Efficient coupling of a single diamond color center to propagating plasmonic gap modes.

We report on coupling of a single nitrogen-vacancy (NV) center in a nanodiamond to the propagating gap mode of two parallel placed chemically grown silver nanowires. The coupled NV-center nanowire system is made by manipulating nanodiamonds and nanowires with the tip of an atomic force microscope cantilever. An efficient coupling of an NV-center to an easily accessible gap plasmon mode is demonstrated and we measure an enhancement of the spontaneous emission decay rate by a factor of 8.3.