the electromagnetic modes. We apply the theory to the particular case wherein a two-level system interacts with a topological gyrotropic material, showing that the nonreciprocity enables exotic light-matter interactions and the opportunity to sculpt and tune the Casimir-Polder forces on the nanoscale. With a quasi-static approximation, we obtain a simple analytical expression for the optical force and unveil the crucial role of surface plasmons in fluctuation induced forces. Finally, we derive the Green function for a gyrotropic material half-space in terms of a Sommerfeld integral.