Higgs mode in a strongly interacting fermionic superfluid

Ultra-cold Fermi gases with tunable interactions have been widely used to investigate the BEC-BCS crossover in the last decade and superfluidity of Fermi gases with strong interaction have shown a variety of rich physics. Excitations and non-equilibrium dynamics related to pairing in strongly interacting atomic Fermi gases was proposed for studying excitations and pairing dynamics in superconductivity, however, experimental realization has been hindered by the difficulty of performing fast enough perturbations to the system.
In this talk, I will show our efforts in exploring Higgs/amplitude mode and non-equilibrium dynamics of strongly interacting Fermi gases of 6Li atoms. By inducing a periodic modulation of the amplitude of the superconducting order parameter ∆ with RF field, we observe an excitation resonance at frequency 2∆/h. For strong coupling, the peak width broadens and eventually the mode disappears when the Cooper pairs turn into tightly bound dimers signalling the eventual instability of the Higgs mode. I will also briefly discuss our experiment of the non-equilibrium dynamics of strongly interacting Fermi gases following rapid interaction quenches. With a fast population transfer, the interaction cross the Feshbach resonances between the different spin components is rapidly quenched, which induces non-equilibrium dynamics beyond prediction of collisionless BCS theory.