Trotter-Suzuki first-order error: ||e^{−i(A+B)t} − (e^{−iAt/n}e^{−iBt/n})^n|| ≤ t²·||[A,B]||/(2n)

Trotter 1959 / Suzuki 1976: for non-commuting Hamiltonians H = A + B, exp(−iHt) is approximated by the product formula (exp(−iA t/n) exp(−iB t/n))^n. The first-order error scales as ε(n) ≤ t²·||[A,B]||/(2n) — quadratic in t, inverse in n.…