Searching for Breakdowns of Classical Spin Rotation Models in Weakly-Interacting Fermi Gases

Weakly-interacting Fermi gases have been modeled as classical spin chains in energy space. This spin vector evolution model is able to predict the spin-density profiles successfully for short (<1s) spin evolution after coherent excitation. However, fitting this model to out-of-time order correlation measurements requires a scattering length that is 2.5 times larger than the measured value, and the spin-density amplitude diverges from the model at longer evolution times. We will report our recent measurements attempting to understand these discrepancies.