Zero-error capacity of quantum channels and noiseless subsystems

摘要

This paper investigates connections between the theory of quantum noiseless subsystems and the zero-error capacity of quantum channels. In particular, we show that if we have a noiseless subsystem state ρ supported by a projector Ρ, then any quantum state with components in the subspace Ρ~⊥ is adjacent to ρ. This result has some interesting implications for the quantum states of the optimum (S, P) for which the zero-error capacity is reached.