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

这项研究使用了PI小组开发的一种创新的混合离子中性原子粒子陷阱，作为观察低能离子与被激光冷却到接近绝对零度（~0.001开尔文）的原子的反应和碰撞的工具。磁光阱（MOT）中的冷原子可以用来冷却原子或分子离子的共捕获样品，以研究在接近空间温度下离子-原子相互作用。使用混合阱，将测量冷的、被捕获的Na+和Ca+原子离子以及Na2+分子离子与超冷钠（Na）原子的反应速率，以及交感碰撞冷却速率。该研究在精密光谱学、基本常数、太阳系和星际介质中的天体物理过程、原子离子钟和量子计算等方面具有技术应用。离子中性混合阱结合了两个独立但空间重叠的同心阱：MOT和保罗射频离子阱。具体来说，该项目将涉及Na和Ca+之间绝对电子交换速率常数的直接实验测量，研究其对碰撞能量和离子和/或原子激发态种群的依赖。这些速率将与模拟进行比较。捕获Ca+离子的共振辐射吸收光谱将作为陷阱的温度探头进行研究，并将通过使用共感冷却碰撞，而不是传统的激光冷却，在陷阱内形成小晶格的限制，离子库仑“晶体”的可能性。一名研究生在之前的NSF资助下完成了他的实验原子物理学博士学位，另外两名博士水平的学生预计将在新的资助下完成他们正在进行的论文研究。在之前的资助中，一名物理数学专业的本科生从事模拟工作，还有两名来自海德堡大学的硕士级交换生从事实验工作。物理学本科生和研究生都要参与这个项目的独立研究工作。学生将在原子和分子物理的基本实验技术方面接受广泛的教育：在高真空（类似于太空的条件）下的激光和碰撞冷却和捕获，以及冷离子操作，捕获，探测和激光光谱。2013年，PI在巴西圣保罗大学圣卡洛斯校区的一个研讨会上就这种混合陷阱的研究做了一次受邀演讲，有5位物理学诺贝尔奖获得者参加了会议。研究成果经常在出版物和地方、国家和国际会议上发表。

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.