Bulletin of the American Physical Society
50th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics APS Meeting
Volume 64, Number 4
Monday–Friday, May 27–31, 2019; Milwaukee, Wisconsin
Session V09: Ion-Atom and Atom-Atom Collisions |
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Chair: Eric Hudson, Penn State Room: Wisconsin Center 103DE |
Friday, May 31, 2019 8:00AM - 8:12AM |
V09.00001: Control of atom-ion interactions at low temperatures Michael Mills, Prateek Puri, Elizabeth West, Christian Schneider, Eric Hudson We discuss experiments performed in the MOTion trap, a hybrid atom-ion trap comprised of a linear quadrupole trap and a co-located magneto-optical trap. We describe our studies of excited-state atom-ion interactions at low temperatures, where we observe a suppression of collisions due to the electric field of the ion shifting the transition energies of the neutral. This low-temperature suppression of excited-state collisions is important for the prospect of sympathetically cooling molecular ions with ultracold atomic gases, where unwanted excited-state chemistry would otherwise destroy the molecular ion. We propose a general method to eliminate this suppression by introducing a laser resonant with the shifted transition, addressing the atom-ion pair at a specified internuclear separation, enabling the study of these interactions in the ultracold regime and allowing control of low-temperature atom-ion reactions. We also introduce a new method of controlling collision energy. By varying the axial confinement voltages of our ion trap, we shuttle the ions through the cloud of neutral atoms at a precise velocity, providing a general technique with energy resolutions improved over current methods by an order of magnitude for collision temperatures ranging from a few mK to 10s of K. [Preview Abstract] |
Friday, May 31, 2019 8:12AM - 8:24AM |
V09.00002: Cold ion-neutral chemistry: Measurement of charge-exchange reaction rates in the $\textrm{Na} + \textrm{Ca}^+$ system using a hybrid atom- ion trap Jonathan Kwolek, Douglas Goodman, Benjamin Slayton, Reinhold Blumel, James Wells, Frank Narducci, Winthrop Smith We present new state-selective measurements of charge-exchange reaction rates between Na[$^2\textrm{S}$, $^2\textrm{P}$] and $\textrm{Ca}^+$[$^2\textrm{S}$, $^2\textrm{D}$] using a hybrid trap consisting of a linear Paul trap and a concentric magneto-optical trap (MOT). We measure reaction rates by monitoring the decay of the trapped ion population when overlapped with a MOT, which depend strongly on the ion-cloud temperature and laser-controlled quantum states of the Na and $\textrm{Ca}^+$ reactants. The optically dark $\textrm{Ca}^+$[$^2\textrm{S}$, $^2\textrm{D}$] ion temperature is controlled by either excess micromotion heating or sympathetic cooling from the Na MOT. We find evidence of both endothermic and exothermic reactions, the strongest of which is the Na[$^2\textrm{P}$] on $\textrm{Ca}^+$[$^2\textrm{D}$] with a reaction rate ~$10^{-8}\;\textrm{cm}^3/\textrm{s}$, which exceeds the classical Langevin limit. This work was supported by NSF PHY-1307874. [Preview Abstract] |
Friday, May 31, 2019 8:24AM - 8:36AM |
V09.00003: On the applicability of approximate methods in the elastic scattering between atoms and molecules near room temperature Constantinos Makrides, Eite Tiesinga Despite increases in computational capabilities, fully quantum numerical evaluation of scattering properties remains a computationally intensive problem. For atom-atom scattering, many simplified methods of computation have been used, which can often come to within a few percent of the true value of cross sections. Additionally, analytical models can also produce satisfactory results, such as the Born-approximation for the long-range phase shift between two alkali metals for room-temperature collisions. This particular approximation, has been rather robust and highlights the sensitivity of the cross section on the description of the long-range potential. The same model can be extended in certain regimes to atom-molecule scattering; however, the degree to which these models are applicable is not well understood. Our recent closed-coupled calculations on the Li+H$_2$ system have shown that elastic scattering properties are in disagreement with this Born-approximation, even for room-temperature collision energies, where one would expect the approximation to be applicable. Motivated by this discrepancy, we explain this difference. We additionally provide guidance for when the approximation is valid by studying the Li+Li and Li+He collisions. [Preview Abstract] |
Friday, May 31, 2019 8:36AM - 8:48AM |
V09.00004: X-ray emission measurements following charge exchange with atomic H using merged beams C. Ambarish, A. Roy, D. Wulf, F. T. Jaeckel, D. McCammon, D. Seely, V. Andrianarijaona, C. C. Havener, R. Zhang A novel experiment to study X-ray emission following charge exchange (CX) between highly charged ions and atomic hydrogen is currently in progress using the University of Wisconsin and Goddard Space Flight Center X-ray quantum micro calorimeter detector (XQC). Ions present in the solar wind and planetary exospheres can be generated by an ECR ion source at Oak Ridge National Laboratory (ORNL) and merged with a neutral H beam spanning six orders of magnitude in collision energy. The (n,l) distributions of captured electrons with atomic H as a target is the remaining elusive benchmark for modeling of CX processes. Our measurements of Balmer series line ratio with Ne[IX] + He are compared to ratios constructed from Multi-channel Landau-Zener (MCLZ) calculations [1], which are used to produce atomic data needed to characterize X-ray emissions from a variety of astrophysical objects. The measured line ratios are in excellent agreement with the calculations for the 4s $\rightarrow$ 4p emission, while indicating an increasing state-selectivity for the 4d and 4f states. Details of the apparatus design with initial low background spectra will also be presented. [1] D. Lyons, R. S. Cumbee, and P. C. Stancil, Astrophys. J 232, 27 (2017). [Preview Abstract] |
Friday, May 31, 2019 8:48AM - 9:00AM |
V09.00005: ABSTRACT WITHDRAWN TBD [Preview Abstract] |
Friday, May 31, 2019 9:00AM - 9:12AM |
V09.00006: Experimental demonstration of cooling of trapped ions by atoms of higher mass Sourav Dutta, S. A. Rangwala Buffer gas cooling is one of the most widespread methods to cool ions trapped in a Paul trap. The method relies on elastic collisions of the ions with pre-cooled atoms. However, cooling by a uniformly distributed buffer gas has a limitation -- the ion cooling occurs only if the coolant atoms are lower in mass compared to the trapped ion. We surpass this limitation by using a localized ensemble of ultracold atoms. We experimentally demonstrate, for the first time, that cooling of low-mass trapped ions by atoms of higher mass is possible. In particular, we show that trapped $^{\mathrm{39}}$K$^{\mathrm{+}}$ ions are cooled by magneto-optically trapped ultracold $^{\mathrm{85}}$Rb atoms. The atom:ion mass ratio ($=$ 2.18) is well beyond any theoretical predictions for uniform buffer gas cooling. The result opens up the possibility of cooling trapped H$_{\mathrm{2}}^{\mathrm{+}}$ using ultracold $^{\mathrm{6}}$Li atoms. [Preview Abstract] |
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