Witnessing the Quantum Nature of Spacetime in a Lab

Anupam Mazumdar (University of Groningen)

November 21, 2024

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Abstract: Quantum field theories and classical general relativity accurately model all observations to date. Although theoretically, quantum gravity is much studied, it has no empirical evidence yet. This makes “is spacetime/gravity quantum?” one of our most important open questions. I have pioneered an ambitious idea with my collaborators “spin entanglement witness for quantum gravity,” to test the quantum nature of gravity in a lab. It exploits quantum information ideas and combines a quantum spin with cooling/trapping quantum technologies. It is based on entangling two neutral quantum masses solely by their gravitational interaction while all other interactions are mitigated, e.g. electromagnetic (EM) interactions between the masses. It proves the quantum nature of gravity, as classical gravity cannot mediate quantum correlations (entanglement). The potentially realisable protocol requires meeting a rich set of challenges: mitigating the EM interactions and background, creating spatial quantum superpositions for massive objects, and measuring spin correlations to witness the entanglement. We must also protect the quantum superpositions from heating, recoil, blackbody radiation, acceleration, seismic and gravity gradient noises.