Sound Propagation and Correlation of Quantum Degenerate $^{133}$Cs-$^6$Li Bose-Fermi Mixtures*

We investigate interactions and dynamics of Bose-Einstein condensates(BECs) of $^{133}$Cs atoms immersed in degenerate Fermi gases(DFGs) of $^6$Li atoms. At quantum degeneracy, the interplay between particle-hole excitations of DFGs and phonon excitations of the BECs gives rise to a variety of interesting phenomenon. Based on in-situ imaging and optical potential projection, we excite and image sound propagation in the Bose-Fermi mixtures with tunable interactions across an interspecies Feshbach resonance. Surprisingly, stable sound propagation is observed across the resonance. Furthermore, we develop fast dual species in situ imaging to study correlations of bosonic and fermionic fields in the presence of strong interspecies interactions.