Communication over a fully quantum relay channel is considered. We establish three bounds based on different coding strategies, i.e., partial decode-forward, measure-forward, and assist-forward. Using the partial-decode forward strategy, the relay decodes part of the information, while the other part is decoded without the relay's help. The result by Savov et al. (2012) for a classical-quantum relay channel is obtained as a special case. Based on our partial-decode forward bound, the capacity is determined for Hadamard relay channels. In the measure-forward coding scheme, the relay performs a sequence of measurements and then sends a compressed representation of the measurement outcome to the destination receiver. The measure-forward strategy can be viewed as a generalization of the classical compress-forward bound. At last, we consider quantum relay channels with orthogonal receiver components. The assist-forward bound is based on a new approach, whereby the transmitter sends the message to the relay and simultaneously generates entanglement assistance between the relay and the destination receiver. Subsequently, the relay can transmit the message to the destination receiver with rate-limited entanglement assistance.

翻译：本文研究了完全量子中继信道上的通信问题。我们基于三种不同的编码策略建立了三个界，即部分解码转发、测量转发和辅助转发。采用部分解码转发策略时，中继解码部分信息，而其余部分则无需中继协助即可解码。Savov等人（2012）针对经典-量子中继信道的结果可作为本研究的特例获得。基于我们的部分解码转发界，确定了Hadamard中继信道的容量。在测量转发编码方案中，中继执行一系列测量，然后将测量结果的压缩表示发送给目的接收端。测量转发策略可视为经典压缩转发界的推广。最后，我们研究了具有正交接收分量的量子中继信道。辅助转发界基于一种新方法：发送端将消息传送至中继，同时在接收端与中继之间生成纠缠辅助。随后，中继可在速率受限的纠缠辅助下将消息传输至目的接收端。