Fidelity-Guaranteed Entanglement Routing with Distributed Purification Planning

2026-04-30

AI Summary

This work addresses the challenge of achieving end-to-end Bell pair fidelity that meets application-specific thresholds in quantum networks, a problem often overlooked or managed via centralized control in existing routing schemes. The authors propose Q-GUARD, the first fully distributed routing protocol that provides on-demand fidelity guarantees: it exchanges link-state information only within k-hop neighborhoods, allocates per-hop fidelity targets based on the Werner state averaging rule, constructs purification cost tables, and selects paths using segment-local expected effective throughput (EXG). They further introduce Q-GUARD-WS, which non-uniformly allocates purification resources according to heterogeneous link hardware quality. Experiments on a 100-node heterogeneous network show that Q-GUARD increases the success rate of qualifying 4-hop paths from below 20% to over 85% and nearly doubles the service radius; Q-GUARD-WS further achieves significant throughput gains in highly heterogeneous scenarios.

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.

Problem

• entanglement routing
• fidelity guarantee
• distributed protocol
• quantum networks
• purification

Innovation

• entanglement routing
• fidelity guarantee
• distributed purification
• expected-goodput
• quantum network