  We have verified a mechanism for Raman excitation of atoms through continuum
levels previously obtained by quantum optimal control using the
multi-configurational time-dependent Hartree-Fock (MCTDHF) method. For the
optimal control, which requires running multiple propagations to determine the
optimal pulse sequence, we used the computationally inexpensive time-dependent
configuration interaction singles (TDCIS) method. TDCIS captures all of the
necessary correlation of the desired processes but assumes that ionization
pathways reached via double excitations are not present. MCTDHF includes these
pathways and all multiparticle correlations in a set of time-dependent
orbitals. The mechanism that was determined to be optimal in the Raman
excitation of the Ne $1s^22s^22p^53p^1$ valence state via the metastable
$1s^22s^12p^63p^1$ resonance state involves a sequential resonance-valence
excitation. First, a long pump pulse excites the core-hole state, and then a
shorter Stokes pulse transfers the population to the valence state. This
process represents the first step in a multidimensional x-ray spectroscopy
scheme that will provide a local probe of valence electronic correlations.
Although at the optimal pulse intensities at the TDCIS level of theory the
MCTDHF method predicts multiple ionization of the atom, at slightly lower
intensities (reduced by a factor of about 4) the TDCIS mechanism is shown to
hold qualitatively. Quantitatively, the MCTDHF populations are reduced from the
TDCIS calculations by a factor of 4.
