Quantum cryptography done on standard broadband fibre

The "uncrackable codes" made by exploiting the branch of physics called quantum mechanics have been sent down kilometres of standard broadband fibre.

This "quantum key distribution" has until now needed a dedicated fibre separate from that used to carry data.

The technique, reported in Physical Review X, shows how to unpick normal data streams from the much fainter, more delicate quantum signal.

It may see the current best encryption used in many businesses and even homes.

The quantum key distribution or QKD idea is based on the sharing of a key between two parties - a small string of data that can be used as the basis for encoding much larger amounts.

Certainly in a corporate environment it's already affordable, and as time goes on I'm sure we'll see the technology get cheaper”

Tiny, faint pulses of laser light are used in a bid to make single photons - the fundamental units of light - with a given alignment, or polarisation. Two different polarisations can act like the 0s and 1s of normal digital data, forming a means to share a cryptographic key.