Quantum tunneling is a phenomenon in quantum physics where a particle passes through a barrier that it shouldn’t be able to cross according to classical physics.
Classical View vs Quantum View:
Classical Physics:
Imagine a ball rolling toward a hill.
If the ball doesn't have enough energy, it can't roll over the hill.
It stops and rolls back down.
Quantum Physics:
If the "ball" is a quantum particle, it behaves like a wave.
Even if it doesn't have enough energy to climb the hill (barrier), there’s still a chance it will appear on the other side — as if it had tunneled through it.
Why Does This Happen?
Quantum particles are described by wavefunctions, which spread out in space.
When a particle hits a barrier, its wavefunction doesn't stop — it decays inside the barrier but doesn’t go to zero.
On the other side, there’s still a small probability of finding the particle.
If that probability isn’t zero, the particle can "tunnel through" the barrier.
Real-World Examples of Quantum Tunneling:
Nuclear Fusion in the Sun:
Protons repel each other due to electric charge.
In classical physics, they shouldn't get close enough to fuse.
But quantum tunneling lets them get close enough to fuse and power the Sun.
Tunnel Diodes & Flash Memory:
Used in electronics where electrons tunnel through thin insulating layers.
This enables very fast switching and data storage.
Scanning Tunneling Microscope (STM):
Measures tiny currents from electrons tunneling between a sharp tip and a surface.
Lets scientists “see” individual atoms.
Key Takeaway:
Quantum tunneling means particles can break the rules of classical physics — they can pass through barriers that should be impossible to cross.
It’s like a ghost walking through a wall — not because it's magic, but because physics allows a tiny chance it can happen.
