A bipartite quantum channel represents the interaction between systems,
generally allowing for exchange of information. A special class of bipartite
channels are the no-signaling ones, which do not allow communication. In Ref.
[1] it has been conjectured that all no-signaling channels are mixtures of
entanglement-breaking and localizable channels, which require only local
operations and entanglement. Here we provide the general realization scheme,
giving a counterexample to the conjecture.Comment: 4 pages, revtex
