2021/05/26 by Raphael Dahan, Alexey Gorlach, Urs Haeusler +8 · 2 citations
Physics and Astronomy · #quant-ph #physics.acc-ph #physics.optics
paper · pdf · doi:10.1126/science.abj7128
published as Science 17 Sep 2021
arxiv created 2021/05/26 · arxiv updated 2021/10/26
The fundamental interaction between free electrons and light stands at the base of both classical and quantum physics, with applications in free-electron acceleration, radiation sources, and electron microscopy. Yet, to this day, all experiments involving free-electron light interactions are fully explained by describing the light as a classical wave, disregarding its quantum nature. Here, we observe quantum statistics effects of photons on free-electron-light interactions. We demonstrate interactions passing continuously from Poissonian to super-Poissonian and up to thermal statistics, unveiling a surprising manifestation of Bohr's Correspondence Principle: the transition from quantum walk to classical random walk on the free-electron energy ladder. The electron walker serves as the probe in non-destructive quantum detection, measuring the photon-correlation g(2) (0) and higher-orders g(n) (0). Unlike conventional quantum-optical detectors, the electron can perform both quantum weak measurements and projective measurements by evolving into an entangled joint-state with the photons. Our findings suggest free-electron-based non-destructive quantum tomography of light, and constitute an important step towards combined attosecond-temporal and sub-A-spatial resolution microscopy.