1/f Flux Noise in Josephson Phase Qubits

TL;DR

This paper introduces a novel measurement method for low-frequency 1/f flux noise in Josephson phase qubits, revealing flux noise as the dominant source and challenging existing defect-based noise models.

Contribution

It presents a new technique to measure sub-Hz flux noise and provides evidence that flux noise exceeds critical-current noise, questioning standard defect models.

Findings

Flux noise dominates over critical-current noise in phase qubits

Measured flux noise levels are higher than predicted by defect models

New measurement method enables low-frequency noise analysis below 1Hz

Abstract

We present a new method to measure 1/f noise in Josephson quantum bits (qubits) that yields low-frequency spectra below 1Hz. Comparison of noise taken at positive and negative bias of a phase qubit shows the dominant noise source to be flux noise and not junction critical-current noise, with a magnitude similar to that measured previously in other systems. Theoretical calculations show that the level of flux noise is not compatible with the standard model of noise from two-level state defects in the surface oxides of the films.