Fig. 1: Triangle quantum network.

Three sources ϱa, ϱb and ϱc distribute parties to three nodes, Alice, Bob, and Charlie (A, B, and C). The colors yellow, blue, and red are associated to the sources ϱa, ϱb, and ϱc respectively. Alice, Bob, and Charlie each end up with a bipartite system X = X1X2 on which they perform a local channel \({{{{{{{{\mathcal{E}}}}}}}}}_{X}^{(\lambda )}\) (X = A, B, C) depending on a classical random variable λ.