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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.

5 votes
2 answers
980 views

Infinite square well: wall with infinitesimal thickness

Given an infinite square well, it doesn't matter how thick the wall is, the particle is trapped inside the two walls. If we make the wall of arbitrarily small but finite thickness, the particle is sti …
Leo L.'s user avatar
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2 votes
1 answer
125 views

Does the eigenbasis associated with an observable changes after measuring a different observ...

Suppose a system is initially in a superposition: $$\psi(x) = \sum\limits_{i}|c_i\phi_i(x)\rangle$$ After a position measurement, the wave function collapses to one of the position eigenfunctions,$\ph …
Leo L.'s user avatar
  • 729
2 votes
1 answer
815 views

How does magnetic monopole arise from Berry curvature?

The Berry connection is defined as $$A_n(R)=i\left<\psi_n(R)\right|\nabla_R\left|\psi_n(R)\right>$$ and it is mathematically analogous to the vector potential. We can then naively define the Berry c …
Leo L.'s user avatar
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2 votes

Three operators commuting with each other

Yes. For example, when calculating angular momentum of a hydrogen atom (ignoring fine structure or hyperfine structure), the eigenbases (which are described by spherical harmonics) are simultaneously …
Leo L.'s user avatar
  • 729
2 votes
0 answers
271 views

Interpretation of induced force between two Dirac delta potential wells

My question is based on MIT OCW course 8.04 problem set 6 question 5(e). https://ocw.mit.edu/courses/physics/8-04-quantum-physics-i-spring-2013/assignments/MIT8_04S13_ps6.pdf Consider two Dirac delt …
Leo L.'s user avatar
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1 vote

Examples of antiunitary operator other than time reversal operator

Just for future reference, an example I encountered recently is the following: in the Bogoliubov-de Gennes (BdG) theory of superconductivity, the Hamiltonian has particle-hole symmetry. And the corres …
Leo L.'s user avatar
  • 729
1 vote
0 answers
73 views

One spin-1/2 particle in B field in a 3D harmonic potential (Part I)

Consider a spin-1/2 particle in a magnetic field (say in z direction) and in a harmonic potential. For the 3D harmonic oscillator component, The Hamiltonian $H_1= \frac{p^2}{2m}+\frac{1}{2}m\omega ^2r …
Leo L.'s user avatar
  • 729
1 vote
2 answers
417 views

One spin-1/2 particle in B field in a 3D harmonic potential (Part III)

Consider a spin-1/2 particle in a magnetic field (say in z direction) and in a harmonic potential. For the 3D harmonic oscillator component, The Hamiltonian $H_1= \frac{p^2}{2m}+\frac{1}{2}m\omega ^2r …
Leo L.'s user avatar
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0 votes
1 answer
317 views

Examples of antiunitary operator other than time reversal operator

It is well-known that time reversal operation is implemented as an anti-unitary operator. I wonder what are some other examples of anti-unitary operators that appear in the context of quantum mechanic …
Leo L.'s user avatar
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0 votes

Diffracted Electrons vs Particulate Electrons (Collapsed): Is there an experimental differen...

I think this famous experiment of electrons building up an interference pattern one by one answers your question. http://www.datadeluge.com/2017/03/demonstration-of-singleelectron-buildup.html When a …
Leo L.'s user avatar
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0 votes
1 answer
439 views

Spin-1 particle polarization direction

For spin-1 particle, I don't quite understand how the following relationship is derived: $$\left|+1\right>=-\frac{1}{\sqrt2}(\hat e_x+i\hat e_y)$$ $$\left|0\right>=\hat e_z$$ $$\left|-1\right>=\frac{1 …
Leo L.'s user avatar
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-1 votes
Accepted

Why energy eigenstates form orthonormal basis

The first important property of a Hermitian operator is that it only has real eigenvalues. Try show it yourself starting from the eigenvalue equation: $$ \hat H \psi_n(x) = E_n\psi_n(x)$$ taking adjoi …
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