Efficient diamond-based single photon source

Efficient collection of single photons radiated by a single solid state quantum emitter—like the nitrogen vacancy (NV) center in diamond—is an important prerequisite for future applications in applied physical and quantum information science. For NV centers in diamond nano-crystals, tapered optical fibers (TOF) with a subwavelength diameter waist are a particularly attractive platform, promising coupling efficiencies up to 36%.

Until now, evanescent coupling of fluorescence photons to a single guided mode of a TOF has been achieved for various solid state quantum emitters, molecules, and laser cooled atomic vapors. To bring these emitters into the strong evanescent optical field at the surface of the nanofiber, several non-deterministic deposition techniques have been applied. However, for real applications in quantum information science, e.g., the photonic quantum-bus-mediated coupling of NV-centers in a lattice, deterministic positioning of single solid state quantum emitters onto the submicron waist of a TOF with nm position control is desirable.

Artistic view of our experiment

In a recent experiment we demonstrate a significant step towards deterministic coupling of a single solid state quantum emitter to a tapered optical fiber. A diamond nano-crystal hosting a single NV-center is optically selected with a confocal scanning microscope and positioned deterministically onto the subwavelength-diameter waist (here 260 nm) of a tapered optical fiber with the help of an atomic force microscope. By comparing photon count rates of the fiber-guided and the free-space modes and with the help of numerical finite-difference time domain simulations, we determine a coupling efficiency of ≈10%. Our findings are a promising starting point for future integration of NV-centers into photonic quantum networks.