Quantum Tunneling
A quantum phenomenon where a particle passes through a potential energy barrier higher than the particle's kinetic energy.
Governing formula
T ≈ exp(-2 k L), k = √(2 m (V₀ - E)) / ℏ
SI unit
Dimensionless (Transmission Probability)
In depth
Due to the wave-like nature of matter, a particle's wave function does not drop abruptly to zero at a barrier face, but decays exponentially inside the barrier region. If the barrier is thin, a finite non-zero wave amplitude survives on the far side, allowing the particle to tunnel through.
Examples in the real world
Nuclear alpha decay in heavy elements, thermonuclear proton-proton fusion powering the Sun, and Scanning Tunneling Microscopy (STM).