  This paper and the results therein are geared towards building a basic
toolbox for calculations in quantum information theory of quasi-free fermionic
systems. Various entropy and relative entropy measures are discussed and the
calculation of these reduced to evaluating functions on the one-particle
component of quasi-free states.
  The set of quasi-free affine maps on the state space is determined and fully
characterized in terms of operations on one-particle subspaces. For a subclass
of trace preserving completely positive maps and for their duals, Choi matrices
and Jamiolkowski states are discussed.
