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A quantum advantage for inferring causal structure




The problem of inferring causal relations from observed correlations is relevant to a wide variety of scientific disciplines. Yet given the correlations between just two classical variables, it is impossible to determine whether they arose from a causal influence of one on the other or a common cause influencing both. Only a randomized trial can settle the issue. Here we consider the problem of causal inference for quantum variables. We show that the analogue of a randomized trial, causal tomography, yields a complete solution. We also show that, in contrast to the classical case, one can sometimes infer the causal structure from observations alone. We implement a quantum-optical experiment wherein we control the causal relation between two optical modes, and two measurement schemes—with and without randomization—that extract this relation from the observed correlations. Our results show that entanglement and quantum coherence provide an advantage for causal inference.

Author(s): Ried, K. and Agnew, M. and Vermeyden, L. and Janzing, D. and Spekkens, R. W. and Resch, K. J.
Journal: Nature Physics
Volume: 11
Number (issue): 5
Pages: 414--420
Year: 2015
Month: March

Department(s): Empirical Inference
Bibtex Type: Article (article)
Paper Type: Journal

DOI: 10.1038/nphys3266
State: Published


  title = {A quantum advantage for inferring causal structure},
  author = {Ried, K. and Agnew, M. and Vermeyden, L. and Janzing, D. and Spekkens, R. W. and Resch, K. J.},
  journal = {Nature Physics},
  volume = {11},
  number = {5},
  pages = {414--420},
  month = mar,
  year = {2015},
  month_numeric = {3}