An optical method for polarizing free electrons in a laboratory setting

Polarized electrons are electrons in which the spins have a „preferred” orientation, or are preferentially oriented in a particular direction. The realization of these electrons has significant implications for physics research, as it paves the way for the creation of promising materials and the implementation of new experiments.

Researchers from East China Normal University and Henan Academy of Sciences recently introduced a new method for polarizing free electrons in a laboratory setting, which uses light beams from an optical device near a sample. Their article, published Physical review lettersIt can open up interesting new possibilities for high-energy physics, quantum technology development and materials science.

„The initial idea for this study took root two years ago when I was a postdoctoral researcher in the group of Prof. Francisco Javier García de Abajo, renowned for his theoretical work on optical excitations in electron beams,” said Deng Pan. from the study told Phys.org. „Since then, the field of photon-stimulated near-field electron microscopy (PINEM) has gained momentum, emerging as a major topic in electron microscopy.”

PINEM is a promising microscopic technique that will allow researchers to manipulate the quantum properties of electrons, revealing new quantum computing mechanisms that rely on free electrons. Previous works have primarily attempted to use this technique to manipulate the orbitals and momenta of electrons. In their study, Pan and his colleague Hongxing Xu set out to investigate its potential use in polarizing free electrons.

„I began to question whether a similar approach could be used to change the spin state of electrons or to polarize electron beams,” Pan said. „In discussions with many experts in electron beam theory, most of them believed that such an effect could not be detected because the magnetic field in the electromagnetic field is significantly weaker than the electric field component. As a result, it was surprising and unexpected. My calculations eventually demonstrated a significant electron polarization effect within the optical near field. .”

The optical method introduced by Pan and Xu takes inspiration from PINEM because it is based on a similar approach. The researchers used a nanowire array (i.e. a periodic nanostructure) with a carefully designed lattice constant. Their design ensured a field matching between the input electron velocity and the structure, ensuring strong interactions between them.

„There is a fundamental difference between my proposal and the PINEM project,” Pan explained. „The PINEM effect is induced by an electric field component parallel to the electron beam. In contrast, we used a transverse electric (TE) near-field, which only has an electric field perpendicular to the electron beam. Why did we choose this TE near-field? Answer with another fascinating topic in nanophotonics Closely coupled, this is known as transverse spin angular momentum or spin-orbit interaction in optical near-fields.”

The TE near field used by researchers consists of a circularly polarized magnetic field. As a result, it can be used to manipulate the spins of electrons, just as other fields are used to control quantum spins.

„A spinning electron beam is proving to be an invaluable tool in studying magnetic materials and high-energy physics in other areas,” said Pan. „Our research also sheds light on the realization that the magnetic field component in the optical near field, although weak compared to the electric field component, can be leveraged to achieve unexpected effects.”

Pan and Xu were among the first to introduce a reliable optical method to produce spin electrons in a laboratory environment. In the future, their approach could be adapted and used by other research groups to create spin-polarized electron beams, while encouraging the development of new quantum computing approaches that optimize the spins of electrons and photons.

„With the direction provided by this work, there is more extensive theoretical space to explore, such as the possibility of quantum information processing that combines electron and photon spins,” Pan added. „However, I believe the most important aspect is the experimental demonstration of the proposal outlined in this study. I have already discussed this work with several experimenters, and they have expressed confidence in the feasibility of achieving our results in experiments.”