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Secure quantum cryptography for real-world devices

Technology News |
By Andre Rousselot


European researchers have shown for the first time the use of quantum cryptography without the need for additional communications channels, opening up real world applications.

The research, led by the University of Oxford along with ETH Zurich, EPFL and the University of Geneva in Switzerland and CEA in France, demonstrated a complete quantum key distribution protocol immune to the vulnerabilities of physical devices.

Existing QKD implementations rely on communicating between trusted quantum devices and so might be vulnerable to quantum hacking by exploiting a mismatch between the quantum states or the measurements implemented and their theoretical modelling.

The newly demonstrated approach instead allows secure communication between devices without needing to know much about them.

“The real breakthrough here is that we were not just able to show that our quantum network had theoretically good enough performance to do this new kind of QKD, but that we were actually able to do it in practice and get all the way to distributing a shared secret key,” said Professor David Lucas from the University of Oxford. “Although originally designed for experiments in quantum computing, this shows the versatility of quantum networking for other applications.”

The experiment is based on high quality quantum entanglement using an optical fibre link generating entanglement between two trapped-ion qubits. This provided 95,628 key bits with device-independent security from 1.5 million entangled (Bell) pairs created during eight hours of run time with the information on the measurement results inaccessible to an eavesdropper.

Previous work on QKD already removed the assumption of limited computational power, but required the communicating parties to trust their quantum devices instead. The quantum key distribution demonstrated in this new research however, can guarantee privacy with only a few general assumptions about the physical apparatus used.

The foundation for this ‘device-independent’ scheme relies on the validity of quantum theory, and can be certified by measurement statistics observed during the experiment.

As well as working with international partners, the University of Oxford leads the Quantum Computing and Simulation (QCS) Hub, a collaboration between 17 UK universities which is part of a national programme focused on driving forward quantum technologies in the UK.

“It’s only been made possible because of sustained investment from the UK’s National Quantum Technology Programme, via the NQIT and QCS Hubs – it requires many years of development to achieve the level of technical sophistication needed for these experiments,” said Lucas.

Toshiba has demonstrated quantum key transfer over a QKD network and setup a business unit in Cambridge to manufacture systems.

www.oxford.ac.uk; www.nature.com/articles/s41586-022-04941-5

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