Imaging transient electronic coherences in molecules with ultrafast vortex electron diffraction

The rapid advancement of attosecond techniques has opened up new possibilities for tracking electron motion. Electronic coherence, a key aspect of attosecond electron dynamics, emerges not only immediately after laser excitation in molecules but also during nonradiative electronic relaxation facilitated by conical intersections. At conical intersections, two or more electronic states become degenerate, leading to the breakdown of the Born-Oppenheimer approximation. Consequently, the role of transient electronic coherences in molecules has become central to understanding various photochemical and photophysical processes, with the potential to control electron motion and influence reaction outcomes. However, two major challenges remain. The first is the ability to probe exclusively the contributions of electronic coherence to the signal, with no contribution from electronic populations. The second is achieving real-space imaging of the associated time-dependent evolution of electron density. Here, we propose a novel time-resolved vortex electron diffraction technique to spatially resolve transient electronic coherences in isolated molecules. By analyzing helical dichroism diffraction signals, the contribution of electronic populations cancels out, isolating the purely electronic coherence signals. This allows direct monitoring of the time evolution and decoherence of transient electronic coherences in molecules.