Free-space multi-user quantum network with high key rate

TL;DR

This paper demonstrates a scalable free-space quantum network with twelve channels and high key rates, enabling secure multi-user quantum communication without active switching.

Contribution

It introduces a passive, scalable free-space multiplexing architecture using a single entanglement source for multi-user quantum networks.

Findings

Achieved record coincidence rates over 3×10^4 s^-1 between nodes.

Sifted key rate exceeds 400 kbps per pair.

Network is fully passive, scalable, and compatible with fibre integration.

Abstract

Emergent quantum networks are the essential ingredient for securely connecting multiple users worldwide, extensively deployed in both fibre and free-space. An essential element is the multiplexing of entanglement to multiple users, overcoming the peer-to-peer restriction of quantum key distribution (QKD), so far successfully shown in fibre-based architectures. Here, we demonstrate a free-space quantum space division multiplexing architecture using just one entanglement source to realise a fully connected twelve-channel quantum network for seamless QKD connections between six users. The network achieves record coincidence rates exceeding $3 \times 10^{4}$ s$^{-1}$ between any pair of nodes on the network, for sifted key rate of over 400 kbps. Our approach overcomes the active switching hurdle that has hindered the free-space deployment of quantum multiplexing, is fully passive, easily scalable to more nodes and compatible with fibre-based integration, thus opening a new path to scalable and resource-efficient quantum networks that utilise free-space links.