Ultrafast plasmonic field oscillations and optics of molecular resonances caused by coherent exciton-plasmon coupling

We study optical properties and coherent dynamics of a hybrid system consisting of one quantum dot and one metallic nanoparticle when its excitations are governed by its collective molecular states (dark and bright states), rather than excitons or plasmons. We predict that in the bright state the exciton states of the quantum dot are optically dressed, forming standard Mollow spectra with ac Stark shifts enhanced by plasmonic effects. In the dark state the optics of the quantum dot is dominated by a combination of two seemingly uncorrelated processes: (i) coherent generation of a superfluorescent state that supports ultranarrow gain in the absence of population inversion, and (ii) plasmonic broadening and red shifting of pure exciton states, as if the laser field does not exist. We show that the coherent exciton-plasmon coupling in such a system can form an analog of Rabi flopping in the plasmonic field, causing its ultrafast oscillation, when the laser is red detuned from the quantum dot transition. For blue-detuning we predict generation of time delay in the field experienced by the quantum dot, before the system is transferred to its dark state.