Single-photon detection is a requisite technique in quantum-optics experiments in both the\noptical and the microwave domains. However, the energy of microwave quanta are four to five\norders of magnitude less than their optical counterpart, making the efficient detection of\nsingle microwave photons extremely challenging. Here we demonstrate the detection of a\nsingle microwave photon propagating through a waveguide. The detector is implemented\nwith an impedance-matched artificial L system comprising the dressed states of a driven\nsuperconducting qubit coupled to a microwave resonator. Each signal photon deterministically\ninduces a Raman transition in the L system and excites the qubit. The subsequent\ndispersive readout of the qubit produces a discrete ââ?¬Ë?clickââ?¬â?¢. We attain a high single-photondetection\nefficiency of 0.66Ã?±0.06 with a low dark-count probability of 0.014Ã?±0.001 and a\nreset time of B400 ns. This detector can be exploited for various applications in quantum\nsensing, quantum communication and quantum information processing.
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