Observation of quantum interference in the plasmonic Hong-Ou-Mandel   effect
  We report direct evidence of the bosonic nature of surface plasmon polaritons (SPPs) in a scattering-based beamsplitter. A parametric down-conversion source is used to produce two indistinguishable photons, each of which is converted into a SPP on a metal-stripe waveguide and then made to interact through a semi-transparent Bragg mirror. In this plasmonic analog of the Hong-Ou-Mandel experiment, we measure a coincidence dip with a visibility of 72%, a key signature that SPPs are bosons and that quantum interference is clearly involved. 
G. Di Martino, Y. Sonnefraud, M. S. Tame, S. K\'ena-Cohen, F.   Dieleman, \c{S}. K. \"Ozdemir, M. S. Kim and S. A. Maier
quant-ph cond-mat.mes-hall physics.optics