High-Purity Single Photon Extraction from Diamond Nitrogen-Vacancy Centers in Low-Numerical-Aperture Optical Systems via Defect-Selective Metalens Printing

Abstract

Solid-state quantum emitters, such as nitrogen-vacancy (NV) centers in diamond, offer a promising route toward scalable quantum technologies. However, their random spatial distribution and inherently broad dipole emission severely hinder high-purity single-photon extraction-particularly in low-numerical-aperture (NA) optical systems, which are essential for compact and scalable quantum photonic systems. Here, a defect-selective metalens integration approach is presented that allows precise and efficient single photon collection from individual NV centers, even under ultra-low-NA optical systems. Using an in situ transfer-printing process, high-purity silicon dioxide metalenses are stamped precisely and deterministically onto selected NV centers located 25 mu m below the diamond surface. This integration reshapes the broad dipolar emission of the targeted NV center into a tightly collimated, low-divergence beam, achieving a 40-fold enhancement in photon collection efficiency with an objective lens of NA = 0.07. Notably, emission is detected exclusively from metalens-coupled NV centers, effectively filtering out background noise from neighboring defects. Second-order correlation measurements yield g(()2())(0) = 0.04, unambiguously confirming the generation of high-purity single photons. This scalable, site-specific approach addresses key limitations in low-NA operation, opening the door to compact and fiber-integrated solid-state quantum photonics.