Theory of microwave single-photon detection using an impedance-matchedΛsystem

By properly driving a qubit-resonator system in the strong dispersive regime, we implement an ``impedance-matched'' Λ 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 Λ system and evaluate its performance as a detector. We achieve a high detection efficiency without relying on precise temporal control of the input pulse shape and under a conservative estimate of the system parameters. The detector can also be reset quickly by applying microwave pulses, which allows a short dead time and a high repetition rate.