Quantum coherence between cavity and artificial atom in a superconducting circuit QED ladder system

TL;DR

This paper demonstrates quantum coherence between a cavity and an artificial atom in a superconducting circuit QED system, observing Autler-Townes splitting and Rabi oscillations directly in the cavity spectrum.

Contribution

It introduces a three-level ladder system in circuit QED and directly observes quantum coherence effects through cavity spectrum analysis.

Findings

Observation of Autler-Townes splitting in cavity spectrum

Detection of quantum coherence Rabi oscillations

Clear doublet transmission and anomalous dispersion spectra

Abstract

We have created a quantum three-level ladder system with the cavity dispersive energy level in a superconducting circuit quantum electrodynamics system consisting of a transmon qubit and a cavity, and have directly observed the Autler-Townes splitting effect instead of representing it by the probability of the qubit being at each level. A coupler tone is applied on the transition between the second excited state of transmon and cavity dispersive level, while the cavity spectrum is probed. A doublet transmission and anormalous dispersion spectrum of the cavity level is clearly shown. The inverse Fourier transform of cavity spectrum indicates that there is a quantum coherence Rabi oscillation of the populations between cavity and qubit.