Space-based mm/mg-scale Laser Interferometer for Quantum Gravity

Abstract: The experimental verification of the quantum nature of gravity represents a milestone in quantum gravity research. Recently, interest has grown for testing it via gravitationally induced entanglement (GIE). Here, we propose a space-based interferometer inspired by the LISA Pathfinder (LPF). Unlike the LPF, our design employs two smaller gold-platinum test masses, each weighing the milligram scale, surrounded by a shield below 2 K, and positioned side by side with a millimeter scale separation. This configuration enables the detection of GIE through simultaneous measurements of differential and common-mode motions. We simulate quantum measurements of these modes taking into account gas damping, black-body radiation, and cosmic-ray collisions to estimate the integration time for GIE detection. Our results show that GIE can be demonstrated with a few modifications to the LPF setup.