RQC Seminar

122nd RQC Seminar

  • Speaker

    Dr. Lara Faoro
    ( Google Quantum AI )

  • Date

    16:00-17:00, June 11, 2024 (Tuesday)

  • Venue

    Hybrid(ZOOM・ Wako C61 Welfare ＆ Conf. 2F Large Meeting Room）

  • Title

    Quasiparticles vs TLS

  • Inquiries

    rqc_info[at]ml.riken.jp

Abstract
In superconducting qubits, decoherence is mainly attributed to two interfaces: substrate-metal (SM) and metal-air (MA), each with distinct chemical properties. Both interfaces host two-level systems (TLS) that interact with quantum superconducting qubits, hindering their operation in certain frequency ranges. One significant challenge associated with TLS is their unpredictability. Gamma rays and cosmic rays impinging on the substrate generate high-energy electrons, holes, and phonons in the bulk, which can reach the SM interface and induce fluctuating fields, leading to shifts in TLS frequencies.
In this talk, I will focus on the theoretical framework of the microscopic phenomena in the environment of superconducting qubits. I will explore the strong correlation between quasiparticle poisoning and TLS instabilities. A key theoretical finding is that the formation of traps with long-lived quasiparticles is a natural occurrence in superconducting films. High-energy radiation provides a mechanism to generate the quasiparticles that fill these traps. This results both in an additional source of highly coherent TLS that pose a threat to qubits and an additional relaxation mechanism for conventional TLS.



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