Photonic hopfions: Light shaped as a smoke ring that behaves like a particle

We can frequently find in our daily lives a localized wave structure that maintains its shape upon propagation--picture a smoke ring flying in the air. Similar stable structures have been studied in various research fields and can be found in magnets, nuclear systems, and particle physics. In contrast to a ring of smoke, they can be made resilient to perturbations. This is known in mathematics and physics as topological protection.