{
  "id": "1402.5927",
  "version": "v2",
  "published": "2014-02-24T19:40:55.000Z",
  "updated": "2015-03-10T18:04:52.000Z",
  "title": "Limitations on Quantum Key Repeaters",
  "authors": [
    "Stefan Bäuml",
    "Matthias Christandl",
    "Karol Horodecki",
    "Andreas Winter"
  ],
  "comment": "11+38 pages, 4 figures, Statements for exact p-bits weakened as non-locking bound on measured relative entropy distance contained an error",
  "categories": [
    "quant-ph",
    "cs.IT",
    "math.IT"
  ],
  "abstract": "A major application of quantum communication is the distribution of entangled particles for use in quantum key distribution (QKD). Due to noise in the communication line, QKD is in practice limited to a distance of a few hundred kilometres, and can only be extended to longer distances by use of a quantum repeater, a device which performs entanglement distillation and quantum teleportation. The existence of noisy entangled states that are undistillable but nevertheless useful for QKD raises the question of the feasibility of a quantum key repeater, which would work beyond the limits of entanglement distillation, hence possibly tolerating higher noise levels than existing protocols. Here we exhibit fundamental limits on such a device in the form of bounds on the rate at which it may extract secure key. As a consequence, we give examples of states suitable for QKD but unsuitable for the most general quantum key repeater protocol.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2014-02-24T19:40:55.000Z",
      "abstract": "A main application of quantum communication is the distribution of entangled particles for use in quantum key distribution (QKD). Due to unavoidable noise in the communication line, QKD is in practice limited to a distance of a few hundred kilometers and can only be extended to longer distances by use of a future quantum repeater, a small-scale quantum computer which performs iterated entanglement distillation and quantum teleportation. The existence of entangled particles that are undistillable but nevertheless useful for QKD raises the question for a quantum key repeater which works beyond the limits of entanglement distillation. In this work we show that any such apparatus is severely limited in its performance; in particular, we exhibit entanglement suitable for QKD but unsuitable for the most general quantum key repeater protocol. The mathematical techniques we develop can be viewed as a step towards opening the theory of entanglement measures to networks of communicating parties.",
      "comment": "7+41 pages, 1 figure",
      "journal": null,
      "doi": null
    },
    {
      "version": "v2",
      "updated": "2015-03-10T18:04:52.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "limitations",
      "performs iterated entanglement distillation",
      "small-scale quantum computer",
      "entangled particles",
      "longer distances"
    ],
    "publication": {
      "doi": "10.1038/ncomms7908",
      "journal": "Nature Communications",
      "year": 2015,
      "month": "Apr",
      "volume": 6,
      "pages": 6908
    },
    "note": {
      "typesetting": "TeX",
      "pages": 38,
      "language": "en",
      "license": "arXiv",
      "status": "editable",
      "adsabs": "2015NatCo...6E6908B"
    }
  }
}