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 present measurements of interspecies thermalization between ultracold samples of
133Cs and either
174Yb or
170Yb. The two species are trapped in a far-off-resonance optical dipole trap and
133Cs is sympathetically cooled by Yb. We extract effective interspecies thermalization cross sections by fitting the thermalization measurements to a kinetic model, giving ${\ensuremath{\sigma}}_{\mathrm{Cs}^{174}\mathrm{Yb}}=\left(5\ifmmode\pm\else\textpm\fi{}2\right)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}13}\phantom{\rule{0.16em}{0ex}}{\mathrm{cm}}^{2}$ and ${\ensuremath{\sigma}}_{\mathrm{Cs}^{170}\mathrm{Yb}}=\left(18\ifmmode\pm\else\textpm\fi{}8\right)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}13}\phantom{\rule{0.16em}{0ex}}{\mathrm{cm}}^{2}$. We perform quantum scattering calculations of the thermalization cross sections and optimize the CsYb interaction potential to reproduce the measurements. We predict scattering lengths for all isotopic combinations of Cs and Yb. We also demonstrate the independent production of
174Yb and
133Cs Bose-Einstein condensates using the same optical dipole trap, an important step toward the realization of a quantum-degenerate mixture of the two species.
We probe the collective dynamics of a quantum degenerate Bose-Bose mixture of 133Cs and 174Yb with attractive interspecies interactions. Specifically, we excite vertical center-of-mass oscillations of the Cs condensate. We 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 with experiment 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. By further tuning the interaction strength of Cs using a broad Feshbach resonance, we explore the stability of the degenerate mixture. We observe collapse of the Cs condensate mediated by the attractive Cs-Yb interaction when aCs<50a0, well above the single-species collapse threshold, in good agreement with simulations.
We report the creation of dual-species Bose-Einstein condensates (BECs) of
7Li and
133Cs. These BECs are formed in a bichromatic optical dipole trap created with 1550-nm and 780-nm laser beams. During the production process, an external magnetic field of 886~G is applied to adjust the scattering lengths to
aCs=123a0,
aLi=484a0, and
aLiCs=248a0. These scattering lengths allow for efficient evaporation and sympathetic cooling. The dual-species BECs are typically produced with
1.5×104 Cs atoms and
6.0×103 Li atoms. This quantum degenerate mixture of Li and Cs provides an ideal platform for exploring phenomena such as polarons and Efimov trimers, as well as for creating ground-state LiCs molecules.
We probe the collective dynamics of a quantum degenerate Bose-Bose mixture of
133Cs and
174Yb with attractive interspecies interactions. Specifically, we excite vertical center-of-mass oscillations of the Cs condensate. We 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 with experiment 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. By further tuning the interaction strength of Cs using a broad Feshbach resonance, we explore the stability of the degenerate mixture. We observe collapse of the Cs condensate mediated by the attractive Cs-Yb interaction when
aCs<50a0, well above the single-species collapse threshold, in good agreement with simulations.
We report the creation of dual-species Bose-Einstein condensates (BECs) of
7Li and
133Cs. These BECs are formed in a bichromatic optical dipole trap created with 1550- and 780-nm laser beams. During the production process, an external magnetic field of 886 G is applied to adjust the scattering lengths to
aCs=123a0,aLi=484a0, and
aLiCs=248a0. These scattering lengths allow for efficient evaporation and sympathetic cooling. The dual-species BECs are typically produced with $1.5\ifmmode\times\else\texttimes\fi{}{10}^{4}$ Cs atoms and $6.0\ifmmode\times\else\texttimes\fi{}{10}^{3}$ Li atoms. This quantum degenerate mixture of Li and Cs provides an ideal platform for exploring phenomena such as polarons and Efimov trimers, as well as for creating ground-state LiCs molecules.