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arXiv:0902.2229 · Physical Review A

Measurement of inelastic losses in a sample of ultracold Rb85

P. A. Altin, Nicholas P. Robins, Rachel Poldy, J. E. Debs, D. Döring, C. Figl, J. D. Close

Published Jan 29, 2010• 10 citations
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Abstract

We report on measurements of inelastic loss processes in ultracold $^{85}\mathrm{Rb}$ $|F=2\ensuremath{\rangle}$ atoms. Our apparatus creates ultracold $^{85}\mathrm{Rb}$ clouds by sympathetic cooling with a $^{87}\mathrm{Rb}$ reservoir in a quadrupole-Ioffe magnetic trap and subsequently in a weak, large-volume optical dipole trap. We demonstrate strong sympathetic cooling of $^{85}\mathrm{Rb}$ in the magnetic trap, increasing its phase-space density by three orders of magnitude with no detectable loss in number. Ultracold samples created in this way are used to observe the variation of inelastic loss in $^{85}\mathrm{Rb}$ $|F=2, {m}_{F}=\ensuremath{-}2\ensuremath{\rangle}$ clouds as a function of magnetic field near the $155$-G Feshbach resonance and to measure the decay due to inelastic losses in all five Zeeman sublevels of the $F=2$ manifold, finding a particularly high three-body recombination rate in the lowest energy state. We have also observed and characterized a previously unobserved loss feature at $219.9(1)$ G with a width of $0.28(6)$ G, which we associate with a narrow Feshbach resonance predicted by theory.

DOI
10.1103/physreva.81.012713

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We report on measurements of inelastic loss processes in ultracold 85Rb^{85}\mathrm{Rb}85Rb ∣F=2\ensuremath⟩|F=2\ensuremath{\rangle}∣F=2\ensuremath⟩ atoms. Our apparatus creates ultracold 85Rb^{85}\mathrm{Rb}85Rb clouds by sympathetic cooling with a 87Rb^{87}\mathrm{Rb}87Rb reservoir in a quadrupole-Ioffe magnetic trap and subsequently in a weak, large-volume optical dipole trap. We demonstrate strong sympathetic cooling of 85Rb^{85}\mathrm{Rb}85Rb in the magnetic trap, increasing its phase-space density by three orders of magnitude with no detectable loss in number. Ultracold samples created in this way are used to observe the variation of inelastic loss in 85Rb^{85}\mathrm{Rb}85Rb ∣F=2,mF=\ensuremath−2\ensuremath⟩|F=2, {m}_{F}=\ensuremath{-}2\ensuremath{\rangle}∣F=2,mF​=\ensuremath−2\ensuremath⟩ clouds as a function of magnetic field near the 155155155-G Feshbach resonance and to measure the decay due to inelastic losses in all five Zeeman sublevels of the F=2F=2F=2 manifold, finding a particularly high three-body recombination rate in the lowest energy state. We have also observed and characterized a previously unobserved loss feature at 219.9(1)219.9(1)219.9(1) G with a width of 0.28(6)0.28(6)0.28(6) G, which we associate with a narrow Feshbach resonance predicted by theory.
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Inelastic collision rates for ultracold 85Rb{}^{85}\mathrm{Rb}85Rb atoms in the F=2F\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}2F=2, ${m}_{f}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}\ensuremath{-}2$ state have been measured as a function of magnetic field. At 250 gauss (G), the two- and three-body loss rates were measured to be ${K}_{2}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}(1.87\ifmmode\pm\else\textpm\fi{}0.95\ifmmode\pm\else\textpm\fi{}0.19)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}14}{\mathrm{cm}}^{3}/\mathrm{s}$ and ${K}_{3}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}({4.24}_{\ensuremath{-}0.29}^{+0.70}\ifmmode\pm\else\textpm\fi{}0.85)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}25}{\mathrm{cm}}^{6}/\mathrm{s}$, respectively. As the magnetic field is decreased from 250 G towards a Feshbach resonance at 155 G, the inelastic rates decrease to a minimum and then increase dramatically, peaking at the Feshbach resonance. Both two- and three-body losses are important, and individual contributions have been compared with theory.
Inelastic collision rates for ultracold 85 Rb atoms in the F=2, m f =-2 state have been measured as a function of magnetic field.At 250 Gauss (G), the two-and three-body loss rates were measured to be K 2 =1.87±0.95±0.19x 10 -14 cm 3 /s and K 3 =4.24+0.70 -0.29 ±0.85 x 10 -25 cm 6 /s respectively.As the magnetic field is decreased from 250 G towards a Feshbach resonance at 155 G, the inelastic rates decrease to a minimum and then increase dramatically, peaking at the Feshbach resonance.Both two-and three-body losses are important, and individual contributions have been compared with theory.
This thesis reports the observation of interspecies Feshbach resonances in an ultracold mixture of Rb and Cs atoms. A versatile combined magnetic and optical potential has been designed and constructed which is capable of bringing both 87Rb^{87}\rm{Rb}87Rb and 133Cs^{133}\rm{Cs}133Cs to degeneracy, and reaching high phase-space density in 85Rb^{85}\rm{Rb}85Rb. High phase-space density mixtures are the first step required in the production of ultracold polar molecules, the topic of much current research. The apparatus capitalises on the efficient capture of atoms by a magnetic trap from a magneto-optical trap, and the efficient sympathetic cooling of Cs by Rb therein. Upon transfer to the crossed optical dipole trap condensates in excess of 1×1061\times10^{6}1×106 87Rb^{87}\rm{Rb}87Rb atoms and approximately 1×1051\times10^{5}1×105 133Cs^{133}\rm{Cs}133Cs atoms are produced after direct evaporation and gravito-magnetic tilting of the potential. The observation of six interspecies 87Rb^{87}\rm{Rb}87Rb-133Cs^{133}\rm{Cs}133Cs Feshbach resonances are reported, three of which had only been predicted theoretically, allowing testing and development of the theoretical model. Furthermore, the extrapolation of this model has predicted numerous Feshbach resonances between 85Rb^{85}\rm{Rb}85Rb and 133Cs^{133}\rm{Cs}133Cs, none of which have been experimentally observed prior to this work. The versatile nature of this apparatus is discussed, including the application of the current system to cooling of 85Rb^{85}\rm{Rb}85Rb. Initial experiments observed seven interspecies resonances, including a broad s-wave resonance at a magnetic field of (644±2)(644\pm2)(644±2) G which is in excellent agreement with the theoretical prediction. Further work has revealed that fourteen Feshbach resonances exist in the 0-700 G magnetic field range between 85Rb^{85}\rm{Rb}85Rb and 133Cs^{133}\rm{Cs}133Cs atoms in the ∣2,+2⟩\left|2,+2\right\rangle∣2,+2⟩ and ∣3,+3⟩\left|3,+3\right\rangle∣3,+3⟩ states, respectively. Several of these resonances would be ideal for magneto-association of RbCs molecules, prior to transfer to the rovibrational ground-state.
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We report on the observation of two Feshbach resonances in collisions between ultracold 6Li^{6}\mathrm{Li}6Li and 87Rb^{87}\mathrm{Rb}87Rb atoms in their respective hyperfine ground states $\ensuremath{\mid}F,{m}_{F}⟩=\ensuremath{\mid}1∕2,1∕2⟩$ and \ensuremath{\mid}1,1⟩. The resonances show up as trap losses for the 6Li^{6}\mathrm{Li}6Li cloud induced by inelastic Li-Rb-Rb three-body collisions. The magnetic field values where they occur represent important benchmarks for an accurate determination of the interspecies interaction potentials. A broad Feshbach resonance located at 1066.92G1066.92\phantom{\rule{0.3em}{0ex}}\mathrm{G}1066.92G opens interesting prospects for the creation of ultracold heteronuclear molecules. We furthermore observe a strong enhancement of the narrow ppp-wave Feshbach resonance in collisions of 6Li^{6}\mathrm{Li}6Li atoms at 158.55G158.55\phantom{\rule{0.3em}{0ex}}\mathrm{G}158.55G in the presence of a dense 87Rb^{87}\mathrm{Rb}87Rb cloud. The effect of the 87Rb^{87}\mathrm{Rb}87Rb cloud is to introduce Li-Li-Rb three-body collisions occurring at a higher rate than Li-Li-Li collisions.