Coupling of nitrogen-vacancy centers in a nanodiamond to a silver nanocube

Spontaneous emission (SE) of nitrogen-vacancy centers (NV-centers), which are contained in a single nanodiamond (ND), placed near a silver nanocube, is investigated both experimentally and theoretically. The ND-cube system is assembled with an atomic force microscope, allowing us to directly compare its SE properties to that of the isolated ND. It is demonstrated that the cube coupled NV-centers exhibit strongly polarized SE. For optimal pump laser polarization, the rate of photons is enhanced by a factor of 4.1, with the excited state lifetime being reduced by a factor of 4.1. The enhancement of photon rate is a consequence of local field enhancement of the pump laser, while the SE polarization and lifetime reduction results from coupling of NV-centers to the localized surface plasmon mode of the nanocube. The experimental observations are in qualitative agreement with the model of SE from randomly oriented electric dipoles, allowing us to reveal the underlying physics of the investigated configuration.