Age of Entanglement in Satellite Repeater Chains with Intermittent Availability

TL;DR

This paper introduces the Age of Entanglement (AoE), a new metric for quantifying the freshness of quantum entanglement in satellite-based repeater networks, and develops optimal control policies to minimize AoE under stochastic conditions.

Contribution

It extends classical Age of Information metrics to quantum networks, models a satellite-assisted repeater chain with probabilistic entanglement and decoherence, and derives AoE-optimal policies using Markov decision processes.

Findings

AoE effectively captures entanglement freshness in quantum networks.

Dynamic policies outperform simple entanglement generation strategies.

Decoherence and link intermittency significantly impact entanglement quality.

Abstract

Timely availability of high-fidelity entanglement is essential for emerging quantum networks. This paper introduces the Age of Entanglement (AoE) as a novel performance metric that captures the freshness of bipartite entanglement under continuous distribution in quantum repeater chains. AoE extends classical Age of Information (AoI)-based metrics to quantum networking by capturing storage, decoherence, and probabilistic entanglement generation and swapping. We study a satellite-assisted quantum repeater network in which entangled pairs are generated probabilistically, stored in quantum memories that suffer from decoherence, and combined to form end-to-end entangled links. Satellite-ground connectivity is intermittent and modeled as a two-state Markov chain. The resulting AoE minimization problem is formulated as an infinite-horizon Markov decision process (MDP), where control actions determine when to generate, store, or swap entangled pairs under stochastic link availability and memory degradation. Using relative value iteration, we characterize AoE-optimal policies and evaluate their performance numerically. Our results highlight the impact of decoherence, imperfect operations, and visibility dynamics, and show that the proposed dynamic policies significantly outperform swap-as-soon-as-possible and greedy entanglement generation strategies. Our results provide practical design and control guidelines for satellite-enabled quantum repeater chains supporting continuous entanglement distribution.