极性分子的精密光谱测量和激光冷却

Precision measurement based on atom and molecules is a hot topic now. Compare with atoms, molecules have more complex energy and freedom, and have their unique position in precision measure. Some electric filed sensitive measurement (such as EDM) is much better to be done with molecules. Similar with atom, making molecules colder can reduce the uncertain caused by motion, increase the intergoation time, and improve the precision of measurement. Because of this, cold molecules have been studied for more than 20 years. But tradition method (Such as Stark decelarator, Zeeman decelarrator) works with a conservative field, which can slow molecules but not increase the phase space density. In last few years, a new direction, laser cooling of polar molecules, have been developed quickly, cooler and denser molecules samples are expected to be achieved. This project focus on this new cooling method. We choose BaF as the target molecule. First measure the spectrum precisely with the help of buffer gas cooling. Then combine with the microwave remixing technique, extend the laser cooling techniques to BaF. Such research will set a solid foundation of the molecules-based precision measurement, quantum control and studying the many-body physics.

基于原子、分子的精密测量是目前研究热点和前沿。分子比原子具有更复杂的能级结构和更多的自由度，在精密测量方面具有自己独特的位置，一些对电场敏感的物理量（比如电子永久电偶极矩），用分子来进行测量可以有更高的精度。和原子类似，为了提高测量的精度，需要将分子冷却下来。但是传统分子冷却手段（电场Stark减速、磁场Zeeman减速等），由于使用保守势场，并不能提高分子的相空间密度，目前已进入一个瓶颈期。近年来，国际上新兴了一个方向，激光冷却极性分子，可以获得更低温度，更高密度的分子气体。本项目聚焦于实验研究这类新型分子冷却技术。选择BaF分子，结合缓冲气体冷却技术，首先精密测量分子的光谱特性。然后结合微波混合技术，将激光冷却扩展到双原子分子上，实现分子的冷却，为下一步研究基于分子的精密测量打下基础。

该项目自主研发了一套适用于分子实验冷分子产生系统，以及激光稳频系统，成功地产生了BaF分子束，并在实验上和理论上探索了BaF分子激光冷却的可行性，取得了一系列先进的研究成果，主要包括：.1.实验方面，研发了一套基于缓冲气体冷却原理的冷分子发生装置，在实验上用4K的氦气为缓冲气体获得4K的BaF冷分子，并精确测定其相关的超精细结构光谱。[文章发布在Phys. Rev. A 95, 032701 (2017) ]。利用激光和BaF分子多次作用，增加作用时间，观测激光对分子束的偏转效应。[文章发布在Phys. Rev. A 96, 053401 (2017)]。技术方面，利用传输腔锁频技术实现了对多束特殊频率的激光的长时间的锁定，线宽小于2MHz。[文章发表在J. Opt. Soc. Am. B 35(7) 1658 (2018)]。.2.理论方面，分析了BaF分子激光冷却的可行性并提出了激光冷却的实验方案。[文章发表在Phys. Rev. A 94, 063415 (2016)]；理论上设计了针对II-型MOT（磁光阱）跃迁塞曼减速方案，解决目前II-型MOT跃迁的分子或原子减速中遇到的困难[Phys. Rev. A 100, 053402 (2019)]。..项目组共发表SCI论文9篇。