Quantum states characterization for the zero-error capacity
  The zero-error capacity of quantum channels was defined as the least upper bound of rates at which classical information can be transmitted through a quantum channel with probability of error equal to zero. This paper investigates some properties of input states and measurements used to attain the quantum zero-error capacity. We start by reformulating the problem of finding the zero-error capacity in the language of graph theory. This alternative definition is used to prove that the zero-error capacity of any quantum channel can be reached by using tensor products of pure states as channel inputs, and projective measurements in the channel output. We conclude by presenting an example that illustrates our results. 
Rex A C Medeiros (ENST Paris and UFCG Brazil), Romain Alleaume (ENST   Paris), Gerard Cohen (ENST Paris), Francisco M. de As...