# Observable quantum entanglement due to gravity

## TL;DR

This paper explores the potential to observe quantum entanglement generated by gravity between massive objects, analyzing experimental setups with optomechanical systems and released masses, to guide future tests of quantum gravity.

## Contribution

It provides a systematic analysis of gravitationally induced entanglement in optomechanical and free masses setups, estimating experimental parameters needed for detection.

## Key findings

- Entanglement can be generated in both trapped and released mass scenarios.
- Optomechanical setups require high coherence and squeezing, similar to LIGO.
- Released masses can produce detectable entanglement faster, without macroscopic superpositions.

## Abstract

No experiment to date has provided evidence for quantum features of the gravitational interaction. Recently proposed tests suggest looking for the generation of quantum entanglement between massive objects as a possible route towards the observation of such features. Motivated by advances in optical cooling of mirrors, here we provide a systematic study of entanglement between two masses that are coupled gravitationally. We first consider the masses trapped at all times in harmonic potentials (optomechanics) and then the masses released from the traps. This leads to the estimate of the experimental parameters required for the observation of gravitationally induced entanglement. The optomechanical setup demands LIGO-like mirrors and squeezing or long coherence times, but the released masses can be light and accumulate detectable entanglement in a timescale shorter than their coherence times. No macroscopic quantum superposition develops during the evolution. We discuss the implications from such thought experiments regarding the nature of the gravitational coupling.