Bright single-photon sources based on self-aligned quantum dots in tapered nanowire waveguides

Abstract

Single quantum dots embedded in tapered nanowire waveguides have emerged as leading candidates for designing high efficiency single-photon and entangled photon sources, with efficiencies exceeding 90%. Here we have developed a bottom-up growth approach that allows for independent control of boththe quantum dot size, and position, as well as the nanowire shape. Importantly, by design, the single quantum dot is always found perfectly on the nanowire axis. By integrating a gold mirror at the base of a tapered nanowire waveguide we obtain a 20-fold enhancement in the single-photon flux in comparison to no waveguide. The 20-fold enhancement is accompanied by a shortening of the exciton lifetime as the quantum emitter couples to the fundamental waveguide mode with an increased rate. Finally, the optical quality of the emitter is drastically improved by removing the nanowire stacking faults in the vicinity of the quantum dot. As a result, we demonstrate very pure single-photon emission with a probability of multi-photon emission below 1%, and an emission line width that is reduced by at least an order of magnitude (<30 μeV) as compared to when stacking faults were present in the nanowire (as high as 10-100 per micron). The demonstrated brightness of our single-photon source (42 % efficiency), combined with the very pure single photon emission and high spectral purity is encouraging in development of future quantum technologies based on nanowires, such as interfacing remote quantum bits or constructing a secure quantum network.