"With an exponential speed-up, problems which would take centuries to solve on present-day computers (could) be solved in days," lead researcher Albert Chang, a physicist at Duke University at Durham, N.C., told United Press International.

Modern computers work by coding information into a series of ones and zeros -- binary digits known as bits. This code is conveyed via transistors, minute switches that can be flicked either on or off to represent a one or a zero.

Quantum computers would take advantage of a strange phenomenon called superposition, in which objects such as electrons or atoms can exist in two places, or spin in two opposite directions, at the same time. This means computers built on quantum physics could have quantum bits -- also known as qubits -- that exist in both on and off states simultaneously.

Using this property, quantum computers could run every possible on-off combination at once, making them incomparably faster than conventional devices when it comes to solving certain problems, such as code-breaking.

The qubits the research team developed are quantum dots -- what Chang calls "puddles of electrons." The key to quantum dots is a property known as spin. Electrons spin on their axes much as Earth spins on its poles.

"When two electrons occupy the same space, they must pair with opposite spins, one electron with 'up' spin, the other 'down,'" Chang explained. This grants the pair a net spin of zero.

The Duke researchers collected 40 to 60 pairs of electrons in a puddle roughly 5,000 times smaller than a grain of sand within a semiconductor wafer of gallium arsenide and aluminum gallium arsenide. Then they added a single, additional unpaired electron. This extra electron imparted a net spin of up or down to the quantum dot.

The team placed a pair of quantum dots near each other, both with the same net spin. Using eight tiny converging wires called gates, the researchers found they could direct how much the separate quantum dots would leak into one another.

By slowly varying the amount of leakage, the quantum dots influenced each other. Because they want to occupy the same location, if both occupied the up spin, one or the other would want to switch to down spin. By controlling leakage properly, both quantum dots become qubits -- both in superposition, spinning both up and down.

To run super fast calculations, quantum computers need to scale up from a handful of qubits to dozens, if not hundreds.

"There are many types of hardware systems proposed for realizing a scalable quantum computer," Chang said. "Most will turn out to be impractical for scaling up to a large size. But ours have a potential advantage. It seems possible to scale them up into large systems that can work together because we can control their behavior more effectively. Many systems are limited to a handful of qubits at most, far too few to be useful in real-world computers."

Chang said the quantum transistor developed by his team "is particularly intriguing, since we know a lot about controlling and fabricating precise device structures from the broad knowledge base and technological know-how of the semiconductor industry."

The system has a number of drawbacks, however. For one thing, it operates in super-freezing cold of 45 millikelvin, or only 45 thousandths of a degree above absolute zero -- nearly minus 450 degrees Fahrenheit. This is to prevent any stray heat from destabilizing the very delicate state of superposition the qubits occupy.

"One of the directions we want to go in is to make this even colder, like to get below 10 millikelvin," Chang said. "You may say then, if the system has to be kept in a special cryostat (supercold state), it's not practical. I would say the reverse. You have a computer that can perform this kind of computation. What price tag would you put on it? Five million dollars or a couple of billion?"

Another problem is it currently takes hours, if not days, to measure the system. To run quantum calculations, scientists want to get results before the qubits destabilize and run "at gigahertz speeds, billionths of a second time scales," Chang said. "I would put a two- to five-year time scale that we'll get another significant advance."

Chang admitted that, at this stage, "what we've done is just a physics experiment, nothing more."

Still, this type of science is promising long-term.

"There will be no impact on the market from quantum computing for at least 10 years," said Victor Wheatman, vice president of information technology security at Gartner Inc., a financial analysis firm in San Jose, Calif.

He told UPI he expects funding for Chang's line of work to emerge "not just from the National Science Foundation, but intelligence agencies, because they have a vested interest in this."

He said work on quantum computing is growing at university and national research labs, and at industrial giants such as AT&T, IBM, Hewlett-Packard, Lucent and Microsoft.

"This is one of the most exciting areas of pure research," Wheatman commented.

All rights reserved. Copyright 2004 by United Press International. Sections of the information displayed on this page (dispatches, photographs, logos) are protected by intellectual property rights owned by United Press International. As a consequence, you may not copy, reproduce, modify, transmit, publish, display or in any way commercially exploit any of the content of this section without the prior written consent of by United Press International.

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