A nanokelvin microwave freezer for molecules

When a highly diluted gas is cooled to extremely low temperatures, bizarre properties are revealed. Thus, some gases form a so-called Bose-Einstein condensate—a type of matter in which all atoms move in unison. Another example is supersolidity: a state in which matter behaves like a frictionless fluid with a periodic structure. Physicists expect to find particularly diverse and revealing forms of quantum matter when cooling gases consisting of polar molecules. They are characterized by an uneven electrical charge distribution. Unlike free atoms, they can rotate, vibrate and attract or repel each other. However, it is difficult to cool molecular gases to ultra-low temperatures. A team of researchers at the Max Planck Institute of Quantum Optics (MPQ) in Garching has now found a simple and effective way to overcome this roadblock. It is based on a rotating field of microwaves.