Hybrid quantum photonics based on artificial atoms placed inside one hole of a photonic crystal cavity

Abstract: Spin-based quantum photonics promise to realize distributed quantum computing and quantum networks. The performance depends on efficient entanglement distribution, where the efficiency can be boosted by means of cavity quantum electrodynamics. The central challenge is the development of compact devices with large spin-photon coupling rates and high operation bandwidth. Photonic crystal cavities comprise strong field confinement but put high demands on accurate positioning of an atomic system in the mode field maximum. Color center in diamond, and in particular the negatively-charged Silicon-Vacancy center, emerged as a promising atom-like systems. Large spectral stability and access to long-lived, nuclear spin memories enabled elementary demonstrations of quantum network nodes including memory-enhanced quantum communication. In a hybrid approach, we deterministically place SiV$^-$-containing nanodiamonds inside one hole of a one-dimensional, free-standing, Si$_3$N$_4$-based photonic crystal cavity and coherently couple individual optical transitions to the cavity mode. We optimize the light-matter coupling by utilizing two-mode composition, waveguiding, Purcell-enhancement and cavity resonance tuning. The resulting photon flux is increased by more than a factor of 14 as compared to free-space. The corresponding lifetime shortening to below 460 ps puts the potential operation bandwidth beyond GHz rates. Our results mark an important step to realize quantum network nodes based on hybrid quantum photonics with SiV$^-$- center in nanodiamonds.