ARCHIVED - Building a quantum computer

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February 09, 2009— Ottawa, Ontario

Today's computers, from laptops to supercomputers, employ microchips that contain millions of tiny transistors. Each transistor is a kind of on-off switch that directs streams of millions of electrons representing binary zeros and ones that form the basis for all digital computing.

But what if a computer exclusively used the quantum properties of electrons rather than their classical properties? These computers would transcend today's microprocessors by following completely different quantum physics rules to solve problems.

The NRC-IMS team of Drs. Pawel Hawrylak, Andy Sachrajda, Sergei Studenikin and Guy Austing (left to right), with a liquid helium cryostat. The cryostat cools equipment that measures NRC's semiconductor quantum dot structures.

The NRC-IMS team of Drs. Pawel Hawrylak, Andy Sachrajda, Sergei Studenikin and Guy Austing (left to right), with a liquid helium cryostat. The cryostat cools equipment that measures NRC's semiconductor quantum dot structures.

"There's a whole class of mathematical problems that are very, very hard to do with a regular computer, even if it's very fast. But if you can build a quantum computer, some of these problems become much easier to do," says Dr. Guy Austing of the NRC Institute for Microstructural Sciences (NRC-IMS) in Ottawa.

Dr. Austing is quick to point out that useful quantum computers, first envisaged about 50 years ago, could take up to another 50 years to build. But NRC teams are working on it. And many other university, military and commercial electronics research groups around the world are doing basic research in many directions to find the best ways to employ atoms, ions, photons, superconductors and semiconductors for quantum calculations.

The approach of Dr. Austing and his colleagues involves nano-electronics based on gallium arsenide semiconductor structures called "quantum dots" that can work even with one or two electrons at a time. Gallium arsenide is already used in some specialized electronics, so it's possible that quantum computers could be built using current manufacturing equipment and processes. However, "the behaviour we see in the transistors we are now investigating is quite different than what you see in today's commercial transistors," stresses Dr. Austing.

He explains that while today's computer transistors control the flow of basic "bits" of binary information, quantum computers would shuffle different, more complicated information units called "qubits." One of the main quantum properties of a qubit, called "superposition," means that rather than being in a state of either zero or one, it can be in an intermediate state — a combination of zero and one at the same time. Another property, called "entanglement," means that if a certain quantum object was split in two, for instance, a measurement on one part at one location would influence the outcome of the measurement on the other part at another location, no matter how far apart the two locations.

While these concepts may boggle non-physicists, in simple terms they mean that a quantum computer may excel at performing a number of well-known mathematical algorithms related to certain important, "exponentially difficult" problems.

If a quantum computer can be built, says Dr. Austing, "it would not be a universal panacea." We're unlikely to use them in our laptops or mobile phones. The silicon-based microchips already in common use are best for those.

However, quantum computers could model the workings of quantum systems — like atoms and molecules — giving us a far better understanding of the building blocks of matter. Simulating new biological, chemical or pharmaceutical molecules faster and better would affect many lives — the total combined economic value of these industries was recently estimated at about $3 trillion annually around the world, says Dr. Austing.

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