# Vacuum-induced Autler-Townes splitting in a superconducting artificial atom

## TL;DR

This paper experimentally investigates vacuum-induced Autler-Townes splitting in a superconducting artificial atom, demonstrating control over microwave reflection spectra and the transition from quantum to classical regimes.

## Contribution

It reports the first observation of vacuum-induced Autler-Townes splitting in a superconducting atom and explores its tunability with resonator photons.

## Key findings

- Autler-Townes splitting observed in reflection spectrum.
- Transition from quantum to classical splitting regimes.
- Control of microwave reflection using single photons.

## Abstract

We experimentally study a vacuum-induced Autler-Townes doublet in a superconducting three-level artificial atom strongly coupled to a coplanar waveguide resonator and simultaneously to a transmission line. The Autler-Townes splitting is observed in the reflection spectrum from the three-level atom in a transition between the ground state and the second excited state when the transition between the two excited states is resonant with a resonator. By applying a driving field to the resonator, we observe a change in the regime of the Autler-Townes splitting from quantum (vacuum-induced) to classical (with many resonator photons). Furthermore, we show that the reflection of propagating microwaves in a transmission line could be controlled by different frequency single photons in a resonator.