Silicon quantum computing leap made

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Silicon quantum computing leap made

Last Updated: Wednesday, January 19, 2011 | 3:51 PM ET

By Chung CBC News

A key step toward silicon-based quantum computers has been made by an

international team of researchers.

The scientists showed that quantum bits of data, known as " qubits, " could be

encoded within a type of silicon similar to that used in conventional computing.

Their findings were published online in Nature Wednesday. The lead author of the

study is , a Canadian from Ottawa and Kitchener-Waterloo, Ont.,

doing her D. Phil. degree in physics at the University of Oxford in the U.K.

" Nobody's entangled quantum bits in a solid state system before, " said Mike

Thewalt, a physics professor at Simon Fraser University in Burnaby, B.C., who

co-authored the paper.

" One of the reasons that people are looking at silicon specifically is if we can

think of a way of doing that, then you inherit all of that technology that's

been used for silicon electronics. "

Quantum computers have the potential for exponentially greater computing power

than conventional computers. They are based on laws of physics that apply to

very small particles like electrons and are very different from the classical

laws of physics that we are familiar with in daily life.

Such computers encode data using a phenomenon called entanglement, which

permanently links two objects so that each is affected by the experience of the

other, no matter how far apart they are.

Up until now, the entangled systems that researchers have been able to observe

and control have involved mainly photons — two particles of light — or atomic

gases.

But and her colleagues demonstrated that billions of phosphorus atoms

embedded in a silicon crystal can be put into the same quantum state. That state

involves the entanglement of two data bits within each atom.

While that sounds impressive, Thewalt said, it would actually be a bigger deal

if researchers had shown entanglement in a single phosphorus atom.

" If you want to build a quantum computer, what you're going to have to do is

entangle a single phosphorus and do something with it and then measure what

happened at the end, " he said.

Many different approaches to quantum computing are currently being researched,

and " they're all a long way from fruition, " said Thewalt.

Perfect material

Thewalt's contribution was figuring out what type of material could be used for

the experiment — a special type of silicon called isotopically enriched, or

istopically " pure, " silicon.

Thewalt had commissioned a sample of the special silicon to use in studies

involving light. He later contacted 's research advisor, Morton,

with the idea that a leftover chunk could be used for a quantum entanglement

experiment.

His lab analyzed it and " picked out the best parts, " then sent the sample to

Morton.

The material was key because normal silicon generates a lot of background

signals that swamp the signals that researchers are trying to measure, Thewalt

said. The background signals also make the information stored in the phosphorus

atoms fade far more quickly, making it more difficult to conduct experiments and

measurements. Isotopically enriched silicon overcomes those difficulties.

" It's like a perfect host material, " Thewalt said.