A crucial step towards the 6th generation (6G) of networks would be a shift in communication paradigm beyond the limits of Shannon's theory. In both classical and quantum Shannon's information theory, communication channels are generally assumed to combine through classical trajectories, so that the associated network path traversed by the information carrier is well-defined. Counter-intuitively, quantum mechanics enables a quantum information carrier to propagate through a quantum path, i.e., through a path such that the causal order of the constituting communications channels becomes indefinite. Quantum paths exhibit astonishing features, such as providing non-null capacity even when no information can be sent through any classical path. In this paper, we study the quantum capacity achievable via a quantum path and establish upper and the lower bounds for it. Our findings reveal the substantial advantage achievable with a quantum path over any classical placements of communications channels in terms of ultimate achievable communication rates. Furthermore, we identify the region where a quantum path incontrovertibly outperforms the amount of transmissible information beyond the limits of conventional quantum Shannon's theory, and we quantify this advantage over classical paths through a conservative estimate.

翻译：迈向第六代（6G）网络的关键一步将是通信范式超越香农理论极限的转变。在经典与量子香农信息论中，通信信道通常假定通过经典路径进行组合，从而使得信息载体所经过的相关网络路径是明确定义的。反直觉的是，量子力学使得量子信息载体能够通过量子路径传播，即该路径的构成通信信道之间的因果顺序变得不确定。量子路径展现出令人惊叹的特性，例如即使无法通过任何经典路径发送信息时，仍能提供非零容量。在本文中，我们研究了通过量子路径可实现的量子容量，并建立了其上下界。我们的研究揭示了在终极可达通信速率方面，量子路径相较于任何经典信道布局所具备的显著优势。此外，我们确定了量子路径在超越传统量子香农理论极限方面无疑优于可传输信息量的区域，并通过保守估计量化了其相对于经典路径的优越性。