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Cold Physics is Hot Topic


People have always been fascinated by how to make things cold. As mankind's understanding of cold has evolved, so have the applications. They range from refrigeration to low temperature physics, where atoms are chilled to almost absolute zero (-273.15°C).

When 19th century scientists first tried to liquefy oxygen, it seemed an impossible task. At the annual meeting of the American Association for the Advancement of Science, the audience got a glimpse of that historic drama, in a sneak preview of a documentary titled, Absolute Zero. It shows the challenges these scientists overcame to liquefy hydrogen, and later, helium. Those discoveries a century ago led to the refrigeration technologies that produce quick-frozen peas and liquefied oxygen for rocket fuel. Super cold helps in the production of microchips and fast computers.

More applications are up ahead, thanks to researchers who study super cold things.

Devices that incorporate super cold fluids can provide more accurate measurements
According to Stanford University professor Mark Kasevich, "There was a huge factor of precision that was tantalizing and out there for us to go out there and grab." He says the sensitivity of these new instruments allows observers to spot the subtle changes to the earth that can hint at the presence of minerals, such as diamonds, or oil deposits. "We think we could be 10 or 100 times better than the existing technology," he estimates, "and that should help you find these oil and mineral deposits that much quicker."

Super-cooling lets scientists study fundamental principles
For instance, says University of California-Berkeley scientist Richard Packard, super-cooled helium seems to defy the way that gravity normally forces fluids to flow, which is consistently downward. His team has been able to demonstrate how superfluid helium oscillates back and forth between areas of different pressure. The effect may allow more sensitive detection of the earth's rotation, as well as earthquake studies.

Scientists also use cold temperatures to put their experiments in a kind of slow motion
University of Colorado physicist Heather Lewandowski explains that makes extremely tiny subjects - like molecules and atoms - easier to monitor. "Let's say [you have an experiment] about a meter long, you're only going to have a millisecond or so to really interrogate that and study that molecule before it zips across your experiment. Now, if you cool down these molecules, you have a much longer time to interrogate the molecule and thus you can more precisely measure things about the molecular system."

Scientists have been studying cold atoms for two decades. Lewandowski is looking at a newer frontier: super-cooled molecules. "We really want molecules because of their complex nature," she says, "and [we want them] cold, so we simplify things and study them for a long time." Because they're more complex than atoms, they're harder to catch in action. But that complexity reveals more about chemical reactions, which may lead to better medicines. It also might produce faster quantum computers.

The first step, Lewandowski says, is figuring out how to slow down a molecule. Back at her lab at the University of Colorado, her team starts with molecules at a normal room temperature and pressure. They send these into a metal container that's about a cubic meter, and looks like a submarine hatch. "This is our vacuum chamber," she says, adding with a laugh, "This is where all of the magic happens. This is where we make the cold molecules and slow them down."

In the vacuum chamber, the molecules expand, which quickly cools them to nearly absolute zero. Next, Lewandowski's team uses electric fields that gently slow the molecules, and chill them even more. Molecules are too complex to get as cold as a simple atom. But Lewandowski says they'll come close, "a few billionths of a degree above absolute zero. It's sort of impossible to get to absolute zero. There's always some little bit of motion left."

But in that fine-tuned range between slowing tiny bits of matter and stopping them entirely, Lewandowski says there's plenty to discover.

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