Floquet-engineered nondispersive wave packets in helium under combined periodic and static fields

We report the numerical observation of two-electron nondispersive wave packets in fully three-dimensional helium subjected to a linearly polarized monochromatic field. These localized quantum states follow periodic trajectories of the classical three-body Coulomb system without dispersion. The system is modeled using a spectral configuration interaction approach based on Coulomb-Sturmian functions, combined with Floquet theory and complex scaling. The resulting quasienergy spectrum reveals the existence of long-lived Floquet states arising from near-resonant coupling between frozen planet configurations.