  Entanglement can be distributed using a carrier which is always separable
from the rest of the systems involved. Up to now, this effect has predominantly
been analyzed in the case where the carrier-system interactions take the form
of ideal unitary operations, thus leaving untested its robustness against
either non-unitary or unitary errors. We address this issue by considering the
effect of incoherent dynamics acting alongside imperfect unitary interactions.
In particular, we determine the restrictions that need to be placed on the
interaction time, as well as the strength of the incoherent dynamics. We find
that with non-unitary errors, we can still successfully distribute
entanglement, provided we measure the carrier in a suitable basis. Introducing
imperfections in the unitary dynamics, we show that entanglement gain is
possible even with substantial unitary errors. Moreover, certain variations in
the strength of the unitary dynamics can allow for greater robustness against
non-unitary errors. Therefore, even in experimental settings where unitary
operations cannot be carried out without imperfections, it is still possible to
generate entanglement between two systems using a separable carrier.
