  While detection of optical photons is today achieved with very high
efficiencies, the detection of microwave fields at the photon level still poses
non-trivial experimental challenges. In this Letter we propose a model of
microwave photodetector which is based on the use of an electro-opto-mechanical
system. Using state of the art technology, we show how single microwave photons
can efficiently be converted into optical photons which are then measured by
standard optics. The overall quantum efficiency of our microwave detector tends
to one for achievable values of the optical and microwave cooperativity
parameters. Our scheme could be used for sensing and scanning very faint
microwave fields, as they may occur in radio astronomy, satellite and deep
space communications.
