[
  {
    "id": "ARR-2026-564FZ70CSN83KACD-v1",
    "type": "article",
    "title": "Quantum reference activation of classical symmetric channels",
    "author": [
      {
        "literal": "Lluis Eriksson"
      }
    ],
    "issued": {
      "date-parts": [
        [
          2026,
          10,
          27
        ]
      ]
    },
    "publisher": "AIRR.SCIENCE",
    "archive": "AIRR.SCIENCE",
    "archive_location": "ARR-2026-564FZ70CSN83KACD",
    "version": "v1",
    "genre": "Research preprint",
    "URL": "https://airr.science/papers/ARR-2026-564FZ70CSN83KACD/versions/v1/",
    "note": "Research preprint; ARR-2026-564FZ70CSN83KACD v1. Not peer reviewed by AIRR. Working paper; not admitted to the AIRR accepted collection.",
    "abstract": "We determine the complete equal-reference contraction coefficients of a classical symmetric channel with an arbitrary finite quantum reference. For an alphabet of size n and stochastic parameter -1/(n-1) <= lambda <= 1, the coefficients for the SLD metric, minimal chi-square divergence, triangular Petz divergence, BKM metric and Umegaki relative entropy equal (n-1)lambda^2/[1+(n-2)lambda]. A cyclic harmonic bound supplies the upper estimate and a separable classical-quantum simplex supplies matching faithful limits. The ordinary classical coefficient is n lambda^2/[2+(n-2)lambda]. Every restriction to two input symbols retains that ordinary coefficient even with a quantum reference, so classical binary-support reduction fails in the complete setting. At the exclusion endpoint, the complete coefficient is one although every two-symbol restriction has coefficient 1/(n-1). A family of actual binary measurements, controlled by the classical output, witnesses near-unit retention for a fixed three-symbol channel and a fixed three-dimensional reference. Input, quantum output and measured output relative entropies all tend to log 2. Conditioning grows exponentially and the useful probabilities become rare; no robust communication or capacity advantage is claimed. Adverse finite examples and review-context limitations are retained."
  }
]