Superactivation of Quantum Channels is Limited by the Quantum Relative   Entropy Function
  In this work we prove that the possibility of superactivation of quantum channel capacities is determined by the mathematical properties of the quantum relative entropy function. Before our work this fundamental and purely mathematical connection between the quantum relative entropy function and the superactivation effect was completely unrevealed. We demonstrate the results for the quantum capacity; however the proposed theorems and connections hold for all other channel capacities of quantum channels for which the superactivation is possible. 
Laszlo Gyongyosi, Sandor Imre
quant-ph cs.IT math.IT