Park Juliana J, Lu Yu-Kun, Jamison Alan O, Tscherbul Timur V, Ketterle Wolfgang
MIT-Harvard Center for Ultracold Atoms, Research Laboratory of Electronics, Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, USA.
Institute for Quantum Computing, University of Waterloo, Waterloo, Ontario, Canada.
Nature. 2023 Feb;614(7946):54-58. doi: 10.1038/s41586-022-05635-8. Epub 2023 Feb 1.
Collisional resonances are important tools that have been used to modify interactions in ultracold gases, for realizing previously unknown Hamiltonians in quantum simulations, for creating molecules from atomic gases and for controlling chemical reactions. So far, such resonances have been observed for atom-atom collisions, atom-molecule collisions and collisions between Feshbach molecules, which are very weakly bound. Whether such resonances exist for ultracold ground-state molecules has been debated owing to the possibly high density of states and/or rapid decay of the resonant complex. Here we report a very pronounced and narrow (25 mG) Feshbach resonance in collisions between two triplet ground-state NaLi molecules. This molecular Feshbach resonance has two special characteristics. First, the collisional loss rate is enhanced by more than two orders of magnitude above the background loss rate, which is saturated at the p-wave universal value, owing to strong chemical reactivity. Second, the resonance is located at a magnetic field where two open channels become nearly degenerate. This implies that the intermediate complex predominantly decays to the second open channel. We describe the resonant loss feature using a model with coupled modes that is analogous to a Fabry-Pérot cavity. Our observations provide strong evidence for the existence of long-lived coherent intermediate complexes even in systems without reaction barriers and open up the possibility of coherent control of chemical reactions.
碰撞共振是重要的工具，已被用于改变超冷气体中的相互作用，以在量子模拟中实现前所未知的哈密顿量，从原子气体中创造分子以及控制化学反应。到目前为止，这种共振已在原子 - 原子碰撞、原子 - 分子碰撞以及束缚非常弱的费什巴赫分子之间的碰撞中被观测到。由于可能的高态密度和/或共振复合体的快速衰变，超冷基态分子之间是否存在这种共振一直存在争议。在此，我们报道了在两个三重态基态NaLi分子之间的碰撞中出现的一个非常明显且狭窄（25 mG）的费什巴赫共振。这个分子费什巴赫共振有两个特殊特征。首先，由于强化学反应性，碰撞损失率比背景损失率提高了两个多数量级，背景损失率在p波普适值处达到饱和。其次，共振位于一个磁场处，此时两个开放通道几乎简并。这意味着中间复合体主要衰变为第二个开放通道。我们使用一个类似于法布里 - 珀罗腔的耦合模模型来描述共振损失特征。我们的观测为即使在没有反应势垒的系统中存在长寿命相干中间复合体提供了有力证据，并开辟了对化学反应进行相干控制的可能性。
