Single Laser Can Stop Molecular Tumbling Motion: Scientists

Molecules can easily be trapped and held precisely in place using laser techniques. But the molecules persist in rotating as if they were never trapped. For years, scientists had struggled to find a simple method to stop a trapped, rotating molecules. Now researchers at the Northwestern University have developed a single laser cooling technique which can stop the tumbling motion of a molecule dead in its tracks.

A faster and easier technique to control molecules

Brian Odom, a professor of physics and astronomy at the Weinberg College of Arts and Sciences and lead author of the study, said it’s counter-intuitive that molecules get colder when you shine intense laser light on them. Odom said his team modified the spectrum of a broadband laser to remove almost all the rotational energy of the illuminated molecules.

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Using their customized laser, Odom and his colleagues illuminated a single laser on trapped aluminum monohydribe molecules to cool them from room temperature to minus 452 degrees Fahrenheit within a fraction of a second. The abrupt drop in temperature stopped the persistent tumbling motion of molecules. Findings of the study appeared in the journal Nature Communications. This technique is easier, faster and more efficient than any of the previously developed techniques to control molecules.

The single laser technique opens doors to quantum computing

Other researchers have in the past used cumbersome liquid helium cryostats to cool the molecules. But Odom said they successfully cooled the molecules to their lowest quantum rotational state using room temperature apparatus. Odom used the singly charged aluminum monohydride molecules because they don’t vibrate when interacting with a laser. Aluminum monohydride is inexpensive and can be used in a wide variety of applications.

Controlling the rotational state of molecules is essential in using them to build ultra-fast quantum computers, machines whose processing power would be much faster than modern computers. Besides quantum information processing, other potential applications of this new ability to stop molecular tumbling include tests of whether fundamental constants are static or they change over time.