New answers tagged quantum-spin
2
votes
Do protons and electrons actually precess?
Existing answers seem a bit unclear to me, so here goes...
Yes, they do precess. The easiest way to see this is in the average properties (also called expectation value). You can define a vector $\bf \...
- 56.5k
0
votes
How can a mean-field hubbard model describe itinerant ferromagnetism?
That is because apart from local Hubbard interaction there is a hopping term which induces interaction between different sites. Only both these terms lead to long range ferromagnetic correlation. For ...
0
votes
Why does spin acting along $x$ on the spin up state yield spin down?
One way to look at it is that $S_x$ is that since
$$
S_x|\alpha\rangle = \frac{\hbar}{2}|\beta\rangle,\\
S_x|\beta\rangle = \frac{\hbar}{2}|\alpha\rangle,
$$
then
$$
S_x\left(|\alpha\rangle \pm |\beta\...
- 57.4k
6
votes
Why does spin acting along $x$ on the spin up state yield spin down?
...What I'm stuggling to understand is why applying $\hat{S}_{x}$ to $\ | \alpha \rangle \ $ yields $\ | \beta \rangle \ $ from an intuitive perspective beyond just plugging in the for $\hat{S}_{x}$ ...
- 17.4k
0
votes
Accepted
Is there any measurement of electron spin that doesn't involve magnetic moment?
The electron is also and always a magnetic dipole. Its electric field (its elementary electric charge) is regarded as its outstanding property. If the history of the discovery of the electron had ...
- 10k
4
votes
Stern–Gerlach experiment - what's so strange?
When a magnetic dipole is deflected by the magnetic field it releases the potential energy as light as it comes to rest. We measure the amount of deflection and therefore the initial orientation of ...
- 705
2
votes
Stress-energy tensor spin-1 coupling
If you couple a field to the stress energy tensor in the Lagrangian, then you modify the stress energy tensor. For example, in linearized gravity, the Lagrangian contains a coupling $h_{\mu\nu} T^{\mu\...
- 46.3k
2
votes
Accepted
Decomposing direct product of spin-$s$ representation into direct sum
Here is the highest-weight idea:
Consider a $2j+1$ representation of $su(2)$ with states $|j,m\rangle_1$, along with another $2s+1$ representation $|s,m'\rangle_2$, consider
$$|j\rangle_1 |s\rangle_2 =...
- 3,930
1
vote
Does the electromagnetic field "spin"?
An electromagnetic field has no charge or current and cannot ct as the source of another electromagnetic field. Hence, an electric field can never generate a magnetic field.
What Faraday's law means ...
- 22.8k
2
votes
Confusion about spin in 1 dimension
As you point out, there is no rotation group in 1 dimension. Spin must obey the same Lie algebra/group as angular momentum. You cannot have it in a dimensionality that cannot support the other.
So ...
- 60.3k
1
vote
Theoretical calculation of Electron Paramagnetic Resonance (EPR) spectra
Your instincts are largely correct, but I'll clarify and provide some additional context for electron paramagnetic resonance (EPR) or electron spin resonance (ESR) spectroscopy. In EPR/ESR ...
- 41
1
vote
How to derive the projection operator for multiple spins in terms of spin operators?
The projector
$$
P_j = \sum_{m=-j}^{j}\left|j,m\right>\left<j,m\right|
$$...
For two spin-1/2 I can have the three projection operator as follows:
$$
P_0 = 1/4 - \vec S_1 \cdot \vec S_2\\
P_1 = ...
- 17.4k
2
votes
Accepted
How to derive the projection operator for multiple spins in terms of spin operators?
If you are restricting to the space of two spin-1/2 particles, then the reason goes as follows. (We set $\hbar=1$.)
It is a fact that
$$
\vec{S}_1\cdot\vec{S}_2 = \frac{1}{2}\left(S^2-S_1^2-S_2^2\...
- 6,879
1
vote
Spin/Helicity-Density Matrices in Particle Physics
Up until now the most useful texts I found are:
[1] "Spin Formalism and Applications to New Physics Searches", by Howard E. Haber (https://arxiv.org/abs/hep-ph/9405376)
[2] "...
2
votes
Accepted
Theoretical calculation of Electron Paramagnetic Resonance (EPR) spectra
Yes in theory, while varying $B_0$ might initially seem more computationally intensive than varying B₁, modern EPR equipment and software have made both approaches relatively straightforward. The ...
- 676
1
vote
Accepted
Bloch vector, maaster equation, and Bloch equation
The idea is to expand a density matrix in terms of a set of matrices that can serve as a basis. For an $n\times n$ matrix, one needs $n^2$ such matrices. It turns out that the generators in the ...
- 14.1k
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