【作者】 张恒；

【导师】 胡忠坤； 周敏康；

【作者基本信息】 华中科技大学 ， 无线电物理， 2021， 博士

【摘要】 精密重力测量在地球物理、基础科学研究、资源勘探等领域都发挥着重要的作用。冷原子干涉重力仪作为测量绝对重力值的高精度仪器,受到国内外多个研究小组的广泛关注。其中原子团温度是冷原子干涉重力仪的重要参数,由温度引入的原子团扩散效应不仅会限制仪器灵敏度,还会贡献系统误差,影响测量的准确度。制备超冷原子是解决上述问题的有效途径之一:一方面可以改善原子干涉仪的条纹对比度,提高仪器灵敏度,另一方面也有助于研究和评估相关的系统误差。因此,超冷原子的制备对于高精度原子干涉重力测量具有重要的应用价值,值得对其进行深入研究。本文首先在理论上介绍了超冷原子的制备方法和原子干涉重力测量原理,并通过数值模拟,分析了在原子干涉重力测量中使用超冷原子的潜在优势。其次,设计并搭建了一套全新的超冷原子干涉重力测量装置,主要包括超高真空系统、光路系统以及相关的适配系统,可用于实现超冷原子的快速制备和原子干涉重力测量。实验上,采用基于双大束结构的全光偶极阱,实现了蒸发冷却并完成了超冷原子的快速制备。在3s内可以制备温度低于100n K的⁸⁷Rb原子团,其数目约为1×10⁵个,通过进一步蒸发冷却,在3.2s内实现了原子团的玻色-爱因斯坦凝聚,其温度低于30n K,原子数目约为4×10⁴个。之后,在装置上实现了基于超冷原子的干涉重力测量,仪器采样率为0.25Hz,对装置的稳定性进行了初步优化后,其分辨率可以达到5μGal@3000s(1μGal=1×10^-8m/s²)。在此基础上,采用温度为30n K的超冷原子,在干涉时间T_in=80ms时获得了对比度为76%的重力测量干涉条纹,相较于温度为2μK的原子增加了25%。此外,使用超冷原子减小了本装置中的波前畸变效应,当原子团温度为30n K时,通过测量光学元件面形评估出波前畸变效应为（0.2±0.4）μGal。并通过30n K-6μK大范围内的原子团温度调制实验,在当前5μGal分辨率下,对波前畸变效应评估结果进行了验证,调制实验结果在误差范围内与评估结果一致。更多还原

【Abstract】 Precision gravity measurement plays an important role in various fields such as geophysics,fundamental physics,natural resource detection.Due to its advantages of high potential sensitivity and long-term continuous operation,the atom interferometry gravimeter has received extensive attention by various research groups internationally.The temperature of the atom is an important parameter of the atom gravimeter.The expansion of the atom cloud is directly affected by the temperature of the atom,which will not only limit the sensitivity of the instrument,but also induces systematic errors and affect the accuracy of the measurement.The preparation of ultra-cold atoms is one of the effective ways to solve those problems:on the one hand it can help improve the contrast of the atom interferometer fringe,thereby increasing the sensitivity,on the other hand,it can also help us to evaluate the related systematic errors.Therefore,the preparation of ultra-cold atoms has important application value for high-precision atom interferometry gravity measurements,and it is worthy of in-depth study.Firstly,we introduced the preparation method of ultra-cold atoms and the principle of atom interferometry gravity measurement,and then analyzed the potential advantages of using ultra-cold atoms in atom interferometry gravity measurement through numerical simulation.Secondly,a gravimeter based on ultra-cold ⁸⁷Rb atoms was designed and built,which mainly includes ultra-high vacuum system,optical system and related adaptation system,which can be used to realize the rapid preparation of ultra-cold atoms and atom interferometry gravity measurements.On this device,an all-optical dipole trap based on double reservoirs beam configuration is used to realize evaporative cooling and accomplish the rapid preparation of ultra-cold atoms.The atoms with a temperature lower than 100n K can be prepared in 3s,and the number of atoms is about 1×10⁵.Through further evaporative cooling,the Bose-Einstein condensation of atoms can be realized within 3.2s,and the temperature can be lower than30n K with an atom number of 4×10⁴.After the preparation,the gravimeter based on ultra-cold atoms is realized with a sampling rate of 0.25Hz,and it could reach a resolution of5μGal@3000s after optimization.Finally,the effect related to temperature of atoms in atom interferometry gravity measurements is investigated.Firstly,by using ultra-cold atoms with a temperature of 30n K,the fringe contrast of 76%is obtained with the interference time T_in=80ms,which is increased by 25%compared to that with the temperature of 2μK.Secondly,the wavefront aberration effect is reduced in our apparatus by using ultra-cold atoms.The wavefront aberration effect is estimated to be（0.2±0.4）μGal at temperature of 30n K by measuring the surface quality of the optical components.The evaluation result was verified by modulating the temperature of the atoms in a wide range from 30n K-6μK,and the experimental results is consistent with the theoretical calculations at a resolution of 5μGal.更多还原