When someone’s being difficult, annoying or generally uncool, they’re said to “have no chill.” That’s certainly not a problem for a group of molecules used by MIT scientists in a groundbreaking experiment, which were chilled down to 500 nanokelvins – very nearly absolute zero. It’s the coldest temperature that scientists have ever been able to chill molecules down to, and they were rewarded with exotic states of matter never before observed.
Generally, molecules are zipping by us constantly – they may be the building blocks of matter, but they don’t behave like matter. Until you cool them down, at least. By cooling down the molecules in sodium potassium (NaK), the researchers were able to slow down their natural vibrations and cause them to act more or less as a cohesive body.
“We are very close to the temperature at which quantum mechanics plays a big role in the motion of molecules,” Zwierlein says. “So these molecules would no longer run around like billiard balls, but move as quantum mechanical matter waves. And with ultracold molecules, you can get a huge variety of different states of matter, like superfluid crystals, which are crystalline, yet feel no friction, which is totally bizarre. This has not been observed so far, but predicted. We might not be far from seeing these effects, so we’re all excited.”
The MIT technique actually involved cooling atoms and then forming them into molecules, which allowed them to surpass temperature records. The only problem was that when formed together, they were chemically unstable – collisions with room-temperature molecules led them to degrade quickly. The researchers were able to encapsulate them in light crystals to improve stability, but it makes it difficult to observe them in the real world.
“In the case where molecules are chemically reactive, one simply doesn’t have time to study them in bulk samples: They decay away before they can be cooled further to observe interesting states,” Zwierlein says. “In our case, we hope our lifetime is long enough to see these novel states of matter.”