Realizing the capability to visualize electron motion in atoms and molecules is one of the fundamental pursuits in modern science. Ultrashort flashes of light have in principle the desired resolution in time to track electrons in action; however, the resolution in space is limited. Electron motion has thus been possible to be capture (reconstruct) only from indirect measurements. Scanning tunneling microscope (STM), on the other hand, can look directly into electrons and their distribution in atoms and molecules; however, here the resolution in time is limited to only a few milliseconds. Space-time resolution required to capture electron motion directly in sub-Ångstrom dimensions and few hundreds of attoseconds. Manish Garg and his colleagues from the Max Planck Institute for Solid State Research have realized a space-time quantum microscope by integrating ultrashort laser pulses with an STM, which can achieve the desired space-time resolution to directly visualize electron motion1. After successful demonstration of atomic space-time resolving capability of our microscope1, the team has recently realized real-space and real-time imaging of valence electron motion in molecules2. Motion of electrons between different quantum states in molecules were directly imaged (visualized) in the microscope.
The capability to directly image electronic motion in molecules in real-space and real-time opens completely new avenues to understand chemical transformations driven by electron transfer; for example, in photosynthetic molecules and other light harvesting molecules, and to the unambiguous observation of electron dynamics in complex molecular systems, two-dimensional materials and superconductors.
1Garg et al. Science 367, 411-415 (2020).
2Garg et al. Nature Photonics, 2021 (https://www.nature.com/articles/s41566-021-00929-1 )