Prof. Benjamin J. McMorran: "Shaping Electrons for Studies of Magnetism, Nano-optics, and Interaction-Free Measurements"
Advances in optics and detectors for electrons enable new investigations of electron physics and quantum imaging techniques at the nanoscale. Here we report the use of nanofabricated holographic apertures to sculpt electrons for using in a versatile interferometric scanning transmission electron microscope (STEM). Also known as STEM holography, a technique pioneered by Cowley, this technique allows the implementation of several quantum imaging techniques. For example, we apply it to probe the coherence and symmetry of nano-optical excitations as well as demonstrating interaction-free measurements. Electrons in superpositions of paths can excite the same optical transition in a nanoplasmonic structure, albeit from different positions. These two paths still interfere, despite the inelastic scattering interaction with the specimen. We observe that the excitation of a plasmon introduces a relative π phase shift between the two probes, which could in principle be used to measure transitions below the energy resolution of the microscope. In another set of experiments, we use the same set up to demonstrate interaction-free measurements, a type of quantum measurement protocol in which the presence of an object can be detected without a probing particle interacting with it. Such measurement techniques provide a new way to explore how electrons interact with nanosystems, and could also provide a way to reduce the electron dose required to image objects in the TEM.