Casimir-Polder interaction of neutrons with metal or dielectric surfaces

TL;DR

This paper predicts a novel repulsive Casimir-Polder interaction between a neutron and a surface, which could influence neutron experiments and is comparable to gravitational effects.

Contribution

It introduces the concept of a repulsive magnetic Casimir-Polder interaction involving neutrons and surfaces, a phenomenon not previously characterized.

Findings

The interaction is repulsive, unlike typical electric Casimir-Polder forces.

The magnitude is smaller than atom-surface forces but comparable to gravitational potential.

The effect could impact future neutron interference experiments.

Abstract

We predict a repulsive Casimir-Polder-type dispersion interaction between a single neutron and a metal or dielectric surface. We consider a scenario where a single neutron is subject to an external magnetic field. Due to its intrinsic magnetic moment, the neutron then forms a magnetisable two-level system which can exchange virtual photons with a nearby surface. The resulting dispersion interaction between a purely magnetic object (neutron) and a purely electric one (surface) is found to be repulsive, in contrast to the typical attractive interaction between electric objects. Its magnitude is considerably smaller than the standard atom--surface Casimir-Polder force due to the magnetic nature of the interaction and the smallness of the electron-to-neutron mass ratio. Nevertheless, we show that it can be comparable to the gravitational potential of the same surface and should be taken into consideration in future neutron interference experiments.