Inverse design of immersion metasurfaces for optimal photon collection from solid-state qubits

Solid-state qubits such as the nitrogen-vacancy (NV) center in diamond are initialized and measured using optical excitation and single-photon emission. Scalable applications of these systems therefore require efficient optical interfaces that can optimally collect these emitted photons and couple them directly into an optical fiber. A metasurface patterned above the emitter can accomplish both tasks; however, conventional metasurface design techniques prove insufficient for simultaneously optimizing the coupling efficiency and numerical aperture (NA) over the full emission spectrum of atom-scale emitters like the NV center. Here, we employ inverse design techniques to design fabricable structures that optimize the total photon collection from an NV center in bulk diamond into a desired field profile. We demonstrate high performance and a design framework that can readily be adapted to other platforms.