Quantum cryptography has emerged from the laboratory and into the real world.

Using properties of quantum physics, the technique encrypts data with keys that reveal if they have been intercepted or tampered with. US company Magiq and Swiss firm ID Quantique have already sold hardware to several customers keen to protect data with quantum cryptography. Governments and armed forces are thought to be among the first users of the technology.

Encryption usually involves scrambling data with long numeric keys that stop other people reading it. The information inside the message is effectively kept secure because of the time it would take an eavesdropper to sort through all possible keys used to scramble the data. But quantum cryptography scrambles data in a different way by using the strange properties of the quantum world to guarantee that keys have been swapped securely.

Information about the key is encoded on to a single photon of light. Quantum physics guarantees that the properties of the photon will change if anyone intercepts it and tries to read the information off it. Once two parties have swapped a key that they know to be safe they can be sure that the messages they are sending each other are secure.

Once connected to a fibre-optic network the Magiq hardware allows companies to set up a virtual network they can use to send data encoded with quantum keys.

Although the technology is already in use, there are still some limitations to iron out.
For instance there is a limit to the distance that photons can travel before they lose coherence which makes it impossible to read key information. The current record for long-distance quantum key distribution is 120km.

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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.

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