  In this paper we show how to calculate explicitly the exponential of certain
matrices, which are evolution operators governing the interaction of the four
level system of atoms and the radiation, etc. We present a consistent method in
terms of the magic matrix by Makhlin.
  As a closely related subject, we derive a closed form expression of the
Baker-Campbell-Hausdorff formula for a class of matrices in SU(4), by use of
the method developed by the present authors in quant-ph/0610009.
