论文标题
简单通道中量子容量的通用非添加性
Generic nonadditivity of quantum capacity in simple channels
论文作者
论文摘要
确定量子通道的能力是量子信息理论中的一个基本问题。尽管对跨量子通道的信息流进行了严格的编码定理，但由于超级添加的效应，它们的能力很差。研究这些现象对于加深我们对量子信息的理解很重要，但简单而干净的超添加通道的例子很少。在这里，我们研究了一个名为鸭嘴兽通道的渠道家族。它最简单的构件，一种QUTRIT通道，显示与各种量子信道共同使用时，可以显示相干信息的超级添加性。高维家庭成员与擦除通道一起表现出量子能力的超级增强性。受伴侣纸[IEEE Trans中引入的“自旋分配猜想”。 inf。理论69（6），第3825-3849页，2023年； ARXIV：2202.08380]，我们对量子能力的超级添加性的结果扩展到较低维通道以及较大的参数范围。特别是，与先前的结果形成鲜明对比的是，超级添加性发生在两个弱添加通道之间。值得注意的是，在所有示例中，一种新颖的传播策略都可以实现超级促进性。我们的结果表明，超级促进性比以前想象的要普遍得多。即使两个参与通道具有较大的量子容量，它也可以在各种渠道上发生。
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 super-additivity effects. Studying these phenomena is important for deepening our understanding of quantum information, yet simple and clean examples of super-additive channels are scarce. Here we study a family of channels called platypus channels. Its simplest member, a qutrit channel, is shown to display super-additivity of coherent information when used jointly with a variety of qubit channels. Higher-dimensional family members display super-additivity of quantum capacity together with an erasure channel. Subject to the "spin-alignment conjecture" introduced in the companion paper [IEEE Trans. Inf. Theory 69(6), pp. 3825-3849, 2023; arXiv:2202.08380], our results on super-additivity of quantum capacity extend to lower-dimensional channels as well as larger parameter ranges. In particular, super-additivity 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 super-additivity in all examples. Our results show that super-additivity 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.
