In a cold cloud of sodium and rubidium atoms, physicists have for the first time assembled molecules that rotate like spinning tops. Usually, in ultracold experiments, atoms pair up without rotation, like two people holding hands and standing still. Here, the pairs got an extra kick: they spin around a common axis, and this rotation changes their behavior.
To create such pairs, the scientists used a magnetic field. It acts like glue: at a certain setting, the field makes sodium and rubidium atoms attract each other and form a molecule. First, the researchers found the right field strength — about 284 gauss (roughly 600 times stronger than Earth's magnetic field). Then they paired the atoms and obtained two types of molecules: some spun one way, others the opposite way, like tops spun in different directions.
Such rotating molecules are a new tool for exploring the quantum world. Rotation gives molecules "character": they can interact with neighbors differently depending on the direction of spin. This is similar to how gears in a clock only mesh when turned the right way. In the future, this could help create new quantum materials and model chemical reactions more precisely.
The magnetic field that binds atoms into molecules is about 600 times stronger than Earth's field, but thousands of times weaker than that in an MRI machine.