  It is by now well established that noise itself can be useful for performing
quantum information processing tasks. We present results which show how one can
effectively reduce the error rate associated with a noisy quantum channel, by
counteracting its detrimental effects with another form of noise. In
particular, we consider the effect of adding on top of a purely Markovian
(Lindblad) dynamics, a more general form of dissipation, which we refer to as
generalized-Markovian noise. This noise has an associated memory kernel and the
resulting dynamics is described by an integro-differential equation. The
overall dynamics are characterized by decay rates which depend not only on the
original dissipative time-scales, but also on the new integral kernel. We find
that one can engineer this kernel such that the overall rate of decay is
lowered by the addition of this noise term. We illustrate this technique for
the case where the bare noise is described by a dephasing Pauli channel. We
analytically solve this model, and show that one can effectively double (or
even triple) the length of the channel, whilst achieving the same fidelity,
entanglement, and error threshold. We numerically verify this scheme can also
be used to protect against thermal Markovian noise (at non-zero temperature),
which models spontaneous emission and excitation processes. A physical
interpretation of this scheme is discussed, whereby the added
generalized-Markovian noise causes the system to become periodically decoupled
from the background Markovian noise.
