Ultracold mixtures of metastable He and Rb: scattering lengths from ab   initio calculations and thermalization measurements
  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. 
S. Knoop, P. S. \.Zuchowski, D. K\c{e}dziera, \L. Mentel, M.   Puchalski, H. P. Mishra, A. S. Flores, W. Vassen
cond-mat.quant-gas physics.atom-ph quant-ph