  Realizing strong coupling between a single quantum emitter (QE) and an
optical cavity is of crucial importance in the context of various quantum
optical applications. While Rabi splitting of single quantum emitters coupled
to high-Q diffraction limited cavities have been reported in numerous
configurations, attaining single emitter Rabi splitting with a plasmonic
nanostructure is still elusive. Here, we establish the analytical condition for
strong coupling between a single QE and a plasmonic nanocavity and apply it to
study various plasmonic arrangements that were shown to enable Rabi splitting.
We investigate numerically the optical response and the resulting Rabi
splitting in metallic nanostructures such as bow-tie nanoantennas, nanosphere
dimers and nanospheres on a surface and find the optimal geometries for
emergence of the strong coupling regime with single QEs. We also provide a
master equation approach to show the saturation of a single QE in the gap of a
silver bow-tie nanoantenna. Our results will be useful for implementation of
realistic quantum plasmonic nanosystems involving single QEs.
