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arXiv:1211.2888 · Physical Review A

Ultracold mixtures of atomic 6 Li and 133 Cs with tunable interactions

Shih-Kuang Tung, Colin Parker, Jacob Johansen, Cheng Chin, Yujun Wang, Paul S. Julienne

Published Jan 3, 2013• 84 citations
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Abstract

We report the experimental and theoretical study of two-body interactions in a ${}^{6}$Li-${}^{133}$Cs Fermi-Bose mixture. Using a translatable dipole trap setup, we have successfully trapped the two species in the same trap with temperatures of a few microkelvins. By monitoring atom number loss and interspecies thermalization, we identify five $s$-wave interspecies Feshbach resonances in the lowest two scattering channels. We construct a coupled channels model using molecular potentials to fit and characterize these resonances. Two of the resonances are as wide as 6 mT (60 G) and thus should be suitable for creating Feshbach molecules and searching for universal few-body scaling.

DOI
10.1103/physreva.87.010702

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We report on the observation of 19 interspecies Feshbach resonances in an optically trapped ultracold Bose-Fermi mixture of 133Cs{}^{133}\text{Cs}133Cs and 6Li{}^{6}\text{Li}6Li in the two energetically lowest spin states. We assign the resonances to sss- and ppp-wave molecular channels by a coupled-channels calculation, resulting in an accurate determination of LiCs ground-state potentials. Fits of the resonance position based on the undressed asymptotic bound state model do not provide the same level of accuracy as the coupled-channels calculation. Several broad sss-wave resonances provide prospects to create fermionic LiCs molecules with a large dipole moment via Feshbach association followed by stimulated Raman passage. Two of the sss-wave resonances overlap with a zero crossing of the Cs scattering length, which offers prospects for the investigation of polarons in an ultracold Li-Cs mixture.
We investigate ultracold collisions in a novel mixture of ^{6}Li and ^{53}Cr fermionic atoms, discovering more than 50 interspecies Feshbach resonances via loss spectroscopy. Building a full coupled-channel model, we unambiguously characterize the ^{6}Li-^{53}Cr scattering properties and yield predictions for other isotopic pairs. In particular, we identify various Feshbach resonances that enable the controlled tuning of elastic s- and p-wave ^{6}Li-^{53}Cr interactions. Our studies thus make lithium-chromium mixtures emerge as optimally suited platforms for the experimental search of elusive few- and many-body regimes of highly correlated fermionic matter, and for the realization of a new class of ultracold polar molecules possessing both electric and magnetic dipole moments.
This thesis reports on scattering experiments performed with an ultracold mixture of fermionic 6Li and bosonic 133Cs atoms, studying two-, few-, and many-body effects in a highly mass-imbalanced system. To this end, the existing apparatus for the creation of ultracold gases is extended and improved by gray molasses cooling of 6Li and high-resolution absorption imaging. s-, p-, and d-wave Feshbach resonances in the two energetically lowest hyperfine channels are detected via atom-loss and binding energy spectroscopy. These measurements in combination with the coupled channels modeling provide a ten-fold improved parametrization of the interspecies s-wave scattering length and precise determination of the LiCs molecular potential curves. For the first time effects of spin-rotation coupling in Feshbach resonances are observed, reflected in a triplet splitting of the p-wave components. The influence of the intraspecies scattering length on the heteronuclear Efimov scenario is studied by means of threebody loss rate measurements in the vicinity of two Feshbach resonances, characterized either by a positive or negative intraspecies scattering length. The measurements are quantitatively compared to the hyperspherical adiabatic formalism. The positive intraspecies scattering length can be interpreted as three-body parameter. The impact of few-body physics in the many-body impurity problem is discussed and prospects for realization of quantum degenerate Bose-Fermi mixtures with large mass imbalance are provided.
This thesis reports on the tunability of interactions in ultracold Bose-Fermi mixtures of Cesium and Lithium. The \nfirst realization of an optically trapped \n6Li -133Cs mixture enabled to perform trap loss spectroscopy measurements to identify \nmagnetic Feshbach resonances. A total of 19 interspecies Feshbach resonances, all in the magnetic field range between 650 G and 950 G, were observed for the two energetically lowest spin states of each species. Two 5 G broad and especially two 60 G broad s-wave resonances give perspectives to produce a dipolar quantum gas of LiCs ground state molecules as well as to study the Efimov effect in highly mass imbalanced systems. In addition, a unique relative tunability of intra- and interspecies \nscattering lengths was found which makes the 6Li -133Cs system also well suited for the investigation of polarons. Evaporative cooling was performed on optically trapped samples which contained only one of the species. In this way, Bose-Einstein condensates of 6Li molecules as well as 133Cs samples at a phase-space density of p = 4 · 10^2 were prepared. All experiments were performed in a new apparatus, which has been designed and set up during this thesis.
We observe interspecies Feshbach resonances due to sss-wave bound states in ultracold $^{39}\mathrm{K}\ensuremath{-}^{133}\mathrm{Cs}$ scattering for three different spin mixtures. The resonances are observed as joint atom loss and heating of the K sample. We perform least-squares fits to obtain improved K-Cs interaction potentials that reproduce the observed resonances, and carry out coupled-channel calculations to characterize the scattering and bound-state properties for 39K^{39}\mathrm{K}39K-Cs, 40K^{40}\mathrm{K}40K-Cs, and 41K^{41}\mathrm{K}41K-Cs. Our results open up the possibilities of tuning interactions in K-Cs atomic mixtures and of producing ultracold KCs molecules.
We report on the observation of interspecies Feshbach resonances in an ultracold, optically trapped mixture of Rb and Cs atoms. In a magnetic-field range up to 300 G we find 23 interspecies Feshbach resonances in the lowest spin channel and two resonances in a higher channel of the mixture. The extraordinarily rich Feshbach spectrum suggests the importance of different partial waves in both the open and closed channels of the scattering problem along with higher-order coupling mechanisms. Our results, on one hand, provide fundamental experimental input to characterize the Rb-Cs scattering properties and, on the other hand, identify possible starting points for the association of ultracold heteronuclear RbCs molecules.