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.
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