Superconducting qubits are hampered by flux noise produced by 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 report that H atoms either embedded in, or adsorbed on, an
a-Al2O3(0001) surface have sizeable spin moments ranging from 0.81 to 0.87 uB
with energy barriers for spin reorientation as low as ~10 mK. Furthermore, H
adatoms on the surface attract gas molecules such as O2, producing new spin
sources. We propose coating the surface with graphene to eliminate H-induced
surface spins and to protect the surface from other adsorbates.Comment: 12 pages, 4 figure
