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.

Limits on inference of gravitational entanglement

“…The visibility decays to its minimum value at t = π/ω, when the atom is maximally entangled with the harmonic oscillator (8). The visibility then returns to the maximum value 1 at t = 2π/ω, when the atom is fully disentangled from the harmonic oscillator.…”

“…The search for a full theory of quantum gravity is a major open problem in modern physics. The difficulty to find such a theory has even raised conceptual questions on the need for the quantization of gravity [1][2][3][4][5][6][7][8]. One major challenge is the lack of experimental evidence.…”

Shadow process tomography of quantum channels

“…In a very different regime, many recent proposals have been made to experimentally determine if Newtonian gravity can entangle meso-to-macroscopic objects in a lab [3][4][5][6][7]. Understanding whether the channel generated by the gravitational interaction is unitary or not is crucially important in determining the implications of these experiments [25]. These experiments typically involve just a few low-dimensional systems (e.g., two qubits [4]), and so the above exponential scaling does not present a substantial difficulty.…”

Path-entangling evolution and quantum gravitational interaction

“…Stimulated by these works [1,2], those advanced studies [3][4][5][6] were done, and there are several works on gravity-induced entanglement in other proposals, for example, levitated nanoparticles or mechanical oscillators [7,8], optomechanical systems [9][10][11][12] and their hybrid model [13,14]. Further, the field theoretical aspects of gravity-induced entanglement have been discussed [15][16][17][18].…”