Controlling a group velocity of light by magnetic field
  We have shown that quantum interference in a driven quasi-degenerate two-level atomic system can be controlled by an externally applied magnetic field. We demonstrate that the mechanism of optical control is based on quantum interference, which allows one to implement both electromagnetically induced transparency and electromagnetically induced absorption in one atomic system. Dispersion of such the medium allows one to control group velocity of propagation of light pulses be ultra-slow or superluminal via applied magnetic field. 
Yu.M.Golubev (1), T.Yu.Golubeva (1), Yu.V.Rostovtsev (2), M.O.Scully   (2) ((1) V. A. Fock Physics Institute, St.Petersburg,...