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Open Access Publications from the University of California

Candidate Source of Flux Noise in SQUIDs: Adsorbed Oxygen Molecules.

  • Author(s): Wang, Hui
  • Shi, Chuntai
  • Hu, Jun
  • Han, Sungho
  • Yu, Clare C
  • Wu, RQ
  • et al.

A major obstacle to using superconducting quantum interference devices (SQUIDs) as qubits is flux noise. We propose that the heretofore mysterious spins producing flux noise could be O_{2} molecules adsorbed on the surface. Using density functional theory calculations, we find that an O_{2} molecule adsorbed on an α-alumina surface has a magnetic moment of ~1.8 μ_{B}. The spin is oriented perpendicular to the axis of the O-O bond, the barrier to spin rotations is about 10 mK. Monte Carlo simulations of ferromagnetically coupled, anisotropic XY spins on a square lattice find 1/f magnetization noise, consistent with flux noise in Al SQUIDs.

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