{
  "annotation_id": "220a5b5c-2166-4f10-a94f-083718b9f986",
  "date_created": "2026-03-02T18:01:39.267000Z",
  "date_modified": "2026-03-02T18:01:39.267000Z",
  "file_hash": "69175a6565f1dd8e4155d5df5a7973d16a71712d8de20597ec8a1d4d29f67f8a",
  "private": false,
  "record": {
    "abstract": "We give a complete analysis of covariant measurements on two spins. We\nconsider the cases of two parallel and two antiparallel spins, and we consider\nboth collective measurements on the two spins, and measurements which require\nonly Local Quantum Operations and Classical Communication (LOCC). In all cases\nwe obtain the optimal measurements for arbitrary fidelities. In particular we\nshow that if the aim is determine as well as possible the direction in which\nthe spins are pointing, it is best to carry out measurements on antiparallel\nspins (as already shown by Gisin and Popescu), second best to carry out\nmeasurements on parallel spins and worst to be restricted to LOCC measurements.\nIf the the aim is to determine as well as possible a direction orthogonal to\nthat in which the spins are pointing, it is best to carry out measurements on\nparallel spins, whereas measurements on antiparallel spins and LOCC\nmeasurements are both less good but equivalent.",
    "arxiv_id": "quant-ph/0004035",
    "authors": [
      "S. Massar"
    ],
    "categories": [
      "quant-ph"
    ],
    "doi": "10.1103/PhysRevA.62.040101",
    "journal_ref": "Phys. Rev. A 62, 040101 (2000)",
    "title": "Collective versus local measurements on two parallel or antiparallel   spins",
    "url": "https://arxiv.org/abs/quant-ph/0004035"
  },
  "schema_id": "dorsal/arxiv",
  "source": {
    "execution_id": "757e9dbf-b9a5-4651-b39e-16c722eef35a",
    "id": "arXiv Dataset IDs",
    "type": "Model",
    "variant": "snapshot-2026-03-01",
    "version": "0.1.0"
  },
  "user_id": 1000002
}