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US boffins build, test working 2-qubit quantum processor

Beryllium ions used in place of undead cats

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Federal boffins in America say they have built the first computer processing device able to handle quantum-mechanical numbers expressed as "qubits". Whereas a regular bit is either 1 or 0, a qubit can be 1, 0 or some of both just as a metaphorical cat in a box may be dead, alive or in a mysterious semi-undead waveform zombie condition.

The device was developed by scientists at the US National Institute of Standards and Technology (NIST). According to the inventors, the new kit is a step forward on earlier and more primitive quantum gear in that it is programmable.

"This is the first time anyone has demonstrated a programmable quantum processor for more than one qubit," says NIST postdoc researcher David Hanneke. "It's a step toward the big goal of doing calculations with lots and lots of qubits. The idea is you'd have lots of these processors, and you'd link them together."

The machine's two qubits are held in the form of individual beryllium ions, which "are held in an electromagnetic trap and manipulated with ultraviolet lasers". There are also a brace of magnesium ions in the trap for the purpose of cooling the beryllium ions.

The NIST crew say they have verified that their gear is properly programmable by testing out 160 of the possible different programs one can write for a two-qubit device. Though there are an infinity of possible programs, according to the scientists, their properly-random check of 160 is sufficiently representative to show that the device works.

If many such devices could be successfully hooked together to create a quantum computer, various major consequences could be expected - not least the breaking of encryption regarded today as completely uncrackable. The NIST announcement, unsurprisingly, mentions the importance of the team's work to "national priority areas, such as information security", and the US military are also known to be interested in the idea.

There's plenty of work ahead before practical quantum computers can be assembled, however. At the moment, the 2-qubit processor is only 79 per cent accurate. With many such devices working together, this would be unacceptable. The NIST team acknowledge that accuracy needs to be "boosted substantially" before much progress can be made.

Hanneke and his colleagues' paper, Realization of a programmable two-qubit quantum processor, is published in Nature Physics. It can also be read online here (pdf). ®

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