{
  "annotation_id": "12e56a8b-6115-4dc6-977c-d0fbc67917c6",
  "date_created": "2026-03-02T18:01:52.222000Z",
  "date_modified": "2026-03-02T18:01:52.222000Z",
  "file_hash": "eb863fbc1fa871ecfce656ac6fd107b823a89f4cb706b184d736edb7dfee5636",
  "private": false,
  "record": {
    "abstract": "When estimating an unknown single pure qubit state, the optimum fidelity is\n2/3. As it is well known, the value 2/3 can be achieved in one step, by a\nsingle ideal measurement of the polarization along a random direction. I\nanalyze the opposite strategy which is the long sequence of unsharp\npolarization measurements. The evolution of the qubit under the influence of\nrepeated measurements is quite complicated in the general case. Fortunately, in\na certain limit of very unsharp measurements the qubit will obey simple\nstochastic evolution equations known for long under the name of time-continuous\nmeasurement theory. I discuss how the outcomes of the very unsharp measurements\nwill asymptotically contribute to our knowledge of the original qubit. It is\nreassuring that the fidelity will achieve the optimum 2/3 for long enough\nsequences of the unsharp measurements.",
    "arxiv_id": "quant-ph/0205150",
    "authors": [
      "Lajos Diosi"
    ],
    "categories": [
      "quant-ph"
    ],
    "doi": "10.1002/prop.200310009",
    "journal_ref": "Fortschr. Phys. 51 (2003) 96-101",
    "title": "Single qubit estimation from repeated unsharp measurements",
    "url": "https://arxiv.org/abs/quant-ph/0205150"
  },
  "schema_id": "dorsal/arxiv",
  "source": {
    "execution_id": "d856fe42-eb64-4391-8d11-706beacdd3a1",
    "id": "arXiv Dataset IDs",
    "type": "Model",
    "variant": "snapshot-2026-03-01",
    "version": "0.1.0"
  },
  "user_id": 1000002
}