Disentangling the impact of quasiparticles and two-level systems on the statistics of superconducting-qubit lifetime

Abstract

Temporal fluctuations in the superconducting qubit lifetime, T1, present additional challenges in the pursuit of fault-tolerant quantum computing. Although the exact mechanisms remain unclear, T1 fluctuations are generally attributed to strong coupling between the qubit and a few near-resonant two-level systems (TLSs), which can exchange energy with an ensemble of thermally fluctuating two-level fluctuators (TLFs) at low frequencies. Here, we report T1 measurements of qubits with varying geometrical footprints and surface dielectrics as a function of temperature. By analyzing the noise spectrum of the qubit depolarization rate, Γ1=1/T1, we disentangle the contributions of TLSs, nonequilibrium quasiparticles (QPs), and equilibrium (thermally excited) QPs to the variance in Γ1. We find that the Γ1 variance in qubits with smaller footprints is more susceptible to QP and TLS fluctuations than that in larger-footprint qubits. Furthermore, the QP-induced variances in all qubits align with the theoretical framework of QP diffusion and fluctuation. These findings offer valuable insights for future qubit design and engineering optimization.

Source-reported materials — not catalogue approval

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