Rudolf Haindl

Affiliation: Max Planck Institute for Multidisciplinary Sciences and Georg August University of Göttingen (Germany)

Research Interests: Physics, Electron Microscopy

Title: Coulomb-correlated few-electron states in a transmission electron microscope beam

Abstract: Correlations between electrons are at the core of numerous phenomena in atomic, molecular, and solid-state systems. However, harnessing free-particle correlations remains challenging, with the recent implementation of nanoscale single-electron sources [1] and observation of anti-bunching in electron beams [2, 3, 4]. A powerful approach to induce strong inter-electron interactions is femtosecond-triggered photoemission from nanotips [5,6] with high spatial and temporal confinement. However, ensemble-averaged detection typically conceals few-body effects. In this work, we characterize Coulomb correlations in laser-triggered electron number states generated at a Schottky field emitter in an ultrafast transmission electron microscope [7]. Based on an event-based detection scheme, we separate the state-averaged spectrum into the n-state components with a characteristic n-peak spectral shape. Furthermore, we identify a characteristic pair-correlation energy of around 2 eV. The strong inter-particle energy exchange is caused by acceleration-enhanced inter-particle Coulomb interaction, as confirmed by trajectory simulations. State-sorted beam caustics reveal a discrete increase in virtual source size, a longitudinal source shift, and a pronounced angular distribution of the few-electron states compared to single-electron pulses. The high fidelity of few-electron pulses in conjunction with single-particle detection enables the application of various experimental schemes typically employed in quantum optics. Specifically, we propose a scheme to generate an electron beam with sub- and super-Poissonian two-electron statistics. Applications of such beams include heralded single-electron sources and may foster new developments in free-electron quantum optics and quantum-enhanced electron microscopy.