Distant partners. In this sketch, two cesium atoms in high Rydberg states form a weakly bound molecule about 1 micrometer across, comparable to the size of typical bacteria.
Strongly bound diatomic molecules such as H2 or O2 are less than a nanometer across. Surprisingly, scientists have been able to create two-atom molecules more than a thousand times larger by using exotic atoms that attract one another only very weakly. Now, a pair of physicists have calculated what makes these “macrodimers” stable, and they have verified their predictions by creating micrometer-sized molecules containing two cesium atoms. The macrodimers could have applications in quantum computing.
Interest in these macromolecules stems from the challenges they pose to conventional understanding of molecules and bonds. More than a decade ago, physicists predicted that molecules with interatomic distances as large as 1 micrometer might be created by using a pair of atoms in so-called Rydberg states. These are atoms in which a single outer-shell electron has been excited to a high quantum state so that it orbits far away from the nucleus. Although Rydberg atoms are unstable, they can live as long as tens of microseconds, and experimenters have succeeded in creating macrodimers from them, confirming their existence indirectly by destroying them and detecting specific spectroscopic signatures .
APS Focus: Giant Molecule Made from Two Atoms, Mark Buchanan