{
  "id": "1404.5735",
  "version": "v1",
  "published": "2014-04-23T08:15:17.000Z",
  "updated": "2014-04-23T08:15:17.000Z",
  "title": "Quantum discord for general X and CS states: A piecewise-analytic-numerical formula",
  "authors": [
    "M. A. Yurischev"
  ],
  "comment": "32 pages, 17 figures",
  "categories": [
    "quant-ph"
  ],
  "abstract": "Quantum discord is a function of density-matrix elements (and through them, e.~g., of temperature, applied fields, time, and so forth). The domain of such a function in the case of two-qubit system with X or centrosymmetric (CS) density matrix can consist at most of three subdomains: two ones, where the quantum discord is expressed in closed analytical forms (Q_0 and Q_{\\pi/2}), and an intermediate subdomain in which for determining the quantum discord Q_\\theta it is required to solve numerically a one-dimensional minimization problem to find the optimal measurement angle \\theta\\in(0,\\pi/2). Exact equations for determining the boundaries between these subdomains are obtained and solved for a number of models. The Q_\\theta subdomains are discovered in the anisotropic spin dimers in external field. On the other hand, coinciding boundaries and therefore sudden transitions between optimal measurement angles \\theta=\\pi/2 and \\theta=0 are observed in dynamics of spin currying particles in closed nanopore and also in phase flip channels. In latter cases the solutions are entirely analytical.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2014-04-23T08:15:17.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "quantum discord",
      "cs states",
      "piecewise-analytic-numerical formula",
      "optimal measurement angle",
      "one-dimensional minimization problem"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 32,
      "language": "en",
      "license": "arXiv",
      "status": "editable",
      "adsabs": "2014arXiv1404.5735Y"
    }
  }
}