In mixed systems of trapped ions and cold atoms, the ions and atoms can coexist at different temperatures. This is primarily due to their different trapping and cooling mechanisms. The key questions of how ions can cool collisionally with cold atoms and whether the combined system allows stable coexistence, need to be answered. Here we experimentally demonstrate that rubidium ions cool in contact with magneto-optically trapped rubidium atoms, contrary to the general experimental expectation of ion heating. The cooling process is explained theoretically and substantiated with numerical simulations, which include resonant charge exchange collisions. The mechanism of single collision swap cooling of ions with atoms is discussed. Finally, it is experimentally and numerically demonstrated that the combined ion-atom system is intrinsically stable, which is critical for future cold chemistry experiments with such systems.
We measure the collision rate coefficient between laser cooled Rubidium (Rb) atoms in a magnetooptical trap (MOT) and optically dark Rb + ions in an overlapping Paul trap. In such a mixture, the ions are created from the MOT atoms and allowed to accumulate in the ion trap, which results in a significant reduction in the number of steady state MOT atoms. A theoretical rate equation model is developed to describe the evolution of the MOT atom number, due to ionization and ion-atom collision, and derive an expression for the ion-atom collision rate coefficient. The loss of MOT atoms is studied systematically, by sequentially switching on the various mechanisms in the experiment. Combining the measurements with the model allows the direct determination of the ion-atom collision rate coefficient. Finally the scope of the experimental technique developed here is discussed.
We report an experimental apparatus and technique which simultaneously traps ions and cold atoms with spatial overlap. Such an apparatus is motivated by the study of ion-atom processes at temperatures ranging from hot to ultra cold. This area is a largely unexplored domain of physics with cold trapped atoms. In this article we discuss the general design considerations for combining these two traps and present our experimental setup. The ion trap and atom trap are characterized independently of each other. The simultaneous operation of both is then described and experimental signatures of the effect of the ions and cold atoms on each other are presented. In conclusion, the use of such an instrument for several problems in physics and chemistry is briefly discussed.
We present a dynamic ion-atom hybrid trap for studies of cold ion-neutral collisions and reactions with a significantly improved energy resolution compared to previous experiments. Our approach is based on pushing a cloud of laser-cooled Rb atoms through a stationary Coulomb crystal of cold ions using precisely controlled, tunable radiation-pressure forces. We demonstrate the tuning of the atom kinetic energies over an interval ranging from 30 mK up to 350 mK with energy spreads as low as 24 mK inferred from the comparison of experimental time-of-flight measurements with Monte Carlo trajectory simulations. We also demonstrate first applications of our method to the investigation of chemical reactions. Our development opens up perspectives for accurate studies of the energy dependence of the reaction rates, the dynamics and the reaction-product ratios of ion-neutral processes in the cold regime. It also paves the way for the realisation of fully energy-and state-controlled cold-collision experiments.
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