Casimir-Polder repulsion: Polarizable atoms, cylinders, spheres, and ellipsoids

TL;DR

This paper explores conditions under which Casimir-Polder forces can be repulsive between various anisotropic objects, providing new examples and clarifying the systematics of Casimir repulsion.

Contribution

It introduces new instances of Casimir repulsion involving anisotropic atoms and conducting objects, and clarifies the conditions necessary for repulsion.

Findings

Repulsion occurs for anisotropic atoms near conducting cylinders.

Repulsion does not occur outside a conducting sphere.

Classical repulsion exists between a conducting ellipsoid and an electric dipole.

Abstract

Recently, the topic of Casimir repulsion has received a great deal of attention, largely because of the possibility of technological application. The general subject has a long history, going back to the self-repulsion of a conducting spherical shell and the repulsion between a perfect electric conductor and a perfect magnetic conductor. Recently it has been observed that repulsion can be achieved between ordinary conducting bodies, provided sufficient anisotropy is present. For example, an anisotropic polarizable atom can be repelled near an aperture in a conducting plate. Here we provide new examples of this effect, including the repulsion on such an atom moving on a trajectory nonintersecting a conducting cylinder; in contrast, such repulsion does not occur outside a sphere. Classically, repulsion does occur between a conducting ellipsoid placed in a uniform electric field and an electric dipole. The Casimir-Polder force between an anisotropic atom and an anisotropic dielectric semispace does not exhibit repulsion. The general systematics of repulsion are becoming clear.