Long-time-scale energy relaxation dynamics of tunable transmon qubits as a tool for loss metrology*

Superconducting qubits are one of the promising platforms demonstrating quantum speedupin terms of quantum computation. However, there are numerous loss factors acting on supercon-ducting qubits, and they pose a limitation on qubit coherence [1]. Fluctuations in qubit energyrelaxation time (T₁) over time and frequency can be used to discriminate between coherent two-level-system (TLS) defects and other loss mechanisms [2]. In this talk, I will illustrate the implementation of this method to improve cryogenic microwave metrology toward optimization of qubit performance. Here, I will focus on our implementation of a frequency-tunable transmon qubit as both a detector for TLS and a method to distinguish between loss mechanisms, and demonstrateits excellence on doing inter-laboratory comparisons, for example the SQMS Round Robin experiment. In addition, I will discuss calibration and measurement details, and include comparisons ofTLS dynamics and populations between subsequent cooldowns in my discussion.

[1] C. R. H. McRae et al., Review of Scientific Instruments, 91(9):091101, 2020.

[2] P. V. Klimov et al., Phys. Rev.Lett., 121:090502, Aug 2018.