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WORLD SCIENTIFIC eBooks

Magnetic Field Dependence of Ultracold Inelastic Collisions near a Feshbach Resonance

Jacob Roberts, N. R. Claussen, Simon L. Cornish, Carl Wieman

Published Jan 1, 2008• 7 citations
Publisher

Abstract

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.

DOI
10.1142/9789812813787_0080

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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.
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.
We report on measurements of inelastic loss processes in ultracold 85Rb^{85}\mathrm{Rb}85Rb $|F=2\ensuremath{\rangle}$ 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 $|F=2, {m}_{F}=\ensuremath{-}2\ensuremath{\rangle}$ 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.
Abstract Ultracold atoms prepared in excited internal states can escape from the trap through inelastic collisions. A magnetic field can be used to suppress the s-wave loss rate coefficient near an s-wave Feshbach resonance. However, at the temperature of μK the p-wave loss rate coefficient becomes increasingly important as the temperature increases. The unsuppressed p-wave loss rate coefficient can far exceed the suppressed s-wave loss rate coefficient, and severely restricts the reduction of the total loss rate coefficient. We calculate the collision rate coefficients of ultracold 85Rb and 87Rb atoms prepared in excited hyperfine and Zeeman states using the coupled-channel method. We find that in R b 85 ( F 1 = 3 , m F 1 = 3 ) + R b 87 ( F 2 = 1 , m F 2 = − 1 ) and R b 85 ( F 1 = 2 , m F 1 = − 2 ) + R b 87 ( F 2 = 2 ,
We report on the observation of five Feshbach resonances in collisions between ultracold 7Li^{7}\mathrm{Li}7Li and 87Rb^{87}\mathrm{Rb}87Rb atoms in the absolute ground-state mixture where both species are in their $\ensuremath{\mid}f,{m}_{f}⟩=\ensuremath{\mid}1,1⟩$ hyperfine states. The resonances appear as trap losses for the 7Li^{7}\mathrm{Li}7Li cloud induced by inelastic heteronuclear three-body collisions. The magnetic field values where they occur are important quantities for an accurate determination of the interspecies interaction potentials. Results of coupled channels calculations based on the observed resonances are presented and refined potential parameters are given. A very broad Feshbach resonance centered around 649G649\phantom{\rule{0.3em}{0ex}}\mathrm{G}649G should allow for fine-tuning of the interaction strength in future experiments.
K) molecules in the rovibrational ground state. We prepare the atoms and molecules in various hyperfine levels of their ground states and observe the loss of molecules as a function of the magnetic field. The atom-molecule Feshbach resonances are identified by observing an enhancement of the loss. We have observed 11 resonances in the magnetic field range of 43 to 120 gauss. The observed atom-molecule Feshbach resonances at ultralow temperatures probe the three-body potential energy surface with exceptional resolution and will help to improve understanding of ultracold collisions.
We prepare mixtures of ultracold CaF molecules and Rb atoms in a magnetic trap and study their inelastic collisions. When the atoms are prepared in the spin-stretched state and the molecules in the spin-stretched component of the first rotationally excited state, they collide inelastically with a rate coefficient k_{2}=(6.6±1.5)×10^{-11} cm^{3}/s at temperatures near 100 μK. We attribute this to rotation-changing collisions. When the molecules are in the ground rotational state we see no inelastic loss and set an upper bound on the spin-relaxation rate coefficient of k_{2}<5.8×10^{-12} cm^{3}/s with 95% confidence. We compare these measurements to the results of a single-channel loss model based on quantum defect theory. The comparison suggests a short-range loss parameter close to unity for rotationally excited molecules, but below 0.04 for molecules in the rotational ground state.