We establish tight connections between entanglement entropy and the approximation error in Trotter–Suzuki product formulas for Hamiltonian simulation. Product formulas remain the workhorse of quantum simulation on near-term devices, yet standard error analyses yield worst-case bounds that can vastly overestimate the resources required for structured problems.

For systems governed by geometrically local Hamiltonians with maximum entanglement entropy $S_{max}$ across all bipartitions, we prove that the first-order Trotter error scales as $O(t^2 S_{max} polylog(n) / r)$ rather than the worst-case $O(t^2 n / r)$, where $n$ is the system size and $r$ is the number of Trotter steps. This yields improvements of order $n^2$ for one-dimensional area-law systems and order $n^{3/2}$ for two-dimensional systems, up to logarithmic factors. We extend these bounds to higher-order Suzuki formulas, where the improvement factor involves $2^{p S^* / 2}$ for the $p$-th order formula.

We further establish a separation result demonstrating that volume-law entangled systems fundamentally require order $n$ more Trotter steps than area-law systems to achieve the same precision, up to logarithmic factors.

Our analysis combines Lieb–Robinson bounds for locality, tensor network representations for entanglement structure, and new commutator–entropy inequalities that bound the expectation value of nested commutators by the Schmidt rank of the state. These results have immediate applications to quantum chemistry, condensed matter simulation, and resource estimation for fault-tolerant quantum computing.