Single-photon-driven high-order sideband transitions in an ultrastrongly coupled circuit quantum electrodynamics system

TL;DR

This paper reports the experimental observation of high-order sideband transitions driven by single photons in an ultrastrongly coupled circuit QED system, revealing new quantum phenomena and advancing understanding of ultrastrong light-matter interactions.

Contribution

First experimental demonstration of high-order sideband transitions at the single-photon level in an ultrastrongly coupled circuit QED system.

Findings

Observation of high-order red and blue sideband transitions

Coupling strength reaching 10% of the resonator frequency

Signatures mainly due to ultrastrong Rabi coupling

Abstract

We report the experimental observation of high-order sideband transitions at the single-photon level in a quantum circuit system of a flux qubit ultrastrongly coupled to a coplanar waveguide resonator. With the coupling strength reaching 10% of the resonator's fundamental frequency, we obtain clear signatures of higher-order red and first-order blue-sideband transitions, which are mainly due to the ultrastrong Rabi coupling. Our observation advances the understanding of ultrastrongly-coupled systems and paves the way to study high-order processes in the quantum Rabi model at the single-photon level.