Researchers working have successfully transmitted quantum bits (qubits) over 600 kilometers of optical fiber while managing to preserve the fragile quantum data encoded in the particles.
Led by Cambridge-based researchers from Toshiba, the project, published in the Nature Photonic journal, claims it will help facilitate the creation of the next-generation quantum internet.
The quantum internet is described as a network for quantum devices to exchange information, which among other benefits will enhance the security of the communications to essentially create an unhackable transmission, thanks to quantum cryptography.
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The distance-record breaking effort from researchers from Toshiba was made possible thanks to a new technology that stabilizes the environmental fluctuations in the fiber cables.
Dubbed dual band stabilization, the method involves sending two signals with different wavelengths, the first of which cancels out the rapidly varying fluctuations in the optical fiber, while the other makes finer adjustments to correct phase variations.
One of the first targets for the application of the new stabilization technique has been to ferry Quantum Key Distribution (QKD), which is a secure communication protocol that leverages security keys based on the laws of physics rather than mathematical complexity.
The researchers note that commercial QKD systems are limited to about 100-200 km of fiber. Toshiba proposed the Twin Field QKD protocol as a way to extend the distance in 2018, and finally with the dual band stabilization technique, its researchers have now implemented Twin Field QKD over hundreds of kilometers.
"With the new techniques we have developed, further extensions of the communication distance for QKD are still possible and our solutions can also be applied to other quantum communications protocols and applications,” said Mirko Pittaluga, one of the Toshiba researchers who worked on the project.
Reportedly, the company hopes the new technique can be used to create secure communication links between cities like London, Paris, Brussels, Amsterdam and Dublin.
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