Phase-dependent optical effects in a four-level quantum system near a plasmonic nanostructure

We study the linear absorption and dispersion properties of a four-level double-V-type quantum system near a plasmonic nanostructure. The quantum system interacts with two orthogonal circularly polarized laser fields with the same frequency and different phases and electric field amplitudes. We find that the presence of the plasmonic nanostructure leads to strong modification of the absorption and dispersion spectra for one of the laser fields, in the presence of the other, and show that one can use the phase difference and the relative electric field amplitudes of the two laser fields for efficient control of the optical properties of the system. Effects such as complete optical transparency, zero absorption with nonzero dispersion, and gain without inversion are obtained.