Control of concerted back-to-back double ionization dynamics in helium


Our article sheds light on the control of the motion of the ionized electrons during double ionization. To first order, the field only drives the electron into the same direction (front-to-back motion). In this paper, our goal was to achieve the opposite, back-to-back motion, where both electrons are ejected into opposite directions. This is only possible via an interplay between the inter-particle forces and the potential. By extensive usage of four different control procedures (local control, derivative-free optimizations of basis expansions, Krotov method, and control of the classical equations of motions), we could identify pulse characteristics that lead to the desired back-to-back motion. Additionally, we were able to identify a simple, classical two-step mechanism. Besides these new physical results, this contribution also discusses new methodologies for using local control procedures for this difficult system and employs a new method to efficiently propagate the wavefunction in time [H. R. Larsson, B. Hartke and D. J. Tannor, J. Chem. Phys., 145, 204108 (2016)].