Autler-Townes splitting in a three-dimensional transmon superconducting qubit

TL;DR

This paper reports the observation of Autler-Townes splitting in a superconducting transmon qubit within a 3D microwave cavity, demonstrating high-fidelity dark states and precise control of quantum states.

Contribution

It presents the first clear observation of Autler-Townes splitting in a 3D transmon qubit with detailed density matrix simulations and high-fidelity dark state preparation.

Findings

Autler-Townes splitting observed at low drive amplitudes.

High coherence time (~40 μs) enables precise spectroscopy.

Dark state fidelity estimated at 99.6-99.9%.

Abstract

We have observed the Autler-Townes doublet in a superconducting Al/AlOx/Al transmon qubit that acts as an artificial atom embedded in a three-dimensional Cu microwave cavity at a temperature of 22 mK. Using pulsed microwave spectroscopy, the three lowest transmon levels are isolated, eliminating unwanted effects of higher qubit modes and cavity modes. The long coherence time (~40 us) of the transmon enables us to observe a clear Autler-Townes splitting at drive amplitudes much smaller than the transmon level anharmonicity (177 MHz). Three-level density matrix simulations with no free parameters provide excellent fits to the data. At maximum separation, the fidelity of a dark state achieved in this experiment is estimated to be 99.6-99.9%.