Hydrogen as a Source of Flux Noise in SQUIDs*

Superconducting qubits are hampered by flux noise produced by fluctuating surface spins from a variety of microscopic sources. Recent experiments indicated that hydrogen (H) atoms may be one of those sources. Using density functional theory calculations, we found sizeable magnetic moments arising from H atoms either embedded in, or adsorbed on, an α-Al₂O₃(0001) surface. We also find that H adatoms on the surface attract gas molecules such as O₂, producing new spin sources. We propose to use a coating layer (e.g., graphene) to eliminate the H-induced magnetization.