Free-fall Interferometer towards Gravitational Entanglement

Gravitational phenomena involving large objects like the Earth are very apparent, such as the orbiting moon or the falling apple. Quantum phenomena, on the other hand, are usually observed in systems of small particles, such as quantum interference of single atoms. These effects are less apparent but are routinely studied in the laboratory and used in various technical instruments. Gravity and the quantum world live on opposite ends of the mass spectrum. The interplay between gravity and quantum systems remains a big hole in our understanding of fundamental physics. Experimentally, it is uncharted territory. Since gravity behaves quite differently than, for instance, electromagnetic interactions, there might be surprises waiting for us at the quantum level. Theoretically, a satisfactory quantum theory of gravity has remained elusive, and observational input is desperately needed to narrow down what such a theory has to look like. The experimental challenge to explore gravity in the quantum regime is bringing objects with larger masses and gravitational interaction strength into the quantum regime. Specifically, massive objects need to be put in spatially extended quantum states. In such a delocalized state, the particle simultaneously experiences multiple trajectories or regions of space. While this is straightforward for low-mass particles, new techniques are necessary to scale up the quantum state extension of larger- mass objects. If you then have a particle with sufficient mass and delocalization, you can investigate whether the generated gravitational field is also in a quantum state, similar to other quantum interactions. This project explores a novel approach to preparing macroscopic objects in quantum states. Instead of applying forces to the macroscopic bodies to hold them in the laboratory, we let them freely fall and evolve without any troublesome interactions. If this approach proves successful, it would be an important step towards testing the quantum nature of gravity in the future.