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Quantum Leap

An advance at Toshiba could speed adoption of quantum cryptography.

Since 2002, when quantum cryp­tography was first commercially launched as the new gold standard in secure communication, only a handful of particularly paranoid early adopters have subscribed to it. But now a breakthrough by Toshiba is promising to make the technology more competitive with traditional cryptography and push it into the mainstream.

Toshiba has discovered a way to make quantum-cryptographic data more stable and to transmit it at five times the current rate. “We have made the technology much more stable and easier to use,” says Andrew Shields, who is head of Toshiba’s Quantum Information Group in Cambridge, England. Shields says Toshiba is talking with financial institutions in the City of London about installing the system later this year.

Quantum cryptography allows two parties to send secret encryption keys to each other while testing to see if anyone has attempted to intercept them. The keys are sent, one photon at a time, over standard optical fibers; each photon represents a binary 1 or 0. What makes the system so secure is that any attempt by an eavesdropper to intercept the photons will alter them – alerting the sender to a security breach. The problem: the hardware used to generate the photons is extremely sensitive to temperature fluctuation and movement, so it requires continual adjustment by experts.

Toshiba’s solution is to send two signals. “Along with the single-photon pulse we send a second, brighter, guardian pulse,” Shields explains. The guardian pulse provides a reference point for the receiving hardware, which automatically adjusts to ensure that the photon paths are aligned. The result: a system that Toshiba researchers have shown is able to operate 24 hours a day, seven days a week, without any human intervention.

“Stability is an old issue with quantum cryptography,” says Grégoire Ribordy, CEO and cofounder of id Quantique, the Swiss startup that was the first company to launch a quantum cryptography product. Id Quantique, which currently has about a dozen customers, uses a different method to get around the need for constant human attention. That method, however, limits the distance that a key-carrying light signal can travel to about 100 kilometers, and limits the rate of transmission to about 10 kilobits per second.

With Toshiba’s technology, on the other hand, the signal can travel up to 122 kilometers or reach rates of up to 100 kilobits per second (though not at the same time), which should make it more attractive to security-conscious businesses like banks and insurance companies. And faced with the prospect of quantum computers – which have the potential to crack all of today’s codes and render traditional encryption utterly useless – such companies may soon want all the quantum bandwidth they can get their hands on.

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