Finding quantum characteristics in gravity has interested physicists for many decades.While there has been significant progress on the theoretical side, the experimental side still needs to yield sufficient evidence to prove the quantum nature of gravity.Therefore, the Bose et al.-Marletto-Vedral (BMV) experiment is proposed to resolve this problem.This paper analyzes two variations from the experiment that introduce the following changes: 1) linear increase in distance between masses and 2) significant time length for splitting and recombining.These variables affect the wave function by influencing the phases picked up during evolution and thus produce effects on the quantum witness.Nonetheless, despite these impacts, the entanglement between masses is reduced but not destroyed.At the end of this paper, the meaning of witnessing entanglement in the BMV experiment is discussed.Although proving the non-classicality of gravity does not guarantee the quantum nature of gravity, the experiment is sufficient to rule out classical gravity in the research of the nature of gravity.
The paper presents a scheme to detect entanglement arising from the quantum nature of gravity between a spin qubit and photons, using Stokes parameters. One of the crucial tests of the general theory of relativity is the bending of light due to the curvature. Recently, a quantum counterpart of this experiment to test the quantum nature of the gravitational interaction has been proposed, in which the spin-2, massless graviton yields entanglement between matter and a photon sector. Hence, it provides one of the most crucial experimental signatures for testing the quantum nature of gravity in a lab, since only spin-2-induced entanglement can yield the correct deflection of light due to matter. Here, we propose a positive partial-transpose (PPT) witness criterion for witnessing such an entanglement. We scan the entangled states in this context by studying the overlap of the final state, which is proportional to the entanglement phase. We exploit the Stokes observables to measure the photon state and the spins in the matter sector, thereby constructing a witness for the quantum nature of gravity in this setup. To quantify this entanglement, we will couple the photon to a local oscillator, whose phase need to be controlled to probe the orthogonal components of the macroscopic interference in the laser beam. We have shown that for a non-maximally entangled state mediated by the quantum nature of gravity, the witness attains a maximal negativity of
−0.052. Our findings indicate that this witness effectively detects entanglement within the range
0.71≤∣γ∣<1, where
γ is the overlap between the two coherent states of the photon, providing a clear signature of quantum correlations.
Quantum information concepts and quantum technologies have opened the prospect of probing the quantum nature of gravity in table-top experiments. Most proposals rely on detecting gravitationally mediated entanglement, which requires measurements on both interacting systems. Here we propose an alternative test based on witnessing quantum memory effects in the dynamics of a single system. We show how the quantum memory concept allows the non-classicality of the interaction between two systems to be certified through local measurements on only one of them. We then develop a novel quantum memory witness, making the approach applicable to gravitationally coupled harmonic oscillators. This witness requires no assumptions about the dynamics, such as Gaussianity. Our results show that the quantumness of gravitational dynamics can be certified with access to only one subsystem, opening the door to asymmetric implementations that can offer conceptual and experimental advantages to probing the quantum nature of the gravitational interaction.