Noise types in correlation-based target detection

Quantum illumination (QI) [1] is a general name for a class of target detection protocols, where an entangled state is used to illuminate a region of space where a reflecting target may be present. Storing part of the state and sending the other part to the target, QI can suppress the sources of uncorrelated noise by using the correlations in frequency, phase, and arrival time between the stored state and the target return state [2,3]. This alleviates the task of detecting a weakly reflecting target against a strong background [4]. After initial proposal based on the entangled photon pairs, QI has been extended [5] to the case of Gaussian states, which are easier to prepare and manipulate.