Microwave Photon-Number Amplification

We experimentally demonstrate a microwave photon-multiplication scheme which combines the advantages of a single-photon detector and a power meter by multiplying the incoming photon number by an integer factor. Our first experimental implementation achieves an n=3-fold multiplication with 0.69 efficiency in a 116 MHz bandwidth up to an input photon rate of 400 MHz. It loses phase information but does not require any dead time or time binning. We expect an optimized device cascading such multipliers to achieve number-resolving measurement of itinerant photons with low dark count, which would offer new possibilities in a wide range of quantum-sensing and quantum-computing applications.