Ultracold atom-ion collisions are an emerging field of research that can ultimately lead to their precise quantum control. In collisions in which the ion is prepared in an excited state, previous studies showed that the dominant reaction pathway was charge exchange. Here, we explored the outcome products and the energy released from a single ultracold collision between a single ${}^{88}\mathrm{Sr}^{+}$ ion and a single ${}^{87}\mathrm{Rb}$ atom prepared in excited metastable and ground electronic states, respectively, with control over their relative spins. We found that the ion's long-lived $D_{5/2}$ and $D_{3/2}$ states quench after roughly three collisions, acquiring immense kinetic energy in the process. By performing single-shot thermometry on the ion after the collision, we identified two dominant reaction pathways: electronic excitation exchange and spin-orbit change. In contrast to previous experiments, we observed no charge-exchange events. These processes are theoretically understood to occur through Landau-Zener avoided crossings leading to the observed reaction pathways. We also found that spin orientation has almost no effect on the reaction pathways, due to strong Coriolis-spin mixing. Our results provide a deeper understanding of ultracold atom-ion inelastic collisions and offer additional quantum control tools for the cold chemistry field.

中文翻译：

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直接观察超冷原子-离子激发交换

超冷原子离子碰撞是一个新兴的研究领域，最终可能导致其精确的量子控制。在碰撞中，离子以激发态制备，以前的研究表明，主要的反应途径是电荷交换。在这里，我们探索了结果产物以及单个物体之间的一次超冷碰撞所释放的能量${}^{88}r^{+}$ 离子和单 ${}^{87}b$分别以激发的亚稳态和基态电子状态制备原子，并控制它们的相对自旋。我们发现离子的寿命很长$d_{5/2}$ 和 $d_{3/2}$大约3次碰撞后，态变冷，在此过程中获得了巨大的动能。通过对碰撞后的离子进行单次测温，我们确定了两个主要的反应途径：电子激发交换和自旋轨道变化。与以前的实验相反，我们没有观察到电荷交换事件。从理论上讲，这些过程是通过Landau-Zener避免交叉而导致观察到的反应途径发生的。我们还发现，由于强烈的科里奥利-自旋混合，自旋取向几乎对反应路径没有影响。我们的结果提供了对超冷原子离子非弹性碰撞的更深刻理解，并为冷化学领域提供了其他量子控制工具。