Physics

Quantum Tunnelling

Fire a wave packet at a wall taller than its energy. Classically it bounces straight back; as a wave, part of it leaks through the wall and out the far side.

|ψ|², where the particle might bebarrier V₀energy E

Transmitted—

—

Particle energy E 0.122

Barrier height V₀ 0.18

Barrier width 6

Energy E—

Barrier V₀—

Transmitted—

Reflected—

What to observe

With the red wall above the amber energy line (V₀ > E) nothing should get through, yet a slice of the packet tunnels out the far side.
Widen the wall from 4 to 12 and the transmitted share drops about a hundredfold: inside the wall the wave decays exponentially.
Drop the wall below E and most of the packet sails over, but some stillreflects, which no classical particle would do.

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