All-optical formation of quantum degenerate mixtures

We report the realization of quantum degenerate mixed gases of ytterbium (Yb) isotopes using all-optical methods. We have succeeded in cooling attractively interacting ${}^{176}\mathrm{Yb}$ atoms via sympathetic cooling down to below the Bose-Einstein transition temperature, coexisting with a stable condensate of ${}^{174}\mathrm{Yb}$ atoms with a repulsive interaction. We have observed a rapid atom loss in ${}^{176}\mathrm{Yb}$ atoms after cooling down below the transition temperature, which indicates the collapse of a ${}^{176}\mathrm{Yb}$ condensate. The sympathetic cooling technique has been applied to cool a ${}^{173}\mathrm{Yb}\text{−}{}^{174}\mathrm{Yb}$ Fermi-Bose mixture to the quantum degenerate regime.

Figure 1

(Color online) Absorption images of (a) ${}^{174}\mathrm{Yb}$ and (b) ${}^{176}\mathrm{Yb}$ atoms and density distribution integrated over the vertical direction of ${}^{176}\mathrm{Yb}$ atoms after $12\mathrm{ms}$ of a free expansion. The data are averaged over five measurements. The solid line shows the fit by the Bose-Einstein distribution function, and the dashed line shows the Gaussian fit to the wings, yielding a temperature of $T\sim 120\mathrm{nK}$. Although a small “peak” can be seen in the center of the density distribution of ${}^{176}\mathrm{Yb}$ atoms, we cannot confirm that it is a BEC fraction because of residual fringes in our imaging system.

Figure 2

Number of ${}^{174}\mathrm{Yb}$ (solid circles) and ${}^{176}\mathrm{Yb}$ (open circles) atoms after evaporation. Each data point is the average of three measurements. A rapid decrease in the number of ${}^{176}\mathrm{Yb}$ atoms indicates that the collapse of a condensate in ${}^{176}\mathrm{Yb}$ occurs.

Figure 3

(Color online) Absorption images [(a) and (b)] and density distributions [(c) and (d)] integrated over the vertical direction of ${}^{173}\mathrm{Yb}$ and ${}^{174}\mathrm{Yb}$ atoms after a free expansion of $6\mathrm{ms}$ and $10\mathrm{ms}$, respectively. The optical density is normalized by the number of atoms for each sample. The data are averaged over five measurements.