  Theories of spontaneous wavefunction collapse offer an explanation of the
possible breakdown of quantum mechanics for macroscopic systems. However, the
challenge of resolving predicted collapse signatures above background noise has
precluded conclusive tests. Here, we propose to overcome this challenge using a
superconducting qubit to precisely readout the collapse-induced heating of a
mechanical resonator. We show that the ability to strongly couple the qubit to
the resonator can enable both fast measurements and initialization of the qubit
close to its ground state. Combined this greatly suppresses the influence of
quasiparticle heating of the qubit, which we predict to be the dominant noise
source. We find that bulk acoustic wave resonances can amplify the collapse
induced heating due to their ultra-low dissipation. Together, this could enable
a conclusive test of collapse models.
