  The design and analysis of controllers to regulate excitation transport in
quantum spin rings presents challenges in the application of classical feedback
control techniques to synthesize effective control, and generates results in
contradiction to the expectations of classical control theory. In this paper,
we examine the robustness of controllers designed to optimize the fidelity of
an excitation transfer to uncertainty in system and control parameters. We use
the logarithmic sensitivity of the fidelity error as the measure of robustness,
drawing on the classical control analog of the sensitivity of the tracking
error. In our analysis we demonstrate that quantum systems optimized for
coherent transport demonstrate significantly different correlation between
error and the log-sensitivity depending on whether the controller is optimized
for readout at an exact time T or over a time-window about T.
