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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1answer
259 views

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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35 views

How can I calculate the total rotation a detuned pulse will apply a nuclear spin?

I'm trying to model the effect a radiofrequency pulse will have on a nuclear spin at different detunings. The pulse has a sech lineshape, a pulse area (time integral of the pulse envelope) of $\frac{π}...
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106 views

How to utilize the Rashba effect in spin field effect transistor?

The conventional nano-electronics are confronting many bottlenecks and spin-based devices have become the candidate for the next-generation nano-electronics (spintronics). A semiconducting channel ...
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152 views

Why is boson spin number related to attraction and repulsion?

The accepted answer to this question says Since the electroweak interaction is mediated by spin 1 bosons, it is the case that "like (charge) repels like and opposites attract". Another answer ...
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Question about the spin of the antiparticle of $Δ^-$

Ι came across a statement in a physics book that the spin of the antiparticle of baryon $Δ^-$ is 1/2. I know that the spin for regular $Δ^-$ is 3/2, and - as far as I know - the spin of particles and ...
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84 views

Sequential spin measurement misunderstanding

I'm having some trouble understanding something concerning sequential measurements. Suppose we have a wave function consisting of a superposition of spin up and spin down in the z direction (spin=1/...
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Why is the transition from the $3s$ state to $3p$ state in nitrogen observable in the emission spectrum but not in absorption?

Why can one observe an electronic transition of the $3s$ state to the $3p$ state in the emission spectrum of the nitrogen atom, but not in its absorption spectrum? I know that the selection rules ...
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Is it possible to create coherence in a two-level system starting from the maximally mixed state?

I know how to create coherence between two states if I have a pure state. For example if the system is in pure state $|1\rangle = \begin{bmatrix}1\\0 \\\end{bmatrix}$ then density matrix is given by $\...
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47 views

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 ...
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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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172 views

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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106 views

Racah's Derivation of CG coefficients

I have what is hopefully a quick question. In Racah's 1942 paper Theory of Complex Spectra II, the author utilizes the action of $J_+$ on the Clebsch Gordan expression: $$ \begin{align*} &|j m\...
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59 views

Microscopic and macroscopic description of spin waves

Hamiltonian Consider the one-dimensional Heisenberg ferromagnet specified by the Hamiltonian $$H = -\frac{|J|}{2}\sum_{i,\delta} \mathbf{S}_i\cdot \mathbf{S}_{i+\delta}.$$ Here $i$ labels the spin ...
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312 views

Hamiltonian in rotating frame

I have a Hamiltonian for spin in a magnetic field $$ \hat{H}(t) = \mathbf{B}(t) \cdot \mathbf{\hat{S}}$$ $\mathbf{B}(t) =B_x(t) \hat{\mathbf{x}} + B_y(t)\hat{\mathbf{y}} + B_z(t)\hat{\mathbf{z}}$ is ...
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Is entanglement *not* intrinsic to state, but dependent on division into subsystems? (Susskind QM)

I'm working through Susskind's "Quantum Mechanics" book (TTM series), which I quite like. Background In Lecture 7 (Chapter 7), he studies a 2-spin system. A single spin has eigenvectors: $$|u\...
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192 views

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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33 views

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 ...
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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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56 views

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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Can the existence of antimatter be inferred from Matrix Mechanics?

It is well known that Antimatter was first predicted by interpreting the matrices that show up in the Dirac Equation as indicating its existence. Dirac factorizes $E^2=p^2+m^2$ ($c=1,\hbar=1$) into $...
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what is the meaning of projection of spin along z axis

Spin is an internal degree of freedom, which has no classical analogue. So what is the meaning of its projection along z-axis? if it is the internal degree of freedom and its Hilbert space is a 2-...
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Spin of electron [duplicate]

While reading 'The Universe in a Nutshell' by Stephen Hawking, I came across the example of cards and how he used it to explain concept of spin and fermions and bosons. There he defined 'Spin' as ...
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Symmetric and antisymmetric states of spin singlet/triplet

I'm studying the book "Quarks and Leptons: An Introductory Course In Modern Particle Physics". When I reach chapter 2 (page 33), I encounter this exercise problem that I couldn't understand: ...
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Why can't we infer the amplitude of the spin vector components from the spin probability when the latter is 50%?

I'm currently reading Quantum Mechanics: The Theoretical Minimum. I'm stuck trying to understand a minor point in the book where the authors seem to suggest that we can know the probability of ...
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Don't the magnets slip and turn in Stern-Gerlach experiment, if their orientation is not aligned with the applied magnetic field?

I was watching two videos on YouTube: In this video, there is an attempt to explain what spin is, using analogy of magnets. But here it is shown that magnets which are not aligned with magnetic field ...
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Hamiltonian Matrix for XXZ Model

Given the XXZ model Hamiltonian, $H = -\frac{1}{2}\sum^{N}_{i}(\sigma_{i}^{x}\sigma_{i+1}^{x}+\sigma_{i}^{y}\sigma_{i+1}^{y}+\Delta\sigma_{i}^{z}\sigma_{i+1}^{z})$ The two-site Hamiltonian reads $H ...
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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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Is there any “singlet state” for 3 or more spin 1/2 particles?

Every system with $N$ or more electrons lies in a Hilbert space $H=H_{\text{space}} \otimes H_{\text{spin}}$, with $H_{\text{space}}=H_{\text{space}}^{1}\otimes\cdots\otimes H_{\text{space}}^{N}$ and $...
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Experimental examples of how to realize POVM

Say I have a spin qubit that is one of two states $\vert\psi_1\rangle$ or $\vert\psi_2\rangle$ and $\langle \psi_2 \vert \psi_1 \rangle \neq 0$. To perform an unambiguous state discrimination, we ...
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Is there an apparatus that measures neutrino spin?

Anytime any reference is made to spin at the quantum level the Stern-Gerlach experiment is sited for reference. I was curious how individual particles "atoms" or subatomic particles are isolated to ...
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Decay of neutral kaon into two pions and conservation of angular momentum

I am asked the following question: A kaon $K^0$ decays into two pions $\pi^0$, being this two pions particles with spin zero. Using the conservation of angular momentum and the fact that the two pions ...
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Triplet states and the Hund's rule in identifying the ground state configuration (open shell)

I referred to some of the questions about Hund's rule on StackExchange, such as this for example, but still wasn't able to have my question resolved. (the wikiepdia page has $E_{ex} = C - \frac{1}{2}...
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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 ...
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482 views

What is the difference between parallel and antiparallel spins for a pair of nucleons?

What is the difference between parallel and antiparallel spins for a pair of nucleons? My understanding is that nucleons have a strong tendency to pair - proton with proton, neutron with neutron, ...
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Feynman V. III - Ch. 12 - deriving eqn 12-47

Working my way through Feynman V.III. Sec. 12-6 derives Eqn 12-47. I follow all the steps until the equation, but cannot see how he gets 12-47 from 12-46. Appears that he's using the rule: If $\langle+...
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What is charge relaxation and spin relaxation in an atom/ artificial atom?

I want to understand the difference between these two terms.
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What is the spin of an electron in the presence of a monopole?

Consider a spinor field in $3$ dimensions, coupled to a $\mathrm U(1)$ gauge field. The spinor has charge $q\in\mathbb N$ spin $1/2$. According to arXiv:1712.00020 (cf. the discussion below eq.2.48), ...
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Time average value of Spin operator

From the book Introduction to Quantum Mechanics by Griffiths,. In the section 6.4.1 (weak field zeeman effect) Griffiths tells that the time average value of $S$ operator is just the projection of $S$ ...