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arXiv · 2604.27042

Onset of superactivation of quantum capacity

Marco Parentin·Bjarne Bergh·Nilanjana Datta·Mark M. Wilde
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Abstract

Superactivation of quantum capacity is the phenomenon whereby two quantum channels, each with zero quantum capacity, can exhibit a strictly positive capacity when used in tandem. In this work, we explore superactivation in the previously unexplored non-asymptotic regime of finitely many channel uses. We give a definition of finite-blocklength superactivation and propose numerical methods that can certify it. Then, focusing on the 50% erasure and positive-partial-transpose channels considered in the original work on superactivation, we show that as few as 17 uses of the joint channel already enable qubit transmission with a fidelity unattainable by any number of uses of either channel alone, demonstrating a strong finite-blocklength form of superactivation and opening the door to experimental demonstration.

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Marco Parentin, Bjarne Bergh, Nilanjana Datta, Mark M. Wilde. 2026-04-29. Onset of superactivation of quantum capacity. https://arxiv.org/abs/2604.27042

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