Subluminal and superluminal pulse propagation via spin coherence in a defect dielectric medium

Propagation of Gaussian pulse in a defect dielectric medium in the presence of spin coherence is theoretically investigated. We consider a dielectric slab doped with semiconductor quantum well nanostructure. We show that the reflected and transmitted pulses can be tuned from subluminal to superluminal by changing spin coherence in a slab. Our result predicts that the group velocity of the reflected and transmitted pulses in different wavelengths depend on the thickness of the slab, intensity of the coupling field and relative phase between applied fields.