  Refocusing, or dynamical decoupling, is a coherent control technique where
the internal dynamics of a quantum system is effectively averaged out by an
application of specially designed driving fields. The method has originated in
nuclear magnetic resonance, but it was independently discovered in atomic
physics as a ``coherent destruction of tunneling''. Present work deals with the
analysis of the performance of ``soft'' refocusing pulses and pulse sequences
in protecting the coherence of a qubit system coupled to a quantum oscillator.
