Fidelity-Guaranteed Entanglement Routing with Distributed Purification Planning

TL;DR

Q-GUARD is a distributed entanglement routing algorithm that guarantees fidelity thresholds for quantum networks, significantly improving success rates and service radius over existing methods.

Contribution

The paper introduces Q-GUARD, a novel distributed protocol for fidelity-guaranteed entanglement routing, including an extension that optimizes purification efforts based on hardware quality.

Findings

Q-GUARD increases qualified success rate from under 20% to over 85% for 4-hop paths.

Q-GUARD nearly doubles the qualified service radius compared to baseline methods.

Q-GUARD-WS further improves throughput under hardware heterogeneity.

Abstract

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.