Helium Rydberg states in parallel electric and magnetic fields

The n=60, L z =0 angular momentum manifold in helium is studied in the presence of an electric field parallel to a fixed magnetic field (B=0.1539 T). Results obtained from a CW laser-atomic beam experiment are compared with diagonalization calculations and with a WKB approximation including core effects. Core-induced anticrossings have been analysed in detail. The supersymmetry, including quasi-crossings in hydrogen to occur at the same value of the electric field strength, does not apply for L z =0 manifolds in non-hydrogenic Rydberg atoms.