High Refractive Index and Enhanced Cross-kerr Nonlinearity in Five-level Quantum Systems Near Plasmonic Structure

In this paper, we study the enhancement of the index of refraction and giant cross-Kerr nonlinearity in a five-level quantum system near plasmonic nanostructure via probe field amplification. We find that due to the presence of plasmonic nanostructure, the medium becomes phase-dependent, and therefore, the linear and nonlinear properties of the quantum system can be modified by adjusting the relative phase of applied fields. We display the effect of distance between quantum system and plasmonic nanostructure on the refraction index of the medium and find that for a proper distance, the large refractive index with probe gain can be obtained when the relative phase between applied fields is tuned. Moreover, due to interaction between the quantum system and probe and coupling light, we obtain the cross-Kerr nonlinearity by solving the coupled amplitude equations under the weak probe approximation.