Geometrical dependence of low frequency noise in superconducting flux qubits

TL;DR

This study introduces a measurement method for low-frequency flux noise in superconducting flux qubits and reveals how qubit design, especially wiring geometry and ground plane presence, influences noise levels, highlighting magnetic impurities as a key source.

Contribution

The paper presents a direct measurement technique for flux noise and systematically investigates how qubit geometry and fabrication conditions affect noise, providing insights into noise mitigation.

Findings

Flux noise varies minimally among identical designs.

Wiring length and width significantly affect flux noise levels.

Superconducting ground planes reduce flux noise.

Abstract

A general method for directly measuring the low-frequency flux noise (below 10 Hz) in compound Josephson junction superconducting flux qubits has been used to study a series of 85 devices of varying design. The variation in flux noise across sets of qubits with identical designs was observed to be small. However, the levels of flux noise systematically varied between qubit designs with strong dependence upon qubit wiring length and wiring width. Furthermore, qubits fabricated above a superconducting ground plane yielded lower noise than qubits without such a layer. These results support the hypothesis that localized magnetic impurities in the vicinity of the qubit wiring are a key source of low frequency flux noise in superconducting devices.