Second-order decoherence mechanisms of a transmon qubit probed with thermal microwave states

TL;DR

This paper investigates second-order decoherence mechanisms in superconducting transmon qubits using thermal microwave states, revealing insights into parasitic losses, temperature-dependent dephasing, and two-level state fluctuations.

Contribution

It provides experimental evidence for how thermal microwave states affect decoherence processes in transmon qubits, including parasitic losses and parameter fluctuations.

Findings

Resonator filter efficiency is quantified, revealing parasitic loss channels.

Dephasing rate exhibits a $T^{3}$ temperature dependence.

Two-level state fluctuations show a $T^{2}$ dependence under thermal microwave influence.

Abstract

Thermal microwave states are omnipresent noise sources in superconducting quantum circuits covering all relevant frequency regimes. We use them as a probe to identify three second-order decoherence mechanisms of a superconducting transmon. First, we quantify the efficiency of a resonator filter in the dispersive Jaynes-Cummings regime and find evidence for parasitic loss channels. Second, we probe second-order noise in the low-frequency regime and demonstrate the expected $T^{3}$ temperature dependence of the qubit dephasing rate. Finally, we show that qubit parameter fluctuations due to two-level states are enhanced under the influence of thermal microwave states. In particular, we experimentally confirm the $T^{2}$-dependence of the fluctuation spectrum expected for noninteracting two-level states.