Torque of guided light on an atom near an optical nanofiber

TL;DR

This paper analytically and numerically investigates how guided light exerts axial orbital and spin torques on a two-level atom near an optical nanofiber, revealing angular momentum transfer mechanisms governed by conservation laws.

Contribution

It provides a detailed analysis of the generation and transfer of orbital and spin torques from guided light to an atom, highlighting the role of angular momentum conservation in the Minkowski formulation.

Findings

Orbital torque includes recoil from spontaneous emission.

Photon and atomic angular momenta can convert into atomic orbital angular momentum.

Angular momentum transfer does not separate into orbital and spin components.

Abstract

We calculate analytically and numerically the axial orbital and spin torques of guided light on a two-level atom near an optical nanofiber. We show that the generation of these torques is governed by the angular momentum conservation law in the Minkowski formulation. The orbital torque on the atom near the fiber has a contribution from the average recoil of spontaneously emitted photons. Photon angular momentum and atomic spin angular momentum can be converted into atomic orbital angular momentum. The orbital and spin angular momenta of the guided field are not transferred separately to the orbital and spin angular momenta of the atom.