  Quantum emitters located in proximity to a metal nanostructure individually
transfer their energy via near-field excitation of surface plasmons. The energy
transfer process increases the spontaneous emission (SE) rate due to
plasmon-enhanced local field. Here, we demonstrate significant acceleration of
quantum emitter SE rate in a plasmonic nano-cavity due to cooperative energy
transfer (CET) from plasmon-correlated emitters. Using an integrated plasmonic
nano-cavity, we realize up to six-fold enhancement in the emission rate of
emitters coupled to the same nano-cavity on top of the plasmonic enhancement of
the local density of states. The radiated power spectrum retains the plasmon
resonance central frequency and lineshape, with the peak amplitude proportional
to the number of excited emitters indicating that the observed cooperative SE
is distinct from super-radiance. Plasmon-assisted CET offers unprecedented
control over the SE rate and allows to dynamically control the spontaneous
emission rate at room temperature enabling an SE rate based optical modulator.
