̽��ֱ�� of Cambridge - quantum cryptography

Researchers demonstrate the UK’s first long-distance ultra-secure communication over a quantum network

sc604 — Mon, 07 Apr 2025 23:38:58 +0000

̽��ֱ��team, from the Universities of Bristol and Cambridge, created the network, which uses standard fibreoptic infrastructure, but relies on a variety of quantum phenomena to enable ultra-secure data transfer.

̽��ֱ��network uses two types of quantum key distribution (QKD) schemes: ‘unhackable’ encryption keys hidden inside particles of light; and distributed entanglement: a phenomenon that causes quantum particles to be intrinsically linked.

̽��ֱ��researchers demonstrated the capabilities of the network via a live, quantum-secure video conference link, the transfer of encrypted medical data, and secure remote access to a distributed data centre. ̽��ֱ��data was successfully transmitted between Bristol and Cambridge – a fibre distance of over 410 kilometres.

This is the first time that a long-distance network, encompassing different quantum-secure technologies such as entanglement distribution, has been successfully demonstrated. ̽��ֱ��researchers presented their results at the 2025 Optical Fiber Communications Conference (OFC) in San Francisco.

Quantum communications offer unparalleled security advantages compared to classical telecommunications solutions. These technologies are immune against future cyber-attacks, even with quantum computers, which – once fully developed – will have the potential to break through even the strongest cryptographic methods currently in use.

In the past few years, researchers have been working to build and use quantum communication networks. China recently set up a massive network that covers 4,600 kilometres by connecting five cities using both fibreoptics and satellites. In Madrid, researchers created a smaller network with nine connection points that use different types of QKD to securely share information.

In 2019, researchers at Cambridge and Toshiba demonstrated a metro-scale quantum network operating at record key rates of millions of key bits per second. And in 2020, researchers in Bristol built a network that could share entanglement between multiple users. Similar quantum network trials have been demonstrated in Singapore, Italy and the USA.

Despite this progress, no one has built a large, long-distance network that can handle both types of QKD, entanglement distribution, and regular data transmission all at once, until now.

̽��ֱ��experiment 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 last decade by the same team, supported by 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,” said co-author Dr Rui Wang, Lecturer for Future Optical Networks in the Smart Internet Lab's High Performance Network Research Group at the ̽��ֱ�� of Bristol. “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.”

“This marks the culmination of more than ten years of work to design and build the UK Quantum Network,” said co-author Adrian Wonfor from Cambridge’s Department of Engineering. “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.”

“This is a significant step in delivering quantum security for the communications we all rely upon in our daily lives at a national scale,” said co-author Professor Richard Penty, also from Cambridge and who headed the Quantum Networks work package in the Quantum Communications Hub. “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.”

“This is an extraordinary achievement which highlights the UK’s world-class strengths in quantum networking technology,” said Gerald Buller, Director of the IQN Hub, based at Heriot-Watt ̽��ֱ��. “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.”

̽��ֱ��current UKQN covers two metropolitan quantum networks around Bristol and Cambridge, which are connected via a ‘backbone’ of four long-distance optical fibre links spanning 410 kilometres with three intermediate nodes.

̽��ֱ��network uses single-mode fibre over the EPSRC National Dark Fibre Facility (which provides dedicated fibre for research purposes), and low-loss optical switches allowing network reconfiguration of both classical and quantum signal traffic.

̽��ֱ��team will pursue this work further through a newly funded EPSRC project, the Integrated Quantum Networks Hub, whose vision is to establish quantum networks at all distance scales, from local networking of quantum processors to national-scale entanglement networks for quantum-safe communication, distributed computing and sensing, all the way to intercontinental networking via low-earth orbit satellites.

Reference:
R. Yang et al. ‘A UK Nationwide Heterogeneous Quantum Network.’ Paper presented at the 2025 Optical Fiber Communications Conference and Exhibition (OFC): https://www.ofcconference.org/en-us/home/schedule/

Researchers have successfully demonstrated the UK’s first long-distance ultra-secure transfer of data over a quantum communications network, including the UK’s first long-distance quantum-secured video call.

MR.Cole_Photographer via Getty Images

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Talking about a revolution: 25 years of BT and Cambridge

skbf2 — Fri, 14 Oct 2022 09:24:46 +0000

Cambridge and BT have been working together for more than 25 years developing new technologies, exploring human behaviour and considering how those two things come together to shape our world.

Ultra-secure form of virtual money proposed

sc604 — Tue, 07 May 2019 23:00:50 +0000

̽��ֱ��theoretical framework, dubbed ‘S-money’, could ensure completely unforgeable and secure authentication, and allow faster and more flexible responses than any existing financial technology, harnessing the combined power of quantum theory and relativity. In fact, it could conceivably make it possible to conduct commerce across the Solar System and beyond, without long time lags, although commerce on a galactic scale is a fanciful notion at this point.

Researchers aim to begin testing its practicality on a smaller, Earth-bound scale later this year. S-money requires very fast computations, but may be feasible with current computing technology. Details are published in the Proceedings of the Royal Society A.

“It’s a slightly different way of thinking about money: instead of something that we hold in our hands or in our bank accounts, money could be thought of as something that you need to get to a certain point in space and time, in response to data that’s coming from lots of other points in space and time,” said Professor Adrian Kent, from Cambridge’s Department of Applied Mathematics and Theoretical Physics, who authored the paper.

̽��ֱ��framework developed by Professor Kent can be thought of as secure virtual tokens generated by communications between various points on a financial network, which respond flexibly to real-time data across the world and ‘materialise’ so that they can be used at the optimal place and time. It allows users to respond to events faster than familiar types of money, both physical and digital, which follow definite paths through space.

̽��ֱ��tokens can be securely traded without delays for cross-checking or verification across the network, while eliminating any risk of double-trading. One way of guaranteeing this uses the power of quantum theory, the physics of the subatomic world that Einstein famously dismissed as “spooky”.

̽��ֱ��user’s privacy is maintained by protocols such as bit commitment, which is a mathematical version of a securely sealed envelope. Data are delivered from party A to party B in a locked state that cannot be changed once sent and can only be revealed when party A provides the key – with security guaranteed, even if either of the parties tries to cheat.

Other researchers have developed theoretical frameworks for ‘quantum’ money, which is based on the strange behaviour of particles at the subatomic scale. While using quantum money for real world transactions may be possible someday, according to Kent, at the moment it is technologically impossible to keep quantum money secure for any appreciable length of time.

“Quantum money, insofar as it’s currently understood, would require long-term storage of quantum states, or quantum memory,” said Kent. “This would require an awful lot of resources, and even if it becomes technologically feasible, it may be incredibly expensive.”

While the S-money system requires large computational overhead, it may be feasible with current computer technology. Later this year, Kent and his colleagues hope to conduct some proof-of-concept testing working with the Quantum Communications Hub, of which the ̽��ֱ�� of Cambridge is a partner institution. They hope to understand how fast S-money can be issued and spent on a network using off-the-shelf technologies.

“We’re trying to understand the practicalities and understand the advantages and disadvantages,” said Kent.

Patent applications for the research have been filed by Cambridge Enterprise, the ̽��ֱ��’s commercialisation arm.

Reference:
Adrian Kent. ‘S-money: virtual tokens for a relativistic economy.’ Proceedings of the Royal Society A (2019). DOI: 10.1098/rspa.2019.0170

A new type of money that allows users to make decisions based on information arriving at different locations and times, and that could also protect against attacks from quantum computers, has been proposed by a researcher at the ̽��ֱ�� of Cambridge.

Instead of something that we hold in our hands or in our bank accounts, money could be thought of as something that you need to get to a certain point in space and time

Adrian Kent

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Fiber Optic Cable Blue

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. Images, including our videos, are Copyright © ̽��ֱ�� of Cambridge and licensors/contributors as identified. All rights reserved. We make our image and video content available in a number of ways – as here, on our main website under its Terms and conditions, and on a range of channels including social media that permit your use and sharing of our content under their respective Terms.

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Laser technique promises super-fast and super-secure quantum cryptography

sc604 — Mon, 04 Apr 2016 15:06:38 +0000

Researchers have developed a new method to overcome one of the main issues in implementing a quantum cryptography system, raising the prospect of a useable ‘unbreakable’ method for sending sensitive information hidden inside particles of light.

By ‘seeding’ one laser beam inside another, the researchers, from the ̽��ֱ�� of Cambridge and Toshiba Research Europe, have demonstrated that it is possible to distribute encryption keys at rates between two and six orders of magnitude higher than earlier attempts at a real-world quantum cryptography system. ̽��ֱ��results are reported in the journal Nature Photonics.

Encryption is a vital part of modern life, enabling sensitive information to be shared securely. In conventional cryptography, the sender and receiver of a particular piece of information decide the encryption code, or key, up front, so that only those with the key can decrypt the information. But as computers get faster and more powerful, encryption codes get easier to break.

Quantum cryptography promises ‘unbreakable’ security by hiding information in particles of light, or photons, emitted from lasers. In this form of cryptography, quantum mechanics are used to randomly generate a key. ̽��ֱ��sender, who is normally designated as Alice, sends the key via polarised photons, which are sent in different directions. ̽��ֱ��receiver, normally designated as Bob, uses photon detectors to measure which direction the photons are polarised, and the detectors translate the photons into bits, which, assuming Bob has used the correct photon detectors in the correct order, will give him the key.

̽��ֱ��strength of quantum cryptography is that if an attacker tries to intercept Alice and Bob’s message, the key itself changes, due to the properties of quantum mechanics. Since it was first proposed in the 1980s, quantum cryptography has promised the possibility of unbreakable security. “In theory, the attacker could have all of the power possible under the laws of physics, but they still wouldn’t be able to crack the code,” said the paper’s first author Lucian Comandar, a PhD student at Cambridge’s Department of Engineering and Toshiba’s Cambridge Research Laboratory.

However, issues with quantum cryptography arise when trying to construct a useable system. In reality, it is a back and forth game: inventive attacks targeting different components of the system are constantly being developed, and countermeasures to foil attacks are constantly being developed in response.

̽��ֱ��components that are most frequently attacked by hackers are the photon detectors, due to their high sensitivity and complex design – it is usually the most complex components that are the most vulnerable. As a response to attacks on the detectors, researchers developed a new quantum cryptography protocol known as measurement-device-independent quantum key distribution (MDI-QKD).

In this method, instead of each having a detector, Alice and Bob send their photons to a central node, referred to as Charlie. Charlie lets the photons pass through a beam splitter and measures them. ̽��ֱ��results can disclose the correlation between the bits, but not disclose their values, which remain secret. In this set-up, even if Charlie tries to cheat, the information will remain secure.

MDI-QKD has been experimentally demonstrated, but the rates at which information can be sent are too slow for real-world application, mostly due to the difficulty in creating indistinguishable particles from different lasers. To make it work, the laser pulses sent through Charlie’s beam splitter need to be (relatively) long, restricting rates to a few hundred bits per second (bps) or less.

̽��ֱ��method developed by the Cambridge researchers overcomes the problem by using a technique known as pulsed laser seeding, in which one laser beam injects photons into another. This makes the laser pulses more visible to Charlie by reducing the amount of ‘time jitter’ in the pulses, so that much shorter pulses can be used. Pulsed laser seeding is also able to randomly change the phase of the laser beam at very high rates. ̽��ֱ��result of using this technique in a MDI-QKD setup would enable rates as high as 1 megabit per second, representing an improvement of two to six orders of magnitude over previous efforts.

“This protocol gives us the highest possible degree of security at very high clock rates,” said Comandar. “It could point the way to a practical implementation of quantum cryptography.”

Reference:
L.C. Comandar et al. ‘Quantum key distribution without detector vulnerabilities using optically seeded lasers.’ Nature Photonics (2016). DOI: 10.1038/nphoton.2016.50

A new method of implementing an ‘unbreakable’ quantum cryptographic system is able to transmit information at rates more than ten times faster than previous attempts.

This protocol gives us the highest possible degree of security at very high clock rates

Lucian Comandar

Depiction of indistinguishable photons leaving through the same output port of a beam splitter

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