Exploring Single-Photon Recoil on Free Electrons.

Recent advancements in time-resolved electron and photon detection enable novel correlative measurements of electrons and their associated cathodoluminescence (CL) photons within a transmission electron microscope. These studies are pivotal for understanding the underlying physics in coherent CL processes. We present experimental investigations of energy-momentum conservation on the single particle level, achieved through coincidence detection of electron-photon pairs. This not only enables unprecedented clarity in detecting weak signals otherwise obscured by nonradiative processes but also provides a new experimental pathway to investigate momentum-position correlations to explore entanglement within electron-photon pairs.