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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Why does a violation of locality not imply a violation of relativity?

This question is closely related to: What counts as information? Taking the specific example, again, of the EPR experiment. I think everyone agrees on the following: The act of measuring the ...
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1answer
100 views

How did Schrödinger come up with his equation?

So all of the people who studied QM know the famous Schrödinger equation. I have read that it was not derived, but it is a postulate; something that is just real. Some people have tried to explain ...
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55 views

Intuition behind the solutions of the Schrodinger equations

I am learning the basic and easy first examples of the most common problems in Quantum Mechanics,and while trying to find solution to the Schrodinger equation,i find myself struggling with the ...
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32 views

What is Bell Measurement (wrt its use in quantum teleportation)?

Bell measurement is joint quantum-mechanical measurement of two qubits, so that after the measurement the two qubits will be maximally entangled. According to the answer here, this is acceptable ...
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1answer
30 views

Why should odd-ordered electric multipole moments vanish?

In the multipole expansion of the radiation field of a nuclear, it is considered that the odd-ordered poles (like electric octupole) must vanish in order to conserve parity. But there exist many ...
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1answer
30 views

How are anti-unitary operators applied?

I was reading about anti-unitary operators from Wikipedia. They give an example of an anti-unitary operator: were $K$ is complex conjugate operation. $\sigma_y$ is defined with respect to two ...
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1answer
47 views

Quantum mechanics prediction for Bremsstrahlung?

Does quantum mechanics predict the Bremsstrahlung Phenomena? I know it is predicted by classical mechanics through Maxwell's equations, but does QM predict this phenomena and how so?
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41 views

Understanding Quantum point contact

Am I correct in saying that quantum contact is : for a quantum heterostructure, by applying a voltage between two needle shaped split gate, it would deplete the electrons beneath it, therefore ...
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56 views

Double-slit experiment, dielectric material containing the two parallel slits

This is concerning the double-slit experiment. This is concerning the material containing the two parallel slits. Are there experiments where the material containing the two parallel slits -- is ...
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1answer
73 views

Why do $H$ and $L^2$ commute in spherically symmetric potential?

In this PDF document (a lecture by Shivaly Reddy, page 13), he says that $L^2$ is independent of $r$; therefore it commutes with any function of $r$. This seems related to a problem in ...
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1answer
80 views

Fiber bundle understanding of the wavefunction

Usually people say that given a wavefunction $\Psi$ although $|\Psi(\cdot, t)|^2$ is the probability density for the position random variable at time $t$, the wavefunction $\Psi$ itself has no ...
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0answers
36 views

What kind on transformations can be applied on density matrices?

Completely positive trace preserving maps ( CPTP ) transform a valid density matrix to another, then why do we only talk about unitary transformations on density matrices ( $\rho \to U\rho ...
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2answers
61 views

Commuting observables and CSCO's

I've been looking at some basic quantum mechanics all day in an attempt to better my understanding of the subject. While going over the proof that commuting operators are compatible, I started getting ...
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2answers
98 views

Would $[\hat{Q},\hat{H}]$ correspond to an observable? [closed]

Would $[\hat{Q},\hat{H}]$ correspond to an observable? Where $\hat{Q}$ is an observable and $\hat{H}$ is the Hamiltonian. Surely that would just mean that $[\hat{Q},\hat{H}]$ would commute i.e. = 0?: ...
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3answers
124 views

Messed up units!

In the article, Environment-assisted quantum transport, $\gamma$ is a constant equal to $2\pi kT/\hbar*E_{R}/(\hbar\omega_{c})$ where $T$ is the temperature, $k$ is the Boltzmann constant. ...
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2answers
108 views

$\hat{L}_{x}$ and $\hat{L}_{y}$ do not commute… or do they?

So $\hat{L}_{x}$ and $\hat{L}_{y}$ do not commute: $ [ \hat{L_{x}}, \hat{L_{y}}] = i\hbar \hat{L_{z}}$ But, what if we perform this operation on a state such that: $\hat{L_{z}} \phi_{l, m_{l}} = ...
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2answers
144 views

The expectation value of entanglement entropy of composite system in a random pure state

I'm trying to compute the expectation value of entanglement entropy of composite system in a random pure state, but I'm running into some problems. The system we are considering is composed of two ...
2
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1answer
60 views

Distributional Extension of a Hilbert Space

This question comes from the Complexification section of Thomas Thiemann's Modern Canonical Quantum General Relativity, but I believe it just deals with the foundations of quantum mechanics. The ...
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0answers
12 views

Recommend a read [duplicate]

I am new to this field and looking for novice books to buy on physics and quantum physics...Any introductory literature recommendation would be highly appreciated. Thank you
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0answers
44 views

Potential in Schrödinger equation when doing a Galilean transformation

I was looking at the quantum mechanics book by Bransden and Joachain, specifically at the section about Galilean transformations, and I was trying to find out what they did here for the potential ...
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2answers
32 views

How to determine whether a nuclear transition would be electric octupole, or hexadecapole?

The transition from one nuclear state to another is classified as quadrupole/octupole, etc, depending on the units on angular momentum transferred. But depending on the angular momentum of the two ...
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1answer
35 views

Expectation value of total angular momentum $\langle J \rangle$

[I am working with Griffiths Introduction to Quantum Mechanics, 3rd Edition. My problem is general but if you want to look I am reading from ch 4.1 in which the weak-field Zeeman Effect is being ...
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1answer
75 views

Relationship between those two “exponentials”

Let $G$ be a Lie group and $L(G)$ it's Lie algebra. We know that every left-invariant vector field $X$ in $G$ is complete, and so one can consider the integral curve defined for all $t\in \mathbb{R}$ ...
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30 views

Relation between energy band gap and atomic number

Is there any relation between energy band gap in group4 elements and their atomic numbers? It might be just a trivial observation but I noticed How from Carbon to Germanium the band gap went from ...
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3answers
110 views

“Complete” confusion

The word "complete" seems to be used in several distinct ways. Perhaps my confusion is as much linguistic as mathematical? A basis, by definition, spans the space; some books call this "complete" -- ...
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5answers
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A Quantum Mechanics question that no one can answer [closed]

One of the professors in our department asked the following question on a Quantum Mechanics exam: Write me a Quantum Mechanics question below. If I can answer it, you will get 6 points and if I ...
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1answer
76 views

Photoelectric effect – Why does one electron absorb one photon?

When I read about the photoelectric effect, I came across this: "The electrons could not absorb more than one photon to escape from the surface, they could not therefore absorb one quanta and then ...
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2answers
99 views

Is entanglement a consequence of the uncertainty principle?

I am an aspiring physicist and once, I asked my professor on what triggers quantum entanglement and he graciously remarked "The great uncertainty principle!" - I was slightly confused and didn't say ...
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2answers
115 views

Wheeler's delayed choice experiment

In Wheeler's delayed choice experiment (http://en.wikipedia.org/wiki/Wheeler%27s_delayed_choice_experiment) When the experimental apparatus does not contain a final interfering mirror, the photon is ...
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0answers
24 views

Is local oscillator light polarised?

If a laser is used as a local oscillator in the homodyne setup does this mean the light it produces is polarised? (I am looking at this from the context of quantum physics and random number ...
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0answers
53 views

Noether Current and Feynman Diagrams

My question is simple. Assume that there is no anomaly and we have found from the lagrangian that there is a conserved current. I want to know what this means in terms of feynman diagrams, not in ...
3
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0answers
61 views

Driving $\sigma$ transition with light in superposition of $\pi_x$ and $\pi_y$ polarization of slightly different frequencies

Lets assume the following experiment. Circularly polarized laser light is sent through a Mach-Zender interferometer $\left(l_1 = l_2 \sim \,\mathrm{cm}\right)$ made up of polarizing beam splitters ...
2
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2answers
108 views

Time evolution of a wavepacket

I do not understand why if $H\psi = E\psi$, then the time-evolution of the wavefunction is given by $e^{-iEt/h}\psi(x)$.
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0answers
109 views

Ghost in the quantization of relativistic particle

It is well known that in the quantization of certain relativistic theories such electromagnetism or relativistic string negative norm states could arise when quantizing covariantly. Acting with ...
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1answer
40 views

Why must the Berry phase in 2d parameter space be $\pi$?

I am reading a paper and it seems that the author states that the Berry phase in 2d must be $\pi$. Is this true? If so, why?
3
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1answer
109 views

What is the purpose of the imaginary portion of the wave function?

I recently watched this video. I'm trying to learn about the origin of the wave function and therefore understand its use in the Schrödinger Equation. However at the end of the video I understood up ...
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1answer
201 views

About a recent experiment which claims reality doesn't exist until we measure it?

Reality doesn't exist until we measure it, Quantum Experiment confirms. Is this one more experiment which is the victim of how news generally hypes stuff like this? This is a section from the ...
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0answers
43 views

Entanglement between the electrons in the Laughlin wave function

Consider the $1/3$-Laughlin wave function $$ \Psi \propto \exp \left(-\sum_i |z_i|^2 \right) \prod_{1\leq i<j\leq N} (z_i-z_j)^3 . $$ It cannot be written in the form of a Slater determinant, ...
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2answers
88 views

Why does Bohr's stationary orbits not radiate energy? [duplicate]

I am presently in high school trying to understand the Bohr's theory. I somewhat familiar with Maxwell's laws but very soon I'll learn about them thoroughly. So please could anyone explain with ...
2
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1answer
32 views

systems of particles that are not symmetric or anti-symmetric; Helium 4

Suppose I have an electron and a proton, and that the electron is in the spin-up state, and that the proton is in the spin-down state. The particles are distinguishable, so I should just be able to ...
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2answers
110 views

Electron energy in hydrogen

Is the energy of the electron in a random hydrogen atom in a superposition of all eigenvalues (some value upon measurement) or you will find it most likely in the ground state. I want to clarify my ...
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1answer
40 views

Notation for $N$-particle wave functions

If we have one particle we first look at an orthonormal basis of the one-particle Hilbert space $|n\rangle$. Here $n$ is the abbreviation for a compete set of quantum numbers, for example $n = ...
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1answer
27 views

Half wave plate in front of polarising beam splitter?

I have seen (in e.g. quantum random number generators) a half wave plate in front of a polarising beam splitter. But why do we need it and what would be different if we did not have it?
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4answers
100 views

Importance of local conservation of probability

In almost every textbook of quantum mechanics we can find the derivation of the local conservation of probability. $$\nabla\cdot\vec{J}+\partial_t (\psi^*\psi)=0$$ where $\vec{J}$ is probabilty ...
2
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2answers
90 views

Spin angular momentum conservation and entanglement

Suppose we have a system with $S=0$ . Suddenly, this system decays into two particles, A and B, so we know the sum of the spin of these two particles is zero. Suppose we measure the spin of A in the z ...
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0answers
52 views

Transition Amplitude vs. Transition Probability

In quantum mechanics, a physical system corresponds to a Hilbert space $\mathscr{H}$. States correspond (not in a one-to-one way) to points in $\mathscr{H}$ and the physical postulate is that the ...
2
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1answer
64 views

Proofs on operator algebra [closed]

I'd like to ask the community to please verify the first two proofs below and help me get through the last one since I seem to be stuck. Thank you in advance. Proof 1: Given two noncommutting ...
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0answers
58 views

When the exponent of sum is a product of exponents?

In quantum mechanics we solve the Schrodinger equation in terms of exponential $$\left|\psi(t)\right\rangle = e^{-it(\alpha\hat{X} + \hat{Y})}\left|\psi_0\right\rangle$$ where $\hat{H} = ...
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1answer
50 views

Why do momentum and position have the same direction in space in the Heisenberg Uncertainty Principle?

It is known that $\Delta p \Delta x \geq \frac{h}{4\pi}$. I read that the two uncertainties must be along same axes. Why is that so?
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1answer
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How to derive Uncertainty Principle relation?

How to derive Heisenberg Uncertainty Principle relation?