Estimating the gravity field impact on a 10 meter atom interferometer

A large variety of scientific experiments as well as common applications require more and more precise knowledge of gravity g, its derived quantities, and their change in time. For several phenomena the effect on g can be modelled for any given location, e.g., Earth tides and the redistribution of mass in the ocean and the atmosphere. Considering the desired sensitivity of future instruments, these models have to be evaluated for their suitability. The gravitational effect of the instrument itself is typically either neglected or determined once and assumed to be stable. Local changes in gravity, e.g., changes in the groundwater table at a laboratory, are often neglected. The vertical gradient in gravity is assumed to be linear and stable in time and, depending on the size of the experiment, this often is a valid assumption. In case of the Very Long Baseline Atom Interferometer (VLBAI), a 10m vertical atom interferometer currently being installed at Leibniz Universität Hannover/HITec with the scope of precise gravity, gravity gradient measurements and tests of the universality of free fall, higher order corrections have to be estimated. This is especially relevant, since the instruments extends over three floors, experiencing non-linear gravity variations when passing the concrete floor of the building. Additionally, the impact of the instrument itself and its supporting structure has to be evaluated. Since the VLBAI has the potential to serve as a reference providing g for the comparison with classical gravimeters in the future, a transfer of g from the effective measuring height of the atom interferometer to a location accessible with an absolute gravimeter is required. Thus, changes in the local gravity field have to be investigated for their effect on the gradient within the instrument