Positional correlation in laser-excited three-body Coulomb systems

Using a novel six-laser excitation scheme we have created heliumlike planetary states (nlNd) in barium with n{≥}30, N{≥}60, and l{≥}4, which are equivalent of a true three-body Coulomb system. Extremely strong positional correlation effects were observed and quantitatively explained by the repulsion between a ``frozen'' outer electron and the highly polarizable inner electron. The model was experimentally verified by removing the outer electron and recording the inner electron excitation in the presence of an equivalent electric field.