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.

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Why do some factorized states have different probability than others in terms of Clebsch-Gordan coefficients?

When adding a spin-1 to a spin-1/2, we have a six-dimensional Hilbert space spanned by the factorized states $$ \left \{ \left | j_1=1, m_1 \right \rangle \otimes \left |j_2= \frac{1}{2}, m_2 \right \...
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How would a free particle with known spin evolve?

I searched a lot for a Hamiltonian of a pauli spinor with no potential energy but got no luck, so I tried deriving one my own. I took an overkill shortcut and used pauli's equation: $$i\hbar \frac{\...
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Stern-Gerlach experiment/magnets in relation to Wigner's Ideal Experiment

My question comes from a small section about Wigner's experiment in the book 'The Interpretation of Quantum Mechanics' by Roland Omnes. I've attached two pages below to show what I'm referencing. My ...
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Crystal field therory and high-to-low spin state transition

Following is a paragraph from one of the papers I am reading. In this paragraph, the author tries to compare the energy difference between high and low spin states for d6 and d5 ions. However, he/she ...
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Quantum Entanglement communication from bunker

When a proton is entangled with its pair when one measures a spin state the other measures an opposite. While this technique cannot be used for superluminal communication (communication across time) ...
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Physical Situations of Specific Stress Energy Tensor?

I'm having trouble picturing what the physical situation of a non-symmetric stress would be. Say I have a stress tensor $T_{ab} = \begin{pmatrix} T_{00} & T_{01}& 0 & 0 \\ 0&T_{11}&...
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Relationship between spin and wave-function (in geometric algebra)

I am interested in determining which 'feature' of the wave-function are responsible for fixing the spin of the matter is relates to; or more precisely, an "algorithm" or "procedure"...
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Why this Non-Hermitian Operation is non-existential?

Question is pretty simple, here is the first part. Consider a spin-1/2 particle. I have two polariser kind of device which detects their spin along the axis of polariser. (I am using polariser in a ...
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Energy of infinite number of particles in a box

I have N particles of spin $\frac{1}{2}$ and I know all of them are in the ground state, in an infinite potential well ( box $1-D$). I have to find the energy of ground state . also when $N \to \infty$...
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Combination of 3 spin $\frac{1}{2}$ particles to yield a state of net spin $\frac{1}{2}$

I did some prior research to this question on stackexchange before posting my question. Due to my limited knowledge in this field, I am not sure if my question is unique since there has been ample ...
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Some resources on quantising spin 2 fields in flat and curved space time

I want to understand how one can quantize spin 2 fields. Any resource which starts with a flat background before moving on to curved backgrounds would be great. So far, I have found this article but I ...
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Bogoliubov-Valatin transformation generalisation

Considering the following Heisenberg Hamiltonian (with spin $S$ , and $J<0$ for the case of an antiferromagnet) when we only consider interactions between first neighbors in a square lattice in the ...
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Why spin-aligned nucleons bind stronger together

Protons bind to neutrons only if their spin is parallel to each other. Is there an easy explanation for this? What force is responsable for this spin dependence?
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Problem in the derivation of the Landé $g$-factor

I was watching a lecture on Youtube (https://www.youtube.com/watch?v=NSac7cMQnJw&t=971s) where the professor derives the Landé $g$-factor for the weak-field Zeeman effect. As part of the ...
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$g$-Tensor of an electron

The $g$-tensor is said to take account of the crystal field, influencing measurements in ESR-experiments. There is a concrete formula from Gerloch and McMeeking to calculate the matrix-elements of the ...
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About applying the angular momentum conservation to $\beta$ decay or similar decays

Consider the $\beta^-$ decay: $$n^0\to p^++e^-+{\bar\nu}_e.$$ The spin angular momenta of all the particles are given by $$S_n=S_p=S_e=S_{\nu_e}=1/2.$$ Therefore, by the addition of the angular ...
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Energy of Quantum Magnetic Dipole

When Amperian loop model is adopted, the energy of magnetic dipole under external field $\vec{B}_{ext}=B\hat{z}$ constitutes of 3 part: $-\vec{m}\cdot\vec{B}$ from work against mechanical force $\...
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Hamiltonian of an electron in a magnetic field

Suppose I have an electron in a magnetic field given by: $$\vec{B}=B\hat{z}$$ The potential energy of this system is given by: $$U=-\vec{\mu} \cdot \vec{B}=\frac{g\mu_B}{\hbar}\vec{S} \cdot \vec{B}$$ ...
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Can you measure an electrons spin in multiple ways before measuring its entangled partner?

One example of this is can you measure an electron for up/down spin, then for left/right spin before measuring its quantum partner for left/right spin again? I have tried looking for examples of how ...
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Why does general irreducible representation $(A, A)$ of a quantum field correspond to traceless symmetric tensor of rank $2A$? [duplicate]

I understand that under rotation, we will have components that transform like integer spin $(2A, 2A-1, ...... 0)$ from decomposition of $(A, A)$ representation. The scalar is the trace, therefore ...
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Spinor rotations - experimental confirmation [duplicate]

The map $$ S \in SU(2) \to R(S) \in SO(3) $$ is two-to-one. A rotation $ R(2\pi) = 1 $ acting on vectors in 3-space is the image of two rotations $ S(0) = 1 $ and $ S(2\pi) = -1 $ acting on spinor-...
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Do quantum measurements violate conservation laws?

When we measure the spin angular momentum of a particle in an axis different to its current spin, we change the direction of its spin, which taken by itself would be a violation of the law of ...
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Why electron spin align to the direction of magnetic fields?

If we consider localized and unpaired spins in a condensed matter system, the spins align to the direction of applied magnetic fields. We can calculate the magnetization by considering canonical ...
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Isn't There A Much Simpler Way To Explain Why Quantum Entaglement At Distance Isn't Utile - That Spins Already Exist & React To Detection Predictably? [closed]

Tell me if this concept works for explaining in a much simpler way, why purposeful entanglement outcomes like FTL communication cannot work - and without relying on complex analyses of 'spooky action',...
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Can a charged particle emit light because of their intrinsic angular momentum even when they are stationary?

Maxwell's laws state that an electric field in motion (here, possessing angular momentum) should produce a magnetic field and an electromagnetic wave (light). All charged particles with spin (...
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Pauli exclusion during an NMR or EPR pulse

If we perform a $\pi/2$-pulse on a pair of spins initally in the singlet state $|S\rangle = \frac{1}{\sqrt{2}}\big(|\uparrow\downarrow\rangle-|\downarrow\uparrow\rangle\big)$, in theory we arrive in ...
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Looking for Experimental Result Data for Bell's Inequality, especially at 60 degrees

I've been looking for an experiment (for Bell's Inequality, using Bell's 60 degree test angle) which shows counts and resulting correlation percentage calculated. I want to see if a) for 99 runs 66 ...
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Physical meaning of adding two spin operators

When we add who spin operators, one in $x$ and the other in $z$ direction, dose it make any physical sense? Do the eigenvalues of this sum is also equal to a sum of their eigenvalues?
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Why are composite particles grouped with force carrying particles?

This Huge confusion with Fermions and Bosons and how they relate to total spin of atom says a hydrogen atom is a boson. I'm confused. I thought bosons were force carrying - e.g. a photon, gluon, etc?
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Separability of an Hamiltonian with spin

I'd like to know if this Hamiltonian $\hat{H}=\frac{p^2}{2m}+\frac{1}{2}m\omega^2r^2+\frac{A}{\hbar^2}(J^2-L^2-S^2)$ is separable into two parts $H_1=\frac{p^2}{2m}+\frac{1}{2}m\omega^2r^2$ and $H_2=\...
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What is the probability of finding one spin of a doublet system as spin up

How can I calculate the probability of finding one spin of a doublet as spin up? Suppose I have the following system: $$|\psi\rangle=(|\uparrow\rangle \otimes |\downarrow\rangle + |\downarrow\rangle \...
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Exponential of sum of spin operators

Let us consider a system of two spins, each with spin $S$. Let $\vec{S}_1$ and $\vec{S}_2$ be the two operators representing the $\mathfrak{su}(2)$ algebra. Consider now the exponential of the square ...
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Thermally activated delayed fluorescence

In thermally activated delayed fluorescent (TADF) molecules, we consider 25% molecules in singlet first excited state and 75% in triplet, statistically, on electrical excitation after carrier ...
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Is the magnon dispersion equivalent to a plot of energies vs state number?

I am using QuSpin to plot spin-chain energies against their state number. I get discrete plots that look remarkably like the magnon dispersions. Are they the same? I don't think they would be because $...
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Isotope stability in alkali vs alkaline earth metals

Why do alkaline earth metal atoms (and those with similar atomic structure, like Yb and Cd) have more stable isotopes than alkali metal atoms?
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2 answers
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Why are fermionic atoms less prevalent than bosonic ones?

Many atoms have no stable fermionic isotopes. Those that do typically have more stable bosonic isotopes than fermionic ones. Furthermore, the fermionic isotopes of most atoms are lower in natural ...
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2 answers
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Could a non-pointlike structure of elementary particles explain their spin?

Elementary particles are considered point-like. Which makes the concept of spin rather problematic. It can neatly be described by group theoretical considerations, but that offers no explanation what ...
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The nuclear spins of alkali metals

Looking at the different isotopes of alkali metals and their nuclear spins, I notice that nearly all of their bosonic isotopes have nuclear spin of 3/2. Surely there must be an explanation in nuclear ...
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Symmetry of spin wave function

I know that for orbital angular momentum, the symmetry under interchange of two particles of the orbital wave function is $(-1)^{L}$. Also, for a two spin-$1/2$ system, if the total spin couples into ...
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4 answers
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Precise definitions for higher spin operators

I am trying to understand the matrices and vectors presented in this section https://en.wikipedia.org/wiki/Spin_(physics)#Spin_projection_quantum_number_and_multiplicity I am looking for a reference ...
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1 vote
1 answer
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Can one measure two components of spin exactly by measuring two components of entangled, say, electrons?

Of a single electron, two different components of spin can't be have simultaneously well defined values. But what if we entangle two of them and we measure, say, $(S_1)_z$ and $(S_2)_x$ simultaneously....
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2 votes
1 answer
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In Helium, why does more tightly bound mean the electrons are further apart?

In helium, the triplets ($S=1$) are lower in energy (more negative) than the singlets $S=0$. One reason given by my lecturer is that in a triplet the spins of the two electrons are the same, then by ...
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Why doesn't the Hydrogen atom, as described by the Dirac equation, collapse?

In Griffiths quantum mechanics, it's noted that the exact energies for the Dirac equation, involving fine structure, are $$E_{nj} = mc^2 \left\{ \left[1 + \left(\frac{\alpha}{n-(j+1/2)+\sqrt{(j+1/2)^2 ...
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2 votes
2 answers
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Why is the decay channel $H \to \gamma\gamma$ direct evidence that the spin of the Higgs must be different from one?

The title says it all really, I searched this website and came across a post with a question titled Why is the Higgs boson spin 0?. But it doesn't really answer my question in the title. But this next ...
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1 answer
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The mathematics of different particle rotations

So, in general (if I understand this correctly): Force particles behave differently than matter particles under rotation The matter particles need a 720° rotation to put them back into their initial ...
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Spin conservation in indirect optical transitions in bilayer TMDC

While I was reading this paper (https://arxiv.org/abs/2108.09129), I got confused with the spin conservation in optical transitions in bilayer 2D semiconductors. In figure 3(d), indirect transition ...
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How are we sure that the measured proton spin puzzle will be also observed similarly in the neutron thus a neutron spin puzzle?

The EMC experiment in 1988 using muons' deep inelastic scattering, has reported that the contribution of the valence quarks triplet (i.e. up-up-down) in the proton was measured to contribute as little ...
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If a spin singlet cannot change, how can it interact with electromagnetism?

Let's say there's a Hydrogen atom in a spin triplet state. $$ | \downarrow\downarrow \rangle$$ Now let's say a photon with spin 1 came along abs was absorbed by the atom. We don't know if the proton ...
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7 votes
1 answer
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How is a Bose-Einstein condensate produced from sodium atoms that do not have an integer spin?

In 1995 Wolfgang Ketterle at MIT produced a Bose-Einstein Condensate in a gas of sodium-23 atoms, but sodium-23 doesn't have an integer spin. How does this work?
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"Precession" of a free electron

I'd like to gain as deep of an understanding as possible of the following diagram from Introductory Quantum Mechanics, 4th ed., by Richard Liboff: I'm not looking for help with solving the easy ...
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