Compact 2D Fluxonium Qubits Design with Inductive Coupling for Measurement and Control*

The fluxonium, a novel superconducting qubit shunted by a large inductance, has recently exhibited milliseconds coherence times and high-fidelity single/two-qubit gates. A significant advantage of fluxonium lies in its richer matrix elements. At the half- flux point, the phase matrix element of computational states is not only stronger than its charge counterpart but also surpasses the phase matrix elements of non-computational states. It is natural to leverage this inherent strong 0-1 phase coupling to manipulate fluxonium. In this work, we propose a 2D fluxonium architecture with inductive coupling to achieve measurement and control. With all inductive coupling, we achieve a more compact geometric design—reducing the footprint of the resonator-qubit system by a factor 30. The diminished explicit capacitive coupling also holds promise for suppressing sensitivity to external decoherence sources, effectively mitigating dielectric losses between the substrate-metal and metal-air interfaces. We systematically explore various fluxonium designs to study decoherence mechanisms from dielectric loss and photon noise. Finally, we discuss the feasibility of fluxonium-based quantum processing units with the all-inductive coupling architecture.