Way back in 1963 it was calculated that atomic nuclei were superfluid, but they weren't sure about it. Atomic nuclei only have about one hundred particles : is that enough for a superfluid? Yes. Here's how it has been proved.
Let's say two nuclei get quite close but there remains a space in between. If the nuclei are superfluid then a pair of neutrons can "tunnel" back and forth across. A pair may cross from one nucleus to the other and back maybe one and a half times during the flyby. We can't detect this directly but the tunneling neutrons jiggle the protons. The jiggling protons send out gamma rays that we can detect. As you can imagine this very-almost-but-not-quite-a-collision experiment isn't that easy to do, but recently they got precise enough control of the energy of the supercollider that they could produce such flybys reliably. The energy of the resulting gamma rays match those venerable predictions, confirming the effect.
https://physics.aps.org/articles/v14/27