• The UK universities of Bristol and Cambridge have been collaborating on quantum-safe networking developments
• They have achieved live, quantum-secure transfer of encrypted medical data, secure remote access to a distributed datacentre and the world’s first long-distance quantum secured video call.
• It’s the first time a long-distance network using different quantum-secure technologies (including entanglement) has been successfully demonstrated.
• The work is the foundation for a large-scale quantum internet that could connect quantum nodes and devices through entanglement and teleportation on a global scale

In what is being described as “remarkable achievement”, research scientists at two renowned British universities, Bristol and Cambridge, have demonstrated the UK’s first ultra-secure transfer of data over a quantum communications network. The demo, announced by the universities in this press release, also included the country’s first long-distance quantum-secured video call. 

The teams built the network using standard fibre cable infrastructure tweaked to provide massively secure data transfer via the use of two different quantum key distribution (QKD) methodologies. In essence, the system ensures complete “unhackability” by encasing encryption keys in individual photons, the elementary particles of light. Photons have neither mass nor charge and, as such, are an example of a quantum – in this case a discrete and quantifiable packet of energy or matter – that represent the entire spectrum of electromagnetic radiation.  

The demonstration also exploited distributed entanglement, the phenomenon by which quantum particles are intrinsically linked and share the same beginning, the same existence and same end, no matter how far apart they may be – perhaps in a UK university laboratory or billions of light years away on the other side of the universe. When one of the properties of one entangled particle is measured, the properties of the other entangled particle becomes instantly apparent, because they are intrinsically related.

The influence of one entangled particle on the other is what Einstein first described in 1947 as “spooky action at a distance” – spooky because, as far as we know, it is impossible to exceed the speed of light, yet entanglement between remote qubits (the fundamental unit of information in quantum computing) allows quantum information to be transmitted instantaneously by teleportation. At the heart of that spooky theory is ‘spin’. Most particles have an attribute called ‘spin’ that is measured either as ‘up’ or ‘down’: Until the spin of a particle is measured, it exists in a superposition of both ‘spin up’ and ‘spin down’ simultaneously. Yes, it’s Schrödinger again – at an elementary particle level, his theoretical cat is simultaneously alive and dead – until, that is, it is looked at it or interfered with in in any way, then it is either alive or dead, depending on the collapse of the wave form that supported the quantum superposition. 

However, although the speed of quantum communication might seem to be faster than light, it isn’t because, according to today’s physics, it is not possible to use entanglement to send data faster than light because it is not possible to know the state of the entangled particle until it is measured. When the measurement occurs, the quantum state of the spin ‘collapses’ into either up or down, instantaneously collapsing the other particle into the opposite spin. This seems to suggest that the particles communicate with each other through some means faster than the speed of light, even though the speed of light is apparently immutable. Quite a conundrum. 

Research into these and other quantum phenomena is underway all over the planet, not least because it seems likely that entanglement has enormous potential for applications in quantum computing, quantum cryptography and other fields, such as quantum sensing. 

The Bristol and Cambridge teams demonstrated the capabilities of their network via a live, quantum-secure video conference link, the transfer of encrypted medical data, and secure remote access to a distributed datacentre. The data was successfully transmitted between Bristol and Cambridge, a fibre distance of more than 410km. It was the first time a long-distance network using different quantum-secure technologies, such as entanglement distribution, has been successfully demonstrated. The full results of the trial were recently presented in a paper at the recent 2025 Optical Fiber Communications Conference (OFC25) in San Francisco.

Defence against ‘harvest-now, decrypt-later’ threat in the post-quantum world 

Quantum computers (QC) are in their earliest infancy and the models we have now are subject to interference in a myriad of forms, including vibration, temperature changes, insufficiently controlled electromagnetic fields, radiation and many other phenomena that can (and do) disrupt a quantum computer’s very fragile quantum states and cause them to decohere and bring computing operations to a stop. It will be years yet before they become robust enough to work for more than a minute or so before grinding to a halt.

To the global public, the very concept of quantum computing remains an abstruse mystery and a technology that is regarded as being of minimal interest with little impact on day-to-day life. However, quantum technologies are a wide field of research and the developments now taking place in quantum security will be of direct relevance to just about everyone on earth, whether they are aware of it or not, because quantum computers are a massive potential threat to the privacy, security and integrity of all digital communications and data.

Once quantum computers reach a sufficiently advanced state, they will be able to crack even the best of currently unbreakable data encryption enabled by today’s ‘classical’ computers. That’s why the race is on to develop post-quantum-based defence strategies to negate the proliferation of ‘harvest-now, decrypt-later’ programs whereby various nation states and criminal gangs are acquiring as much securely encrypted data as they possibly can. They do this in the knowledge that after “Q-Day” (or Y2Q) – the unknown but inevitable date that cryptographically relevant quantum computers (CRQCs) will be able to decrypt public (and other) encryption systems that rely on prime numbers for their strength – any encrypted data harvested now will be accessible – see Could ‘Q-Day’ be an existential threat to digital economies?

There are two main categories of quantum security: On one side is the development of new algorithms that run on today’s conventional hardware to protect data from future quantum attacks; and on the other is the use of purely quantum communications to make it impossible to decode encryption keys exchanged over networks. 

Post-quantum cryptography (PQC) algorithms apply today’s understanding of quantum computing to devise encryption keys that would at least be very difficult and take a long time for even a quantum computer to crack. However, in the end, a quantum computer would be able to decode the data but it is hoped that by the time that might happen even stronger new algorithms will be available and used to stop the process of the next-generation devices cracking accessing protected data. That option comes with evident but, perhaps, quantifiable inherent risk. 

Meanwhile, quantum key distribution (QKD) also comes in two flavours – discrete-variable (DV) QKD and continuous-variable (CV) QKD. Both distribute secret keys securely, but DV-QKD uses individual photons and discrete values, while CV-QKD uses coherent states and continuous variables by exploiting the characteristics enabled in quantum entanglement whereby two parties can produce a shared random secret key known only to them. Should an eavesdropper attempt to intercept any information transmitted in a QKD quantum state, it would be instantly detected and – this is the strange, perhaps even once again spooky, part – the message would not have been sent in the first place!

The UK’s quantum rich long-distance network  

For some years now, research teams across the world have been building experimental quantum comms systems. For example, China has set up a 4,600km network that connects five cities via both fibre optics and satellites. Meanwhile, in Madrid, Spain, scientists have deployed a smaller network but with nine connection points that use different types of QKD to guarantee the security of shared information. Quantum network trials have also taken place in Italy, Singapore, the US and other countries, but to date, no-one has constructed a long-distance network that can handle both types of QKD, entanglement distribution, and regular data transmission all at once – until now.

The UK experiment hosted by the universities of Bristol and Cambridge demonstrates the potential of quantum networks to accommodate different quantum-secure approaches simultaneously with classical communications infrastructure. It was carried out using the UK’s Quantum Network (UKQN), established over the past decade by the same teams. That effort received funding support from the Engineering and Physical Sciences Research Council (EPSRC), as part of the Quantum Communications Hub, a major collaboration between various universities, numerous private sector companies and public sector bodies brought together to accelerate the development and commercialisation of quantum secure communications technologies and services.

Dr Rui Wang, a lecturer in future optical networks in the Smart Internet Lab’s High Performance Network Research Group at the University of Bristol, and co-author of the paper presented at OFC25, commented: “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.”

His colleague for the research, Adrian Wonfor of Cambridge’s Department of Engineering, and also a co-author of the paper describing the breakthrough, added: “This marks the culmination of more than 10 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.”

A third co-author, Professor Richard Penty of Cambridge University, who manages the quantum networks work team at the Quantum Communications Hub, stated: “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.” (UK Research and Innovation, or UKRI, is a UK government body that allocates research and innovation funding, which in turn comes from the science budget of the UK’s Department for Science, Innovation and Technology.)

Gerald Buller, director of the Integrated Quantum Networks research hub (IQN) at Herriot-Watt University, a public research university in Edinburgh, Scotland, summed-up the Bristol/Cambridge work thus: “This is an extraordinary achievement, which highlights the UK’s world-class strengths in quantum networking technology. This 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.”

To keep up to date with the latest quantum-safe networking developments, check out TelecomTV’s dedicated quantum technology page.

– Martyn Warwick, Editor in Chief, TelecomTV