Quantum networks (QNs) are a promising platform for secure communications, enhanced sensing, and efficient distributed quantum computing. However, due to the fragile nature of quantum states, these networks face significant challenges in terms of scalability. In this paper, the scaling limits of quantum repeater networks (QRNs) are analyzed. The goal of this work is to maximize the overall length, or scalability of QRNs such that long-distance quantum communications is achieved while application-specific quality-of-service (QoS) requirements are satisfied. In particular, a novel joint optimization framework that aims at maximizing QRN scalability, while satisfying QoS constraints on the end-to-end fidelity and rate is proposed. The proposed approach optimizes the number of QRN repeater nodes, their separation distance, and the number of distillation rounds to be performed at both link and end-to-end levels. Extensive simulations are conducted to analyze the tradeoffs between QRN scalability, rate, and fidelity under gate and measurement errors. The obtained results characterize the QRN scaling limits for a given QoS requirement. The proposed approach offers a promising solution and design guidelines for future QRN deployments.

翻译：量子网络（QN）是未来安全通信、增强型传感和高效分布式量子计算的重要平台。然而，由于量子态的脆弱性，这些网络在可扩展性方面面临重大挑战。本文针对量子中继网络（QRN）的扩展极限进行了分析。研究目标是最大化QRN的总体长度（即可扩展性），在满足特定应用服务质量（QoS）要求的前提下，实现长距离量子通信。具体而言，本文提出了一种新颖的联合优化框架，旨在最大化QRN可扩展性的同时，满足端到端保真度和速率方面的QoS约束。所提方法优化了QRN中继节点的数量、它们之间的间距，以及在链路级和端到端级执行的蒸馏轮数。通过大量仿真，分析了门误差和测量误差下QRN可扩展性、速率与保真度之间的权衡关系。所得结果刻画了给定QoS要求下QRN的扩展极限。所提方法为未来QRN部署提供了有前景的解决方案和设计准则。