Abstract
We study the interspecies scattering properties of ultracold Li–Cs mixtures in their two energetically lowest spin channels in the magnetic field range between 800 and 1000 G. Close to two broad Feshbach resonances (FR) we create weakly bound LiCs dimers by radio-frequency association and measure the dependence of their binding energy on the external magnetic field strength. Based on the binding energies and complementary atom loss spectroscopy of three other Li–Cs s-wave FRs we construct precise molecular singlet and triplet electronic ground state potentials using a coupled-channels calculation. We extract the Li–Cs interspecies scattering length as a function of the external field and obtain almost a ten-fold improvement in the precision of the values for the pole positions and widths of the s-wave FRs as compared to our previous work (Pires et al 2014 Phys. Rev. Lett. 112 250404). We discuss implications on the Efimov scenario and the universal geometric scaling for LiCsCs trimers.
Highlights
Universality in few-body systems has been one of the major topics in the ultracold quantum gases for the last decade [1, 2, 3]
These results provide almost an order of magnitude improvement over the previous determination of the Feshbach resonances (FR) positions through the trap-loss measurements [23, 24] and the rf spectroscopy [26], and they are consistent with the recent theoretical analysis [25], if the differences in determining the resonance positions and experimental accuracy are taken into account
This illustrates that the use of atom loss alone is questionable for a reliable determination of the FR pole position, especially if the resonance width is much larger than experimental uncertainties, as it is in the present case
Summary
Universality in few-body systems has been one of the major topics in the ultracold quantum gases for the last decade [1, 2, 3]. Its success can be ascribed to the existence of magnetic interparticle scattering resonances, called Feshbach resonances (FR), at which a two-body bound state crosses the scattering threshold These resonances are routinely employed to tune the interaction strength between the colliding particles [4] and to produce weakly bound dimers by ramping up or down the external magnetic field [5]. Atom loss spectroscopy in combination with theoretical models has become a standard tool in the field of ultracold gases [4] These methods can give an excellent representation of the FR spectrum, typically not all of the observed losses can be unambiguously attributed to an increasing two-body scattering length. With the help of the new mapping of the scattering length in the vicinity of the 843 G LiCs FR we obtain refined Efimov scaling factors of 5.5(2) and 5.0(1.5) for the first and second Efimov period, respectively, where the first period slightly deviates from the universal Efimov scenario of 4.9, as predicted for the Li-Cs system with mass ratio of 22 [28]
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