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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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Electromagnetsm, isospin, spin-1/2, and the early years of quantum mechanics question

An electron going around in a circular orbit produces a magnetic field because there is a varying electric field. But the electric field of the electron itself is a spherically symmetrical field. ...
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Hund's rules in Helium level scheme

If I am not wrong, Hund's rules state that: I) The highest $2S+1$ has the lowest energy. II) For a given $S$, the lowest $L$ has the highest energy. However, I have found in various textbooks the ...
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A puzzle about relativistic spin

I'm suffering from a confusion about relativistic spin. I don't believe my question has been asked before, and I'm sure I've made some silly mistake somewhere, but I can't spot it. So I'm appealing to ...
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Theoretical explanation on calculating magnetic moment of materials in quantum mechanics [closed]

Could someone please provide a comprehensive and in detail theoretical explanation of how to calculates the magnetic moment of a material(total magnetic moment and absolute magnetic moment) of a ...
Thejan Hasaranga's user avatar
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Why Consider Only Triplet States for Spin in $2$-Electron Systems?

I have a question regarding systems of 2 electrons and their spin properties. When the Hamiltonian of a system of 2 electrons can be written as a sum of two single-particle Hamiltonians that are ...
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The Sum of Squared Spin Operators [closed]

I heard someone casually saying that $S_{x}^2 +S_{y}^2 + S_{z}^2 =2$, as if it's common knowledge. Upon calculating it myself, I came to realize that since $S_{i} = \frac{\hbar}{2}\sigma_{i}$ and $\...
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What would be the outcome of an experiment wherein the spin of a qubit is measured in two or more orthogonal directions simultaneously?

Out of curiosity, I am seeing the Leonard Susskind’s Theoretical Minimum lecture series on YouTube and have just started watching the second lecture. As I understand so far, the qubit can have a spin ...
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Fermions in a infinite 1D well and spinorbital

I am learning quantum chemistry. To have a comprehensive understanding of the Slater determinant, I studied the classical problem of two indistinguishable particles in a 1D box with infinite barriers. ...
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Quantum intrinsic spin [closed]

In this Stanford lecture (YouTube, 15m 40s), Prof. Susskind claims that with the emission of a photon, reverse-aligned particles flip from down to up. But if that were the case, then... If a beam of ...
questing-monkey's user avatar
2 votes
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Orthogonal singlet states?

I recently encountered a problem where the inner product of the two product states $|0,0\rangle\otimes|0,0\rangle$ and $|\frac{1}{2},\frac{1}{2}\rangle\otimes |\frac{1}{2},\frac{-1}{2}\rangle$ ...
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Is there any specific terminology for this type of current in spintronics?

In spintronics, there are several types of currents: Spin-polarized current: The two spins flow in the same direction with unequal contributions. Perfectly spin-polarized current: Only one species of ...
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Split Pauli Four-vector as quadratic terms of spinors

If I have the Pauli Four-vector $$x_{\mu}\sigma^{\mu} = \left(\begin{array}{cc} t+z & x-i y \\ x+i y & t-z \end{array}\right)$$ with $\sigma^0$ as Identity Matrix. Is there some way to write ...
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-3 votes
1 answer
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Probabilistic behavior of quantum mechanics [closed]

In a hypothetical scenario, if I were to measure the quantum spin of an electron and it showed "up," and then I traveled back in time without changing the initial conditions, would measuring ...
Vishnu's user avatar
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Why is half-integer spin not observed classically? [duplicate]

It is usually stated that half-integer phenomena is purely quantum. The way in which "half-integerness" manifests itself seems very counterintuitive to me, or I simply do not understand it. ...
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How can rotation about Z be a superposition of rotations in X ($|\uparrow \rangle_z = |\uparrow\rangle_x + |\downarrow\rangle _x $) [closed]

I am fully aware of the mathematical form that relates spinstates when measured from different axes. For example the unnormalized relation: $$|\uparrow_z \rangle = |\uparrow_x \rangle + | \downarrow_x ...
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Why order matters when combining angular momentum

This seems like the answer should be trivial but when decomposing the direct product of 4 spin-$\frac{1}{2}$ states into a direct sum, one gets two singlets, namely $$\frac{1}{\sqrt{2}} \left(\mid{\...
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Boron triplet states

Is it possible to achieve the following electron configuration of triplets in Boron, if you were to align the spins by means of electric field, or magnetic field, or just electromagnetic radiation? [!...
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Decomposing physical degrees of freedom for spin-3 (Schwartz)

In section 8.7.2 of Schwartz, he decomposes the polarization vector for a massive spin-2 particle into 2 transverse and 3 longitudinal components, $$h_{\mu\nu} = h^T_{\mu\nu} + \partial_\mu (\pi^T_\nu ...
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Bell's inequality in Claude Cohen-Tannoudji's Quantum Mechanics Volume III

Claude Cohen-Tannoudji et al, Quantum Mechanics Volume III, 2020 edition, Chapter XXI.F-3-b.$\alpha$ (F-7) on p.2210 states $$\big\langle\hat A(a)\hat B(b) \big\rangle={\cal P_{++}+P_{--}-P_{+-}-P_{-+}...
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Can pilot wave theory explain the evolution and measurement of electron spin? [duplicate]

Pilot wave theory is usually employed to "explain away" the randomness of QM in the context of the motion of particles (the double slit experiment, scattering). However, what about other, ...
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Is intrinsic spin a quantum or/and a relativistic phenomenon?

Ok, this is my reasoning. I am probably making some wrong assumptions here, pls tell me where I am going wrong. Spin as a quantum phenomenon: Quantum phenomena disappear as the Planck constant goes to ...
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Identity for squeezing spin coherent state

Let $S_{\pm} := S_x \pm iS_y$ where $S_i$ are the spin operators satisfying the usual commutation relations $[S_i, S_j] = i\hbar \epsilon_{ijk}S_k$. In Kitagawa & Ueda (1993) it is claimed that $$...
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Scaling equation for the external field H in an Ising like system [closed]

i want to show that the following relation is true for the external field H, starting from the scaling form of the free energy. It is an Ising like System close to a critical point with $M \geq 0$ and ...
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Photoelectron and electron in photoelectric effect [closed]

Could you please help me find some answers, as I have been stuck in this for a while and didn't get understandable answers. what is the difference between the photo electron and an electron. The ...
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Fourier transform of spin Matsubara Green function

Is the spin Matsubara Green function of a generic spin operator (or product of spin operators) bosonic? How can one obtain its frequency decomposition?
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Magnetic moment of two electrons

For two electrons in the sate with S=1 and Sz=0, do we have a magnetic moment? Because the spin on the z axis is zero, thus if we couple it with a magnetic field on the z-direction we get zero.
MTYS's user avatar
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Elastic scattering and conservation of spin

I am trying to understand conservation of spin in QED elastic scattering in these nice notes (VJ Martin, Particle Physics, Spring 2012, University of Edinburgh): https://www2.ph.ed.ac.uk/~vjm/Lectures/...
Mister Mak's user avatar
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What does it mean to carry 'a fraction of the proton's spin'?

The proton spin crisis is an open problem in physics regarding the origin of the spin of the proton. The problem is described as some "fraction of the proton's spin" being unaccounted for. ...
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Why ionization energy of oxygen dips moving from nitrogen to oxygen if the total spin decreased?

How does spin-orbit splitting also affect this or anomalous zeeman effect or decrease in spin when you move from Nitrogen to Oxygen? Bad Teacher: The addition of the second electron into an already ...
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When You place a bunch of electrons on a handkerchief by rubbing can you influence their polarity orientations by a strong magnet? [closed]

We all know that we can basically obtain a considerable number of charges on a material just by mechanical work.When all of that electrons are for a time period in one place can we orient all of their ...
Krešimir Bradvica's user avatar
1 vote
3 answers
501 views

Is spin a fundamental property of QFT?

I am not a physicist, but my understanding is that the Standard Model of particle physics is not the foundational model but rather is emergent from Quantum Field Theory (QFT), and that QFT is within ...
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Why can the spin operator $\hat{S}_\theta $ be defined using $ \hat{S}_x $, $\hat{S}_y $, and $ \hat{S}_z $? How can this be properly derived?

I'm trying to understand the rationale behind the spin operator $ \hat{S}_\theta $ along any axis that makes an angle $ \theta $ with the z-axis in terms of the spin operators $ \hat{S}_x $, $ \hat{S}...
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Spin 1/2 or spin 1, spin 2 systems? [closed]

I have a simple question of how to know what spin system my system has? For example, I am working with manganese monolayers on a metallic substrate. How do I know what is the spin state of Mn? I can ...
Vishesh Saxena's user avatar
2 votes
0 answers
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Variables dependency after unitary transformation

Currently working on tight-binding model with external field that induced an extra phase factor, e.g. Peierls phase $e^{i\frac{q}{\hbar}{\int_{\vec{r}_j}^{\vec{r}_i}}\vec{A}\cdot d\vec{r}}$ which will ...
まこと's user avatar
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Experimental liimits on torque free precession of spin?

Inspired by this question, I'd like to know what experimental limits there are on the torque-free precession of particle spin. This is a classical phenomenon, not part of quantum theory, but only ...
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Does the axis of spin of a particle also rotate?

As a physics enthusiast, I would like to ask about the following curiosities: Particles (that I understand as excitation in a "field") have this property called spin. I would like to ask ...
Jada's user avatar
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Photon Spin and Fermionic Fields

I have a question. It is said that the photon has spin 1. However, the spin of a fermion like the electron is 1/2. What I see is that the fermionic field has 4 fields, $$ \psi = \begin{pmatrix} \psi_{...
Julián Oviedo's user avatar
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What linear map are the Pauli spin matrices a representation of?

Let $T:V\rightarrow W$ be a linear map and let $\mathcal{A}$ and $\mathcal{B} $ be ordered bases for two $\mathbb{F}$-vector spaces $V$ and $W$. Then one can denote the matrix representation of $T$ ...
Caleb Williams's user avatar
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1 answer
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How to Perform Fourier Transform on a Quantum State of Spin-1/2 Particle?

I am currently studying quantum mechanics and need help understanding how to perform the Fourier transform of a particular state. I have a spin-1/2 particle whose momentum and spin state at time $t=0$ ...
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2 answers
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Expressing the spin-1/2 operators in terms of the quantum rotor variables

In this paper, a spin-1/2 Hamiltonian is introduced on a cubic lattice [Eq. (12)]: $$ H_c = -J \sum_{\Box} (S_1^+ S_2^-S_3^+S_4^- + \text{H.c.}), $$ where the sum runs over all plaquettes of the cubic ...
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Transforming spin operators into fermionic operators and finding their anticommutation relations

The Jordan-Wigner transformation (JWT) is a method used in quantum mechanics to map spin operators, which are typically associated with spin-1/2 particles, to fermionic operators, which describe ...
amirhoseyn Asghari's user avatar
2 votes
3 answers
61 views

Circular setup of Stern–Gerlach experiment and repeated measurements

Let us start with the standard Stern–Gerlach experiment which separates an electron beam either up or down as they pass through and are deflected by an inhomogeneous magnetic field. We can find the ...
QEntanglement's user avatar
1 vote
0 answers
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How to actually do calculations with the quantum-mechanical Heisenberg model?

The Heisenberg Hamiltonian in its simplest form is $$\hat{H}= \frac{1}{2} \sum\limits_{i,j} \hat{S}_i \cdot \hat{S}_j.$$ Normally, $\hat{S}$ is assumed to be a classical vector and from this ...
mathematica_guy's user avatar
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1 answer
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Alignment and anti-alignment of spins in magnetic field

Let's say that we spins in a very strong magnetic field. Then, the spins want to align in the same direction as the magnetic field due to torque being exerted on the spins. However, it may happen that ...
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Would it be possible to build the standard model in terms of Joos-Weinberg spinors?

The Joos-Weinberg equation describes spinors of arbitrary spin. Could we replace all of the existing matter fields (scalar, fermionic, gauge, Rarita Schwinger, etc.) with JW spinors and still end up ...
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Stern-Gerlach experiment questions

Assume that we have a Stern-Gerlach device for spin 1/2 particles, with the magnetic field and its gradient in the z-direction. I understand that if the spin is +1/2 then in the Heisenberg picture, ...
MTYS's user avatar
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0 answers
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What $(2+0)d$ classical model becomes the $(1+1)d$ Heisenberg model?

The $(1+1)d$ transverse-field Ising chain is closely related to the $(2+0)d$ Ising model. In particular, the $(2+0)d$ classical Ising model has a transfer matrix that can be written suggestively as $e^...
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Showing that the ground state of the Heisenberg ferromagnet is an eigenstate of the Hamiltonian

The Hamiltonian of a Heisenberg ferromagnet in terms of $S^+, S^-, S^z$ is given by: $$H = -\frac{1}{2}|J| \sum_{i,\vec{\delta}} \left[\frac{1}{2}(S_i^+S^-_{i+\vec{\delta}} + S_i^-S^+_{i+\vec{\delta}})...
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Describing two levels of a spin 1 triplet with zero field splitting as an effective spin 1/2

I am working with NV centers and there one can describe the groundstate triplet of the system with a Hamiltonian of the form: \begin{equation} H_e = D \hat{S_z}^2 + g \mu_B ( B_x \hat{S_x} + B_y \hat{...
mountim's user avatar
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1 answer
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Eigenstates of spin-1 Hamiltonian involving $x,y,z$ components

I am trying to find the energy eigenvalues and eigenstates of the spin-1 system with Hamiltonian operator $$H \enspace = \enspace a J_z^2 + b( J_x^2 - J_y^2 ) \quad , \qquad a, b \in \mathbb{R}$$ or ...
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