Control of quantum electrodynamical processes by shaping electron wavepackets

Liang Jie Wong,Nicholas Rivera,Chitraang Murdia,Ido Kaminer,Marin Soljačić,Thomas Christensen,John D Joannopoulos

doi:10.1038/s41467-021-21367-1

Abstract

Fundamental quantum electrodynamical (QED) processes, such as spontaneous emission and electron-photon scattering, encompass phenomena that underlie much of modern science and technology. Conventionally, calculations in QED and other field theories treat incoming particles as single-momentum states, omitting the possibility that coherent superposition states, i.e., shaped wavepackets, can alter fundamental scattering processes. Here, we show that free electron waveshaping can be used to design interferences between two or more pathways in a QED process, enabling precise control over the rate of that process. As an example, we show that free electron waveshaping modifies both spatial and spectral characteristics of bremsstrahlung emission, leading for instance to enhancements in directionality and monochromaticity. The ability to tailor general QED processes opens up additional avenues of control in phenomena ranging from optical excitation (e.g., plasmon and phonon emission) in electron microscopy to free electron lasing in the quantum regime.

Highlights

Fundamental quantum electrodynamical (QED) processes, such as spontaneous emission and electron-photon scattering, encompass phenomena that underlie much of modern science and technology
We show that it is possible to control spontaneous emission from a free electron through quantum interference enabled by electron waveshaping, just as spontaneous emission from an atom can be controlled through quantum interference between multiple atomic transitions[102] or through multiple atoms, as in superradiance[103]
We begin by presenting a schematic approach that emphasizes the key points

Summary

Introduction

Fundamental quantum electrodynamical (QED) processes, such as spontaneous emission and electron-photon scattering, encompass phenomena that underlie much of modern science and technology. Breakthroughs in manipulating the phase structure of electron wavepackets[86,87] have led to further control over properties such as orbital angular momentum (OAM)[88,89,90], spin angular momentum[91,92], and propagation trajectory[93,94] These structured electron beams can be generated through a variety of means including amplitude and phase holograms[95,96,97,98,99], nanoscale magnetic needles[100], and electron–photon interactions[101]. If QED interactions can be controlled via electron waveshaping, bremsstrahlung could conceivably be made more directional, monochromatic, and versatile by structuring the emitting electron wavepacket, analogous to how radio waves are made more directional through structured emitters like phasedarray antennas This effect would be especially exciting in the hard X-ray regime, since the spatial resolution needed to manipulate the phases of hard X-rays cannot be achieved through material fabrication in optical elements, but is readily achievable through electron interference patterns. The concept we present can be readily extended to processes involving more massive and non-elementary particles, such as neutrons, whose wavefunction can potentially be shaped as well[104,105,106]

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Conclusion