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Maryland Scientists Seek The Lowest Temperature Possible: Absolute Zero

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This machine at the JQI can cool particles down to a billionth of a degree above absolute zero.
WAMU/Stephen Yenzer
This machine at the JQI can cool particles down to a billionth of a degree above absolute zero.

The coldest place in our region isn’t on top of a mountain or deep within a cave — it’s a tiny chamber in a lab, on the campus of the University of Maryland. At the Joint Quantum Institute, Dr. Steve Rolston and his team cool particles down close to the lowest temperature in the universe, what physicists call “absolute zero.”

To understand the concept of absolute zero, it’s important to remember that temperature and motion are inextricably linked. At normal temperatures, molecules are constantly bouncing off one another. But as they cool, they slow down. And at very, very cold temperatures — near absolute zero — they almost stop entirely. Absolute zero is the theoretical point at which all motion stops: about -460 degrees Fahrenheit.

The Joint Quantum Institute relies on ultra-low temperatures to explore the world of quantum mechanics — how particles act at the microscopic level. Studying those particles at normal temperatures can be tricky, but near absolute zero, they’re much easier to observe.

Dr. Rolston uses a laser table covered in tubes, chambers, mirrors, lens, and beam splitters. These help guide a series of lasers into a central chamber, where the particles themselves are cooled. “It seems a little counter-intuitive,” says Dr. Rolston. “But I like to make the analogy that I can slow a bowling ball by bouncing tons of ping-pong balls off it. And that’s sort of what we do with light and atoms.”

By bombarding the atoms with lasers, they can slow them down, and because they’re slower, they’re cooler. The machine at the JQI can cool particles down to a billionth of a degree above absolute zero.

And that temperature drop happens fast, according to Dr. Rolston. “We typically can take an atom down to a few millionth of a degree in a fraction of a second,” he says. “Probably about a hundredth of a second.”

Although the process is fast, it’s not easy. The chamber in which the particles are cooled needs to be a near-perfect vacuum, because even a single room-temperature particle could throw off the experiment.

When turned on, the machine uses green and purple lasers that are bounced around the table and into the chamber. Through a tiny window in the side, one can see a tiny cloud of particles floating in mid-air. “That is maybe 100 million atoms, suspended in space,” says Dr. Rolston. “Probably at a temperature of 50 millionth of a degree above absolute zero.”

Once the particles are “trapped” in this way, Dr. Rolston and his team can study some of the “weird” effects of quantum mechanics, like superconductivity. Dr. Rolston explains that superconductivity is “this cool quantum effect that says certain materials, if you get them cold enough, can conduct electricity without any loss whatsoever.” He says that discovering a “room-temperature superconductor” could be revolutionary.

Past advancements in quantum mechanics have led to the microchip, lasers, and MRI machines. The next big leap could be a quantum computer, which uses light to make calculations. A quantum computer would be orders of magnitude faster than current supercomputers, and able to crack today’s most complex encryption with ease.

It sounds a little like science fiction, but then again, so does the Joint Quantum Institute. In this little room, Dr. Rolston and his colleagues are using a tabletop machine to play with the building blocks of the universe.

[Music: "Joe Cool" by Vince Guaraldi from Vince Guaraldi & The Lost Cues from The Charlie Brown Television Specials]

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