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Scientists have sent messages encrypted using principles of quantum physics over a 250km German commercial telecommunications network, in a milestone towards next-generation data security.
Toshiba Europe researchers have used so-called quantum key distribution (QKD) cryptography to transfer messages over traditional communication systems in a way that would be safe from hackers.
QKD exploits a phenomenon known as quantum entanglement. This refers to the way two subatomic particles’ characteristics can be related, even when separated by a vast distance.
By measuring data from one particle, you can infer information from the other. This allows the pair to serve as keys that can exchange coded messages but are unreadable to outsiders.
The researchers were able to send such quantum messages with standard optical fibre and without specialist ultra-low temperature cooling equipment usually used for these kind of communications. They claim this is the first time such an extensive simplified quantum information exchange has been run on a commercial telecoms network.
Robert Woodward, leader of the fibre QKD research team at Toshiba Europe, said their breakthrough “opens the door to many exciting quantum technologies transitioning out of the lab and into practical networks”.
Quantum networks’ potential resilience to hackers has sparked intense worldwide research interest including in China, which is developing a global satellite-based quantum communications system.
“A near-term practical implication of our findings is that much higher performance QKD is now possible using commercially viable components,” said Woodward, a co-author of a paper on the work published in Nature on Wednesday. “This paves the way for national and international scale deployment of quantum-secure communication infrastructure.”
Governments, companies and academic researchers are racing to improve information security because of emerging technological threats to encrypted sensitive data, such as bank transactions and health records. If efforts to develop powerful computers based on quantum theory succeed, they could crack the complex mathematical calculations on which decades-old cryptographic methods are based.
The novelty of the German experiment, spanning a 254km network between Frankfurt, Kirchfeld and Kehl, lies in the simplicity of the equipment it uses. It avoids relying on expensive and energy-intensive machinery to control temperature and detect the photon particles on which the quantum data transmission relies.
“This paper represents a significant advance for the deployment of secure quantum communication,” said Professor Sandrine Heutz, head of the department of materials at Imperial College London.
“The large-scale deployment of quantum communication relies on practical engineering approaches such as these, combining a focus on sustainability with secure communication over more than 250km.”
Other researchers said the use of a commercial telecoms network distinguished it from the specialist adaptations deployed in China’s extensive quantum communication work on Earth and via satellite.
Using less sophisticated equipment might involve some loss of communication quality, but it opened the way to building large quantum information systems with a variety of capabilities.
“Research teams and governments around the world are building quantum networks at scale, not only for secure communications but also for important day-to-day activities like navigation,” said James Millen, an experimental quantum scientist at King’s College London.
“While it is possible to build a quantum network using satellites, it is more cost-effective to use existing optical fibre infrastructure,” he added.
The use of existing systems creates a potential vulnerability for QKD-based technology through attacks on the infrastructure itself. But the nature of QKD means that any attempts at eavesdropping should be apparent to the parties to the information exchange.
