SU(2) spin-rotation: R(n̂, θ) = exp(−iθ·n̂·σ/2) = cos(θ/2)·I − i·sin(θ/2)·n̂·σ

SU(2) spin-1/2 rotation operator. Setup: Pauli matrices σ^x, σ^y, σ^z with [σ^a, σ^b] = 2i·ε^{abc}·σ^c (SU(2) Lie algebra with the spin-1/2 generators s^a = σ^a/2 — the defining 'fundamental' representation of su(2)). A rotation by angle θ…