Efficient solid-state light-matter interfaces based on dielectric slot waveguides and diamond colour centers

Future applications in applied physical and quantum information science rely on the efficient interaction between light and matter. A prominent representative, single-photon sources, requires two key components: A quantum light source emitting single photons and a waveguiding structure to collect photons and to control their propagation. A very promising candidate for a stable optical quantum emitter are defect centers in diamond as they emit single photons even at room temperature. By using nanodiamonds, light losses due to total internal reflection at the diamond surface can be circumvented. Additionally, the small size of the solid-state emitter offers the possibility to incorporate the nanodiamond into suitable photonic or plasmonic structures. However, as the emission of diamond defect centers can spread over a broad spectral range (compare figure 1c for the spectral distribution of the emission spectrum of an NV-center at room temperature), waveguiding structures offering strong broadband coupling are beneficial. Therefore, our interest lies in the evanescent coupling of diamond colour centers to purely dielectric structures. In a preceding experiment, we demonstrated the coupling of a nitrogen-vacancy center to the evanescent field of a tapered optical fiber with an efficiency of 10% employing an AFM-based in-situ nanomanipulation [1]. However, this evanescent coupling is restricted to a theoretical maximum of 37%. In comparison, dielectric waveguide structures offer significant advantages enabling improvements by specially tailored field configurations. In particular, dielectric slot waveguide structures (figure 1a) promise strong electric field enhancements in the slot region (figure 1b), leading to strong broadband coupling for small slot widths (figure 1c) [2].