Strong coupling of single optical emitters to nano-scale surface plasmons

We present an experimental observation of strong optical coupling between individual, nanocrystal CdSe/ZnS quantum dots and the guided surface plasmon modes of a proximal silver nanowire. The strong coupling between emitter and field is enabled by the unique properties of the plasmon modes on these nanowires. In particular, due to the small size of the nanowires (${\sim}100$ nm in diameter), the surface plasmons are localized transversely to dimensions well below the diffraction limit. An enhancement of the Purcell factor of the system and photon correlations consistent with a single-photon source are observed, and a realistic theoretical model for these processes is presented.