Spin Definition and 1000 Threads

Question about quantum spin: So for the Schrodinger equation, the angular momentum of a wave-packet, whether it is free or confined to a potential well, appears to be calculated in exactly the manner you would expect it to be: L(x) = m*rxv[Psi(x)]. Aside from quantization (decomposing the...

Hi everybody, In most classical or quantum optics texts an angular momentum is considered for the EM radiation as the following: J = ε_0 ∫_V r × [E(r, t) × B(r, t)] d^3 r Then it is claimed that: "Using the usual formula for a double vector product and integrating by parts...

Hi, this probably has been answered somewhere here already, but I was unable to find it. Could someone explain how the spin of a particle is actually measured in an experiment ? Most interesting to me is how the 3d spin vector for 1/2 spin particles is determined experimentally. Cheers.

The spin angular momentum of a spin 1/2 particle is given by S = √(s(s+1))ℏ. If s =1/2, S= ((√3)/2)ℏ So, if s=1 is S= √2ℏ ?

The epr paradox is usually explained as something like: Suppose you have two electrons in the singlet state (+=spin up, -=spin down): lψ>= l+>l-> - l->l+> Now if you measure the spin on the first electron the explanation is (I think) that this collapses one electron onto l+> or l-> such...

Hi PF members. I have got a little worry I am familiar with the Zeeman term that always appears in the Hamiltonian of a spin chain representing the influence of an external magnetic field. I don't know if there is a similar term if the spin was rather in he presence of an electric field ( I...

I am reading a text about the splitting of the energy levels in crystals caused by the spin orbit interaction. In particular, the argument is treated from the point of view of the group theory. The text starts saying that a representation (TxD) for the double group can be obtained from the...

Homework Statement An alkali atom, on it's fundamental state, passes through a Stern-Gerlach apparatum, which will only transmit atoms with their spins aligned along the +z direction. After that the atoms travel, during a finite time τ, through a region of constant magnetic field...

So I know this might be a lot to read but I am having a very hard time understanding how to use the formulas in degenerate perturbation theory. Here is the problem I am on. Homework Statement A system of two spin-1/2 particles is described by the following Hamiltonian...

quantum spin vs ...spin I keep hearing people say, "comparing particle spin to a spinning top will lead you in the wrong direction." I'm curious.. what exactly is the difference between the two?

What is the link between the polarisation of light and photon spin?

In my textbook there is an equation for the precession frequency: Ω = τ/Iω The derivation in the book shows no difference in the spin angular momentum at time t = 0 and t = delta t but when I tried it I got that the denominator of the above equation must be the 'new' angular momentum (at t...

Hi, please could someone provide me with an explanation of the differences between the magnetic quantum number and the spin. I thought that the magnetism of an electron/fermion comes from its intrinsic quantum angular momentum (i.e. its quantum spin) which was evidenced by the Stern–Gerlach...

Homework Statement Consider an electron with spin \frac{1}{2} and orbital angular momentum l=1. Write down all possible total angular momentum states as a combination of the product states | l=1 , m_l > | s = \frac{1}{2} , m_s > Homework Equations Lowering operator : J_- |j, m> =...

Hi, please could someone explain the notion that particles of 1/2 integer spin do not look the same when turned through 360 degrees. This notion seems to crop up when I read around QM but nobody seems to explain how this came about. So my question is this - what experiment shows/confirms that...

Suppose we consider the spin 1/2 measurement matrices B=\frac{1}{\sqrt{2}}\left(\begin{array}{cc} 1 & 1\\1&-1\end{array}\right) and A=diag(1,-1) it's easy to show that B^2=A and a normalized eigenstate of B |\Psi\rangle=\left(\begin{array}{c}a\\b\end{array}\right) with eigenvalue 1 ...

What is the Lagrangian of interaction of photon and spin zero charge scalar?The vertex of photon and spin 1/2 charge fermion is proportional with e multiplied vertor gamma matrix,but I do not know what is the vertex of photon and charge scalar.I hear that a vertex is proportional with polynomial...

Dear members, I'd like to collect those properties of "spin" that makes it different to a normal (classical) angular momentum or magnetic moment. Please help me, correct, reword my sentences one by one. I'd like to create a short but still understandable and correct list. 1. Spin quantum...

how actually electron and protons spin? explain me whether this spinning could provide torque to the positive charges then it means electrons and protons keeps rotating under their electrostatic field?

i am actually calculating the nuclear spin of Sodium 23. Here we have 11 protons and 12 neutrons. Now both the nuclei are short of the magic numbers. When I use the shell model for protons and neutrons separately, I found 3 protons in the 1d5/2 sub-shell and 4 neutrons in the same 1d5/2...

Recently, I was thinking about spin and isospin. It's been a while since I've dealt with particle physics, so my knowledge may be a bit rusty. In the Standard Model, we have three interactions with associated coupling constants e, gw and gs. A particle may have three different charges Qe, Qw...

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 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 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...