Observing spin-squeezed states under spin-exchange collisions for a second

Using the platform of a trapped-atom clock on a chip, we have observed the time evolution of spin-squeezed hyperfine clock states in ultracold rubidium atoms on previously inaccessible timescales up to 1\,s. The spin degree-of-freedom remains squeezed after 0.6\,s, which is consistent with the limit imposed by particle loss and compatible with typical Ramsey times in state-of-the-art microwave clocks. The results also reveal a surprising spin-exchange interaction effect which amplifies the cavity-based spin measurement via a correlation between spin and external degrees of freedom. These results open up perspectives for squeezing-enhanced atomic clocks in a metrologically relevant regime and highlight the importance of spin interactions in real-life applications of spin squeezing.