Coulomb-Correlated Few-Electron States in a Transmission Electron Microscope Beam

We report on the observation of Coulomb-correlated pair, triple, and quadruple free-electron states in a transmission electron microscope generated by femtosecond photoemission from a nanoscale field emitter. The electron number states exhibit energy and momentum correlations of about two electronvolts caused by strong acceleration-enhanced inter-particle energy exchange. State-sorted beam caustics reveal a longitudinal source increase and shift. We demonstrate electric-field control of transverse against energy correlations. In conjunction with apertures in the beam, this facilitates highly non-Poissonian electron beam statistics for microscopy and lithography. The high fidelity of few-electron state generation will open new experimental schemes for free-electron beams.