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Keith Ray1 Nicholas Materise1 Jonathan Dubois1 Vincenzo Lordi1

1, Lawrence Livermore National Laboratory, Livermore, California, United States

Superconducting qubits experience decoherence from noise and loss due to the emergent many-body dynamics of surface adsorbates, defects, and impurities. In particular, paramagnetic spins may couple to superconducting loops and resonators through a magnetic field or dielectric response. Paramagnetic spins may reside in Al2O3 surface adsorbed O2 molecules [Phys. Rev. Applied 6, 041001 (2016)], atomic hydrogen [Phys. Rev. Lett. 118, 057703 (2017)], or OH groups [PRL 112, 017001 (2014)]. The magnetic and dielectric properties of such microscopic degrees of freedom will ultimately depend on the materials and local binding geometry dependent interactions between paramagnetic spins. We present results based on density functional theory calculations of the spin anisotropy and interactions of a system of O2 molecules on Al2O3. In this system, the interactions are found to be either ferromagnetic and antiferromagnetic depending on relative O2 orientation. Monte Carlo and Landau-Lifshitz-Gilbert equation simulations parametrized with first principles calculated quantities are employed to describe the emergent behavior of the spin system and how it interacts with the qubit. This is accomplished by integration of the results characterizing the phase diagram of the system, spin vortices, spin-spin correlations, and 1/wα flux noise into macroscopic qubit device models.

*Prepared by LLNL under Contract DE-AC52-07NA27344

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