How to Freeze Out Collisions

Ultracold atoms--at temperatures of just a few nanokelvin--may serve as atomic "clocks" that can measure time with extremely high precision. Of the two types of atoms, bosons and fermions, the former have been pursued most actively as possible atomic clocks. In his Perspective, Inguscio draws attention to the possible advantages of fermions for such applications. He highlights the report by Gupta et al., who show that a fermion clock transition can be realized without collisional shifts. Radio-frequency spectroscopy turns out to be crucial for investigating interacting fermionic actoms as well as for probing the formations of ultracold molecules.