Inelastic collision dynamics of a single cold ion immersed in a Bose-Einstein condensate

Abstract

We investigate inelastic collision dynamics of a single cold ion in a Bose-Einstein condensate. We observe rapid ion-atom-atom three-body recombination leading to formation of weakly bound molecular ions followed by secondary two-body molecule-atom collisions quenching the rovibrational states towards deeper binding energies. In contrast to previous studies exploiting hybrid ion traps, we work in an effectively field-free environment and generate a free low-energy ionic impurity directly from the atomic ensemble via Rydberg excitation and ionization. This allows us to implement an energy-resolved field-dissociation technique to trace the relaxation dynamics of the recombination products. Our observations are in good agreement with numerical simulations based on Langevin capture dynamics and provide complementary means to study stability and reaction dynamics of ionic impurities in ultracold quantum gases.

Cold chemistry: a few-body perspective on impurity physics of a single ion in an ultracold bath

“…In three-body collisions involving charged and neutral particles, the charged-neutral interaction surpasses the neutral-neutral interaction in the energetic pooling towards three-body recombination, which translates into two important features. The first is that molecular ions are preferentially formed in comparison to neutral molecules [81,83,84], as it is sketched on panel (i) of Figure 3. In other words, reaction channel (2) is dominant for ion-atom-atom collisions.…”

Tracking a Single Ion in an Ultracold Gas

“…The observations are also able to characterize chemical reactions that occur between the ion and the atoms. Credit: Credit: APS/Alan Stonebraker experiments with a single ion traversing a Bose-Einstein condensate (BEC), which is a quantum gas of cold neutral atoms [1]. The precise tracking of the ion shows that the transport is diffusive and reveals the character of the ion-atom collisions.…”

“…To investigate the transport scenario experimentally, the Stuttgart-based group studied a single rubidium ion (Rb + ) in a cigar-shaped BEC of about one million neutral rubidium (Rb) atoms [1]. The team initially produced the Rb + ion in the center of the 50-µm-long Rb cloud through a two-step process.…”

“…The current experimental setup does, however, offer another window into ion behavior, besides transport. The researchers observe that a large fraction of the Rb + ions undergo a particular chemical reaction, three-body recombination, with Rb atoms [5,6]. Here, an ion forms a weakly bound Rb + 2 dimer with a Rb atom, while a second Rb atom carries away part of the released binding energy.…”

“…The Rb + 2 dimer can be easily discriminated from the Rb + ion because it arrives later at the ion detector as a result of its larger mass. Remarkably, the group was able to estimate the typical binding energy of the Rb + 2 dimer in a separate set of experimental runs [5]. By applying a suitable electric field, the weakly bound Rb + 2 dimer can be ripped apart-converting it back to a Rb + ion and a neutral Rb atom.…”