  Robust open-loop steering of a finite-dimensional quantum system is a central
problem in a growing number of applications of information engineering. In the
present paper, we reformulate the problem in the classical control-theoretic
setting, and provide a precise definition of {\em robustness} of the control
strategy. We then discuss and compare some significant problems from NMR in the
light of the given definition. We obtain quantitative results that are
consistent with the qualitative ones available in the physics literature.
