Ultracold molecules hint at quantum behaviour

By achieving the lowest temperature ever recorded, scientists have managed to create ultracold molecules which seem to exist in exotic state. 

A research team at the Massachusetts Institute of Technology used a gas mixture of sodium potassium to cool molecules to 500 nanokelvins – just above absolute zero (-273°C) – to create ultracold molecules.

“We are very close to the temperature at which quantum mechanics plays a big role in the motion of molecules,” said research leader Professor Martin Zwierlein.

In the study, published in the journal Physical Review Letters, the team used lasers and evaporative cooling to cool clouds of individual sodium and potassium atoms to temperatures just above absolute zero. To form ultracold molecules the team applied a magnetic field to prompt the atoms to bond – a mechanism known as Feshbach resonance.

At the record-low temperature, the scientists observed the motion of the atoms and found that they are a million times slower and it takes them half a minute to move 2.5cm. They also discovered that the formed molecules are relatively long-lived and stable whilst also exhibiting very strong dipole moments causing strong imbalances in electric charge.

Professor Zwierlein said: “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. In our case, we hope our lifetime is long enough to see these novel states of matter. 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.”

To begin to see exotic states of matter, the scientists believe that molecules have to be cooled to absolute zero.

“Now we’re at 500 nanokelvins, which is already fantastic, we love it. A factor of 10 colder or so, and the music starts playing,” said Professor Zwierlein.

Paper: http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.114.205302