Quantum Superpositions of Free Electron Orbital Angular Momentum

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Electrons are the tiniest particle of matter, the smallest spark of charge, and smallest bit of magnet. We power our cities with these small, charged, magnetic objects, and use them to store, process, and communicate information. It was recently discovered that an electron moving by itself in vacuum can possess an additional, potentially useful, property: orbital motion. Individual free electrons can also exist in combinations of these orbital states, and can even be made to exhibit orbital motions in opposite directions at the same time. The purpose of this project is to understand the fundamental nature of these new electron states by creating such mixed orbital states in electron beams, such as counter-rotating circular orbits, and to investigate new ways to measure the different types of orbital motion present in a mixture. To do so, a commercial instrument that is typically used for nanoscale imaging (transmission electron microscope) will be used. The electron beam inside this instrument will be made to pass through nanoscale gratings carefully designed with complicated patterns. The effect on the beam will be measured using detectors downstream from the gratings. If successful, this research will provide a new way to manipulate the electron as well as measure this new quantum property, paving the way for future technologies in quantum electronics and providing new ways to probe orbital motion in matter. Like all quantum mechanical waves, the wave function of a single free electron can be twisted on itself to form a quantum vortex. The purpose of this project is to investigate the fundamental quantum nature of these states by placing free electrons in coherent superpositions of orbital states using nanoscale diffraction holograms and other new electron optical devices. Electrons in superpositions of counter-rotating circular orbits form an electron interferometer in free space, and it can be used to probe geometric phases, spatial coherence, and orbital angular momentum-dependent phase shifts of the electron wavefunction. In addition to experiments preparing superpositions of orbital states, the project also develops ways to nondestructively measure and sort them, potentially providing new information from scattered electrons.