ABSTRACT
This chapter presents a synopsis on nonclassical light, emphasizes the roles of different quantum amplifiers, and discusses the problem of overcoming the detrimental effect of loss. The generation of two-photon coherent state (TCS) and near-number state (NNS) via nonlinear optical processes are, in some sense, surprisingly similar. This similarity is in addition to that between TCS and number-phase minimum uncertainty states when the nonclassical effects are small. It seems to arise from an underlying intrinsic quantum correlation. Nonclassical light do not propagate well. This is because significant loss, be it radiative, absorption, or otherwise, is often incurred during propagation. Nonclassical light with matching detection leads to significant improvement in signal-to-noise (SNR) ratio. Even in situations where SNR is not the most appropriate performance measure, it is clear that the low noise characteristics of TCS and NNS, or simply their difference from classical states, could be useful.
