Quantum gravity witness via entanglement of masses: Casimir screening

Abstract

A recently proposed experimental protocol for quantum gravity induced entanglement of masses (QGEM) requires in principle realizable, but still very ambitious, set of parameters in matter-wave interferometry. Motivated by easing the experimental realization, in this paper, we consider the parameter space allowed by a slightly modified experimental design, which mitigates the Casimir potential between two spherical neutral test masses by separating the two macroscopic interferometers by a thin conducting plate. Although this setup will reintroduce a Casimir potential between the conducting plate and the masses, there are several advantages of this design. First, the quantum gravity induced entanglement between the two superposed masses will have no Casimir background. Secondly, the matter-wave interferometry itself will be greatly facilitated by allowing both the mass 10 −16-10 −15 kg and the superposition size x ∼ 20 μm to be a one-two order of magnitude smaller than those proposed earlier, and thereby also two orders of magnitude smaller magnetic field gradient of 10 4 Tm −1 to create that superposition through the Stern-Gerlach effect. In this context, we will further investigate the collisional decoherences and decoherence due to vibrational modes of the conducting plate.

Qudits for witnessing quantum-gravity-induced entanglement of masses under decoherence

“…A similar proposal was also made in [15]. This has attracted significant interest from the research community [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] and an experimental initiative in creating a macroscopic superposition with the Stern-Gerlach setup [32]. The above proposal has been coined quantum gravity-induced entanglement of masses (QGEM), which exploits the loophole that as local operations and classical communications are unable to entangle the two quantum states if they are not entangled, to begin with, quantum communication is required to generate the entanglement as highlighted in [13].…”

“…In particular, we consider how quickly different setups can generate entanglement according to a generalized model of the QGEM experiment and how many measurements would be required to witness that entanglement. We test our findings in the presence of decoherence, furthering the analyses presented in [19][20][21][22].…”

Realization of a complete Stern-Gerlach interferometer: Toward a test of quantum gravity

“…An important point here is that, already at 10 9 atoms, the gravitational interaction becomes stronger than the spin-spin interaction at a distance of 100 μm. We note that ( 61 ) also talks of 10 −16 kg, which is less than 10 10 atoms. Let us emphasize that although high accelerations may be obtained with multiple spins, in the following, we discuss only the case of a macroscopic object with a single spin, as the observable of such a quantum-gravity experiment is entanglement between two spins, and averaging over many spins may wash out the signal.…”

“…We will also not deal with the issue of the Casimir-Polder or diamagnetic interactions that may arise. These issues have been dealt with extensively in previous works ( 18 , 61 ). While we believe that all discussed applications noted here, including the two parallel interferometers for the quantum-gravity experiment, may be done in the longitudinal configuration presented in the experimental part of this paper, transverse [i.e., two-dimensional (2D)] interferometers may also be realized with the same techniques discussed here.…”

Can We Detect the Quantum Nature of Weak Gravitational Fields?

“…The MV argument can be generalized and used to devise another method for detecting the quantum mechanical nature of gravity: let A and B be quantum mechanical matter systems while C describes the gravitational field; if AB only interacts via gravity and one can detect the appearance of entanglement, this would imply that the gravitational field must be quantized. This idea has been independently used by a number of authors, and proposals for experimental tests of quantum gravity have been put forward using spins [66] and massive systems [27,67,68]. See also [69] for related ideas applied to quantum optomechanic experiments.…”