Efficient Extraction of Zero-Phonon-Line Photons from Single Nitrogen-Vacancy Centers in an Integrated GaP-on-Diamond Platform

Realizing a scalable quantum network based on defects in diamond is impeded by the difficulty of collecting the photons that are useful for generating spin-spin entanglement. By integrating the diamond N00exV center with a single-mode waveguide in a I00exI00exI-V semiconductor photonic circuit, the authors achieve photon collection rates above the theoretical limit for free-space, nonresonant collection. This performance meets or exceeds that of all-diamond photonic circuits, and along with the scale of integration shows the potential of this hybrid platform for quantum information processing.