Sympathetic cooling of the Ba+ion by collisions with ultracold Rb atoms: Theoretical prospects

Abstract

State-of-the-art ab initio techniques have been applied to compute the potential energy curves of the (BaRb) + molecular ion in the Born-Oppenheimer approximation for the singlet and triplet states dissociating into the ground state 1 S Rb + ion and the Ba atom in the ground 1 S state, the lowest singlet or triplet D excited states, and for the singlet and triplet states dissociating into the ground state 2 S Rb atom and the ground state 2 S Ba + ion. The ground state potential energy was obtained with the coupled cluster method restricted to single, double, and nonperturbative triple excitations. The first triplet states in the Σ, Π, and ∆ symmetries were computed with the restricted open-shell coupled cluster method restricted to single, double, and nonperturbative triple excitations. All other excited state potential energy curves were computed using the equation of motion approach within the coupled-cluster singles, doubles, and linear triples framework.The long-range coefficients describing the electrostatic, induction, and dispersion interactions at large interatomic distances are also reported. The electric transition dipole moments governing the X 1 Σ → 1 Σ, 1 Π have been obtained as the first residue of the polarization propagator computed with the linear response coupled-cluster method restricted to single and double excitations. Nonadiabatic radial and angular coupling matrix elements, as well as the spin-orbit coupling matrix elements have been evaluated using the multireference configuration interaction method restricted to single and double excitations with a large active space. With these couplings, the spin-orbit coupled (relativistic) potential energy curves for the 0 + and 1 states relevant for the running experiments have been obtained. Finally, relativistic transition moments and nonadiabatic coupling matrix elements were obtained from the nonrelativistic results and spin-orbit eigenvectors. The electronic structure input has been employed in the single channel scattering calculations of the collisional cross sections between the Ba + ion and Rb atom. Both nonrelativistic and relativistic potentials were used in these calculations. Our results show that the inelastic cross section corresponding to the charge transfer from the Rb atom to the Ba + ion is much smaller than the elastic one over a wide range of energies up to 1 mK. This suggests that sympathetic cooling of the Ba + ion by collisions with ultracold Rb atoms should be possible.2

Ground- and excited-state properties of the polar and paramagnetic RbSr molecule: A comparative study

“…Other studies concern CaLi [41][42][43], LiBe [44,45]. More recently the electronic structure of the related molecular ions containing one alkali atom and Ca + [46], Sr + [47] or Ba + [48][49][50][51] with various high-level approaches have been published in relation with experiments aiming at creating cold molecular ions in merged cold ion and cold atom traps.…”

Reexamination of the calculation of two-center, two-electron integrals over Slater-type orbitals. III. Case study of the beryllium dimer

“…[4] for interpretation of the observed subradiant states of Sr 2 . Electronic structure calculations can also be used to predict new schemes for the formation of ultracold diatomic molecules [5][6][7][8][9]. Apart from that, state-ofthe-art first-principles calculations are used in metrology e.g.…”

Structure and interactions of ultracold Yb ions and Rb atoms

“…Indeed, the usual effective range expansion is modified by logarithmic terms in the wave-number expansion [15]. In the last few years theoretical studies of ultracold atom-ion collisions included the investigation of the occurrence of magnetic Feshbach resonances with a view to examining the tunability of the atom-ion interaction focusing on the specific 40 Ca + -Na system [16] and calculations of the single-channel scattering properties of the Ba + ion with the Rb neutral atom [17], which suggest the possibility of sympathetic cooling of the barium ion by the buffer gas of ultracold rubidium atoms with a considerable efficiency.…”