When does noise increase the quantum capacity?

@article{Brando2012WhenDN,
  title={When does noise increase the quantum capacity?},
  author={Fernando G. S. L. Brand{\~a}o and Jonathan Oppenheim and Sergii Strelchuk},
  journal={Physical review letters},
  year={2012},
  volume={108 4},
  pages={
          040501
        }
}
Superactivation is the property that two channels with zero quantum capacity can be used together to yield a positive capacity. Here we demonstrate that this effect exists for a wide class of inequivalent channels, none of which can simulate each other. We also consider the case where one of two zero-capacity channels is applied, but the sender is ignorant of which one is applied. We find examples where the greater the entropy of mixing of the channels, the greater the lower bound for the… 

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