Konwersatorium im. Leopolda Infelda

The S-wave scattering length of metastable, spin-polarized helium has been experimentally determined in the BEC experiments carried out in 2001 and has since been used to interpret the behavior of the helium condensate. In my talk I shall show that the state-of-the-art electronic structure theory can reliably be used to predict this observable from first principles. It will also be shown that recent very accurate photoassociation spectroscopy measurement of the energy of the least bound state of the spin-polarized helium dimer provides a stringent test of the relativistic theory of interatomic interactions and the theory of the coupling of electronic and nuclear motion.