From the point of view of the quantum network between superconducting quantum circuits, microwave-photon detection is a key technology.
However, single-photon detection in the microwave domain is still a challenging task because of the photon energy four to five orders of magnitude smaller than in optics.
Here, we implement a deterministic entangling gate between a superconducting qubit and a propagating microwave pulse mode reflected by a cavity containing the qubit. Using the entanglement and the qubit readout, we demonstrate a QND detection of a single microwave photon.