  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 from 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 enabling generation and readout of mechanical quantum states. In the
original proposal, the mechanical resonator was a carbon nanotube, containing
$10^6$ nucleons. Here, in order to probe quantum mechanics at a more
macroscopic scale, 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 to create non-Gaussian mechanical states out of
equilibrium with their environment and then 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 device provides a new route to feasibly test decoherence mechanisms
beyond standard quantum theory.
