Tabletop experiments for quantum gravity: a user’s manual

Abstract

Recent advances in cooling, control, and measurement of mechanical systems in the quantum regime have opened the possibility of the first direct observation of quantum gravity, at scales achievable in experiments. This paper gives a broad overview of this idea, using some matter-wave and optomechanical systems to illustrate the predictions of a variety of models of low-energy quantum gravity. We first review the treatment of perturbatively quantized general relativity as an effective quantum field theory, and consider the particular challenges of observing quantum effects in this framework. We then move on to a variety of alternative models, such as those in which gravity is classical, emergent, or responsible for a breakdown of quantum mechanics. * Electronic address: carney@umd.edu arXiv:1807.11494v2 [quant-ph]

Exploring the unification of quantum theory and general relativity with a Bose–Einstein condensate

“…In the GQSR proposal, there is nothing necessarily preventing a gravitational field from being in a quantum superposition, only that there must, at least, be a time limitation for this that is dependent on the mass distribution of the system. This is in contrast to other proposed theories, such as a fundamental semiclassical gravity theory, where gravity is necessarily a classical effect, and no entanglement can ever be generated [21,26]. 4 Although the testable prediction can be derived using gravity in its non-relativistic limit, gravity is, as far as we know, best described using GR and so it can be enlightening to consider the experiments from a GR-like point-of-view [22].…”

“…This has inspired many theoretical and experimental studies (for a review see e.g. [21]) and would test an important prediction of the quantizing gravity approach in the Newtonian gravity limit (the testable prediction can be derived when just considering applying QT to gravity in its non-relativistic limit, where the theories would be expected to be compatible in the conventional approach) 4 .…”

Entanglement dynamics of two mesoscopic objects with gravitational interaction

“…Let us now consider the interaction between the particles via the Hamiltonian (1). Importantly, the system Hamiltonian commutes with the environmental coupling (4), rendering the total dynamics also exactly solvable regardless of the details of the enviroment operator R. Indeed, as we transform to the interaction picture by substituting ρ = U (t)ρ I (t)U † (t), where U (t) = e −iHt , we find that the interacting density matrix ρ I (t) follows the dynamics of two independent particles interacting only with the environment given by equation (7). Assuming that at t = 0 the system is in the state |+ +| ⊗ |+ +|, we find the density matrix of the system at time t to be…”

“…Each particle is then split into a superposition of two positions that are separated by a distance L orthogonally to their initial separation. Based on recent advances in setting up mesoscopic systems in superposition [6][7][8][9][10][11], the authors of Ref. [3] suggested as physically relevant quantities m 1 ≈ m 2 ≈ 10 −8 kg, d ≈ 200µm, and we can assume L d. In the original proposal [3], the particles are split into superpositions of positions in the same direction as their initial separation, see Figure 1(b).…”

Quantum sensing with nanoparticles for gravimetry: when bigger is better

“…A driving force for creating quantum states of more massive objects, beyond proving their feasibility, is to test theories of gravity. The gravitational interaction has so far presented itself as classical [22]. It is unknown whether gravity acts as a quantum interaction, for example, via virtual graviton exchange [23], or if in fact gravity is responsible for wave function collapse.…”