  We describe how the effect of charge noise on a pair of spins coupled via the
exchange interaction can be calculated by modelling charge fluctuations as a
random telegraph noise process using probability density functions. We develop
analytic expressions for the time dependent superoperator of a pair of spins as
a function of fluctuation amplitude and rate. We show that the theory can be
extended to include multiple fluctuators, in particular, spectral distributions
of fluctuators. These superoperators can be included in time dependent analyses
of the state of spin systems designed for spintronics or quantum information
processing to determine the decohering effects of exchange fluctuations.
