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 ...

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18 views

A wave is passing through a potential barrier

Let assume a wave is passing through a potential barrier. Like this: What will be happened to the amplitude or the shape of the wave during the movement through the potential barrier? {assuming ...
0
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0answers
15 views

Repulsive potential for free fermions

My question -which is probably easy to answer for a physicist- stems from trying to understand the repulsive interaction between fermions. For instance the fact that states of multifermion systems are ...
12
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4answers
11k views

Is it possible to reproduce Double-slit experiment by myself at home?

I want to reproduce this experiment by myself. What I need for this. What parameters of slits and laser/another light source it needs? Is it possible to make DIY-detector?
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0answers
42 views

Is this solvable? Time-dependent perturbation theory

The question is A hydrogen atom is placed in a time-dependent homogeneous electric field given by $$ \varepsilon(t) = \varepsilon_0(t^2 + \tau^2)^{-1} $$ where $\varepsilon_0$ and ...
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3answers
53 views

Problem with tracing over the environment and obtaining reduced density operator [on hold]

I'm reading an article by Bas Henson given here. On page 25 he deals with the double slit experiment Given the wavefunction which is his equation 1.75, he claims he has traced over the environment ...
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1answer
60 views

Lippmann-Schwinger equation and $T$ expansion

Lippmann-Schwinger equation, in operator form, is: $$ T=V+V\frac{1} {E-H_0+i \hbar \varepsilon} T=:V+V\Theta_0T, $$ where $H_{tot}=H_0+{V}$ is the hamiltonian ($H_0$ is the free particle hamiltonian ...
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3answers
596 views

Why is momentum quantized in a 1D box even though the operator doesn't give eigenstates?

We don't get eigenstates of momentum when we operate momentum operator in the wave function of particle in a 1D box problem yet we say momentum is quantized in this situation. Why is it so?
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1answer
52 views

Completeness relations of eigenstates in the Heisenberg picture

I've been reading Srednicki's introduction to path integrals and I'm slightly unsure of the notation that he uses for the completeness relation of position eigenstates in the Heisenberg picture. In ...
1
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0answers
34 views

What is special about quantum entanglement? [duplicate]

Get two pieces of paper. In secret write the same number on both papers. Transfer one paper to the Moon. Look to the paper which is left at the Earth. Voila! We know what is on the Moon paper. The ...
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3answers
64 views

Can't we consider that EmDrive is Pushing against Space itself? [on hold]

When something move through space it pushes against something else in space with equal force. However, EmDrive warps space around. So can't we say it's pushing against space itself, and thus momentum ...
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0answers
40 views

What does $(I + iδH^t)(I-iδH)$ equal to? [on hold]

$I$ is equal to 1, $δ$ is a small change. According to 43:04-43:10 of this video http://theoreticalminimum.com/courses/quantum-mechanics/2012/winter/lecture-4 \begin{align} \ i{ δ }(H^t-H)=0 ...
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0answers
56 views

How to find $\langle x^2 \rangle$ of a wavefunction $\psi(x,t)$ [closed]

I know how to find $\langle x \rangle$ of such a function, but I'm not sure of how to find the variance or $\langle x^2 \rangle$ of this continuous function. Any help would be greatly appreciated. ...
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1answer
93 views

Prove that Laughlin's 3-electron states are a complete set of states

In R. B. Laughlin's 1983 Physical Review B article, Quantized motion of three two-dimensional electrons in a strong magnetic field, Laughlin separates out the center of mass motion of the electrons, ...
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1answer
41 views

Oscillation of Atom

What exactly does it mean when one says 'one atom of Caesium 137 oscillates 9,192,631,770 times'? I do understand the general thing about oscillation but what exactly is the oscillation of atom, what ...
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1answer
45 views

De Broglie's Matter wave equation dividing by zero

I was just thinking about De Broglie's matter wave equation: $\lambda=\frac{h}{p}$ where $p$ is the momentum of the object. But what if the object is at rest? Won't we be dividing by zero? What if we ...
1
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1answer
41 views

Meaning of expectation value of product of non-commuting operators

Let $\hat{A}$ and $\hat{B}$ be Hermitian observables with spectra labeled by $a$ and $b$. Then we can write \begin{equation} \hat{A} = \sum_a a\, \hat{P}_a \end{equation} \begin{equation} \hat{B} = ...
2
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2answers
109 views

Is there any $SU(\infty)$ gauge theory in quantum field theory?

The groups $U(N)$ and $SU(N)$ are the most important Lie groups in quantum field theory. The most popular are the $U(1),SU(2),SU(3)$ groups (these gauge groups form the Standard model). But is there ...
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1answer
218 views

spooky nonlocal communication, or bad abstract?

I'm referring to this recent paper, "Experimental Proof of Nonlocal Wavefunction Collapse for a Single Particle Using Homodyne Measurements" by Fuwa et al. published in Nature Communications. ...
2
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2answers
94 views

Can an electron go along different paths at once in a circuit

A single electron moves along a circuit and comes to a fork in the wires. The wires separate but come back together near the end of the circuit. From what I know, the electron will travel along all ...
1
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1answer
39 views

Books on waves with Fourier Transforms

There are many waves and oscillations books out there that also include Fourier analysis but very few give the subject a thorough treatment, they just pass it in a few pages. If anybody has any ...
3
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6answers
488 views

Fermion vs. Bosons and particle vs. wave: is there a link?

I'm puzzled since several years on this basic aspect of quantum mechanics. Quantum theory is supposed to describe particle-wave symmetry of our world. It also describes our universe in term of bosons ...
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2answers
201 views

Is entropy a meaningful concept on a quantum level?

My naive assumptions, as I really am at a pretty basic stage in QM, are as follows: Classically, entropy gives us a practical measure of the direction of time, as opposed to our physical laws which, ...
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0answers
41 views

What's the physical meaning of the different entanglement entropy of mixed bipartite systems?

As we know, for pure bipartite systems, the entanglement entropy are the same for both subsystems. But this is not the case for mixed states. Can anyone explain what's the physical meaning of this ...
2
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1answer
34 views

Sources to learn about Berry phases and Adiabatic Theorem

I recently went through Griffiths' Quantum Mechanics text and there is a chapter called the Adiabatic Theorem that includes Berry phase and the Aharonov-Bohm effect. As I found them very ...
2
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1answer
130 views

Quantum fluctuation

According to the quantum fluctuation concept, a particle and its corresponding antiparticle appear out of nothing only to annihilate and emit some energy in the form of electromagnetic waves. Does ...
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0answers
28 views

How to form a density matrix? [on hold]

forming a density matrix when two independent states are there
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0answers
43 views

Can a density matrix be complex? [on hold]

Normally a density matrix is thought of as a statistical ensemble of pure states. However, after using the Time-Evolution Equation (or Master Equation) to evolve a density matrix, they start to have ...
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0answers
19 views

Can there be a link between non-locality and non-Markovianity?

Non-locality is a curious feature that is linked to the violation of Bell inequality of any form. It arise from the impossibility of simultaneous joint measurements of observables. The ...
4
votes
1answer
258 views

Does tunneling transmission probability depend on the density of states or velocity?

In some quantum text books [1], the tunneling transmission formula depends only on the density of states of 2 regions (DOS) involved in tunneling. ($T(E) = C \times DOS_1(E) \times DOS_2(E)$, where C ...
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votes
2answers
90 views

Why is local realism not possible with QM?

In Mermin's thought experiment (pdf) particles are sent to two detectors A and B with 3 settings each. If the particle passes the test, we get a green (G) light, else red (R). Now in QM we could send ...
0
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1answer
46 views

Barycenter and relative coordinates for schroedinger equation of the hydrogen atom

Heyho, i just realized i am not sure how one gets from: $\Big(-\frac{\hbar^2}{2m_e} \Delta_{r_e} - \frac{\hbar^2}{2M_P} \Delta_{r_p} +V(r) \Big)\Psi(r_e,r_p) = E \Psi(r_e,r_p)$ to: ...
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3answers
96 views

Is there free will? [on hold]

From what I've understood about the answer to this question quantum physics doesn't contradict determinism, but instead it simply isn't achievable only because of our universe's nature: we are unable ...
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3answers
361 views

Bound states of the $V(x)=\pm \delta'^{(n)}(x)$ potential?

The $\delta(x)$ Dirac delta is not the only "point-supported" potential that we can integrate; in principle all their derivatives $\delta', \delta'', ...$ exist also, do they? If yes, can we look for ...
4
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0answers
74 views

Is there a proof that the number of eigenstates is countable for a bound system?

When you solve Schrödinger equation for a free particle with no boundary conditions your eigen states are indexed by quantum number $k \in \mathbb R $ and $\mathbb R$ isn't countable but if you add a ...
-2
votes
1answer
21 views

magnet repulsion in a cylinder [on hold]

Firstly, Am doing a research project on the use of repulsion of magnets to form a car shock absorbers. Can the forces of repulsion manage to absorb the shock of a 2.0 ton car?
0
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1answer
34 views

Fourier expansion and transform - what about the phase of the waves that i am adding?

Say we have a wave on the surface of the water and we want to describe it as a sum of other waves. So we use Fourier expansion to add waves of different wavelengths. For simplicity, say we have to ...
1
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3answers
65 views

Is there an example of a situation where you need a continuous spectrum?

If you had a hydrogen atom you could say that you want to be able to ionize them. But if you then add the potential due to the earth, e.g. ...
13
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1answer
487 views

How to evaluate this sum of coupling coefficients?

I would like to evaluate the following summation of Clebsch-Gordan and Wigner 6-j symbols in closed form: $$\sum_{l,m} C_{l_2,m_2,l_1,m_1}^{l,m} C_{\lambda_2,\mu_2,\lambda_1,\mu_1}^{l,m} \left\{ ...
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0answers
10 views

Can QKD nodes use a constantly evolving key?

In QKD we know that we can generate random secret keys using quantum entangled photons, measuring their qubits and then using noise reduction to negotiate probably similar bits between Alice and Bob. ...
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0answers
81 views

Bell's inequality, “complete plans” and spooky action at a distance

What am I proposing and asking? In Mermin's thought experiment entangled particles, i.e. photons are sent to two machines A and B with 3 settings each. The idea of a "complete plan" how to react to ...
0
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0answers
51 views

Can you have more than two entangled particles? [duplicate]

Given the diagram on the wikipedia page for Quantum Entanglement we a beam of photons hitting a crystal which splits the beam into to entangled particles. Is it possible to split the beam into four ...
2
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1answer
119 views

What is Z3 exciton?

I am searching and studying excitons and I confronted with a term named Z3 exciton. What is it? And what is its difference with, for instance Z1 or Z2 exciton?
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0answers
68 views

Decay of excited electron from Schrödinger equation?

I'm currently studying for a quantum mechanics exam. I found some old exams which has the following question I'm trying to solve. Please tell me if my reasoning is wrong. Can you see from the ...
-1
votes
1answer
60 views

How to model matter in code [on hold]

I've always had a passion for science, understanding and programming. Given my interests, I thought a cool thing to do would be to model real world theories in code (with visuals) so that others may ...
1
vote
1answer
52 views

Can one detect a single photon through measuring its impulse/momentum on a mirror?

Can one detect a single photon through measuring its impulse/momentum on a mirror? If the answer if YES or theoretically possible, photon path and interference fringes can be detected simultaneously ...
0
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1answer
64 views

Children of entangled particles

Theres a photo on the wikipedia page Quantum Entanglement there's a image of a photon being split into two entangled photons via crystal. I used this picture to demonstrate the scenario below. ...
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0answers
61 views
0
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1answer
15 views

Are the produced entangled photons in type II SPDC always in phase?

Are the produced entangled photons in type II SPDC (spontaneous parametric down conversion) always in phase? In Kim's delayed choice quantum eraser, two entangled photons are produced by a BBQ ...
2
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0answers
67 views

Symmetry in quantum mechanics

I originally asked this on the maths site, but I'll repost it here. Let $\mathcal{H}$ be the separable Hilbert space associated to some quantum system, and let $\langle\cdot,\cdot\rangle ...
4
votes
1answer
79 views

Does a Buckyball spin like an electron or like a baseball?

Does a Buckyball spin like an electron or like a baseball? We are often told that an electron does not really spin like a baseball. Only one (or two, if you count up and down) spin states, for ...