Directional spontaneous emission and lateral Casimir-Polder force on an atom close to a nanofiber

TL;DR

This paper investigates how an excited atom near a nanofiber exhibits asymmetric spontaneous emission and experiences a lateral Casimir-Polder force due to the interaction of its dipole with the fiber, impacting optical trapping and cooling.

Contribution

It demonstrates the existence of a lateral Casimir-Polder force on an atom near a nanofiber caused by dipole-image interactions, a novel insight into atom-surface quantum forces.

Findings

Asymmetric emission pattern for specific dipole orientations.

Presence of a resonant lateral Casimir-Polder force along the fiber.

Implications for optical trapping and laser cooling techniques.

Abstract

We study the spontaneous emission of an excited atom close to an optical nanofiber and the resulting scattering forces. For a suitably chosen orientation of the atomic dipole, the spontaneous emission pattern becomes asymmetric and a resonant Casimir--Polder force parallel to the fiber axis arises. For a simple model case, we show that the such a lateral force is due to the interaction of the circularly oscillating atomic dipole moment with its image inside the material. With the Casimir--Polder energy being constant in the lateral direction, the predicted lateral force does not derive from a potential in the usual way. Our results have implications for optical force measurements on a substrate as well as for laser cooling of atoms in nanophotonic traps.