Questions tagged [quantum-spin]
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.
1,641
questions
0
votes
0answers
24 views
How physicists came to the conclusion that a photon has spin? [duplicate]
From Stern–Gerlach experiment, physicists came to the conclusion that each electron has spin. But from which experiment physicists came to the conclusion that a photon has spin and it is 1. If a ...
1
vote
0answers
37 views
Why the SUSY particles of fermions have spin 0 but not 1?
As the supersymmetric particles have spin which differs by half, why cant the superpartners have a spin = 1. Why does it always have to be 0?
3
votes
1answer
92 views
+150
The Spin Term of the Angular Momentum Tensor in Relativistic Quantum Mechanics
In Relativistic Quantum Mechanics, an Angular Momentum Tensor is defined ($J_{\nu \mu}$). This tensor is divided into two terms, one responsible for the spin angular momentum ($S_{\nu \mu}$) and one ...
0
votes
3answers
113 views
Would a metamaterial change its properties if one used different isotopes of an atom in its construction?
Given one had a metamaterial of a given type, containing some limited types of elements... if one were to use just one isotope of a given element (assuming it had more than one) in the construction ...
0
votes
0answers
28 views
Transitions between states
In the time dependent perturbation theory, transition between two states requires time dependent hamiltonian, V(t).
The question is, why the constant or time independent perturbation does is not ...
0
votes
0answers
28 views
Interaction (Dirac) picture and time dependent perturbation theory
Why in many, if not all, references that discuss the time dependent perturbation theory, they start the discussion with the interaction (Dirac) picture, although, what we need is only solving the time ...
2
votes
1answer
63 views
Does spin angular momentum change with reference frame?
I am guessing that the angular momentum of a particle measured by different inertial observers (no gravity) is different. At the same time, since quantum spin is an intrinsic property,
Is it true ...
0
votes
0answers
36 views
What is the Schrodinger equation of $n$th spin particle? [closed]
I get those equations from this https://readingfeynman.org/tag/schrodingers-equation-for-spin-1-particles/
The schrodinger equation for spin zero particle like pion
$$i\hbar\frac{\partial \psi}{\...
-1
votes
0answers
36 views
Creation $n$-particle states [closed]
The n-particle states are defined by the creation operators on the vacuum state
orthonormalized
How we prove that the n particle states are ?
How we prove:
7
votes
2answers
349 views
Spin drift velocity?
I am currently reading this Phys Rev paper by H C Torrey. In this paper, he derives the Bloch equations with an additional diffusion term. He says that the current density is given by
$$\mathbf j_{\...
0
votes
2answers
33 views
Addition of two angular momenta
In addition of angular momenta, does both the relations depict the same thing?
$$
\vec{J} = (\vec{J_1}\otimes 1 +1\otimes \vec{J_2})
$$
$$
\vec{J} = (\vec{J_2}\otimes 1 +1\otimes \vec{J_1})
$$
32
votes
3answers
2k views
Why can interaction with a macroscopic apparatus, such as a Stern-Gerlach machine, sometimes not cause a measurement?
Consider a Stern-Gerlach machine that measures the $z$-component of the spin of an electron. Suppose our electron's initial state is an equal superposition of
$$|\text{spin up}, \text{going right} \...
0
votes
1answer
619 views
Spin conservation in $\beta^+$ decay
In $\beta^+$ decay, a proton (consisting of 2 up and 1 down quarks) decays into a neutron (1 up and 2 down quarks), a positron and an electron neutrino.
(Image source: https://commons.wikimedia.org/...
2
votes
2answers
321 views
Deriving the Pauli-Schrödinger equation from the Dirac equation
Since the Schrödinger Pauli equation describes a non-relativistic spin ½ particle. This equation must be an approximation of the Dirac equation in an electromagnetic field. I was trying to derive this ...
-1
votes
1answer
18 views
How to get the quantum state from total spin? [closed]
I have total spin is S=2 (from nuclear spin S=3/2 and electron spin S=1/2). How can I get the quantum state?
0
votes
1answer
74 views
$N$ identical spin 1/2 particles [closed]
In the answer of the question below, I have two doubts:
$1.$ why we divide by $2$ in the square bracket?
and
$2$. I know that the states I will need are $n=0, 1, 2, ..., N/2-1$, but why in the ...
7
votes
1answer
190 views
Direct measurement of $\mathbf S^2$
For concreteness, consider two spin-1/2 particles with spin vectors $\mathbf S_i=(S_i^x,S_i^y, S_i^z)$. The total Hilbertspace is four-dimensional, and as a basis we can take the (simultaneous) ...
1
vote
1answer
128 views
Correct Visualization of a Spin Wave in a Ferromagnetic material
One way of describe a ferromagnetic material is the Heisenberg hamiltonian
$ H = -\frac{J}{2} \sum_{<i,j>} $S$_i$S$_j$
where $J$ measures the interaction between spins (positive for ...
8
votes
2answers
441 views
What exactly does the belt/plate trick demonstrate?
I am reasonably familiar with the math behind spinors, the fact that $SU(2)$ is the universal (double) cover of $SO(3)$, etc.
I've often seen the "belt trick" and the "plate trick" used to motivate ...
0
votes
1answer
76 views
Why does spin determine particle statistics?
I understand that "spin" refers to the intrinsic angular momentum of a particle, which relates to the magnetic moment of a particle. I mostly follow the "Background" section of the spin-statistics ...
-2
votes
0answers
22 views
Commutation relations spin operators
How can I prove
$S_{i}^{+}S_{i}^{-}+S_{i}^{-}S_{i}^{+} =1$
?
Could it be because if I am using spin-1/2 particles the spin operators obey fermionic anti commutation relations?
0
votes
0answers
36 views
Angular momentum conservation of muon decay
In the (anti-)muon decay process from the weak interaction, specifically
$\mu^+ \rightarrow e^+ + \nu_e + \bar{\nu}_\mu$
how should I address the angular momentum conservation in the muon rest frame?...
0
votes
1answer
86 views
What's the difference between spinor and spin?
Some related information might be found here: What is the difference between a spinor and a vector or a tensor? and Wikipedia seemed to have an explanation but was not very clear.
From what I read, ...
3
votes
2answers
87 views
How would you calculate the ratio of electric repulsion between two electrons and magnetic attraction?
Electrons have both magnetic dipole moments and charge. Two electrons separated by a distance would repel electrically but it stands to reason they would rotate their spins so their magnetic poles ...
3
votes
2answers
367 views
What is a scalar particle?
I was studying particle physics and I saw the word "scalar particle" many times, also in books. On the internet there wasn't any thing about it.
So can anyone say what is a scalar particle ?
1
vote
0answers
56 views
How is it known that a photon has a spin of 1? [duplicate]
I have heard that a photon has a spin of 1 compared to the electron's spin 1/2 but photons have no charge and therefore they should also have no magnetic field. Electron's spin is known because it's ...
2
votes
2answers
547 views
Rabi problem for a spin-1 particle
I'm trying to solve, analitically, the transition probability of a spin-1 particle in a magnetic field
$$
\vec{B}=B_0\hat{k}+b(\cos{\omega t}\hat{i}+sin{\omega t}\hat{j}).
$$
In particular I want to ...
-1
votes
1answer
59 views
Why do antineutrinos have a spin of 1/2? [closed]
When the isotope Nitrogen-14 (which has a nuclear spin of 1) undergoes beta decay, it releases an electron, which has a spin of -1/2. Since the mass of the Nitrogen-14 isotope stays the same (albeit, ...
4
votes
2answers
173 views
Why does a photon have spin 1?
Are we taking the photon spin to be one to describe electromagnetic force or there is any equation (is it relativistic Schrodinger or Dirac equation?) with a solution that tells us that its value is ...
0
votes
1answer
35 views
Spin of the particle and degrees of freedom
Wigner showed that irreducible representations of the Poincare group can be listed, depending of the mass being zero or larger then zero, as $2J+1$ dimensional representations where $J$ is half-...
0
votes
1answer
143 views
Why does a spinning nucleon generate a magnetic field?
I am trying to understand how NMR works, but I am not sure why a spinning nucleon produces a magnetic field. Is this a consequence of the quark structure inside?
1
vote
1answer
108 views
How to theoretically/experimentally prove that spin can not be treated as a classical (rotational) motion? [closed]
As well known, spin could not be thought of as a rotational motion in classical mechanics, i.e. it's an intrinsic property.
But how to prove it? i.e. how to mathematically/experimentally show that ...
13
votes
5answers
2k views
What are some useful ways to imagine the concept of spin as it relates to subatomic particles?
The answers in this question: What is spin as it relates to subatomic particles?
do not address some particular questions regarding the concept of spin:
How are some useful ways to imagine a ...
13
votes
1answer
899 views
Did the Feynman heuristic of “simple effects have simple causes” fail for spin statistics?
Someone here recently noted that "The spin-statistics thing isn't a problem, it is a theorem (a demonstrably valid proposition), and it shouldn't be addressed, it should be understood and celebrated."
...
0
votes
1answer
50 views
Is it possible for a charged particle to have no spin? [duplicate]
Can a charged point particle ever have spin zero? If not why?
13
votes
4answers
2k views
Why are there no elementary charged, spin-zero particles?
In the spirit of a related inquiry, I would like to know if there's a basis for understanding why there aren't any elementary particles that have non-zero electric charge but zero spin?
Can such a ...
0
votes
0answers
10 views
Measurement of spin correlation and polarization
I have a project about measurement of spin polarization and correlation of top quark pairs. I am gonna analyze real collision data from LHC. Before that I had one class about undergraduate level ...
0
votes
1answer
17 views
An explanation for the form of the spin component operator for a measurement made at an angle in the $x$-$y$ plane
I have three Pauli spin matrices corresponding to the spin states along each Cartesian axis. For some rotation about $\Phi_n$ about the $z$-axis we have:$$S_n=S_xsin(\Theta)cos(\Phi) +S_ysin(\Theta)...
1
vote
1answer
70 views
Is it possible to increase the orbital angular momentum (OAM) of a photon?
When the photon is emitted, can you change the angular speed? This has been experimented with vortex beams but I don’t quite understand how it works.
Also, an optional follow up question, would a ...
1
vote
0answers
37 views
Spin Hall effect
I am trying to understand the paper by Dyakonov and Perel (1971) "Possibility of orienting electron spins with current", but cannot see how they obtain the phenomenological equations for spin density ...
1
vote
1answer
160 views
Supersymmetry beyond $D=11$ spacetime dimensions
Taking into account the higher spin theories, from which string theory is an effective field theory, I just wondering if there is something to do to extend supersymmetry to any dimension without any ...
3
votes
1answer
74 views
Existence of spin-$\frac{1}{2}$ representation corresponds to $\text{SO}(3)$ having double cover?
I come across this article:
https://skullsinthestars.com/2016/03/29/1975-neutrons-go-right-round-baby-right-round/
I quote here a part of this article:
Spin 1/2 particles like the electron, ...
1
vote
2answers
198 views
Interpretation of Ising model simulations
I've been working on numerically solving the Ising model in a study of phase transitions, but I'm having difficulty finding material to help me discuss the results. I'm studying spontaneous ...
0
votes
1answer
21 views
Product states - Addition of angular momentum
In the book Quantum Mechanics - Franz Schwabl, in chapter 10, equation (10.4) says
Since all the properties of angular momenta and their eigenstates hold for the total angular momentum J .We can ...
2
votes
1answer
113 views
Don't the magnets slip and turn in Stern-Gerlach experiment, if their orientation is not aligned with the applied magnetic field?
I was watching two videos on YouTube:
In this video, there is an attempt to explain what spin is, using analogy of magnets. But here it is shown that magnets which are not aligned with magnetic field ...
0
votes
1answer
60 views
Is quantum entanglement contradictory with Schrödinger's cat?
As I understand, an electron spin is in a superposition state until the spin is observed. Due to the observation, it will either be spin up or spin down.
Due to quantum entanglement, if one electron ...
1
vote
1answer
63 views
Spin of electron using Levi Civita symbol
Problem is probably trivial, but I can't seem to find a fault in the argument.
If we write the Dirac equation as
$$(c\vec{\alpha}\cdot \mathbf{p} + \beta mc^2) \psi = i\hbar \frac{\partial \psi}{\...
2
votes
0answers
82 views
Making sense of the Pauli equation's notation
The Pauli equation is the generalization of the Schrodinger equation to charged particles in an electromagnetic field. It is written in a very compact way with heavy use of operators, so it can be ...
2
votes
1answer
56 views
Decomposition of spherical harmonics via Clebsh-Gordan coefficients
The tensor product of two states with spin can be decomposed into irreducible representations via Clebsh-Gordan coefficients
$$|j_1, m_1, j_2, m_2 \rangle = \sum C^{JM}_{j_1, m_1, j_2, m_2} |JM\...
-3
votes
2answers
167 views
How according QM do permanent magnets rotate?
When two magnets are placed close to each other they turn and orient parallel. I suppose this is due mostly to spin of the unpaired electrons. But in QM a spin just orients up or down. 1. How are ...
