Fig. 2: Semicausal channel. | npj Quantum Information

Fig. 2: Semicausal channel.

From: Quantum causal inference with extremely light touch

Fig. 2

Semicausal channels are bipartite channels which can be decomposed into either \({{\mathcal{M}}}_{BC}\,{\circ}\; {{\mathcal{N}}}_{AC}\) or \({{\mathcal{N}}}_{AC}\,{\circ}\; {{\mathcal{M}}}_{BC}\) where C is an ancilla, as in the above circuit. The circles here indicate possible measurements. In this example, which is consistent (only) with cases 1, 3 and 5 in Fig. 1, A can causally influence B, while the inverse is not true.

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