← Quantum Mechanics

# Applications of Quantum Tunneling

Sunday, February 27, 2022

## Alpha Decay

Protons and neutrons in an atomic nucleus can group into two protons and two neutrons. This particle, called an alpha particle can be emitted in a form of radioactive decay. However, in order to be emitted, it must overcome the repulsive Coulomb potential. Alpha particles are emitted, however, and can be observed in laboratory experiments.

## Nuclear Fusion in Stars

In a somewhat opposite process from alpha decay mentioned before, nuclear particles in stars collide and fuse to form a heaver nucleus. The particles must overcome the barrier from the other direction, and if it were not for quantum tunneling, stellar fusion would not occur and stars would not shine.

## Ammonia Inversion

In an ammonia molecule ($\text{NH}_3$), the nitrogen atom experiences Coulomb repulsion by the hydrogen atoms, preventing it from transitioning to the other side of the molecule plane. However, due to quantum tunneling, this process actually does occur and the nitrogen atom tunnels back and forth upwards of $10^{10}$ times per second.

## The Tunnel Diode

A tunnel diode is a device that uses the phenomenon of tunneling. The current that flows is a direct result of electrons tunneling over a potential barrier. The height of the barrier can be changed to affect the switching frequency of the device.

## The Josephson Junction

In superconductors, linked pairs of electrons can travel with no electrical resistance. If a thin insulating layer is sandwiched between two superconductors, the electron pairs can tunnel between the two superconductors. This is used in highly sensitive measurements of very weak magnetic fields.

## The Scanning Tunneling Microscope

Scanning tunneling microscopes can be used to image the surfaces of materials to observe individual atoms. A probe is placed about 1 nanometer from the surface of a material, then some electrons tunnel into the probe. The current of these electrons is measured and used to form an image of the surface as the probe moves around.