We evaluate the performance of two architectures for network-wide quantum key distribution (QKD): Relayed QKD, which relays keys over multi-link QKD paths for non-adjacent nodes, and Switched QKD, which uses optical switches to dynamically connect arbitrary QKD modules to form direct QKD links between them. An advantage of Switched QKD is that it distributes quantum keys end-to-end, whereas Relayed relies on trusted nodes. However, Switched depends on arbitrary matching of QKD modules. We first experimentally evaluate the performance of commercial DV-QKD modules; for each of three vendors we benchmark the performance in standard/matched module pairs and in unmatched pairs to emulate configurations in the Switched QKD network architecture. The analysis reveals that in some cases a notable variation in the generated secret key rate (SKR) between the matched and unmatched pairs is observed. Driven by these experimental findings, we conduct a comprehensive theoretical analysis that evaluates the network-wide performance of the two architectures. Our analysis is based on uniform ring networks, where we derive optimal key management configurations and analytical formulas for the achievable consumed SKR. We compare network performance under varying ring sizes, QKD link losses, QKD receivers' sensitivity and performance penalties of unmatched modules. Our findings indicate that Switched QKD performs better in dense rings (short distances, large node counts), while Relayed QKD is more effective in longer distances and large node counts. Moreover, we confirm that unmatched QKD modules penalties significantly impact the efficiency of Switched QKD architecture.

翻译：本文评估了两种全网量子密钥分发（QKD）架构的性能：中继QKD与交换QKD。中继QKD通过多链路QKD路径为非相邻节点中继密钥，而交换QKD则利用光交换机动态连接任意QKD模块，以在它们之间建立直接的QKD链路。交换QKD的一个优势在于其端到端分发量子密钥，而中继方案依赖于可信节点。然而，交换QKD的实现取决于QKD模块的任意匹配。我们首先对商用离散变量QKD（DV-QKD）模块的性能进行了实验评估；针对三家供应商，我们分别测试了标准/匹配模块对以及非匹配模块对的性能，以模拟交换QKD网络架构中的配置。分析表明，在某些情况下，匹配对与非匹配对之间生成的密钥率（SKR）存在显著差异。基于这些实验结果，我们开展了全面的理论分析，评估了两种架构在全网范围内的性能。我们的分析基于均匀环形网络，推导了最优密钥管理配置及可实现消耗密钥率的解析公式。我们比较了不同环网规模、QKD链路损耗、QKD接收机灵敏度以及非匹配模块性能惩罚下的网络性能。研究结果表明，交换QKD在密集环形网络（短距离、多节点）中表现更优，而中继QKD在较长距离且节点数较多的场景下更为有效。此外，我们证实非匹配QKD模块的性能惩罚会显著影响交换QKD架构的效率。