Molecular Attoscope: Pulse Shape Spectroscopy of Electronic Coherence

Tracking the coupled motion of electrons and nuclei on their intrinsic timescales is essential to understanding and controlling photochemical transformations. While attosecond techniques have provided unprecedented insight into electronic dynamics, they have largely been restricted to ionic systems, with nuclear motion often neglected or indirectly inferred. Here, we demonstrate a "molecular attoscope", which uses shaped laser pulses in the deep ultraviolet to perform a coherent measurement of electronic and nuclear dynamics in an entangled wave packet in neutral benzene. This enables us to trace both the 856-attosecond-period electronic motion and the 36-femtosecond-period nuclear motion. We observe electronic coherence persisting over hundreds of optical cycles, modulated by nuclear dynamics. Our holographic approach is general, and lays the groundwork for coherent measurements capable of visualizing the evolution of the coupled electronic-nuclear wave function in real time.