New Low Temperature Record Set by Large Molecules

The four-atom molecule is the largest uncooled molecule to just 100 billionths of a degree below absolute zero.

Techniques researchers use to cool individual atoms, such as applying lasers or magnetic forces to them, have little effect on molecules. This is especially true for molecules made up of many atoms. Because to be very cold, the molecules must be very still. The more moving parts a molecule has, the more opportunities it has to move and heat up.

“There's a joke that we study molecules not because they're easy, but because they're difficult,” he says. Luo Xinyu at the Max Planck Institute for Quantum Optics in Germany. He and his colleagues were able to make a four-atom molecule even cooler than before.

They started with thousands of molecules made up of one sodium atom and one potassium atom, trapped them in an airless chamber, and cooled them, or made them very still, with magnetic forces and bursts of light.of lowest possible temperature 0 Kelvin, or absolute zero; these molecules were only 97 billionths of a billionth of a degree Kelvin.

To turn these diatomic molecules into tetraatomic molecules, the researchers needed to combine them in pairs without warming them up. They used microwave fields to “glue” the molecules together, based on the following theoretical calculations. Tao Xi and Suey Chinese Academy of Sciences. “I didn't really know if I could put these molecules together, but Tao's team did the calculations and he said to me, 'This is possible, give it a try.'” says Luo.

Their attempt was successful. The researchers created about 1,100 molecules, each containing two potassium atoms and two sodium atoms, at a temperature of 134 billionths of a billionth of a kelvin. This is the largest molecule ever to reach this cryogenic temperature.

“One of the reasons we make molecules ultracold in the first place is so we can have more control over them, and this is a big step forward in that sense,” he says. john bourne At the University of Colorado Boulder. This new experiment is important not only because the molecules are at unprecedented temperatures, but also because at the coldest temperatures molecules can enter known quantum states and be forced into other states or processes. accuratelyhe says.

Luo says the atoms in these molecules are not “glued” to each other as strongly as the atoms in molecules at room temperature. But making them is a necessary step in studying complex chemical reactions, which are easier to observe when they are very cold and slow.

Next question is Is there something else, perhaps an even larger molecule? Using similar microwave technology, it could be made from similarly frigid materials at extremely low temperatures, he said. sebastian will At Columbia University in New York. “I think we are looking at exciting new opportunities in quantum chemistry!” he says.