  The corrected capacity of a quantum channel is defined as the best one-shot
capacity that can be obtained by measuring the environment and using the result
to correct the output of the channel. It is shown that (i) all qubit channels
have corrected capacity log 2, (ii) a product of N qubit channels has corrected
capacity N log 2, and (iii) all channels have corrected capacity at least log
2. The question is posed of finding the channel with smallest corrected
capacity in any dimension d.
