Elastic and Inelastic Collisions of Single Cs Atoms with an Ultracold Rb Cloud

Nicolas Spethmann, F. Kindermann, Shincy John +3 more

Tomáš Šikorský, Ziv Meir, Ruti Ben-shlomi +2 more

Nicolas Spethmann, Farina Kindermann, Shincy John +3 more

We report on controlled doping of an ultracold Rb gas with single neutral Cs impurity atoms. Elastic two-body collisions lead to a rapid thermalization of the impurity inside the Rb gas, representing the first realization of an ultracold gas doped with a precisely known number of impurity atoms interacting via s-wave collisions. Inelastic interactions are restricted to a single three-body recombination channel in a highly controlled and pure setting, which allows us to determine the Rb-Rb-Cs three-body loss rate with unprecedented precision. Our results pave the way for a coherently interacting hybrid system of individually controllable impurities in a quantum many-body system.

Amir Mohammadi

For my dissertation, I have carried out experiments with a single Ba+ ion which is immersed in a cloud of ultracold neutral Rb atoms. For trapping cold ions and ultracold neutral atoms, we use a linear Paul trap and a far-detuned optical trap, respectively. In the first part of my dissertation, I use the elastic and reactive collisions between the atoms and the ion to minimize the ion excess-micromotion in the Paul trap. I show in my thesis that by minimizing losses in the Rb cloud which are due to the elastic and reactive ion-atom collisions one can suppress excess-micromotion quite well by additional radio-frequency fields that are applied to the Paul trap. In the second part, I studied the evolution of a single BaRb+ molecule while it continuously collides with ultracold Rb atoms. The BaRb+ molecule forms within one ms when we immerse the cold Ba+ ion into a dense gas of Rb. The molecule is initially weakly-bound and can undergo a sequence of elastic, inelastic, reactive, and radiative processes. I investigated these processes by developing methods for discriminating between different ion species, electronic states, and kinetic ion energy ranges.

Chun-Cheng Tsao, Yinde Wang, J. Weiner +1 more

Stefan Schmid, Arne Härter, Johannes Hecker Denschlag

We investigate the interaction of a laser-cooled trapped ion (Ba+ or Rb+) with an optically confined ⁸⁷Rb Bose-Einstein condensate. The system features interesting dynamics of the ion and the atom cloud as determined by their collisions and their motion in their respective traps. Elastic as well as inelastic processes are observed and their respective cross sections are determined. We demonstrate that a single ion can be used to probe the density profile of an ultracold atom cloud.