Mesoscopic Molecular Ions in Bose-Einstein Condensates

We study the possible formation of large (mesoscopic) molecular ions in an ultracold degenerate bosonic gas doped with charged particles (ions). We show that the polarization potentials produced by the ionic impurities are capable of capturing hundreds of atoms into loosely bound states. We describe the spontaneous formation of these hollow molecular ions via phonon emission and suggest an optical technique for coherent stimulated transitions of condensate atoms into a specific bound state. These results open up new possibilities for manipulating tightly confined ensembles.

Figure 1

Diagrams of atom capture by an ion. In (a), the spontaneous capture in level $v$ is followed phonon emission (with corresponding rates). In (b), the stimulated rate from the condensate $c$ to the bound level $v$, also may produce heating, i.e., population of noncondensate atoms $nc$, in (c).

Figure 2

$W_v^{\mathrm{c}\mathrm{a}\mathrm{p}}$ as a function of $\xi$ for various values of $a_v$ corresponding to the states $2{\Sigma }_g^{+}$ and $2{\Sigma }_u^{+}$ of $\mathrm{N}{\mathrm{a}}_{\mathrm{2}}^{\mathrm{+}}$ [7], and $a_v\sim R_c$ for both Na and Rb. The two limiting behaviors and the equilibrium points for Na and Rb at 10 nK are shown.