AQP Seminar: Modeling and design of low-loss devices for circuit quantum electrodynamics

Abstract: 

Circuit quantum electrodynamics (cQED), utilizing superconducting microwave circuits, is a promising platform for realizing large-scale quantum computing and quantum technological applications in general. One of the major factors hindering the development of cQED-based quantum computers is the decoherence of the superconducting qubits arising from several sources of loss in the circuitry. In particular, dielectric losses due to two-level-system (TLS) defects occurring in the substrate and in the thin dielectric regions at the material interfaces of the devices potentially limit, e.g., the lifetimes of the qubits and quality factors of the employed coplanar-waveguide (CPW) resonators. These losses can be simulated utilizing finite-element modeling, but reliable extraction of the relevant material parameters required for accurate modeling is challenging, introducing uncertainty in the simulations.

In this talk, we discuss the effects of geometric properties and certain fabrication techniques of cQED devices on the TLS-related dielectric losses, utilizing finite-element simulations. Moreover, we study the measurement-based extraction of material parameters of the circuitry by nonlinear optimization, extending our recent work [1]. Finally, we look at some of the novel methods we are currently developing to address these issues.

References

[1] V Lahtinen and M Möttönen 2020 J. Phys.: Condens. Matter 32 405702