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arXiv · 2603.04082

Air-stable bright entangled photon-pair source from graphene-encapsulated van der Waals ferroelectric NbOI2

Mayank Joshi·Mengting Jiang·Yu Xing·Yuerui Lu·Jie Zhao·Ping Koy Lam·Syed M Assad·Xuezhi Ma·Young-Wook Cho
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Abstract

Van der Waals (vdW) ferroelectrics are emerging nonlinear photonic materials that combine large second-order susceptibility \c{hi}(2) with heterostructure compatibility, offering an attractive route toward miniaturized spontaneous parametric down-conversion (SPDC) sources. However, vdW SPDC sources operating under continuous irradiation in air remain limited in low brightness and poor operational stability, as oxygen and moisture exposure, together with pump-induced heating, lead to material degradation and permanent damage. Here we demonstrate an air-stable, bright SPDC source based on ferroelectric NbOI2 enabled by graphene encapsulation. Graphene provides robust environmental protection and can effectively supress pump induced degradation by enhancing heat dissipation. We report a record photon-pair generation absolute rate of 258 Hz and a normalized brightness of 19,900 Hz/(mW.mm). Leveraging this stabilized platform, we further generate polarization entangled photon pairs with 94% fidelity with respect to the maximally entangled Bell states from graphene-encapsulated 90{\deg} twisted bilayer NbOI2. Our results establish a practical and air-stable vdW ferroelectric SPDC platform that overcomes key limitations of existing vdW quantum light sources and provides a viable pathway toward scalable, integrated entangled photon sources for on chip quantum photonics.

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Mayank Joshi, Mengting Jiang, Yu Xing, Yuerui Lu, Jie Zhao, Ping Koy Lam, Syed M Assad, Xuezhi Ma, Young-Wook Cho. 2026-03-04. Air-stable bright entangled photon-pair source from graphene-encapsulated van der Waals ferroelectric NbOI2. https://arxiv.org/abs/2603.04082

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