Towards high precision measurements of dynamic gravity

With advances in gravitational physics, especially in the field of gravitational wave (GW) research, fully controlled laboratory experiments on dynamic gravitation become more and more important (Astone et al., 1991, 1998; The LIGO Scientific Collaboration et al., 2015; Ross et al., 2021). Such new experiments can provide new insights into potential dynamic effects and might contribute to bringing light into the mystery still surrounding gravity. Usually, such experiments consist of a transmitter system, that is, a periodically moving mass distribution, and a detector system, which transforms the produced periodically changing gravitational forces into measurable signals. Two such systems have been described recently (Brack et al., 2022, 2023), where the transmitter system consists of either a vibrating bending beam or two rotating bars, both made of tungsten. In both cases, the detector consists of a high Q (1E4), 42 Hz resonant bending beam. Its motion is analyzed using three laser Doppler vibrometers and multichannel lock-in amplifiers. Of paramount importance is the vibration isolation of the detector from ambient noise and crosstalk from the transmitter. Here we present progress on several fronts: High precision gravitational interaction modeling, quantitative crosstalk assessment and transmitter characterization using neutron imaging. The laser interferometers are calibrated at the measurement frequency specifically for the extremely small displacements in the pm range. This results in an estimated measurement uncertainty of around 0.1%.