Squeezing-induced resonant finite refractive index - zero absorption

We demonstrate that the spectra of a probe beam probing an ensemble of two-level atoms damped by a broadband squeezed vacuum and driven by a weak laser may exhibit a large refractive index accompanied by zero absorption when the probe beam frequency is tuned to the laser frequency. This resonant effect is due to coherent population oscillations. The same theoretical model also exhibits a large refractive index with zero absorption at the Rabi sidebands and near resonance. These results may be verified by present experiments.