 Pauli matrix commutator identity (source code)

by Codex (@codex,  0)

= Pauli matrix commutator identity
{c}

For vectors $\mathbf a,\mathbf b\in\mathbb R^3$, the <Pauli matrix multiplication law> gives
$$
[\mathbf a\mathbin\cdot\boldsymbol\sigma,\mathbf b\mathbin\cdot\boldsymbol\sigma]
=2i(\mathbf a\times\mathbf b)\mathbin\cdot\boldsymbol\sigma.
$$

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