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arXiv · 2608.27202

Strong Converse Exponent of Quantum State Merging

Mario Berta·Hao-Chung Cheng·Roberto Rubboli·Marco Tomamichel
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Abstract

We determine the strong converse exponent for the entanglement cost of quantum state merging, showing that it is characterized by the optimized $\alpha$-$z$ conditional R\'enyi entropies with $z=\alpha/2\in[1/2,1]$. This contrasts with the sandwiched conditional R\'enyi entropies that typically govern strong converse exponents in quantum information theory. As a consequence, we derive the strong converse exponent of the partially smoothed conditional min-entropy in purified distance. This exponent is governed by club-sandwiched conditional entropies, whereas global smoothing leads to a sandwiched expression.

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Mario Berta, Hao-Chung Cheng, Roberto Rubboli, Marco Tomamichel. 2026-08-27. Strong Converse Exponent of Quantum State Merging. https://arxiv.org/abs/2608.27202

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