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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53 views

What's the opposite of spin collapse? Superposition as a verb?

With regard to photon spin, I'm trying to figure out what the word is for being "more random" as opposed to collapsing and being "more determined" If I were to say "the spin collapsed", how would I ...
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Will entangeld particles stay entangled?

I want to consider an experiment: We create two entangled particles a and b such that the spin of each is opposite to the other. We then measure spin in z direction (1). So we get a is up and b is ...
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174 views

Must the total orbital angular momentum quantum number $L$ be less than the principal quantum number $n$? If so, why?

I am studying LS coupling and term symbols. In my textbook, there is an exercise: Why is it impossible for a $2\ ^{2}\text{D}_{3/2}$ state to exist? The answer says, the total orbital angular ...
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Conjugate of total spin operator

I got a lattice, and the total spin operator for x and for y, for that lattice. I know that the x component conmutes with an operator called staggered spin operator in y. I also know that the ...
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Spin-orbit interaction for titanium in the excited state $(3d)^1(4p)^1$

Let's look at a Ti-atom in an excited state with 2 valence electrons $(3d)^1(4p)^1$. What term schemes $^{2S+1}L_J$ do we have for this state considering spin-orbit interaction? My take: For both ...
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83 views

Bosonic representation of $SU(N)$: what values can $n_b$ take?

In Assa Auerbach's book on page 166, he describes the construction of a bosonic representation of $SU(N)$ where the generators $S^{mn} \rightarrow b^\dagger_m b_n$. I'm a bit confused about the ...
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How do you go about guessing the ground-state spin and parity of a nucleus?

How do you go about guessing the ground-state spin and parity of a nucleus? Questions of this form seem to be asked frequently here, e.g., for 19F, 23Na, and 87Rb and 40K.
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132 views

Computing the spin degrees of freedom for a massless particle in $D$ dimensions

According to the paper A Lagrangian formulation of the classical and quantum dynamics of spinning particles, a relativistic spinless particle in $D$ spacetime dimensions can be described by the ...
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192 views

Why does Fluorine-19 have a nuclear spin of 1/2?

According to the nuclear shell model, $^{19}F$ has one unpaired proton in the $6$-fold degenerate $1d_{5/2}$ state, which means the orbital angular momentum is $l = 2$ and the total angular momentum ...
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Zero field splitting only defined for $S>\frac{1}{2}$?

Why do we only consider the spin-spin interaction between unpaired electrons? For reference the wikipedia page for zero field splitting says The classic case for ZFS is the spin triplet, i.e., the ...
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How to experimentally measure spin of photon?

Given that we know the spin of photon should be +1 or - 1, is there any experiment to directly measure and confirm it? I looked up stern-gerlach experiment is used on charged particle not photon.
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37 views

Deriving spin rotation with the commutator of function relation

I'm trying to derive the rotation effect of the spin operator from the commutation relation (from here): $$\left[f(A), B\right] = \left[A, B \right]\frac{\partial f}{\partial A}$$ I started by doing: ...
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How is a NMR spectrum obtained?

I am reading about NMR, and from what I'm understanding it should give information on the transition energies in the spectrum of the nuclear spin in a magnetic field. What I don't understand is how ...
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414 views

Wave function of a system of two identical fermions

In N. Zettili's 'Quantum Mechanics Concepts and Applications' [chapter 8, solved problem 8.3], we have to find wave function and ground state energy of a system having two identical fermions and in ...
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46 views

Action of rotation operator on spin 1/2 system

In Sakurai book on QM in chapter 3, he states the following relation $$e^{\frac{iS_z\phi}{\hbar}}[(\rvert+\rangle\langle-\rvert)+(\rvert-\rangle\langle+\rvert)]e^{\frac{-iS_z\phi}{\hbar}}$$ $$=e^{\...
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Intuition for the supertrace identity in supersymmetry

In pretty much every introductory book/lecture notes I've come across, one finds the expression for the mass matrices for scalars, fermions and vector bosons for a generic Lagrangian, and simply ...
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Conformal Ward identities for spinor operators

How do you derive conformal Ward identities for operators with spin? You can see in Penedones's notes (page 6) ( https://arxiv.org/abs/1608.04948 ) a brief derivation of Ward identities for general ...
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Commutation relations

Given that the Hamiltonian for Muonium spin in zero magnetic field is $$\hat{H} = a \vec I \cdot \vec J$$ where $\vec I$ is the spin of a muon, and $\vec J$ is the spin of the electron, what is the ...
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Spin conservation in spontaneous parametric down-conversion (SPDC)

If one pump photon "decays" through the process of spontaneous parametric down-conversion into two photons how can the spin be conserved?
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How can I explicitly express the Ising Hamiltonian in matrix form?

I am reading this book about numerical methods in physics. It has the following question: Consider the Ising Hamiltonian defined as following $$H=-\sum_ {i=1}^{N-1} \sigma_i^x \sigma_ {i+1} ^x + h ...
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105 views

Quadratic formula not working in Quantum Mechanics? [closed]

In quantum mechanics the raising operator of a system with quantum number $s$ and $m$ is such that $$\hat{S}^+|s,m\rangle = \hbar \sqrt{s(s+1)-m(m+1)}|s,m+1\rangle$$ Since there must exists a $m_\...
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126 views

Explanation of the sign of Clebsch-Gordan coefficients

These are the Clebsch-Gordan coefficients when the orbital and spin-angular momenta of a single spin 1/2 particle are added. I'm not able to understand the explanation. What I can understand is that: ...
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Why light have angular momentum?

Light carries momentum which is an intrinsic property or ability to move something at least how I interpret it, I got no issue on how it is able to conserve momentum when it is absorbed by another ...
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It is found that diamgnetic materials weigh less when placed in a magnetic field.Why?

I've always had this question as to why diamagnetic materials weigh less when places in a magnetic field but I haven't found the answer on books or online so far .
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What does the energy-resolved spin density averages show?

What does the energy-resolved spin density averages show? Spin density refers to the density of states for spin up and down, my question is what does energy-resolved refer and how can be the energy-...
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Spin statistics from the fundamental group of $SO(D)$

I read the answer to this question and am very intrigued by its simple and elegant explanation of the emergence of anyon, boson & fermion statistics. @Trimok basically says: In a space-time ...
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170 views

Can a particle have an “actual” spin?

I know that a particle can have an orbital momentum and a spin which is intrinsic to the particle and doesn’t really have to do with the particle spinning. But can particles have an additional ...
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66 views

2$\pi$ Rotation on integer vs half-integer spin states

I want to know how to get the following result: $$ e^{-i2\pi J_y / \hbar}|j, m\rangle = (-1)^{2j}|j, m\rangle $$ for an arbitrary spin state $|j, m \rangle$. What I've tried is to expand the ...
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What is the Newman-Penrose (NP) form of Rarita-Schwinger (RS) equation?

Does anyone knows how to write down the Rarita-Schwinger equation in Newman-Penrose formalism?
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213 views

Ising to QUBO mapping for quantum annealing

I'm trying to solve an optimisation problem by simulating quantum annealing using the path-integral Monte Carlo Metropolis approach. So far I have formulated the problem as an Ising model with the ...
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Is spin 1 described by $SO(3)$ or $SU(2)$ [duplicate]

What spin is described by which rotation group? I always only find information about spin-1/2
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Problems on perturbation theory with spin

Problems on perturbation theory with spin (solve all perturbations up to only its first-order approximation): Taking into account the relativistic correction of electron kinetic energy and spin-orbit ...
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54 views

Matrix representation composite system

I am considering an assignment involving the Hubbard model. A state is given by $|\Phi\rangle=-|2\uparrow1\downarrow\rangle-|1\uparrow2\downarrow\rangle$ where particle 1 and 2 are electrons. The ...
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105 views

Is there an Heisenberg uncertainty relation for light polarisation?

While reading some questions about the polarisation of a photon, I was wondering about its quantum mechanical representation as a classical vector in the electromagnetic field operator : \begin{...
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48 views

Identical Spin Fermions in the same orbital state: Finding total spin

Say we have two identical spin 3/2 particles in the same orbital state. What are the possible total spin? I know that there is a simple formula for adding angular momenta, but this breaks down when ...
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62 views

Supersymmetry: spin of the superpartners

I'm currently working on my master thesis, and I need to know a bit of supersymmetry. I have been looking the theory and I have a basic knowledge about it. I have a problem with understanding the ...
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37 views

Achiral system with Dzyaloshinskii-Moriya interaction?

From my tentative understanding, Dzyaloshinskii-Moriya (DM) interaction determines a certain chirality by its special mixed product form while its existence only requires the breaking of inversion ...
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137 views

In which direction does the positron's magnetic moment point?

Suppose I have an electron, with its spin pointing in some direction, so that the magnetic moment caused by the spin is pointing upwards. Then, I hold a positron next to the electron so that their ...
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The physical (classical) significance of the spinor representation of an electron

I have read through this question Rotation of Particle and this paper What is Spin. I have a basic understanding of the math treatment of spin in relation to electrons, but my question is: Can we ...
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151 views

Relation between spin and polarization of photon? [duplicate]

What is the possible spin configuration of photon? And does spin has any relation with polarization?
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Can fermions and bosons exist in the same representation?

Some people have made theories where they claim fermions and bosons exist in the same representation for example $E_8$. I can't see how this is possible. But say for example it is. This would imply ...
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why do we relate spin with angular momentum operator in quantum mechanics? [duplicate]

In fact angular momentum is the generator of rotation around an axis. If the axis passes through the center of mass of the object then it is spinning. spin in QM can be a property of point particle(...
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Photon Spin in Fluorescence and Phosphorescence

I think i still lack basic understanding of how absorption and emission of light actually works. Like fluorescence is the radiative transition from an excited singlet state to the ground (singlet) ...
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A dreidel on a spinning table

In the spirit of the holidays. Let's assume that a dreidel is spinning counter-clockwise at frequency $f$ on a table. From external point of view, what will I see if I rotate the table clockwise at ...
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Zero uncertainity in components of angular momentum in Hydrogen atom

It is given that L and Lz,Lx,Ly commute.(L is total angular momentum, Lx is angular momentum along x axis). So, I can simultaneously know the value of let's say L and Lz. But, if I perform huge no of ...
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90 views

How does the Pauli exclusion work on fermions but not on bosons?

How does fractional spin effect the symmetry of combined wavefunctions? Why is Planck constant the universal anchor for determining if a particle is a Boson or a Fermion?
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How are Quantum Mechanical energy levels related to atom shells?

I'm currently taking Quantum Mechanics in school and I came across a table displaying the following in the given order: $E_n (\text{energy levels}), g_n (\text{eigen functions})$ $n \ l, [m]$ $E_1, ...
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Ground state of Beryllium (${\rm Be}$)

Why is the ground state of Beryllium (${\rm Be}$) with electronic configuration $[{\rm He}]2s^2$ is $^1S_0$ and not $^3S_1$? The state $^3S_1$ has higher spin multiplicity.
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How does the ground state of the quantum Ising model relate to Schrodinger equation?

The Hamiltonian $$H = -\sum_{i\in V} h_i \sigma_i^z -\sum_{(i,j)\in E} J_{ij} \sigma_i^z\sigma_j^z - \Gamma\sum_{i\in V} \sigma_i^x$$ is kind of the cost function of the quantum annealing optimization ...
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140 views

Are permanent magnets a relativistic effect?

The relationship between Electromagnetism and Special Relativity is something that always amazed me but I haven't fully understood yet. Misconceptions and contradictions seem to be widespreaded, and ...