Can the displacemon device test objective collapse models

Testing the limits of the applicability of quantum mechanics will deepen our understanding of the universe and may shed light on the interplay between quantum mechanics and gravity. At present there is a wide range of approaches for such macroscopic tests spanning matter-wave interferometry of large molecules to precision measurements of heating rates in the motion of micro-scale cantilevers. The "displacemon" is a proposed electromechanical device consisting of a mechanical resonator flux coupled to a superconducting qubit, which could be used to generate and observe quantum interference between centre-of-mass trajectories in the motion of a resonator. In the original proposal, the mechanical resonator was a carbon nanotube, containing $10^6$ nucleons. Such a superposition would be massive by comparison to the present state-of-the-art, but still small compared with the mass scales on which we might feasibly test objective collapse models. Here, instead of a carbon nanotube, we propose using an aluminium mechanical resonator on two larger mass scales, one inspired by the Marshall-Simon-Penrose-Bouwmeester moving-mirror proposal, and one set by the Planck mass. For such a device, we examine the experimental requirements needed to perform a more macroscopic quantum test and thus feasibly detect the decoherence effects predicted by two objective collapse models: Di\'{o}si-Penrose and continuous spontaneous localization. Our protocol for testing these two theories takes advantage of the displacemon architecture by analyzing the measurement statistics of a superconducting qubit. We find that with improvements to the fabrication and vibration sensitivities of these electromechanical devices, the displacemon interferometer provides a new route to feasibly test decoherence mechanisms beyond standard quantum theory.