Exploring the Boundary of Classical Simulability with Error Mitigation on IBM Quantum Devices

Rapid progress in quantum hardware is bringing experiments on IBM devices to the edge of classical simulability. However, without error mitigation, noise severely limits circuit volumes that can be accurately executed on quantum hardware. We apply characterization-based error mitigation using QESEM to recover noise-free expectation values from large quantum circuits on state-of-the-art IBM processors. The experiments probe regimes that challenge state-of-the-art tensor network and Pauli propagation methods run on the Fugaku supercomputer. Our results show how accurate error mitigation enables meaningful physical results from noisy hardware and delineates the boundary where quantum processors begin to outperform classical methods, marking a practical step toward near-term quantum advantage.