Private Quantum Coding for Quantum Relay Networks
  The relay encoder is an unreliable probabilistic device which is aimed at helping the communication between the sender and the receiver. In this work we show that in the quantum setting the probabilistic behavior can be completely eliminated. We also show how to combine quantum polar encoding with superactivation-assistance in order to achieve reliable and capacity-achieving private communication over noisy quantum relay channels. 
Laszlo Gyongyosi, Sandor Imre
quant-ph cs.IT math.IT