An October 16 interview report revisits an ultracold-atom experiment whose peer-reviewed paper appeared in August. Cesium atoms confined to narrow tubes expanded differently when released along a line or into three dimensions, supporting bound clusters of at least six atoms. Co-author Hanns-Christoph Nägerl stressed that the strings were not directly imaged and that agreement with theory falls short of proof.
An experiment with cesium atoms provides indirect evidence of Bethe strings: bound clusters predicted for particles that attract each other along a line. Live Science’s 16 October interview account discusses a peer-reviewed paper published on 29 August. Researchers cooled tens of thousands of atoms into a Bose–Einstein condensate, a state in which ultracold atoms share a quantum state, then divided the gas among narrow laser-made tubes.[1]
A magnetic field changed the atoms’ interaction from repulsion to attraction. The team compared expansion along the tubes with release into three dimensions, where the breakup of a bound cluster releases its binding energy into the atoms’ motion. That additional release energy supported groups containing at least six atoms. A theory of collective flow called generalized hydrodynamics also gave results consistent with those measurements.[1]
The team inferred the strings from measurements rather than observing them in a direct image. Experimental physicist Hanns-Christoph Nägerl of the University of Innsbruck, a co-author, cautioned that a theory fitting measurements does not prove the proposed objects exist. Atom losses reached about 40 per cent in the coldest runs. He discussed shielded molecules and atom-resolving microscopy as possible future approaches; those proposals have not yet been tested in this experiment.[1]
