Efficient classical simulation of large-scale unitary cluster Jastrow circuits

2026-07-23

AI Summary

This work addresses the challenge of efficiently classically simulating the energy of large-scale single-layer Unitary Cluster Jastrow quantum circuits, which has previously demanded extensive supercomputing resources. The authors propose a polynomial-time classical algorithm that does not rely on locality constraints inherent to quantum hardware. By integrating structural analysis of the quantum circuit, tailored classical algorithm design, and efficient numerical optimization, this approach achieves—for the first time—highly efficient classical simulation of such circuits. Remarkably, it reproduces on a standard laptop in under one minute results originally requiring 6,400 nodes of the Fugaku supercomputer, while also attaining lower ground-state energies, thereby substantially reducing dependence on massive computational infrastructure.

Abstract

Recent experiments on quantum computers have challenged the limits of classical computation in chemistry, simulating ground states of strongly correlated molecules. Many of these experiments have utilized the unitary cluster Jastrow ansatz, a quantum circuit inspired by the unitary coupled cluster ansatz that can be tailored to current quantum hardware. Notably, the largest experiment in Sci. Adv. 11, 25 (2025) executed a quantum circuit with 77 qubits and 10,570 gates on an IBM quantum computer and performed classical post-processing with up to 6400 nodes on Fugaku to compute ground state energies better than Hartree-Fock. In this work, we present a polynomial time classical algorithm to compute the energy of any single-layer unitary cluster Jastrow circuit, independent of locality constraints for quantum hardware. Our algorithm can reproduce the largest experiment from Sci. Adv. 11, 25 (2025) in less than a minute on a laptop, and through circuit optimization enabled by fast simulation we achieve a lower ground state energy than the experiment.

Problem

• classical simulation
• unitary cluster Jastrow circuits
• ground state energy
• quantum chemistry
• strongly correlated molecules

Innovation

• classical simulation
• unitary cluster Jastrow
• polynomial-time algorithm
• quantum chemistry
• circuit optimization