A graph-separation theorem for quantum causal models
Author(s): J. Pienaar, Č. Brukner
Journal: New Journal of Physics
DOI Number: http://dx.doi.org/10.1088/1367-2630/17/7/073020
Link: Link to publication
A causal model is an abstract representation of a physical system as a directed acyclic graph (DAG), where the statistical dependencies are encoded using a graphical criterion called 'd-separation'. Recent work by Wood and Spekkens shows that causal models cannot, in general, provide a faithful representation of quantum systems. Since d-separation encodes a form of Reichenbach's common cause principle (RCCP), whose validity is questionable in quantum mechanics, we propose a generalized graph separation rule that does not assume the RCCP. We prove that the new rule faithfully captures the statistical dependencies between observables in a quantum network, encoded as a DAG, and reduces to d-separation in a classical limit.