Noise in superconducting qubits and spin glasses

Abstract

Flux noise in superconducting quantum interference devices (SQUIDs) is produced by spins on the surface of metals. We have modeled these with Monte Carlo simulations of 2D and 3D Ising spin glasses that produce magnetization noise S_M consistent with flux noise. The frequency dependence of the magnetization noise goes as 1/f^α where the exponent a varies slightly with temperature. In 3D the noise power spectrum in the order parameter q goes as 1/ f^1.4 at T_c. The low frequency noise in both q and the magnetization is a maximum at T_c.