A QRD was designed to eliminate the background radiation as much as possible. It should contain two devices which would interconvert visible light to microwaves.
First the top converter couples two entangled beams, a microwave one (red wavy line) and a visible one (red straight line); then the microwave reflection is converted to visible light that interferes with the initial visible beam in the detector.
Quantum illumination is the term I believe to aid with sensing of weakly reflective targets when in a noisy background from visible light to microwaves.
Similar idea would be used in magnetic resonance for medical purposes.
At the core of it all is a so-called electro-optomechanical converter (microwaves <-> visible wavelengths). This device would consist of optical and microwave cavities for storing each kind of radiation, with a nanoscale vibrating object (such as a piezoelectric crystal or a metallic membrane) serving as the connection between the two. The oscillator can couple electromagnetic vibrations in the two cavities, despite their different frequencies.
This being said, I am not really an expert in the field of quantum entanglement so take my words with a grain of salt.
S. Lloyd “Enhanced Sensitivity of Photodetection via Quantum Illumination”
J. Bochmann, A. Vainsencher, D. D. Awschalom, and A. N. Cleland, “Nanomechanical Coupling between Microwave and Optical Photons”
R. W. Andrews, R. W. Peterson, T. P. Purdy, K. Cicak, R. W. Simmonds, C. A. Regal, and K. W. Lehnert, “Bidirectional and Efficient Conversion between Microwave and Optical Light”
EDIT: This is a simplified sketch. I do not know the math behind it but it shouldn't be anything spectacular.