A Tunable Waveguide-Coupled Cavity Design for Efficient Spin-Photon   Interfaces in Photonic Integrated Circuits
  A solid state emitter coupled to a photonic crystal cavity exhibits increased photon emission into a single frequency mode. However, current designs for photonic crystal cavities coupled to quantum emitters have three main problems: emitters are placed near surfaces that can degrade their optical properties, the cavity fluorescence cannot be collected into a single useful mode for further routing, and post-fabrication tuning is not currently possible in a stable and reversible manner for each node individually. In this paper, we introduce a hybrid cavity design with minimal fabrication of the host material that keeps the emitter $\geq100\,$nm from all surfaces. This cavity has an unloaded quality factor ($Q$) larger than $1\times10^6$ and a loaded $Q$ of $5.5\times10^4$ with more than 75% of the emission coupled directly into an underlying photonic integrated circuit built from a convenient material that provides low loss waveguides. Finally this design can be actively and reversibly tuned onto resonance with the emitter, allowing tuning over more than 10 times the cavity linewidth while maintaining $\geq50$% of the $Q$ factor with no effects to other cavities on the same chip. 
Sara Mouradian and Dirk Englund
physics.optics quant-ph