Classical physics serves as a valid approximation to quantum mechanics in many systems where multiple interacting particles are only partially observed. While scattering processes typically induce delocalization and entanglement, unobserved entanglement causes decoherence effects that localize particles in space and time, making classical descriptions increasingly appropriate. Understanding and observing the transition from multi-particle quantum mechanics to a classical ensemble of point particles remains a significant challenge in many-body quantum physics.

In this study, we experimentally investigate the coherence and entanglement of strongly interacting electrons in a free electron gas generated within a transmission electron microscope. By utilizing dense femtosecond electron pulses generated from a needle tip, we explore the impact of many-particle Coulomb scattering processes on the coherence and entanglement of post-selected electron pairs. Our diagnostic techniques involve two-electron quantum walks in coherent laser fields. The findings reveal that while electron pairs maintain partially coherent wavefunctions, quantum entanglement is significantly reduced, dropping to just a few percent due to decoherence effects. These results offer valuable insights into many-body quantum optics and quantum thermalization and hold practical implications for applied research in particle accelerators and electron microscopy.

Offek Tziperman

M.Sc. student under the supervision of Prof. Ido Kaminer.