In 1931, physicist Hans Bethe analyzed a single row of electrons, each with a spin that could point up or down. He worked out the mathematics showing that if a few spins flip, they can stick together and travel down the row as a single unit. Decades later, researchers found that Bethe's method also applies to larger particles moving along a line, such as atoms. When those particles attract each other, theory predicts they will bind into clusters called Bethe strings.
Now, an experiment using ultracold atoms arranged in a linear 'necklace' has provided evidence for these clusters. The results were published August 29 in the journal Nature Communications. The discovery addresses a fundamental mystery: how countless interacting particles give rise to the properties of materials around us, from magnets to computer chips. Ultracold atoms offer a clean and adjustable platform for studying such complex many-body systems, allowing researchers to probe phenomena that are difficult to predict or simulate theoretically.
While the finding is not expected to immediately lead to new technologies, it validates a theoretical prediction from the early days of quantum mechanics and demonstrates the power of ultracold atom experiments as quantum simulators for condensed matter physics.