The story actually goes back to April 2010, when Toshiba announced that it had succeeded in maintaining quantum key distribution over a 50 kilometer distance. Key distribution is the basis of quantum cryptography. The data can be encrypted by conventional symmetric methods – but the key is transmitted separate to the data under the principles of quantum mechanics. Each bit of the key is encoded on a single photon of light. Any attempt to intercept or read any of the photons will necessarily change the encoding, destroying the decryption key and maintaining the secrecy of the communication.
It is believed that such systems are already in use by military and governments, but wider implementation has remained out of reach because of the sheer cost. The light encoded photons have had to be sent on a separate fiber. This, says Dr Andrew Shields, assistant managing director at Toshiba Research Europe Ltd, “has greatly restricted the applications of quantum cryptography in the past, as unused fibers are not always available for sending the single photons, and even when they are, can be prohibitively expensive.”
The new breakthrough announced today is the ability to transmit both data and key on the same fiber, effectively eliminating any extra channel cost. Now, announces Toshiba, its engineers and scientists have “succeeded in extracting the very weak signals used for quantum cryptography from ordinary telecom fibres transmitting data traffic. It means that existing telecom networks can now be secured with this ultimate form of encryption.”
The principle involves sending the single photon and the data at different wavelengths on the same fiber. A receiving detector, “sensitive only for a very brief window (100 millionths of a micro-second) at the expected arrival time of the single photons,” is able to separate key from data.
It will be some time, of course, before all of the components are realistically available on the open market, but Zhiliang Yuan, who worked on the research, told Reuters the team plan to carry out field tests on the system. He predicted it could be rolled out commercially within a few years.