  In this work we discuss the ability of different types of ancillas to control
the decoherence of a qubit interacting with an environment. The error is
introduced into the numerical simulation via a depolarizing isotropic channel.
After the correction we calculate the fidelity as a quality criterion for the
qubit recovered. We observe that a recovery method with a three-qubit ancilla
provides reasonable good results bearing in mind its economy. If we want to go
further, we have to use fault-tolerant ancillas with a high degree of
parallelism, even if this condition implies introducing new ancilla
verification qubits.
