Attosecond Imaging of Electronic Wave Packets

Quantum coherence among electronic states forms dynamical electronic wave packets. An electronic wave packet has significant spatial evolution besides its temporal evolution, due to the delocalized nature of composing electronic states. However, the spatial evolution was not previously accessible to experimental investigations at the attosecond time scale. We show attosecond spatial imaging of wave packet motion can be achieved with the phase-resolved two-electron-angular-streaking (PR-2eAS) method. We show the technique can distinguish the two electrons arising from double ionization processes to image the first frame of an ultrafast spin-orbit wave packet in the krypton cation. Furthermore, we capture the motion of an even faster wave packet in the xenon cation for the first time: an electronic hole being re-filled 1.2 fs after it was produced, and the hole-filling was observed in the opposite side where the hole was born.