Photon pair generation from lithium niobate metasurface with tunable spatial entanglement

TL;DR

This paper predicts that ultrathin lithium niobate metasurfaces can generate and tune spatially entangled photon pairs, offering a compact and flexible alternative to bulky nonlinear crystals for quantum applications.

Contribution

It introduces a novel approach using nonlinear metasurfaces to generate and actively tune spatial entanglement of photon pairs, surpassing traditional bulk crystal limitations.

Findings

Spatial entanglement degree can be tuned by pump wavelength and beam size.

Metasurfaces enable diverse emission patterns and rates.

Strong angular dispersion facilitates entanglement control.

Abstract

Two-photon state with spatial entanglement is an essential resource for testing fundamental laws of quantum mechanics and various quantum applications. Its creation typically relies on spontaneous parametric down-conversion in bulky nonlinear crystals where the tunability of spatial entanglement is limited. Here, we predict that ultrathin nonlinear lithium niobate metasurfaces can generate and diversely tune spatially entangled photon pairs. The spatial properties of photons including the emission pattern, rate, and degree of spatial entanglement are analysed theoretically with the coupled mode theory and Schmidt decomposition method. We show that by leveraging the strong angular dispersion of the metasurface, the degree of spatial entanglement quantified by the Schmidt number can be decreased or increased by changing the pump laser wavelength and a Gaussian beam size. This flexibility can facilitate diverse quantum applications of entangled photon states generated from nonlinear metasurfaces.