Quantum state resolved few-body collisions and reactions at ultralow temperatures

虽然原子的三体和四体碰撞是自然界中一些最基本的过程，但它们仍然没有被完全理解。为了回答一些重要的、开放的问题，我们建议在这里以完全状态解决的方式实验研究这种超冷状态下的少体碰撞。利用超冷87Rb原子和87Rb2分子制备了碰撞粒子的初始量子态，并在碰撞后测量了双原子产物的量子态。为此，我们将采用并进一步开发我们小组最近发现的一种高度选择性的检测方法。它是基于共振增强的多光子电离分子和一个有效的后续离子检测。我们将研究两种不同的碰撞过程：1)87Rb的三体重组，形成一个Rb2分子。2)激发态的超冷Rb2分子在与Rb原子或另一个Rb2分子碰撞时松弛到更深的束缚态。我们的实验涉及到最近才进入的超冷化学的新研究领域。因此，我们希望我们的研究能够提供大量新的见解。除了获得对超冷反应性或非弹性少体碰撞的基本理解外，我们工作的一个重要动机是学习如何获得对化学反应的控制。我们期望所提出的实验将引领冷态到态化学的年轻领域，特别是对于具有许多反应路径的系统。

While three- and four-body collisions of atoms are some of the most fundamental processes in nature, they are still not fully understood. In order to answer some of the important, open questions, we propose here to experimentally investigate such few-body collisions in the ultracold regime in a fully state-resolved manner. Using ultracold 87Rb atoms and 87Rb2 molecules we prepare an initial quantum state of colliding particles and after the collision we measure the quantum states of the diatomic products. For this, we will employ and further develop a highly selective detection method that our group has recently discovered. It is based on resonance-enhanced multi-photon ionization of molecules and an efficient subsequent ion detection. We will study two different kinds of collisional processes: 1) Three-body recombination of 87Rb where a Rb2 molecule is formed. 2) Relaxation of an excited ultracold Rb2 molecule to a more deeply bound state in a collision with either a Rb atom or another Rb2 molecule. Our experiments tackle the novel research field of ultracold chemistry which only recently has become accessible. Therefore we expect our research to deliver a large number of new insights. Besides gaining a fundamental understanding of ultracold reactive or inelastic few-body collisions, an important incentive for our work is to learn how to gain control over chemical reactions. We expect that the proposed experiments will lead the young field of cold state-to-state chemistry, in particular for systems with many reaction paths.