{
  "annotation_id": "694e1d3a-f861-4bfc-9053-8a198f5546e0",
  "date_created": "2026-03-02T18:02:12.980000Z",
  "date_modified": "2026-03-02T18:02:12.980000Z",
  "file_hash": "0b6ba0d1675604c1d0a1ef3515f4885393e6ee881ff44c3703bb670d48334765",
  "private": false,
  "record": {
    "abstract": "State estimation is usually analyzed in the situation when copies are in a\nproduct state, either mixed or pure. We investigate here the concept of state\nestimation on correlated copies. We analyze state estimation on correlated N\nqubit states, which are permutationally invariant. Using a correlated state we\ntry to estimate as good as possible the direction of the Bloch vector of a\nsingle particle reduced density matrix. We derive the optimal fidelity for all\npermutation invariant states. We find the optimal state, which yields the\nhighest estimation fidelity among the states with the same reduced density\nmatrix. Interestingly this state is not a product state. We also point out that\nstates produced by optimal universal cloning machines are the worst form the\npoint of view of estimating the reduced density matrix.",
    "arxiv_id": "quant-ph/0412155",
    "authors": [
      "Rafal Demkowicz-Dobrzanski"
    ],
    "categories": [
      "quant-ph"
    ],
    "doi": "10.1103/PhysRevA.71.062321",
    "journal_ref": "Phys. Rev. A 71, 062321 (2005)",
    "title": "State estimation on correlated copies",
    "url": "https://arxiv.org/abs/quant-ph/0412155"
  },
  "schema_id": "dorsal/arxiv",
  "source": {
    "execution_id": "b39b048d-3a3b-454f-ad0f-7c60464b6855",
    "id": "arXiv Dataset IDs",
    "type": "Model",
    "variant": "snapshot-2026-03-01",
    "version": "0.1.0"
  },
  "user_id": 1000002
}