Evolution of $1/f$ Flux Noise in Superconducting Qubits with Weak Magnetic Fields

• DOI: 10.48550/arxiv.2301.07804
• Publication Date: 2023-01-01
• Authors: David A. Rower; Lamia Ateshian; Lauren H. Li; Max Hays; Dolev Bluvstein; Leon Ding; Bharath Kannan; Aziza Almanakly; Jochen Braumüller; David Kim; Alexander Melville; Bethany M. Niedzi...; Mollie E. Schwartz; Jonilyn Yoder; Terry P. Orlando; Joel I-Jan Wang; Simon Gustavsson; Jeffrey A. Grover; Kyle Serniak; Riccardo Comin; William D. Oliver
• Keywords: Dephasing; Flux qubit

The microscopic origin of $1/f$ magnetic flux noise in superconducting circuits has remained an open question for several decades despite extensive experimental and theoretical investigation. Recent progress devices quantum information highlighted the need to mitigate sources qubit decoherence, driving a renewed interest understanding underlying mechanism(s). Though consensus emerged attributing surface spins, their identity interaction mechanisms remain unclear, prompting further study. Here we apply weak in-plane fields capacitively-shunted (where Zeeman splitting spins lies below device temperature) study flux-noise-limited dephasing, revealing previously unexplored trends that may shed light on dynamics behind emergent noise. Notably, observe enhancement (suppression) spin-echo (Ramsey) pure dephasing time up $B=100~\text{G}$. With direct spectroscopy, transition from approximately Lorentzian frequency dependence 10 Hz reduction above 1 MHz with increasing field. We suggest these are qualitatively consistent increase spin cluster sizes These results should help inform complete theory circuits.