Subluminal and superluminal light propagation via interference of incoherent pump fields

We investigate the dispersion and the absorption properties of a weak probe field in a four-level atomic system by using the incoherent pumping fields. It is shown that the slope of the dispersion changes from positive to negative with the interference of incoherent pumping process. It is also demonstrated that the group velocity of the light pulse can be controlled with the rates of incoherent pumping fields.