Single-Mode Phase-Conjugate Receiver for Microwave Quantum Illumination with a Lossy Optical Memory

Microwave quantum illumination with entangled pairs of microwave signal and optical idler modes can achieve sub-optimal performance with joint measurement of the signal and idler modes. Here, a testbed for microwave quantum illumination is proposed with an optical memory simulated with a delay line in the idler mode. It provides the amount of input two-mode squeezing necessary to compensate for the loss of optical memory while maintaining a quantum advantage over a coherent state. When the memory is lossy, the input two-mode squeezing has to be higher through high cooperativity in the optical mode. Under the testbed, a single-mode phase conjugate receiver is proposed consisting of a low-reflectivity beam splitter, an electro-optomechanical phase conjugator, and a photon number-resolving detector. The performance of the newly proposed receiver approaches the sub-optimal quantum advantage of 3 dB. Furthermore, the receiver achieves the quantum advantage even with an on-off detection while being robust against the loss of the memory.