The first quantum computer network has gone online, linking Harvard University to network installer BBN Technologies, and offering some of the strongest encryption in the world.

Although point-to-point quantum cryptography equipment has been available since the spring, the Darpa Quantum Network is the first fully fledged quantum network. The six network servers link over fibre optic cable and will soon be extending the network to Boston University.

"People think of quantum cryptography as a distant possibility," said Chip Elliott, a principal scientist at BBN Technologies and leader of its quantum engineering team, in a statement.

"But the Darpa Quantum Network is up and running today underneath Cambridge [Massachusetts]. BBN has built a set of high-speed, full-featured quantum cryptography systems and has woven them together into an extremely secure network."

Quantum computing provides near-invulnerable encryption that cannot be eavesdropped upon. Encryption keys are sent via a pattern of single polarised photons and can be changed 100 times per second.

The method is also spy proof, since any third-party observation of the photons changes their properties.

BBN Technologies helped develop the initial backbone of the internet, Arpanet, and developed the first network email. The company is currently involved with developing quantum communications systems for satellites.