Principles of Quantum Mechanics · Problem 14.4.1

Spin — R. Shankar

Physics — Quantum Mechanics · ehrenfest-angular-momentum-precession

Problem

Show that if

H = -\gamma \mathbf{L} \cdot \mathbf{B}

, and

\mathbf{B}

is position independent,

\frac{d\langle \mathbf{L} \rangle}{dt} = \langle \boldsymbol{\mu} \times \mathbf{B} \rangle = \langle \boldsymbol{\mu} \rangle \times \mathbf{B}