They haven't really. Quantum tunneling is a well known phenomenon, which makes it
appear that you have moved something faster than the speed of light. You have to be careful about what you mean by something's velocity.
For instance, If I shine a laser-pointer on the moon, it will make a spot (okay, pretend it's a good enough laser that it retains coherence and isn't absorbed by the atmosphere. And we've a good telescope to watch). A flick of my wrist can send that dot to the other side of the moon, and it won't take much to make that
spot travel faster than the speed of light.
Does this violate special relativity? No, although it can be tempting to think so. But that 'dot' on the moon is not a real thing; it carries no energy nor information. So it's quite alright for it to move faster than
c.
These tunelling experiments are much the same thing. If you're interested, check out
this site.
Even if you don't buy that argument, I
know this can't have violated causality, because the theory they have verified with these experiments (QED) is built around special relatvity and quantum mechanics combined. And theories that make predictions that contradict their assumptions are not popular in physics.