Mathematical Institute, University of Oxford, Woodstock Road, Oxford OX2 6GG, United Kingdom.
Centre for Quantum Technologies, National University of Singapore, 3 Science Drive 2, 117543, Singapore.
Phys Rev Lett. 2019 Oct 11;123(15):150502. doi: 10.1103/PhysRevLett.123.150502.
The capacity of a channel is known to be equivalent to the highest rate at which it can generate entanglement. Analogous to entanglement, the notion of a causality measure characterizes the temporal aspect of quantum correlations. Despite holding an equally fundamental role in physics, temporal quantum correlations have yet to find their operational significance in quantum communication. Here we uncover a connection between quantum causality and channel capacity. We show the amount of temporal correlations between two ends of the noisy quantum channel, as quantified by a causality measure, implies a general upper bound on its channel capacity. The expression of this new bound is simpler to evaluate than most previously known bounds. We demonstrate the utility of this bound by applying it to a class of shifted depolarizing channels, which results in improvement over previously known bounds for this class of channels.
通道的容量被认为等同于它能够产生纠缠的最高速率。类似于纠缠，因果关系度量的概念描述了量子相关的时间方面。尽管在物理学中具有同样基本的作用，但时间量子相关性在量子通信中尚未找到其操作意义。在这里，我们揭示了量子因果关系和通道容量之间的联系。我们表明，通过因果关系度量来量化的两个噪声量子通道末端之间的时间相关量，意味着对其通道容量的一般上限。这个新边界的表达式比大多数以前已知的边界更容易评估。我们通过将其应用于一类移位的去极化通道来证明这个边界的实用性，这导致了对此类通道的以前已知边界的改进。
