Quantum Defect Theory description of weakly bound levels and Feshbach resonances in LiRb

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The multichannel quantum defect theory (MQDT) in combination with the frame transformation (FT) approach is applied to model the Fano-Feshbach resonances measured for ⁷Li⁸⁷Rb and ⁶Li⁸⁷Rb [Marzok et al. Phys. Rev. A 79 012717 (2009)]. The MQDT results show a level of accuracy comparable to that of previous models based on direct, fully numerical solutions of the the coupled channel Schrödinger equations (CC). Here, energy levels deduced from 2-photon photoassociation spectra for ⁷Li⁸⁵Rb are assigned by applying the MQDT approach, obtaining the bound state energies for the coupled channel problem. Our results confirm that MQDT yields a compact description of photoassociation observables as well as the Fano-Feshbach resonance positions and widths.