Particles can ghost through solid barriers with 100% efficiency if they are moving slowly enough.
In the normal world, hitting a wall harder usually gives you a better chance of breaking through. This anomalous tunneling effect proves that for certain quantum particles, the opposite is true. As their energy approaches zero, they pass through barriers as if the walls weren't even there. This behavior is a universal law dictated by the specific symmetries of the system. It means that slow-moving waves can navigate through cluttered environments without losing any strength.
Anomalous tunneling as a low-energy theorem for Nambu-Goldstone modes
arXiv · 2604.27489
Anomalous tunneling refers to the phenomenon in which the transmission coefficient through a potential barrier approaches unity as the energy of an incident particle or quasiparticle tends to zero. This counterintuitive effect has been reported in systems exhibiting spontaneous symmetry breaking (SSB), such as superfluids, yet the general conditions for its occurrence remain unclear. In this Letter, we establish that anomalous tunneling of Nambu-Goldstone (NG) modes is a universal low-energy the