Microscopic origin of 1/f flux noise in SQUIDs and qubits · revision history

Revision 2

Accepted · core change · record

Changes against revision 1:

Title
Microscopic origin of 1/f flux noise in SQUIDs and qubits
Plain
Superconducting loops show slow magnetic-flux fluctuations of nearly the same size whatever the loop size or material. Unpaired electron spins on surfaces are blamed, but what they are and how they produce a 1/f spectrum is not settled.
Precise · changed · core
Revision 1: Low-frequency flux noise S_Phi(1 Hz)^(1/2) ~ 1-10 micro-Phi_0/Hz^(1/2) ($\Phi_0=hc/2e$), weakly dependent on loop area, is attributed to surface spins of density $\sim 5e13\,\mathrm{cm}^{-2}$ (Koch, DiVincenzo and Clarke 2007). Identify the spin species (adsorbed O2, hydrogen, dangling bonds) and the dynamics producing $1/f$ (spin clusters, spin-glass dynamics, spin diffusion), consistent with the measured temperature dependence and the correlation between flux noise and inductance noise.
Revision 2: Low-frequency flux noise $S_{\Phi}(1\,\mathrm{Hz})^{1/2} \sim 1-10\,\mathrm{micro}-\Phi_0/\mathrm{Hz}^{1/2}$ ($\Phi_0=hc/2e$), weakly dependent on loop area, is attributed to surface spins of density $\sim 5 \times 10^{13}\,\mathrm{cm}^{-2}$ (Koch, DiVincenzo and Clarke 2007). Identify the spin species (adsorbed $\mathrm{O_2}$, hydrogen, dangling bonds) and the dynamics producing $1/f$ (spin clusters, spin-glass dynamics, spin diffusion), consistent with the measured temperature dependence and the correlation between flux noise and inductance noise.
Settled by
Surface treatments that remove a candidate species and reduce flux noise by the predicted amount, together with a spin model reproducing spectrum, temperature dependence and cross-correlations.
Kind
well-posed
Answer type
identification
References
(empty)
Literature status
partially-resolved
Status note
Experiments since 2016 link part of the noise to adsorbed molecular oxygen; the spin dynamics producing 1/f remain disputed.
Posed since
1987

Decisions