Memory-assisted quantum key distribution (MA-QKD) systems are among novel promising solutions that can improve the key-rate scaling with channel loss. By using a middle node with quantum storage and measurement functionalities, they offer the same key-rate scaling with distance as a single-node quantum repeater. However, the distance at which they can surpass the nominal key rate of repeaterless systems, in terms of bits per second, is typically long, owing to the efficiency and/or interaction time issues when one deals with quantum memories. This crossover distance can be a few hundred kilometres, for instance, when one relies on the exchange of infinitely many key bits for the key-rate analysis. In a realistic setup, however, we should account for the finite-key effects in our analysis. Here, we show that accounting for such effects would actually favour MA-QKD setups, by reducing the crossover distance to the regime where realistic implementations can take place. We demonstrate this by rigorously analysing a decoy-state version of MA-QKD, in the finite-key regime, using memory parameters already achievable experimentally. This provides us with a better understanding of the advantages and challenges of working with memory-based systems.

中文翻译：

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内存辅助诱饵态量子密钥分配的有限密钥分析

内存辅助量子密钥分配 (MA-QKD) 系统是新的有前途的解决方案之一，可以通过信道损失提高密钥速率缩放。通过使用具有量子存储和测量功能的中间节点，它们提供与单节点量子中继器相同的密钥速率随距离缩放。然而，由于处理量子存储器时的效率和/或交互时间问题，它们可以超过无中继器系统的标称密钥速率（以每秒位数计）的距离通常很长。例如，当一个人依赖于无限多的密钥位交换来进行密钥率分析时，这个交叉距离可以是几百公里。然而，在实际设置中，我们应该在分析中考虑有限键效应。这里，我们表明，通过减少到可以发生实际实现的机制的交叉距离，考虑到这种影响实际上有利于 MA-QKD 设置。我们通过严格分析 MA-QKD 的诱饵状态版本来证明这一点，在有限密钥机制中，使用已经可以通过实验实现的内存参数。这使我们可以更好地了解使用基于内存的系统的优势和挑战。