  We present a scheme for photonic transistors based on photons and phonons in
a cavity electromechanical system, which is consisted of a superconducting
microwave cavity coupled to a nanomechanical resonator. Control of the
propagation of photons is achieved through the interaction of microwave field
(photons) and nanomechanical vibrations (phonons). By calculating the
transmission spectrum of the signal field, we show that the signal field can be
efficiently attenuated or amplified, depending on the power of a second
`gating'(pump) field. This scheme may be a promising candidate for
single-photon transistors and pave the way for numerous applications in
telecommunication and quantum information technologies.
