Generic nonadditivity of quantum capacity in simple channels
Generic nonadditivity of quantum capacity in simple channels
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DOI：
10.1103/physrevlett.130.200801
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发表时间：
2022-02
影响因子：
8.6
通讯作者：
Felix Leditzky;D. Leung;Vikesh Siddhu;Graeme Smith;J. Smolin
中科院分区：
文献类型：
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作者：
Felix Leditzky;D. Leung;Vikesh Siddhu;Graeme Smith;J. Smolin
确定量子通道的容量是量子信息论中的一个基本问题。尽管有严格的编码定理量化了量子通道上的信息流，但由于超可加性效应，人们对它们的能力知之甚少。研究这些现象对于加深我们对量子信息的理解非常重要，但简单明了的超加性通道的例子却很少。在这里，我们研究了称为鸭嘴兽通道的通道家族。它最简单的成员是 qutrit 通道，当与各种量子位通道联合使用时，它显示出相干信息的超可加性。高维家族成员表现出量子容量的超可加性以及擦除通道。受我们的配套论文 [F. Leditzky, D. Leung, V. Siddhu, G. Smith, 和 J. A. Smolin, 量子通道动物园的鸭嘴兽, IEEE Transactions on Information Theory (IEEE, 2023), 10.1109/TIT.2023.3245985]，我们关于量子容量超可加性的结果扩展到低维通道以及更大的参数范围。特别是，超加性发生在两个弱加性通道之间，每个通道本身都具有大容量，这与之前的结果形成鲜明对比。值得注意的是，单一的、新颖的传输策略在所有示例中都实现了超可加性。我们的结果表明，超可加性比之前想象的要普遍得多。它可以在多种通道上发生，即使两个参与通道都具有很大的量子容量。
Determining capacities of quantum channels is a fundamental question in quantum information theory. Despite having rigorous coding theorems quantifying the flow of information across quantum channels, their capacities are poorly understood due to superadditivity effects. Studying these phenomena is important for deepening our understanding of quantum information, yet simple and clean examples of superadditive channels are scarce. Here we study a family of channels called platypus channels. Its simplest member, a qutrit channel, is shown to display superadditivity of coherent information when used jointly with a variety of qubit channels. Higher-dimensional family members display superadditivity of quantum capacity together with an erasure channel. Subject to the "spin-alignment conjecture" introduced in our companion paper [F. Leditzky, D. Leung, V. Siddhu, G. Smith, and J. A. Smolin, The platypus of the quantum channel zoo, IEEE Transactions on Information Theory (IEEE, 2023), 10.1109/TIT.2023.3245985], our results on superadditivity of quantum capacity extend to lower-dimensional channels as well as larger parameter ranges. In particular, superadditivity occurs between two weakly additive channels each with large capacity on their own, in stark contrast to previous results. Remarkably, a single, novel transmission strategy achieves superadditivity in all examples. Our results show that superadditivity is much more prevalent than previously thought. It can occur across a wide variety of channels, even when both participating channels have large quantum capacity.