Dilution and resonance enhanced repulsion in non-equilibrium fluctuation forces

TL;DR

This paper demonstrates that non-equilibrium electromagnetic fluctuation forces between macroscopic objects can be repulsive and tunable by temperature differences, material resonances, and dilution, enabling stable equilibrium configurations.

Contribution

It shows that non-equilibrium conditions can induce and enhance repulsive fluctuation forces between macroscopic objects, expanding the understanding beyond equilibrium scenarios.

Findings

Repulsive forces can be achieved between macroscopic slabs at different temperatures.

Tuning material resonances enhances the repulsive effect.

Dilution reduces dielectric contrast, further increasing repulsion.

Abstract

In equilibrium, forces induced by fluctuations of the electromagnetic field between electrically polarizable objects (microscopic or macroscopic) in vacuum are always attractive. The force may, however, become repulsive for microscopic particles coupled to thermal baths with different temperatures. We demonstrate that this non-equilibrium repulsion can be realized also between macroscopic objects, as planar slabs, if they are kept at different temperatures. It is shown that repulsion can be enhanced by (i) tuning of material resonances in the thermal region, and by (ii) reducing the dielectric contrast due to "dilution". This can lead to stable equilibrium positions. We discuss the realization of these effects for aerogels, yielding repulsion down to sub-micron distances at realistic porosities.