📝 SummarXiv

Abstract

This work investigates the nature of the ground state of the antiferromagnetic Heisenberg model on minimal kagome cells -- a triangle and a star -- using the variational quantum eigensolver (VQE) algorithm on real quantum hardware. We demonstrate that the ground state preparation is achievable using a shallow hardware-efficient quantum circuit with a naturally Euclidean parameter space. Our custom ansatz is capable of accurately recovering essential properties such as the spin correlation terms for each edge without explicit error mitigation. These features are found to be less sensitive to noise. We exploited the Fubini-Study metric in constructing the ansatz, ensuring a singularity-free parameter space. With this ansatz design, the quantum natural gradient coincides with the normal gradient, complemented with a backtracking search for dynamic step size adaptation. We refer to this regime as the implicit adaptive quantum natural gradient descent. It achieves faster convergence in fewer iterations compared to simultaneous perturbation stochastic approximation (SPSA), while maintaining competitive runtime with the metric being analytically constant. We further apply error mitigation techniques, including zero noise extrapolation (ZNE) and qubit-wise readout error mitigation (REM). While ZNE does not obey the Rayleigh-Ritz variational principle, the conditions under which REM preserves it are discussed.