It is basically a phenomenon in which particles move through a barrier that is otherwise forbidden according to classical physics laws. This barrier can be a physically obstructed medium, such as an insulator or a vacuum, or a region of high potential energy.
The mechanism of quantum tunneling
Let us suppose a situation where we have to ride our bicycles across a hilltop. Classically speaking, the bicycle will only climb the hilltop if it has enough energy to climb up to it. However, quantum mechanically, the cycle will move to the other side of the hilltop even if its energy is less than the required energy. (It’s just an analogy to understand the concept, a bicycle is definitely not a quantum object).
According to the laws of quantum mechanics, a particle can behave both as a particle and wave. So, when it comes to the phenomenon of quantum tunneling, the wave nature of the particle comes into the picture. Now suppose, an electron has to cross a potential barrier that is much higher than the energy carried by its wave.
In regions where the potential energy is higher than the wave’s energy, the amplitude of the wave decays exponentially. If the region is narrow enough, the wave can have a non-zero amplitude on the other side. Hence, we have a non zero probability of finding the particle on the other side of the barrier, which was classically impossible.
How does quantum tunneling sustain our Sun?
We all know that the Sun produces heat and light energy by fusing hydrogen nuclei. The hydrogen nuclei slam together to produce helium atoms. However, most hydrogen atoms in the Sun’s core don’t have enough energy to stick together. To fuse, they have to overcome the forces of repulsion of their positive charges, i.e., the Coulomb barrier. But generally, they don’t have enough energy to do so.
Then, how is our sun still fusing hydrogen nuclei and producing energy? This is where quantum tunneling comes to the rescue! With quantum tunneling, the hydrogen nuclei can cheat. They have enough energy to get relatively close to each other, and then they tunnel through the remaining barrier to stick together.
Hence, thanks to the tunneling phenomenon, the Sun’s nuclei can fuse even though they don’t have enough energy to fuse on their own. Remember, not all nuclei will tunnel; only some will. But, even this small probability is enough to keep our Sun alive. Quantum tunneling is thus an important component in supporting fusion reactions in stars, and ultimately, our life.
Some other applications :
Apart from being highly useful in the nuclear fusion of stars, quantum tunneling also plays an important role in radioactive decay. It is among the central non-trivial quantum effects in quantum biology. Proton tunneling is a key factor in the spontaneous mutation of DNA. Moreover, this phenomenon is of great importance in the working of semiconductor devices, tunnel diodes, and even in the working of superconducting junctions. Cutting short, quantum tunneling indirectly plays an important role in sustaining our everyday needs and hence, is a booming sector of research, development, and advancement these days.