[
  {
    "id": "ARR-2026-564FZ70CSN83KACD-v2",
    "type": "article",
    "title": "Support and quantum-reference activation of classical channels",
    "author": [
      {
        "literal": "Lluis Eriksson"
      }
    ],
    "issued": {
      "date-parts": [
        [
          2026,
          10,
          28
        ]
      ]
    },
    "publisher": "AIRR.SCIENCE",
    "archive": "AIRR.SCIENCE",
    "archive_location": "ARR-2026-564FZ70CSN83KACD",
    "version": "v2",
    "genre": "Research preprint",
    "URL": "https://airr.science/papers/ARR-2026-564FZ70CSN83KACD/versions/v2/",
    "note": "Research preprint; ARR-2026-564FZ70CSN83KACD v2. Not peer reviewed by AIRR. Working paper; not admitted to the AIRR accepted collection.",
    "abstract": "For an arbitrary finite classical channel K, we characterize when quantum side information prevents strict relative-entropy contraction. The complete equal-reference Umegaki coefficient equals one if and only if the Doeblin common-component coefficient d(K)=sum_y min_i K(y|i) vanishes. Positive d(K) gives the known upper 1-d(K). For the converse, one channel-independent family of faithful separable classical-quantum hypotheses, with reference dimension equal to the input alphabet size, admits channel-dependent binary readouts whose input, output and measured relative entropies tend to log 2. Explicit scalar bounds make this convergence uniform over all zero-Doeblin channels with a fixed input alphabet, even as supports and output cardinalities vary. For symmetric channels we additionally determine exact SLD, minimal chi-square, triangular, BKM and Umegaki coefficients: (n-1)lambda^2/[1+(n-2)lambda]. Every two-symbol restriction retains its ordinary classical coefficient, exposing the failure of classical binary-support reduction. Conditioning, rare events and parameter-dependent effects remain essential costs. Certified asymmetric examples, failed numerical selectors and regularizer counterexamples are retained. No capacity advantage, robust implementation, minimal reference dimension or worldwide priority is claimed."
  }
]