High-coherence fluxonium qubits manufactured with a wafer-scale-uniformity process
Fei Wang, Kannan Lu, Huijuan Zhan, Lu Ma, Feng Wu, Hantao Sun, Hao Deng, Yang Bai, Feng Bao, Xu Chang, Ran Gao, Xun Gao, Guicheng Gong, Lijuan Hu, Rui-Zi Hu, Honghong Ji, Xizheng Ma, Liyong Mao, Zhijun Song, Chengchun Tang · Physical Review Applied · 2025
Fluxonium qubits are recognized for their high coherence times and high operation fidelities. These are attributed to their unique design incorporating a superinductor, which is typically implemented using an array of over 100 Josephson junctions; however, this complexity poses significant fabrication challenges, particularly in achieving high yield and junction uniformity with traditional methods. Here, we introduce an overlap process for Josephson-junction fabrication that achieves nearly 100% yield and maintains uniformity across a 2-inch (50.8-mm) wafer with less than 5% variation for the phase-slip junction and less than 2% for the entire junction array. We use a compact junction array design that achieves state-of-the-art dielectric loss tangents and flux noise levels, as confirmed by multiple devices. This enables fluxonium qubits to reach energy relaxation times exceeding 1 ms at the flux-frustration point. This work paves the way for scalable, high-coherence fluxonium processors using processes compatible with complementary metal-oxide semiconductor manufacturing, marking a significant step toward practical quantum computing.