| Electromagnetically induced transparency (EIT) is a quantum coherence effect by which a strong laser is used to cancel absorption for a second, weaker laser propagating in the same medium. Within the transparency window, dispersion is large, permitting the observation of very small group velocities and other effects. We generalize EIT to a five level atom in which two driven ground state doublets, denoted {|b⟩, |b⟩} and {|c⟩, |c'⟩}, interact with an excited state, |a⟩. We call systems with this level configuration "dressed interacting ground states (DIGS) systems.;We study the DIGS configuration under two sets of initial conditions. In the first, we consider a closed system that is initially in the ground state |b⟩. We find that the EIT spectrum is modified to include two new features located within the transparency window, whose widths and locations can be tuned by the external fields. In the vicinity of these features, we find small windows of very large dispersion and suppressed absorption, permitting group velocities up to two orders of magnitude smaller than an identically configured EIT system without the additional couplings. In the second case, we permit population to accrue in the second ground state doublet by introducing incoherent pumping terms. When the population of | c'⟩ exceeds the population of |b⟩, the absorption resonances already described become amplification resonances. For larger populations in |c'⟩, the dispersion between these amplification lines changes sign, leading to a prediction of superluminal and negative group velocities. Varying the pumping rate can smoothly change the group velocity in the system from sub- to superluminal. In all cases, we derive analytic solutions. Our results for the pumped atom are of particular relevance because they describe as a limiting case a system that has received wide attention in the literature, but has only been studied numerically.;We also consider a manifestation of the DIGS level configuration in a double well Bose-Einstein condensate. Here, coherent tunneling between the wells replaces the electromagnetic couplings between ground states. In this case, the new features could be used for precision measurements of atomic tunneling, thermometry, and non-local control of light propagation. |
