In quantum Shannon theory, the way information is encoded and decoded takes advantage of the laws of quantum mechanics, while the way communication channels are interlinked is assumed to be classical. In this Letter, we relax the assumption that quantum channels are combined classically, showing that a quantum communication network where quantum channels are combined in a superposition of different orders can achieve tasks that are impossible in conventional quantum Shannon theory. In particular, we show that two identical copies of a completely depolarizing channel become able to transmit information when they are combined in a quantum superposition of two alternative orders. This finding runs counter to the intuition that if two communication channels are identical, using them in different orders should not make any difference. The failure of such intuition stems from the fact that a single noisy channel can be a random mixture of elementary, noncommuting processes, whose order (or lack thereof) can affect the ability to transmit information.

中文翻译：

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不确定因果关系的辅助下的增强沟通

在量子香农理论中，信息的编码和解码方式利用了量子力学定律，而通信通道的互连方式则被认为是经典的。在这封信中，我们放宽了经典组合量子信道的假设，这表明量子通信网络将量子信道以不同的阶数叠加在一起，可以完成传统的量子香农理论中不可能实现的任务。特别地，我们表明，当完全去极化通道的两个完全相同的副本以两个替代顺序的量子叠加在一起时，它们就能够传输信息。这一发现与直觉相反，直觉是，如果两个通信渠道相同，则以不同的顺序使用它们应该没有任何区别。