Arbitrary unitaries in orbital angular momentum of single photons

TL;DR

This paper presents a straightforward method to construct arbitrary quantum gates on the orbital angular momentum of single photons, enabling high-dimensional quantum information processing with resource-efficient optical schemes.

Contribution

It introduces a simple, general approach for implementing any unitary operation on OAM states, including a resource-saving parallelization scheme using conventional optical elements.

Findings

Explicit construction of arbitrary unitaries on OAM of single photons.

Demonstration of subspace multiplexing with high-dimensional OAM qudits.

Resource-efficient parallelization scheme for quantum gates.

Abstract

A simple argument is presented that explicitly shows how to construct an arbitrary quantum gate acting on orbital angular momentum (OAM) of single photons. The scheme can be applied to implement subspace multiplexing, where a single high-dimensional OAM qudit represents effectively a stack of multiple independent lower-dimensional qudits. A special subclass of unitaries composed of single-photon controlled gates is studied in detail and notable examples of the general approach are discussed. The generalization of the simple argument leads to the parallelization scheme, which results in the savings of resources. The presented schemes utilize only conventional optical elements and apply not only to single photons but also to classical light.