Adsorbed Oxygen Molecules as a Source of Flux Noise in SQUIDs

ORAL

Abstract

A major obstacle for using superconducting quantum interference devices (SQUIDs) as qubits is the flux noise generated by fluctuating magnetic spins on the surface of SQUIDs. Using density functional theory (DFT) calculations, we investigated O2 adsorbates and various vacancies on an $\alpha $-alumina surface as spin candidates. Their spectroscopic features are directly compared to experimental data using the x-ray magnetic circular dichroism. The calculated magnetic anisotropy energy for the spin of O2 to rotate within a plane perpendicular to the axis of the O-O bond is only about 12 mK (or $\sim$ 1 $\mu $eV) so we believe that O2 molecules are the main source of flux noise in Al SQUIDs.

*Work at Fudan was supported by the 1000-Telent funds. Work at UCI was supported by DOE-BES (Grant No. DE- FG02-05ER46237) and by NERSC for computing time.

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Authors

  • Hui Wang

    • Department of Physics, Fudan University, Shanghai 200433, China

  • Zhe Wang

    • Department of Physics, Fudan University, Shanghai 200433, China

  • Jun Hu

    • Department of Physics and Astronomy, University of California, Irvine, CA 92697-4575, USA

  • Chuntai Shi

    • Department of Physics and Astronomy, University of California, Irvine, CA 92697-4575, USA

  • Clare C. Yu

    • Department of Physics and Astronomy, University of California, Irvine, CA 92697-4575, USA

  • Ruqian Wu

    • Department of Physics and Astronomy, University of California, Irvine, CA 92697-4575, USA