Scientists and engineers have reported back on a project to use quantum cryptography in a real-time network.
Their international network, created in collaboration with ID Quantique and linking the Geneva metropolitan area to CERN in France, ran for more than one-and-a-half years from the end of March 2009 to the beginning of January 2011.
It's the longest ever deployment of a quantum key distribution (QKD) network and, says the team, shows its robustness and reliability.
The mathematical algorithms commonly used for encryption are becoming increasingly easy to crack as computing power improves.
Quantum key distribution (QKD) is widely seen as the amswer, as it allows two parties to share a secret key before using it to protect data sent over a network.
"In a theoretical scenario where Alice and Bob want to protect a piece of information with a quantum key, Alice would send a stream of photons to Bob with each one having a specific orientation, called polarisation: photons can 'spin' vertically, horizontally and diagonally," explain the researchers
"Bob would then attempt to measure the photons coming in by randomly choosing which direction to measure them in. Sometimes he will choose the correct orientation, other times he won't. Alice and Bob would then share the measurements using classical communication methods, simply stating if Bob was right or wrong, but not mentioning the actual direction the photons were spinning in."
QKD is widely described as unbreakable, as any potential eavesdropper would actually destroy the photons while trying to measure them.
While QKD is not a new phenomenon, it hasn't before been tested over a long period in a real-world situation.
"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," says study co-author Dr Damien Stucki of the Institute of Physics and German Physical Society.
"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."