Metropolitan all-pass and inter-city quantum communication network

TL;DR

This paper reports the successful demonstration of a metropolitan all-pass quantum communication network with four nodes and an inter-city link, enabling secure quantum key distribution and real-time voice communication.

Contribution

It introduces integrated QKD terminals, an optical switching module for arbitrary connectivity, and a trusted relay architecture for inter-city links, advancing practical quantum networks.

Findings

Operational quantum network with 4 nodes and inter-city link

Real-time voice communication using one-time pad encryption

Automated, stable, and scalable quantum communication system

Abstract

We have demonstrated a metropolitan all-pass quantum communication network in field fiber for four nodes. Any two nodes of them can be connected in the network to perform quantum key distribution (QKD). An optical switching module is presented that enables arbitrary 2-connectivity among output ports. Integrated QKD terminals are worked out, which can operate either as a transmitter, a receiver, or even both at the same time. Furthermore, an additional link in another city of 60 km fiber (up to 130 km) is seamless integrated into this network based on a trusted relay architecture. On all the links, we have implemented protocol of decoy state scheme. All of necessary electrical hardware, synchronization, feedback control, network software, execution of QKD protocols are made by tailored designing, which allow a completely automatical and stable running. Our system has been put into operation in Hefei in August 2009, and publicly demonstrated during an evaluation conference on quantum network organized by the Chinese Academy of Sciences on August 29, 2009. Real-time voice telephone with one-time pad encoding between any two of the five nodes (four all-pass nodes plus one additional node through relay) is successfully established in the network within 60km.