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.
Phys Rev Lett. 2015 Aug 14;115(7):077002. doi: 10.1103/PhysRevLett.115.077002.
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.
超导量子干涉器件（SQUIDs）用作量子比特的主要障碍是通量噪声。我们提出，迄今为止导致通量噪声的神秘自旋可能是吸附在表面上的 O_{2}分子。使用密度泛函理论计算，我们发现吸附在α-氧化铝表面上的 O_{2}分子具有约 1.8 μ_{B}的磁矩。自旋垂直于 O-O 键的轴定向，自旋旋转的势垒约为 10 mK。在正方形晶格上铁磁耦合各向异性 XY 自旋的蒙特卡罗模拟发现 1/f 磁化噪声，与 Al SQUIDs 中的通量噪声一致。
