  We present an ab initio study of the nonsequential strong-field ionization
dynamics of a model two-electron atom with helium character. Single- and
double-ionization events are characterized and displayed using detector signals
extracted at different points in the two-electron two-dimensional space. The
double photoelectron momentum distribution is calculated via coherent
path-summation over virtual particle trajectories. Insights into different
ionization and electron recollision pathways are gained from detailed
virtual-particle tracking and energy-time readouts. This study demonstrates the
extension of virtual detector theory to strong-field multi-electron quantum
dynamics and highlights the importance of the evolving quantum phase in
quasi-classical electron propagation.
