Speaker: Dr. Vincenzo Lordi, Lawrence Livermore Lab
Abstract: The practicality of superconducting qubits for scalable quantum computing applications is limited by decoherence noise that reduces the useful lifetime of the quantum states. While various theories explain possible mechanisms for the decoherence, the microscopic origins at the level of the materials comprising actual devices remain largely unknown. Such knowledge is essential to enabling rational improvement of fabrication processes for higher performing qubits. First-principles simulations at the atomic level provide a useful tool to probe the materials origins of decoherence. Here, we discuss recent work investigating magnetic fluctuators associated with materials defects that can contribute decoherence noise in these systems. In particular, native defects and adsorbates on the surface of sapphire and dangling bond defects on the surface of amorphous silica will be discussed. In addition, interactions among spins on surfaces can be important, and we present detailed calculations on the energetics of such interactions. We find that the spin-spin coupling strength can be strongly influenced by lattice strain and the presence of defects. Finally, an analysis of the correlations between local structural and electronic properties of amorphous materials will be presented in this context.