Extremely slow propagation of a light pulse in an ultracold atomic vapor: A Raman scheme without electromagnetically induced transparency

We describe a Raman scheme where the group velocity of an optical pulse can be altered dramatically. With this none electromagnetically-induced-transparency scheme, we show that when on a two-photon resonance, a light pulse can propagate with extremely slow group velocity. Both pulse narrowing and broadening can occur depending upon the choice of two-photon detuning. When using a tuned far-off two-photon resonance, we show that the pulse propagates “superluminally” in the medium with pulse narrowing. © 2001 The American Physical Society.