In this work, we present a quantum algorithm for direct first-principles simulation of electron-nuclear dynamics on a first-quantized real-space grid. Our algorithm achieves best-in-class efficiency for block-encoding the pre-Born-Oppenheimer molecular Hamiltonian by harnessing the linear scaling of swap networks for implementing the quadratic number of particle interactions, while using a novel alternating sign implementation of the Coulomb interaction that exploits highly optimized arithmetic routines. We benchmark our approach for a series of scientifically and industrially relevant chemical reactions. We demonstrate over an order-of-magnitude reduction in costs compared to previous state-of-the-art for the NH3+BF3 reaction, achieving a Toffoli cost of 8.7×109 per femtosecond using 1362 logical qubits (system + ancillas). Our results significantly lower the resources required for fault-tolerant simulations of photochemical reactions, while providing a suite of algorithmic primitives that are expected to serve as foundational building blocks for a broader class of quantum algorithms.
@article{arxiv.2602.11272,
title = {Efficient Simulation of Pre-Born-Oppenheimer Dynamics on a Quantum Computer},
author = {Matthew Pocrnic and Ignacio Loaiza and Juan Miguel Arrazola and Nathan Wiebe and Danial Motlagh},
journal= {arXiv preprint arXiv:2602.11272},
year = {2026}
}