Is there any evidence that subatomic particles are affected by gravity?

If so what experiment has been done to show this?

Answer

Yes. For the phrasing of this question, the neutron qualifies.

Neutrons have been slowed and collected, which are diverted from nuclear reactors via beamports. The methods for doing this are quite complicated, but in the final state, they are confined within a box where the "walls" present a nuclear barrier to the neutrons. The neutrons have a wavelength longer than the spacing between atoms in the wall, thus, they bounce off. An interesting fact about the design is that the containment area doesn't need a "top" because the neutrons are at such a low energy that thermal movement isn't enough for them to leap out. This phenomenon, alone, is a physical demonstration of gravitational affects on subatomic particles.

So thorough is our understanding and testing of these particles in gravity, that quantized levels of height have been observed for ultra-cold neutrons.