Brief
Physicists create and observe Bethe strings in ultracold atom experiment
The Innsbruck team used cesium atoms near absolute zero to form one‑dimensional bound states predicted by Hans Bethe.
By Felo News Desk · Published
Scientists at the University of Innsbruck have produced and detected quantum structures called Bethe strings, fulfilling a prediction made by Nobel laureate Hans Bethe in 1931. The work, led by quantum physicist Hanns‑Christoph Nägerl and published in Nature Communications, used ultracold cesium atoms confined to one‑dimensional tubes.
What happened
The researchers first cooled a cloud of cesium atoms to a few billionths of a degree above absolute zero. They then split the cloud into several thousand narrow tubes, each providing a one‑dimensional environment. By tuning the inter‑atomic interactions from repulsive to attractive, the atoms bound together in clusters of varying size, some containing six or more particles. These clusters constitute the Bethe strings.
What the report adds
The experiment demonstrates two key behaviours. First, when the strings were allowed to expand while remaining inside the tubes, they collided with one another yet remained intact, showing that the bound states survive collisions in one dimension. Second, when the confinement was removed and the atoms expanded into three‑dimensional space, the strings disintegrated, confirming that Bethe strings can exist only in a strictly one‑dimensional setting.
What was said
"One of the simplest experiments was to let the strings expand," Milena Horvath, a lead author, told ScienceDaily. She added, "This is a remarkable feature of the strings: they can collide without breaking apart."
How it came about
Hans Bethe first proposed that particles confined to one dimension could form collective bound states, later named Bethe strings, in a 1931 paper. For decades the idea remained theoretical. The Innsbruck team collaborated with theory groups at the University of Amsterdam and the Technical University of Munich to design an experiment that could realise the required conditions. Their success provides a highly controllable platform for studying many‑body quantum physics, building on recent advances such as the quantum‑energy‑ladder measurements reported by Felo News on 1 October 2026.
Key facts
- Bethe strings were created using ultracold cesium atoms confined to one‑dimensional tubes. (sciencedaily.com)
- The experiment was led by Hanns‑Christoph Nägerl at the University of Innsbruck. (sciencedaily.com)
- Clusters of up to six or more atoms were observed, confirming the bound‑state nature of Bethe strings. (sciencedaily.com)
- When released into three dimensions, the strings fell apart, showing they exist only in one dimension. (sciencedaily.com)
- Milena Horvath said the strings can collide without breaking apart. (sciencedaily.com)
Sources
- [1] sciencedaily.com — originally reported as “A quantum prediction from 1931 just came to life”
