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Scientists achieved quantum communication over fiber more than 600 kilometers long

A new study extends the range of fiber-based quantum communications beyond 600km for the first time. Scientists implemented a new signal stabilization technique and used the twin-field quantum key distribution (QKD) protocol.

Mirko Pittaluga from Toshiba Europe Limited and the University of Leeds said, “This will allow us to build national and continental scale fiber networks connecting major metropolitan areas. Together with satellite links, we can now envisage truly global quantum networks.”

Quantum key distribution allows two people in different places to establish a common secret string of bits by exchanging photons typically transmitted over an optical fiber. Achieving transmission over long distances has a fundamental limit to how far the photons can travel before the signal degrades due to scattering or absorption.

Optical repeaters solve this problem for traditional fiber optic data transmission; however, creating a reliable repeater for quantum encoded information is challenging.

The newly developed twin-field QKD protocol has potentially overcome the distance limitation, but it requires fibers to be used over long distances.

In this study, scientists created an experimental setup and phase stabilization technique for twin-field QKD. The stabilization approach, based on wavelength division multiplexing, uses two optical reference signals at different wavelengths to minimize the phase fluctuations over long distances.

Scientists demonstrated that the new approach could accomplish repeater-like performance while tolerating optical losses beyond the traditional limit of 100 dB over a 605-kilometer-long quantum channel. They were also able to test different variants of the TF-QKD protocol. The new stabilization approach could also be applied to other quantum communication protocols and applications, such as improving interferometric telescopes.

These results were obtained in a laboratory environment, but recently obtained experimental evidence confirms the applicability of this stabilization technique on field-deployed fibers. The team is now working to perform a field trial test.

Mirko Pittaluga from Toshiba Europe Limited and the University of Leeds, both in the UK, will present the research at the Frontiers in Optics + Laser Science Conference (FiO LS) all-virtual meeting, 01 – 04 November 2021.

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