Gate-Tunable Field-Compatible Fluxonium

Hybrid superconducting circuits have been used to investigate mesoscopic superconductivity, but mostly just at low magnetic fields, as typical Al-based circuits are incompatible with magnetic fields, and superconducting circuits are sensitive to external magnetic flux noise. To overcome these challenges, the authors build a hybrid fluxonium system composed of (Nb,Ti)N, with a gradiometric design. They observe the spectrum of the hybrid fluxonium in fields of up to 1T, and probe the φ₀ Josephson effect. These results enable future exploration of topological superconductivity, as well as readout of long-lifetime spin-polarized qubits using superconducting circuitry.