Researchers prove durability of quantum network

Cryptography is the practice of protecting information from third parties and has long been achieved by encrypting data with a set of complex mathematical algorithms; however, with the power of computers continuing to increase, it is becoming harder to make these algorithms watertight. Published in New Journal of Physics, the new study documents the longest ever deployment of a quantum key distribution (QKD) network and demonstrates its robustness and reliability when coupled with a real time telecommunications network. QKD is a process that enables two parties to share a secret key before using it to protect data they want to send over a network. The key is built up from a stream of photons and protects information by each photon being sent with a specific polarisation; vertical, horizontal and diagonal. As the photons arrive, they can be measured by randomly choosing which direction to measure them in. Sometimes the correct orientation will be chosen, other times it won't. The measurements are then shared using classical communication methods, but not mentioning the actual direction the photons were spinning in. Wrong measurements are discarded and the correct ones are used to encrypt secret data. QKD works in such a way that if a third party tries to get hold of the key, the photons are destroyed when trying to measure them. While not a new phenomenon, to become more widespread its reliability needed to be thoroughly tested. The international network, created in collaboration with ID Quantique, installed in the Geneva metropolitan area and crossing over to the site of CERN in France, ran for more than one and a half years from the end of March 2009 to the beginning of January 2011. Co-author of the study, Dr Damien Stucki, said: "This experiment is a big step in the direction of a wider deployment of QKD in telecommunications networks. From a scientific point of view, the deployment of the quantum layer over a duration of 21 months with high reliability is very significant. The SwissQuantum network was very reliable, with the only interruptions coming from external problems, such as power cuts and air conditioning problems, not the QKD layer."