Abstract
Ion–atom interactions are a comparatively recent field of research that has drawn considerable attention due to its applications in areas including quantum chemistry and quantum simulations. In first experiments, atomic ions and neutral atoms have been successfully overlapped by devising hybrid apparatuses combining established trapping methods, Paul traps for ions and optical or magneto-optical traps for neutral atoms, respectively. Since then, the field has seen considerable progress, but the inherent presence of radiofrequency (rf) fields in such hybrid traps was found to have a limiting impact on the achievable collision energies. Recently, it was shown that suitable combinations of optical dipole traps (ODTs) can be used for trapping both atoms and atomic ions alike, allowing to carry out experiments in absence of any rf fields. Here, we show that the expected cooling in such bichromatic traps is highly sensitive to relative position fluctuations between the two optical trapping beams, suggesting that this is the dominant mechanism limiting the currently observed cooling performance. We discuss strategies for mitigating these effects by using optimized setups featuring adapted ODT configurations. This includes proposed schemes that may mitigate three-body losses expected at very low temperatures, allowing to access the quantum dominated regime of interaction.
Highlights
The study of interactions between neutral atoms and ions is a highly topical and promising area of research at the intersection of several disciplines including atomic physics, chemistry and quantum simulations [1,2,3,4,5,6,7,8,9,10,11,12]
While recent experiments in bichromatic traps have demonstrated the onset of sympathetic cooling, as summarized in Figure 3, one open question is if the employed method is suitable for achieving thermal equilibration of the ion with the surrounding neutral atom gas, allowing for entering the s-wave scattering regime
During experimental phases where the ion is confined by rf fields, this can be achieved by employing a method based on parametric excitation [45] of parasitic ions, e.g., Rb+ and Rb2+, at twice their respective oscillation frequencies in the Paul trap [44,46,47,48]
Summary
The study of interactions between neutral atoms and ions is a highly topical and promising area of research at the intersection of several disciplines including atomic physics, chemistry and quantum simulations [1,2,3,4,5,6,7,8,9,10,11,12]. Controlled Rydberg excitation can be used to achieve very low kinetic energies of ions positioned in an atomic cloud [22,25,26] Another approach that was successfully applied to achieve sympathetic cooling close to the quantum regime makes use of the fact that the impact of heating depends on the atom-ion mass ratio and can be mitigated by immersing ions with a large mass, e.g., Yb+ in a cloud of extremely light neutral atoms such as Li [15]. A generic scheme for combining ions and atoms in a way that allows for observing ultracold interactions in the quantum regime has been a sought-after goal in the field
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