Quantum repeater networks distribute entanglement over long distances but must balance fidelity, delay, and resource contention. Prior work optimized throughput and end-to-end fidelity, yet little attention has been paid to the freshness of entanglement-the time since a usable Bell pair was last delivered. We introduce the Fidelity-Age (FA) metric, which measures this interval for states whose fidelity exceeds a threshold Fmin. A renewal formulation links slot-level success probability to long-run average FA, enabling a stochastic control problem that minimizes FA under budget and memory limits. Two lightweight schedulers, FA-THR and FA-INDEX, approximate Lyapunov-drift-optimal control. Simulations on slotted repeater grids show that FA-aware scheduling preserves throughput while reducing extreme-age events by up to two orders of magnitude. Fidelity-Age thus provides a tractable, physically grounded metric for reliable and timely entanglement delivery in quantum networks.

翻译：量子中继网络可在长距离上分发纠缠态，但必须权衡保真度、时延和资源争用。先前的研究优化了吞吐量和端到端保真度，然而很少关注纠缠态的时效性——即自上一次成功交付可用贝尔对以来所经过的时间。我们引入了保真度-时效（FA）度量，用于衡量保真度超过阈值 Fmin 的量子态所经历的该时间间隔。通过更新过程建模，将时隙级成功概率与长期平均 FA 联系起来，从而构建了一个在预算和内存限制下最小化 FA 的随机控制问题。两种轻量级调度器 FA-THR 和 FA-INDEX 实现了对李雅普诺夫漂移最优控制的近似。在分时隙中继网格上的仿真表明，FA 感知调度在保持吞吐量的同时，能将极端时效事件减少高达两个数量级。因此，保真度-时效为量子网络中可靠且及时的纠缠态分发提供了一个可处理且基于物理实际的度量标准。