title: Candidate Source of Flux Noise in SQUIDs: Adsorbed Oxygen Molecules.
abstract: 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.
authors: State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai 200433, China. 2, Department of Physics and Astronomy, University of California, Irvine, California 92697-4575, USA.|Department of Physics and Astronomy, University of California, Irvine, California 92697-4575, USA.
authors: Hui
authors: H
authors: Wang
authors: Department of Physics and Astronomy, University of California, Irvine, California 92697-4575, 2, Department of Physics, University of Wisconsin– Madison, Madison, Wisconsin 53706, USA USA.
authors: Chuntai
authors: C
authors: Shi
authors: Department of Physics and Astronomy, University of California, Irvine, California 92697-4575, USA.
authors: Jun
authors: J
authors: Hu
authors: Department of Physics and Astronomy, University of California, Irvine, California 92697-4575, USA.
authors: Sungho
authors: S
authors: Han
authors: Department of Physics and Astronomy, University of California, Irvine, California 92697-4575, USA.
authors: Clare C
authors: CC
authors: Yu
authors: State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai 200433, China.|Department of Physics and Astronomy, University of California, Irvine, California 92697-4575, USA.
authors: R Q
authors: RQ
authors: Wu