The gravitational field has been measured to induce a measurable phase difference in neutron interferometry. See, for example, the [COW experiment][1], originally published by Colella, Overhauser, and Werner in     [*Phys.Rev.Lett.* 34][2] (1975).


  [1]: https://skullsinthestars.com/2015/05/20/1975-the-year-that-quantum-mechanics-met-gravity/
  [2]: https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.34.1472