  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.
