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Register a new userCross-dimensional relaxation of $^7$Li-$^{87}$Rb atomic gas mixtures in a spherical-quadrupole magnetic trap
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We measure the interspecies interaction strength between $^7$Li and $^{87}$Rb atoms through cross-dimensional relaxation of two-element gas mixtures trapped in a spherical quadrupole magnetic trap. We record the relaxation of an initial momentum-space anisotropy in a lithium gas when co-trapped with rubidium atoms, with both species in the $|F=1, m_F = -1rangle$ hyperfine state. Our measurements are calibrated by observing cross-dimensional relaxation of a $^{87}$Rb-only trapped gas. Through Monte Carlo simulations, we compare the observed relaxation to that expected given the theoretically predicted energy-dependent differential cross section for $^7$Li-$^{87}$Rb collisions. The experimentally observed relaxation occurs significantly faster than predicted theoretically, a deviation that appears incompatible with other experimental data characterising the $^7$Li-$^{87}$Rb molecular potential.
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We report on measurements of cross-species thermalization inside a magnetically trapped spin-polarized mixture of $^{87}$Rb and $^7$Li atoms with both atoms in their respective low field seeking magnetic substates $|F=2,m_F=2right>$. Measurement of the thermalization velocity in the ultracold regime below $10 mu$K allows for the derivation of the absolute value of the pure triplet s-wave scattering length governing the interaction. We find $|a_{7,87}|=(59pm19) a_{rm B}$. We propose to study both species in the condensed regime to derive the sign of $a_{7,87}$. In this context, we present numerical solutions to the coupled Gross-Pitaevskii equation based on the hypothesis of a positive sign. According to the simulations, phase separation of the Li and Rb $|2,2right>$ clouds occurs along with a mean-field stabilization allowing for larger atom numbers of condensed $^7$Li atoms before collapse sets in. Observation of this mean-field stabilization would directly fix the sign of $a_{7,87}$. We discuss our results in the light of this proposal.
We report investigation of near-resonance light scattering from a cold and dense atomic gas of $^{87}$Rb atoms. Measurements are made for probe frequencies tuned near the $F=2to F=3$ nearly closed hyperfine transition, with particular attention paid to the dependence of the scattered light intensity on detuning from resonance, the number of atoms in the sample, and atomic sample size. We find that, over a wide range of experimental variables, the optical depth of the atomic sample serves as an effective single scaling parameter which describes well all the experimental data.
We have studied hetero- and homonuclear excited state/ground state collisions by loading both $^{85}$Rb and $^{87}$Rb into a far off resonant trap (FORT). Because of the relatively weak confinement of the FORT, we expect the hyperfine structure of the different isotopes to play a crucial role in the collision rates. This dependence on hyperfine structure allows us to measure collisions associated with long range interatomic potentials of different structure: such as long and short ranged; or such as purely attractive, purely repulsive, or mixed attractive and repulsive. We observe significantly different loss rates for different excited state potentials. Additionally, we observe that some collisional channels loss rates are saturated at our operating intensities (~15 mW/cm$^{2}$). These losses are important limitations in loading dual isotope optical traps.
We report on the observation of two Feshbach resonances in collisions between ultracold $^6$Li and $^{87}$Rb atoms in their respective hyperfine ground states $|F,m_F>=|1/2,1/2>$ and $|1,1>$. The resonances show up as trap losses for the $^6$Li 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 1066.92 G opens interesting prospects for the creation of ultracold heteronuclear molecules. We furthermore observe a strong enhancement of the narrow p-wave Feshbach resonance in collisions of $^6$Li atoms at 158.55 G in the presence of a dense $^{87}$Rb cloud. The effect of the $^{87}$Rb cloud is to introduce Li-Li-Rb three-body collisions occurring at a higher rate than Li-Li-Li collisions.
We report on the observation of five Feshbach resonances in collisions between ultracold $^7$Li and $^{87}$Rb atoms in the absolute ground state mixture where both species are in their $|f,m_f>=|1,1>$ hyperfine states. The resonances appear as trap losses for the $^7$Li 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 649 G should allow for fine tuning of the interaction strength in future experiments.
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