Investigation of microwave loss in oxide/superconductor heterostructures by in-situ oxide deposition

Yen-Hsun Glen Lin^1*, Kuan-Hui Lai¹, Lawrence Boyu Young¹, Wan-Sin Chen¹, Yen-Hsiang Lin², Jueinai Kwo², Minghwei Hong¹

¹Graduate Institute of Applied Physics and Department of Physics, National Taiwan University, Taipei, Taiwan
²Department of Physics, National Tsing Hua University, Hsinchu, Taiwan

* Presenter:Yen-Hsun Glen Lin, email:yhglenlin@phys.nthu.edu.tw

Two-level systems (TLS) hosted in defective dielectric layers are the major hurdle causing decoherence in superconducting quantum circuits. Aluminum (Al) is used in many superconducting qubits, and the TLS in Al₂O_3-x/Al heterostructure thus plays a critical role in the decoherence of the qubits.

In this work, we employed in-situ Al₂O₃ deposition approach to investigate the dielectric loss in the oxide/superconductor heterostructure. The superconducting Al films were grown by molecular beam epitaxy (MBE) in an ultra-high-vacuum multi-chamber growth-analysis system. The all-in-situ growth process enables us to monitor the quality of the oxide/superconductor interface during the heterostructure formation and to fully control the oxide quality and thickness. We characterized different Al₂O₃/Al heterostructures made by the in-situ oxide preparation method to investigate the microwave dielectric loss in superconducting states. We also demonstrated high internal quality factors over 1 million in these in-situ prepared oxide/superconductor heterostructures.

This work is supported by the National Science and Technology Council (NSTC), Taiwan, through grant numbers NSTC 112-2119-M-007-009- and 112-2811-M-007-066.

Keywords: in-situ, two-level systems, microwave, dielectric loss, superconducting films