Entanglement resources can increase transmission rates substantially. Unfortunately, entanglement is a fragile resource that is quickly degraded by decoherence effects. In order to generate entanglement for optical communication, the transmitter and the receiver first prepare entangled spin-photon pairs locally, and then the photon at the transmitter is sent to the receiver through an optical fiber or free space. Without feedback, the transmitter does not know whether the entangled photon has reached the receiver. The present work introduces a new model of unreliable entanglement assistance, whereby the communication system operates whether entanglement assistance is present or not. While the sender is ignorant, the receiver knows whether the entanglement generation was successful. In the case of a failure, the receiver decodes less information. In this manner, the effective transmission rate is adapted according to the assistance status. Regularized formulas are derived for the classical and quantum capacity regions with unreliable entanglement assistance, characterizing the tradeoff between the unassisted rate and the excess rate that can be obtained from entanglement assistance. It is further established that time division between entanglement-assisted and unassisted coding strategies is optimal for the noiseless qubit channel, but can be strictly suboptimal for a noisy channel.

翻译：纠缠资源可显著提升传输速率。然而，纠缠是一种脆弱的资源，会因退相干效应而迅速退化。为在光通信中生成纠缠，发射端与接收端首先在本地制备纠缠的自旋-光子对，随后发射端的光子通过光纤或自由空间发送至接收端。无反馈条件下，发射端无法知晓纠缠光子是否到达接收端。本文提出了一种新型不可靠纠缠辅助模型，在该模型中，无论纠缠辅助是否存在，通信系统均可正常运行。尽管发送端对此不知情，但接收端能够判断纠缠生成是否成功。若失败，接收端解码的信息量减少。如此，有效传输速率可根据辅助状态自适应调整。我们推导了经典与量子容量区域在不可靠纠缠辅助下的正则化公式，刻画了无辅助速率与通过纠缠辅助所获额外速率间的权衡关系。进一步证明，在无噪量子比特信道中，纠缠辅助编码与无辅助编码的时分复用策略是最优的，但在有噪信道中该策略可能严格次优。