Low-frequency Noise in Josephson Junctions for Superconducting Qubits

TL;DR

This study investigates low-frequency noise in Al/AlOx/Al Josephson junctions across a wide temperature range, revealing temperature-dependent spectral behavior and implications for qubit coherence times.

Contribution

It provides detailed measurements of resistance fluctuations in Josephson junctions, highlighting defect effects and noise saturation at low temperatures, which impact qubit performance.

Findings

Spectral density follows 1/f law between 300 K and 5 K.

Defects distort the spectrum below 5 K.

Spectral density decreases linearly with temperature down to 1 K and saturates below 0.8 K.

Abstract

We have studied low-frequency resistance fluctuations in shadow-evaporated Al/AlOx/Al tunnel junctions. Between 300 K and 5 K the spectral density follows a 1/f-law. Below 5 K, individual defects distort the 1/f-shape of the spectrum. The spectral density decreases linearly with temperature between 150 K and 1 K and saturates below 0.8 K. At 4.2 K, the spectral density is about two orders of magnitude lower than expected from a recent survey [D. J. Van Harlingen et al., Phys. Rev. B 70, 064510 (2004)]. Due to the saturation below 0.8 K the estimated qubit dephasing times at 100 mK are only about two times longer than calculated by Van Harlingen et al.