{
  "annotation_id": "c94c229d-e4b4-4420-b06d-da47614a60e3",
  "date_created": "2026-03-02T18:01:59.541000Z",
  "date_modified": "2026-03-02T18:01:59.541000Z",
  "file_hash": "bdbfb0d6c6574f655df18767dc26080a5a49df50587854ec989bee316661ab4c",
  "private": false,
  "record": {
    "abstract": "We discuss the problem of estimating a general (mixed) qubit state. We give\nthe optimal guess that can be inferred from any given set of measurements. For\ncollective measurements and for a large number $N$ of copies, we show that the\nerror in the estimation goes as 1/N. For local measurements we focus on the\nsimpler case of states lying on the equatorial plane of the Bloch sphere. We\nshow that standard tomographic techniques lead to an error proportional to\n$1/N^{1/4}$, while with our optimal data processing it is proportional to\n$1/N^{3/4}$.",
    "arxiv_id": "quant-ph/0307199",
    "authors": [
      "E. Bagan",
      "M. Baig",
      "R. Munoz-Tapia",
      "A. Rodriguez"
    ],
    "categories": [
      "quant-ph"
    ],
    "doi": "10.1103/PhysRevA.69.010304",
    "journal_ref": "Phys. Rev. A 69, 010304 (2004)",
    "title": "Collective vs local measurements in qubit mixed state estimation",
    "url": "https://arxiv.org/abs/quant-ph/0307199"
  },
  "schema_id": "dorsal/arxiv",
  "source": {
    "execution_id": "d6b8f6a5-c902-4800-92f8-0ef0af49d2d0",
    "id": "arXiv Dataset IDs",
    "type": "Model",
    "variant": "snapshot-2026-03-01",
    "version": "0.1.0"
  },
  "user_id": 1000002
}