Identifying and Engineering Two-Level Systems in Superconducting Qubits – Part I

Amorphous Al₂O₃ is a fundamental component of modern superconducting qubits. While amorphous oxides offer distinct advantages, such as directional isotropy and a consistent bulk electronic gap, in realistic systems these compounds support two-level systems (TLSs) which couple to the qubit, expediting decoherence. We perform a first-principles study of amorphous Al₂O₃ and identify low-energy modes in the electronic and vibrational spectra [1]. Analysis of these modes, including their spatial distribution and dipole moment, provides evidence for their role as TLSs. Potential strategies to mitigate the effect of TLSs on the qubit through use of Nb and Ta based oxides is discussed.