Ultracold cesium atoms challenge rules of physics, refuse to heat up

Researchers at the University of Innsbruck have demonstrated that ultracold cesium atoms can defy the expected process of thermalisation, where systems typically absorb energy and lose order by heating up. By cooling about 100,000 cesium atoms to just billionths of a degree above absolute zero and confining them in one-dimensional microscopic tubes, the team subjected the atoms to repeated laser pulses intended to jolt and heat them. Contrary to classical expectations, after an initial period, the atoms’ momentum distribution ceased to spread even after hundreds of energy kicks, effectively freezing into a stable quantum state with nearly identical velocities rather than dispersing chaotically. This discovery challenges a fundamental assumption in physics that interacting many-particle systems inevitably thermalise and lose coherence. It confirms longstanding theoretical predictions that quantum effects can protect such systems from heating and entropy increase, a phenomenon difficult to observe experimentally due to the complexity of many-body interactions. The ability to prevent thermalisation is crucial for advancing quantum technologies like sensors, memories,