Kali Wilson (University of Strathclyde) gives a webinar on “Collective dynamics of quantum degenerate Cs-Yb mixtures”.

We form quantum degenerate Bose-Bose mixtures of Cs and Yb with either attractive (Cs+174Yb) and repulsive (Cs+170Yb) interactions. In both scenarios we use a bichromatic optical dipole trap to control the relative Cs and Yb trap depths, and enable sympathetic cooling of Cs by Yb [1]. We probe the collective dynamics of the attractive Cs+174Yb mixture. Specifically, we excite vertical center of mass oscillations of the Cs condensate, and observe significant damping for the Cs dipole mode, due to the rapid transfer of energy to the larger Yb component, and the ensuing acoustic dissipation. Numerical simulations based on coupled Gross-Pitaevskii equations provide excellent agreement, and additionally reveal the possibility of late-time revivals (beating) which are found to be highly sensitive to the Cs and Yb atom number combinations [2,3]. By further tuning the interaction strength of Cs using a broad Feshbach resonance, we explore the stability of the degenerate mixture, and observe collapse of the Cs condensate mediated by the attractive Cs-Yb interaction, in good agreement with simulations. This opens up new prospects for the study of the BEC to quantum droplet phase transition. In this context, a key advantage of Cs-Yb mixtures is that the Cs scattering length may be precisely tuned without affecting Yb. Additionally, the very different atomic structure of Cs and Yb enables species-specific optical traps with low photon scattering rates. These advantages may prove invaluable for precise studies of binary fluid dynamics in both Bose-Bose and Bose-Fermi Cs-Yb mixtures.

[1] K.E. Wilson, A. Guttridge et al., PRA 103, 033306 (2021).

[2] K.E. Wilson, A. Guttridge et al., arXiv:2012.11008.

[3] I.K. Liu et al. (in preparation).