Classicalization of Nonclassical Quantum States in Loss and Noise – Some No-Go Theoremes

The general problem of performance advantage obtainable by the use of nonclassical transmitted states over classical ones is considered. Attention is focused on the situation where system loss is significant and additive Gaussian noise may be present at the receiver. Under the assumption that the total received state is classical, rigorous output density operator representations and their trace distance bounds are developed for classical and nonclassical states. A practical No-Go theorem is enunciated for typical applications with high loss. The recent work on quantum illumination is discussed as an example of our no-go results.