Hyperentanglement of two photons in three degrees of freedom

TL;DR

This paper reports the first experimental realization of a genuine hyperentangled state of two photons entangled in three degrees of freedom, demonstrating maximum entanglement in a 6-qubit system.

Contribution

It introduces a novel method to generate and characterize a 6-qubit hyperentangled state across polarization, momentum, and emission modes.

Findings

Successful creation of a 6-qubit hyperentangled state

Complete characterization using a chained interferometric apparatus

First demonstration of maximum entanglement in such a system

Abstract

A 6-qubit hyperentangled state has been realized by entangling two photons in three degrees of freedom. These correspond to the polarization, the longitudinal momentum and the indistinguishable emission produced by a 2-crystal system operating with Type I phase matching in the spontaneous parametric down conversion regime. The state has been characterized by a chained interferometric apparatus and its complete entangled nature has been tested by a novel witness criterium specifically introduced for hyperentangled states. The experiment represents the first realization of a genuine hyperentangled state with the maximum entanglement between the two particles allowed in the given Hilbert space.