Communication and measurement with squeezed states

The principles are elaborated which underlie the applications of general nonclassical states to communication and measurement systems. Relevant classical communication concepts are reviewed. Communication and measurement processes are compared. The possible advantages of nonclassical states in classical information transfer are assessed. The significance of novel quantum amplifiers and duplicators in communication is emphasized. A general approach is developed for determining the ultimate accuracy limit in quantum measurement systems. It is found that bandwidth or mode number is a most important parameter and ultrahigh precision measurement is possible in systems with a fixed energy but many modes. The problem of the standard quantum limit in monitoring the position of a free mass is also addressed.