Science https://doi.org/czsn (2019)

Compared with atoms, molecules are much more complex owing to the additional rotational and vibrational degrees of freedom. This complexity makes it challenging to cool them all the way down to their ground state, and to reach the quantum degenerate regime where the thermal de Broglie wavelength exceeds the intermolecule distance. After a decade of effort, this goal has now been achieved by Luigi De Marco and co-workers, who have created a degenerate Fermi gas of potassium–rubidium polar molecules.

The molecules were made by cooling potassium and rubidium atoms to a few hundred nanokelvin and coherently associating them into deeply bound states. At the lowest achievable temperature, a Fermi–Dirac distribution shown in the density profile signified that the Fermi gas deviated from its classical regime. The quantum correlation caused a reduction of the density fluctuations, leading to the suppression of chemical reactions and molecular losses, thus making the system surprisingly long-lived and promising for future applications.