Some day, we may compute with atoms

The Baltimore Sun

Some day within the imaginable future, the powerful computers that guide our world may be surpassed by a new generation of super-machines that would outperform current silicone chips with the same relentless power the transistor showed in its victory over the vacuum tube and the chip in its triumph over the transistor.

The new machines - called "quantum computers" by researchers - would manipulate the physical state of some of the smallest bits of matter to perform basic computational functions with lightning speed, offering performance that would dwarf the capacity of the fastest existing conventional computers.

The speedup could be a great boon in code-breaking and other areas of national security, not to mention the study of physics, chemistry, materials science, nanotechnology, biology, medicine and the global climate, all of which are limited today by the slow speed of simulations on conventional computers.

Because of the machines' extraordinary promise, researchers at an array of public and private institutions are racing to find ways to make quantum computing work.

In recent days, progress in the race was reported by a team of researchers at the National Institute of Standards and Technology laboratories in Gaithersburg.

Led by Nobel Prize-winning physicist Bill Phillips, the team built a laser-cooled atom chiller with magnets and a vacuum-sealed chamber, all powered by what team member Ben Brown calls a "rat's nest" of wires that looks like a prop in a science fiction movie.

"It's a monstrosity," Brown said, a bit of pride in his voice.

But with this instrument the NIST group was able to superchill and manipulate thousands of atoms in a kind of primitive information exchange that has never been done before, a step widely viewed as an advance toward successful quantum computing.

Their report on that success, published in the journal Nature, has attracted attention from colleagues around the world.

"It's very clever, a nice step forward," said Joahnnes Hecker Denschlag, a physicist at Austria's University of Innsbruck working on a similar approach to quantum computing.

The NIST researchers achieved their breakthrough by inserting chunks of metal into the vacuum chamber, heating it into a gas, then freezing it to the chilliest temperature possible and zapping it with the lasers from different angles.

"I call it playing with Legos, for grown-ups," said Brown.

The work is the latest development in an NIST effort that began about six years ago to use lasers to trap and control atoms as a first step in the design of a quantum computer, according to Trey Porto, an NIST physicist whose lab houses the laser cooler.

If researchers succeed in completing a quantum computer, an early use is likely to be protecting encryption codes now designed to ensure online security for everything from credit-card transactions to government Web sites.

"There are hundreds of groups working on it," Denschlag said.

But most experts believe quantum computers are at least a decade from reality because of the remaining roadblocks to building one.

"It's analogous to making a transistor. There is a tremendous potential, but we don't know what the end product will look like, or how long it will take to get there, " said Patricia J. Lee, a co-author of the NIST paper on the project. "We're just at that beginning stage."

To understand the work, it helps to know that conventional computers store and retrieve bits of information using tiny electrical charges to represent sequences of numeric ones and zeroes. Computers use the order of the ones and zeroes to translate everything from digital images to the text in your boss' e-mail.

Scientists searching for a quantum equivalent of this process are taking different approaches. Some are manipulating the photons, the particles of light; others are working with electrons and still others are trying to trap and manipulate energy levels of ions, which are electrically charged atoms, Brown said.

Brown and Lee are manipulating uncharged atoms.

Every approach takes advantage of two properties unique to quantum mechanics, the researchers say.

First, quantum bits of information, or qubits, can exist in a "superposition" state, functioning as both 1s and 0s in a way that makes it possible to perform multiple calculations at the same time. Quantum computers also may use a phenomenon known as entanglement, so that when two or more qubits become entangled, their properties link up, according to Brown and others.

But the quantum designers also share the same problem: Achieving entanglement is a delicate process and so far it has been impossible for entangled particles to survive long enough to perform any calculations. As the qubits get closer to each other, it becomes harder to manipulate any single qubit without affecting those near it and breaking off the entanglement.

"Each one of these steps, the creation of the qubits, the entanglement itself, is an opportunity for the information that you're trying to store to be degraded," Brown said.

For the experiment, the NIST researchers placed rubidium atoms inside the vacuum chamber; pumped out the air to create a vacuum, and heated the metal to turn it into a gas. Using the same kind of lasers found in TV remotes and CD players, they blasted the atoms with lasers and applied a magnetic field to super-cool them to minus 460 degrees Fahrenheit.

At room temperature, atoms move in random, chaotic ways. But when chilled to such ultra-low temperatures in a vacuum, they lock together and behave as a single, predictable mass.

"All the atoms start to march in step with one another and when you do something to one atom, it's like doing it to all of them," Lee said.

The researchers then used lasers to form an optical lattice - a sort of bed for the atoms made from light rays - and applied radio waves that "flipped" the spin of the atoms, so upward-spinning atoms began spinning down, and vice versa.

By changing the polarization of light in the lattice, they joined the atoms together in paired sites or beds, forcing them to interact, become entangled and oscillate, so that they go in and out of entanglement. The researchers call the resulting atomic exchange of information a "quantum square dance."

For their next project, NIST researchers will try to improve on the process and separate the entangled atoms so they can be manipulated individually, Porto said.

"There's a lot we still have to do," he said.

dennis.obrien@baltsun.com

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