  Given an quantum dynamical semigroup expressed as an exponential
superoperator acting on a space of N-dimensional density operators, eigenvalue
methods are presented by which canonical Kraus and Lindblad operator sum
representations can be computed. These methods provide a mathematical basis on
which to develop novel algorithms for quantum process tomography, the
statistical estimation of superoperators and their generators, from a wide
variety of experimental data. Theoretical arguments and numerical simulations
are presented which imply that these algorithms will be quite robust in the
presence of random errors in the data.
