单激光束能使分子停止翻转运动

In the quantum world, making the simple atom behave is one thing, but making the more complex molecule behave is another story. Now Northwestern University scientists have figured out an elegant way to stop a molecule from tumbling so that its potential for new applications can be harnessed: shine a single laser on a trapped molecule and it instantly cools to the temperature of outer space, stopping the rotation of the molecule.

"It's counterintuitive（违反直觉的） that the molecule gets colder, not hotter when we shine intense laser light on it," said Brian Odom, who led the research. He is an assistant professor of physics and astronomy in the Weinberg College of Arts and Sciences. "We modify the spectrum of a broadband laser, such that nearly all the rotational energy is removed from the illuminated molecules. We are the first to stop molecular tumbling in such a powerful yet simple way."

It is not very difficult to trap many types of molecules and hold them precisely in place, Odom said, but they stubbornly persist in rotating just as much as if they were not trapped at all. Using their customized laser, he and his colleagues cooled singly charged aluminum monohydride molecules from room temperature to 4 degrees Kelvin (minus 452 degrees Fahrenheit) in a fraction of a second. The abrupt temperature drop stopped the molecules' normally persistent tumbling motion in its tracks.

Such control of molecules, of their rotational and vibrational states, is essential to using molecules in the construction of superfast quantum computers -- machines whose processing power would be exponentially faster than today's computers.

The new technique is faster, easier and more practical and efficient than techniques developed thus far to control molecules. Details will be published Sept. 2 by the journal Nature Communications.