{
  "id": "1412.4006",
  "version": "v1",
  "published": "2014-12-12T14:38:25.000Z",
  "updated": "2014-12-12T14:38:25.000Z",
  "title": "Experimental Superposition of Orders of Quantum Gates",
  "authors": [
    "Lorenzo M. Procopio",
    "Amir Moqanaki",
    "Mateus Araújo",
    "Fabio Costa",
    "Irati A. Calafell",
    "Emma G. Dowd",
    "Deny R. Hamel",
    "Lee A. Rozema",
    "Časlav Brukner",
    "Philip Walther"
  ],
  "comment": "10 pages, 7 figures, 2 tables",
  "categories": [
    "quant-ph"
  ],
  "abstract": "In a quantum computer, creating superpositions of quantum bits (qubits) in different states can lead to a speed-up over classical computers [1], but quantum mechanics also allows for the superposition of quantum circuits [2]. In fact, it has recently been theoretically predicted that superimposing quantum circuits, each with a different gate order, could provide quantum computers with an even further computational advantage [3-5]. Here, we experimentally demonstrate this enhancement by applying two quantum gates in a superposition of both possible orders to determine whether the two gates commute or anti-commute. We are able to make this determination with only a single use (or query) of each gate, while all quantum circuits with a fixed order of gates would require at least two uses of one of the gates [3]. Remarkably, when the problem is scaled to N gates, creating a superposition of quantum circuits is likely to provide an exponential advantage over classical algorithms, and a linear advantage over quantum algorithms with fixed gate order [4]. The new resource that we exploit in our experiment can be interpreted as a \"superposition of causal orders\". We demonstrate such a superposition could allow some quantum algorithms to be implemented with an efficiency that is unlikely to be achieved on a quantum computer with a fixed gate order.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2014-12-12T14:38:25.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "quantum gates",
      "experimental superposition",
      "quantum computer",
      "fixed gate order",
      "quantum algorithms"
    ],
    "publication": {
      "doi": "10.1038/ncomms8913",
      "journal": "Nature Communications",
      "year": 2015,
      "month": "Aug",
      "volume": 6,
      "pages": 7913
    },
    "note": {
      "typesetting": "TeX",
      "pages": 10,
      "language": "en",
      "license": "arXiv",
      "status": "editable",
      "adsabs": "2015NatCo...6E7913P"
    }
  }
}