Fundamental characteristic property of particles which together with orbital angular momentum acts as the generator of rotations and which doesn't have a classical equivalent but is sometimes compared to and contrasted with classical intrinsic angular momentum.

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What is the physical implication of a homomorphism between SU(2) and SO(3)?

It can be shown that there exists a homomorphism between $SU(2)$ and $SO(3)$. What is the physical implication of a homomorphism actually? I know that in physics $SU(2)$ acts on a space of spin 1/2 ...
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32 views

Klein Gordon, Dirac, Proca [on hold]

How do we know these equations : Klein-Gordon, Dirac, Proca is for spin 0, spin 1/2 , spin 1? How did people find Klein Gordon doesn't work for spin 1/2?
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L-S Coupling (Atomic Physics) Ground State [on hold]

Can someone please explain to me why in the second configuration the ground state is associated with $L=F=3$ and $J = 7/2 $? ** Another question: Should we always take $J$ as even? if yes, why?
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69 views

Parity operators and spin

Consider the following excerpt from Weinberg's Lectures on Quantum Mechanics: I follow everything up until the last statement in the excerpt. In fact, from other things I've read, it seems that one ...
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1answer
58 views

Do gravitational waves radiate isotropically?

Do gravitational waves radiate equally in all directions? If so, is this an inherent property of all gravitational waves or is it just due to how they are normally produced? In other words, in a ...
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41 views

Showing classical spin tensor is time independent for free particle

Reading through Weinberg's gravitation book, the following definition is given for the spin tensor (Pauli-Lubanski psuedovector): $$ S_\alpha = \frac{1}{2}\epsilon_{\alpha\beta\gamma\delta} ...
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24 views

How does a linearly polarized spin 1/2 wave look like?

Spin 1 waves are easy to illustrate and a linearly polarized spin 2 wave looks like this, but what is the counterpart for a spin 1/2 wave?
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66 views

What type of fields are continuous spin representations?

Continuous spin representations (infinite dimensional representations of the Lorentz group) are pretty rarely discussed, and usually not in that much mathematical details. And usually it is done in a ...
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18 views

Precession or projection?

A spin of 1/2 in a magnetic field is known to rotate around the direction of the field. But then it is also stated that it must be projected spin up or down. Is this simultaneous or happens after ...
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58 views

A few questions on quarks, gluons and the strong force

I wanted to answer for myself some pretty fundamental questions pertaining to the strong interaction, color charge and quarks, but I'm sort of stumbling on a few. So I wanted to find the ...
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77 views

Does electron spin? [duplicate]

Spin quantum number I was reading above article on spin quantum number. It says Uhlenbeck, Goudsmit, and Kronig introduced the idea of the self-rotation of the electron, which would naturally ...
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2answers
61 views

Why doesn't precessing a spin cause a measurement?

When an electron is placed in a magnetic field, its spin precesses. Why doesn't this reveal the spin via angular momentum being transferred into the environment? Impractical Thought Experiment ...
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24 views

Counting states

Assume we have 6 particles, 3 with spin $\frac{1}{2}$ and another 3 with spin 1. The particles are distinguishable. The energy of a spin s is $\epsilon=-s \mu H$. How many energy states the system ...
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37 views

The quantum state measurement in the eigenbasis of unknown hamiltonian

Let's say we have some physical system in the unknown hamiltonian $H$, which can be represented with the sum of Pauli matrices. For one two-level system it can be set as $H \propto \vec{n}\vec\sigma$, ...
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1answer
36 views

Does the electrons in Stern-Gerlach aplliance change their energies and how?

When an electron goes thru a Stern-Gerlach appliance it changes its spin projection. Then there must be a change of energy content of the electron due to this event. But it is also known that magnetic ...
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20 views

Clarification: non-relativistic fine structure of a one-electron atom

The fine structure energy shift (in the non-relativistic limit) for a single-electron atom due to spin-orbit coupling is given by $$\Delta ...
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2answers
72 views

Calculating the expectation value of spin [closed]

Consider the state-space with a base formed by the eigenstates of the operator $\hat{S}_z$. For the state $|\phi\rangle=\frac{1}{\sqrt2}|+\rangle_z-\frac{1}{\sqrt2}|-\rangle_z$, what is the value ...
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9 views

Lorentzian nature of reflected microwave power in Electron Spin Resonance

Reflected microwave power has Lorentzian shape when plotted against frequency in ESR. How to mathematically prove this?
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1answer
53 views

Decoupling coupled differential equations in dynamically coupled two state system

Consider the following dynamically coupled two state hamiltonian, $$H=-B\sigma_z-V(t)\sigma_x.$$Taking the eigenfunctions of $\sigma_z$ ($|+>$ and $|- >$) as basis vectors, we have the wave ...
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12 views

Counting the possible states for an electron configuration

How do you find the terms and energy levels for the electron configuration $(n_1p)(n_2 p)(n_3 s)$ in the case of LS coupling, where $n_1, n_2$ and $n_3$ are different? How do you find the number of ...
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Change in Q factor on tuning external magnetic field in Electron spin resonance experiment

Does the Q factor of the cavity resonator show a dip at the resonant value of the external magnetic field while performing an ESR experiment?If so, what is the physical reason behind it?
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1answer
17 views

Connection between singlet, triplet two-electron states and the Slater determinant

I'm confused about a number of things concerning two-electron systems and spin. Here is (perhaps too much) exposition, skip to "the problem" if you want: Consider the helium atom in the simplified ...
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42 views

Collective angular momentum , Dicke states and indistinguishable particles

During course of quantum mechanics we dealt with addition of angular momenta. If we have two particles with spin $j_1$ and $j_2$ we can introduce total spin operator: $$\mathbf{J} = \mathbf{j}^{(1)} ...
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51 views

Can particle quantum spin be described with a wave function? [closed]

I'm a little confused about the idea of spin. It's been non-technically described to me as "like magnetic dipole moment", except only two possible "directions". But I feel like that's a bad analogy, ...
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40 views

Addition of $N$ spin halves

If I have two spin-halves, then \begin{align} \frac{1}{2} \otimes \frac{1}{2} = 0 \oplus 1. \end{align} If I have three spin-halves, then \begin{align} \frac{1}{2} \otimes \frac{1}{2} \otimes ...
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67 views

Stern-Gerlach experiment with Bosons

I'm new to this forum and I'm studying semiconductor physics at the moment. I just wanted to ask a thing about the concept of spin: when it was studied for the first time, in the Stern-Gerlach ...
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Explanation of absorption from Bloch Equation

Suppose in a magnetic resonance experiment the microwave/rf field is applied in x-direction.How to say that the component of magnetization which is out of phase with the microwave magnetic field leads ...
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108 views

A spin zero graviton?

Why can the graviton not be a spin 0 particle? On a similar note why can it not be a spin 4, spin 6 particle?
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27 views

Is it possible to measure the spin of an electron without moving it?

I know that the position and spin operators commute, so it is theoretically possible. What I want to know is, what experiments currently exist that achieve this?
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Why is a particles magnetic moment proportional to its spin?

the magnetic moment of a particles is given by, m=kS, where k is a constant the gyromagnetic ratio but where does this equation come from, is it just from experiments?
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52 views

Non coherence of Fermions and Bosons through $U(1)$

I "know" the textbook answer why we cannot write, $$ |\psi\rangle = a|j=\tfrac{1}{2}\rangle + b|j=1\rangle $$ as "each term in the quantum superposition transforms differently under $U(1)$", $$ ...
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29 views

Spin Orbital Coupling matrix in p-orbital basis

So I have the following Hamiltonian inherited from atomic Physics: $H_{SOC}=\alpha \vec{L}\cdot \vec{S}=\frac{\alpha}{2}(L^{+}\sigma^{+}+L^{-}\sigma^{-}+ L^{z}\sigma^{z})$ Where L is the angular ...
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75 views

What is a soft photon?

I accidentally came across the words "soft photon" today after reading a few blogs. There was some discussion of special situations involving gauge redundancies and a theorem by Weinberg. What is a ...
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41 views

Why does a magnet loose magnetic strength when heated?

Magnet manufacturing companies, for example Dexter Magnetic Technologies do not hesitate to explain the effects of heat upon magnets - citing how it degenerates the magnetic properties with levels of ...
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29 views

Spin Orbit Coupling Hamiltonians

I am really struggling with something fundamental. I keep coming across two versions of the hamiltonian for spin orbit coupling: $H_{soc}=\frac{\mu_B}{2c^2}(v \times E) \cdot \sigma $ $\mu_B =$ ...
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Do bosons and fermions produce the same interference pattern in a double slit experiment?

I have read that when bosons interfere they do so by adding the probability amplitudes, then I read that when fermions interfere they do so by subtracting the probability amplitudes. The usual double ...
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1answer
30 views

Uncoupled and coupled bases for electrons in hydrogen atom?

I'm given that for an electron in a hydrogen atom, $L=2$ and $S=1/2$ (quantum numbers associated with $L^2$ and $S^2$). I'm also given that for the uncoupled representation, the basis function is ...
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Expressing Spin State |r> As Linear Superposition of |u> and |d>: Basic Linear Algebra?

Background This question, from Quantum Mechanics: The Theoretical Minimum started with the following assumption(?) $$|r\rangle = \frac{1}{\sqrt 2}|u\rangle + \frac{1}{\sqrt 2}|d\rangle$$ I'm now ...
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1answer
122 views

What experiment would you perform to establish that the photon has spin 1?

I see that you can use a Stern-Gerlach apparatus for massive particles that can be deflected, but that doesn't work for photons. What would you do instead to measure photon spin in a lab?
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Why does parahydrogen have a lower energy than orthohydrogen?

I found this on the wikipedia page on spin isomers of hydrogen: Parahydrogen is in a lower energy state than is orthohydrogen. It seem almost like it is obvious but I am having trouble reasoning ...
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New Ideas for a observable Quantum Spin experment

After hearing about the new state of matter-Quantum Spin Liquid, I got interested in how these experiments would take place and what is expected to be observed. After searching for some videos online ...
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How can an oscillating spin current in a nanostructure be observed or measured?

Through calculation it's predicted there's pure spin current oscillating in a nanostructure. Here by "pure" I mean the charge current is zero. One can imagine two electrons of opposite spin are moving ...
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33 views

the probability amplitude of a photon

In one of Richard Feynman's lecture, he says that the angle of amplitude of a given path depends on what time the photon is emitted from the source. How does the angle of amplitude depend on time ...
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How does the electromagnetic field of an electron and a rotating ball of charge behave in a co-rotating reference frame?

First time poster, hope I'm not breaking any rules. Basically I'm curious about how far the classical analogy of an electron as a rotating ball of charge can be stretched. The situation I'm ...
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1answer
76 views

How to manipulate higher spin systems (higher than spin 1/2) using a given operator?

I’ve been reading ¨Halzen, F., and A. D. Martin. Quarks and Leptons. New York: Wiley Text Books, January 1984. ISBN: 9780471887416¨, and I’d like some clarification of a concept, please: I’m ...
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55 views

Spin 3/2 along an arbitrary direction [closed]

Consider a particle of spin 3/2. Find the matrix for the component of the spin along a unit vector with arbitrary direction n. Find its eigenvalues and eigenvectors. I know that the general spin ...
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1answer
184 views

Spin state after boost

I am working through Weinberg's QFT book, and in problem 1 in chapter 2 I ran into copious amounts of algebra, so I am trying to "cheat" a little by using some assumptions, but am unsure of their ...
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76 views

Fermionic ladder operators [closed]

After reading Dirac's method for finding the eigen energies of a harmonic oscillator by means of ladder operators and commutation relations, I tried making some exercises on them. First I did a ...
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Is the spin of an electron based on its direction of angular momentum? [duplicate]

Is the spin of an electron based on its direction of angular momentum? Is it based on the right hand rule of angular momentum? Does Spin up means that the electron is spinning anti-clockwise and spin ...
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Basic Quantum Entanglement

Quantum entanglement means that multiple particles are linked together in a way such that the measurement of one particle's quantum state determines the possible quantum states of the other particles. ...