Spin Definition and 1000 Threads

Let's say we have 200 electrons. The first batch of 100 of those electrons are prepared in a way that 50% are UP in the x-axis while 50% are DOWN in the x direction. The order is unknown. The second batch of 100 electrons are prepared in the same manner but in the y axis. Bob picks one...

So consider a 2D system with a circular potential and a spin-orbit interaction: V(r) = V_0 \theta(r_0 - r) + c r_0 V_0 L_z S_z \delta(r-r_0) where θ is step function. So the operators Lz and Sz commute with the Hamiltonian are are therefore conserved quantities. For the same reasons...

The S_{z} operator for a spin-1 particle is S_{z}=\frac{h}{2\pi}[1 0 0//0 0 0//0 0 -1] I'm given the particle state |\phi>=[1 // i // -2] What are the probabilities of getting each one of the possible results? Now... we can say the possible measure results will be 1,0,-1 and the...

According to QM, given two entangled electrons A and B, if you measure the y-axis spin on A to be up, then you know electron B's y-axis spin is down. Also according to QM, if i understood it properly, you cannot then go on to measure the x-axis spin on B, because then you would know both y...

σx|x>=+|x> σx|-x>=-|-x> These equations also follows for σy and σz corresponds states |y> and |z>. if we measure along axis X then X state vector let it go which means up spin and opposite not go through which means down spin. and also same for y and z axis. But, σx|u>=|d> σx|d>=|u>...

Hi, The transmission of nano devices are generally done without cosidering the spin polarization. However, as I saw in some papers, the effect of spin is sometimes included. How can I decide to use spin or not when simulationg transmission of nanoscale devices? Thanks in advance...

Mellow, all Physics Forum member, Please help me to have the answer of question, Why electron spin is +-1/2. What is the reason of integral spin of subatomic particle?

Hi folks, In his seminal work of 1937, Wigner showed that the rest mass and (absolute) spin of a particle are the same for all observers related by Lorentz transformation. Does anyone know whether these quantities are also preserved under transformations to relatively accelerated observers...

Hi, If you have a even-even nuclei which is deformed, you get a rotational spectrum of 0+,2+,4+,... I don't understand why the parities are positive for even I and why all members of a rotational band must have the same parity. I read about this in Krane's book: an introduction to nuclear...

The wavefunction for a spin 1/2 particle is a spinor field of the form \psi(\mathbf{x},t)=\left( \begin{array}{cc} \psi_{+}(\mathbf{x},t)\\ \psi_{-}(\mathbf{x},t) \end{array} \right). \psi_{+}(\mathbf{x},t) is the amplitude that the particle is both spin up and located at position x at time...

Let me apologize in advance for not reading the entire rotating disk thread. I think that the following question is closely related, but if it was answered in that thread, I didn't spot it. Let us consider the following timelike congruences, which maps congruence parameters t,r,theta and z...

hi guys, i have a question about the orbit-spin relationship of the celestial objects. for example in our solar system i understand the orbital period becomes lengthy for the planets more distant than the sun, it's logical, but what happens with their spinning motion..? i don't understand why...

Spin superposition--am I understanding things right? Hi, I am going to sound ridiculous, but I was watching an online lecture on QM and the professor mentioned spins can be in superposition (as in a particle's spin can be in a superposition between different spins--if I heard right). I'm...

Hello all! I'm trying to wrap my head around this quantum entanglement thingy. As far as I have understood, if you have two entangled particles, say two electrones, it is impossible to predict their spins since they are thought to be in superposition of both up and down. But if you measure...

Spin and "intrinsic angular momentum" After searching this forum for what exactly spin is my inference is that it is a misnomer for an electrons "intrinsic angular momentum"...so some doubts; may be I am being too blunt; What is the difference between +1/2 and -1/2 spin? Is the electron...

Homework Statement Hi there, thanks in advance for any help! I have a first order DE: \frac{\partial \vec{m}}{\partial t} = -\vec{m} \times \vec{h}_{eff} + \alpha \vec{m} \times \frac{\partial \vec{m}}{\partial t} (a scaled Landau-Lifshitz-Gilbert equation) where m is a magnetism...

Homework Statement A cubical box whose sides are length L contains eight electrons. As a multiple of $$\frac{h^2}{2mL^2}$$ what is the energy of the ground state of the eight electrons? Assume the electrons do not interact with each other but do not neglect spin. Homework Equations...

Homework Statement The problem is stated on page 10 and it is number 9. http://panda.unm.edu/pandaweb/graduate/prelims/QM_F11.pdfHomework Equations I know how to write Sy in the z basis for either spin up or down and I have all the spinors.The Attempt at a Solution I tried solving for |ψ(t)> by...

Two questions 1) The total orbital spin angular momentum is given as L2=l(l+1). What is the source of or meaning of the (l+1). 2) Similarly for the electron the total spin angular momentum is given as S2-1/2(1/2+1) hbar2. Is the total angular momentum precessing to give sz 1/2 hbar object?

Hello, I need to understand the following: Considering an element Sulfur - S which has 16 electrons. How do we calculate the valency electron of S? Please correct me if I am wrong:2+2+6+2+4=16. So, the valency electron = 4+2=6 Is it that always valency electron is the addition of...

Is there a connection between the Dirac four spinor and "spin up", i.e one of the four spinor states is spin up or are these two separate unconected things.

Ok, so for some reason this section of the GRE book makes 0 sense to me ... maybe because i haven't taken the class yet, maybe I'm missing something ... It says "If you have a spin-1 particle with m = +1 and a spin-1/2 particle with m = +1/2, then m_tot = +3/2 (this part makes sense, you just...

Homework Statement Consider a system consists of two subsystem A and A' in which A contains 3 spins and A' contains 2 spins. Suppose that, when the systems A and A' are initially separated from each other, measurements show the total magnetic moment of A to be - 3{\mu _0} and the total...

I have a pair of non interacting, identical 1/2 spin fermions in a one dimensional infinite square well with walls at x=0 and x=L. One particle is in ground state, the other in first excited state. This two-particle system has total spin quantum number S=0 I have normalized energy...

In general I could understand the meaning of spin.But in quantum level it is getting more complicated that I couldn't understand what is integral spin and all.can anyone explain it in a macroscopic level?

Schrodinger's equation is what is used to determine the probability of finding a particle somewhere, but where are charge and spin? How do you know if the probability wave you solved for is for a proton or electron or some other particle? I see m in the equation for plugging in mass, but nothing...

There is something I'm struggling with and I can't seem to find the problem. We have the Z spinbase with: z = (1/sqrt(2))² <BRA|*(|s_z,+> + |s_z,->) which gives following z matrix: 1 0 0 1 and we have for X: |s_x, +> = 1/sqrt(2) |s_z,+> + |s_z,->) |s_x, -> = 1/sqrt(2)...

Forgive me in advance if this appears to be a dumb question but, as I was reviewing a few basic chemistry topics, namely orbital hybridization, I came across a question. From what I gather, according to Hund's Rule, an electron must be put into all open orbitals before the remaining orbitals can...

When entangled photons are generated from a cascade of a Calciums' 6s level this inequality : n[y+z-] + n[x-y+] ≥ n[x-z-] is derived for what is equivalent to spin in photons. When the detectors at A and B are parallel the perfect anti correlations are due to conservation laws of angular...

I'm a bit confused about quasars and neutron stars but is it the case that quasars are much much denser than our star and spin many times per second? I think the sun completes one rotation in about 25 days and it's spinning at about 4467mph. I'm pretty sure that density will effect the speed...

The below might need lots of corrections/modifications, since spin is a hard concept to grasp and I don't understand it much. We know that: The angular momentum (spin) of a photon does not have an analogy in classical mechanics. however let's use a loose/inaccurate analogy of something that...

Singularity Spin Mechanics Okay I within the last week too a look at a article about black hole spin and in this article it was said by a scientist that black hole's spin near the speed of light that are supermassive blazars I was thinking if a object is spinning wouldn't that make this...

In his book on GR, Wald writes "the notion of the mass and spin of a field requires the presence of a flat background metric...which one has in the linear approximation but not in the full theory..." Why do we need a flat background metric to define a field's mass and spin?

Say I have a particle in the rest frame with spin up in the z direction. If I boost the system in x direction, does the spin still point in the z direction? Why or why not? In Dirac Spinor, if I choose "spin up", namely setting \phi=\begin{bmatrix}1\\0\end{bmatrix} in the notation shown in...

Homework Statement For a homework problem, I have to work out ##\frac{d(\langle \hat{S}_x \rangle )}{dt}## for the four-by-four spin matrix ##\hat{S}_x##. I have a spin matrix ##\hat{S}_x## and I need to use the generalized Ehrenfest theorem. My problem is that I'm not sure whether my approach...

Permanent magnet can degenerate by many ways. But it really needed in compact generator to convert mechanical force into electric But are there any other way to generate electric from mechanical force without magnet? I want to design self exited magnet for dynamo. It need tobe an effect that...

Question. Is there a quantum reason why a lone electron in any of the three available (x,y,z) 2P orbital energy states must always be spin-up or spin-down ? Every figure I see always shows a single electron as spin-up for the three 2P energy states, but is there a quantum theory constraint...

The regular spin orbit Hamiltonian is H_{SO} = \frac{q\hbar}{4 m^2 c^2}\sigma\cdot(\textbf{E}\times \textbf{p}) If I consider a 2D system where E = E(x,y) and p is treated as an operator, i.e. \hat{p} = \hat{i}p_x + \hat{j}p_y then, clearly E and p do not commute, so this doesn't look like...

Why are the Pauli matrices multiplied by 1/2 ?? Why are they represented as σ1/2 σ2/2 and σ3/2 and not just σ1 σ2 σ3 ?

1 - How does an electron's spin generate its own magnetic field? 2 - Why are only the orientations of electrons taken into account in statements such as "permanent magnets are created when the orientations of the spin of the electrons are orientated in the same direction" when protons also have...

Hi, i have been trying to figure how to solve this problem, i just don't know how to proceed Homework Statement A particle with spin s=1 has due to rotational invariance all three states |s_z\rangle=1, |s_z\rangle=0 and |s_z\rangle=-1 degenated with energy E_0>0. Then its introduced an...

I have found what I think is the correct answer I just want to check an assumption. The magnetic field points in the +ve z-direction. We are given the initial state vector \left| A \right\rangle_{initial}=\frac{1}{5}\left[ \begin{array}{c}3\\4\end{array} \right] Am I right in thinking that...

Homework Statement Find expectation values ##\langle \hat{S}_x \rangle##, ##\langle \hat{S}_y \rangle##, ##\langle \hat{S}_z \rangle## in state ##|\psi \rangle =\frac{1}{\sqrt{2}}(|+\rangle +|- \rangle)## ##|+\rangle## and ##|-\rangle## are normalized eigen vectors of ##z## projection of...

Hey Everyone, I'm working on a question and can't quite get the answer out. QUESTION: Part (a) "\left|\alpha\right\rangle and \left|\beta\right\rangle are the eigenfunctions for neutrons polarized respectively along positive and negative z directions. If the neutron, initially in...

Homework Statement Find the eigenvalues and eigenstates of the spin operator S of an electron in the direction of a unit vector n; assume that n lies in the xz plane. Homework Equations S|m>= h m|m> The Attempt at a Solution This question is from Zettili QM and they have...

Homework Statement "A spin 1/2 electron in a hydrogen atom is placed in a time-independent magnetic field B=B0(k) The electron's spin starts in the |z+> state at t=0. Calculate probability o ffinding the electron in the |y-> state as a function of time for t>0. Homework Equations...

Given two spin-1/2 particles, the overall spin of the pair decomposes into a spin singlet and a spin triplet. Using the Clebsch-Gordon series and referring to the z-axis, we find the spin singlet is: ##|\Psi^- \rangle = \frac{1}{\sqrt{2}}(|\uparrow_z \downarrow_z \rangle - |\downarrow_z...

Homework Statement Hi All, this problem is related to spin-1/2 in an arbitrary direction, in particular building off of, but going beyond, Griffiths QM 4.30. I am given an unnormalized general spin state, \chi in the z basis, and then asked "in what direction is the spin state pointing?"...

Show that all hermitian 2x2 matrices with trace 0 are elements of three dimensional vector space in \mathbb{R}, which basis vectors are Pauli spin matrices. Any clues on how to begin? :/

What makes the world spin?