A Modern Approach to Quantum Mechanics · Problem 1.9

Rotation of Basis States and Matrix Mechanics — John S. Townsend

Physics — Quantum Mechanics · uncertainty-sx-eigenstate

Problem

Verify that

\Delta S_x = \sqrt{\langle S_x^2\rangle - \langle S_x\rangle^2} = 0

for the state

|{+}\mathbf{x}\rangle