Speaker
Description
Hyperentangled photon pairs are key resources for quantum high-dimensional communications, information processing, imaging, and fundamental studies of nonclassical phenomena. Polarization, orbital angular momentum (OAM), and frequency offer complementary resources for multidimensional quantum photonics [1]. However, conventional generation of such states relies on bulk nonlinear crystals combined with complex optical assemblies to tailor spontaneous parametric down-conversion (SPDC), restricting the technology to laboratory environments. Miniaturizing such sources and achieving stable operation has therefore become an active research direction, motivating the development of new physical approaches.
Metasurfaces are ultrathin structures composed of nanoscale resonators, which can control the properties of light within subwavelength thickness, with the additional benefit of high stability to the environment. It was shown that nonlinear metasurfaces can generate photon-pairs with quantum entanglement in either of spectral, spatial, or polarization degree of freedom [2]. However, hyperentangled photon-pair generation from a single nonlinear metasurface has not yet been realized.
Here, we report the first experimental demonstration of intrinsic generation of polarization-OAM hyperentangled photon pairs from a nonlinear metasurface. We designed the metasurface to support a broad-angle telecom-band resonance and enable enhanced coherent generation of structured two-photon states. Under an optical-vortex pump excitation, we measured the generation of OAM-correlated photon pairs and verified strong entanglement in both OAM and polarization through quantum-state tomography. Crucially, an experimentally measured hyperentanglement witness [3] of $W=-0.32$ violates the separability bound by more than three standard deviations, certifying that the photon pairs are simultaneously entangled in polarization and OAM. Numerical simulations of the full biphoton wavefunction further predict frequency entanglement, indicating three degrees of freedom OAM-polarization-frequency hyperentanglement under our experimental conditions. The metasurface source is shown to be highly stable, opening a pathway towards a broad range of free-space quantum applications.
$\small{\mathrm{[1]~A.~Forbes}~\textit{et}~\textit{al},\mathrm{~Nat.~Photon.}~\textbf{19},~\mathrm{1291~(2025).}}$
$\small{\mathrm{[2]~H.~Barati~Sedeh}~\textit{et}~\textit{al},\mathrm{~Photon.~Res.}~\textbf{14},~\mathrm{B249~(2026).}}$
$\small{\mathrm{[3]~G.~Vallone}~\textit{et}~\textit{al},\mathrm{~Phys.~Rev.~A}~\textbf{78},~\mathrm{062305~(2008).}}$
| I am the presenting author | Yes |
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