Physicists first cooled molecules to 220 nanokelvin. This was possible due to collisions with ultracold sodium atoms, according to a study by scientists from the Massachusetts Institute of Technology, led by Nobel laureate Wolfgang Ketterle, which was published in the journal Nature.
In the past few decades, physicists have made great strides in cooling atoms to a temperature close to absolute zero. Such experiments are carried out using lasers when irradiated, atoms lose energy and move more slowly – and, as a result, are cooled.
It is impossible to repeat the same experiment with molecules – because of their complex shape until now, it has been possible to cool molecules to only ten millikelvins (0.01 K).
In a new study, physicists found a way to cool molecules to an even lower temperature using an atom trap created at the end of the 20th century – only in place of atoms in a new experiment, it was redone for molecules.
The principle of operation of the classic version of the trap is that the device selectively passes the hottest atoms and mixes them with the cold ones. Hot take away excess energy from a cloud of cold, and then fly out, causing cold atoms to cool even more.
The researchers partially repeated the design of the trap by adding lasers to it. The experiment involved lithium and sodium atoms, the hottest of which bombarded a cloud of molecules.
As a result, the temperature in the experimental setup dropped to 200 nanokelvin (0.0000002 K) – this is a record low value, which is five times lower than the limits imposed by the laws of quantum physics.
“Similar methods have long been used to cool atoms. Initially, I was not sure that our methodology would work. But, since we did not know this for sure, we still conducted an experiment. Now we can say for sure that for lithium and sodium molecules this approach works. Whether it is suitable for other substances, we have yet to find out”.
Wolfgang Ketterle, lead author of the study