Transparency and slow light in a four-level quantum system near a plasmonic nanostructure

We study theoretically the effects of a plasmonic nanostructure on the linear absorption and dispersion spectrum of a four-level double- V-type quantum system. In the quantum system under study one V-type transition is influenced by the interaction with surface plasmons while the other V-type transition interacts with free-space vacuum. As plasmonic nanostructure we consider a two-dimensional array of metal-coated dielectric nanospheres. We analyze the optical properties of a linearly polarized laser field that couples the lowest state with the upper states in the free-space transitions. We show that, due to the presence of the plasmonic nanostructure, effects of optical transparency are created. These effects are also complemented by the existence of slow light.