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arXiv:1102.1576 · Physical Review A

Dual-species Bose-Einstein condensate of Rb87 and Cs133

Daniel McCarron, H. W. Cho, Daniel L. Jenkin, Michael P. Köppinger, Simon L. Cornish

Published Jul 13, 2011• 232 citations
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Abstract

We report the formation of a dual-species Bose-Einstein condensate of $^{87}\mathrm{Rb}$ and $^{133}\mathrm{Cs}$ in the same trapping potential. Our method exploits the efficient sympathetic cooling of $^{133}\mathrm{Cs}$ via elastic collisions with $^{87}\mathrm{Rb}$, initially in a magnetic quadrupole trap and subsequently in a levitated optical trap. The two condensates each contain up to $2\ifmmode\times\else\texttimes\fi{}{10}^{4}$ atoms and exhibit a striking phase separation, revealing the mixture to be immiscible due to strong repulsive interspecies interactions. Sacrificing all the $^{87}\mathrm{Rb}$ during the cooling, we create single-species $^{133}\mathrm{Cs}$ condensates of up to $6\ifmmode\times\else\texttimes\fi{}{10}^{4}$ atoms.

DOI
10.1103/physreva.84.011603

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We report the formation of a dual-species Bose-Einstein condensate of 87Rb^{87}\mathrm{Rb}87Rb and 133Cs^{133}\mathrm{Cs}133Cs in the same trapping potential. Our method exploits the efficient sympathetic cooling of 133Cs^{133}\mathrm{Cs}133Cs via elastic collisions with 87Rb^{87}\mathrm{Rb}87Rb, initially in a magnetic quadrupole trap and subsequently in a levitated optical trap. The two condensates each contain up to 2\ifmmode×\else\texttimes\fi1042\ifmmode\times\else\texttimes\fi{}{10}^{4}2\ifmmode×\else\texttimes\fi104 atoms and exhibit a striking phase separation, revealing the mixture to be immiscible due to strong repulsive interspecies interactions. Sacrificing all the 87Rb^{87}\mathrm{Rb}87Rb during the cooling, we create single-species 133Cs^{133}\mathrm{Cs}133Cs condensates of up to 6\ifmmode×\else\texttimes\fi1046\ifmmode\times\else\texttimes\fi{}{10}^{4}6\ifmmode×\else\texttimes\fi104 atoms.
This thesis reports the formation of a dual-species Bose-Einstein condensate of 87^{87}87Rb and 133^{133}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 133^{133}133Cs via elastic collisions with 87^{87}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\sim10^{-25}-10^{-26}∼10−25−10−26~cm6/^{6}/6/s}. The two condensates each contain up to \mbox{2×1042\times10^{4}2×104} atoms and exhibit a striking phase separation, revealing the mixture to be immiscible due to strong repulsive interspecies interactions. Sacrificing all the 87^{87}87Rb during the cooling leads to the creation of single-species 133^{133}133Cs condensates of up to \mbox{6×1046\times10^{4}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 Cs2_{2}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 report on the production of a $^{41}\mathrm{K}\text{\ensuremath{-}}^{87}\mathrm{Rb}$ dual-species Bose-Einstein condensate in a hybrid trap, consisting of a magnetic quadrupole and an optical dipole potential. After loading both atomic species in the trap, we cool down 87Rb^{87}\mathrm{Rb}87Rb first by magnetic and then by optical evaporation, while 41K^{41}\mathrm{K}41K is sympathetically cooled by elastic collisions with 87Rb^{87}\mathrm{Rb}87Rb. We eventually produce two-component condensates with more than 105{10}^{5}105 atoms and tunable species population imbalance. We observe the immiscibility of the quantum mixture by measuring the density profile of each species after releasing them from the trap.
We present the production of dual-species Bose-Einstein condensates (BECs) of 39K^{39}\mathrm{K}39K and 87Rb^{87}\mathrm{Rb}87Rb. Preparation of both species in the $\left|F=1,{m}_{F}=\ensuremath{-}1\right\ensuremath{\rangle}$ state enabled us to exploit a total of three Feshbach resonances, which allows for simultaneous Feshbach tuning of the 39K^{39}\mathrm{K}39K intraspecies and the $^{39}\mathrm{K}\text{\ensuremath{-}}^{87}\mathrm{Rb}$ interspecies scattering length. Thus dual-species Bose-Einstein condensates were produced by sympathetic cooling of 39K^{39}\mathrm{K}39K with 87Rb^{87}\mathrm{Rb}87Rb. A dark spontaneous force optical trap was used for 87Rb^{87}\mathrm{Rb}87Rb to reduce the losses in 39K^{39}\mathrm{K}39K due to light-assisted collisions in the optical trapping phase, which can be of benefit for other dual-species experiments. The tunability of the scattering length was used to perform precision spectroscopy of the interspecies Feshbach resonance located at 117.56(2) G and to determine the width of the resonance to 1.21(5) G by rethermalization measurements. The transition region from miscible to immiscible dual-species condensates was investigated and the interspecies background scattering length was determined to 28.5a028.5{a}_{0}28.5a0​ using an empirical model. This paves the way for dual-species experiments with 39K^{39}\mathrm{K}39K and 87Rb^{87}\mathrm{Rb}87Rb BECs ranging from molecular physics to precision metrology.
We report the creation of dual-species Bose-Einstein condensates (BECs) of 7Li^{7}\mathrm{Li}7Li and 133Cs^{133}\mathrm{Cs}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{a}_{\mathrm{Cs}}=123{a}_{0}, {a}_{\mathrm{Li}}=484{a}_{0}aCs​=123a0​,aLi​=484a0​, and aLiCs=248a0{a}_{\mathrm{LiCs}}=248{a}_{0}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.
Dual-species Bose-Einstein condensates of 23^{23}23Na and 41^{41}41K with tunable interactions
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We report on the production of a 41 K- 87 Rb dual-species Bose–Einstein condensate with tunable interspecies interaction and we study the mixture in the attractive regime; i.e., for negative values of the interspecies scattering length a 12 . The binary condensate is prepared in the ground state and confined in a pure optical trap. We exploit Feshbach resonances for tuning the value of a 12 . After compensating the gravitational sag between the two species with a magnetic field gradient, we drive the mixture into the attractive regime. We let the system evolve both in free space and in an optical waveguide. In both geometries, for strong attractive interactions, we observe the formation of self-bound states, recognizable as quantum droplets. Our findings prove that robust, long-lived droplet states can be realized in attractive two-species mixtures, despite the two atomic components possibly experiencing different potentials.