Enhanced Photon-Pair Generation from a van der Waals Metasurface.

Quantum photon pairs play a pivotal role in many quantum applications. Metasurfaces, two-dimensional arrays of nanostructures, have been studied intensively to enhance and control pair generation via spontaneous parametric downconversion (SPDC). Van der Waals (VdW) layered materials have emerged as promising candidates for nonlinear materials in quantum light sources, owing to their high nonlinear susceptibility and compatibility with on-chip integration. In this work, we present the first demonstration of SPDC from a metasurface composed of the VdW material 3R-MoS. The nanoresonators support quasi-bound states in the continuum (qBIC) with a quality factor of up to 120, enhancing light-matter interactions. This design achieves a 20-fold increase in SPDC rate compared to an unstructured film and significantly higher brightness, resulting in enhanced quantum photon-pair generation. This work establishes a new approach for utilizing van der Waals metasurfaces in the generation of quantum photon pairs, opening avenues for advanced quantum applications.