Knob of adjusting light group velocity in an inhomogeneously broadened degenerate two-level atomic medium by a magnetic field

We proposed a simple model for investigating subluminal and superluminal light propagation via an external magnetic field in an inhomogeneously broadened degenerate two-level atomic medium. We show that a magnetic field can be utilized as a knob to control the absorption/dispersion properties and group index of the medium. By changing the magnitude and reversing the direction of the magnetic field, the positive group index is converted to the negative group index at the center of the EIT window, corresponding with the propagation of a weak light pulse from subluminal to superluminal. Moreover, the influence of the Doppler broadening effect on the group index is also included, making the results approach to actual conditions. Therefore, the suggested model may be helpful for the application realization of optical storage in quantum computers and quantum information processing.