  Quantum emitters, such as q-dots and dye molecules, in the immediate vicinity
of plasmonic nanostructures, resonantly excite surface plasmon-polaritons
(SPPs) under incoherent pump. The efficiency in the excitation of SPPs
increases as the number of the emitters, because the SPP field synchronizes
emission of the coupled emitters, in analogy with the superadiance (SR) of
coupled emitters in free space. Using fully quantum mechanical model for two
emitters coupled to a single gold nanorod, we predict up to 15% increase in the
emission yield of single emitter compared to only one emitter coupled to the
nanorod due to plasmonic SR. (XW: I use emission yield because the quantum
efficiency is one for emitters in free space and there is no room for
enhancement). Such emission enhancement is stationary and should be observable
even with strong dissipation and dephasing under incoherent pump. Solid-state
quantum emitters with blinking behaviors may be utilized to demonstrate such
plasmonic SR emission enhancement. Plasmonic SR may find implications in the
excitation of non-radiative modes in plasmonic waveguides; and lowing threshold
of plasmonic nanolasers.
