Researchers from the Universities of Bristol and Cambridge have successfully demonstrated the UK’s first long-distance ultra-secure data transfer over a quantum communications network, as well as the first long-distance quantum-secured video call.
The researchers designed the network, which uses ordinary fibreoptic infrastructure but relies on a range of quantum phenomena to enable ultra-secure data transit.
The network employs two forms of quantum key distribution (QKD) schemes: ‘unhackable’ encryption keys hidden inside light particles and distributed entanglement, a phenomenon that allows quantum particles to be naturally connected.
The researchers proved the network's capabilities using a live, quantum-secure video conferencing link, encrypted medical data transfer, and secure remote access to a distributed data center. The data was successfully transported between Bristol and Cambridge, a fiber distance of almost 410 km.
This is the first practical demonstration of a long-distance network including various quantum-secure technologies such as entanglement distribution. The researchers presented their findings at the 2025 Optical Fiber Communications Conference (OFC) in San Francisco.
Quantum communications provide unrivaled security advantages over traditional telecommunications methods. These technologies are resistant to future cyber-attacks, including quantum computers, which, once fully developed, will have the ability to break through even the most advanced cryptographic methods currently in use.
In recent years, researchers have been working on developing and deploying quantum communication networks. China recently established a vast network spanning 4,600 kilometers, connecting five cities using fibreoptics and satellites. In Madrid, researchers built a smaller network with nine connection points that employ several types of QKD to securely share data.
In 2019, researchers at Cambridge and Toshiba demonstrated a metro-scale quantum network with record key rates of millions of key bits per second. In 2020, researchers in Bristol developed a network that could share entanglement across numerous users. Similar quantum network trials have been conducted in Singapore, Italy, and the United States.
Despite this advancement, no one has yet developed a big, long-distance network capable of simultaneously handling both types of QKD, entanglement distribution, and regular data transmission.
The experiment demonstrates the ability of quantum networks to accept several quantum-secure techniques while also supporting traditional communications infrastructure. It was carried out on the UK's Quantum Network (UKQN), which was created over the last decade by the same team with funding from the Engineering and Physical Sciences Research Council (EPSRC) and as part of the Quantum Communications Hub project.
This is a crucial step toward building a quantum-secured future for our communities and society. More importantly, it lays the foundation for a large-scale quantum internet—connecting quantum nodes and devices through entanglement and teleportation on a global scale.
Dr Rui Wang, Study Co-Author and Lecturer for Future Optical Networks, Smart Internet Lab's High Performance Network Research Group, University of Bristol
“This marks the culmination of more than ten years of work to design and build the UK Quantum Network. Not only does it demonstrate the use of multiple quantum communications technologies, but also the secure key management systems required to allow seamless end-to-end encryption between us,” added study co-author Adrian Wonfor from Cambridge’s Department of Engineering.
“This is a significant step in delivering quantum security for the communications we all rely upon in our daily lives at a national scale. It would not have been possible without the close collaboration of the two teams at Cambridge and Bristol, the support of our industrial partners Toshiba, BT, Adtran and Cisco, and our funders at UKRI,” study co-author Professor Richard Penty, also from Cambridge and who headed the Quantum Networks work package in the Quantum Communications Hub added.
Gerald Buller, Director of the IQN Hub, based at Heriot-Watt University, stated, “This is an extraordinary achievement which highlights the UK’s world-class strengths in quantum networking technology. This exciting demonstration is precisely the kind of work the Integrated Quantum Networks Hub will support over the coming years, developing the technologies, protocols and standards which will establish a resilient, future-proof, national quantum communications infrastructure.”
The current UKQN encompasses two metropolitan quantum networks in Bristol and Cambridge, which are connected by a ‘backbone’ of four long-distance optical fiber lines spanning 410 km and three intermediate nodes.
The network employs single-mode fiber via the EPSRC National Dark Fiber Facility (which offers dedicated fiber for research purposes) and low-loss optical switches that enable network reconfiguration of both classical and quantum signal traffic.
With support from a newly funded EPSRC project known as the Integrated Quantum Networks Hub, the team will build on this work. The project's goal is to create quantum networks at all distance scales, from intercontinental networking via low-Earth orbit satellites to national-scale entanglement networks for quantum-safe communication, distributed computing, and sensing.