  An experiment based on a trapped Ytterbium ion validates the inertial theorem
for the SU(2) algebra. The qubit is encoded within the hyperfine states of the
atom and controlled by RF fields. The inertial theorem generates analytical
solutions for non-adiabatically driven systems that are `accelerated' slowly,
bridging the gap between the sudden and adiabatic limits. These solutions are
shown to be stable to small deviations, both experimentally and theoretically.
As a result, the inertial solutions pave the way to rapid quantum control of
closed, as well as open quantum systems. For large deviations from the inertial
condition, the amplitude diverges while the phase remains accurate.
