<title>Application of quantum nondemolition measurement in quantum optical communication</title>

Abstract

In this paper, the method will be introduced, it's called Quantum Nondemolition measurement. The purpose is to realize a new measuring method to surpass quantum limit. It provides a new mithod of overcoming quantum noise. In principle, it can use any precision to detect a certain weak signal. Finally. the application of QND Measurement in optical communication will be introduced. Keywords: quantum limit, measurment, quantum optical communication 1. QUANTUM NONDEMOLITON MEASUREMENT 1.1 Basic concept Quantum Nondemolition Measurement (QND) was first suggested by the former Russian V.B.Braginsky et a11'1H.At the time they wanted to explore the weak gravity wave in the astrophysics. The gravity wave is rather weak, even lower than standard quantum fluctuation noise and the aim of QND is to overcome the noise, surpass the quantum limitation to reach the ultrahigh accuracy which the classical measurement method can not arrive at.The well-known uncertainty relation shows two non-corresponding relations between the conjugate mechanics and heavy quantum fluctuation. For example, [x, p} = i, then xp h,where AA = {<A > _ <> 2} 1/2 , If we me a precise measurement on one of them (such as measurement of to to make Lr smaller), the fluctuatuon of another (such as p) mechanics quantity will become larger. In most cases, the fluctuation of latter mechanics quantity wifi couple back through certain procedure in the evolution of the system to make the previous fluctuation of the system to make the previous fluctuation of the former mechanics quantity become larger and the fluctuation is random and Supported by Heilongjiang Natural Science Fund O-8194-2294-O/96/$6.OO SPIE Vol. 2893 /557 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/15/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx