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Why Consider Only Triplet States for Spin in $2$-Electron Systems?

This is slightly strange. In any case what matters is that the fermionic states should be fully antisymmetric w/r to permutations of the particles, and that means spin and spatial degrees of freedom. ...
ZeroTheHero's user avatar
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1 vote

What would be the outcome of an experiment wherein the spin of a qubit is measured in two or more orthogonal directions simultaneously?

A measurement is a physical process that creates a record of some property of a physical system. Since a measurement is a physical process it is constrained by the laws of physics, which include the ...
alanf's user avatar
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0 votes
Accepted

Bell's inequality in Claude Cohen-Tannoudji's Quantum Mechanics Volume III

Let $$R(\theta):=\begin{bmatrix}\cos\frac\theta2 & -\sin\frac\theta2 \\ \sin\frac\theta2 & \cos\frac\theta2 \end{bmatrix},\ \theta\in \mathbf R, \quad D := \begin{bmatrix}1 & 0 \\ 0 & -...
Hans's user avatar
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2 votes
Accepted

Orthogonal singlet states?

Is there an issue in my reasoning or in my understanding of spin states? In both. You are abusing Dirac notation, meant to defocus from side issues and omit other labels (and bases of tensor calculus ...
Cosmas Zachos's user avatar
1 vote

Probabilistic behavior of quantum mechanics

If you have two identically prepared systems, say two copies of the state $ \alpha \vert \uparrow \rangle + \beta \vert \downarrow\rangle$, with $\vert \alpha\vert^2+\vert\beta\vert^2=1$, you might ...
ZeroTheHero's user avatar
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0 votes

Why is half-integer spin not observed classically?

Electron spin has been interpreted classically in the context of the theory of stochastic electrodynamics (classical electromagnetism + zero-point field - the field causing the Casimir force): Cetto, ...
Andrei's user avatar
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1 vote

Why is half-integer spin not observed classically?

Ferromagnets are a classical manifestation of electron spin. MRI is a classical manifestation of nuclear, mostly proton, spin. Both are spin half. What you are looking for is a -1 factor upon 360$^\...
my2cts's user avatar
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5 votes

Why is half-integer spin not observed classically?

The other answers are great, and it's very much true that you can totally write down a classical field theory with half-integer-spin fields. That notion still feels kind of odd, though, because all ...
Rokas Veitas's user avatar
2 votes

Why is half-integer spin not observed classically?

Why is half-integer spin not observed classically? Why do you single out half-integer spin? Are you implying that integer spin can be observed classically? If neither integer spin nor half-integer ...
MadMax's user avatar
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2 votes

How can rotation about Z be a superposition of rotations in X ($|\uparrow \rangle_z = |\uparrow\rangle_x + |\downarrow\rangle _x $)

(I’m sorry to say) there is so much confusion in the title and the post… First, a rotation about $\hat z$ is not a superposition of rotations about $\hat x$. In fact, what you have written has ...
ZeroTheHero's user avatar
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2 votes

How can rotation about Z be a superposition of rotations in X ($|\uparrow \rangle_z = |\uparrow\rangle_x + |\downarrow\rangle _x $)

Think about spin as an internal degree of freedom, similar to the polarization of an electromagnetic wave. This is the approach taken to explain the Stern-Gerlach experiment at the start of Sakurai's &...
agaminon's user avatar
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3 votes

Is intrinsic spin a quantum or/and a relativistic phenomenon?

There is nothing that distinguishes the spin from the magnetic dipole Spin was introduced into physics when it was realized that, in addition to its interaction with electric fields, the electron also ...
HolgerFiedler's user avatar
19 votes
Accepted

Is intrinsic spin a quantum or/and a relativistic phenomenon?

SPIN ORIGIN Spin is a purely relativistic property. It comes in fact from the representation theory of the Lorentz group (the relativistic symmetries group). In classical mechanics, you have ...
LolloBoldo's user avatar
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7 votes

Is intrinsic spin a quantum or/and a relativistic phenomenon?

The classical electromagnetic field has spin $S=1$. In my paper A theory of electromagnetism with uniquely defined potential and covariant conserved spin I proved this and defined the electromagnetic ...
my2cts's user avatar
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13 votes

Is intrinsic spin a quantum or/and a relativistic phenomenon?

There is nothing quantum about spin. When the great mathematician Élie Cartan first introduced the concept of spinor in 1913, it's a purely classical concept of geometry. Quantum mechanics has not ...
MadMax's user avatar
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3 votes

Is intrinsic spin a quantum or/and a relativistic phenomenon?

I do not know how to discuss this for general spin, but I will try to give a concrete answer for spin 1/2. In non-relativistic quantum mechanics spin is usually discussed as some independent ...
Maik H.'s user avatar
  • 88
1 vote

Identity for squeezing spin coherent state

$[S_z,S_+] = S_+$ hence, $S_z.S_+ = S_+.(S_z + 1)$ similarly, $(S_z)^2.S_+ = S_z.S_+.(S_z + 1) = S_+.(S_z + 1)(S_z + 1)$ therefore, $(S_z)^n.S_+ = S_z.S_+.(S_z + 1)^{n-1} = S_+.(S_z + 1)^n$ From this ...
quantumbro's user avatar
1 vote

Identity for squeezing spin coherent state

I believe the $\hbar$ in your S commutation relation is superfluous, as per your source, since it has been absorbed in the definition of t. You then obviously have, power-wise, $$ F(S_z) S_+ = S_+ F(...
Cosmas Zachos's user avatar

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