Coupling of single quantum dots to a photonic crystal waveguide

Efficient and high quality single-photon sources is a key element in quantum information processing using photons. As a consequence, much current research is focused on realizing all-solid-state nanophotonic single-photon sources. Single photons can be harvested with high efficiency if the emitter is coupled efficiently to a single enhanced mode. One popular approach has been to couple single quantum dots to a nanocavity but a limiting factor in this configuration is that in order to apply the photon it should subsequently be coupled out of the cavity, reducing the overall efficiency significantly. An alternative approach is to couple the quantum dot directly to the propagating mode of a photonic waveguide. We demonstrate the coupling of single quantum dots to a photonic crystal waveguide using time-resolved spontaneous emission measurements. A pronounced effect is seen in the decay rates of dots coupled to the waveguide compared to dots not coupled to the waveguide. The frequency dependence of the coupling is compared to theoretical calculations and a good agreement is found. From the decay rates the efficiency of emission into the waveguide mode is estimated and values from 50 % to 90 % are found demonstrating the high efficiency of the coupling.