Newton, entanglement, and the graviton

Abstract

Many experiments have recently been proposed to test whether non-relativistic gravitational interactions can generate entanglement. In this note, I consider the extent to which these experiments can test if the graviton exists. Assuming unitarity and Lorentz invariance of the $S$-matrix, I demonstrate that this "Newtonian entanglement" requires the existence of massless bosons, universally coupled to mass, in the Hilbert space of low-energy scattering states. These bosons could be the usual spin-2 gravitons, but in principle there are other possibilities like spin-0 scalar gravitons. I suggest a concept for a more refined experiment to rule these out. The special role of $d=3+1$ spacetime dimensions and the possibility that unitarity is violated by gravity are highlighted.

11 pages + appendices. Dedicated to the memory of Steve Weinberg

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• On inference of quantization from gravitationally induced entanglement
• Gravity entanglement, quantum reference systems, degrees of freedom
• Generating quantum entanglement between macroscopic objects with continuous measurement and feedback control
• Mass-independent scheme for enhancing spatial quantum superpositions
• Semi-classical gravity phenomenology under the causal-conditional quantum measurement prescription
• Consistency between causality and complementarity guaranteed by the Robertson inequality in quantum field theory
• Effects of photon field on entanglement generation in charged particles
• Signatures of Quantum Gravity in the Gravitational Self-Interaction of Photons
• Photonic Implementation of Quantum Gravity Simulator
• Graviton noise:the Heisenberg picture