Demonstration of displacement sensing of a mg-scale pendulum for mm- and mg- scale gravity measurements

TL;DR

This paper demonstrates a highly sensitive displacement sensor using a mg-scale pendulum, capable of detecting gravitational interactions between small masses, opening new avenues for quantum gravity experiments.

Contribution

It introduces a novel displacement sensing method with a mg-scale pendulum, achieving unprecedented sensitivity for small mass gravitational coupling detection.

Findings

Achieved a quality factor of 10^8 in the pendulum

Detected gravitational coupling between small masses at mm separation

Paved the way for quantum regime gravitational experiments

Abstract

Gravity generated by large masses has been observed using a variety of probes from atomic interferometers to torsional balances. However, gravitational coupling between small masses has never been observed so far. Here, we demonstrate sensitive displacement sensing of the Brownian motion of an optically trapped 7-mg pendulum motion whose natural quality factor is increased to $10^8$ through dissipation dilution. The sensitivity for an integration time of one second corresponds to the displacement generated by the gravitational coupling between the probe and a mm separated 100 mg mass, whose position is modulated at the pendulum mechanical resonant frequency. Development of such a sensitive displacement sensor using a mg-scale device will pave the way for a new class of experiments where gravitational coupling between small masses in quantum regimes can be achieved.