Potassium molecules cooled to temperatures just above absolute zero could exhibit strange behaviors. In a new study, researchers brought molecules of gas down to just above the coldest possible temperature.
Sodium potassium (NaK) molecules were cooled to just 500-billionths of a degree Celsius over absolute zero. At this temperature, no more energy remains in molecules that can be extracted as heat. The temperature to which the gas was lowered is a million times colder than interstellar space.
Molecules of air typically collide into each other at speeds of several hundreds of miles per hour. Researchers have long suspected that if gases were frozen down to temperatures just above absolute zero, the molecules would all act together as a single unit. This strange form of matter has never been seen, remaining a theoretical idea.
When researchers brought the gas down to these ultracold temperatures, they found the magnetic difference in between poles of molecules became more pronounced. The molecules were also found to become longer-lived as collisions between the molecular units became less frequent. Molecules in this super-cooled state traveled just inches per second, vibrating and tumbling at the lowest possible rate.
"We are very close to the temperature at which quantum mechanics plays a big role in the motion of molecules. So these molecules would no longer run around like billiard balls, but move as quantum mechanical matter waves," Martin Zwierlein of the Massachusetts Institute of Technology (MIT) said.
Sodium potassium was selected for the study due to the fact that it is an example of the simplest class of molecules. The structure is made up of just two atoms — one each of potassium and sodium, bound together like a dumbbell.
Molecules tumble and vibrate erratically, making it difficult for the material to freeze. Doing so with single atoms is a much easier task. Bringing the sodium potassium molecules to just above absolute zero was accomplished in a multistage process.
The first step involved evaporative cooling and lasers to slow down motions of the molecules. Later, magnets were used to coax the molecules into binding with one another, forming a single large, supercold molecule. However, these bonds only bind the molecules together weakly, allowing the particles to vibrate faster than desired. A pair of lasers was then employed to bind the molecules together as a more cohesive hole.
Some of the theoretical properties of such supercold materials are bizarre when compared with the behavior of matter at room temperature.
"[W]ith 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," Zwierlein said.
Analysis of supercold sodium potassium was detailed in the journal Physical Review Letters.