  We consider two capacity quantities associated with bipartite unitary gates:
the entangling and the disentangling power. For two-qubit unitaries these two
capacities are always the same. Here we prove that these capacities are
different in general. We do so by constructing an explicit example of a
qubit-qutrit unitary whose entangling power is maximal (2 ebits), but whose
disentangling power is strictly less. A corollary is that there can be no
unique ordering for unitary gates in terms of their ability to perform
non-local tasks. Finally we show that in large dimensions, almost all bipartite
unitaries have entangling and disentangling capacities close to the maximal
possible (and thus in high dimensions the difference in these capacities is
small for almost all unitaries).
