Surface-code hardware Hamiltonian

Abstract We present a scalable framework for accurately modeling many-body interactions in surface-code quantum processing units. Combining a concise diagrammatic formalism with high-precision numerical methods, our approach efficiently evaluates high-order, long-range Pauli string couplings and maps complete chip layouts onto exact effective Hamiltonians. Applying this method to surface-code architectures, such as Google’s Sycamore lattice, we identify three distinct interaction regimes: computationally stable phase, error-dominated phase, and hierarchy-inverted phase. Our analysis reveals that even modest increases in residual qubit-qubit crosstalk can invert the interaction hierarchy, driving the system from a computationally favorable phase into a topologically ordered regime. This framework thus serves as a powerful guide for optimizing next-generation high-fidelity surface-code hardware and provides a pathway to investigate emergent quantum many-body phenomena.