Mammoth molecules: Pairs of cesium atoms (illustrated) can be bonded together into molecules the size of bacteria, like the E. coli – shown here for scale. The outermost electron in each atom has been boosted to high energy, creating a state known as a Rydberg atom. These giant molecules may be useful in future for the development of quantum computers.
The molecules of unusual size are formed from pairs of Rydberg atoms — atoms with an electron that has been boosted into a high-energy state. Such electrons orbit far from their atom’s nucleus and, as a result, can feel the influence of faraway atoms.
To create the molecules, researchers cooled cesium atoms nearly to absolute zero, hitting them with lasers to form Rydberg atoms that bound together in pairs. These molecules are about one thousandth of a millimeter in size — a thousand times the size of a typical molecule — scientists report August 19 in Physical Review Letters.
“I think it’s fundamentally interesting and important because it’s such a curious thing,” says physicist David Petrosyan of the Institute of Electronic Structure & Laser at the Foundation for Research and Technology–Hellas in Heraklion, Greece. “The size of these molecules is huge.”
This is not the first time such molecules have been created, but the previous evidence was not clear-cut. “Before, maybe it wasn’t clear if this is really a molecule in the sense that it’s vibrating and rotating. It could have been just two atoms sitting therewith very weak interactions or no interactions,” says Johannes Deiglmayr, a physicist at ETH Zürich and a coauthor of the study.
Deiglmayr and collaborators measured the molecules’ binding energies — the energy that holds the two atoms together. Additionally, the scientists made detailed calculations to predict the molecules’ properties. These calculations were “extensive and seemed to match really well with their measurements,” says physicist Phillip Gould of the University of Connecticut in Storrs.
The result has practical implications, Petrosyan notes. In quantum computers that use atoms as quantum bits, scientists perform computations by allowing atoms to interact. Rydberg atoms can interact with their neighbors over long distances, and when bound together, the atoms stay put at a consistent distance from one another — a feature that may improve the accuracy of calculations.
Previously, researchers have used rubidium atoms to make another type of large molecule, formed from Rydberg atoms bonded with normal atoms. But these wouldn’t be useful for quantum computation, Petrosyan says, as they rely on a different type of bonding mechanism.