Electron matter waves with internal torque

TL;DR

This paper demonstrates how to shape electron wave packets with internal torque using chiral laser light, enabling control of angular momentum at atomic and sub-atomic scales in femtoseconds.

Contribution

It introduces a method to induce and control internal torque in electron matter waves through interaction with chiral laser light, a novel approach in electron microscopy.

Findings

Created electron wave packets with internal torque.

Achieved femtosecond control of matter wave chirality.

Demonstrated correlation between orbital angular momentum and energy.

Abstract

Angular momentum and torque are important principles for basic and applied physics on any spatial scales, for example, in elementary particles, cold gases, optical tweezers, quantum information technology, metamaterials, gyroscopes or astrophysical entities. Investigating or controlling angular momentum in atoms or sub-atomic structures requires torque on femtosecond and picometer scales, far below the capabilities of laser light. Here we shape the electrons in an electron microscope into wave packets with a time-dependent chirality and internal torque. We intersect the electron beam with chiral laser light to create discrete energy sidebands by multiple helical photon absorptions that create a correlation between orbital angular momentum and kinetic energy. Dispersion of these partial waves due to the electron rest mass then converts each single electron into a wave function with internal torque. Under our control, a left-handed matter wave becomes right-handed in femtosecond times. Such quantum objects will facilitate research on angular momentum and chirality on atomic and sub-atomic scales.