Enhanced coherent optical effects in -shaped hybrid quantum-plasmonic systems

In this study, we investigate the coherent optical phenomena exhibited by a hybrid quantum-plasmonic system in Xi configuration composed of four energy levels, featuring two closely spaced uppermost energy levels interacting with a weak probe field and a strong control field. The lower leg of Xi system engages with the free-space vacuum, while the upper leg responds to interactions with surface plasmons. We reveal a significant transformation in the absorption and dispersion characteristics of this quantum system. This evolution is influenced by the interplay between quantum interference resulting from the presence of plasmonic nanostructures and the effects of incoherent pumping. In the absence of an incoherent pump field, we observe the emergence of multiple distinct absorption profiles, each containing optical transparency windows nestled amidst absorption spectral peaks. Introduction of an incoherent pump field leads to two well-defined symmetrical gain dips, each separated by a frequency corresponding to the dressed eigenstates of the system. This unique gain behavior persists whether or not population inversion occurs. We also show that these effects can be complemented with the existence of fast or slow light, expanding the range of optical phenomena that can be harnessed within this quantum system.