[
    {
        "id": "osp-26925",
        "type": "article-journal",
        "title": "Quantum Advantage for Two-Party Differential Privacy",
        "author": [
            {
                "family": "Alabi",
                "given": "Daniel"
            },
            {
                "family": "Khabiboulline",
                "given": "Emil T."
            }
        ],
        "URL": "https://omanscience.com/en/articles/quantum-advantage-for-two-party-differential-privacy",
        "language": "en",
        "issued": {
            "date-parts": [
                [
                    2026
                ]
            ]
        },
        "abstract": "We introduce information-theoretically private quantum protocols for two-party Hamming distance when both parties must output the same estimate. Classically, for input length $n$, information-theoretic protocols require $Ω(\\sqrt{n})$ error under pure differential privacy and $Ω(\\sqrt{n}/\\log n)$ error under strong approximate differential privacy, whereas computational security permits $O(1)$ error. In Klauck's honest, nonpreemptive, message-preserving model, we give an $O(n)$-communication quantum protocol with pure $\\varepsilon$ quantum differential privacy (QDP) and expected error at most $\\frac{2}{\\sinh \\varepsilon}+γ$, for every $γ>0$. For approximate $(\\varepsilon, δ)$ QDP, an exact hockey-stick divergence calculation yields strictly smaller error, while preserving the $O(1)$-versus-$Ω(\\sqrt{n}/\\log n)$ separation for $δ=o(1/n)$. Thus, quantum communication achieves $O(1)$ information-theoretic error, matching the accuracy available classically only under computational assumptions. The main construction uses a guarded coherent round trip and an equal-Gram rigidity principle that prevents an honest player from retaining input-dependent complementary information. We separate this model from weaker prescribed-channel privacy, which already admits an exact classical realization, and from fully retention-robust security, against which measurement-and-abort attacks remain possible. Therefore, we identify preservation of non-orthogonal quantum messages as a resource for privacy."
    }
]