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# Questions tagged [quantum-mechanics]

Quantum mechanics describes the microscopic properties of nature in a regime where classical mechanics no longer applies. It explains phenomena such as the wave-particle duality, quantization of energy and the uncertainty principle and is generally used in single body systems. Use the quantum-field-theory tag for the theory of many-body quantum-mechanical systems.

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### Understanding quantum mechanics [on hold]

Forgive me for this dumb question but what are matter waves of particles? are they particles being spread out in a space like waves or the particles are still "particles" but matter waves are ...
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### What happens in an infinitely long potential step when $E<V$?

In the case of a potential step when $E<V$, the transmission coefficient of the particle is zero. However, there is also an exponentially decaying wavefunction of the particle in that classically ...
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### Two particle Heisenberg model with field

I'm having trouble solving a problem with a phase transition of this system. We are considering the following Hamiltonian: $$H=-J \vec{S_1}\vec{S_2}-\mu b (S_{1z}+S_{2z})$$ And I've studied it in ...
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### Symmetric potential well different solutions

I have solved $H|\psi\rangle=E_{n}|\psi\rangle$ with $V(x)=0$ from $-a<x<a$ and $\infty$ otherwise. If I propose a solution of the form $\psi(x)=A_{n}e^{ikx}+B_{n}e^{-ikx}$ I arrive to the ...
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### The expected value of $x$

How to get the expected value of $x$ in the momentum space?
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### Experimental preparation of an electron plane wave with given momentum in quantum mechanics

Boiling electrons off a hot filament constitutes a preparation providing a mixed ensemble with nearly Maxwellian distribution of momentum eigenstates. To further purify the ensemble, one can let the ...
15 views

### A relation for the state of a scatteing process

I am studying the article "A Formal Optical Model", of Bell and Squires (the article is here https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.3.96) where they proof that the self-energy of ...
81 views

### What does it mean to simulate a quantum system?

What does it mean by simulating quantum system? Can I simulate Young's double slit experiment with a quantum computer? If yes, won't it violate no-cloning theorem?
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### Input Output formalism for a single-sided cavity in quantum optics, all modes same direction?

I have been trying to understand the input output formalism for a cavity by reading chapter 7 of Walls and Milburn (D. F. Walls and G. J. Milburn. Quantum optics. Springer, 2006.). There is something ...
783 views

### Relativistic correction to Hydrogen atom - Perturbation theory

Given the relativistic correction $$H_1' = - \frac{p^4}{8m^3 c^2}$$ to the Hamiltonian (i.e. a perturbation), what does it mean when $[H_1', \mathbf{L}] = 0$? The book I'm reading says this implies ...
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### Could ripples in the fabric of reality explain the double slit experiment? [on hold]

I was looking at the single photon double slit experiment and how they achieved having just one photon at a time passing through the slit: they emitted 100 photons per second(in the variant I found ...
237 views

### Barrier Potential for bound states

I'm having this problem for a while, but I'm still failing to realize what really is bothering me in this, so here is my attempt on explaining my doubt: I have the time-independent Schrodinger ...