This week in science | Science

A dilute atomic gas, cooled to a very low temperature, can enter the so-called quantum degenerate regime, where the quantum properties of the gas take over. This regime has been achieved for both bosonic and fermionic atoms, but the molecules, with their many internal states, represent a particular challenge. From Marco et al. cooled a bulk gas of fermionic molecules of potassium and rubidium up to a quantum degeneracy (see Zelevinsky Perspective). The authors first cooled the atomic potassium and rubidium gases separately and then bound them together into potassium and rubidium molecules before returning them to their ground state. The density profile of the molecular gas reveals the quantum nature of the system, which in turn keeps the gas stable by suppressing chemical reactions.

Science, this number p. 853; see also p. 820