Research On Preparation Of Ultra-cold Atoms And Related Effects In Atom Gravimeters

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 of5?Gal@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 2?K.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)?Gal 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-6?K,and the experimental results is consistent with the theoretical calculations at a resolution of 5?Gal.