From [1] I'm reading up on a recent expeirment that used a neutron/gravity spectrometer to look for evidence of dark matter and dark energy. I haven't got to review enough material to say something truly pithy here yet, but I thought I'd point you towards the stuff that's available. First, here's a discussion of the experiment [1] from Texas A&M's own Dr. Schleich. He's talked about this kind of thing before, (using neutrons for experiments involving gravity). In fact, a little more than a year ago he gave a talk here on the KC interferometer and how it measured the acceleration due to gravity as opposed to the gravitational redshift as claimed by the authors[2]. His summary of the current set of experiments comes with the added bonus of a pointer to the open access version of the Physics Review Letters article on the experiment [3]. If you'd like to know how exactly you reflect a neutron from a wall without using coulombic forces which ...