Principle Experiment Of Measuring Gravity Gradient By Atom Interferometry

Measuring the gravity gradient has important applications on underground structure detection, recoverying the earth's gravity field, as well as measuring the gravitational constant and testing the equivalence law. This work demonstrate a gravity gradient measurement by atom interferometry using double atomic fountains based on a single magnetic-optical-trap (MOT). According to the preliminary result, in our gravity gradient measurement, a resolution of about 100E is achieved at an integration time of 100s with a baseline of 0.45m.We adopt stimulated Raman transition to manipulate the 87Rb atoms to realize the atom interferometry, which can then be used to measure the gravity gradient. Firstly, the atoms are loaded using the MOT and then launched to form an atomic fountain. In their way of flight, a slice of cold atoms in a very narrow range of velocity and in magnetic insensitive state are selected. After that the prepared atoms are subjected to aπ/2-π-π/2 Raman pulse consequence to split, reflect and combine the atomic wavepacket, which makes the atom to interfere. During that process the gravity accerleration information is written into the phase of the wavepacket. Finally the atoms in different states are detected and the transition probability is obtained, from which the acceleration can be extracted. With two such atom interferometers at different heights formed by double atomic fountains, the gravity gradient can be measured.In this dissertation, the state preparation, detection of the atoms, and the realization of double atomic fountains, as well as the preliminary result of the gravity gradient measurement are described in detail. Furthermore, the noise and the systematic errors in the gravity gradient measurement have been analysed. We find that the dominated noise comes from the detection process, and the bias induced by the inhomegeneity of the magnetic field is one of the severe errors. We have proposed and domenstrated a simultaneous differential method using two atom interferometers formed by double atomic fountains, which can effectively improve the resolution in measuring the magnetic-field gradient. Based on this study, we prospect the future work in measuring the gravity gradient at the end.