"The phenomenon of tunneling, which has no counterpart in classical physics, is an important consequence of quantum mechanics."
http://abyss.uoregon.edu/~js/glossary/quantum_tunneling.html
"Quantum tunnelling is a phenomenon which becomes relevant at the nanoscale and below. It is a paradox from the classical point of view as it enables elementary particles and atoms to permeate an energetic barrier without the need for sufficient energy to overcome it."
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3768233/
"It is a part of quantum mechanics, a branch of physics. Electrons have wave-like properties and they can pass through impenetrable barriers. This is the phenomenon called quantum tunneling.
Quantum mechanics says that electrons can behave like waves and also like particles. They can pass an energy barrier if it is thin enough, so to make it more simple, particles can pass through walls, doors if they are thin enough."
https://yourtimetravelexperience.com/quantum-tunneling-explained
"Quantum tunneling is a phenomena in which a quantum particle tunnels through a barrier which cannot be classically crossed. It is a purely quantum mechanical phenomena and does not have any classical explanation."
https://unfoldanswers.com/what-is-quantum-tunneling/
"The quantum world is a pretty wild one, where the seemingly impossible happens all the time: Teensy objects separated by miles are tied to one another, and particles can even be in two places at once. But one of the most perplexing quantum superpowers is the movement of particles through seemingly impenetrable barriers."
https://www.livescience.com/quantum-tunneling-observed-and-measured.html