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    "headline": "The Channel-Distance Algorithm Meets Its Lower Bound",
    "slug": "the-channel-distance-algorithm-meets-its-lower-bound",
    "dek": "The estimator uses order square-root-d over epsilon queries, matching the known lower bound for unknown unitary channels.",
    "summary": "The estimator uses order square-root-d over epsilon queries, matching the known lower bound for unknown unitary channels.",
    "body_text": "Diamond distance determines the best single-use probability of distinguishing two quantum channels. A new algorithm estimates that distance between unknown d-dimensional unitary channels to additive error epsilon using order square-root-d over epsilon calls to the channels and their inverses. The authors show this query complexity matches an existing lower bound, making it optimal in that model. The result is an algorithmic theorem, not a report of device-level runtime or noise performance.",
    "why_it_matters": "The estimator uses order square-root-d over epsilon queries, matching the known lower bound for unknown unitary channels.",
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      "The result is an algorithmic theorem, not a report of device-level runtime or noise performance."
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    "first_published_at": "2026-10-31T09:00:00.000-04:00",
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        "text": "The estimator uses order square-root-d over epsilon queries, matching the known lower bound for unknown unitary channels.",
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        "qualification": "The result is an algorithmic theorem, not a report of device-level runtime or noise performance."
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    "tags": [
      "quantum algorithms",
      "channel distance",
      "query complexity",
      "theory"
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  "sources": [
    {
      "source_id": "source-2026-10-31-013",
      "title": "arXiv preprint 2610.40623, original v1",
      "publisher": "arXiv",
      "url": "https://arxiv.org/abs/2610.40623v1",
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      "published_at": "2026-10-28T20:00:00.000-04:00",
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    "name": "The Machine Press",
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  "cite_this_report": {
    "title": "The Channel-Distance Algorithm Meets Its Lower Bound",
    "publisher": "The Machine Press",
    "published_at": "2026-10-31T09:00:00.000-04:00",
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