Estimating the information transmission capability of a quantum channel remains one of the fundamental problems in quantum information processing. In contrast to classical channels, the information-carrying capability of quantum channels is contextual. One of the most significant manifestations of this is the superadditivity of the channel capacity: the capacity of two quantum channels used together can be larger than the sum of the individual capacities. Here, we present a one-parameter family of channels for which as the parameter increases its one-way quantum and private capacities increase while its two-way capacities decrease. We also exhibit a one-parameter family of states with analogous behavior with respect to the one- and two-way distillable entanglement and secret key. Our constructions demonstrate that noise is context dependent in quantum communication.

翻译：估算量子信道的信息传输能力仍是量子信息处理中的基本问题之一。与经典信道不同，量子信道的信息承载能力具有情境依赖性，其最显著的表现之一是信道容量的超可加性：两个量子信道联合使用的容量可能超过各自容量之和。本文提出一族单参数信道，随着参数增大，其单向量子容量和私密容量增加，而双向容量却减少。同时，我们构建了一族具有类似行为的单参数量子态，该行为涉及单向与双向可蒸馏纠缠及私密密钥。这一构造表明，噪声在量子通信中具有情境依赖性。