An electron is not just a point. It is a probability cloud, smeared out in space. When such a cloud collides with a powerful laser pulse, it can emit a high-energy photon — a gamma quantum. And this photon can be not just ordinary but twisted, like a corkscrew, carrying orbital angular momentum.
Previously, it was believed that the twist of a photon depended only on the properties of the laser and the incoming particles. But the authors of this work looked at the electron itself: its transverse shape, how the cloud is distributed sideways relative to the direction of motion, directly sets the spectrum of twist in the emitted photons. This is similar to how the shape of holes in a showerhead determines the pattern of water jets. A narrow Gaussian cloud gives one set of moments, a vortex electron gives another, and an arbitrary shape gives its own unique pattern.
This approach turns the shape of the electron cloud into a tool. By changing it, one can pre-design the desired distribution of twisted gamma quanta. This paves the way for creating sources of twisted gamma radiation with tailored properties — a sort of light factory where each photon comes out with a precisely measured twist.
The orbital angular momentum of a photon is like the Earth's rotation around the Sun, but for a light particle. Such twisted light can carry more information than ordinary light.