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

Abstract 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.