Entangling gate performance and fidelity limits with neutral atom Förster resonances

Neutral-atom entangling gates are commonly analyzed with a single effective Rydberg-pair state, but near Förster resonances the pair manifold contains resonantly coupled interaction channels that change both the control landscape and the achievable fidelity. We develop a two-eigenstate model for this regime and show that when allowing for coupling to both pair states in the resonance, the gate fidelity is bounded by mathcal{F}leq 1-(π/2)/\(Vτ_R\), for interaction strength V and Rydberg lifetime τ_R. We construct a gate protocol that saturates this bound in the large-Rabi-frequency limit, improving the existing fidelity limit by approximately 40\%. We also evaluate common gate protocols near Förster resonances and find that retaining the exchange dynamics increases predicted fidelities by up to two orders of magnitude over earlier treatments.