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 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. ...
0
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1answer
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 ...
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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 ...
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0answers
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 ...
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0answers
19 views

Proof of Exponential Decay Behavior of Time Correlation Functions

For a given protein, I know that the NMR Spectroscopy magnet generates a field $\mathrm{B_o}$ and that the interactions with the spins in the local environment generates a much smaller field $\mathrm{...
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28 views

How much of a Stern-Gerlach apparatus do you need to constitute a measurement?

As I understand it a Stern-Gerlach experiment just applies a non-uniform magnetic field onto a beam of particules. In so doing, it changes the orientation of the particules (first?), and then bends ...
0
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1answer
34 views

Representation of spin operators in a two electrons system

I've studied that the spin space of an electron is a two-dimensions Hilbert space. A possible representation of this space can be constructed defining: $$\chi_+ = \begin{pmatrix}1 \\ 0 \end{pmatrix} \...
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0answers
41 views

Atom-photon interaction

When we describe interaction of atom with EM field, we consider the interaction term in Hamiltonian as follows $$ W(t) = -\frac{e}{2\mu c} (\hat{A} \hat{p} + \hat{p} \hat{A}) + \frac{e^2}{2\mu c^2} \...
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0answers
19 views

Why are magnetic quantum numbers assigned like they are assigned in the paper on WS2 monolayers?

Now I'm reading the following paper: Sie, E.J., et al., 2015. Valley-Selective Optical Stark Effect in Monolayer WS2. ‎Nat. Mater., 14, 290-294 And they assigned magnetic quantum number to valence ...
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0answers
59 views

Are all particles in the universe quantum-entangled on some level?

The CMB indicates the universe was in a thermal equilibrium early on, which I understand indicates causal connection. There appears to have been some rapid expansion, and the universe now appears to ...
3
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1answer
21 views

What are possible ways to construct J-matrices (higher order Pauli matrices)?

I'm looking for possible ways to construct $J$-matrices. $J$-matrices are the higher-order version of Pauli matrices. Pauli matrices are suited for spin-1/2 systems, while J-matrices can be for any ...
0
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1answer
23 views

Total spin of many photon thermal state [closed]

I need to find the total spin of a large spin 1/2 ensemble in thermal state: I'm trying to find a formula for $\operatorname{Tr}(S^2 \rho)$ where $\rho=\frac{1}{Z}e^{\beta S_z}$ is the thermal state ...
0
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0answers
33 views

Grover's algorithm - how to capture eventual answer?

I don't fully understand what is the output of algorithm: a. Is it "value Y you search exists in your input", or b. Is it "value Y you search sits in location X of input". And another question: "what ...
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1answer
25 views

Effect of the translation operator affected by spin?

I'm reading an introductory review on quantum walks and at some point it incorporates spin into the translation operator in a way that I don't follow. Initially it states that the translation by ...
-3
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2answers
68 views

In handling two 1/2-spin particles, why is there only one singlet state? [closed]

Why is $\left|\uparrow\uparrow\right\rangle +\left|\downarrow\downarrow\right\rangle$ not discussed, despite having a total spin s = 0?
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0answers
4 views

Muon spin operator

I want to calculate the expectation value of the muon spin operator as a function of time. I found some expressions for the muon spin Polarisation. How can I make a connection between the two?
0
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1answer
55 views

How to prove that quantum computers can't solve problems outside PSPACE quickly?

What are general methods to prove that certain complexity class is not proper superset of PSPACE class, and how to apply them in quantum case (for BQP class, for example).
2
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1answer
49 views

Clebsch-Gordan Coefficients - Neutron can't decay into a proton and electron.

I've been reading in Weinberg's Lectures on Quantum Mechanics and in a note under the text it said that I can use the Clebsch-Gordan Coefficients to show that a neutron can't decay into a proton and ...
5
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3answers
151 views

When we say electron spin is 1/2, what exactly does it mean, 1/2 of what?

When we say electron has spin of $\frac{1}{2}$, is that the value of the total spin of electron, or the projection on z axis, or the spin quantum number? When we say "electron has spin of $\frac{1}{2}...
0
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3answers
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 ...
3
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1answer
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 ...
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1answer
100 views

How is hydrogen fine structure currently accounted for? [closed]

At a usually reliable site, Hyperphysics, the fine structure of Hydrogen is accounted for by the interaction between the B-field generated by the orbit of the electron, $0.4\:\mathrm{T}$ at $1s$ and $...
0
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0answers
24 views

Applications of exponential family Markov random fields in statistical physics

Ising model and its relatives are popular in statistical physics. Are there any physical systems that can be characterized by exponential family Markov random fields (e.g., the one in http://arxiv.org/...
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0answers
11 views

Specific microstate(s) corresponding to total angular momentum quantum number

Given a certain number of electrons in a certain electronic configuration (say, d$^2$ or (n$_1$p)(n$_2$d)), all combinations of the quantum numbers $m_l$ and $m_s$ can be constructed. Each of these ...
7
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Is it possible to have a photon with -1 spin?

Wikipedia states that a photon has a spin of value 1. What I want to know is this: are there two possible spins for photons, i.e. +1 and -1 (like electrons, which can have +1/2 or -1/2)? If the spin ...
0
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1answer
42 views

Time reversal symmetry for non-orientable manifold

From a recent paper by Kapustin(https://arxiv.org/abs/1406.7329), he argued that for non-orientable manifold with spin structure $Pin^{\pm}$, the corresponding time reversal symmetry $T$ squares to ${...
3
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1answer
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 ...
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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 ...
0
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0answers
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, ...
4
votes
1answer
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 ...
3
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2answers
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 ...
0
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0answers
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 ...
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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 ...
-5
votes
1answer
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 ...
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1answer
48 views

Quantum state after change of magnetic field

I have the following conditions: $\lvert\psi(0)\rangle=\lvert+\rangle_x=\frac{1}{\sqrt{2}}\lvert+\rangle+\frac{1}{\sqrt{2}}\lvert-\rangle$. So the state at $t=T$ is $\lvert\psi(t)\rangle=\frac{1}{\...
0
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1answer
56 views

Intuition for defining basis for Hamiltonian in momentum representation

I am going through Quantum information approach to the Ising model: Entanglement in chains of qubits by Stelmachovic et al. In Section A.4, the authors determines the eigenvalues and eigenstates of ...
2
votes
0answers
45 views

Bosonization for unequal left/right Fermi velocities

The standard exposition of bosonization/Luttinger liquid theory in textbooks treats the case that left and right channels share the same absolute value of Fermi velocity. Is it possible to relax this ...
3
votes
1answer
57 views

Forbidden transition

My question concerns something I just read on wikipedia whilst looking up forbidden transitions, here: https://en.wikipedia.org/wiki/Forbidden_mechanism#Gamma_decay Specifically, this sentence: "...
1
vote
3answers
203 views

How do we know that an electron “spins”?

As far as I know, you can't necessarily isolate an electron to observe it, you can only observe its effects on other particles due to fields. Moreover, we can't know an electron's exact location or ...
4
votes
2answers
88 views

Is there a relation between spin and the spin group?

In Quantum Mechanics spin appears as one type of angular momentum. Indeed, in Quantum Mechanics one angular momentum on the state space $\mathcal{E}$ is a triplet of observables $\mathbf{J}=(J_1,J_2,...
0
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1answer
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 ...
2
votes
1answer
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 ...
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0answers
33 views

Identical bosons with spin interactions eigenstates

Suppose that we have two particles where each of them has s=1 and it is in a harmonic oscillator potential and there is also a spin interaction. The hamiltonian of the system is :$$H=\frac{p_1^2}{2m}+\...
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vote
1answer
142 views

How to find this spin wavefunction? [closed]

If an electron is in a state that the probability of measuring spin along the +x axis is $P(+x)=\dfrac{1}{2}$ and the probability of measuring spin along the +y axis is $P(+y)=\dfrac{1}{2}$, what is ...
0
votes
2answers
105 views

Total spin of system of two spin-$1/2$ particles

Consider a quantum system of two spin one half particles. Let $\alpha(1)$ be 'spin up' for first system, and $\beta(1)$ 'spin down' for first system, and likewise for second system. We have $$ \chi = \...
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0answers
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 ...
3
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1answer
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 ...
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1answer
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 ...
2
votes
1answer
70 views

Are the 'clock' and 'shift' operators used in Qudit codes physically realizable?

I've recently started doing some reading on the subject of qudit codes. In particular, i'm interested in the frequently used clock and shift operators. Can these operators be physically realized? Or,...
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1answer
49 views

Reason behind choosing the invariant states for an operator which commutes with an adiabatic Hamiltonian

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 ...