Resonance fluorescence readout of a superconducting qubit

In many atomic or color centers physics experiments the state of a (typically long-lived) qubit is measured by exciting a transition to a (typically short-lived) higher energy level and collecting the fluoresced photons. We adapted this scheme to the measurement of a qubit transition of a multi-level fluxonium artificial atom embedded in a waveguide. In this scheme the qubit transition must be tuned below the waveguide's cutoff while the readout transition must stay in the pass-band. We discuss how the proposed scheme can offer a measurement rate comparable to the ones obtained in conventional dispersive circuit QED experiments and present initial experimental results.