  Selective transfer of information between spin-1/2 particles arranged in a
ring is achieved by optimizing the transfer fidelity over a readout time window
via shaping, externally applied, static bias fields. Such static control fields
have properties that clash with the expectations of classical control theory.
Previous work has shown that there are cases in which the logarithmic
differential sensitivity of the transfer fidelity to uncertainty in coupling
strength or spillage of the bias field to adjacent spins is minimized by
controllers that produce the best fidelity. Here we expand upon these examples
and examine cases of both classical and non-classical behavior of logarithmic
sensitivity to parameter uncertainty and robustness as measured by the $\mu$
function for quantum systems. In particular we examine these properties in an
11-spin ring with a single uncertainty in coupling strength or a single bias
spillage.
