Quantum Tunneling

By: Mohammad Ali, Yvonne Pham

SRJC

PHYS43, Spring 2014

Origination

• The earliest idea of quantum tunneling was proposed by Louis de Broglie. He proposed that waves of mater have a wavelength inversely proportional to their velocity. This was proposed in 1923. Fast forward 4 years and Friedrich Hund was the first to make use of quantum mechanical barrier penetration when discussing the theory of molecular spectra in 1927.

Introduction-What is it?

• Quantum tunneling falls under the domain of quantum mechanics: the study of what happens at the quantum scale. This process cannot be directly perceived, but much of its understanding is shaped by the macroscopic world, which classical mechanics cannot explain.

• Quantum tunneling occurs when particles move through a barrier that should be impossible to move through according to classical physics.

• The barrier can be an insulator, a vacuum, or it can be a region of high potential energy.

What Is It?

• To understand this, particles attempting to travel between potential barriers can be compared to a ball trying to roll over a hill. Classical mechanics predicts that particles that do not have enough energy to classically surmount a barrier will not be able to reach the other side. Thus, a ball without sufficient energy to surmount the hill would roll back down. In quantum mechanics, these particles can, with a very small probability, tunnel to the other side, thus crossing the barrier. Here, the ball could, in a sense, borrow energy from its surroundings to tunnel through the wall or roll over the hill, paying it back by making the reflected electrons more energetic than they otherwise would have been.

• The reason for this difference comes from the treatment of matter in quantum mechanics as having properties of waves and particles.

Process

• Consider a particle with energy E in the inner region of a one-dimensional potential well, V. If analyzed with classical mechanics, if E is less than V, the particle will remain in the well forever. If E is greater than V, then the particle can get out of the well. But this is not the case. Using quantum mechanics, the particle can escape even if its energy is less than V, but the PROBABILITY is less depending on the difference of E and V. There is a possibility that the particle will tunnel through the potential barrier and have the same energy as before.

Process

This process relies on Heisenberg’s Uncertainty principle. Because this process of tunneling relies on probability, several variables that affect the probability are:

– The mass of the object

– The thickness of the barrier

– The ability to penetrate the barrier.

BUT just because quantum tunneling relies on probability, it does not in no way assume that this process is only theoretical.

Importance

• Tunneling plays an essential role in several physical, chemical, and biological phenomena, such as radioactive decay or the manifestation of large kinetic isotope effects in chemicals of enzymatic reactions.

• In a case, scientists measured electrons escaping from atoms without having the necessary energy to do so. The outcome is that tunneling occurs in less than a few hundred attoseconds. (10^-18 sec). This phenomenon initiates many fast processes, which are very basic in nature. Quantum tunneling is important because it is a fundamental process of nature which is responsible for many things on which life itself is dependent.

• It has even been hypothesized that the very beginning of the universe was caused by a tunneling event, allowing the universe to pass from a "state of no geometry" (no space or time) to a state in which space, time, matter, and life could exist.

Application

• Radioactive Decay- particle tunneling out of a nucleus causing radioactive decay.

• Cold Emission-Occurs in semi- and superconductors. The electron jumps from surface of a metal to follow a voltage. If the electric field is large enough and thin, it allows the electron to tunnel through. Important for flash devices.

• Touch Screens/Artificial skin- because it provides a smaller insulating gap

Future of Quantum Tunneling

• In the present day, the world is moving to a world of nanotechnology. In this technology, we will definitely need a thorough understanding at what occurs at the atomic scale. This includes quantum tunneling. As has been already said, transistors, scanning tunneling microscope. This technology already exists!!! Soon enough it will be in every part of our everyday.

Simple Summary

Video: https://www.youtube.com/watch?v=cTodS8hkSDg

Work Cited

• http://postezy.com/voh/classes%5CWinter12%5C115BID31%5CPhysicsToday_2002.pdf

• http://www.cas.miamioh.edu/~jaegerh/phy293/questions/history.pdf • http://www.livescience.com/20380-particles-quantum-tunneling-

timing.html • http://abyss.uoregon.edu/~js/glossary/quantum_tunneling.html • http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/barr.html • https://www.youtube.com/watch?v=cTodS8hkSDg • http://en.wikipedia.org/wiki/Quantum_tunnelling • http://prezi.com/efx2wmk8ovh7/quantum-tunneling-and-its-applications/ • http://prezi.com/efx2wmk8ovh7/quantum-tunneling-and-its-applications/ • http://profmattstrassler.com/articles-and-posts/particle-physics-

basics/tunneling-a-quantum-process/

The A Team