  Copying information is an elementary operation in classical information
processing. However, copying seems rather different in the quantum regime.
Since the discovery of the universal quantum cloning machine, much has been
found from the fundamental point of view about quantum copying. But a basic
question as to the utility of universal quantum cloning remains. We have
considered its application in quantum state restoration by using cloning
circuit for state estimation. It might be expected that classical information
from the state estimation might help restore the quantum state that was
disturbed during transmission. We find that the fidelity of the final state is,
interestingly, independent of error probabilities inside the channel. However,
this also turns out to impose a severe constraint on our original aims.
