# Decoherence benchmarking of superconducting qubits

## TL;DR

This study benchmarks superconducting qubit decoherence over days, revealing fluctuations caused by two-level systems and capacitance noise, emphasizing the importance of regular calibration for reliable quantum computing.

## Contribution

It provides a detailed statistical analysis of qubit decoherence fluctuations and identifies the sources, such as TLS instabilities and capacitance noise, advancing understanding of qubit stability.

## Key findings

- Mean relaxation time T1 = 49 μs
- Dephasing time T2* = 95 μs
- TLS fluctuations impact qubit stability

## Abstract

We benchmark the decoherence of superconducting qubits to examine the temporal stability of energy-relaxation and dephasing. By collecting statistics during measurements spanning multiple days, we find the mean parameters $\overline{T_{1}}$ = 49 $\mu$s and $\overline{T_{2}^{*}}$ = 95 $\mu$s, however, both of these quantities fluctuate explaining the need for frequent re-calibration in qubit setups. Our main finding is that fluctuations in qubit relaxation are local to the qubit and are caused by instabilities of near-resonant two-level-systems (TLS). Through statistical analysis, we determine switching rates of these TLS and observe the coherent coupling between an individual TLS and a transmon qubit. Finally, we find evidence that the qubit's frequency stability is limited by capacitance noise. Importantly, this produces a 0.8 ms limit on the pure dephasing which we also observe. Collectively, these findings raise the need for performing qubit metrology to examine the reproducibility of qubit parameters, where these fluctuations could affect qubit gate fidelity.