Robust steering of n-level quantum systems

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