Enhancing Coherence Properties of Superconducting Quantum Circuits via Materials Engineering

The circuit quantum electrodyamics (cQED) platform is one of the leading hardware systems for universal quantum computation. Continual improvement of the coherence properties of these cQED devices are crucial for realizing a robust quantum processor. This relies heavily on careful material selection and optimisation [1, 2]. In a recent study, transmon qubits made with α-tantalum capacitor pads showed longer lifetimes compared to their all-aluminium counterparts [3, 4].<br/>Inspired by this finding, we study the effect of varying selected fabrication and geometrical parameters on the performance of planar tantalum resonators to better understand the reasons behind this improvement. We do in a frequency-multiplexed, seamless superconducting enclosure [5], which provides a effective testbed with good isolation from environment noise and high measurement throughput. This work will contribute to the development of compact high-quality resonators, which are key building blocks for realizing robust information encoding in multi-photon bosonic states.<br/>References<br/>[1] Kjaergaard, M., Schwartz, M. E., Braumüller, J., Krantz, P., Wang, J. I. J., Gustavsson, S., & Oliver, W. D. (2020). Superconducting qubits: Current state of play. Annual Review of Condensed Matter Physics, 11, 369-395.<br/>[2] McRae, C. R. H., Wang, H., Gao, J., Vissers, M. R., Brecht, T., Dunsworth, A., ... & Mutus, J. (2020). Materials loss measurements using superconducting microwave resonators. Review of Scientific Instruments, 91(9), 091101.<br/>[3] Place, A. P., Rodgers, L. V., Mundada, P., Smitham, B. M., Fitzpatrick, M., Leng, Z., ... & Houck, A. A. (2021). New material platform for superconducting transmon qubits with coherence times exceeding 0.3 milliseconds. Nature communications, 12(1), 1-6.<br/>[4] Wang, C., Li, X., Xu, H., Li, Z., Wang, J., Yang, Z., ... & Yu, H. (2021). Transmon qubit with relaxation time exceeding 0.5 milliseconds. arXiv preprint arXiv:2105.09890.<br/>[5] Axline, C., Reagor, M., Heeres, R., Reinhold, P., Wang, C., Shain, K., ... & Schoelkopf, R. J. (2016). An architecture for integrating planar and 3D cQED devices. Applied Physics Letters, 109(4), 042601.