{
  "id": "1603.00043",
  "version": "v1",
  "published": "2016-02-29T21:14:59.000Z",
  "updated": "2016-02-29T21:14:59.000Z",
  "title": "Witnesses of causal nonseparability: an introduction and a few case studies",
  "authors": [
    "Cyril Branciard"
  ],
  "comment": "15 pages, 7 figures",
  "categories": [
    "quant-ph"
  ],
  "abstract": "It was recently realised that quantum theory allows for so-called causally nonseparable processes, which are incompatible with any definite causal order. This was first suggested on a rather abstract level by the formalism of process matrices, which only assumes that quantum theory holds locally in some observers' laboratories, but does not impose a global causal structure; it was then shown, on a more practical level, that the quantum switch---a new resource for quantum computation that goes beyond causally ordered circuits---provided precisely a physical example of a causally nonseparable process. To demonstrate that a given process is causally nonseparable, we introduced in [Ara\\'ujo et al., New J. Phys. 17, 102001 (2015)] the concept of witnesses of causal nonseparability. Here we present a shorter introduction to this concept, and concentrate on some explicit examples to show how to construct and use such witnesses in practice.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2016-02-29T21:14:59.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "causal nonseparability",
      "case studies",
      "introduction",
      "causally nonseparable process",
      "global causal structure"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 15,
      "language": "en",
      "license": "arXiv",
      "status": "editable",
      "adsabs": "2016arXiv160300043B"
    }
  }
}