Continuous-Variable Entangled States of Light carrying Orbital Angular Momentum

TL;DR

This paper demonstrates the first generation and full characterization of bipartite continuous-variable Gaussian entangled states of light carrying orbital angular momentum, advancing quantum information encoding in high-dimensional spaces.

Contribution

It introduces a method to generate and measure continuous-variable entanglement with orbital angular momentum using a q-plate and homodyne detection, expanding quantum state control.

Findings

Successfully generated bipartite Gaussian entangled states with orbital angular momentum.

Reconstructed the quantum-state covariance matrix via quadrature measurements.

Showed potential for multipartite entanglement in a single optical beam.

Abstract

The orbital angular momentum of light, unlike spin, is an infinite-dimensional discrete variable and may hence offer enhanced performances for encoding, transmitting, and processing information in the quantum regime. Hitherto, this degree of freedom of light has been studied mainly in the context of quantum states with definite number of photons. On the other hand, field-quadrature continuous-variable quantum states of light allow implementing many important quantum protocols not accessible with photon-number states. Here, we present the first generation and complete experimental characterization of a bipartite continuous-variable Gaussian entangled state endowed with non-zero orbital angular momentum. A q-plate is used to transfer the continuous-variable entanglement initially generated in polarization into orbital angular momentum. We then apply a reconfigurable homodyne detector to various combinations of orbital angular momentum modes in order to reconstruct the entire quantum-state covariance matrix, by directly measuring the fluctuations of quadrature operators. Our work is a step towards generating multipartite continuous-variable entanglement in a single optical beam.