What is quantum tunneling?

[fahmidsadeque]

Quantum-Tunneling is statistically possible passing of energetic walls, which would classically not be possible.
In QM Particles, whether Elementary or Compound, are described by a QM-wave-function ϕ(xμ) in complex Hilbert-space. The absolute squared wave-function ϕ⋅(xμ)ϕ(xμ) represents the possibility of detecting the particle at position xμ.
For example the Schrödinger-equations describes the wave-function. When a wave-function passes a region which it could classically never pass, the QM-wave-function always allows the possibility to pass this region with possibility > zero.
This is so-called quantum-tunneling
(collected)