The torsional motion of a pendulum has several attractive properties as a sensor. Firstly, when properly balanced, the torsional mode is insensitive to the swing motion of the pendulum, therefore largely insensitive to external vibrations. Secondly, by suspending the pendulum with a thin wire, the thermal noise in the torsional motion can be made very small. Combined with a high-precision readout of the pendulum motion using an optical lever, these factors allow for sensing very small torques applied to the pendulum. Finally, pendulums in the mg-scale offer a promising route towards observing gravitationally mediated quantum correlations, at large enough separations that Casimir forces do not enter. In this project, we aim to:
- Control and sense the Coulomb interaction between a mg-scale torsional pendulum and a mg-scale source mass.
- Observe gravitational coupling between the source mass and test mass at mm-scale separations.
- Perform feedback cooling of the torsion pendulum, towards making the motion quantum-noise limited
