Giant atoms

The instable Rydberg state is defined as a state intermediate between the moderately excited state and the ionized state (photoionization) in the framework of a planetary atomic model representing various excitation processes involving the valence electron. The absorption of a photon with an energy slightly below the ionization energy takes the valence electron up to a Rydberg state corresponding to a very large orbit around the atomic core. These giant atoms highly sensitive to outer perturbations, are easily destroyed; their ability to emit radio waves allow them to be observed outside the interstellar space. Some transitions involving orbits of order n = 300, corresponding to atoms of 2μm in diameter, have been detected. In the laboratory, the combination of laser excitation and electric detection made it possible to prepare and study atoms with n up to 100. The species more frequently investigated are alkali metals (Na, Rb, Cs) rare gases (He, Xe ...) alkaline earths (Ba, Ca ...) and the uranium atom of possible economic interest in view of isotope separation