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Fibre network breakthrough has implications for data security

Researchers have devised a new protocol that they claim vastly extends the range of quantum key distribution over fibre networks

Computer scientists at Toshiba Research Europe’s Cambridge laboratory have made a breakthrough in quantum key distribution (QKD) that extends its transmission range over 500km of fibre, which could potentially enable sensitive data to be transmitted securely across intercity optical fibre networks.

QKD can be used to distribute the digital keys needed to protect sensitive data, and its security hinges on encoding each bit of the key on a single light particle, or photon.

Due to the laws of quantum mechanics, any attempt to read these photons will alter the encoding and introduce anomalies, which mean the secrecy of the key can therefore be guaranteed. QKD is therefore starting to be considered as an important tool for protecting critical information moving across communications infrastructure.

Toshiba’s scientists have now found a way to enhance key rate and transmission distance, meaning the final secure key rate can be several orders of magnitude greater than what is currently possible.

Up to now, the range of QKD has been limited because the photons can be scattered and lost from the fibre. Toshiba’s breakthrough, which is being called twin-field QKD, changes this.

Twin-field QKD differs from conventional QKD in that, whereas previously single photons were sent from one end of the fibre to the other end, twin-field QKD enables light pulses to be sent from both ends of the fibre to a central location.

Provided it is impossible to tell from which end the photon is coming, the technique therefore effectively doubles the transmission distance.

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While conventional QKD systems could be chained together to accomplish the same goal, this would require the waystations are in secure locations, but Toshiba said twin-field QKD needs no physical protection in the central location.

“Twin-field QKD would enable a bank in London to connect to a datacentre in Leeds via a link that can guarantee the secure transmission of customer data,” said Cambridge Research Laboratory assistant managing director, Andrew Shields.

“At present, the bank would have to place trust in intermediate nodes at secure, guarded locations between London and Leeds. Our breakthrough means that businesses can create a QKD network that connects their sites across the country for the first time.”

Tim Whitley, BT head of research and managing director of the telco’s Adastral Park R&D centre, said the breakthrough was an important step in the commercial development of quantum cryptography.

“Our secure quantum communication showcase at Adastral Park already demonstrates how financial institutions can secure links between offices and branches and off-site datacentres, which are prevalent throughout the financial sector,” he said.

“The application of twin-field QKD would extend that capability to sites anywhere in Europe, for example, making it possible to securely network an organisation at a national and international level.”

Toshiba’s research team hopes to develop the concept of twin-field QKD and refine it through further experimentation in the coming months.

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