Scientists have moved one step closer to the “unhackable” network by developing a device that can send single photons in a regular stream over a fiber optic link.

Quantum key exchange takes advantage of the Heisenberg Uncertainty Principle, which states that it is impossible to measure a quantum particle without changing its state. Any attempt to intercept a message such as an encryption key will result in a detectable change, allowing the sender and receiver to verify the secrecy of the exchange.

But even this may not be completely secure, because of possible flaws in the transmission. "Attenuated lasers sometimes produce more than one photon at a time and the problem there is someone can split off one of those photons without disturbing the other," said Dr Andrew Shields, head of the Quantum Information Group of Toshiba Research Europe.

A new technique, pioneered by researchers at Toshiba Research Europe in Cambridge, England, is based on a tiny device called a "quantum dot", a very small semi-conductor made of indium arsenide. It measures just 45 nanometers in radius and 10nm in height.

Shields said this was a much better method of transmission as there was a far less chance of a quantum dot emitting two photons at the same time than other methods: ten orders of magnitude less than a laser. "The new device is very important as it will stop this kind of attack," he said.

Experts in encryption welcomed the developments and said it could make a real difference to the security industry.

"I have been watching numerous developments like this going on around the world," said Peter Jaco, CEO of data encryption company Becrypt. "It is compelling if the technology can be delivered in a commercial fashion. If it starts to take off, it could change the whole market.

Scientists are hoping to develop the product commercially within the next year.

As reported in SC Magazine in late March, the UK is leading the way in this new form of cryptography.

www.toshiba-europe.com/research/