Questions tagged [quantum-tunneling]

Quantum tunneling is a classically-forbidden quantum effect that allows a bound object with energy less than the boundary to penetrate it with a small probability. A notable example is $\alpha$-decay

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How to convert the problems of quantum mechanics that we usually solve for plane waves to gaussian wavepackets?

I want to solve a barrier potential problem for a Gaussian Wavepacket moving at a velocity v= $\frac{p_0}{m}$. Normally we consider plain wave functions of the following type $$\Psi (x) = Ae^{ikx} + ...
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Question regarding stopping a quantum tunneling simulation and integrating it

There is this wonderful blog that discusses how to simulate quantum tunneling (https://physicspython.wordpress.com/2019/10/27/quantum-tunneling-part-3/) I am new to using python to do physics, and ...
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Why don't electrons tunnel out of atoms?

The overlap of a free electron wavefunction and a bound electron wavefunction is nonzero. So why don't electrons slowly bleed out of atoms? If any wavefunction enters a free particle state it will ...
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Why is the conductance of a metal-insulator-metal tunnel junction parabolic?

For bias voltages below the tunnel junction barrier heights (and below the Fowler-Nordheim limit), tunnel junctions have a parabolic conductance as a function of bias. Is this due to the metallic ...
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Is muon-catalyzed fusion a form of pycnonuclear reaction?

Muon-catalyzed fusion is a form of fusion where the electron in a hydrogen atom is replaced by a much heavier muon, which orbits 196 times closer than an electron and allows it to approach other ...
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How unlikely is it that particles tunnel (comparatively) very long distances?

My understanding of quantum tunneling is that when you're not measuring a particle's position you can't know exactly where it is, just where it might be, and that sometimes it happens to be on the ...
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Why do helium balloons deflate?

Helium balloons deflate–even when they are made from metal foil. How does this happen exactly? Is there any chance that quantum tunneling plays a role here? The thought is that the helium atoms inside ...
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Tunneling in Infinite potential well [duplicate]

In quantum mechanical tunneling particle doesn't scale the potential but instead find a short route to cross barrier. Then why is tunneling only possible in case of finite square well potential and ...
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Scanning tunneling microscopy effect (contrast from bottom of 100 Å thick metal layer) analogous to thin-film interference and Newton's rings?

I haven't used a Green's function in 30 years and need some help understanding the use in this context. I. B. Altfeder, D. M. Chen, and K. A. Matveev 1998 Imaging Buried Interfacial Lattices with ...
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Transmission Coefficient of Finite Square Well

Now I was calculating the Transmission Coefficients of finite square well potential and found something weird The transmission coefficient is given by $$T=\left[1+\frac{V_o^2\sin^2(2ka)}{4E(E+V_o)}\...
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Why can't quantum tunnelling carry energy or information faster than light?

A few experimenters have at one time or another claimed that quantum tunnelling allows the transfer of information or energy at superluminal speeds. One was the idea that music was carried across a ...
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Does detecting particle or delayed choice affect quantum tunneling?

As much I have read quantum tunneling is propagation of wave function through barrier, and it is possible because of wave nature of particles. Now my question is will particle tunnel if it is detected ...
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Tunneling in Dissipative Environment (II)

This is another question that extends my previous question A Problem on Tunneling in Dissipative Environment. In order to figure my first question out (which I still haven't) I am reading the section ...
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Scattering from finite square well and the transmission coefficient

Suppose we have a typical finite square well where $\lim_{x \to \pm\infty} V(x)=0$ and $V(x)=-V_0$ for all $x\in[-a,a]$ where $V_0>0$. The finite square well admits both bounds state solutions (...
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Given Quantum Tunnelling, and a High Enough Velocity, Could Two Objects Theoretically Pass Through One Another?

I apologize if this has been answered before -- The answer may be out there, but I may just not have the proper terminology to find it. I was messing around with Universe Sandbox, and noticed that if ...
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Is tunnel microscope destruct a bit the material, by extracting electrons from the probed material?

The tunnel microscope probes the electrons of a material by quantum tunneling effect. As a consequence of the migration of electrons, is the tunnel microscope "destroying" a bit the material,...
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Finite Potential Barrier Where $E=V_0$

If we have a free particle of energy E incident on a potential $V$ $$V(x) = \begin{cases}0 & x \leq 0 \\ V_0 & 0 < x < L \\ 0 & x \geq L\end{cases}$$ We find that the wave function $\...
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When an electron tunnels through a barrier, where would it be found when measured? [duplicate]

When an electron with E < V approaches a step in potential energy, the wave function will exponentially decay at the step, meaning there is still a finite possibility of the electron being found at ...
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How does QFT explain QM phenomena?

I've been studying QFT for a couple of years now, and until today I haven't encountered any of the phenomena that I've studied in my QM course: tunneling, entanglement, probability measurements and ...
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Particle in a classically allowed region vs forbidden region

So what would the momentum be in either of these regions? In terms of the infinite square well where the potential, $V(x) = 0\leq x\leq a$ and infinity otherwise. In the otherwise case, the potential ...
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Quantum Tunnelling Likelihood in Sun

So I have a question in regard to quantum tunnelling. Firstly, I've been given a question to calculate the kinetic energy of a proton inside the sun where the sun has an internal temperature of $$𝑇 ∼ ...
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Why is the alpha particle in alpha decay considered to be in a potential well?

I understand that when modelling alpha decay, it is useful to consider the $\alpha$ particle as being preformed, in a region confined to the daughter nuclei. I also understand that the term $V_{0}$ ...
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Can vacuum breakdown occur from a positively charged surface?

Against a sufficiently large voltage, resistance is futile. Although the vacuum is a very good insulator, electrical breakdown can occur even in a perfect vacuum in the presence of a very strong ...
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Energy Levels in Double Finite Well potentials [closed]

Why is there a behaviour where $E_1$ and $E_2$ are close to each other? This question is already answered before but I did not understand the explanation about symmetric and asymmetric terms as I do ...
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Materials based on quantum tunneling: conductivity

Suppose you have a nanocomposite wire in which electrons can move through it exclusively with the electron tunneling between conductive nanoparticles that are within optimal distance (like in figure ...
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Energy level splitting in two-state systems

I was learning basic quantum mechanics using Feynman Lectures on Physics. In Chapter 8 Feynman has described ammonia inversion due to tunnelling. Feynman has first used the base states as the two ...
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Why do helium fuse in the Sun?

Initially there are lots of hydrogen atoms and trace elements in the Sun. Despite insufficient energy for the hydrogen to fuse in the core, quantum tunneling saved the day and invoke proton-proton ...
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What is the significance of the electron's wavelength for Momentum and Energy Resolved Tunneling Spectroscopy (MERTS)?

The technique called momentum and energy resolved tunneling spectroscopy (MERTS) is based on quantum tunnelling, whereby an electron can traverse a barrier which has a thickness of less than 3nm, by ...
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How does the barrier affects quantum tunneling?

I am picturing a sine wave acting as a barrier for my quantum tunneling experiment, it can be an electric field etc. Now I have an electron whereby a portion of its probability intersects and even ...
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What actually is a potential barrier in quantum mechanics?

I'm new to quantum mechanics, and I was wondering what actually is a potential barrier in quantum mechanics? I understand that it is similar in a way to a hill in classical mechanics except that we ...
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How does the energy splitting in a double well potential scale?

It is well known in quantum mechanics that in an 1D double well potential there is an energy splitting between the ground state $\psi_0(x)$ and the first state $\psi_1(x)$ despite them being nearly ...
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Possibility of staying within nucleus for a electron according to Uncertainty Principle

Academic Problem: According to Uncertainty Principle, show that electron can't stay within nucleus. That's a general problem indeed. Anyway, we know that uncertainty of position in this case can't ...
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Resonant tunneling for wavepackets, simulation - what exactly is happening here?

I have been learning various ways to solve TDSE and naturally, wavepacket motion seemed like a good test case to check the algorithms. Then, of course, I wanted to see one of the most interesting ...
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Am I misunderstanding something, or are these Wikipedia statements about quantum tunneling wrong? Badly stated?

From https://en.wikipedia.org/wiki/Quantum_tunnelling#Introduction_to_the_concept : The reason for this difference comes from treating matter as having properties of waves and particles. One ...
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Tunneling in quantum field theory

Tunneling in QM is well defined phenomenon since for a real potential the number of particles remain constant. But when we switch to field theory the number of particles need not to remain constant ...
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Regarding the quantum nature of floating gate transistor - tunneling, coherence, spectrum

In a floating gate transistor, the gate is electrically isolated. I have a few questions regarding the quantum nature of this device: It is sometimes mentioned that, to store or deduct charges from ...
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Potential step and tunneling effect

We know that thanks to the tunnel effect, in the case of a finite potential step and considering a stationary state, when a plane wave encounter the step the probabability that the wave-particle ...
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Bound states on a Quantum Dot and Tunneling on and off the Dot

Question is essentially: How can the states on a quantum dot be bound when we can tunnel onto them? If plane wave states can tunnel onto them, these plane waves states and the 'bound' states will have ...
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Calculating the lateral resolution of scanning tunnel microscope

I'm sorry in advance for this post, because I know that homework type questions are not allowed here. I have to calcualte the radial distribution of the tunnel current $j(r)$ from the surface of a ...
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Pertubation Theory

For long-range barrier tunneling, consider three qubits governed by the Hamiltonian $H$. $$ H = -J(\sigma_1^+\sigma_2^-+\sigma_1^-\sigma_2^++\sigma_3^+\sigma_2^-+\sigma_3^-\sigma_2^+)+\frac{U}2\sigma^...
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Nuclear reactions in stars: tunneling?

Energy production in stars occurs mainly when a nucleus absorbs a proton or fuses with another nucleus. Some examples: (i) $\rm{p}(\rm{p},\rm{e}^+\nu)\rm{d}~$ and $~\rm{d}(\rm{p},\gamma)^3\rm{He}~$ ...
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Quantum Tunneling and Negative Kinetic energy

I don't understand how a particle can exist with negative kinetic energy. Consider this scenario: Here, an electron is tunneling through a potential barrier (The total energy of the electron is less ...
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Understanding conductivity at nanoscale and validity of Ohm's law

Nanoparticles such as gold and silver are becoming more and more used to print circuit or enhance electrical properties of another material. But I have not been able to find sources that clarify how ...
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Conservation of energy in quantum tunneling

By this question, a particle can tunnel to inside a potential barrier. One aspect of this process that was not addressed in the answers was the conservation of energy. Motivated by this question, I am ...
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Does the wavelength of an individual quantum particle affect its chances of quantum tunneling through a barrier?

I've read elsewhere about the energy of a wave or wave packet, and the amplitude of its probability amplitude, affecting its odds of quantum tunneling... But what about the wavelength or frequency of ...
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Transmission coefficient of a Gaussian wave packet through a potential barrier

I have simulated the scattering of a gaussian wave packet with a potential barrier (Crank-Nicolson), and through many simulations I have determined the dependence of the transmission coefficient with ...
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Tunneling effect - causes

I'm currently studying QM, and in my class tunneling effect was mentioned, but with no details. I was wondering what exactly causes this effect? Is this due to the wave characteristics of the particle,...
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Blocking quantum effects

A Faraday cage blocks electromagnetic fields, provided they are not intense enough to change the state to something non-conductive (e.g. slicing it in two with a laser). Is there any analogous system ...
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Can current and voltage be linked by an uncertainty relation when electrons tunnel through a barrier?

Quantum tunneling has been shown to be linked to uncertainty relations for some observables involved in the system. For instance, if we consider electrons tunneling through a potential barrier it can ...
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Why does quantum tunneling increase de-broglie wavelength?

The picture (taken from a textbook) shows how quantum tunneling occurs with electrons. Why does the de-Broglie wavelength of the electron change when doing this? It does not make intuitive sense to ...

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