  In this article, the basic principle of target detection based on Gaussian
state quantum illumination (QI) has introduced. The performance of such system
has compared with its classical counterpart, which employs the most classical
state of light, i.e., coherent state, to illuminate the target region. By
deriving the maximum range equation, we have demonstrated that the quantum
illumination based target detection system is especially advantageous at low
transmission powers, which make these systems suitable for short range
applications like biomedical imaging or covert detection schemes.
