  Monolithic integration of quantum emitters in nanoscale plasmonic circuitry
requires low-loss plasmonic configurations capable of confining light well
below the diffraction limit. We demonstrate on-chip remote excitation of
nanodiamond-embedded single quantum emitters by plasmonic modes of dielectric
ridges atop colloidal silver crystals. The nanodiamonds are produced to
incorporate single germanium-vacancy (GeV) centers, providing bright,
spectrally narrow and stable single-photon sources suitable for highly
integrated circuits. Using electron-beam lithography with hydrogen
silsesquioxane (HSQ) resist, dielectric-loaded surface plasmon polariton
waveguides (DLSPPWs) are fabricated on single crystalline silver plates so as
to contain those of spin-casted nanodiamonds that are found to feature
appropriate single GeV centers. The low-loss plasmonic configuration enabled
the 532 nm pump laser light to propagate on-chip in the DLSPPW and reach to an
embedded nanodiamond where a single GeV center is incorporated. The remote GeV
emitter is thereby excited and coupled to spatially confined DLSPPW modes with
an outstanding figure-of-merit of 180 due to a ~6-fold Purcell enhancement,
~56% coupling efficiency and ~33 {\mu}m transmission length, revealing the
potential of our approach for on-chip realization of nanoscale functional
quantum devices.
