Photonic implementation of quantum gravity simulator

Detecting gravity-mediated entanglement can provide evidence that the gravitational field obeys quantum mechanics. We report the result of a simulation of the phenomenon using a photonic platform. The simulation tests the idea of probing the quantum nature of a variable by using it to mediate entanglement and yields theoretical and experimental insights, clarifying the operational tools needed for future gravitational experiments. We employ three methods to test the presence of entanglement: the Bell test, entanglement witness, and quantum state tomography. We also simulate the alternative scenario predicted by gravitational collapse models or due to imperfections in the experimental setup and use quantum state tomography to certify the absence of entanglement. The simulation reinforces two main lessons: (1) which path information must be first encoded and subsequently coherently erased from the gravitational field and (2) performing a Bell test leads to stronger conclusions, certifying the existence of gravity-mediated nonlocality.