In Nature Phys. 11, 668 (2015) (Ref. [1]), a composite particle prepared in a
pure initial quantum state and propagated in a uniform gravitational field is
shown to undergo a decoherence process at a rate determined by the
gravitational acceleration. By assuming Einstein's Equivalence Principle to be
valid, we demonstrate, first in a Lorentz frame with accelerating detectors,
and then directly in the Lab frame with uniform gravity, that the dephasing
between the different internal states arise not from gravity but rather from
differences in their rest mass, and the mass dependence of the de Broglie
wave's dispersion relation. We provide an alternative view to the situation
considered by Ref. [1], where we propose that gravity plays a kinematic role in
the loss of fringe visibility by giving the detector a transverse velocity
relative to the particle beam; visibility can be easily recovered by giving the
screen an appropriate uniform velocity. We finally propose that dephasing due
to gravity may in fact take place for certain modifications to the
gravitational potential where the Equivalence Principle is violated.Comment: 5 pages, 3 figure
