Quantum Key Distribution moves out to 250 km

Editor's Note: In the world of communications and information, secrecy and security are paramount. Firms are always on the lookout for ways to make their security unbreakable, hence the field of cryptography. Using quantum key distribution essentially makes the sending and receiving of cryptographic keys unhackable, since any attempt to intercept the communication, because of the laws of quantum mechanics, results in that information being changed.

PhysOrg.com - July 21, 2009, by Lisa Zyga

Quantum key distribution (QKD) could be the next commercial success of quantum physics, and a recent study has taken the field a step closer to this reality. Researchers from the University of Geneva in Switzerland and Corning Incorporated in New York have demonstrated a new QKD prototype that can distribute quantum keys over a distance of 250 km in the lab, improving upon the previous record of 200 km. The scientists hope that the achievement will lead to the goal of distributing quantum keys over intercity distances of 300 km in the near future.

As the researchers explained, the purpose of QKD schemes is to distribute a secret quantum key between two distant locations with security relying on the laws of quantum physics. The idea of QKD was first proposed in 1984, and in 1992, scientists could distribute quantum keys over 32 cm, while the technology has improved from there. Despite these advances, the scientists say, the main challenge is still to achieve higher bit rates over longer distances.

To reach their new record of 250 km, the scientists made three significant improvements to their QKD technique. First, they developed a coherent one way (COW) protocol tailored specifically for quantum communication over optical fiber networks. In addition, they used an improved superconducting single-photon detector to decrease noise, as well as ultra low loss fibers made by Corning to minimize channel loss and improve the distribution rate.

By making these improvements, the physicists could distribute quantum keys in the lab at a rate of 15 bits per second over 250 km of optical fiber, or 6,000 bits per second over 100 km, with low error rates. The system is also fully automated, and can run for hours without human intervention.

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