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

Correlations between electrons are ubiquitous in atomic, molecular, and solid-state systems. Observing such phenomena for free electrons requires a highly degenerate phase space density, readily available by femtosecond photoemission from nanotips [1,2], and benefits from the supreme beam control of electron microscopes [3]. However, ensemble-averaged detection usually prevents studying multi-particle correlations in free-electron beams.

In this work, we use event-based electron microscopy to characterize laser-triggered few-electron pulses generated at a Schottky field emitter [4]. We find surprisingly strong energy correlations of about 2~eV in the two- and three-electron states hinting at a correlated emission process. Furthermore, state-sorted beam caustics show characteristic transverse pair distributions, as well as an increase and a longitudinal shift of the source.

Inducing strong few-electron Coulomb correlations facilitates non-Poissonian electron pulse statistics, promising heralded electron sources, shot-noise-reduced lithography, and applications in free-electron quantum optics and matter wave interferometry.

[1] P. Hommelhoff, et al., Phys. Rev. Lett. 96, 077401 (2006)

[2] C. Ropers, et al., Phys. Rev. Lett. 98, 043907 (2007)

[3] A. Feist, et al., Ultramicroscopy 176, 63-73 (2017)

[4] R. Haindl, et al., arXiv:2209.12300 (2022)