- #1
LagrangeEuler
- 717
- 20
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 spin.
Homework Equations
## \hat{S}_x=\frac{\hbar}{2}\sigma_x ##
## \hat{S}_y=\frac{\hbar}{2}\sigma_y ##
## \hat{S}_z=\frac{\hbar}{2}\sigma_z ##
where sigmas are Pauli matrices.
The Attempt at a Solution
After calculation I get ##\langle \hat{S}_x \rangle=\frac{\hbar}{2}##, ##\langle \hat{S}_y \rangle=0##, ##\langle \hat{S}_z \rangle=0##
Why ##\langle \hat{S}_x \rangle## isn't zero if wave function is superposition of up and down in z-direction? Tnx for the answer!