{
  "annotation_id": "6f2f30fb-4144-43dc-92a6-e8a8c13df265",
  "date_created": "2026-03-02T18:02:12.973000Z",
  "date_modified": "2026-03-02T18:02:12.973000Z",
  "file_hash": "84c77f51bc5fbdd480235bbe353f7c9275afb207a4f756d1c72bc0cb0a4be434",
  "private": false,
  "record": {
    "abstract": "We analyze the estimation of a qubit pure state by means of local\nmeasurements on $N$ identical copies and compare its averaged fidelity for an\nisotropic prior probability distribution to the absolute upper bound given by\ncollective measurements. We discuss two situations: the first one, where the\nstate is restricted to lie on the equator of the Bloch sphere, is formally\nequivalent to phase estimation; the second one, where there is no constrain on\nthe state, can also be regarded as the estimation of a direction in space using\na quantum arrow made out of $N$ parallel spins. We discuss various schemes with\nand without classical communication and compare their efficiency. We show that\nthe fidelity of the most general collective measurement can always be achieved\nasymptotically with local measurements and no classical communication.",
    "arxiv_id": "quant-ph/0412027",
    "authors": [
      "E. Bagan",
      "A. Monras",
      "R. Munoz-Tapia"
    ],
    "categories": [
      "quant-ph"
    ],
    "doi": "10.1103/PhysRevA.71.062318",
    "journal_ref": "Phys. Rev. A 71, 062318 (2005)",
    "title": "Estimation of pure qubit states with collective and individual   measurements",
    "url": "https://arxiv.org/abs/quant-ph/0412027"
  },
  "schema_id": "dorsal/arxiv",
  "source": {
    "execution_id": "2a7c523a-427b-4b74-be86-9a41b0f73da4",
    "id": "arXiv Dataset IDs",
    "type": "Model",
    "variant": "snapshot-2026-03-01",
    "version": "0.1.0"
  },
  "user_id": 1000002
}