On-chip excitation of single germanium-vacancies in nanodiamonds embedded in plasmonic waveguides

Abstract: 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.