  Key requirements for quantum plasmonic nanocircuits are reliable
single-photon sources, high coupling efficiency to the plasmonic structures and
low propagation losses. Self-assembled epitaxially grown GaAs quantum dots are
close to ideal stable, bright and narrowband single-photon emitters. Likewise,
wet-chemically grown monocrystalline silver nanowires are among the best
plasmonic waveguides. However, large propagation losses of surface plasmons on
the high-index GaAs substrate prevent their direct combination. Here, we show
by experiment and simulation that the best overall performance of the quantum
plasmonic nanocircuit based on these building blocks is achieved in the
intermediate field regime with an additional spacer layer between the quantum
dot and the plasmonic waveguide. High-resolution cathodoluminescence
measurements allow a precise determination of the coupling distance and support
a simple analytical model to explain the overall performance. The coupling
efficiency is increased up to four times by standing wave interference near the
end of the waveguide.
