FENDI: Toward High-Fidelity Entanglement Distribution in the Quantum Internet

TL;DR

This paper characterizes the fundamental trade-off between throughput and entanglement quality in quantum networks, providing a polynomial-time approximation scheme for optimizing worst-case fidelity under expected entanglement distribution rate constraints.

Contribution

It introduces a polynomial-time approximation scheme for worst-case fidelity in quantum networks, addressing an NP-hard problem and guiding network design.

Findings

The protocol achieves near-optimal performance within the characterized bounds.

Simulations demonstrate the protocol's effectiveness over existing methods.

The approach provides fundamental bounds on quantum network performance.

Abstract

A quantum network distributes quantum entanglements between remote nodes, and is key to many applications in secure communication, quantum sensing and distributed quantum computing. This paper explores the fundamental trade-off between the throughput and the quality of entanglement distribution in a multi-hop quantum repeater network. Compared to existing work which aims to heuristically maximize the entanglement distribution rate (EDR) and/or entanglement fidelity, our goal is to characterize the maximum achievable worst-case fidelity, while satisfying a bound on the maximum achievable expected EDR between an arbitrary pair of quantum nodes. This characterization will provide fundamental bounds on the achievable performance region of a quantum network, which can assist with the design of quantum network topology, protocols and applications. However, the task is highly non-trivial and is NP-hard as we shall prove. Our main contribution is a fully polynomial-time approximation scheme to approximate the achievable worst-case fidelity subject to a strict expected EDR bound, combining an optimal fidelity-agnostic EDR-maximizing formulation and a worst-case isotropic noise model. The EDR and fidelity guarantees can be implemented by a post-selection-and-storage protocol with quantum memories. By developing a discrete-time quantum network simulator, we conduct simulations to show the characterized performance region (the approximate Pareto frontier) of a network, and demonstrate that the designed protocol can achieve the performance region while existing protocols exhibit a substantial gap.