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arXiv:1305.5935 · Physical Review A

Quantum degenerate mixtures of strontium and rubidium atoms

Benjamin Pasquiou, Alex Bayerle, Slava Malenkova Tzanova, Simon Stellmer, J. Szczepkowski, Mark Parigger, Rudolf Grimm, Florian Schreck

Published Aug 1, 2013• 120 citations
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Abstract

We report on the realization of quantum degenerate gas mixtures of the alkaline-earth-metal element strontium with the alkali-metal element rubidium. A key ingredient of our scheme is sympathetic cooling of Rb by Sr atoms that are continuously laser cooled on a narrow-linewidth transition. This versatile technique allows us to produce ultracold gas mixtures with a phase-space density of up to 0.06 for both elements. By further evaporative cooling we create double Bose-Einstein condensates of ${}^{87}$Rb with either ${}^{88}$Sr or ${}^{84}$Sr, reaching more than $1\ifmmode\times\else\texttimes\fi{}{10}^{5}$ condensed atoms per element for the ${}^{84}$Sr-${}^{87}$Rb mixture. These quantum gas mixtures constitute an important step towards the production of a quantum gas of polar, open-shell RbSr molecules.

DOI
10.1103/physreva.88.023601

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We report on the realization of quantum degenerate gas mixtures of the alkaline-earth-metal element strontium with the alkali-metal element rubidium. A key ingredient of our scheme is sympathetic cooling of Rb by Sr atoms that are continuously laser cooled on a narrow-linewidth transition. This versatile technique allows us to produce ultracold gas mixtures with a phase-space density of up to 0.06 for both elements. By further evaporative cooling we create double Bose-Einstein condensates of 87{}^{87}87Rb with either 88{}^{88}88Sr or 84{}^{84}84Sr, reaching more than 1\ifmmode×\else\texttimes\fi1051\ifmmode\times\else\texttimes\fi{}{10}^{5}1\ifmmode×\else\texttimes\fi105 condensed atoms per element for the 84{}^{84}84Sr-87{}^{87}87Rb mixture. These quantum gas mixtures constitute an important step towards the production of a quantum gas of polar, open-shell RbSr molecules.
Degenerate quantum gases of alkaline-earth-like elements open new opportunities in research areas ranging from molecular physics to the study of strongly correlated systems. These experiments exploit the rich electronic structure of these elements, which is markedly different from the one of other species for which quantum degeneracy has been attained. Specifically, alkaline-earth-like atoms, such as strontium, feature metastable triplet states, narrow intercombination lines, and a non-magnetic, closed-shell ground state. This review covers the creation of quantum degenerate gases of strontium and the first experiments performed with this new system. It focuses on laser-cooling and evaporation schemes, which enable the creation of Bose-Einstein condensates and degenerate Fermi gases of all strontium isotopes, and shows how they are used for the investigation of optical Feshbach resonances, the study of degenerate gases loaded into an optical lattice, as well as the coherent creation of Sr_2 molecules.
The authors report the production of a quantum degenerate mixture of alkali-metal 6{}^{6}6Li and alkaline-earth-metal 84{}^{84}84Sr atoms in a far-off-resonant optical dipole trap. The results could pave the way for studying lithium-strontium polar molecules.
We have produced a quantum degenerate mixture of fermionic alkali-metal 6{}^{6}6Li and bosonic spin-singlet 174{}^{174}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 ($T/{T}_{\mathrm{c}}\ensuremath{\simeq}0.8$) 174{}^{174}174Yb with $2.3\ifmmode\times\else\texttimes\fi{}{10}^{4}$ atoms and Fermi degenerate ($T/{T}_{\mathrm{F}}\ensuremath{\simeq}0.3$) 6{}^{6}6Li with $1.2\ifmmode\times\else\texttimes\fi{}{10}^{4}$ atoms. Quasipure Bose-Einstein condensates of up to $3\ifmmode\times\else\texttimes\fi{}{10}^{4}$ 174{}^{174}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.
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^{6}\mathrm{Li}6Li with evaporatively cooled bosonic 174Yb^{174}\mathrm{Yb}174Yb and, separately, fermionic 173Yb^{173}\mathrm{Yb}173Yb. Using cross-thermalization studies, we also measure the elastic sss-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.
Packing rubidium into quantum degeneracy When atomic gases, such as those of alkali elements, are cooled to very low temperatures, they can reach a state of quantum degeneracy, where their quantum nature comes to the fore. In this process, the very last step is evaporative cooling, in which the hottest atoms are coaxed into leaving the gas. Hu et al. devised a protocol that evades the evaporative cooling step, is faster, and suffers less atom loss. The method rests on iteratively manipulating the laser beams of an optical lattice in which a gas of 87 Rb atoms is held so that the gas becomes progressively denser. The method should be widely applicable to other atomic species. Science , this issue p. 1078
We report on the observation of sympathetic cooling of a cloud of fermionic 6Li atoms which are thermally coupled to evaporatively cooled bosonic 87Rb. Using this technique we obtain a mixture of quantum-degenerate gases, where the Rb cloud is colder than the critical temperature for Bose-Einstein condensation and the Li cloud is colder than the Fermi temperature. From measurements of the thermalization velocity we estimate the interspecies s-wave triplet scattering length |amx|=20(+9)(-6)aB. We found that the presence of residual rubidium atoms in the |2, 1> and the |1, -1> Zeeman substates gives rise to important losses due to inelastic collisions.