基于非重合密集折返光路型原子气室及量子无损测量的高灵敏度全光学原子磁力仪研究

Magnetometers with sensitivity beyond 1fT Hz^-1/2 have significant applications. This research is focused on improving the sensitivity of an atomic magnetometer based on optical rotations utilizing the latest techniques of dense-beam multipass cells as well as quantum nondemolition measurements. We will theoretically study the multiple beam passes generation and their propagation properties, the effect of cell form factors, buffer gases and anti-relaxation coatings on the atomic spin relaxation, and the mechanism of interactions between highly polarized atoms and light in a weak magnetic field. Also we will investigate the essential relationship between the sensitivity of magnetometers and the effective number of atoms, relaxation time, quantum nondemolition measurement and spin squeezing. Experimentally, we will utilize an atomic cell filled with buffer gas and integrated with a multipass cavity with high transmission ratio to notably increase the effective optical path and number of atoms, and obtain very large optical rotations and signal-to-noise ratio via highly polarized atoms. The characters of atomic spin noise will also be analyzed. We will improve the atomic transverse relaxation time by the non-linear spin relaxation effect and perform quantum nondemolition measurements using weak and short pulses. The actual sensitivity will be measured and compared with theorectical results. This research can promote the further understanding of the principle of interactions between atoms and light in a weak field, and help us to solve some significant problems related to atomic magnetometers. This type of magnetometer can be realized with high sensitivity while still keeping small size.

fT级别高灵敏度磁力仪具有重要应用价值。本项目首次将非重合密集折返光路型原子气室应用于基于偏振面旋转的全光学原子磁力仪上并显著提高其灵敏度，同时使用量子无损测量突破基本灵敏度极限。理论上研究非重合密集折返光路的产生原理与腔内光束传输的特性，计算原子气室结构、缓冲气体和抗弛豫涂层对原子自旋弛豫的影响，分析微弱外磁场中高度极化的原子与激光的作用机制；探究有效原子数、弛豫时间、量子无损测量、自旋压缩与灵敏度之间的密切关联。实验上采用一个集成高反射率密集折返光路腔的多组分原子气室来大幅提高有效光程和作用原子数，通过高度极化原子来获得大角度的探测光偏振面旋转并提高信噪比；观察原子自旋噪声特征，利用非线性弛豫效应增大原子弛豫时间，采用弱脉冲进行量子无损测量，分析实际灵敏度并与理论对比。通过本研究可更深入理解外场下光与原子的相互作用机理，解决原子磁力仪研究的关键问题，实现小体积的同时显著提高灵敏度。

全光学的原子磁力仪能够实现更高的灵敏度，且具有能耗低、使用和维护成本低、可靠性高等优势，在许多领域如空间地球物理、地质学、工业无损检测、医学等都有着广泛应用。提升磁力仪的灵敏度非常具有实际应用价值，其研究思路也具有重要的科学意义。在承担项目期间，按照原计划开展相关研究，总体执行情况良好。其中，我们进行了一套基于非重合密集折返光路原子气室的原子磁力仪整体实验装置的搭建，对磁场线圈进行了优化改进，组建了激光稳频和稳功率系统，改善了信号测量电路，优化了探测光模式，并且针对提高原子磁力仪灵敏度方面进行了一定的理论和实验研究。在项目进行过程中，研究了原子气室腔内光束传输的特性，从理论上分析了原子气室结构、抗弛豫涂层与原子自旋弛豫之间的关系，并利用实验对其进行验证，发现了其相互之间具有一定的密切联系；我们通过改进光学系统以及探测光的特性，利用非重合密集折返光路型原子气室，根据理论预期设计了相应的实验方案，研究量子无损探测的方法，寻找突破基本灵敏度极限的理论和实验条件；通过实际测量，发现了原子磁力仪具有了较高的灵敏度，达到600fT/Hz^1/2，受限于硬件测量环境，其实际灵敏度应更高。发表成果并被报道；培养了本科生并指导了研究生；在本项目的研究中还观察到了某些值得思考的新现象，例如原子与气室内壁涂层之间的一些微观相互作用过程和理论预期不一致的反常现象，以及探索到原子磁力仪的新应用等，很值得在今后的相关项目开展深入研究。该项目的研究结果对原子在磁场中与光的相互作用、原子与抗弛豫镀膜的微观作用、全光学类高灵敏度原子磁力仪的基础和应用研究都具有一定的价值。

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