Formation of ultracold²²³Fr¹⁰⁷Ag molecules with greatly enhanced sensitivity.

We theoretically studied the formation the ²²³Fr¹⁰⁷Ag molecule from laser-cooled Fr and Ag atoms by performing fully relativistic electronic-structure calculations of ground and excited states to account for strong spin-dependent relativistic effects in this heavy molecule. We used coupled-cluster CCSD(T) and EOM-CCSD theory of the DIRAC computational suite.

 In addition, we performed couple-channel calculations to describe the scattering between ultracold ²²³Fr and ¹⁰⁷Ag atoms in an external magnetic field. In these simulations, we couple the nonzero electron and nuclear spins of these isotopes through spin-spin coupling due to molecular forces as well as atomic hyperfine and Zeeman interactions. We then predicted the nearest-neighbor level density of Feshbach resonances. These resonances can be used for magneto-association into ultracold weakly and strongly bound FrAg. 

We also performed calculations of the dynamic polarizability of rotational states of FrAg in its ground ν=0 vibrational level of the X electronic state and located magic conditions assuming either linearly or circularly polarized light. Magic conditions occur when the polarizabilities of two rotational states are equal.