Quantum experiments with nanomechanical oscillators are regarded as a test bed for hypothetical modifications of the Schrödinger equation, which predict a breakdown of the superposition principle and induce classical behavior at the macroscale. It is generally believed that the sensitivity to these unconventional effects grows with the mass of the mechanical quantum system. Here we show that the opposite is the case for optomechanical systems in the presence of generic noise sources, such as thermal and measurement noise. We determine conditions for distinguishing these decoherence processes from possible collapse-induced decoherence in continuous optomechanical force measurements.
As noted by Diósi , a factor of 1/2 is missing in the approximate double-commutator equation above Eq. (1) (and in the Supplements below Eq. (S3)); it should read as LCSLρ=-DCSL[x,[x,ρ]]/(2ℏ2). The further contents are not affected by this.
 L. Diósi, Phys. Rev. Lett. 114, 050403 (2015)