Quantum tunnelling

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Quantum tunneling is a phenomenon observed at a quantum scale where a particle with high momentum, when facing a barrier, tunnels through it. This counter-intuitive process can be understood with the knowledge of wave-particle duality of the fundamental particles and explaining it with the uncertainty principle.

For example, consider a particle and a barrier against which it is shot at. There is a high probability that the particle would bounce off the barrier from a classical perspective. At a quantum scale, when the wave function of the particle is observed such that the probability of finding it is high near the barrier, there could still be some probability of finding the particle inside the barrier. In other words, the amplitude of the wave does not go zero immediately. The amplitude decreases exponentially as the width of the barrier increases but never reaches zero. This is a manifestation of the uncertainty principle where the amplitude of the wave function cannot reach zero. And hence, the probability of finding the particle through the barrier and out of it is always possible.

When the barrier width and height is reduced, some of the particles would have a higher probability to tunnel through it in the sense. This is a key phenomenon that is found in the nuclear fusion in stars like the Sun, where some hydrogen atoms fuse through quantum tunneling. Another notable application of quantum tunneling can be observed in the scanning tunneling microscopes, where atoms are observed by tunneling electrons from the atom through a vacuum barrier into a conductive tip hovering above the atoms.

Frequently Asked Questions[edit]

Does quantum tunneling violate the law of conservation of energy?[edit]

No, it does not. The particle that tunnels through the barrier does not gain energy in the classical sense. In the quantum scale, the amplitude of the wave function only decreases exponentially. It never can reach zero due to the uncertainty principle and there is always a little probability of finding the particle through the barrier or out of it. This is one of those moments in the quantum realm where classical physics don’t make much sense.