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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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27 views

Linear Polarization of Single Photon?

I've heard it said (a while ago) that we don't usually speak of a single photon being linearly polarized or unpolarized, but rather we can speak of an ensemble of photons that are linearly polarized ...
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Decay of spin-1/2 particle into two spin-1/2 particles

My question is: Does angular momentum conservation considerations alone forbid a spin-1/2 particle from decaying into two spin-1/2 particles? According to this Phys.SE post, the answer seems to argue ...
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Two particle Heisenberg model with field

I'm having trouble solving a problem with a phase transition of this system. We are considering the following Hamiltonian: $$H=-J \vec{S_1}\vec{S_2}-\mu b (S_{1z}+S_{2z})$$ And I've studied it in ...
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What is a scalar particle?

I was studying particle physics and I saw the word "scalar particle" many times, also in books. On the internet there wasn't any thing about it. So can anyone say what is a scalar particle ?
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How does spin influence the dynamics of quantum mechanical systems?

I have just been introduced to the Klein-Gordon Equation and the Dirac Equation for the first time. The way they were explained to me, these equations govern the (relativistic) evolution of spin-0 and ...
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Mechanism behind spin orbit interaction

The spin orbit coupling can be explained through two different frames one is the electron frame and the other, the lab frame. In the electron frame magnetic field produced by proton current current ...
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Can there be quantum spin liquids in 1D?

It seems like everyone studies quantum spin liquids in either 2D or 3D. Can not there be quantum spin liquids in 1D?
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54 views

Does the spin has a determinate value in magnetic field?

Consider a 1/2 spin particle like proton in magnetic field B in z direction with strength as high as in NMR appliances. Then the anomalous Zeeman Effect occurs. And the particle has two possible ...
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What are the properties and codomain of the spin $\alpha$, $\beta$?

I am following Mike Finnis on interatomic forces in condensed matter. I believe he uses the letter $s_i$ to denote spin number $\pm 1/2$ for fermions for example. But he has two functions $\alpha,\...
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70 views

Physical significance of the ket vector

I'm trying to understand/form an intuition for why a ket-vector, and its associated bra-vector, are appropriate tools to represent the spin of a qubit. Generally speaking, if a system has a state/...
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37 views

(Transverse) Ising Model Higher Than Four Dimensions

First question: Wiki says Ising Model higher than four dimensions can be described by mean field theory. What is the reason for this? Does this mean there is no phase transition for higher dimensions ...
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Deriving the expression for one body density

My textbook (Richard M. Martin - Electronic structure) has the following equation for the one body density of a system of $N$ electrons: $$ \langle \Psi | \Psi \rangle n(r) = \langle \Psi | \hat n(r) |...
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Many Worlds: under which conditions does the branching happen?

I am approaching Many Worlds interpretation and I have a big question that I would like to ask you: I buy the critic moved by Many Worlds supperters to Copenhagen interpretation, saying that Bohm ...
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Spin other than integer and half-integer

I was looking at the Quantum Atlas entry for Spin which had a standard explanation Like many things in the quantum world, spin is quantized, which means that the spin of a particle is limited to ...
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Electron-Hole in Spin-basis

A fellow student and I are arguing about the correct formulation of the hole in spin-basis, as the conjugate of the electron. Are the following correct: $\overline{|\frac{3}{2}, \pm \frac{1}{2} \...
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Neutral hydrogen atoms in inhomogenous magnetic field

In the 1996 gre exam this scenario comes up in a question: a beam of neutral hydrogen atoms in their ground state pass through a region of of strong inhomogenous magnetic field. In the official ...
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Representation of spin in the Fock space

I understand that states of single 1/2-spin particle is just the unique (up to an isomorphism) irreducible representation of $\text{su}(2)_\mathbb{C} = \text{sl}(2,\mathbb{C})$ with dimension 2, but ...
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Spintronics: How can we inject a spin current into/onto a sample without physically touching it, ie: modulation with a field?

So background, I'm imagining a black box scenario where we have some spintronic system. It might be a topological quantum computer that uses spin currents running across it's memory to connect ...
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Central Potential + Coupled Angular Momenta

I am considering a two-state system with a Hamiltonian of the form $$ H = \frac{p_1^2}{2m_1} + \frac{p_2^2}{2m_2} + V_a(|r|) + \bigg(\frac{1}{4}-\frac{S_1\cdot S_2}{\hbar^2}\bigg)V_b(|r|), $$ where ...
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Are electrons in a singlet state still electrons?

Given that some interactions such as electron capture make the electron "disappear" and the output fermion is a neutrino, I wonder what is the rationale behind saying that in the case of two opposite ...
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Writing total angular momentum eigenstates in terms of spin and orbital angular momentum eigenstates

I want to understand how we can derive the simultaneous eigenfunctions of the total angular momentum operator and the z component of the total angular momentum operator in terms of the orbital angular ...
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47 views

Eigenstructure of the Dicke Model

I am beginning a study of the Dicke model and found a very interesting publication: "The Dicke model in quantum optics: Dicke model revisited" by Barry M Garraway in Phil. Trans. R. Soc. A (2011). I ...
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Do electrons in the same orbital but different spin feel each other's Coulomb repulsion?

Or is it irrelevant, as orbitals are QM while Coulomb interactions are classical physics? What I think I understood of orbitals is that particles with the same quantum numbers cannot occupy the same ...
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Does an electron spin axis form a characteristic angle with the direction of its translation?

I looked everywhere I could think of but found no connection between the orientation of the spin and the motion of the same particle. So maybe there is none. Yet, in the case of an electron being ...
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Is the oxygen molecule $O_2$ fermion or boson?

I ask something makes me confused. In generating singlet oxygen molecule, I initially thought a light (photon) can excite the ground state oxygen molecule. However, my colleague said that process is ...
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Loss mechanisms in spin Hall effect (and inverse spin Hall effect with spin pumping)

What are the most important loss mechanisms in the spin Hall effect and the inverse spin hall effect? I use input power $P_1$ to generate a charge current, which will generate a spin current which ...
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2answers
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Representation of spin-1 density matrices

Pauli matrices, together with the identity matrix can generate any $2\times 2$ matrix. By adding the condition that the matrices must be hermitian and with trace 1, we can represent density matrices ...
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Current generated due to spin pumping

Suppose I have a heavy metal (e.g. Pt) and a magnetized magnet adjacent to it (e.g. Co). A spin current $J_s$ results in a current $J_e=J_s/\theta$ where $\theta$ is the spin-hall conductance. When ...
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How can multiple fermions combine to form a boson? [duplicate]

I understand that composite particles with integer spin form a boson. For example a helium nucleus is a boson because it has 2 protons and 2 neutrons. If all of the components on their own are ...
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Polarization of gravitational waves VS polarization of photons

This might be a stupid question, but I think i am mixing important concepts. It is well-known that gravitational waves (GWs) come in two polarizations or two states of helicity: the so called "+" and ...
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Electron spin resonance experiments

Recommend me some good books on ESR. I'm performing an experiment of calculating lande's factor using ESR and I've so many doubts. Please help!
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How can we interpret the components of a polarization four-vector?

The four components of a Dirac spinor can be interpreted in terms of left-chiral and right-chiral spin up and spin down states. How can we interpret the four components of a polarization four vector $...
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Representation of $SU(2)$, i.e., spin

Let \begin{equation} X= \begin{bmatrix} 0 & 1\\ 0 & 0\\ \end{bmatrix}, \qquad Y= \begin{bmatrix} 0 & 0\\ 1 & 0\\ \end{bmatrix}, \qquad H= \begin{bmatrix} 1 & 0\\ 0 & -1\\ \end{...
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Quantum Non-Demolition of entangled superposition using an electron with infinite spin

Disclaimer: I have no idea what I am talking about, as I just started college and barely understand quantum physics. If an electron can have a linear velocity of the speed of light, theoretically ...
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Can we derive $\vec{S}=\frac{1}{2}\vec{\Sigma}$ in a representation independent way in terms $\vec{\alpha},\vec{\beta}$?

For the Hamiltonian $H=(\vec{\alpha}\cdot \vec{p}+\vec{\beta}m)$ of the Dirac equation $i\frac{\partial \psi}{\partial t}=H\psi$, it can be shown that $[H,\vec{L}]=-i(\vec{\alpha}\times\vec{p})$. Now, ...
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1answer
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Electron spin g-factor

I am reading Schwartz's book on Quantum field theory. In the chapter anomalous magnetic moment (chapter 17) he mentions that Dirac equation naturally implies that the electron spin $g$-factor is 2. ...
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Electron spin resonance

What is the principle of electron spin resonance? I'm performing an experiment in which I've a DPPH(paramagnetic) sample and I'm trying to find out the lande's factor using ESR setup. My problem is I'...
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1answer
42 views

Difference between $nh/2π$ and $\sqrt{\ell(\ell+1)}h/2π$

My textbook mentions that the orbital angular momentum is the second formula and the angular momentum of an electron is given by $nh/2π$ in Bohr model. Please help me realise the link between these ...
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Finding Lagrangian density for particle with spin 1 and mass $\mu$

I am trying to solve my first ever QFT problem, which reads as follow: From the wave equation for a particle with spin 1 and mass $\mu$: $$\left[g_{\mu\nu}(\Box+\mu^2)-\frac{\partial}{\partial x^...
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What is the physical interpretation of $\langle S_i^z S_j^z \rangle$?

Let's say, that we have some spin system with multiple sites. This system is in a quantum state denoted by $|\psi \rangle$. When we compute e.g. $\langle S_1^z \rangle = \langle \psi | S_1^z | \psi \...
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How an ultra-relativistic electron near the speed of light keeps its spin velocity without becoming partially superluminal?

If an electron has spin and volume than the point on the surface is rotating at constant speed according to Planck constant defined angular momentum.If this electron accelerates then this point on the ...
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What is a non-local particle in condensed matter physics?

What exactly is "non-local" in physics? How can a particle be non-local particle? Are non-local particles and collective modes related with each other? Are solitons local or non-local? (I am asking in ...
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Calculating expected values $\langle S_x \rangle$ and $\langle S_y \rangle$ in the Heisenberg model

Let's say, that we are considering the basic Heisenberg model with only two spin-particles. So our Hamiltonian can be written as follows: $$ H = \sum_{\langle i,i' \rangle} S^{(x)}_i S^{(x)}_{i'} + S^...
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Relation between intrinsic magnetic moment and moving charges

Moving charges creates magnetic field which is relativistic effect of electric field but magnetic field is also created by the intrinsic magnetic moment. How are they related? How does intrinsic ...
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2answers
30 views

Phase factor when deriving expressions for up/down spin in the $z$-basis

From what I understand, spin in the x direction takes the form $$ |+\rangle_x = a|+\rangle + b |-\rangle $$ (in the z basis), where $a$ and $b$ are complex. You can work out the value of the constants ...
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Questions about unitary condensate wave-function and $p_x+ip_y$ superconductor

I read about the unitary and non-unitary order parameter states here https://journals.aps.org/rmp/abstract/10.1103/RevModPhys.75.657 and https://arxiv.org/abs/1512.01151 The form of the order ...
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How to calcultate the interaction energy of a spin in a ferromagnetic material ? (Heinsenberg model)

In a ferromagnetic material, one cannot set $B=\mu_0 H$ because $M$ cannot be neglected. Then I don't understand why we often read that the energy of a single spin in the material is equal to (...
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Probability and spin dynamics

In the case of spin system, let's consider Sx be along X direction Sy be along Y direction and Sz be along Z direction. We know there is a finite probability for spin up and spin down states in these ...
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Magnetization effect in a free electron gas (Griffiths)

I am having trouble with problem 5.32 of Griffiths Quantum mechanics 3rd edition. The problem consider a free electron gas in which number of spin up and down particles is different and asks for the ...
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1answer
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Complex rabi frequency

I am learning quantum optics. In the book written by Scully includes complex rabi frequency, when dealing with $\Delta$ level configuration, the Hamiltonian including laser-atom interacting concludes ...