Ultrabright Linearly Polarized Photon Generation from a Nitrogen Vacancy Center in a Nanocube Dimer Antenna.

We demonstrate an exceptionally bright photon source based on a single nitrogen-vacancy center (NV center) in a nanodiamond (ND) placed in the nanoscale gap between two monocrystalline silver cubes in a dimer configuration. The system is operated near saturation at a stable photon rate of 850 kcps, while we further achieve strongly polarized emission and high single photon purity, evident by the measured autocorrelation with a g(2)(0) value of 0.08. These photon source features are key parameters for quantum technological applications, such as secure communication based on quantum key distribution. The cube antenna is assembled with an atomic force microscope, which allows us to predetermine the dipole orientation of the NV center and optimize cube positioning accordingly, while also tracking the evolution of emission parameters from isolated ND to the one- and two-cube configuration. The experiment is well described by finite element modeling, assuming an instrinsic quantum efficiency of 0.35. We attribute the large photon rate of the assembled photon source, to increased quantum efficiency of the NV center and high antenna efficiency.