  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.
