What is quantum tunneling?
Quantum tunneling is the quantum mechanical phenomenon in which basically particles on a microscopic scale are able to travel through barriers that would otherwise seem impossible. Though it is possible, the probability is very very small. On the quantum scale, particles don't act like they normally would, rather they exhibit a wavelike behavior. This is what allows electrons to tunnel through barriers. A common example of Quantum tunneling as opposed to 'normal physics'. is seen using a ball and a hill.
The image on the right shows a common example of quantum tunneling at work in comparison to classical physics we all know of.
Classical Physics:
In classical physics we know that in order for the object to roll from one side of the hill to other it would require to have higher intial kinetic energy in comparison to the gravitational potential of the hill(the height of the hill). If the gravitational potential is higher we can say that it would be impossible for the object to reach the other side of the hill. Instead of the ball reaching the other side of the hill, it would roll back down in the opposite direction.
Quantum Mechanics:
In quantum mechanics things work a bit differently. Quantum mechanics tells us that in fact there is a probability that the object is able to appear on the otherside of the hill even if the kinetic energy of the object is less than the gravitational potential energy(the height of the hill). Instead of going up and over the hill like an object normally would, the object has a non-zero probability of possibly tunneling through the hill and reaching the other side, or even sometimes becoming stuck inside the middle of the hill.
Sounds like science fiction?
Classical Physics:
In classical physics we know that in order for the object to roll from one side of the hill to other it would require to have higher intial kinetic energy in comparison to the gravitational potential of the hill(the height of the hill). If the gravitational potential is higher we can say that it would be impossible for the object to reach the other side of the hill. Instead of the ball reaching the other side of the hill, it would roll back down in the opposite direction.
Quantum Mechanics:
In quantum mechanics things work a bit differently. Quantum mechanics tells us that in fact there is a probability that the object is able to appear on the otherside of the hill even if the kinetic energy of the object is less than the gravitational potential energy(the height of the hill). Instead of going up and over the hill like an object normally would, the object has a non-zero probability of possibly tunneling through the hill and reaching the other side, or even sometimes becoming stuck inside the middle of the hill.
Sounds like science fiction?
In the image below we can see the particle or in this case the electron is able to move over to the other side of the barrier but not by going over it, but by tunneling through the potential barrier. Even though according to classical mechanics the particle should hit the barrier and rebound off it moving in the opposite direction, the particle/electron has a zero-non probability of tunneling through.