The first high-speed network link that is so secure it is theoretically unbreakable has been created, thanks to quantum physics.

A team at Toshiba Research Europe in Cambridge, UK, has sent encrypted data at over 1 megabit per second along 50 kilometres of optical fibre. That’s fast enough to stream video.

Secure links like Toshiba’s involve one user sending a secret “key” to the other, encoded into the quantum properties of a string of single photons. Quantum mechanics ensures that any attempt to intercept this quantum key will change it, revealing the attack.

Until now, the fastest way to send the encoded photons was through the air, but the best spanned not much more than 700 metres. For quantum encryption to be practical, the photons need to travel further and use existing infrastructure, such as the optical fibre that already forms the internet’s backbone.


Unfortunately, optical fibre can only transmit light over long distances when it is of a certain wavelength. Individual photons of that wavelength are difficult to detect, but Toshiba has now developed a detector that can pick them up.

Journal reference: Applied Physics Letters (DOI: 10.1063/1.3385293)