Superconducting Gralmonium Qubit Resilient to High Magnetic Fields

Superconducting qubits can be used as information engines to probe and manipulate microscopic degrees of freedom (DOF), whether intentionally designed or naturally occurring in their environment. In the case of magnetically susceptible DOF, the external magnetic field used to polarize them presents a challenge for superconductors and Josephson junctions. Here we demonstrate the operation of a granular aluminum nanojunction fluxonium qubit (Gralmonium), resilient to in-plane magnetic fields beyond one Tesla. By employing a gradiometric fluxonium design, we enhance the qubit’s insensitivity to global magnetic flux fluctuations. The energy relaxation (T₁ = 8 µs) and coherence (T_2E = 2.5 µs) are unaffected by the magnetic field and we observe only minor changes in the qubit spectrum, caused by percent level gap suppression. The gradiometric gralmonium’s field resilience highlights its potential for hybrid quantum architectures that combine superconducting qubits with spin systems.