Fidelity-Age-Aware Scheduling in Quantum Repeater Networks

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.

💡 Research Summary

The paper addresses a critical yet under‑explored aspect of quantum repeater networks: the freshness of entanglement, i.e., how long it has been since a usable Bell pair—one whose fidelity exceeds a required threshold—was last delivered to a user. To quantify this, the authors introduce the Fidelity‑Age (FA) metric, defined as the number of time slots elapsed since the most recent successful delivery of a high‑fidelity entangled pair. By treating each successful delivery as a renewal event, they derive a renewal identity that links the long‑run average FA to the first and second moments of the inter‑delivery interval τ:  (\bar A = \Delta , \mathbb{E}