Phenomenological noise model for superconducting qubits: two-state fluctuators and 1=f noise

TL;DR

This paper introduces a phenomenological noise model for superconducting qubits, showing that a small number of surface spins with large magnetic moments can produce 1/f noise, aligning with experimental observations.

Contribution

It proposes a unified model linking two-state fluctuators to 1/f noise in superconducting qubits, and demonstrates how to extract noise characteristics from experiments.

Findings

Noise spectrum consistent with 1/f noise

Fewer than 100 slow fluctuators influence the qubits

Surface spins with large magnetic moments are likely responsible

Abstract

We present a general phenomenological model for superconducting qubits subject to noise produced by two-state fluctuators whose couplings to the qubit are all roughly the same. In flux qubit experiments where the working point can be varied, it is possible to extract both the form of the noise spectrum and the number of fluctuators. We find that the noise has a broad spectrum consistent with 1=f noise and that the number of fluctuators with slow switching rates is surprisingly small: less than 100. If the fluctuators are interpreted as unpaired surface spins, then the size of their magnetic moments is surprisingly large.