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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Which book (or article) has detailed calculation for Quantum Heisenberg Model for three or four spins? [on hold]

A I need to write a program to calculate Quantum Heisenberg Model for any number of spins (with or without external magnetic field). I know how to do this calculation for two spins. Which book (or ...
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What is the value of the inner product $_x\langle+|-\rangle$?

I know that $\left|_x\langle+|-\rangle\right|^2 = 1/2$, so is it just as simple as taking the square root of $1/2$? Thanks.
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Why is it that the Callan-Gross relation predicts that quark has spin 1/2?

I'm studying deep inelastic scattering, and currently at the part where they say the Callan-Gross relation: $$F_1 (x) = \frac{1}{2x} F_x (x)$$ where $F_1$ and $F_2$ are the dimensionless structure ...
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Finding energy Eigenvalue from two spin Hamiltonian

Let's consider a system of two spins, named spin 1 and spin 2. Let's also consider, in a Hamiltonian, spin part has been defined as $\sigma_1 \cdot \sigma_2$. For example: $$H= E_0 + \sigma_1 \...
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Representation of spin-$1/2$ operators in terms of Majorana fermions

I am reading Quantum Field Theory in Condensed Matter Physics by A.M. Tsvelik. In Chapter 20, it is claimed that introducing three Majorana fermions $\gamma^\mu_i$ on each site $i$ of the lattice (...
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What differences would be observed in the Stern-Gerlach experiment when using neutral fluorine (Z=9) and neutral sodium (N=11)

I have been working through some past exam papers for my Quantum Mechanics module, and one of the questions is what would be different about observing the results of the Stern-Gerlach experiment when ...
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Hydrogen hyperfine structure from H2-molecule, interacting H-atoms or independent H-atoms?

On hyperphysics the hyperfine structure of hydrogen is compared to that of deuterium: According the Hyperfine structure on Wikipedia In atoms, hyperfine structure arises from the energy of the ...
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Interaction between electrons in which the magnetic dipole moments interact more strongly than their electric fields

Asking a question Has anyone tried to incorporate the electrons magnetic dipole moment into the atomic orbital theory?, I was curious whether anyone has attempted to relate the intrinsic property of ...
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Trying to understand spin in quantum mechanics

I'm trying to understand the concept of spin in Quantum Mechanics. I'm reading "Road to Reality" by Penrose, which despite not being a textbook, is reputed to give one a deep insight into physical ...
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Electron to electron interaction

I am interested to know if it would be possible to calculate the magnetic attraction between two electrons at zero space between their magnetic poles against electrostatic repulsion between them in ...
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How does angular momentum get quantized? [duplicate]

We know that the magnitude and direction of angular momentum is quantized in quantum mechanics. We can explain the quantization with the help of quantum numbers. But actually who is responsible for ...
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Does spin add energy to a quantum mechanical system?

If a particle (let's say an electron, a 1/2 spin particle) has spin component $S_z=\hbar/2$. Does the spin contribute to the total energy of the electron? For example, without considering the spin, ...
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Confusion about Stern-Gerlach experiment

Why does the particle always have the same spin magnitude $\pm \frac{1}{2}\hbar$? In classical mechanics we can split a vector into components but in quantum mechanics due to uncertainty principle ...
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What is the (triplet) eigenstate for two electrons? [duplicate]

Let's assume I have a harmonic oscillator which is one dimensional. What is my plan is to work the the two electron's spin states and my requirement is that they have to be in the triplet sates. Lets ...
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Mathematical Rigorousness of Taking the Thermodynamical limit of a finite size quantum model

Suppose I have nearest Neighbour Quantum Ising model with a transverse field. $$\hat{H} = \sum_{i}S^{x}_iS^{x}_{i+1} + h\sum_i S^{z}_i$$ Through Jordan-Wigner and Bogoliubov transformation, one finds ...
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zero spin particles' spin states

We know that the full wave function of spin particles have two parts. One is the spin part and another is the spatial part. Let's assume I have given a wave function which is the spatial part: $$\...
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Question about choosing the time reversal operator

According to the "QFT Nutshell" page 102-104 about Time reversal, the author said about applying the time reversal to the spin 1/2 system. Let $T=UK$, where $K$ complex conjugates everything to ...
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Gravitons from linearized gravity

Linearizing gravity as follows: $$ g_{\mu\nu}=\eta_{\mu\nu}+h_{\mu\nu} $$ Up to this point, everything is a 4x4 matrice. How does one eventually recover a spin-2 particle which, according to https:/...
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Stern-Gerlach experiment interpretation [on hold]

It seems to me there is a problem with the usual interpretation of the Stern-Gerlach experiment. Sending a magnetic dipole on a path through a magnetic field would, on classical assumptions, affect ...
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Quantum Monte Carlo Loop Algorithm for quantum spin: why is the freezing graph present in ferromagnetic Ising model?

I study the loop algorithm (Evertz et al). I cannot understand, why the freezing graph type where we have to flip all 4 spins together is not present for the quantum-XY model and the anti-/...
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Has anyone tried to incorporate the electrons magnetic dipole moment into the atomic orbital theory?

The Pauli exclusion principle is related to the electrons spin. The quantum numbers are complete only with the spin quantum number. I am curious whether anyone has attempted to relate the intrinsic ...
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38 views

What magnetic interaction makes spin not conserved?

If $[S_i,H]\neq0$ or $[S^2,H]\neq0$, we might say spin is not a good quantum number in the system. But is there any more practical or detailed criterion? Or certain families of magnetic interaction ...
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Trouble understanding Sakurai's calculation of $\exp\left(\frac{iS_Z\phi}{\hbar}\right) \;S_x \; \exp\left(\frac{-iS_Z\phi}{\hbar}\right)$

I'm having some trouble with a derivation in Sakurai's Modern Quantum Mechanics (specifically Derivation 1 on §3.2, p. 159), where he computes $$ \exp\left(\frac{iS_Z\phi}{\hbar}\right) \;S_x \; \exp\...
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Tunneling elements in the Hubbard model

Consider the tunneling Hamiltonian in the Hubbard model for a 1D lattice of quantum dots. $$\begin{align}\hat{H}_t=t\displaystyle\sum_{i,j,\sigma}c_{i,\sigma}^{\dagger}c_{j\sigma}+c^{\dagger}_{j,\...
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Spin vs orbital angular momenta in QFT

I couldn't find past answers that quite match what I wanted, so I will try to ask in slightly different manner. In QM, we have total angular momentum operator $\vec{J}$ (I dropped the hat for ...
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Does electron affinity decrease with charging?

Lets consider two materials A having higher electron affinity than B while both are not too far off. If they are both insulators and A accumulate charges due to triboelectric effect. Than after a ...
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Why is there no state of total spin 0 for spin-1 and spin-2?

To my understanding, decomposing the tensor product of two particles with spins $s_1$ and $s_2$ works as follows: $$\mathcal{H_{s_1}}\otimes \mathcal{H_{s_2}}=\mathcal{H_{s_1+s_2}}\oplus\mathcal{H_{...
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Using entangled qubits to communicate [duplicate]

After reading up on quantum mechanics considering entangled qubits I was asking myself this simple question: If one qubit (A) positioned on earth is entangled with another qubit (B) which is - say - ...
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Are there compelling reasons not to organize the elementary particles by charge and spin? [closed]

I don't like the way the standard model is currently displayed (see second picture for reference). It does a poor job of abstracting the information into something understandable. As far as I ...
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Factorizing spin part and space of many electron wave function of an atom's ground state

I am trying to write the ground state wave function of a 10 electron atom as a product of space part and anti-symmetric spin part. $$1s\uparrow,1s\downarrow$$ $$2s\uparrow, 2s\downarrow$$ $$2p_{x}\...
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Quantum Mechanical Treatment of the Spin Echo

I'm trying to find the expectation value of the spin in the $y$ direction after applying a $\pi/2$-$\pi/2$ sequence of pulses. In Slichter's Principles of Magnetic Resonance, he does a $\pi/2$-$\pi$ ...
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Help with understanding Pauli matrices in specific Hamiltonian

I am trying to explicitly write out using matrices a Hamiltonian given in this condensed matter paper. In eq (3) of the paper, we have: $$ \hat{H} = a t (\tau k_x \hat{\sigma_x} + k_y \hat{\sigma_y} ) ...
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Gilbert original paper (1955) reference

I'm looking for the Gilbert's original paper where he derives the gyromagnetic Landau Lifshitz Gilbert (LLG) equation of motion from a variational principle. Most of the people cite: Gilbert, ...
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Does pseudospin break the crystal symmetry?

Pseudospin is a concept to describe a superposition of two quantum states. Sometimes, I see a pseudospin texture in the momentum space which breaks a crystal symmetry. A simple example is the ...
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In Energy Transition theory, what will happen after all spins flipped into $-z$?

For a spin-1/2 dipole the dipole can only be aligned parallel or antiparallel to the B0 field so the energy can take only two values. There are about 8 out of 2 million protons could be polarized. In ...
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Effect of different reference frame on quantum entanglement measurement

According to what I read about entanglement, when you measure the spin of one of the entangled particles all the possibilities collapse to one value immediately and the other particle will give the ...
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The stark effect of Hydrogen

I have read the stark effect of Hydrogen (calculating energy levels of the n=2 states of a Hydrogen atom placed in an external uniform electric field along the positive z-direction) from Quantum ...
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Exchange statistics from topology of configuration space

I'm trying to understand Leinaas and Myrheim's famous 1976 argument for exchange symmetry of the wavefunction. If we consider the configuration space $\mathcal{M}_2$ for two identical particles ...
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Scalar product of eigenstates of $\hat{S}_z$ and $\hat{S}_x$ operators

Suppose that $|s_z\rangle$ and $|s_x\rangle$ are eigenvectors of operators $\hat{S}_z$ and $\hat{S}_x$ correspondingly, with $s_z$ and $s_x$ being eigenvalues. Is there a known formula for the scalar ...
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Why the geometrical frustration (spin ice model) has never been studied in superparamagnetic size range?

I'm trying to understand the effect of geometrical frustration in assembly of superparamagnetic nanoparticles but I can't find any reference. Does anyone know how magnetism can be affected by ...
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When an electron changes its spin, or any other intrinsic property, is it still the same electron?

I am not asking why an intrinsic property, like spin can have more then a single value. I understand particles (electrons) can come to existence with either up or down spin. I am asking why it can ...
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Why can a renormalizable quantum field theory only include spin 0, 1/2 and 1 fields?

Hitoshi Murayama writes in his 221A Lecture Notes on Spin How do we choose spin when you introduce a field, then? A consistent ( i.e. , renormalizable) quantum field theory can include only spin 0, ...
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How does one determine the number of eigenstates of a system with a given spin? [closed]

I have had a true/false question in a practice exam stating: For a spin 3/2 system (S=3/2), there are only four spin eigenstates. which is true. (solutions) I do not understand how one can ...
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Entangled states and separable states

B Two electrons in the same orbital is clearly an entangled quantum state since it is not a tensor product: $$|\psi\rangle=\frac{1}{\sqrt{2}}(|\uparrow\rangle \otimes|\downarrow\rangle-|\downarrow\...
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Transformation under rotation for electrons and photons

For the question What all has intrinsic spin? it was answered that Spin is a number that tells you how the state of the object transforms under rotations. How I imagine such rotations for photons ...
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Is the magnetic dipole of the electron an intrinsic property?

The profound answer to the question How permanent magnets work? starts with Sub-atomic particles such as electrons, protons, and neutrons (and many others) have a fundamental quantity called a spin ...
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Does the Schrodinger Equation care about spin?

I have taken the non-relativistic limit of the Klein-Gordon and Dirac equation, and both have brought me to the Schrodinger equation. The Klein-Gordon equation describes spin 0 particles, and the ...
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Quantized value of spin angular momentum and underlying mysteries

I think the quantized value of the spin angular momentum is $\hbar/2 $ rather than $\hbar $ is the basic reason for the $4\pi$ rotation of a wave function to retain its initial state again? Is it true?...
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Position representation of spin states and spin operators

How can we represent a spin states $ \lvert S_x:+\rangle, \lvert S_y:+\rangle,\lvert S_z:+\rangle ,\lvert S_x:-\rangle, \lvert S_y:-\rangle $ and $\lvert S_z:-\rangle$ in position representation ...
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Why don't all electrons contribute to total orbital angular momentum of an atom?

There are 47 electrons in a Silver atom, but talking about its orbital angular momentum we only take the outermost valence electron which occupies the 5s orbital. Why don't the remaining inner 46 ...