# Physicists Observe Century-Old Quantum Bethe String Theory Researchers successfully created atomic necklaces to validate long-standing quantum mechanics predictions. - **Source:** [Latest from Live Science](https://www.livescience.com/feeds.xml) - **Published:** 2026-10-16 - **Topic:** [Business](https://brifing.si/c/business) - **Original article:** - **On Brifing:** https://brifing.si/s/8b619a9e-83a3-432e-8169-39cfee08ae6b ## Century-Old Theoretical Foundation In 1931, physicist Hans Bethe proposed that electron spins in a row could form clusters if they attract each other. These theoretical structures, known as Bethe strings, describe how particles bind together. Recent experiments have finally provided empirical evidence for these clusters using ultracold cesium atoms in a controlled laboratory environment. ## Creating Atomic Necklaces Researchers at the University of Innsbruck utilized a Bose-Einstein condensate to form these atomic structures. By using laser beams to isolate atoms into thousands of thin, one-dimensional tubes, they prevented the typical collapse seen in three-dimensional gas. This configuration allowed the atoms to align like pearls on a string, maintaining their stability. ## Magnetic Field Manipulation The team initially maintained repulsion between the cesium atoms to ensure stability. By applying a magnetic field, they gradually reduced this repulsion to zero and shifted the interaction toward attraction. This precise control allowed the formation of multiple Bethe strings of varying sizes, including clusters containing more than six individual atoms simultaneously. ## Measuring Binding Energy Direct observation of the strings remained impossible with current technology. Instead, researchers measured the expansion speed of the atom clouds when released. They discovered that three-dimensional clouds spread with three times the energy of one-dimensional ones. This energy difference provided the necessary data to estimate the binding strength of the atomic clusters. ## Generalized Hydrodynamics Alignment The experimental results closely matched predictions from generalized hydrodynamics, a theory describing gases as fluids composed of various particle types. This framework tracks the flow of different particle species over time rather than monitoring individual atoms. The data suggests that these strings behave exactly as the mathematical models predicted decades ago. ## Transient Nature of Strings These quantum states are inherently short-lived due to the influence of the surrounding three-dimensional environment. During the coldest experimental runs, the team observed a 40% loss of atoms as the strings decayed into ordinary cesium molecules. This instability highlights the difficulty of maintaining such delicate quantum states for extended observation periods. ## Future Experimental Pathways Hanns-Christoph Nägerl proposes using microwave shielding to protect ultracold molecules from collisions, potentially extending the lifespan of these strings. Alternatively, quantum gas microscopy could allow for direct imaging of individual strings. These methods aim to move beyond indirect evidence toward a more granular understanding of how quantum systems settle over time. ## Building Model Materials The long-term objective involves assembling model materials piece by piece, similar to a LEGO construction. By controlling both particle movement and spin flips, researchers hope to simulate complex quantum systems. While Bethe strings are currently a diversion, they remain a fundamental component in understanding how interacting particles dictate material properties. ## Sources covering this story - https://www.livescience.com/physics-mathematics/physicists-froze-a-necklace-of-atoms-and-witnessed-a-quantum-phenomenon-predicted-100-years-ago — --- _Summary written by Brifing from the original reporting. Copyright in the original article belongs to its publisher; read the full piece at the link above._