Research On Principle Experiment Of The Atom-Interferometry-based G Measurements

The gravitational constant is a fundamental physical constant which is the first discovered constant but meantime is the lowest-accurate one,since the gravitational interaction is weak and cannot be shielded.The measurement results of the gravitational constant given by worldwide relevant groups are of high accuracy but do not match with each other within the error ranges.It is supposed that there are unknown systematic errors for G measurements.An effective way to explore unknown systematic errors is to use different approaches to perform independent G measurements.Atom interferometry provides a new method for measuring the gravitational constant which is fundamentally different from conventional torsion-balance approaches.This paper presents the research on G measurement by atom interferometry in our laboratory.The main research contents and achievements include in the following three aspects:(1)The source masses moving and positioning device is designed and built,and the parameters related to the source masses are measured and the corresponding influence on G measurement is evaluated.The moving and positioning device of the source masses for the close and far configuration is designed and built,and the movement and positioning of 12 spherical source masses with a total weight of 232 kg for the close and far configuration is realized,and the positioning accuracy reaches the level of 16 μm.The related parameters such as vacuum mass,diameter,roundness and eccentricity of 12 spherical source masses are measured,and the corresponding systematic error is evaluated,resulting a contribution of 443 ppm for our G measurement.(2)The atom clouds parameter measurement device is designed and built,and the related parameters of the atom clouds is measured and the corresponding systematic error is evaluated.A CCD-based measurement device for characterizing atom clouds is designed and built.A method of in-situ calibration of the imaging system magnification is proposed for the first time,which explores the free fall distance of the atom cloud as dimension reference,and a precision of 1% for calibrating the imaging system’s magnification is achieved.A differentiation measurement is performed by reversing the direction of the probe beam to suppress the influence of the probe beam on the measurement of the horizontal positions of the atom cloud.Finally,the measurement of the atom cloud-related parameters at the sub-millimeter level is realized,and the corresponding systematic error is evaluated,giving a contribution of 432 ppm for our G measurement.(3)The principle measurement of the gravitational constant by atom interferometry is realized.Based on the construction of the source mass and the measurement of the parameters of the atom clouds,the measurement of the gravitational constant is performed by combining the source masses and the atom interferometry gravity gradiometer.Differential measurement between the close and far configuration of the source masses is carried out,realizing the principle measurement of G by atom interferometry in our laboratory.The resultant statistical uncertainty is 1051 ppm.This paper presents in detail the above-mentioned research work on the measurement of gravitational constant by atomic interferometry during my Ph.D.,which points out the improvement direction for the future measurement of G by atom interferometry aimed at100 ppm level.