  We explore a strategy for protecting the evolution of a qubit against the
effects of environmental noise based on the application of controlled
time-dependent perturbations. In the case of a purely decohering coupling, an
explicit sequence of control operations is designed, able to average out the
decoherence of the qubit with high efficiency. We argue that, in principle, the
effects of arbitrary qubit-environment interactions can be removed through
suitable decoupling perturbations acting on the system dynamics over time
scales comparable to the correlation time of the environment.
