# 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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### Total Orbital Angular Momentum and its relation to $M_L$ & Symmetry

I am currently working through the physics governing how electrons arrange themselves within an atom into orbitals, and I have two related questions. Note that all the atoms I talk about are ...
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### “Dark Matter” vs. “Dark Spin”

I am rephrasing an answer to another PSE question as an new question here. Dark matter is invoked to explain the 'observed space-time geometry that does not match with predictions'. According to the ...
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### Eigenstates of a Hamiltonian [closed]

For a particle with a spin of 1/2, which was exposed to both magnetic fields $B_{0}=B_{z}e_z$ and $B_1=B_xe_x$ I already found the eigenvalues of its Hamiltonian which is given by \begin{...
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### Good Quantum numbers in $L$-$S$ coupling

I'm having a hard time understanding a few things about L-S and j-j coupling in 2 (or more) electron atoms. What I picked up from our lectures is the following: The Hamiltonian can be "broken up" ...
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### Discrepancy regarding Husimi Probability distribution calculation

I am trying to simulate a system of j qubits and for visualization of the dynamics considering the Husimi distribution of the state. To carry out the projection onto coherent states I have proceeded ...
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### What is a hypercomplex quantity?

An extract from the book "Quantum Mechanics and the Path Integrals" by Richard P. Feynman and A. R. Hibbs: We can state the correct law for $P(x)$ mathematically by saying that $P(x)$ is the ...
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### Weyl spinor's spin direction

I am a bit confused about the spin direction for a Weyl spinor. So as far as I understand, a Weyl spinor represents a massless fermion and it is an eigenstate of the helicity operator. Now say we have ...
71 views

### Destruction of Mott phase by a external magnetic field

I want to ask the underlying reason for the destruction of Mott insulating phase by an external magnetic field. I know that for a normal band insulator, the transition to a metallic phase can be ...
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### What about the (1, 1/2), or (3/2, 1/2) representations of the Lorentz group?

All irreducible finite dimensional complex representations of the Lorentz group can be specified by two positive half-integers, i.e. $(j_1, j_2)$. The $(0,0)$ representation is the trivial scalar ...
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### Is there a standard convention for whether the term “handedness” refers to helicity or chirality?

I was under the impression that the "handedness" of a massive spin-1/2 particle refers to its chirality rather than its helicity. This answer, this one and Srednicki's QFT textbook seem to use the ...
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### Klein-Gordon-Equation contains no Spin

I have a question about an argument used in Schwabl's "Advanced Quantum Mechanics" concerning the properties of the Klein-Gordan-Equation (see page 120): Since the eigenenergies of free solutions are ...
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### From spin representation of state vector to other representation

I have learned that the state vector (ket vector) can have many representations, and the laws of quantum mechanics give one the ability to change between representation. But there is a subtle point ...
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### Is there a maximum frequency at which hysteresis appears?

If a ferromagnetic material is immersed in an alternating magnetic field at frequency $\omega$, the material will follow a hysteresis cycle at that frequency. But if that frequency is high enough, the ...
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### Klein-Gordon-Equation provides a Scalar Theory that doesn't contain Spin [duplicate]

I'm reading actually Schwabl's "Advanced Quantum Mechanics" and encounter an understanding problem while considering the Klein-Gordan-equation. Here the excerpt: Obviously, since the eigen energies ...
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### Lorentz transform of spin particles

Let's say that I see a particle (i.e. an electron) is moving along the y-axis and has a spin of -1/2 along the z-direction. Now, if another person who is moving with certain velocity v along the y-...
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### Photons have Spin 1 - Franz Gross' Relativistic Quantum mechanics and Field Theory

I've got a question regarding the derivation of spin 1 for photons in Franz Gross' Relativistic Quantum Mechanics and Field Theory. From pages 50 to 56 he attempts to derive "how this [spin 1] comes ...
321 views

### Why is there a maximum number of supersymmetries?

Where does the NO-GO theorem for a maximum number of supersymmetries come from? I read from here https://en.wikipedia.org/wiki/Supersymmetry that number is 32, and that fixes the number of spacetime ...
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### Reduced density matrix of the edge spin-1/2 in AKLT spin chain

I am trying to understand the paper titled, "Entanglement in a Valence-Bond-Solid State" by Fan, Korepin, and Roychowdhury (https://arxiv.org/abs/quant-ph/0406067). I was able to understand the ...
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### How is the product $L\cdot S$ between orbital and spin angular momentum operators defined? Do they act on the same or different Hilbert spaces?

For an electron, are the Hilbert spaces for the spin angular momentum and the orbital angular momentum the same or are they different? If they're different, how do we justify the operator $L\cdot S$ ...
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### Practical/experimental difference between (quantum) Heisenberg and (classical) Ising model

I have read a few discussions about the difference between the Heisenberg model (using quantum spin operators) and Ising model (with spins $\pm 1$), notably this one or this Quora post. All the ...
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### Does the spin travel as a wave?

The electromagnetic field (wave) has a spin. The electromagnetic wave travels at the speed of light. Does the spin associated with the electromagnetic wave travel at the speed of light too? If so ...
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### Why does an electron have spin? [duplicate]

An electron is assumed to be a point particle that does not have structure and volume. Why does it have spin? Does this imply that the electron has volume? It is hard to imagine that a point (without ...