Surface spin fluctuations probed with flux noise and coherence in Josephson phase qubits

TL;DR

This study investigates how inductor geometry affects surface spin fluctuations, flux noise, and qubit coherence in Josephson phase qubits, revealing that increased inductance raises flux noise and dephasing, with noise correlation length between 6 and 400 micrometers.

Contribution

It provides the first detailed analysis linking inductor geometry to flux noise and qubit coherence, confirming theoretical predictions with experimental data.

Findings

Wider inductor traces do not affect flux noise or dephasing time.

Increased inductance raises flux noise and qubit dephasing.

Flux noise spectrum agrees with theoretical models within 10%.

Abstract

We measure the dependence of qubit phase coherence and surface spin induced flux noise on inductor loop geometry. While wider inductor traces change neither the flux noise power spectrum nor the qubit dephasing time, increased inductance leads to a simultaneous increase in both. Using our protocol for measuring low frequency flux noise, we make a direct comparison between the flux noise spectrum and qubit phase decay, finding agreement within 10% of theory. The dependence of the measured flux noise on inductor geometry is consistent with a noise source correlation length between 6 and 400 um.