What are some of the experiments taking place for studying gravity at the quantum mechanical level?

I don't know of any experiments that have shown gravity to be quantized.  The energy levels you would need exceed what we can (and maybe ever will be able to) generate.

Were you thinking maybe of experiments that send particles across two paths at different gravitational potential?  The one whose path goes at higher potential should oscillate at a slightly different rate, so it will have a phase shift, which you can measure by recombining the beams and letting them interfere.

While that experiment is neat, I don't see how it tells you anything about the quantization of the gravitational field.

See if you can dig up a link to what you're thinking of.

The experiments at the large hadron collider in Geneva are focused on discovering the Higgs Boson, a theoretical particle that would explain connections between mass, inertia and gravity. However, many suspect that gravity is not quantized and there are no particle interactions of this force, that gravity is a result of spacetime perterbation, as in Einstiens relativity.

The quest for a theory of quantum gravity is well under way. Google "quantum gravity" to get some useful links about the theory and experimental methods for testing the theory. This is cutting-edge research.