Physicists Create Bethe Strings in an Ultracold Gas for the First Time

Nearly a century after Hans Bethe predicted them in 1931, researchers from Innsbruck, Amsterdam and Munich have created and observed "Bethe strings" — bound groups of particles — in an ultracold gas of cesium atoms. The findings were published in Nature Communications.

• Cesium atoms were cooled to a few billionths of a degree above absolute zero
• The gas was split among thousands of narrow tubes, confining atoms to one dimension
• Strings included clusters of six or more particles and survived collisions intact
• Removing confinement broke the strings, releasing extra energy in 3D expansion