Quantum Keys Transmitted Over Record-Breaking 404 km

404 is no error, but the distance in kilometers that scientists have successfully transmitted quantum information over a optical fiber network.

AsianScientist (Nov. 29, 2016) – Chinese researchers have set a new world record in quantum communications, securely transmitting information over a distance of 404 km. Their results have been published in Physical Review Letters.

Encryption is critical in many aspects of modern life, however, perfectly secure communication can only be achieved using the strong correlations, or entanglement, between quantum objects. Quantum key distribution (QKD) makes it possible for two distant users to share a key with unconditional security. However, existing protocols for measurement device-independent QKD only work up to a maximum distance of less than 200km, limiting its practical application.

In the present study, a team of researchers led by Professor Pan Jianwei at the University of Science and Technology of China used ultralow-loss optical fibers to transmit photons over distances of 102 to 404 km. To prevent eavesdropping attacks, they used an optimized four-intensity decoy-state method that sends out decoy pulses of light.

For each length, the researchers also determined the maximum speed by which cryptographic keys could be securely distributed. Compared with earlier experiments, they demonstrated a 500-fold increase in speed, reaching a key-distribution rate that would be sufficient to ensure encrypted voice transmission by telephone.

This record-breaking implementation of the MDIQKD method not only provides a new distance record for both MDIQKD and all types of QKD systems but also, more significantly, achieves a distance that the traditional Bennett-Brassard 1984 QKD would not be able to achieve with the same detection devices even with ideal single-photon sources. This work represents a significant step toward proving and developing feasible long-distance QKD.

The article can be found at: Yin et al. (2016) Measurement-Device-Independent Quantum Key Distribution Over a 404 km Optical Fiber.


Source: Chinese Academy of Sciences.
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