Orbital angular momentum of photons and the entanglement of Laguerre-Gaussian modes

TL;DR

This paper reviews the development and experimental investigation of orbital angular momentum (OAM) of photons, highlighting its potential for quantum information and the fundamental questions it raises in quantum physics.

Contribution

It provides a comprehensive review of key experiments on photonic OAM and discusses future research directions in quantum protocols and fundamental questions.

Findings

OAM enables encoding large amounts of information on single photons.

Experimental evidence confirms the quantum entanglement of OAM modes.

Open questions remain about the full potential and applications of photonic OAM.

Abstract

The identification of orbital angular momentum (OAM) as a fundamental property of a beam of light nearly twenty-five years ago has led to an extensive body of research around this topic. The possibility that single photons can carry OAM has made this degree of freedom an ideal candidate for the investigation of complex quantum phenomena and their applications. Research in this direction has ranged from experiments on complex forms of quantum entanglement to the interaction between light and quantum states of matter. Furthermore, the use of OAM in quantum information has generated a lot of excitement, as it allows for encoding large amounts of information on a single photon. Here we explain the intuition that led to the first quantum experiment with OAM fifteen years ago. We continue by reviewing some key experiments investigating fundamental questions on photonic OAM and the first steps into applying these properties in novel quantum protocols. In the end, we identify several interesting open questions that could form the subject of future investigations with OAM.