  It has been proposed that quantum features of the gravitational field can be
exposed experimentally by employing gravity as a mediator of entanglement. We
show that in order to witness this type of entanglement experimentally, strong
limits on acceleration noise, which has been neglected in previous work, must
be overcome. In the case of two particles of similar mass, Casimir-Polder
forces lead to a fundamental limit of tenths of femtometers per second squared
per root Hertz. Limits are between three and six orders of magnitude less
strict for two particles of unequal mass, depending on collisional decoherence.
