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Quantum Key Distribution (QKD) achieved over record 421 km

A collaboration between The Quantum Technologies Group at the University of Geneva, ID Quantique and Corning Incorporated has yielded a successful test of Quantum Key Distribution over a new record of 421 km.

Since its first experimental demonstration over 32 cm on an optical table, researchers have been pushing the boundaries of QKD over optical fibre. In a recent experiment, Alberto Boaron et al – backed by The Quantum Technologies Group at the University of Geneva, ID Quantique and Corning Incorporated – have extended the technology’s maximum range to 421 km.

This has surpassed the previous record of 404 km over fibre, and importantly has achieved key rates that were over 100 times higher than previous demonstrations over similar distances.

In an announcement posted on the University’s GAP-Quantum Technologies site, also featured by the American Physical Society, Boaron et al spoke about how they “push all the limits to new heights by optimising all parts of the QKD system including increasing the generation rate of the quantum states to reach 2.5 GHz and high-performance single-photon detectors developed in-house, which have very high efficiency and low noise.”

About the experiment

The research team relied on a quantum random number generator from IDQ’s Quantis range in combination the NIST SP800-90 recommended AES-CTR cryptographically secure pseudo random number generator.

The setup also included an ultralow-loss (ULL) optical fibre, electro-optical system with a high repetition rate and a low-noise detection unit based on superconducting nanowire single-photon detectors.

The result was a success thanks to the low number of dark counts that, when combined with a modification of a loss-tolerant protocol, achieved the best long-distance performance of any fibre-optic QKD to-date. A repetition range of 2.5 GHz is one of the highest ever used in QKD experiments and the system’s stability was proved by running it for over 24 hours.

Implications for Quantum Key Distribution

Since the original test over 32 cm, extending the maximum range of QKD has been a primary research goal. The inherent security, resistance to environmental perturbations and forward secrecy that quantum cryptography offers brings a host of benefits to the wider commercial sector, an area IDQ is already working in with the Cerberis3 QKD System, Clavis3 QKD Platform and Quantis range of quantum random number generators.

Commercial interest in the technology will continue to grow with the impending age of quantum computers, meaning that researchers will only be more enthusiastic to keep bettering the process in terms of both distance and efficiency.

“This is a great achievement. Reaching such transmission distances will help build quantum communication networks between cities, and this is key in a post-quantum era”, says Grégoire Ribordy, CEO ID Quantique. “IDQ is proud to maintain close ties with the academic world, especially with the Quantum Technologies group of the University of Geneva, from which the company started.”

Read the full Physical Review Letter here.

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