Laser Cooling Halts Trapped Molecule's Rotation

It’s relatively easy to trap molecules using lasers, yet they persist in rotating as if they were not trapped at all.

But a new laser cooling technique has helped a team from Northwestern University stop a trapped, rotating molecule dead in its tracks.

“We modify the spectrum of a broadband laser such that nearly all the rotational energy is removed from the illuminated molecules,” said Dr. Brian Odom, an assistant professor of physics and astronomy in Northwestern’s Weinberg College of Arts and Sciences.

In the study, the researchers used a customized laser to cool singly charged aluminum monohydride molecules from room temperature to minus 452 °F in a fraction of a second. The abrupt temperature drop immediately stopped the molecules’ tumbling motion.

The aluminum monohydride molecules were used because they do not vibrate when interacting with a laser.

“If I want to slow down a molecule, quantum mechanics tells me that it happens in steps,” Odom said. “And there is a very lowest step that we can get the molecule down to, which is what we’ve done.”

The new technique is faster, easier and more practical than conventional molecule control methods, the researchers said. Such control of molecules’ rotational and vibrational states is essential to using them in the construction of quantum computers.

“There is a lot you can do if you get one species of molecule under control,” Odom said.

The research was published in Nature Communications (doi: 10.1038/ncomms5783).