Cambridge lab sets quantum key world record

Researchers can now shift encryption keys around at speeds of 1Mbps.

The hugely promising security technology of Quantum Key Distribution (QKD) has moved an important step closer to commercialization with the announcement by UK-based researchers that they can now shift encryption keys around at speeds of 1Mbps.

If that sounds like modest throughput in an age of multi-gigabit networking, it does have one important implication for the technology - it makes it possible for secure QKD to be used on optical networks with multiple nodes. Until now, the low secure key distribution speeds, typically as low as 10Kbps over a 20km distance, restricted the technology to point-to-point links.

The "breakthrough", made at one of the world's leading centers of QKD expertise, the Toshiba Cambridge Research Labs (CRL), was the result of engineers finding a way to make hardware more able to filter the 'electron avalanches' that normally limit the technology than has previously been possible.

The team has spent years working on QKD, setting a number of records for speed over distance.

Quantum encryption harnesses principles at the heart of quantum physics to guarantee not the data stream itself - that uses conventional mathematical algorithms and transmission - but the keys used to encrypt it. The bits that make up keys are encrypted into patterns of photons, which if intercepted in any way whatsoever, corrupt the communication, revealing that an attack has been undertaken.

If the principle is 100 percent guaranteed, relating the physics to semiconductor engineering is tougher. The problem is that each photon used to communicate the key triggers an 'avalanche' of electrons, some of which becomes electronic noise that can introduces key errors. Researchers can counter this problem by turning off the equipment to dampen the effect, or just limiting clock speeds to 10MHz, both of which restrict throughput.

Headed by Dr. Andrew Shields, the CRL team has now developed a way to harness usable signals from much weaker electron fields without propagating noise, allowing clock speeds to be ramped up to over 1GHz. According to Shields, this allows a raw bit rate of 9Mbits/s over a 20km fiber link, or 1MBits/s in fully secure mode. The number of nodes is still low at four, but it is a step forward.

"Together, the dramatic increase in bit rate and the possibility of network deployment, herald a breakthrough in the applicability of QKD technology. We plan now to develop a fully functional prototype of the high bit rate QKD system for use in quantum networks," he said.

He believed the hardware could be developed into a rack-mounted form factor within 3-5 years. In combination with the multi-node capability, this would herald the point at which QKD technology would be sold to real customers. Because of the cost of the components, and complexity of the underlying management, he predicted that QKD would most likely start life as service sold by network providers.

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John E. Dunn

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