Many quantum-network applications require end-to-end Bell pairs whose fidelity exceeds a request-specific threshold, but existing entanglement routing algorithms either optimize only throughput without regard for fidelity or enforce fidelity guarantees using centralized controllers with global link-state knowledge. We present Q-GUARD, an online entanglement routing algorithm that enforces per-request fidelity thresholds within a distributed protocol model in which nodes exchange link-state information only with their $k$-hop neighbors. After link outcomes are realized in each slot, Q-GUARD builds per-link purification cost tables from realized Bell pairs, allocates per-hop fidelity targets using a Werner-state equal-split rule, and selects between candidate path segments using a segment-local expected-goodput (EXG) metric that jointly accounts for swap success, purification overhead, and resource availability. We also introduce Q-GUARD-WS, an extension that exploits per-link hardware quality estimates to allocate purification effort non-uniformly across hops. On synthetic 100-node topologies with heterogeneous link fidelity and stochastic BBPSSW purification, Q-GUARD raises the qualified success rate from under 20\% to over 85\% on 4-hop paths and nearly doubles the qualified service radius in Euclidean distance relative to throughput-only and naive-purification baselines, while Q-GUARD-WS provides additional throughput gains under high hardware heterogeneity.

翻译：许多量子网络应用要求端到端贝尔对的保真度超过特定请求的阈值，但现有纠缠路由算法要么仅优化吞吐量而不考虑保真度，要么使用具有全局链路状态知识的集中式控制器来强制执行保真度保证。我们提出Q-GUARD，一种在线纠缠路由算法，在分布式协议模型中强制实施每请求的保真度阈值，其中节点仅与其$k$跳邻居交换链路状态信息。在每个时隙链路结果实现后，Q-GUARD从已实现的贝尔对构建每链路纯化成本表，使用Werner态等分规则分配每跳保真度目标，并利用段局部期望好吞吐量（EXG）指标在候选路径段之间进行选择，该指标联合考虑交换成功、纯化开销和资源可用性。我们还引入Q-GUARD-WS，一种扩展，利用每链路硬件质量估计在跳间非均匀分配纯化努力。在具有异构链路保真度和随机BBPSSW纯化的合成100节点拓扑上，Q-GUARD将4跳路径上的合格成功率从不到20%提高到超过85%，并在欧几里得距离上将合格服务半径相对于仅吞吐量和朴素纯化基线几乎翻倍，而Q-GUARD-WS在高硬件异质性下提供额外的吞吐量增益。