Decoherence and Revival in Attosecond Charge Migration Driven by Non-adiabatic Dynamics

Charge migration is driven by a coherent superposition of electronic states and evolves on the single-femtosecond time scale. A key open question concerns the effect of nuclear motion and electronically non-adiabatic dynamics on charge migration. This work represents the first experimental characterization of both. We report the measurement of a series of quantum beats with a half-period of only 690 as in strong-field excited neutral silane using attosecond transient absorption spectroscopy at the silicon L-edge. With the help of Multi-Configurational Time-Dependent Hartree simulations, these beats are interpreted to be caused by the coherent excitation of multiple valence-excited states and a 3-eV-higher-lying Rydberg state. These beats are observed to decohere due to nuclear motion within 10 fs and to display a revival after 50 fs in both theory and experiment. The recoherence is found to result from the concentration of the valence-state population in the lowest electronically excited states due to non-adiabatic population transfer, as well as the electronically adiabatic dynamics in the valence and Rydberg excited states. By showing that electronic coherence in molecules can be created through strong-field electronic excitation, maintained through non-adiabatic population transfer and have the possibility of reviving after being initially decohered by nuclear motion, these experimental and theoretical results give unprecedented insight into the intriguing mechanisms of attochemistry.