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arXiv:0811.0671 · Physical Review A

All-optical formation of quantum degenerate mixtures

Takeshi Fukuhara, Seiji Sugawa, Yosuke Takasu, Yoshiro Takahashi

Published Feb 3, 2009• 127 citations
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Abstract

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 $^{173}\mathrm{Yb}\text{\ensuremath{-}}^{174}\mathrm{Yb}$ Fermi-Bose mixture to the quantum degenerate regime.

DOI
10.1103/physreva.79.021601

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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^{176}\mathrm{Yb}176Yb atoms via sympathetic cooling down to below the Bose-Einstein transition temperature, coexisting with a stable condensate of 174Yb^{174}\mathrm{Yb}174Yb atoms with a repulsive interaction. We have observed a rapid atom loss in 176Yb^{176}\mathrm{Yb}176Yb atoms after cooling down below the transition temperature, which indicates the collapse of a 176Yb^{176}\mathrm{Yb}176Yb condensate. The sympathetic cooling technique has been applied to cool a 173Yb\ensuremath-174Yb^{173}\mathrm{Yb}\text{\ensuremath{-}}^{174}\mathrm{Yb}173Yb\ensuremath-174Yb Fermi-Bose mixture to the quantum degenerate regime.
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 report on the formation of a stable quantum degenerate mixture of fermionic ^{6}Li and bosonic ^{133}Cs in an optical trap by sympathetic cooling near an interspecies Feshbach resonance. New regimes of quantum degenerate Bose-Fermi mixtures are identified. With moderate attractive interspecies interactions, we show that a degenerate Fermi gas of Li can be fully confined in a Cs Bose-Einstein condensate without external potentials. For stronger attraction where mean-field collapse is expected, no such instability is observed. Potential mechanisms to explain this phenomenon are discussed.
We describe in detail our recent experiments on quantum degenerate gases of ytterbium (Yb) atoms. Up to now Bose–Einstein condensates of 174 Yb and 170 Yb, and a Fermi degenerate gas of 173 Yb have been realized by efficient evaporative cooling in a crossed far-off resonant trap. Our studies showed that the efficient escape from the trap and rapid thermalization are important for efficient evaporative cooling. We also describe some recent experiments using Yb Bose–Einstein condensates such as the achievement of a scalar atom laser, the observation of an optical coherent transient, and successful loading into an optical lattice. Finally, the future prospects using Yb quantum degenerate gases are discussed in detail.
We report on the generation of a quantum degenerate Fermi-Fermi mixture of two different atomic species. The quantum degenerate mixture is realized employing sympathetic cooling of fermionic 6Li and 40K gases by an evaporatively cooled bosonic 87Rb gas. We describe the combination of trapping and cooling methods that proved crucial to successfully cool the mixture. In particular, we study the last part of the cooling process and show that the efficiency of sympathetic cooling of the 6Li gas by 87Rb is increased by the presence of 40K through catalytic cooling. Because of the differing physical properties of the two components, the quantum degenerate 6Li-40K Fermi-Fermi mixture is an excellent candidate for a stable, heteronuclear system allowing the study of several so far unexplored types of quantum matter.
Evaporative cooling of ultracold Yb atoms near the quantum-degenerate regime was experimentally studied. Three bosons of 170 Yb, 172 Yb, 176 Yb and two fermions of 171 Yb and 173 Yb were evaporatively cooled in a crossed far-off resonant trap (FORT). We observed that 170 Yb and 172 Yb were not concentrated into the crossed region. We found that, in the cases of 176 Yb atoms, atoms were concentrated well into the crossed region. The following evaporative cooling in the crossed region, however, did not work well. We performed the simultaneous trapping and sympathetic cooling in the crossed FORT by use of 172 Yb-174Yb, 174 Yb- 176 Yb, 172 Yb- 176 Yb, and 171 Yb- 174 Yb pairs. We observed that evaporative cooling worked well. This result shows that we succeeded in the enhancement of the atom collision rate. Especially, by use of 174 Yb- 176 Yb mixture, we obtained cold 176 Yb whose phase space density was 0.02. We observed a large atom loss, which limited the further sympathetic evaporative cooling. We also evaporatively cooled 174 Yb in a 1D optical lattice. Evaporative cooling worked very well because the atoms were initially trapped at a high density. After evaporative cooling, we obtained very cold atoms, and T/T F was estimated to be 1.2.