Quantum tunneling | Easy explanation | Science

in StemSociallast month (edited)


Any object cannot overcome all obstacles in its path. For example, if you throw a ball facing the wall of your room, the ball will hit the hard wall and bounce back to you. We observe such incidents every day. But if your thrown ball goes through a solid wall without any holes, then you will surely think it is magic or a miracle. This kind of phenomenon happens all the time in case of small particles. Scientists call it quantum tunneling. Similarly, quantum tunneling is a phenomenon in quantum mechanics where a subatomic particle can cross a potential barrier that is not possible according to our mechanics or not supported by mechanics .

Quantum tunneling is important in several ways even though mechanics does not support it. Quantum tunneling continues to occur in our Sun's nuclear fusion. Nuclear fusion would not have been possible in our Sun without quantum tunneling. The temperature of the Sun's core is not high enough to allow atomic nuclei to overcome the Coulomb barrier and achieve thermonuclear fusion. But nuclear fusion still happens because of this quantum tunneling. Quantum tunneling increases the probability of breaking through the Coulomb barrier.

Technically, quantum tunneling is also being successfully applied in applications such as tunnel diodes, quantum computing, and scanning tunneling microscopes. So we cannot call quantum tunneling a lunatic's delusion


A tunnel diode is a type of semiconductor diode that is heavily doped p-n junction diode. In this type of doide the electric current decreases as the voltage increases. A tunnel diode conducts a small amount of current through current tunneling. History shows that diodes contributed to the confirmation of quantum tunneling.

We know that electrons behave like waves as they travel. Now imagine a wall (barrier) in the path of this wave of electrons. Normally, the electrons are blocked by the wall (barrier) and travel completely in the opposite direction. But it won't happen at once. Some electrons will pass through the wall to the other side. The opposite side of the wall (barrier) will have the potential to gain electrons. Electrons can even be found in the middle of the wall.


Now the amount of electrons that can be found on the sides and inside of the wall depends on the thickness and height of the wall. The greater the thickness of the wall, the greater the barrier to electron flow. If the height of the wall is high, the electron will not topple it. You can see this kind of quantum tunneling in the image above.

The reason we see our reflection in a mirror is because photons of light particles hit the mirror and are reflected back into our eyes. But not all photons reach our eyes. Some of these photons pass through the mirror and vanish after some time. That is, the photon moves to the other side through quantum tunneling and is not visible to us due to its reduced number. But you can prove it if you have the right tools.

A team of physicists has devised a simple way to measure the quantum tunneling duration . They found out how long the tunneling takes from start to finish, i.e. the time it takes for a particle to enter the barrier and exit through quantum tunneling in the other direction.Ephraim Steinberg, co-director of the Quantum Information Science Program at the Canadian Institute for Advanced Research said

"Quantum tunneling is one of the most fascinating aspects of quantum phenomena, and it's fantastic that we're now able to study it this way," source

The laws of quantum mechanics allow for quantum tunneling, but researchers don't know the details of exactly what happens when a subatomic particle undergoes the tunneling process. Therefore, more research and experiments are needed to explain quantum tunneling in detail.All these physicists were basically trying to do that

One of the difficulties in previous versions of the tunneling time experiment was identifying the moment tunneling starts and stops. To simplify this, the researchers used magnets to create a new type of clock that would tick off a signal as the particle tunnelled.


Subatomic particles spin like a spinning top when the magnets are placed in an external magnetic field. The amount of spin depends on how long the particle remains in the magnetic field. So the Toronto group of scientists used a magnetic field to create their barrier. When the particles are inside the barrier, they move and otherwise the particles do not. Thus, by measuring how long the particles traveled, the researchers determined how long it actually took these atoms to tunnel through the barrier. The researchers are delighted with the test, saying it is a breathtaking technological achievement.

The researchers prepared 8,000 rubidium atoms and cooled them to one billionth above absolute zero. The atoms were given this temperature because otherwise the atoms would be moving randomly at high speeds instead of being in a small jitter. The researchers used a laser to create a magnetic barrier and focused the laser so that the barrier was 1.3 micrometers thick, or about 2,500 rubidium atoms thick. The researchers used another laser that moved rubidium atoms at a speed of about 0.15 inches per second.

According to quantum theory, most of the rubidium atoms found the barrier and about 3% of the atoms broke through the barrier and appeared on the other side. This is due to quantum tunneling. Based on the progress of these atoms, it took them about 0.6 milliseconds to cross the laser barrier, which the observer counted as the result of the experiment.This experiment was able to prove that quantum tunneling is true.

The idea of ​​quantum tunneling came from researching radioactivity. Henri Becquerel was a French engineer, physicist who discovered radioactivity in 1896. Later, Marie Curie and Pierre Curie did more research on radioactivity, which earned them the Nobel Prize in Physics in 1903. However, scientists became more interested in this topic and research began on a large scale. Friedrich Hund first observed quantum tunneling in 1927 when calculating the ground state of a two-well universe. In the same year, Leonid Mandelstam and Mikhail Leontovich discovered quantum tunneling. They were analyzing the implications of the then newly discovered Schrödinger's wave equation for the motion of a particle in a confined space.

Max Born learned about the concept of tunneling after attending a lecture by Gamow. Max Born, a German physicist and mathematician, thinks that this is not limited to nuclear physics, but is a general result of quantum mechanics that can be applied in many ways. Transistor was invented in 1947 and diode was invented much earlier. Electron tunneling was recognized in 1957 through research on transistors and diodes. Leo Esaki, Ivar Yavar and Brian Josephson were awarded the Nobel Prize in Physics in 1973 for predicting superconducting Cooper pair tunneling. In 2016, scientists also learned about quantum tunneling of water. After all this, the concept of quantum tunneling is as clear as water to scientists now, but scientists are trying to learn more about it

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