Topology-Optimized on-Chip Quantum Plasmonic Generator

Scalable integrated single-photon sources are critical for quantum photonics and can enable applications such as high-speed quantum communication and quantum information processing. To establish a scalable platform, the single-photon sources require large on-chip photon extraction rates, which means the emission rates need to be substantially enhanced and the excited photons should be directly coupled to an on-chip circuit. The photon emission rate speed-up is best achieved via coupling to plasmonic nanostructures, while on-chip extraction can be realized by directly coupling emitters to dielectric nanofibers. However, current approaches to enhance emission speed in nanostructures have inadequately tackled the choice of metals and dielectrics. Additionally, they solely concentrate on individual aspects (spontaneous emission rate or coupling efficiency), thereby neglecting comprehensive performance. Here, drawing inspiration from additive manufacturing, a layer-by-layer topology optimization framework is proposed for an on-chip quantum plasmonic generator that can comprehensively enhance the photon extraction rate of the nitrogen-vacancy (NV) center. As a result, a topology-optimized three-layered hybrid structure is obtained that comprehensively enhances the spontaneous emission rate of the NV center and coupling efficiency into a dielectric nanofiber ($F_p\times \eta \approx 30$). The work introduces an innovative approach to material selection and structural design for improving the performance of single-photon sources.