Real-time detection of quasiparticle tunneling events using a transmon qubit directly coupled to a waveguide

Generation and tunneling of non-equilibrium quasiparticles (QPs) [1] due to the absorption of high energy radiation is known to have adverse effects on the performance of superconducting quantum devices [2]. In this study, we investigate the statistics of QP tunneling events in a charge sensitive transmon qubit, strongly coupled to a waveguide. A second charge-insensitive qubit, strongly coupled to the same waveguide, is used to measure the temperature of the radiation field at the resonant frequency of the qubit [3]. Using these two sensors, we study the thermalization timescale of the radiation field and the equilibration of QP tunneling rates after a sudden burst in temperature caused by toggling of a cryogenic mechanical switch. This multi-sensor detection technique offers a unique opportunity to investigate the effects of cryogenic filtering and thermalization strategies on thermal population and QP tunneling rates, paving the way for optimized performance in superconducting quantum devices.

1. Bogoliubov quasiparticles in superconducting qubits, SciPost Phys. Lect. Notes 31 (2021)

2. Environmental radiation impact on lifetimes and quasiparticle tunneling rates of fixed-frequency transmon qubits, Appl. Phys. Lett. 120, 074002 (2022)

3. Primary Thermometry of Propagating Microwaves in the Quantum Regime, Phys. Rev. X 10, 041054 (2020)