# Tagged Questions

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.

65 views

### Why can we approximate dynamics of massive particles by masless and vice versa?

I am puzzled by the following observation. Our descriptions of massless and massive particles are very different. For example, masless particles have only two polarizations, which we call helicities. ...
52 views

### Quantum entanglement of spins

Suppose we have a pair of spins in the state $\left|\Psi\right>=\frac{1}{\sqrt2}(\left|\uparrow\downarrow\right>-\left|\downarrow\uparrow\right>)$. We know that the measurements of the spins ...
34 views

### Why can the y and z-components of spin be measured simultaneously? [duplicate]

I have a gut feeling that this is wrong. By the uncertainty principle where $x,y,z$ are the $x,y,z$ components of spin $$\sigma_{y}\sigma_{z}\geq \frac{\hbar}{2}\langle x \rangle$$ and it can be ...
21 views

### Can Fluctuation-Dissipation Theorem Apply to Magnetic Forces in Multi-Spin Systems

Let's say I have multiple spin systems (atoms in a protein) in a solution of water and the spin systems are all producing a magnetic field $\mathrm{B_{loc}}$ that affects nearby spin systems. Will the ...
19 views

54 views

### Measuring different components of spin simultaneously

I'm reading Griffiths Introduction to QM and I'm having trouble understanding why you can't simultaneously measure the x,y and z components of spin. I know that the uncertainty principle prevents this ...
40 views

### Why objects with magnetic dipole moment sometimes orient towards external B and other times they do precession?

Given the magnetic dipole moment in external uniform magnetic field $\vec{B}$, I am trying to understand why sometimes $\vec{\mu}$ simply aligns with the $\vec{B}$ and stays that way, while other ...
100 views

111 views

### How to evaluate possible values of spin of two photon system?

Photon hasn't well defined quantity such as spin. Instead of it, it is characterized by helicity $h$. Let's assume state of two photons in CM frame (with $\mathbf k$ being the momentum of one of ...
54 views

### Rotating fermion and spin structure on manifold

We know that doing a 2$\pi$ rotation would give a minus sign to wavefunctions of electrons. Since electrons are spin $1/2$ objects. How is this related to the spin structure on the manifold in which ...
29 views

### How to measure the spin of a particle?

How we can measure the spin of a particle from the angular distribution of its decay products? for spin zero particle the distribution is flat while for spin 1 particle the distribution is different, ...
84 views

### (Iso)spin coupling of three particles

I need Isospin calculations to predict the relative amount of strong decays, namely $D^{**0}\to D\pi\pi$, where the $D$ and $\pi$ can be charged or neutral. My problem is the order of contracting the ...
58 views

### Moving of spin up and spin down electrons in a magnetic field [closed]

Suppose we have an electron in a conducting space, and now we apply a magnetic field. Now according to the right hand rule, the electron will have a circular motion in the plane perpendicular to the ...
18 views

### Spin half particle Magnetic field oriented along y-axis

I've been looking over past papers for an upcoming QM exam and have had a few issues wrapping my head around this question. I can follow the common example as seen in Griffiths where the field is ...
62 views

### Electron spinning speed and “matter” it is made from

I wonder how electron may have spin if its model has no space occupied solely by the electron. Is it possible to estimate this rotation speed knowing its mass, charge and magnetic field emerged? If ...
67 views

### Can an electron have two spins? [closed]

Is it possible to imagine that an electron spins at the same time on two different and normal planes? What would the total S be? What kind of magnetic field would ensue, and how would it precess if ...
48 views

47 views

### Why does Carbon-12 have zero nuclear spin?

While studying NMR theory, my textbook explained that only nuclei with odd mass numbers are NMR active because they have non-integer spin quantum numbers and nuclei with an even mass number and atomic ...
39 views

### Relationship Between Magnetic Dipole Moment and Spin Angular Momentum

I am reading Introduction to Quantum Mechanics 1st edition by David J. Griffiths and I have a couple questions about this section on page 160. A spinning charged particle constitutes a magnetic ...
33 views

30 views

### Why don't we see a precession of compass in constant magnetic field?

It is known that spin particles put in magnetic field precess at the Larmor frequency around the axis of magnetic induction B. For example if the spin was perpendicular to B, the spin of the particle ...
64 views

### Tensor product representation of $SO(3)$ in the Hilbert space of particle with spin $S$

For a particle with a spin $S$, the rotation operator is given by $$e^{iJ_i\theta/\hbar}$$ where $J_i$ is the component of the total angular momentum along the direction of the rotation axis. The ...
42 views

### What is the spin of the Kalb-Ramond field?

In bosonic string theory the massless states of the closed string are given by a rank 2 tensor, which is divided into its three irreducible spherical tensors: symmetric traceless, antisymmetric and ...
In the section 4.1 of Quantum Computation by Adiabatic Evolution, Farhi et al proposes a quantum adiabatic algorithm to solve the $2$-SAT problem on a ring. To compute the complexity of the algorithm ...