An ultracold plasma of 26,000 beryllium ions fluoresces when hit by a laser pulse. Ultracold atoms could be used to make quantum computers and sophisticated measuring devices, and may even unlock the mysteries of the big bang.

Image: National Institute of Standards and Technology Once you catch an atom, you can do quite a lot with it. You can make a powerful computer, track infinitesimally small changes in gravity, even model the big bang.

That's what scientists in a field called ultracold physics are doing. Their tools are atoms cooled to near-absolute-zero temperatures, slowed just enough to let physicists harness their quantum properties.

"If you get some atoms moving really slowly, you can control them very well," said University of Virginia physicist Cass Sackett. "And once you bring them to a complete stop, you can do a number of very interesting things."

Albert Einstein and Satyendra Nash Bose predicted the phenomenon in 1925, but these so-called Bose-Einstein condensates were discovered only 12 years ago. They've come a long way in that short time.

Ultracold particles may soon be used to make quantum supercomputers, extra-sensitive measuring devices, navigation systems and even models of the early universe. None of this could be done with regular, old-fashioned states of matter.

Sackett and other ultracold physicists slow atoms by hitting them with lasers, a technique pioneered in 1995 by Eric Cornell, Wolfgang Ketterle and Carl Wieman. In 2001, their work earned them a Nobel Prize in physics.

Normally, atoms don't interact with light. But if the lasers are calibrated to just the right wavelength, the photons and atoms intersect.

One or two, or even a few million, photons won't make much of a difference. At room temperature, atoms spin at speeds of hundreds of thousands of meters per second: Hitting one with a photon, said University of Chicago physicist Cheng Chin, is like tossing a pingpong ball at an onrushing bowling ball.

But bombard a bowling ball with enough pingpong balls, and it can be slowed. The same goes for atoms and photons. The transition from high to low energy is also a considerable temperature decrease – hence the ultracold moniker.

Once they're cold enough, the atoms – usually alkali metals from the left side of the periodic table, which have just one electron in their outer ring and are thus easier to target – are no longer the chaotically bouncing billiard balls of high school science-class analogies. Instead they behave in unison, with each atom's position and momentum identical.

It's this type of ultracold homogeneity that, somewhat counterintuitively, may have existed in the ultrahigh temperatures immediately following the big bang. And by studying the behavior of Bose-Einstein condensates, Chin and other physicists hope to learn more about the origin of the universe.

"In the beginning there was a uniform medium," said Chin. "Essentially, there was no structure. And then there was all kinds of structure. What is the origin of this complexity?"

If that seems a little disconnected from the needs of everyday life, there are plenty of practical applications for ultracold physics.

By capturing the atoms in grids of light and magnetism and then controlling their quantum-variable states, Chin is using ultracold particles to make quantum computer processors with powers beyond our binary-based chips.

"In a classical semiconductor, you interact with a bit (connected to) wiring," Chin said. "We use photons to induce interaction. Your computer could be several hundred atoms floating in a vacuum, their interactions mediated by light."

And this is more than a pretty picture: Such a computer would be far more powerful than any supercomputer in the world.

Scientists need to learn how to better control the atoms before quantum computing becomes a reality. In the meantime, ultracold atoms make great measuring devices.

By tracking the changes induced in the atoms, physicists can make fine-grained deductions about the strength of magnetic or gravitational fields. That's Sackett's specialty, and it could be valuable to oil prospectors because oil deposits, it turns out, cause a minuscule decrease in gravity due to their low density as compared to the Earth's stone core.

Another practical use for ultracold research could come in the form of non-GPS-based navigational systems, which would require reckonings down to a billionth of a degree. Ultracold atoms could take such measurements based on the Earth's rotation.

All in all, it's a heady time for ultracold – and the best is yet to come.

"The field is improving incredibly fast," said Massachusetts Institute of Technology physicist Vladan Vuletic. "The things that are happening now – if you read the proposals 10 years ago, you would have said they were just science fiction."

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