Photon detectors are an elementary tool to measure electromagnetic waves atthe quantum limit and are heavily demanded in the emerging quantum technologiessuch as communication, sensing, and computing. Of particular interest is aquantum non-demolition (QND) type detector, which projects the quantum state ofa photonic mode onto the photon-number basis without affecting the temporal orspatial properties. This is in stark contrast to conventional photon detectorswhich absorb a photon to trigger a `click' and thus inevitably destroy thephoton. The long-sought QND detection of a flying photon was recentlydemonstrated in the optical domain using a single atom in a cavity. However,the counterpart for microwaves has been elusive despite the recent progress inmicrowave quantum optics using superconducting circuits. Here, we implement adeterministic entangling gate between a superconducting qubit and a propagatingmicrowave pulse mode reflected by a cavity containing the qubit. Using theentanglement and the high-fidelity qubit readout, we demonstrate a QNDdetection of a single photon with the quantum efficiency of 0.84, the photonsurvival probability of 0.87, and the dark-count probability of 0.0147. Ourscheme can be a building block for quantum networks connecting distant qubitmodules as well as a microwave photon counting device for multiple-photonsignals.
展开▼
