{
  "annotation_id": "30810235-0c92-4897-827c-14a470dfad50",
  "date_created": "2026-03-02T18:02:33.978000Z",
  "date_modified": "2026-03-02T18:02:33.978000Z",
  "file_hash": "f7561ba179f2a42e3025f6d426a471bbb5ed7e84b976b17dfb7eb48adb487223",
  "private": false,
  "record": {
    "abstract": "We show that there does not exist any universal quantum cloning machine that\ncan broadcast an arbitrary mixed qubit with a constant fidelity. Based on this\nresult, we investigate the dependent quantum cloner in the sense that some\nparameter of the input qubit $\\rho_s(\\theta,\\omega,\\lambda)$ is regarded as\nconstant in the fidelity. For the case of constant $\\omega$, we establish the\n$1\\to2$ optimal symmetric dependent cloner with a fidelity 1/2. It is also\nshown that the $1\\to M$ optimal quantum cloning machine for pure qubits is also\noptimal for mixed qubits, when $\\lambda$ is the unique parameter in the\nfidelity. For general $N\\to M$ broadcasting of mixed qubits, the situation is\nvery different.",
    "arxiv_id": "quant-ph/0612205",
    "authors": [
      "Lin Chen",
      "Yi-Xin Chen"
    ],
    "categories": [
      "quant-ph"
    ],
    "doi": "10.1103/PhysRevA.75.062322",
    "title": "Mixed Qubit Cannot Be Universally Broadcast",
    "url": "https://arxiv.org/abs/quant-ph/0612205"
  },
  "schema_id": "dorsal/arxiv",
  "source": {
    "execution_id": "ea700971-688a-4387-990b-83f612f7cff7",
    "id": "arXiv Dataset IDs",
    "type": "Model",
    "variant": "snapshot-2026-03-01",
    "version": "0.1.0"
  },
  "user_id": 1000002
}