What is Quantum tunnelling: Definition and 31 Discussions

Quantum tunnelling or tunneling (US) is the quantum mechanical phenomenon where a wavefunction can propagate through a potential barrier.
The transmission through the barrier can be finite and depends exponentially on the barrier height and barrier width. The wavefunction may disappear on one side and reappear on the other side. The wavefunction and its first derivative are continuous. In steady-state, the probability flux in the forward direction is spatially uniform. No particle or wave is lost. Tunneling occurs with barriers of thickness around 1–3 nm and smaller.Some authors also identify the mere penetration of the wavefunction into the barrier, without transmission on the other side as a tunneling effect. Quantum tunneling is not predicted by the laws of classical mechanics where surmounting a potential barrier requires potential energy.
Quantum tunneling plays an essential role in physical phenomena, such as nuclear fusion. It has applications in the tunnel diode, quantum computing, and in the scanning tunneling microscope.
The effect was predicted in the early 20th century. Its acceptance as a general physical phenomenon came mid-century.Quantum tunneling is projected to create physical limits to the size of the transistors used in microelectronics, due to electrons being able to tunnel past transistors that are too small.Tunneling may be explained in terms of the Heisenberg uncertainty principle in that a quantum object can be known as a wave or as a particle in general. In other words, the uncertainty in the exact location of light particles allows these particles to break rules of classical mechanics and move in space without passing over the potential energy barrier.
Quantum tunnelling may be one of the mechanisms of proton decay.

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  1. D

    I Decoherence and Quantum tunnelling

    A macroscopic object has the order of Avogadro’s number of particles. That’s over 10^23. So the probability of all of them tunneling, at the same time, is on the order of that original small probability, to the 10^23 power. And then on top of that, you have to factor in the chances of it...
  2. T

    I On what plane of existence do quantum computations occur?

    I was recommended by another mentor to purchase a good book on MWI, which I think should be a thread or poll of its own. Anyway, I might have debased myself too much in that other topic, as I understand on an abstract level how QM works. In my own words, I feel as though possible worlds are...
  3. YoungPhysicist

    B White dwarf quantum tunnelling

    I just finished watching the video "The Last Light Before Eternal Darkness – White Dwarfs & Black Dwarfs" At 5:17 he mentioned quantum tunneling will take up a timespan so long that calling it forever is ok. But nothing takes forever,so,how long will it actually take? ps:I later realized...
  4. S

    A Wavefunction matching two different H, not just V

    Can the basic techniques of wavefunction matching that one would use to calculate the transmission through a step barrier potential and the Dirac hamiltonian of graphene be used for a situation where instead the fermi velocity changes in a step like fashion. i.e. instead of a Hamiltonian like...
  5. J

    Pilot wave theory and quantum tunneling

    Just a question about pilot wave theory as an alternative to SQM. Researchers in ANU have recently shown that quantum tunnelling of a particle through a barrier is instantaneous. Does this finding verify the Copenhagen superposition interpretation of QM and at the same time invalidate the...
  6. W

    Need help modelling Quantum Tunnelling Composites

    Hi all, This is my first post on PF so forgive any rookie errors. I'm a 17 year old British student. I have just finished a month long placement at Newcastle University researching my chosen topic of quantum tunnelling. The placement itself was very disappointing and I had no interaction with...
  7. Jilang

    Quantum tunnelling - what is real?

    Is it correct that that the wavefunction of a particle is well defined in the classically forbidden region? This would seem to suggest that there would be a chance of finding it there. But I think that is not allowed. Have any experiments actually discovered particles in the barrier or do they...
  8. M

    Quantum Tunnelling: Where Does Energy Go?

    Homework Statement The waves amplitude appears to decrease as it tunnels through the barrier. If we think of the amplitude as energy like in a sound wave etc, where does this energy go? The Attempt at a Solution I think it has something to do with the fact that for a matter wave the...
  9. I

    Probability for Quantum tunnelling

    Homework Statement A particle with the energy E < V_{0} (V_{0} > 0) moves in the potential V(x) = 0, x<0 ; V(x)= V_{0}, 0<x<d and V(x)= 0, x>d. Measure the probability that the particle will tunnel through the barrier by calculating the absolute value of the ratio squared...
  10. A

    Quantum tunnelling and black holes

    Just a quick question, that I'm not completely clear about; Quantum tunnelling allows particles to overcome barriers that they classically shouldn't be able to overcome, my question is simply, do/can particles escape a black hole after passing the event horizon due to tunnelling? If not, why...
  11. R

    How Does Quantum Tunneling Affect Particle Reflection?

    Homework Statement A beam of particles of energy E is incident from the left on a rectangular step of infinite width and height U0, situated at the origin, with E > U0, as shown in the diagram. http://img39.imageshack.us/img39/5918/problemda.jpg (a) Write down the Schrodinger equation for...
  12. K

    Radioactivity - quantum tunnelling

    Can anyone link to a synthetic and understandable explanation of radioactivity through basic quantum mechanics? It does not need to be a comprehensive explanation at all, examples or partial explanations are fine. Online class notes are welcome but so are books suggestions. Thanks in advance
  13. H

    Transmission coefficient, quantum tunnelling

    I have been trying to calculate the transmission coefficient for a quantum tunelling case, but I seem to get the coefficient value more than 1. How is that possible? The equation i used is based on the wikipedia page (I am unable to link because I am underpost). Also typically what are...
  14. BWV

    Quantum tunnelling outside the light cone?

    Zee's QFT in a Nutshell makes a short comment in the first chapter about the possibility of particles tunnelling outside their light cone - is there some probability that a particle could do this? I know the neutrino thing has been debunked as a faulty cable, but did not see this offered as an...
  15. BWV

    Quantum tunnelling w/ macroscopic objects

    does not occur because the probabilities are of the magnitude of exp[ -1 / h ], give or take a few decimal places, correct? i.e. 1 / some number with > 10^30 zeros after it (trying to explain this simply to my daughter)
  16. S

    Quantum Tunnelling - Transmission Probability

    Homework Statement It's not really a given problem, it's more of a section of my lecturing I truly just don't understand. I'm given that the probability of transmission (T) is the ratio of the intensities of the transmitted wave and the incident wave. However, a bunch of math gives also that...
  17. T

    Is this a reasonable analogy for quantum tunnelling?

    Hi, I wanted to explain quantum tunnelling to people with no scientific background - I've come up with the following analogy, but I'm only a physics undergrad and I'm not sure if it's a good enough analogy. I can do the maths behind tunnelling but it's just the concept I'm trying to get across...
  18. F

    Tunneling probability and higher order terms in WKB method

    Hi All, I have a question regarding the WKB method for computing tunnelling through barriers. I understand the method and the ability to arrive at a solution as given in the first part (summary) of the first page here: http://www.physics.udel.edu/~msafrono/425/Lecture%2018.pdf Is it...
  19. ShayanJ

    Some problems about Quantum tunnelling

    In quantum tunnelling,as I understood,when a particle reaches the boundry of a potential barrier,it is possible,that the particle passes the barrier and it is performed like disappearing before the barrier and appearing after it.If the latter is the case,so there should be a motin which is...
  20. C

    Quantum Tunnelling Technologies

    Hey guys what are some technologies that use Quantum Tunneling? I've been looking on Google and i havnt had much luck! I just need a point in the right direction so links to websites and such would be greatly appreciated! BTW when searching google i found Quantum Tunnelling Composites which...
  21. ShayanJ

    A question about quantum tunnelling

    I understand quantum tunnelling while thought as the one happening in fusion.But could someone explain the process when we're talking about a particle passing through a physical barrier not just a potential barrier? thanks
  22. A

    Can Quantum Tunnelling Explain the Physicist's Ice Cream Parlor Strategy?

    On the sitcom 'The Big Bang Theory', one of the jokes goes: "A physicist walks into an ice cream parlor and orders an ice cream for himself and one for the empty seat next to him. He does this for weeks until the owner asks him what he's doing. The physicist says, "well, I'm a physicist, and...
  23. N

    What does Wikkepedia mean when they talk about Quantum tunnelling

    This is what it says on Wikipedia : Quantum tunneling refers to the quantum mechanical phenomenon where a particle tunnels through a barrier that it classically could not surmount because its total mechanical energy is lower than the potential energy of the barrier. But I would like to...
  24. C

    Transmission coefficient (quantum tunnelling)

    Homework Statement What is transmission probability (T), when the incident particle energy (E) is equal to the energy of the barrier (U)? Homework Equations Equations to transmission and reflection probabilities. http://i950.photobucket.com/albums/ad348/gs5720/img099.png?t=1278212132...
  25. B

    Quantum tunnelling for a finite-square potential parrier

    Homework Statement At x=0, a proton with a kinetic energy of 10 eV is traveling in the x direction (potential energy = 0). At x = 1nm, it encounters a potential barrier of height 12 eV and width .2nm. The potential returns to 0 at x = 1.2nm. Give the amount of the particle on both sides...
  26. P

    Fermi Question - quantum tunnelling of a person

    Homework Statement The probability of a person quantum mechanically tunnelling through a wall Homework Equations The Attempt at a Solution I'm not too sure how to approach this problem, I calculated the de Broglie wavelength of the person (mass = 60kg, velocity = 30 m/s; These values are...
  27. E

    Probability of quantum tunnelling

    I'm continuing to read Jim Al-Khalili's book Quantum: A Guide for the Perplexed. I'm on page 190; today I just read a few paragraphs and page 176 about quantum tunnelling. My question is this: what does it take to say that an electron, for example, has successfully and definitely tunnelled...
  28. Ε

    Quantum Tunnelling and Spacetime

    Does relativistic quantum mechanics make use of 4 dimensional Minkowskian geometry? Or does it just use special relativity formulated in 3 space dimensions and 1 time dimension? And if quantum mechanics can apply to Minkowskian spacetime, then can something tunnel through time?
  29. T

    A Poll about Quantum Tunnelling

    In the quantum tunnelling process, where an electron tunnels though the potential barrier, we known this to be true by always seeing the electron we test for. We have always found what we were looking for and therefore have NEVER considered or thought about any other vallid or acceptable...
  30. Reshma

    Quantum Tunneling Explained: How Does it Work?

    Could some please explain me how quantum tunneling works?