Control of resonance fluorescence of a four-level quantum emitter near a plasmonic nanostructure

We present a theoretical study of the resonance fluorescence of a four-level double-$\mathsf{V}$-type quantum emitter near a plasmonic nanostructure. The quantum system interacts with two orthogonal circularly polarized laser fields with the same frequency and intensity, but with different phases. For the plasmonic nanostructure we consider a two-dimensional array of metal-coated dielectric nanospheres. We show that the presence of the plasmonic nanostructure leads to strong modification of both the resonance fluorescence spectrum and the transition from antibunching to bunching for the fluorescent photons. In addition, we show that both the resonance fluorescence spectrum and the second-order correlation function are strongly phase-dependent so that the relative phase of laser fields can be used for the efficient control of the resonance fluorescence characteristics. The results are explained by using a dressed-state picture.