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

Monolithic integration of quantum emitters in nanoscale plasmonic circuitry requires low-loss plasmonic configurations capable of confining light well below the diffraction limit. We demonstrated on-chip remote excitation of nanodiamond-embedded single quantum emitters by plasmonic modes of dielectric ridges atop colloidal silver crystals. The nanodiamonds were produced to incorporate single germanium-vacancy (GeV) centres, 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) were fabricated on single crystalline silver plates to contain those of deposited nanodiamonds that are found to feature appropriate single GeV centres. 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 centre was incorporated. The remote GeV emitter was thereby excited and coupled to spatially confined DLSPPW modes with an outstanding figure-of-merit of 180 due to a ~six-fold Purcell enhancement, ~56% coupling efficiency and ~33 μm transmission length, thereby opening new avenues for the implementation of nanoscale functional quantum devices. Quantum emitters: plasmonic connections The field of integrated quantum plasmonics has taken a step forward with the demonstration of on-chip coupling between a single photon source and a plasmonic waveguide. In the approach, a nanodiamond featuring a germanium vacancy (GeV) centre that emits single photons is embedded inside a plasmonic waveguide composed of a ridge of the dielectric hydrogen silsesquioxane atop a layer of silver. Green (532 nm) laser light is coupled to one end of the waveguide via a grating and propagates to the nanodiamond where it excites the GeV centre which emits a single photon that couples into the plasmon mode of the waveguide. The researchers from Denmark, Russia and France behind the work say that the long waveguide transmission lengths (33 µm) and efficient coupling (56%) achieved open new avenues for the development of chip-based quantum circuitry.