Efficient photon coupling from a diamond nitrogen vacancy center by integration with silica fiber.

A central goal in quantum information science is to efficiently interface photons with single optical modes for quantum networking and distributed quantum computing. Here, we introduce and experimentally demonstrate a compact and efficient method for the low-loss coupling of a solid-state qubit, the nitrogen vacancy (NV) center in diamond, with a single-mode optical fiber. In this approach, single-mode tapered diamond waveguides containing exactly one high quality NV memory are selected and integrated on tapered silica fibers. Numerical optimization of an adiabatic coupler indicates that near-unity-efficiency photon transfer is possible between the two modes. Experimentally, we find an overall collection efficiency between 16% and 37% and estimate a single photon count rate at saturation above 700 kHz. This integrated system enables robust, alignment-free, and efficient interfacing of single-mode optical fibers with single photon emitters and quantum memories in solids.