Vol 3 - Landau, Lifshitz - Quantum mechanics - non-relativistic theory (3ed., 1991) · Problem 55.1

Spin

Physics — Landau & Lifshitz · pauli-matrices-function-reduction

Problem

Reduce an arbitrary function of the scalar

a + \mathbf{b} \cdot \hat{\boldsymbol{\sigma}}

linear in the Pauli matrices to another linear function.