  We demonstrate `deterministic' launching of propagative quantum
surface-plasmon polaritons at freely chosen positions on gold plasmonic
receptacles. This is achieved by using as plasmon launcher a near-field
scanning optical source made of a diamond nanocrystal with two Nitrogen-Vacancy
color-center occupancy. Our demonstration relies on leakage-radiation
microscopy of a thin homogeneous gold film and on near-field optical microscopy
of a nanostructured thick gold film. Our work paves the way to future
fundamental studies and applications in quantum plasmonics that require an
accurate positioning of single-plasmon sources and may open a new branch in
plasmonics and nanophotonics, namely scanning quantum plasmonics.
