  We address the issue of the discrimination between two-qubit amplitude
damping channels by exploring several strategies. For the single-shot, we show
that the excited state does not always give the optimal input, and that side
entanglement assistance has limited benefit. On the contrary, feedback
assistance from the environment is more beneficial. For the two-shot, we prove
the in-utility of entangled inputs. Then focusing on individual (local)
measurements, we find the optimal adaptive strategy.
