We report the production of quantum degenerate Bose-Bose mixtures of Cs and Yb with both attractive (Cs + 174Yb) and repulsive (Cs + 170Yb) interspecies interactions. Dual-species evaporation is performed in a bichromatic optical dipole trap that combines light at 1070 nm and 532 nm to enable control of the relative trap depths for Cs and Yb. Maintaining a trap which is shallower for Yb throughout the evaporation leads to highly efficient sympathetic cooling of Cs for both isotopic combinations at magnetic fields close to the Efimov minimum in the Cs three-body recombination rate at around 22 G. For Cs + 174Yb, we produce quantum mixtures with typical atom numbers of NYb ∼ 5 × 104 and NCs ∼ 5 × 103. We find that the attractive interspecies interaction (characterized by the scattering length aCsYb = −75a0) is stabilized by the repulsive intraspecies interactions. For Cs + 170Yb, we produce quantum mixtures with typical atom numbers of NYb ∼ 4 × 104 and NCs ∼ 1 × 104. Here, the repulsive interspecies interaction (aCsYb = 96a0) can overwhelm the intraspecies interactions, such that the mixture sits in a region of partial miscibility
We report the realization of quantum degenerate mixed gases of ytterbium (Yb) isotopes using all-optical methods. We have succeeded in cooling attractively interacting
176Yb atoms via sympathetic cooling down to below the Bose-Einstein transition temperature, coexisting with a stable condensate of
174Yb atoms with a repulsive interaction. We have observed a rapid atom loss in
176Yb atoms after cooling down below the transition temperature, which indicates the collapse of a
176Yb condensate. The sympathetic cooling technique has been applied to cool a $^{173}\mathrm{Yb}\text{\ensuremath{-}}^{174}\mathrm{Yb}$ Fermi-Bose mixture to the quantum degenerate regime.
We have produced a quantum degenerate mixture of fermionic alkali-metal
6Li and bosonic spin-singlet
174Yb gases. This was achieved using sympathetic cooling of lithium atoms by evaporatively cooled ytterbium atoms in a far-off-resonant optical dipole trap. We observe the coexistence of Bose-condensed ($T/{T}_{\mathrm{c}}\ensuremath{\simeq}0.8$)
174Yb with $2.3\ifmmode\times\else\texttimes\fi{}{10}^{4}$ atoms and Fermi degenerate ($T/{T}_{\mathrm{F}}\ensuremath{\simeq}0.3$)
6Li with $1.2\ifmmode\times\else\texttimes\fi{}{10}^{4}$ atoms. Quasipure Bose-Einstein condensates of up to $3\ifmmode\times\else\texttimes\fi{}{10}^{4}$
174Yb atoms can be produced in single-species experiments. Our results mark a significant step toward studies of few- and many-body physics with mixtures of alkali-metal and alkaline-earth-metal-like atoms, and for the production of paramagnetic polar molecules in the quantum regime. Our methods also establish a convenient scheme for producing quantum degenerate ytterbium atoms in a 1064 nm optical dipole trap.
This thesis reports the formation of a dual-species Bose-Einstein condensate of
87Rb and
133Cs in the same trapping potential. Quantum degenerate mixtures exhibit rich physics inaccessible to single species experiments and provide an ideal starting point for the creation of ultracold dipolar molecules. These molecules offer a wealth of new research avenues including precision metrology, quantum simulation and computation. The experimental method exploits the efficient sympathetic cooling of
133Cs via elastic collisions with
87Rb, initially in a magnetic quadrupole trap and subsequently in a levitated optical trap. Evaporative cooling in the dipole trap must compete against a high interspecies three-body inelastic collision rate \mbox{
∼10−25−10−26~cm
6/s}. The two condensates each contain up to \mbox{
2×104} atoms and exhibit a striking phase separation, revealing the mixture to be immiscible due to strong repulsive interspecies interactions. Sacrificing all the
87Rb during the cooling leads to the creation of single-species
133Cs condensates of up to \mbox{
6×104} atoms. In addition this thesis reports the observation of an interspecies Feshbach resonance at 181.7(5)~G and the creation of a pure sample of Cs
2 molecules via magneto-association on the 4(g)4 resonance at 19.8~G. These results represent important steps towards the creation of ultracold polar RbCs molecules.
We realize simultaneous quantum degeneracy in mixtures consisting of the alkali and alkaline-earth-like atoms Li and Yb. This is accomplished within an optical trap by sympathetic cooling of the fermionic isotope
6Li with evaporatively cooled bosonic
174Yb and, separately, fermionic
173Yb. Using cross-thermalization studies, we also measure the elastic
s-wave scattering lengths of both Li-Yb combinations, $|{a}_{^{6}\mathrm{Li}\ensuremath{-}^{174}\mathrm{Yb}}|=1.0\ifmmode\pm\else\textpm\fi{}0.2\text{ }\text{ }\mathrm{nm}$ and $|{a}_{^{6}\mathrm{Li}\ensuremath{-}^{173}\mathrm{Yb}}|=0.9\ifmmode\pm\else\textpm\fi{}0.2\text{ }\text{ }\mathrm{nm}$. The equality of these lengths is found to be consistent with mass-scaling analysis. The quantum degenerate mixtures of Li and Yb, as realized here, can be the basis for creation of ultracold molecules with electron spin degrees of freedom, studies of novel Efimov trimers, and impurity probes of superfluid systems.