Deterministic Minimum-Output-Entropy Nonadditivity via Haagerup's Inequality and Near-Free Permutation Representations
Abstract
We give a deterministic realization of the finite-dimensional quadratic certificate underlying Collins's mixed-unitary proof of minimum-output-entropy nonadditivity. For every fixed integer K≥ 2 and rational η>0 satisfying log K>2(3+η)2, a deterministic polynomial-time algorithm, for every sufficiently large target size N, outputs K permutations on N'=N+oK,η(N) points. Restricting their permutation matrices to the nontrivial standard representation yields real orthogonal Stinespring blocks and a channel ΦN':MN'−1(ℂ)→ MK(ℂ) such that 2Hmin(ΦN') −Hmin(ΦN'⊗ 2) ≥ (log K)/K −2log(1+((3+η)2)/K) >0. The construction combines Haagerup's length-two inequality with the simultaneous deterministic spectral approximation of O'Donnell and Wu. We further show that the constant $3$ is asymptotically sharp on the relevant Hermitian zero-diagonal coefficient class and that the finite spectral transfer is nearly saturated, thereby isolating the finer geometry of the full output body as the natural next level of refinement beyond the scalar-radius method. Finally, a standard covariant extension converts the same deterministic entropy gap exactly into self-tensor superadditivity of the one-shot Holevo quantity.
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BibTeX
@misc{zhen2026deterministic,
title = {{Deterministic Minimum-Output-Entropy Nonadditivity via Haagerup's Inequality and Near-Free Permutation Representations}},
author = {Guocheng Zhen and Chengkai Zhu and Ranyiliu Chen and Xin Wang},
howpublished = {arXiv},
year = {2026},
month = aug,
doi = {10.48550/arxiv.2608.31081},
eprint = {2608.31081},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2608.31081},
}
RIS
TY - UNPB
TI - Deterministic Minimum-Output-Entropy Nonadditivity via Haagerup's Inequality and Near-Free Permutation Representations
AU - Guocheng Zhen
AU - Chengkai Zhu
AU - Ranyiliu Chen
AU - Xin Wang
PY - 2026
DA - 2026/08/31
PB - arXiv
DO - 10.48550/arxiv.2608.31081
UR - https://arxiv.org/abs/2608.31081
AB - We give a deterministic realization of the finite-dimensional quadratic certificate underlying Collins's mixed-unitary proof of minimum-output-entropy nonadditivity. For every fixed integer K≥ 2 and rational η>0 satisfying log K>2(3+η)^2, a deterministic polynomial-time algorithm, for every sufficiently large target size N, outputs K permutations on N'=N+o_K,η(N) points. Restricting their permutation matrices to the nontrivial standard representation yields real orthogonal Stinespring blocks and a channel Φ_N':M_N'−1(ℂ)→ M_K(ℂ) such that 2H_min(Φ_N') −H_min(Φ_N'^⊗ 2) ≥ (log K)/K −2log(1+((3+η)^2)/K) >0. The construction combines Haagerup's length-two inequality with the simultaneous deterministic spectral approximation of O'Donnell and Wu. We further show that the constant $3$ is asymptotically sharp on the relevant Hermitian zero-diagonal coefficient class and that the finite spectral transfer is nearly saturated, thereby isolating the finer geometry of the full output body as the natural next level of refinement beyond the scalar-radius method. Finally, a standard covariant extension converts the same deterministic entropy gap exactly into self-tensor superadditivity of the one-shot Holevo quantity.
ER -