  Active protection of quantum states is an essential prerequisite for the
implementation of quantum computing. Dynamical decoupling (DD) is a promising
approach that applies sequences of control pulses to the system in order to
reduce the adverse effect of system-environment interactions. Since every
hardware device has finite precision, the errors of the DD control pulses can
themselves destroy the stored information rather than protect it. We
experimentally compare the performance of different DD sequences in the
presence of an environment that was chosen such that all relevant DD sequences
can equally suppress its effect on the system. Under these conditions, the
remaining decay of the qubits under DD allows us to compare very precisely the
robustness of the different DD sequences with respect to imperfections of the
control pulses.
