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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Spin 1/2 particle in rotating magnetic field

So, I'm attempting a solution to the following problem: I am given a particle with spin 1/2 in a constant vertical magnetic field and a rotating field in the (x,y) plane. $$B(t) = [B_1\cos(\omega ...
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1answer
41 views

Simple question about using determinant to find eigenvalues of $\hat{S_x} + \hat{S_y}$ [closed]

The problem is: Find the eigenvalues and eigenfunctions of the operator $\hat{S_x} + \hat{S_y}$ where $\hat{S_i}$ is the spin operator in the i direction (i = x,y,z). The first step of their ...
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1answer
30 views

Spin magnetic moment direction of a particle

Is the spin magnetic moment of a fundamental particle like an electron always aligned along the direction of the spin angular momentum (meaning that the magnetic moment and the spin operators have the ...
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34 views

Measuring the spin of an electron with spin +h/2 at an axis 30 degrees off [closed]

The problem: If the z component of an electron spin is $+\hbar/2$, what is the probability that its component along a direction z' that forms an angle $\theta$ with the z axis equals $+\hbar/2$ or ...
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10 views

Application or Applicability Spin Seebeck Effect

I am looking for any application or study of applicability of the Spin Seebeck Effect. I have not found anything good anywhere so far but maybe someone here knows something? Would appriciate any ...
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25 views

A physical basis for Heisenberg ferromagnetic cluster model

Consider the following situation. There are $N$ spins 1/2 (for example 1/2, it may be any other value $s$) and they interact via the Hamiltonian: $$\hat{H}=-\sum_{i\neq j}\frac{J}{N}\hat{\vec{S}}_i ...
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2answers
68 views

Using rotation matrix for spin to write x oriented spin in z-spin basis

$\newcommand{\ket}[1]{\left| #1 \right>}$The problem is to write the ket vector for a particle with spin +1/2 along the x axis, in terms of the standard basis vectors $\ket{+1/2}$ and $\ket{-1/2}$ ...
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2answers
99 views

Why is a photon its own anti-photon?

Two properties of a photon that I have considered in trying to answer this myself : Photons are electrically neutral, so there is no need for "anti-photons" to preserve conservation of charge. Take ...
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1answer
110 views

What is the theory behind spin-transfer torque?

I would like to get a layman's understanding of STT (Spin-transfer torque). By that I mean I don't have time to understand the mathematical and exact physical theory, but I would still very much like ...
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1answer
57 views

Is this definition of orthohelium and parahelium incorrect?

"One electron is presumed to be in the ground state, the 1s state. An electron in an upper state can have spin antiparallel to the ground state electron ($S=0$, singlet state, parahelium) or ...
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2answers
33 views

Spin, isospin, parity etc. in nuclear physics

I have one question regarding these quantum numbers. When I read through my textbook, it sometimes just says something like: "And this atoms ground state has $J^{\pi} = 0^+$ and isospin $+1$" - as an ...
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1answer
66 views

Do particles have spin because there exist spinor representations for the Lorentz group?

I am reading Peskin and Schroeder's An introduction to field theory. They first describe the spinor representation of the Lorentz group, and then they mention the fact that different particles have ...
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1answer
18 views

Angular momentum conservation laws and GHZ article (Greenberger et al 1990)

Can anyone recommend a good book or an online source on angular momentum conservation laws in decay processes? I'm writing a master's thesis concerning Bell inequalities and currently working on GHZ ...
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1answer
58 views

Getting to spins of arbitrary direction

Let me rephrase this question: Let us assume we know that symmetry transformations always look like this: $$U(s)=e^{iKs} $$ with a hermitian Operator K. This tells us that for very small $s$: ...
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0answers
24 views

Expectation value in spin-orbit coupling

So I was just trying a question where it asked to find the Energy shift due to a spin-orbit coupling Hamiltonian to first order using perturbation theory. The Hamiltonian is $$H_{LS} = ...
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1answer
102 views

Classical spin viewed as $SU(2)$

In which sense is the configuration variable of a classical spin $SU(2)$? I can view a classical spin as a unit vector in $\mathbb{S}^2$ (2-dim. sphere), but it seems it is really given by a matrix ...
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1answer
82 views

Find Eigenstates of a Hamiltonian that lets two spin 1/2 interact but also acts on one of them

I have the following Hamiltonian describing two spin 1/2 systems, represented by the pauli matrices $\sigma_1$ and $\sigma_2$: $H = D \sigma_{1z} + J (\sigma_1 \cdot \sigma_2) $. The two spins are ...
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1answer
40 views

Measuring electron spin with multiple Stern–Gerlach apparatus at an angle

To separate the two spins of electron of a particular direction, we use Stern-Gerlach apparatuses to apply a non-uniform Magnetic field. Suppose we have two identical electrons and we know their spin ...
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2answers
105 views

Spin, orbital angular momentum and total angular momentum

If I understand correctly, spin is an intrinsic property of particles, which follows the algebra of angular momentum, but has nothing to do with an "orbital angular momentum" in that the particle is ...
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2answers
138 views

If proton spin emergence from quarks and gluons is mysterious, why is silver atom spin not?

A recent Scientific American article brought up an old issue, which is this: According to quantum chromodynamic models, the emergence of exactly 1/2 unit of spin in a proton (or a neutron, or any ...
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24 views

Explicit Ewald equations for dipole-dipole interaction in a simulation

I'm starting to work with spin ice simulations and I found that it is usual to use the Ewald method for the long-range interactions computation (dipole-dipole in this case). Although I've been reading ...
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1answer
67 views

How to act an operator on a two-particle spin state?

I'm doing an assignment for my quantum class at the moment and I'm having trouble figuring out how to act a Spin operator on a two-particle state - specifically in finding the eigenvalues - I've spent ...
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1answer
91 views

Spin commutation relations

For orbital angular momentum defined as $L= r \times p $ we can prove, in quantum mechanics, the commutation relations. Also, we could prove these relationships through the study of rotations ...
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1answer
115 views

How to obtain a vector relation for the Rabi frequency?

In this paper by Golovach et al.: http://journals.aps.org/prb/abstract/10.1103/PhysRevB.74.165319 there is the following equation for spin evolution: $$\langle \dot{\bf{S}} \rangle=({\boldsymbol ...
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2answers
66 views

Calculations with angular momentum

Is the following correct, when adding 3 angular momenta/spins: \begin{align} 1\otimes 1\otimes \frac{1}{2}&=\left(1\otimes 1\right)\otimes \frac{1}{2} \\ &=\left(2\oplus 1\oplus ...
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1answer
105 views

How to use Clebsch-Gordan coefficients for 3 particles?

I have a Hamiltonian for 3 particles of spin 1 that I boiled down to: \begin{equation} k(\textbf{S}^2+\cdots), \end{equation} where: \begin{equation} \textbf{S}=\textbf{S}_1+\textbf{S}_2+\textbf{S}_3. ...
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1answer
50 views

Question regarding entanglement

Could the paradoxical nature of entanglement be the result of a change in the nature of quantum properties, or an incomplete understanding of such, instead of non-locality?
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43 views

Understanding quantum coherence in biological processes (Magnetoreception)

Moved my questions to the top. Context below. Why is the strength of the electric field and the coupling constant being compared to the inverse coherence time? What is the inverse coherence time? Is ...
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1answer
44 views

Notation of angular momentum operators vs numbers

I'm reading about finding the mass of quarks in mesons. In the lecture notes, it says We need to find $\langle\boldsymbol{s}_q\cdot\boldsymbol{s}_\bar{q}\rangle$. Since $L=0$, then ...
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1answer
74 views

Entanglement and the uncertainty principle

Suppose you have two maximally entangled particles. You measure the spin about the x axis of the first and the spin about the y axis of the second. But both spins cannot be known simultaneously, so ...
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38 views

Mixed spin Ising Model

As we know ferrimagnets can be modeled by the Ising model. I came across this equation in "Compensation Temperature of the Mixed-Spin Ising Model on the Hexagonal Lattice" by W. Figueiredo, M. Godoy, ...
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4answers
147 views

What is the meaning of EM field having curl?

We know that the "sourceful" fields like gravity or electric static field due to charge are all curl=0. But both E/M fields have curl and they mutually "curling" into each other, making them kind of ...
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1answer
607 views

What does it mean for a particle to have spin of 2? [duplicate]

When I first started to study quantum mechanics, my physics text book told that particles have spin of either 1/2 or -1/2. Then I recently read an article saying that gravitons are expected to be ...
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17 views

How to count total spin degeneracies for many spin one half particles?

Given the spin operator for particle $j$ \begin{align} \bar{S}_{j} = \left( \bigotimes_{k=1}^{j-1} I_{k} \right) \otimes \left(\tfrac{\hbar}{2}\bar{\sigma}\right)_{j} \otimes \left( ...
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2answers
51 views

Spin State Energy Levels

When a spin-1/2 particle is placed in a magnetic field that is strong enough and varies slowly enough in space and time, it will become polarized and its spin will either align or anti-align with the ...
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3answers
81 views

Spin in Schrodingers Equations

With the usage of Dirac notation we've gotten around a large amount of of inconvenience that would be dealing with spin. But, I was wondering, do we merely do this because it is inconvenient to try ...
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24 views

Entanglement of two particles with same values of the entangled parameters?

The question For an entangled state consisting of systems A and B, if A is measured when does the wavefunction at B collapse? contains next entangled state: If there are two systems A and B, with ...
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1answer
35 views

Is the Singlet state for Helium with 2 electrons symmetric rather than anti-symmetric as is meant to be for fermions?

I'm looking at two-electron Helium atoms where one electron is in the ground state (due to if it were in other states, it's de-excitation would simply lead to the ionization of the electron). The ...
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2answers
44 views

Is there any macroscopic experiment that reproduces the results of Stern-Gerlach experiments on electron spin?

In a Stern-Gerlach experiment measuring electron spin, electrons are diverted to one of two areas on a detector, rather than ending up in a continuum between those two areas. I'm wondering if there is ...
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37 views

Rotation of a spin polarization meaning

I've got some quantum state $|s\rangle =\left( \begin{array}{c} cos(\frac {\theta}{2})\\ {e}^{i\phi}sin(\frac {\theta}{2})\end{array} \right)$ I operate on it with a Paul matrix $\sigma_z$ and get a ...
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1answer
57 views

Why is this spin expectation value a vector

I'm given a spin state: $|s\rangle$ = some linear combination of $|\uparrow\rangle + |\downarrow\rangle$ possibly with an imaginary component. $\hat{\mu}_e = g\mu_B\hat{\sigma}$ $g$ is the ...
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3answers
71 views

How do I operate on a spin state with a sigma operator?

For any arbitrary spin state $|s\rangle$. How do I operate on it with the Pauli spin matrix, $\hat{\sigma_z}$? Does this have something to do with a Bloch sphere?
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1answer
46 views

How do I find an expectation value for an electron's magnetic moment?

Given a spin state: $|s\rangle$ = some linear combination of $|\uparrow\rangle + |\downarrow\rangle$ possibly with an imaginary component. How do you get from the definition of a magnetic momentum ...
2
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0answers
32 views

Atomic physics, determining levels and terms

In atomic physics I understand there a configurations, terms and levels. I think levels for instance appear because of spin-orbit interactions, so that terms are split. But I'm confused about the ...
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1answer
67 views

Why do $S_x$ and $S_y$ flip up/down spin states but $S_z$ does not?

By using the notation $S\lvert s,m_s\rangle$, such that $\bigl\lvert\frac{1}{2},\frac{1}{2}\bigr\rangle=\lvert+\rangle$ and $\bigl\lvert\frac{1}{2},-\frac{1}{2}\bigr\rangle=\lvert-\rangle$ we can ...
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1answer
53 views

Spin of a particle (Quantum Mechanics) [duplicate]

Why the intrinsic spin cannot be expressed in terms of polar vectors or the orbital variables $\bf r$ and $\bf p$? Or, why do we need matrix representation for Spin?
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49 views

How does the Wigner-Eckart theorem rule Multipole Expansion?

I am wondering why a spin-S particle have only the term up to $k=2S$ in his multipole expansion ? It seems that the Wigner-Eckart theorem shows the relation between spin and multipole expansion but I ...
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1answer
72 views

Why spin-1/2 objects doesn't have quadrupolar magnetic moment?

I'm asking myself more generally why a spin of size S will feature multipolar states of degrees k up to 2S ? (This implies the question in the title : spin-1/2 can't have any quadrupolar ...
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1answer
124 views

Evolution of Eigenstates when two spin systems are coupled

I would like to describe the following situation: We have two spin systems: Spin 1 ($S_1$) and Spin 1/2 ($S_2$). Now imagine you somehow change their interaction so that you can fine-tune the ...
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1answer
72 views

how can a particle can have a spin of 2 [duplicate]

i have seen some analogies of spin using playing cards but i am struggling to grasp the concept due to this making no sense in terms of playing cards