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Technology

Quantum computing

What it is, how it works and the promise it holds

April 11, 2007

When a Vancouver-area company announced in February that it had demonstrated what it claimed was the "world's first commercial quantum computer," the assertion raised a few questions.

Among the scientific community, quantum computer researchers wondered whether D-Wave Systems Inc. really had achieved a goal that top scientists around the world had been unable to fulfill — especially because the small Burnaby, B.C., company had not gone the usual route of publishing a scientific paper for peer review.

Other people who heard about the claim wondered: What is a quantum computer and how does it differ from computers as we know them today?

The question of exactly what sort of machine D-Wave demonstrated remains open.

Although representatives of the U.S. National Aeronautics and Space Administration's Jet Propulsion Labs have confirmed that the NASA facility had manufactured chips designed by D-Wave, the company has yet to publish its research.

D-Wave CEO Herb Martin told CBC News Online that the company has not published its findings because they are seeking patents on their technology, which they are working on developing into a commercial product.

"If I have to put a major effort into convincing the academic scientific community, that's an investment in time I could use to develop my technology," Martin said. "If there's any scientists out there who want to take a look at what we're doing, they would be our guest."

"I wish they are right," Raymond Laflamme, director of the Institute for Quantum Computing at the University of Waterloo, said about D-Wave's claims. "We don't know enough about the system to really assess it until we see a peer review."

However, Laflamme was happy to explain the notion of quantum computing to CBC News Online.

Modern computers

The fundamental difference between quantum computers and modern-day digital computers rests on the underlying physics, Laflamme said.

Modern day digital computers rely on "classical laws" such as those described by Isaac Newton, relating to the interaction of objects and forces. They are the principles that serve as most people's introduction to physics in high school and that explain our day-to-day interactions with the physical world.

"When you drive a car, when you are typing, when you are writing with a pen, you are using classical physics," Laflamme said. These occupy a specific and clearly defined space and behave in a predictable way, he explained.

Modern computers also use classical physics, and are based on the transmission of electricity through circuits. Those circuits are made of millions of microscopic switches or transistors that exist in either one of two possible states: on or off. The information they carry is the most fundamental element of data known in computing, which is called a bit.

In a race to increase computing power by packing more of the components on to a single chip, those transistors are being made ever smaller. But as they start to approach the scale of atoms, they begin to reach a physical limit for miniaturization. In order to continue to increase computing power at current rates using conventional techniques, it would require packing a physically impossible number of transistors on to one chip, Laflamme said.

Enter the domain of the new rules of physics called quantum mechanics — a science that is barely a century old — and the potential to build a quantum computer.

Quantum computers

Quantum mechanics rule particle interactions below the atomic scale, where the conventional laws of physics break down.

Under quantum mechanics, a subatomic particle such as a photon — a particle of light — can be in more than one place at a given time, and if you observe it, you change or "perturb" it, Laflamme said.

That ability to exist in multiple states in multiple locations is the reason quantum computing holds the promise of systems more powerful than any that exist today.

One quantum bit or "qubit" can simultaneously exist in two states: on and off with a value of one and zero.

So, one quantum bit is the equivalent of two conventional bits, but it is not simply a arithmetical doubling. Each qubit would exponentially add computing power to a system, Laflamme explained.

So, just 20 qubits would offer the computing power of 2^20 conventional bits, or about one million bytes — one megabyte — of processing ability. A 30-qubit system would have the power of 2^30 conventional bits, or about one billion bytes — a gigabyte — of power; 40 qubits are equivalent to 2^40 bits — a trillion bytes — or a terabyte system; and 50 qubits would be akin to 2^50 bits or � one quintillion bytes — one petabyte.

As the drive to push the boundaries of computing power runs up against the physical limits of miniaturization, the advantages of a quantum computer become clear, Laflamme said.

"It would be impossible to create a chip with the number of components needed to make a machine work," he said. "Quantum computing means you need an exponential amount less of resources to work."

Technology revolution

The introduction of quantum technology would revolutionize the computer industry by allowing systems to simultaneously perform multiple calculations where traditional computers would have to perform them one at a time, Laflamme said.

"It's not like going from a Pentium to a Pentium 2," he said, referring to the Intel Corp. brand for an earlier line of computer chips. "It's a way to do things that harnesses new laws of physics — We are changing the way we understand information and what it is.

"Quantum computing can be seen as the Holy Grail of controlling the quantum world."

It would also have ripple effects that could see a major change in other spheres of life, he added.

"This opens a completely new door to a new brand of technology that we did not expect," Laflamme said. "Whenever people have been able to understand and harness forces of nature, it has been turned into technology and society has changed," he said, pointing to the wheel, steam power and the understanding of electromagnetism as examples.

Quantum computing power would be able to greatly reduce the time it would take to perform large-scale calculations, such as how drugs interact on a molecular level — potentially leading to breakthroughs in medicine — as well as being able to create unbreakable codes that could be used for national security purposes and in financial transactions, Laflamme said.

Setting aside D-Wave's claims, what is his best guess for when a commercially viable quantum computer might become available?

"If you would have asked me this 10 years ago, I would have said 50 years — not in my lifetime," Laflamme said. But with advances in quantum science, he now thinks he will live to see the day when quantum computers are put to work: "Twenty to 25 years. Of course, that could be off by 10, 15, 20 years."

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