Quantum superposition of massive objects and the quantization of gravity


We argue that the (linearized) gravitational field of a massive object in a quantum superposition has to exhibit genuine quantum features. More concretely, both Planck-length vacuum fluctuations and the quantization of gravitational radiation, i.e. gravitons, prevent apparent violations of the fundamental principles of complementarity and causality.

To show this we re-analyze a previous Gedankenexperiment by Mari and Giovanetti, in which Alice and Bob have local control over quantum superpositions of charged and/or massive bodies. We show the full equivalence between the electromagnetic and the gravitational case. In both scenarios, vacuum fluctuations limit Bob’s ability to localize his particle, and the quantization of radiation introduces decoherence of Alice’s particle. The absence of the first effect would allow Alice and Bob to obtain simultaneously full which-path information and full fringe contrast in an interference experiment. The absence of the second effect would allow the two of them to communicate faster than light. Our results provide support for the view that (linearized) gravity should have a quantum field description.

Article: https://journals.aps.org/prd/abstract/10.1103/PhysRevD.98.126009

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