  Wave function collapse models are considered as the modified theories of
standard quantum mechanics at the macroscopic level. By introducing nonlinear
stochastic terms in the Schr\"odinger equation, these models make predictions,
differently from those of standard quantum mechanics, that it is fundamentally
impossible to prepare macroscopic systems in macroscopic superpositions. The
validity of these models can only be examined by experiments and hence
efficient protocols for this kind of experiments are highly needed. Here we
provide a protocol that is able to probe the postulated collapse effect by
means of the entanglement of the center-of-mass motion of two nanospheres
optically trapped in a Fabry-P\'erot cavity. We show that the collapse noise
results in large reduction of the steady-state entanglement and the
entanglement, with and without the collapse effect, shows distinguishable
scalings with certain system parameters, which can be used to unambiguously
determine the effect of these models.

Quantum Physics;Mesoscale and Nanoscale Physics