Four-photon orbital angular momentum entanglement

TL;DR

This paper demonstrates the generation of four-photon entanglement in orbital angular momentum states, advancing the study of high-dimensional multipartite quantum entanglement for foundational and practical applications.

Contribution

It presents the first experimental realization of four-photon OAM entanglement, enabling exploration of complex quantum states beyond two particles.

Findings

Successfully generated four-photon OAM entangled states

Witnessed genuine multipartite Dicke-type entanglement

Potential applications in quantum metrology and secure communication

Abstract

Quantum entanglement shared between more than two particles is essential to foundational questions in quantum mechanics, and upcoming quantum information technologies. So far, up to 14 two-dimensional qubits have been entangled, and an open question remains if one can also demonstrate entanglement of higher-dimensional discrete properties of more than two particles. A promising route is the use of the photon orbital angular momentum (OAM), which enables implementation of novel quantum information protocols, and the study of fundamentally new quantum states. To date, only two of such multidimensional particles have been entangled albeit with ever increasing dimensionality. Here we use pulsed spontaneous parametric downconversion (SPDC) to produce photon quadruplets that are entangled in their OAM, or transverse-mode degrees of freedom; and witness genuine multipartite Dicke-type entanglement. Apart from addressing foundational questions, this could find applications in quantum metrology, imaging, and secret sharing.