  In recent development of quantum technologies, a frequency conversion of
quantum signals has been studied widely. We investigate the optic-microwave
entanglement that is generated by applying an electro-optomechanical frequency
conversion scheme to one mode in an optical two-mode squeezed vacuum state. We
quantify entanglement of the converted two-mode Gaussian state, where surviving
entanglement of the state is analyzed with respect to the parameters of the
electro-optomechanical system. Furthermore, we show that there exists an upper
bound for the entanglement that survives after the conversion of highly
entangled optical states. Our study provides a theoretical platform for a
practical quantum illumination system.
