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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Why quantum tunneling not happens between orthogonal states? [closed]
I'm reading an article (https://doi.org/10.1002/anie.200390099) to understand more about quantum tunneling in single-molecule magnets. In the article is said that quantum tunneling is not possible ...
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Current in a Superconducting Loop Interrupted by a Josephson Junction
Assuming we have the following circuit consisting of a superconducting loop having the same superconductor material everywhere, and interrupted by the short Josephson junction J1 with a phase ...
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Why the massive spin-1 photon gets more degrees of freedom than massless case; while the massive spin-1/2 electron stays the same as massless case?
Spin 1 field without mass term like photon has 2 real degrees of freedom. The polarization with two states. I think I can denote it as quantum state $|s,s_z> = |1,1>$ and $|1,-1>$.
Spin 1 ...
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Orientation of Magnets in Paramagnetic Substances
We know that electrons can act as magnets and are responsible for the properties of para, diamagnetism, etc.
In particular, paramagnetic and ferromagnetic materials are permanent magnets due to the ...
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Spin Correlation Analogy in Three Particle System
I have recently gone through the section on Bell's Inequality in "Modern Quantum Mechanics" by J.J. Sakurai and Jim Napolitano and I am curious as to weather or not there are analogous ...
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Confusion about irreps of $SU(N)$: is the "color charge" the same as spin 1?
Sorry if the question is too silly or not well stated, I am happy to clarify any point. Also, my presuppositions can be wrong.
Consider a system of spin-$s$ particles: their spin operators $S_x$, $S_y$...
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What's the definition of spin for a particle in $d$-dimensional Minkowski spacetime?
Consider a relativistic quantum theory in d-dimensional flat spacetime. Neglecting possible internal symmetries, a particle is defined as a system whose Hilbert space furnishes the support of an ...
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What is the angle for the polarization of a massless spin-$s$ field to be rotated in order to become orthogonal?
For spinless particles there are no states related to spin.
For spin-1/2 particles like the electron, orthogonal spin states are obtained by rotating the state by $\pi$ radians, like in up $\uparrow$ ...
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How can a mean-field hubbard model describe itinerant ferromagnetism?
I see some textbooks showing how Hubbard model with Mean field approximation can explain ferromagnetism of band electrons(stoner theory), but intuitively I can't understand why an on-site Hubbard ...
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I'm stuck with the conversion of the 3 qubit $W$-state in terms of Pauli's spin matrices so that i can H-P transform them! [duplicate]
Given a state $|\psi\rangle=\frac{1}{\sqrt{3}}(|001\rangle+|010\rangle+|100\rangle)$. What is the density matrix in term of spin operators? Kindly give me detailed solution of this?
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Why does spin acting along $x$ on the spin up state yield spin down?
I'm currently struggling on how to interpret the particular result below:
$$\hat{S}_{x}\ | \alpha \rangle \ = \frac{\hbar}{2}\ | \beta\rangle$$
Where $\ | \alpha \rangle \ $ is the spin up state and $\...
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Phase accumulation in Rabi driving
When a single-qubit gate is operated by Rabi driving for a time $t$, the resulting operator is equivalent to
$ \hat{O} = R_z(\omega t) R_x(\Omega t)$
where $\omega$ is the frequency of the driving ...
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How can we say that the states of spin (+1, -1) represent 2 dimensions when they lie on a 1D number line?
I am having issues understanding why +1, -1 are considered 2 separate dimensions of state in the context of spin. Since, the values lie on a 1 dimensional number line. For example, the number line of ...
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Why does mirror/inversion symmetry exclude nearest-neighbor spin-orbit coupling in the Kane-Mele model?
I've been reading about the Kane-Mele model and noticed that it does not include nearest-neighbor spin-orbit coupling, with explanations often pointing to mirror symmetry as the reason. Could someone ...
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Has the Stern-Gerlach experiment now been carried out with free electrons or protons instead of silver atoms? [duplicate]
At least, why not try with protons, they are much heavier and at the end, any deflection from Lorentz force will not overshadow the Stern- Gerlach phenomenon.
But the question is still, was such ...
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Is there any measurement of electron spin that doesn't involve magnetic moment?
So the way to measure electron spin is to split the beam with a magnet to obtain two beams. Essentially what gets measured is magnetic moment, that is later interpreted as the direction of spin ...
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Stern–Gerlach experiment - what's so strange? [duplicate]
I partially get it but don’t completely understand what is weird about it. Please tell me what I’m getting wrong.
Lets say North(stronger) is on the top and South on the bottom.
I understand the next ...
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Stress-energy tensor spin-1 coupling
Would it be possible for the stress-energy tensor ($T_{\mu\nu}$) to couple to a spin-1 anti-symmetric rank-2 field (like the electromagnetic field strength tensor $F_{\mu\nu}$)? If so, what would be ...
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Decomposing direct product of spin-$s$ representation into direct sum
Direct product of spin-$s$ representations can be decomposed into direct sum of some other spin-s representation:
$$
\{j\}\otimes\{s\}=\sum_{\oplus l=|j-s|}^{j+s}\{l\}
$$
Howard Georgi gives a hint in ...
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Tunneling lowers the energy of a ground state superposition of spins up and down in the quantum Ising model
Considering an Ising model in the quantum scenario in quantum spatial dimension d=1 (that corresponds to classical D=2=d+1 dimension). Starting with the Ising model hamiltonian under the approximation ...
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How does spin $j$ matter contribute to the running of the gauge coupling?
The one-loop beta function $\beta(g)$ for the gauge coupling $g$ with gauge group $G=SU(N_c)$, in a theory with $n_f$ spin-1/2 fermions in a representation $R_f$ of $G$, and $n_s$ complex scalars in a ...
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Confusion about spin in 1 dimension
If spin should not be defined for particles in 1 dimension since we can't do rotations in 1d, like it happens for the orbital angular momentum, then why can we talk about fermions in a 1 dimensional ...
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How to derive the projection operator for multiple spins in terms of spin operators?
Say I have two spin-s angular momenta, $\vec S_1$ and $\vec S_2$.
The Hilbert space is formed by states like
$\left|j,m\right>$, where $0 \leq j \leq 2s$ and for a given $j$ the other quantum ...
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Bloch vector, maaster equation, and Bloch equation [closed]
I was confused about a derivation of Bloch equation in Breuer and Petruccione's The theory of Open Quantum Systems. Can someone gives some hints on derivation from Eq. 3.219 to Eq. 3.226? Specific ...
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Can we derive spin of particle somehow?
so my quantum mechanics teacher told me that spin is just a intrinsic quantity that we just need to accept .But my question is that can we somehow derive the spin of a particle like for example adding ...
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Interaction picture for spin-operator $J_x$ [closed]
I try to find a simple way or even an explicit expression for interaction representation
$$J_x(t):=e^{iJ_zt}J_xe^{-iJ_zt},$$
where $J_x, J_z$ are spin-operators for arbitary spin $j$. I have tried to ...
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Spin/Helicity-Density Matrices in Particle Physics
I am searching for literature explaining the Spin/Helicity-Density Matrix formalism in order to compute "spin-dependent" matrix elements and cross-sections in particle physics.
I would ...
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Dimension of singlet subspace of $2N$ identical spin-1/2 particles
Consider a quantum system of $2N$ identical spin 1/2 particles, each having a 2D Hilbert space $V$. The total Hilbert space is the tensor product $V^{\otimes 2N} \equiv V \otimes \cdots \otimes V$. ...
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Query on Expectation value of Spin-X operator being Invariant with transformation of BASIS
Please correct my calculations below. Where did I go wrong? What did I assume wrong?
Thanks & Regards,
Sarath Chandra.
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Is quantum spin intrinsic, or a function of some other characteristic? [closed]
In my current understanding, I have been told that the spin of quantum particles is simply intrinsic to them. That, particles are simply right-handed or left-handed... just because they are. To me, ...
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Understanding the Nuclear Spin of Boron-10: Why is it Spin-3?
I am delving into the nuclear spin characteristics of Boron-10, which notably has a nuclear spin of 3. While I have a foundational understanding of some quantum mechanical principles, the specific ...
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Theoretical calculation of Electron Paramagnetic Resonance (EPR) spectra
I have read that rather than holding the static magnetic field constant and varying the frequency of the oscillating field in Electron Paramagnetic Resonance/Electron Spin Resonance (EPR/ESR) ...
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Dirac explained spin 1/2 with ribbons and ropes - is there another way? (With answer by Roger Penrose himself - probably)
Dirac used chairs, ropes and scissors to explain spin 1/2. Is this visualization unique?
Or is there any other method to show that 2 rotations and 0 rotations are similar, but 1 rotation is not? (Arms ...
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The relation between spin and momentum in particle state
In quantum field theory, it seems that when we consider a massive particle's spin degree of freedom, we usually do in the particle's rest frame. And I know the little group will only change spin DOF ...
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Fields as Lorentz group irreps, spin and motion equation
My question touches quite a vast subject. I'm looking for a macroscopic answer without a lot of math, just the one needed to feel the answer.
We have $SO(3,1)$ lorentz group, we can give him all the ...
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Time reversal operator acting on $|sm\rangle$ and the $UK$ decomposition [duplicate]
I'm learning the time reversal operator from Notes by Littlejohn. In a system with spin, time reversal operator $\Theta$ can be decomposed,
$$
\Theta=\exp(-\mathrm i\pi S_y/\hbar )K_s,\tag{1}
$$
...
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Question on Spinor choice in QED
In QED (see Peskin and Schoeder's book on QFT or Srednicki's book), to determine the fermion wave-function, we usually start with a spinor of a massive particle that is not moving, say
$$u_+(\vec{p}=\...
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Total Angular Momentum operator in spinor-helicity formalism
I am reading Evidence for a new Soft Graviton theorem, by Cachazo and Strominger. At some point, they express the relation
$$J_{\mu\nu}\sigma^{\mu}_{\alpha\dot{\alpha}}\sigma^{\mu}_{\beta\dot{\beta}}
=...
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Harmonic Oscillators: Expectation value of the exponential of ladder operators
I am working with a spin-boson model. To figure out how the off-diagonal elements of the reduced density matrix for the system evolve, I need to figure out $\langle e^C\rangle$ where $C= c_{1}a+c_2a^{\...
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What is the Majorana stellar representation?
One can geometrically visualize spin-1/2 states using the Bloch sphere. A natural question then is: "Can one geometrically visualize spin-$s$ states using a similar object to the Bloch sphere?&...
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Conceptual difficulties with spin
I thought I had the concept of spin down (literally) but I seem to be a bit rusty. I want clarifications on a few concepts. Let's say I have a particle of spin $\vec{S}$. Consider a direction $\hat{n}$...
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Difference in spin angular momentum
In chemistry, I learnt that the spin angular moment of a single unpaired electron in an atom can be calculated by
$\frac{\sqrt{3} h} {4\pi}$,
but while studying radioactivity, I studied that the spin ...
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Ground state of the Heisenberg XXX model with a coupling?
I have a one-dimensional Heisenberg chain with a Magnetic field with $N$ sites with $J>0$
\begin{equation}
\mathcal{H} = -J \sum_{i = 1}^{N-1} \vec{S_i}\cdot \vec{S_{i+1}}- \sum_{i = 1}^N \vec{H}\...
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Stern-Gerlach Experiment vertical atom distribution
From some of the videos covering the Stern-Gerlach experiment I noticed that electrons / silver atoms that are shot through the magnet are visualized to spread not only into two distinct horizontal ...
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Why assume no degeneracy in Spin operator?
The Stern-Gerlach experiment measures a physical property of a quantum system. We hence associate an operator $\hat{S_z}$ with the observable, in accodance with the postulates of QM.
The eigenvalues ...
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Spin correlations of identical leptons in a Z-boson decay
In 2012, the CMS experiment observed a decay of the $Z$ boson into four leptons: https://inspirehep.net/literature/1190671
The Feynman diagram for this process is shown in this Figure:
Its final ...
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Nuclear-Fusion related Question on Spin
I was studying Nuclear Fusion and came across this nuclear reaction.
I've read that the spin of all particles is conserved in any nuclear reaction.
I was really intrigued because that meant that ...
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Question about spin-$½$ particles
Spin-½ particles needs to rotate 720º to return to its original state. If you rotate it 360º, its state will become opposite, for example $\left| ↑ \right>$ to $-\left| ↑ \right>$. This is my ...
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Direction of spin state from time evolution operator
In a oscillating magnetic field of the form $$\mathbf{B} = B_0 \cos(\omega t)\mathbf{e}_z$$ with Hamiltonian $H = -\gamma \mathbf{B} \cdot \mathbf{S}$, I found that the unitary time evolution operator ...
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Visualization of a potassium atom with electron configuration
Say we have a normal potassium atom. It is understood that its electron configuration is
$$1s^{2}\,2s^{2}\,2p^{6}\,3s^{2}\,3p^{6}\,4s^{1}.$$
This configuration contains the energy levels, orbital ...
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