{
  "id": "1608.01683",
  "version": "v1",
  "published": "2016-08-04T20:03:19.000Z",
  "updated": "2016-08-04T20:03:19.000Z",
  "title": "Experimental Verification of an Indefinite Causal Order",
  "authors": [
    "Giulia Rubino",
    "Lee A. Rozema",
    "Adrien Feix",
    "Mateus Araújo",
    "Jonas M. Zeuner",
    "Lorenzo M. Procopio",
    "Časlav Brukner",
    "Philip Walther"
  ],
  "comment": "11 pages + a 9-page Appendix; 5 figures + 5 in the Appendix",
  "categories": [
    "quant-ph"
  ],
  "abstract": "Investigating the role of causal order in quantum mechanics has recently revealed that the causal distribution of events may not be a-priori well-defined in quantum theory. While this has triggered a growing interest on the theoretical side, creating processes without a causal order is an experimental task. Here we report the first decisive demonstration of a process with an indefinite causal order. To do this, we quantify how incompatible our set-up is with a definite causal order by measuring a 'causal witness'. This mathematical object incorporates a series of measurements which are designed to yield a certain outcome only if the process under examination is not consistent with any well-defined causal order. In our experiment we perform a measurement in a superposition of causal orders - without destroying the coherence - to acquire information both inside and outside of a 'causally non-ordered process'. Using this information, we experimentally determine a causal witness, demonstrating by almost seven standard deviations that the experimentally implemented process does not have a definite causal order.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2016-08-04T20:03:19.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "indefinite causal order",
      "experimental verification",
      "causal witness",
      "seven standard deviations",
      "mathematical object incorporates"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 11,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}