Physicists discover a way to imprint a previously unseen geometrical form of chirality onto electrons

Have you ever placed the palm of your left hand on the back of your right hand in such a way that all fingers point in the same direction? If you have, then you probably know that your left thumb will not touch its right counterpart. Neither rotations nor translations nor their combinations can turn a left hand into a right hand and vice versa. This feature is called chirality.

Scientists at the University of Konstanz have now succeeded in imprinting such a three-dimensional chirality onto the wave function of a single electron. They used laser light to shape the electron's matter wave into left-handed or right-handed coils of mass and charge. Such engineered elementary particles with chiral geometries other than their intrinsic spin have implications for fundamental physics but may also be useful for a range of applications, such as quantum optics, particle physics or electron microscopy.

"We are opening up new potentials for scientific research that have not been considered before," says Peter Baum, corresponding author of the study published in Science and head of the Light and Matter research group at the University of Konstanz.

Chirality of single particles and composites

Chiral objects play a crucial role in nature and technology. In the realm of elementary particles, one of the most important chiral phenomena is spin, which is often compared to a self-rotation of a particle, but is in fact a purely quantum-mechanical property with no classical analog.

An electron, for example, has a spin of one-half and therefore often exists in two potential states: a right-handed and a left-handed one. This fundamental aspect of quantum mechanics gives rise to many important real-world phenomena like almost all magnetic phenomena or the periodic table of the elements. Electron spin is also critical to the development of advanced technologies such as quantum computers or superconductors.

However, there are also composite chiral objects in which none of the constituents is chiral by itself. Our hand, for example, is composed of atoms with no particular chirality, but it is nevertheless a chiral object, as we have learned earlier. The same is true for many molecules in which chirality appears without the need for any chiral constituent.

Whether a molecule is in the left-handed or in the right-handed geometry can make the differences between a healing drug and a harmful substance—both versions can have very different biological effects due to their different three-dimensional geometry.

In materials science and nanophotonics, chirality influences the behavior of magnetic materials and metamaterials, leading to phenomena such as topological insulators or chiral dichroism. The ability to control and manipulate the chirality of composite materials composed of achiral constituents thus offers a rich knob to tune the properties of materials as required for applications.