Measurement of Gravitational Coupling between Micrometer-Sized Masses

The search for experimental evidence for quantum gravity is severely hindered by the relative weakness of the gravitational interaction as compared to the other known fundamental forces. Gravity also remains resistant to unification within the standard model of physics and appears to be fundamentally disconnected from quantum theory. It is therefore an important experimental undertaking to test gravity on all scales. Measurements of the gravitational interaction have usually been confined to mass ranges of kg and above. In a previous iteration of our experimental apparatus [1] we have demonstrated gravitational coupling between millimeter-sized gold spheres with sub-100mg mass using a rotational mechanical oscillator. In this talk we will report on our progress on extending the parameter space by reducing the source mass by more than three orders of magnitude. These improvements allow us to reach a source mass regime in the microgram range.

[1] T Westphal, H Hepach, J Pfaff, M Aspelmeyer - Nature 591, 225–228 (2021)