  The elimination of decoherence of two-state quantum systems interacting with
a thermal reservoir through an external controllable driving field is discussed
in the present paper. The restriction equation with which the external
controllable driving field should agree will be derived. Based on this, we
obtain the time-development equation of the off-diagonal elements of density
operator in the supersymmetric multiphoton two-state quantum systems, which is
helpful for studying the polarization evolution in this two-state quantum
model.
