Effect of gravity curvature on large-scale atomic gravimeters

In terrestrial geodesy, absolute gravimetry is a tool to observe geophysical processes over extended timescales. This requires measurement devices of high sensitivity and stability. Atom interferometers connect the free fall motion of atomic ensembles to absolute frequency measurements and thus feature very high long-term stability. By extending their vertical baseline to several meters, we introduce Very Long Baseline Interferometry (VLBAI) as a gravity reference of higher-order accuracy.

By using state-of-the-art vibration isolation, sensor fusion and well controlled atomic sources and environments on a 10 m baseline, we aim for an intrinsic sensitivity σ_g ≤ 5 nm/s² in a first scenario for our Hannover VLBAI facility. At this level, the effects of gravity gradients and curvature along the free fall region need to be taken into account. We present gravity measurements along the baseline, in agreement with simulations using an advanced model of the building and surroundings [1]. Using this knowledge, we perform a perturbation theory approach to calculate the resulting contribution to the atomic gravimeter uncertainty, as well as the effective instrumental height of the device depending on the interferometry scheme [2]. Based on these results, we will be able to compare gravity values with nearby absolute gravimeters and as a first step verify the performance of the VLBAI gravimeter at a level comparable to classical devices.

The Hannover VLBAI facility is a major research equipment funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation). This work was supported by the DFG Collaborative Research Center 1464 “TerraQ” (Project A02) and is supported by the CRC 1227 “DQ-mat” (Project B07), Germany’s Excellence Strategy EXC-2123 “QuantumFrontiers”, and the computing cluster of the Leibniz University Hannover under patronage of the Lower Saxony Ministry of Science and Culture (MWK) and the DFG. We acknowledge support from “Niedersächsisches Vorab” through the “Quantum- and Nano-Metrology (QUANOMET)” initiative (Project QT3), and for initial funding of research in the DLR-SI institute, as well as funding from the German Federal Ministry of Education and Research (BMBF) through the funding program Photonics Research Germany.

[1] Schilling et al. “Gravity field modelling for the Hannover 10 m atom interferometer”.  Journal of Geodesy 94, 122 (2020)

[2] Ufrecht, Giese,  “Perturbative operator approach to high-precision light-pulse atom interferometry”. Physical Review A 101, 053615 (2020).