Electrons in Rydberg states exhibiting behavior like classical orbits — Lagrange L points.
Rumour spreadin a-round in that Texas town
’bout that shack outside Lagrange
An astronomical solution to an old quantum problem
When a small satellite moves in a sun-earth system there are five stable points at which the satellite remains fixed with respect to the rotating sun-earth system. These are the famous Lagrange L points. In 1994 Bialynicki-Birula et al. showed that stable Lagrange points could be produced in the atomic electron problem by applying a circularly polarized microwave field rotating in synchrony with an electron wave packet in a highly excited state (a so-called Rydberg atom). The electron wave packet then remains localized near the Lagrange point while circling the nucleus indefinitely. Effectively the atom is made to behave quite classically.