Intensity-dependent dispersion under conditions of electromagnetically induced transparency in coherently prepared multi-state atoms

Interest in lossless nonlinearities has focussed on the the dispersive properties of $\Lambda $ systems under conditions of electromagnetically induced transparency (EIT). We generalize the lambda system by introducing further degenerate states to realize a `Chain $ \Lambda $' atom where multiple coupling of the probe field significantly enhances the intensity dependent dispersion without compromising the EIT condition.