Measurement of the Newtonian Constant of Gravitation $G$ by Precision Displacement Sensors

Abstract

The Newtonian constant of gravitation $G$ historically has the largest relative uncertainty over all other fundamental constants with some discrepancies in values between different measurements. We propose a new scheme to measure $G$ by detecting the position of a test mass in a precision displacement sensor induced by a force modulation from periodically rotating source masses. To seek different kinds of experimental setups, laser interferometers for the gravitational wave detection and optically-levitated microspheres are analyzed. The high sensitivity of the gravitational wave detectors to the displacement is advantageous to have a high signal-to-noise ratio of $10^{-6}$ with a few hours of the measurement time, whereas the tunability of parameters in optically-levitated microspheres can enable competitive measurements with a smaller scale setup dedicated to the $G$ measurement. To achieve an accuracy of $G$ better than currently available measurements, developments in force calibration is essential. These measurements can provide an alternative method to measure $G$ precisely, potentially leading to the improvement in the accuracy of $G$, as well as a better search for non-Newtonian gravity at a length scale of $\sim1$ m.