Origin and Suppression of $1/f$ Magnetic Flux Noise

TL;DR

This paper identifies adsorbed molecular O₂ as the main source of magnetic flux noise in superconducting qubits and demonstrates methods to suppress it, significantly improving qubit coherence.

Contribution

It reveals the role of molecular O₂ in flux noise and shows that surface treatments and vacuum improvements can greatly reduce this noise.

Findings

Suppression of static spin susceptibility by over an order of magnitude.

Reduction of $1/f$ flux noise spectral density by more than a factor of 5.

Surface treatment and vacuum improvements effectively reduce magnetic noise.

Abstract

Magnetic flux noise is a dominant source of dephasing and energy relaxation in superconducting qubits. The noise power spectral density varies with frequency as $1/f^\alpha$ with $\alpha \sim 1$ and spans 13 orders of magnitude. Recent work indicates that the noise is from unpaired magnetic defects on the surfaces of the superconducting devices. Here, we demonstrate that adsorbed molecular O$_2$ is the dominant contributor to magnetism in superconducting thin films. We show that this magnetism can be suppressed by appropriate surface treatment or improvement in the sample vacuum environment. We observe a suppression of static spin susceptibility by more than an order of magnitude and a suppression of $1/f$ magnetic flux noise power spectral density by more than a factor of 5. These advances open the door to realization of superconducting qubits with improved quantum coherence.