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تسجيل مستخدم جديدUltracold mixtures of metastable He and Rb: scattering lengths from ab initio calculations and thermalization measurements
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We have investigated the ultracold interspecies scattering properties of metastable triplet He and Rb. We performed state-of-the-art ab initio calculations of the relevant interaction potential, and measured the interspecies elastic cross section for an ultracold mixture of metastable triplet $^4$He and $^{87}$Rb in a quadrupole magnetic trap at a temperature of 0.5 mK. Our combined theoretical and experimental study gives an interspecies scattering length $a_{4+87}=+17^{+1}_{-4}$ $a_0$, which prior to this work was unknown. More general, our work shows the possibility of obtaining accurate scattering lengths using ab initio calculations for a system containing a heavy, many-electron atom, such as Rb.
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We have obtained accurate ab initio quartet potentials for the diatomic metastable triplet helium + alkali-metal (Li, Na, K, Rb) systems, using all-electron restricted open-shell coupled cluster singles and doubles with noniterative triples correctio
ns [CCSD(T)] calculations and accurate calculations of the long-range $C_6$ coefficients. These potentials provide accurate ab initio quartet scattering lengths, which for these many-electron systems is possible, because of the small reduced masses and shallow potentials that results in a small amount of bound states. Our results are relevant for ultracold metastable triplet helium + alkali-metal mixture experiments.
Recently we have reported (Knoop et al. [arXiv:1404.4826]) on an experimental determination of metastable triplet $^4$He+$^{87}$Rb scattering length by performing thermalization measurements for an ultracold mixture in a quadrupole magnetic trap. Her
e we present our experimental apparatus and elaborate on these thermalization measurements. In particular we give a theoretical description of interspecies thermalization rate for a quadrupole magnetic trap, i. e. in the presence of Majorana heating, and a general procedure to extract the scattering length from the elastic cross section at finite temperature based on knowledge of the $C_6$ coefficient alone. In addition, from our thermalization data we obtain an upper limit of the total interspecies two-body loss rate coefficient of $1.5times 10^{-12}$ cm$^3$s$^{-1}$.
We have observed 26 interspecies Feshbach resonances at fields up to 2050 G in ultracold $^6$Li+$^{23}$Na mixtures for different spin-state combinations. Applying the asymptotic bound-state model to assign the resonances, we have found that most reso
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We have calculated the s-wave scattering length of all the even isotopes of calcium (Ca) and barium (Ba), in order to investigate the prospect of Bose-Einstein condensation (BEC). For Ca we have used an accurate molecular potential based on detailed
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We demonstrate coherent control of both the rotational and hyperfine state of ultracold, chemically stable $^{87}$Rb$^{133}$Cs molecules with external microwave fields. We create a sample of ~2000 molecules in the lowest hyperfine level of the rovibr
onic ground state N = 0. We measure the transition frequencies to 8 different hyperfine levels of the N = 1 state at two magnetic fields ~23 G apart. We determine accurate values of rotational and hyperfine coupling constants that agree well with previous calculations. We observe Rabi oscillations on each transition, allowing complete population transfer to a selected hyperfine level of N = 1. Subsequent application of a second microwave pulse allows transfer of molecules back to a different hyperfine level of N = 0.
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