Description:

The field of quantum computing has seen an explosion in research efforts and interest in both academia and industry within recent years. While there are several candidate platforms for quantum computing, superconducting circuits are one of the most promising platforms due to their scalability, design flexibility and stableness to the environment. However, single qubit coherence remains a major limiting factor in building scalable processors based on superconducting qubits. Recently, tantalum-based superconducting qubits have been discovered to enable long lifetimes and coherence times because of their chemical robustness and well-behaved surface oxide [1,2,3,4]. In this talk, I will first talk about our recent work to characterize the dominant sources of loss in state-of-the-art tantalum superconducting circuits. Using systematic measurements of tantalum resonators, we find the dominant source of loss at qubit operating conditions is from two-level systems (TLSs) present at material interfaces and surfaces, including TLSs residing in the amorphous native oxide layer [5,6]. In the second part, I will discuss our strategy for avoiding oxide formation by encapsulating the tantalum with noble metals that do not form native oxide. Microwave loss measurements of superconducting resonators reveal that the noble metal is proximitized, with a superconducting gap over 80% of the bare tantalum at thicknesses where the oxide is fully suppressed, suggesting it as a promising strategy for eliminating surface oxide TLS loss in superconducting qubits [7].

[1] Place, A. P. M. et al. Nat. Comm. 12, 1779 (2021).
[2] Wang, C. et al. npj Quantum Information 8, 3 (2022).
[3] Sivak, V. et al. Nature 616, 50–55 (2023).
[4] Ganjam, S. et al. Nat. Comm. 15, 3687 (2024).
[5] Crowley, K. D. et al., Phys. Rev. X 13, 041005 (2023).
[6] McLellan, R. A. et al. Advanced Science, 2300921 (2023).
[7] Chang, R. D.*, Shumiya, N.* et al. arXiv:2408.13051 (2024).

 Nana Shumiya, Postdoctoral Fellow, Princeton University

Host: Enectali Figueroa-Feliciano