Strong coupling between a 2D fluxonium and Tantalum resonators*

The state-of-the-art superconducting device has a physical error rate that approaches the error-correction threshold but still stands in a crossover regime in which the logical error initially decreases with more physical qubits and later increases back. Further going beyond this break-even point calls for higher coherence physical system which can ensure higher fidelity limit. Fluxonium has been demonstrated to be a potentially better qubit candidate than the traditional transmon design due to its higher coherence and larger anharmonicity. By coupling two fluxoniums with long lifetime tantalum based resonators, we can perform resonator-induced-phase gate or geometric phase gate that is possible to reach lower error rate. In this talk, I will present our preliminary data on fabricating a 2D fluxonium and achieving strong coupling to a tantalum resonator. The tantalum film is cleaned with piranha solution and BOE to etch the oxide and remove hydrocarbons. The results demonstrate that combining 2D fluxonium and resonator-based two-qubit gates is a practical architecture for fault-tolerant quantum computing.