This latest research was done by researchers at the Laboratoire Charles Fabry (LCF) in Palaiseau and the University of Lille. "What we have done here, for the first time to our knowledge, is to measure directly the Van der Waals interaction between two single atoms that are located at a controlled distance, chosen by the experimenter," says Thierry Lahaye, who is part of the LCF team.You can also read more review of this work at APS Physics, and, get a free copy of the paper.
Controlling the distance between normal atoms – while measuring the force between them – is extremely difficult because the relevant distances are tiny. To get round this problem the team used Rydberg atoms, which are much larger than normal atoms. Such atoms have one electron in a highly excited state. This means that they have a very large instantaneous dipole moment – and therefore should have very strong Van der Waals interactions over relatively long distances. They also have unique properties that allow them to be controlled with great precision in the lab.
Nice piece of work.