  Visualizing the electron dynamics in four dimensions of space and time is
crucial to the understanding of several ubiquitous processes in nature. Hence,
ultrafast X-ray and electron imaging tools have been developed to probe the
dynamics of matter by means of the time-resolved diffraction imaging (TRDI). In
this work, we report an extension of the theory underlying the TRDI to the case
of the laser-driven electron dynamics in solid state systems. We demonstrate
that the TRDI signal encodes an essential information about the time-dependent
electron density of the system under study and thus makes it possible to
decipher the ultrafast quantum dynamics and the electron transfer phenomena in
solids. We apply the developed approach to image the laser-driven electron
dynamics in neutral graphene showing that the predictions made by the fully
quantum version of the TRDI deviate significantly from those obtained with the
conventional semiclassical approach.
