The rarefied field of encryption Quantum Key Distribution (QKD) has edged another step closer to real-world use.

Researchers at Toshiba's Cambridge Research Labs (TREL) have now distributed encryption keys at a rate of 1Mbit/s over an extended distance of 50Km, and done so continuously over a 24-hour period. The previous best over 50km was 256kbit/s, but the main advance is the ability to run the system without the need for manual tinkering.

It sounds extremely abstract for a technology that as yet has no commercial application, but the milestone is important, the lab said.

QKD does not improve on encryption per se but the security with which the keys - in the case of QKD these can be incredibly long - can be distributed. What it offers is a technology to distribute those keys with the certainty that any interception will be 100 percent detectible. However, because the keys are so long, the bit rate at which they can be transmitted over given distances becomes a major practical limitation, hence the obsession with speed.

The problem with the equipment needed to make QKD work is that it is easily upset by even the tiniest thermal changes in the physical medium of fibre optic glass filaments, which will stretch relative to one another by nanometres over time. The CRL team has found a way to detect and automatically adjust this movement by physically stretching these fibres to counteract the effect.

"It means the system can be used by anyone. You don't need a quantum physicist to operate it," said project head, Dr Andrew Shields.

"Although the feasibility of QKD with megabits per second has been shown in the lab, these experiments lasted only minutes or even seconds at a time and required manual adjustments. To the best of our knowledge this is the first time that continuous operation has been demonstrated at high bit rates," said Shields.

QKD combines one of the most mathematically intense fields in technology, that of encryption, with one of its most abstruse, that of quantum physics.

With the new development, QKD was now possible at high speed over long periods of time which made it a practical for applications such as video, Shields said.

Practical uses of QKD always seem to be at least three to five years off, but that partly reflects the commercial problems of making the technology affordable and getting it accepted. A big hurdle is the lack of standards, something that developers and standards bodies plan to address.

The team plan to demonstrate the system using a network set up in conjunction with the Japanese National Institute of Communications and Technology (NICT) in Tokyo, with the hope of luring military, government and possibly healthcare sectors that would have a use for it.