How to share Multipartite Entanglement in a Real-World Linear Network Connecting Two Metropoles

TL;DR

This paper explores how to efficiently generate and distribute high-fidelity multipartite entanglement over a real-world linear quantum network connecting Berlin and Frankfurt, focusing on practical constraints like noise, loss, and existing infrastructure.

Contribution

It demonstrates the feasibility of multipartite entanglement distribution in a realistic network using bipartite sources and quantum memories, analyzing performance and cryptographic applications.

Findings

Quantum memories improve entanglement distribution in lossy networks

Multipartite entanglement enables advanced cryptographic protocols

High-fidelity entanglement is achievable over long distances with current infrastructure

Abstract

The development of large-scale quantum communication networks necessitates the efficient distribution of quantum states to enable advanced cryptographic applications and distributed tasks. Multipartite entanglement is a key resource in many of these proposals, yet its generation is experimentally challenging, especially in noisy and lossy networks. While a substantial body of work focuses on the distribution of multi-partite entanglement in star-like topologies, practical implementations often rely on linear network structures constrained by existing infrastructure. In this work, we investigate the generation of high-fidelity multipartite entangled states in a realistic quantum network, leveraging the existing infrastructure of the Q-net-Q project - a real-world long-distance link connecting Berlin and Frankfurt via seven trusted relay nodes. Given that only bipartite entanglement sources are available in our setting and that the network is highly lossy, we explore the role of quantum memories in enhancing multi-partite entanglement distribution and identify key performance requirements. Furthermore, we analyze the feasibility and performance of cryptographic primitives - including (Anonymous) Conference Key Agreement and Quantum Secret Sharing - highlighting the scenarios where the use of multipartite entanglement yields clear advantages.