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Breakthrough for quantum key distribution networks

Technology News |
By Nick Flaherty

An international team of researchers has developed the first distributed QKD network for sharing quantum keys in a breakthrough design.

So far, quantum key distribution has been point to point, even over satellites, but this limits the use in a network. The multiplexed photonic quantum key distribution (QKD) system, published in Science Advances, supports eight users and can be easily scaled up.

“This represents a massive breakthrough and makes the quantum internet a much more realistic proposition,” said Dr Siddarth Joshi, who headed the project at the Quantum Engineering Technology (QET) Labs at the University of Bristol, UK. “Until now, building a quantum network has entailed huge cost, time, and resource, as well as often compromising on its security which defeats the whole purpose.”

“Our solution is scalable, relatively cheap and, most important of all, impregnable. That means it’s an exciting game changer and paves the way for much more rapid development and widespread rollout of this technology,” he said.

Photonic QKD systems use entangled photons to ensure an encryption key is not intercepted.

“Until now efforts to expand the network have involved vast infrastructure and a system which requires the creation of another transmitter and receiver for every additional user. Sharing messages in this way, known as trusted nodes, is just not good enough because it uses so much extra hardware which could leak and would no longer be totally secure.”

The team includes researchers from the UK’s  University of Leeds, Croatia’s Ruder Boskovic Institute (RBI) in Zagreb, Austria’s Institute for Quantum Optics and Quantum Information (IQOQI), in Vienna, and China’s National University of Defence Technology (NUDT) in Changsha.

The team used multiplexing to develop an eight user system with eight transceivers, rather than the 56 that would previously be needed for each user to have a point to point link. The receivers were connected to optical fibres via different locations across Bristol and the ability to transmit messages via quantum communication was tested using the city’s existing optical fibre network.

“Besides being completely secure, the beauty of this new technique is its streamline agility, which requires minimal hardware because it integrates with existing technology,” said Joshi.

The network was created within months for less than £300,000, enabling secure networks for a fraction of the cost today. The system also features traffic management, delivering better network control which allows, for instance, certain users to be prioritised with a faster connection.

“With these economies of scale, the prospect of a quantum internet for universal usage is much less far-fetched. We have proved the concept and by further refining our multiplexing methods to optimise and share resources in the network, we could be looking at serving not just hundreds or thousands, but potentially millions of users in the not too distant future,” said Joshi.

“The ramifications of the COVID-19 pandemic have not only shown importance and potential of the internet, and our growing dependence on it, but also how its absolute security is paramount. Multiplexing entanglement could hold the vital key to making this security a much-needed reality.”  

The research received funding from the Quantum Communications Hubs of the Engineering and Physical Science Research Council (EPSRC), Ministry of Science and Education (MSE) of Croatia, and the Austrian Research Promotion Agency (FFG).

bristol.ac.uk/qet-labs/

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