Physicists Observe Three-Atom Collisions in Ground-Breaking Experiments

A team of physicists in New Zealand has held individual atoms of rubidium in place and observed previously unseen interactions.

Laser-cooled atom cloud viewed through microscope camera. Image credit: University of Otago.

“Our method involves the individual trapping and cooling of three atoms to a temperature of about a millionth of a Kelvin using highly focused laser beams in a hyper-evacuated chamber,” said lead author Dr. Mikkel Andersen, a physicist in the Department of Physics at the University of Otago and the Dodd-Walls Centre for Photonic and Quantum Technologies.

“We slowly combine the traps containing the atoms to produce controlled interactions that we measure.”

When the three atoms approach each other, two form a molecule, and all receive a kick from the energy released in the process. A microscope camera allows the process to be magnified and viewed.

“Two atoms alone can’t form a molecule, it takes at least three to do chemistry,” said co-author Dr. Marvin Weyland, a postdoctoral researcher in the University of Otago and the Dodd-Walls Centre for Photonic and Quantum Technologies.

“Our work is the first time this basic process has been studied in isolation, and it turns out that it gave several surprising results that were not expected from previous measurement in large clouds of atoms.”

The researchers able to see the exact outcome of individual processes, and observed a new process where two of the atoms leave the experiment together.

Until now, this level of detail has been impossible to observe in experiments with many atoms.

“By working at this molecular level, we now know more about how atoms collide and react with one another,” Dr. Weyland said.

“With development, this technique could provide a way to build and control single molecules of particular chemicals.”

“Our research tries to pave the way for being able to build at the very smallest scale possible, namely the atomic scale, and I am thrilled to see how our discoveries will influence technological advancements in the future,” Dr. Andersensaid.

The experiment findings showed that it took much longer than expected to form a molecule compared with other experiments and theoretical calculations, which currently are insufficient to explain this phenomenon.

While the authors suggest mechanisms which may explain the discrepancy, they highlight a need for further theoretical developments in this area of experimental quantum mechanics.

The results appear in the journal Physical Review Letters.

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L.A. Reynolds et al. 2020. Direct Measurements of Collisional Dynamics in Cold Atom Triads. Phys. Rev. Lett 124 (7): 073401; doi: 10.1103/PhysRevLett.124.073401