Interaction-Resilient Scalable Fluxonium Architecture with All-Microwave Gates

TL;DR

This paper introduces a scalable fluxonium-based quantum architecture with all-microwave gates, featuring design strategies to suppress parasitic interactions and achieve fast, low-error multi-qubit operations for large-scale quantum processors.

Contribution

The paper presents a novel fluxonium grid design with techniques to suppress long-range interactions and implement fast, high-fidelity multi-qubit gates, advancing scalable quantum computing.

Findings

Achieved ~63 ns CZ gates with errors below 10^-4

Implemented ~70 ns CZZ gates reducing errors by ~35%

Developed design strategies for suppressing parasitic interactions

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.