Vincenzo Grillo

The Aharonov–Bohm (AB) effect is one of the most striking features of quantum physics, and it is of critical importance to elucidate the role of the electromagnetic potential and its physical meaning. In spite of the fact that it was first proposed in 1949, up to now it has only been demonstrated for electrons and neutrons. We propose the realization of an experiment to study the AB effect for the antiproton, which will have the double feature of being a non-elementary charged particle and at the same time an antiparticle. The experiment will be conducted in collaboration with the ASACUSA (Atomic Spectroscopy And Collisions Using Slow Antiprotons) group at the CERN AD (Antiproton Decelerator), making use of a slow antiproton beam.

Spatial and temporal light modulation is a well-established technology that enables dynamic shaping of the phase and amplitude of optical fields, significantly enhancing the resolution and sensitivity of imaging methods. Translating this capability to electron beams is highly desirable within the framework of a transmission electron microscope (TEM) to benefit from the nanometer spatial resolution of this instrument. In this work, we report on the experimental realization of a photonic-based free-electron modulator integrated into the column of two ultrafast TEMs for presample electron-beam shaping. Electron-photon interaction is employed to coherently modulate both the transverse and longitudinal components of the electron wave function (through lateral phase imprinting and temporal profiling, respectively), while leveraging dynamically controlled optical fields and tailored designs of the electron-laser-sample interaction geometry. Using energy- and momentum-resolved electron detection, we successfully reconstruct the shaped electron wave function at the TEM sample plane. These results demonstrate the ability to manipulate the electron wave function before probing the sample, paving the way for photonics-inspired imaging and spectroscopy techniques in ultrafast electron microscopy.

Rotational invariance is a fundamental aspect of symmetry in scattering processes from atomic potentials. Here, we present an approach for measuring orbital angular momentum (OAM), a key descriptor of rotational symmetry, during measurements of atomic transitions. We use an electron optical OAM sorter in combination with electron energy-loss spectroscopy and model-based fitting to separately measure the π* and σ* antibonding transitions in hexagonal boron nitride on the atomic scale. This approach also offers prospects for efficient and atomically-resolved magnetic chiral dichroism measurements.

Tuneable phase plates for free electrons are a highly active area of research. However, their widespread implementation, similar to that of spatial light modulators in light optics, has been hindered by both conceptual and technical challenges. A specific technical challenge involves the need to minimize obstruction of the electron beam by supporting films and electrodes. Here, we describe numerical and analytical mathematical frameworks for three-dimensional stacks of phase plates that can be used to provide near-arbitrary electron beam shaping with minimal obstruction.

By means of numerical simulations, we demonstrate the innovative use of computational ghost imaging in transmission electron microscopy to retrieve images with a resolution that overcomes the limitations imposed by coherent aberrations. The method requires measuring the intensity on a single pixel detector with a series of structured illuminations. The success of the technique is improved if the probes are made to resemble the sample and the patterns cover the area of interest evenly. By using a simple 8 electrode device as a specific example, a twofold increase in resolution beyond the aberration limit is demonstrated to be possible under realistic experimental conditions. Published by the American Physical Society 2024

Transmission electron microscopy can be described in terms of the measurement, in an appropriate quantum basis, of the quantum state of an electron after scattering through a sample. Recently developed methods for measuring the orbital angular momentum (OAM) of an electron beam using an OAM sorter can be used to reveal the n-fold symmetry of a sample. Here, we introduce and demonstrate a new composite planar chirality operator, which is based on rotation and scaling operators. By using synthetic electron holograms, we show that an electron OAM sorter can be used to determine the scaling symmetries and planar chiralities of relevant objects such as biomolecules, for which the technique could provide faster identification or help to achieve more detailed three-dimensional reconstructions by solving upside-down orientation ambiguities. A statistical analysis shows that, even for very low doses, this can be a solid indicator, even without the need for full imaging of the particle.

Beam shaping—the ability to engineer the phase and the amplitude of massive and massless particles—has long interested scientists working on communication, imaging, and the foundations of quantum mechanics. In light optics, the shaping of electromagnetic waves (photons) can be achieved using techniques that include, but are not limited to, direct manipulation of the beam source (as in x-ray free electron lasers and synchrotrons), deformable mirrors, spatial light modulators, mode converters, and holograms. The recent introduction of holographic masks for electrons provides new possibilities for electron beam shaping. Their fabrication has been made possible by advances in micrometric and nanometric device production using lithography and focused on ion beam patterning. This article provides a tutorial on the generation, production, and analysis of synthetic holograms for transmission electron microscopy. It begins with an introduction to synthetic holograms, outlining why they are useful for beam shaping to study material properties. It then focuses on the fabrication of the required devices from theoretical and experimental perspectives, with examples taken from both simulations and experimental results. Applications of synthetic electron holograms as aberration correctors, electron vortex generators, and spatial mode sorters are then presented.