Symmetry-Protected Basin Localization in Variational Quantum Eigensolvers

Abstract: Variational quantum eigensolvers fail before optimization begins when strong correlation splits the molecular energy landscape into competing basins and the initial state selects a non-ground-state basin. We introduce a geometry-conditioned preconditioner $$\mathcal{P}<em>{\mathrm{eq}}:\mathbf{R}\mapsto\boldsymbolθ_0$$ constrained by the $SE(3)$ covariance of the molecular Hamiltonian, so that nuclear geometry is mapped directly into circuit parameters in the correlated ground-state basin. This basin localization changes the relevant gradient statistics from concentration controlled to curvature controlled. In statevector benchmarks on six stretched molecules, $\mathcal{P}</em>{\mathrm{eq}}$ reduces Hartree--Fock initialization errors by factors of $38\times$--$6250\times$, reaches sub-mHa initialization in CO, LiH, and H$<em>8$, and places N$_2$, H$_2$O, and BeH$_2$ in the mHa-scale correlated basin. In disordered H$</em>{10}$ chains, equivariant basin targeting and stochastic escape reach unit success probability at fixed optimization budget. The procedure performs basin selection before the shot-limited quantum loop; the quantum circuit then refines correlation inside the selected basin.