Marko Gacesa

We investigate the prospects of controlling charge-exchange in ultracold collisions of heteroisotopic combinations of atoms and ions of the same element. The treatment, readily applicable to alkali or alkanine-earth metals, is illustrated in the process $^9$Be$^{+}$ + $^{10}$Be $\leftrightarrow$ $^{9}$Be + $^{10}$Be$^{+}$, which exhibits favorable electronic, nuclear, and hyperfine structure. Feshbach resonances are obtained from quantum scattering calculations in a standard coupled-channel formalism with non-BO terms originating from the nuclear kinetic operator. Near a narrow resonance predicted at 322 G, we find the charge-exchange rate coefficient to rise from practically zero to values larger than $10^{-12}$ cm$^3$/s. Our results suggest controllable charge-exchange reactions between different isotopes of suitable atom-ion pairs with potential applications to quantum systems engineered to study charge diffusion in trapped cold atom-ion mixtures and emulate many-body physics.

We present a theoretical analysis of optical pathways for formation of cold Ca($^1$S)Na$^+$($^1$S) molecular ions via an intermediate state. The formation schemes are based on ab initio potential energy curves and transition dipole moments calculated using effective-core-potential methods of quantum chemistry. In the proposed approach, starting from a mixture of cold trapped Ca$^+$ ions immersed into an ultracold gas of Na atoms, (NaCa)$^+$ molecular ions are photoassociated in the excited E$^{1}Σ^+$ electronic state and allowed to spontaneously decay either to the ground electronic state or an intermediate state from which the population is transferred to the ground state via an additional optical excitation. By analyzing all possible pathways, we find that the efficiency of a two-photon scheme, via either B$^{1}Σ^+$ or C$^{1}Σ^+$ potential, is sufficient to produce significant quantities of ground state (NaCa)$^+$ molecular ions. A single-step process results in lower formation rates that would require either a high density sample or a very intense photoassociation laser to be viable.