Theory of microwave single-photon detection using an impedance-matched $\Lambda$ system

Understand

By properly driving a qubit-resonator system in the strong dispersive regime, we implement an "impedance-matched" $\Lambda$ system in the dressed states, where a resonant single photon deterministically induces a Raman transition and excites the qubit.

• Combining this effect and a fast dispersive readout of the qubit, we realize a detector of itinerant microwave photons.
• We theoretically analyze the single-photon response of the $\Lambda$ system and evaluate its performance as a detector.
• We achieve a high detection efficiency close to unity without relying on precise temporal control of the input pulse shape and under a conservative estimate of the system parameters.