近日，美国哈佛大学教授Kang-Kuen Ni及其研究团队的研究发现核自旋守恒使超冷分子反应的态间控制成为可能。 2020年12月30日出版的《自然—化学》发表了这项成果。

研究组通过在整个反应过程中利用核自旋的守恒来实现这一目标。使用共振增强多光子离子化光谱研究超冷KRb分子间的双分子反应产物，研究人员发现系统保持了近乎完美的对反应物核自旋的记忆，表现在对产物旋转态的强均势取向。通过利用外部磁场改变初始核自旋态的相干叠加，该课题组人员利用这种效应来改变这些产物态的占有率。

通过这种方式，该团队能够以量子态分辨率控制反应的输入和输出。这里展示的技术打开了研究反应产物量子纠缠和超冷反应态-态水平的反应动态的可能。

据了解，反应系统的量子态控制已使潜在相互作用电位的微观探针和以量子统计为主题的反应速率改变成为可能。然而，拓展这样的控制到反应结果的量子态仍然充满挑战。

附：英文原文

Title: Nuclear spin conservation enables state-to-state control of ultracold molecular reactions

Author: Ming-Guang Hu, Yu Liu, Matthew A. Nichols, Lingbang Zhu, Goulven Qumner, Olivier Dulieu, Kang-Kuen Ni

Issue&Volume: 2020-12-30

Abstract: Quantum-state control of reactive systems has enabled microscopic probes of underlying interaction potentials and the alteration of reaction rates using quantum statistics. However, extending such control to the quantum states of reaction outcomes remains challenging. Here, we realize this goal by utilizing the conservation of nuclear spins throughout the reaction. Using resonance-enhanced multiphoton ionization spectroscopy to investigate the products formed in bimolecular reactions between ultracold KRb molecules we find that the system retains a near-perfect memory of the reactants’ nuclear spins, manifested as a strong parity preference for the rotational states of the products. We leverage this effect to alter the occupation of these product states by changing the coherent superposition of initial nuclear spin states with an external magnetic field. In this way, we are able to control both the inputs and outputs of a reaction with quantum-state resolution. The techniques demonstrated here open up the possibilities to study quantum entanglement between reaction products and ultracold reaction dynamics at the state-to-state level.

DOI: 10.1038/s41557-020-00610-0

Source: https://www.nature.com/articles/s41557-020-00610-0