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Hyperentanglement in structured quantum light
Francesco Graffitti (Heriot-Watt University), Vincenzo D’Ambrosio (University of Naples Federico II), Massimiliano Proietti (Heriot-Watt University), Joseph Ho (Heriot-Watt University), Bruno Piccirillo (University of Naples Federico II), Corrado de Lisio (Superconducting and other Innovative Materials and Devices Institute, National Research Council), Lorenzo Marrucci (University of Naples Federico II), Alessandro Fedrizzi (Heriot-Watt University)
Abstract: 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 polarization 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 characterize via two-photon interference and quantum state tomography, achieving near-unity visibilities and fidelities.While hyperentanglement has been demonstrated before in photonic qubits, here we present a rich entanglement structure involving spectrally and spatially structured light, where three different forms of entanglement coexist in the same biphoton state.