{
  "id": "quant-ph/0112115",
  "version": "v1",
  "published": "2001-12-20T04:44:07.000Z",
  "updated": "2001-12-20T04:44:07.000Z",
  "title": "Inequivalence of pure state ensembles for open quantum systems: the preferred ensembles are those that are physically realizable",
  "authors": [
    "H. M. Wiseman",
    "John A. Vaccaro"
  ],
  "comment": "5 pages, no figures",
  "journal": "Phys. Rev. Lett 87, 240402 (2001)",
  "doi": "10.1103/PhysRevLett.87.240402",
  "categories": [
    "quant-ph"
  ],
  "abstract": "An open quantum system in steady state $\\hat\\rho_{ss}$ can be represented by a weighted ensemble of pure states $\\hat\\rho_{ss}=\\sum_{k}\\wp_{k}\\ket{\\psi_k} \\bra{\\psi_k}$ in infinitely many ways. A physically realizable (PR) ensemble is one for which some continuous measurement of the environment will collapse the system into a pure state $\\ket{\\psi(t)}$, stochastically evolving such that the proportion of time for which $\\ket{\\psi(t)} = \\ket{\\psi_{k}}$ equals $\\wp_{k}$. Some, but not all, ensembles are PR. This constitutes the preferred ensemble fact, with the PR ensembles being the preferred ensembles. We present the necessary and sufficient conditions for a given ensemble to be PR, and illustrate the method by showing that the coherent state ensemble is not PR for an atom laser.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2001-12-20T04:44:07.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "open quantum system",
      "pure state ensembles",
      "preferred ensemble",
      "physically realizable",
      "inequivalence"
    ],
    "tags": [
      "journal article"
    ],
    "publication": {
      "publisher": "APS",
      "journal": "Phys. Rev. Lett."
    },
    "note": {
      "typesetting": "TeX",
      "pages": 5,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}