Entanglement in high-dimensional quantum systems, where one or more degrees of freedom of light are involved, offers increased information capacities and enables new quantum protocols. Here, we demonstrate a functional source of high-dimensional, noise-resilient hyperentangled states encoded in time-frequency and vector-vortex structured modes, which in turn carry single-particle entanglement between polarisation and orbital angular momentum. Pairing nonlinearity-engineered parametric downconversion in an interferometric scheme with spin-to-orbital-angular-momentum conversion, we generate highly entangled photon pairs at telecom wavelength that we characterise via two-photon interference and quantum state tomography, achieving near-unity visibilities and fidelities. While hyperentanglement has been demonstrated before in photonic qubits, this is the first instance of such a rich entanglement structure involving spectrally and spatially structured light, where three different forms of entanglement coexist in the same biphoton state.
@article{arxiv.2006.01845,
title = {Hyperentanglement in structured quantum light},
author = {Francesco Graffitti and Vincenzo D'Ambrosio and Massimiliano Proietti and Joseph Ho and Bruno Piccirillo and Corrado de Lisio and Lorenzo Marrucci and Alessandro Fedrizzi},
journal= {arXiv preprint arXiv:2006.01845},
year = {2020}
}