First result for testing semiclassical gravity effect with a torsion balance

TL;DR

This study used a highly sensitive optomechanical system with a torsion pendulum to test for deviations predicted by semiclassical gravity, setting new experimental constraints and highlighting future challenges.

Contribution

Developed an ultra-sensitive optomechanical platform to test semiclassical gravity effects, achieving high sensitivity and proposing new experimental strategies.

Findings

No evidence of semiclassical gravity effects was observed.

Achieved a sensitivity of 0.3urad/rtHz at 2.5mHz.

Identified key challenges and proposed new experimental approaches.

Abstract

The Schr\"odinger-Newton equation, a theoretical framework connecting quantum mechanics with classical gravity, predicts that gravity may induce measurable deviations in low-frequency mechanical systems-an intriguing hypothesis at the frontier of fundamental physics. In this study, we developed and operated an advanced optomechanical platform to investigate these effects. The system integrates an optical cavity with finesse over 350000 and a torsion pendulum with an ultra-low eigenfrequency of 0.6mHz, achieving a high mechanical Q-factor exceeding 50000. We collected data for 3 months and reached a sensitivity of 0.3urad/rtHz at the Schr\"odinger-Newton frequency of 2.5mHz where deviations from the standard quantum mechanics may occur. While no evidence supporting semiclassical gravity was found, we identify key challenges in such tests and propose new experimental approaches to advance this line of inquiry. This work demonstrates the potential of precision optomechanics to probe the interplay between quantum mechanics and gravity.