Spin Definition and 1000 Threads

Homework Statement Two particles with spin 1/2 and are in the spin state: |\psi> = |\uparrow_{1}>|\downarrow_{2}> where |\uparrow_{1}> is a state where particle 1 has spin up along the z-axis and |\downarrow_{2}> is a state where particle 2 is spin down along the z-axis. If...

Sorry if it is a silly question: Photons have spin-1 and therefore they have theoretically three possible spin states (1,0,-1), For the ±1 case I can see the relation to the ±helicity, but what corresponds physically to the 0 state case?

Homework Statement https://fbcdn-sphotos-c-a.akamaihd.net/hphotos-ak-prn2/1483071_10151813160569290_1331827985_n.jpg Homework Equations \left|\psi ,t\right\rangle=\sum_i c_i(t)e^{-\frac{i E_n t}{\hbar}}\left|n\right\rangle The Attempt at a Solution I'm quite lost on how to even start this...

hi all, i am interested in MRI, and i wish to know what is the scientific theory telling us that the spins will precess in phase if they were placed in an external field and exposed to a 90° RF pulse. what i know is that the nuclei will precess at the same angular frequency (or same angular...

Homework Statement I'd like to calculate the probability of a spin flip transition occurring in the ground state of neutral hydrogen. That is, the transition from parallel to anti-parallel spin configuration of the electron and proton. This transition produces the 21-cm line. Homework...

Homework Statement If a particle has spin 1/2 and is in a state with orbital angular momentum L, there are two basis states with total z-component of angular momentum m*hbar l L,s,Lz,sz > which can be expressed in terms of the individual states ( l L,s,Lz,sz > = l L,Lz > l s,sz > ) as l...

In my lecture notes, there is a slide about an external field interacting with a system of electron spins. In this situation can we assume that B=B_0 ( or in other words that μ_0*M =0)? I would think so, but does a system of electron spins imply that these electrons belong to some matter...

Homework Statement What are the possible results of the measurement of the sum of the x and z components of the spin angular momentum of a spin-1/2 particle? Sx = Spin angular momentum operator x Sz = Spin angular momentum operator x Homework Equations The Attempt at a...

can we spin a shpere of air? not the shell only, but the whole volume itself spinning on it's axis, can we do that and let a ball of air spin with momentum, and if it is fast enough, it would form such a centrifugal force that it can maintain itself without keeping on spinning it

It's frequently mentioned in introductory quantum mechanics texts that Goudsmit and Uhlenbeck conjectured that the magnetic moment of an electron was due to angular momentum arising from the electron rotating around its own axis. But then when they tried to calculate how fast it would have to...

Hi, I am having trouble following the Peskin and Schroeder and their derivations to show that a Dirac particle is a spin 1/2 particle (page 60 and 61). I understand how he gets the first (unnumbered) equation on page 61. However, I don't understand how he gets to the second equation...

I'd like to understand better the connection between Hal Haggard's September ILQGS talk http://relativity.phys.lsu.edu/ilqgs/ http://relativity.phys.lsu.edu/ilqgs/haggard091713.pdf http://relativity.phys.lsu.edu/ilqgs/haggard091713.wav and the talk he gave at PI two days ago...

Hi all, Do anyone know what is the spin correlation and what its relation to theNarrow Width Approximation. Regards, Safinaz

Hello everybody, I have a curious excercise, there is a 1/2 spin particle in a magnetic field ##\vec{B}(t)## with ##||\vec{B}(t)||## constant, orientated in an angle ##\theta## from the ##z## axis rotating with an angular speed ##\Omega##. The hamiltonian will be $$H(t)=-\vec{S}\cdot\vec{B}$$...

1. What are the possible eigenvalues of the spin operator \vec{S} for a spin 1/2 particle? Homework Equations I think these are correct: \vec{S} = \frac{\hbar}{2} ( \sigma_x + \sigma_y + \sigma_z ) \sigma_x = \left(\begin{array}{cc}0 & 1\\1 & 0\end{array}\right),\quad...

Homework Statement What is the expectation value of \hat{S}_{x} with respect to the state \chi = \begin{pmatrix} 1\\ 0 \end{pmatrix}? \hat{S}_{x} = \frac{\bar{h}}{2}\begin{pmatrix} 0&1\\ 1&0 \end{pmatrix}Homework Equations <\hat{S}_{x}> = ∫^{\infty}_{-\infty}(\chi^{T})^{*}\hat{S}_{x}\chi...

Homework Statement The evolution of a particular spin-half particle is given by the Hamiltonian \hat{H} = \omega\hat{S}_{z}, where \hat{S}_{z} is the spin projection operator. a) Show that \upsilon = \frac{1}{\sqrt{2}}\begin{pmatrix} e^{-i\frac{\omega}{2}t}\\ e^{i\frac{\omega}{2}t}...

I wondered about them sometime; I came across many theories, such as it might be because the of the black hole at its centre, but another question rises! Why black holes spin? I thought it might be because at first when the black hole was a star just like our sun, before supernovae happening...

If you see a statement like "Spin analysis of H(22S) atom can be achieved through the use of Stern Gerlach interferometry" are they talking about the spin of protons or electrons? Are they perhaps always correlated ie. the same? What about H(22P)?

Dear PhysicsForum, We have just treated the Dirac equation and its lagrangian during our QFT course, but we have only gone in depth in 3+1 dimensions. My question is about what happens to spin in 2+1 dimensions. In 3+1 dimensions we have to use 4 by 4 gamma matrices, but in 2+1 dimensions we...

I understand that the degrees of freedom must match. A Weyl spinor has 2 d.o.f (spin up and spin down), thus the superpartner must also have 2 d.o.f Is there a reason why it is a complex scalar and not of spin-1?

I'm no physicist, so please enlighten me. Is an electron's spin related to the spin of a proton? Do they spin at the same frequency? I read that electrons have a higher magnetic moment and stuff.

I have read about the Stern-Gerlach experiment in Wikipedia, this experiment proved that electron spin could only take two discrete values. The experiment consist in sending neutral charged atoms through a inhomogeneous magnetic field so it would change the particle’s direction a quantity...

Say an electron tunnels from one state, through a tunneling barrier, to another state. Is the spin of that electron preserved (the same before and after)? If an electron is traveling through a bulk phase conductive metal (a wire), is its spin stable in one state? What will happen to its spin...

The detection of spin in Hadrons and Leptons is done through magnetism, a spin 1/2 particle has two states in a magnetic field, an up particle goes up, a down particle goes down. A spin 1 particle has three states, an up/up goes up, a up/down stays straight and a down/down goes down. A spin 3/2...

If we consider a spin 1/2 particle, then, the rotation of the spinor for each direction is given by a rotation matrix of half the angle let say theta Rspin=\left(\begin{array}{cc} cos(\theta/2) & -sin(\theta/2)\\sin(\theta/2) & cos(\theta/2)\end{array}\right) and the new component of the spin...

Homework Statement A beam of spin-1/2 particles is prepared in the state \left|\psi\right\rangle=\frac{2}{\sqrt{13}}\left|+\right\rangle_x+i \frac{2}{\sqrt{13}}\left|-\right\rangle_x a) What are the possible results of a measurement of the spin component Sz, and with what probabilities...

Homework Statement An ultra-centrifuge has a cylindrical disk mounted on an axle that is almost frictionless. The disk spins about an axis through its centre as shown. If the disk is spinning with an angular speed of 4.50 x 10^5 rad/s and the driving force is turned off, its spinning slows...

Homework Statement A qubit is in the state |ψ(0)>=|0> . A magnetic field is applied in the x^ direction at t=0. This corresponds to the Hamiltonian H=BX, where B is a constant and X is the usual bit flip gate. What are the coordinates (θ,ϕ) of this qubit on the Bloch sphere at time t, as a...

Homework Statement A number of spin 1/2 particles are run through a Stern-Gerlach apparatus and when the emerge they all have the same spin wave function (ψ1, ψ2)τ and 9/25 are in the +z direction and 16/25 are in the -z direction with the normal basis column vectors for +z and -z...

This is how I understand it: Bohr argued that universe was inherently unpredictable as was the spin of the particle, and it was only based on probabilities. Einstein argued that the spin of the particle was actually always the same, just that our physics is not capable of determining it. But...

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?