Interaction-Resilient Scalable Fluxonium Architecture with All-Microwave Gates

Abstract

Fluxonium qubits demonstrate exceptional potential for quantum processing; yet, realizing scalable architectures using them remains challenging. We propose a fluxonium-based square-grid design with fast $\sim63$~ns controlled-Z (CZ) gates, achieving coherent errors below $10^{-4}$, activated via microwave-driven transmon couplers. A central difficulty in such large-scale systems with all-microwave gates and, therefore, strong static couplings, is suppressing parasitic interactions that extend beyond nearest neighbors to include next-nearest elements. We address this issue by introducing several design strategies: the frequency allocation of both qubits and couplers, the localization of coupler wavefunctions, and a differential oscillator that suppresses residual long-range interactions. In addition, the architecture natively supports fast $\sim70$~ns CZZ gates -- three-qubit operations composed of two CZ gates sharing a common qubit -- which reduce the incoherent error by $\sim 35\%$ compared to performing the corresponding CZs sequentially. Together, these advances establish an interaction-resilient platform for large-scale fluxonium processors and can be adapted to a variety of fluxonium layouts.