Quantum correlations in electron microscopy
Posted on 11.01.2021 - 23:22
Electron microscopes set a powerful platform for exploring material and optical phenomena with nanoscale resolution through the interaction of free electrons with sample excitations such as phonons, excitons, bulk plasmons, and surface plasmons. The interaction usually results in the spontaneous emission of such excitations, which can be detected directly through cathodoluminescence or indirectly through electron energy loss spectroscopy (EELS). Even stimulated interactions were recently facilitated by coupling lasers into electron microscopes in photon-induced nearfield electron microscopy (PINEM). However, as we show here, the underlying interaction of a free electron and an arbitrary excitation goes beyond what was predicted or measured so far, involving complex decoherence and entanglement patterns of the electron and the excitations. The entanglement of electron– optical-excitations can provide new analytical tools in electron microscopy; for example, it can provide coherence measurements of optical excitations, plasmonic lifetimes, and Bohr radius of excitons. We show how these can be achieved using common configurations in electron diffraction and EELS, revealing significant changes in the electron’s coherence and in other quantum information measures such as purity. Specifically, we find that the EELS after interaction with nanoparticles features discrete resonances, versus a continuum for interaction with surface plasmons. We quantify the post-interaction density matrix of the combined electron–optical-excitation by developing a framework based on macroscopic quantum electrodynamics (MQED). The framework enables to quantify decoherence due to excitations in any general optical environments, also applicable beyond electron microscopy. Particularly in electron microscopy, our work also enriches analytical capabilities and inform the design of quantum information experiments with free electrons, controlling their quantum states and their decoherence by the optical environment.
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Mechel, Chen; Kurman, Yaniv; Karnieli, Aviv; Rivera, Nicholas; Arie, Ady; Kaminer, Ido (2021): Quantum correlations in electron microscopy. The Optical Society. Collection. https://doi.org/10.6084/m9.figshare.c.5216342.v2