Optical angular momentum and atoms

Abstract

Any coherent interaction of light and atoms needs to conserve energy, linear momentum and angular momentum. What happens to an atom's angular momentum if it encounters light that carries orbital angular momentum (OAM)? This is a particularly intriguing question as the angular momentum of atoms is quantized, incorporating the intrinsic spin angular momentum of the individual electrons as well as the OAM associated with their spatial distribution. In addition, a mechanical angular momentum can arise from the rotation of the entire atom, which for very cold atoms is also quantized. Atoms therefore allow us to probe and access the quantum properties of light's OAM, aiding our fundamental understanding of light-matter interactions, and moreover, allowing us to construct OAM-based applications, including quantum memories, frequency converters for shaped light and OAM-based sensors.This article is part of the themed issue 'Optical orbital angular momentum'.

Keywords: atom optics; experimental atom optics; light–matter interaction; orbital angular momentum of light; quantum optics; structured light.

Figure 1.

A variety of light–matter interactions have been driven with OAM light: red- or blue-detuned optical dipole transitions are used for trapping and guiding; OAM can be transferred to a macroscopic rotation of the matter wave via Raman transitions; optical quadrupole transitions are particularly suitable to test the effect of OAM on selection rules; and a sequence of two Raman pulses is used to store OAM as phase information in ground state coherence. (Online version in colour.)