Scientists Observe Bethe Strings in Ultracold Cesium Gas

Researchers have finally created and directly observed the elusive quantum states first predicted by physicist Hans Bethe in 1931. Using an ultracold gas of cesium atoms, the team cooled the atoms to near absolute zero and confined them in thousands of microscopic one‑dimensional tubes. Within this environment, groups of atoms spontaneously bound together without forming ordinary chemical bonds, forming clusters that can contain six or more particles. Remarkably, these clusters—known as Bethe strings—can collide with one another and remain intact, a behavior never seen before. The experiment confirms Bethe’s theoretical prediction and demonstrates a new class of stable, multi‑particle quantum states.