Flux Noise and Spin Dynamics of Multiple Interacting Adsorbates on Superconducting Qubits*

Molecular oxygen, OH groups, and atomic hydrogen surface adsorbates have been identified as possible sources of magnetic flux noise in superconducting qubits. This noise causes decoherence and frequency jitter that can hinder tunable multi-qubit devices. To better understand the spin dynamics of these fluctuating adsorbates we have extended our model for interacting adsorbed paramagnetic O₂ molecules to include other species adsorbed from the device operation atmosphere, including water at different coverages. We calculate the effects of applied fields on the phases of the spin system, its dynamics, and the charge and flux noise generated. To do this we utilize a thermodynamic ensemble generated with Monte Carlo simulations along with Landau-Lifshitz-Gilbert equation simulations for the dynamics, both parametrized with vdW-corrected density functional theory calculations.