Driving-Induced Resonance Narrowing In A Strongly Coupled Cavity-Qubit System

We study a system consisting of a superconducting flux qubit strongly coupled to a microwave cavity. Externally applied qubit driving is employed in order to manipulate the spectrum of dressed states. We observe resonance narrowing in the region where the splitting between the two dressed fundamental resonances is tuned to zero. The narrowing in this region of overlapping resonances can be exploited for long-time storage of quantum states. In addition, we measure the response to strong cavity mode driving, and find a qualitative deviation between the experimental results and the predictions of a semiclassical model. On the other hand, good agreement is obtained using theoretical predictions obtained by numerically integrating the master equation governing the system's dynamics. The observed response demonstrates a process of a coherent cancellation of two metastable dressed states.