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How to Trap Two Different Atoms with a Single Laser ✛

Original: "Simultaneous sub-Doppler laser cooling and optical trapping of bosonic $$^{39}$$K-$$^{133}$$Cs and $$^{41}$$K-$$^{133}$$Cs mixtures"
· Mateusz Bocheński, Jakub Dobosz, Koray Dinçer, Paweł Arciszewski, Mariusz Semczuk
arXiv:2609.09003v1 · 2026-09-08 · CC BY 4.0 · 1 min
Atomic Physics Quantum Gases
Physicists have for the first time stopped and held together atoms of potassium-41 and cesium, a mixture that had previously resisted trapping.

Two different cars drive along the same road, and the same brake slows both down to a walking pace. That is roughly how physicists stopped potassium and cesium atoms: a laser beam pushes each atom against its motion and saps its energy until the atoms are almost motionless.

Laser light acts like a stream of tiny balls. When a photon hits a moving atom, the atom slows down slightly. Millions of such impacts, and the atom crawls at a speed of a few centimeters per second.

Previously, no one had been able to trap a mixture of potassium-41 and cesium: the atoms were lost too quickly. Now scientists have done it for the first time, and in the process found nine new ways to control collisions between potassium-39 atoms and cesium. These methods work like tuning knobs: turn the magnetic field, and the atoms collide more strongly or more weakly. In the future, such mixtures could help assemble molecules for quantum computers.

The mixture's temperature of about 10 microkelvin is only a hundred times above absolute zero. At such a temperature, atoms move at speeds on the order of a few centimeters per second, like a leisurely pedestrian.