Paper detail

Lossless anomalous dispersion and an inversionless gain doublet via dressed interacting ground states (DIGS)

Transparent media exhibiting anomalous dispersion have been of considerable interest since Wang, Kuzmich, and Dogariu [Nature {\bf 406}, 277 (2000)] first observed light propagate with superluminal and negative group velocities without absorption. Here, we propose an atomic model exhibiting these properties, based on a generalization of amplification without inversion in a five-level DIGS system. The system consists of a $Λ$ atom prepared as in standard electromagnetically induced transparency (EIT), with two additional metastable ground states coupled to the $Λ$ atom ground states by two RF/microwave fields. We consider two configurations by which population is incoherently pumped into the ground states of the atom. Under appropriate circumstances, we predict a pair of new gain lines with tunable width, separation, and height. Between these lines, absorption vanishes but dispersion is large and anomalous. The system described here is a significant improvement over other proposals in the anomalous dispersion literature in that it permits additional coherent control over the spectral properties of the anomalous region, including a possible $10^4$-fold increase over the group delay observed by Wang, Kuzmich, and Dogariu.