Cold Atom-Ion Charge-Exchange and Internal Molecular-Ion Sympathetic Cooling in an Ion-Neutral Hybrid Trap

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This research uses an innovative hybrid ion-neutral atomic particle trap developed by the PI's group as a tool for observing reactions and collisions of low energy ions with atoms cooled by lasers to near absolute zero temperature (~0.001 Kelvin). The cold atoms within a magneto-optic trap (MOT) can be used to refrigerate a co-trapped sample of atomic or molecular ions to study ion-atom interactions at temperatures approaching that of space. Cold, trapped Na+ and Ca+ atomic ion, and Na2+ molecular ion reaction rates with ultracold sodium (Na) atoms will be measured, as well as the rates of sympathetic collisional cooling, using the hybrid trap. The research has technical applications to precision spectroscopy, fundamental constants, astrophysical processes in the solar system and interstellar medium, atomic ion clocks and quantum computing. The ion-neutral hybrid trap combines two separate but spatially overlapped and concentric traps: a MOT and a Paul radiofrequency ion trap. Specifically, the project will involve direct experimental measurements of the absolute electron-exchange rate constant between Na and Ca+, investigating its dependence on collision energy and ionic and/or atomic excited-state populations. The rates will be compared with simulations. The resonance radiation absorption spectrum of trapped Ca+ ions will be investigated as a temperature probe of the trap as will the possibility of forming small lattices of confined, ionic Coulomb "crystals" inside the trap by using sympathetic cooling collisions, rather than traditional laser cooling.A graduate student completed his Ph.D. in experimental atomic physics under the previous NSF grant and two additional Ph.D. level students expect to complete their ongoing dissertation research under the new grant. An undergraduate physics-mathematics student worked on simulations during the previous grant, as well as two M.S.-level exchange students from the University of Heidelberg, who did experimental work. Both undergraduate and graduate physics students participate in independent study work on this project. Students receive a broad education in basic experimental techniques of atomic and molecular physics: laser and collisional cooling and trapping at high vacuum (conditions resembling those of space), as well as cold ion manipulation, trapping, detection and laser spectroscopy. The PI gave an invited talk on this hybrid trap research in 2013 at a symposium on the Sao Carlos campus of the University of Sao Paulo, Brazil, attended by 5 physics Nobel Laureates. Research results are frequently presented in publications and at local, national and international meetings.