Experimental progress towards a cryogenic phase-conjugate receiver for microwave quantum illumination

Quantum illumination is a remote detection technique that uses entangled radiation to realize a signal-to-noise ratio improvement compared to best classical methods. The proposed advantage only materializes for low signal photon numbers of << 1 per mode and for targets that are immersed in a bright background noise floor of >> 1 per mode. The latter is not naturally the case for optical detection and poses an outstanding challenge for practical microwave receivers that rely on Josephson junction circuits at cryogenic temperatures. We will discuss our experimental progress towards building a phase-conjugate receiver [1] in the microwave regime at mK temperatures. In the experiment, we use a Josephson parametric converter (JPC) as a source of entangled signal-idler pairs. The signal, after reflecting from a sensitive target, is fed into another JPC operated in phase-conjugation mode. The phase conjugated signal and the idler are then mixed in a beamsplitter. We analyze and benchmark the residual correlations that are required to see the expected error probability enhancement and investigate the noise power handling of the PC receiver which approaches room temperature values after suitable filtering.

[1] S. Guha, B. I. Erkmen, Gaussian-state quantum-illumination receivers for target detection, Phys. Rev. A 80, 052310 (2009).