Researchers Create Butterfly-Shaped Ultracold Molecule from Rubidium Atoms

Physicists cooled rubidium atoms to a few millionths of a degree above absolute zero with lasers and electromagnetic forces, then used additional lasers to enlarge some atoms by displacing their outermost electrons far from the nuclei. They next steered one giant atom’s electron toward a normal-sized rubidium atom, binding the two into a single molecule roughly 25 nanometres across.

@NewScientist reported that each resulting molecule is larger than the diameter of a DNA strand containing billions of atoms and responds to electric fields thousands of times more strongly than typical molecules.

The outermost electron spreads into lobes resembling butterfly wings, fixing the molecule’s overall shape. Herwig Ott at RPTU University Kaiserslautern-Landau led the effort. He said tuning the lasers to produce the precise butterfly configuration required weeks of incremental adjustments, likening the search to examining a road one millimetre at a time from a kilometre away.

Matthew Eiles of Purdue University noted that the experiment concludes two decades of theoretical and experimental work aimed at realizing a predicted “zoo” of giant ultracold molecules. He stated that the butterfly molecule is the final member of that set to be observed.

Michał Tomza at the University of Warsaw said the result opens routes to additional exotic ultracold species that could be heavy, large, and electrically charged.

Weibin Li at the University of Nottingham said the butterfly molecule could serve as a precursor for producing ultracold anions—negatively charged atoms that have resisted standard cooling techniques. Eiles and Ott have already performed mathematical calculations showing how the butterfly molecule can be used to generate such anions.

They expect the first experimental indications within a few years.

“The theory is already written,” Eiles said.