“…enhancement of the refractive index [7], gain in the Autler-Townes doublet [8], modification of absorption linewidth [9], subluminal to superluminal light propagation [10], squeezing [11], and preservation of bipartite entanglement [12] have been reported. Moreover, many remarkable features due to VIC, such as spontaneous emission cancellation [13], phase control of fluorescence [14], probe gain with inversion [15], enhanced two-photon absorption [16], spectral narrowing and squeezing [17,18], splitting of resonances [19], and lossless anomalous dispersion [20] have been predicted in four-level atomic systems.…”