Enhancement of quantum nondemolition measurements with an electro-optic feed-forward amplifier

Methods for the enhancement of optical quantum nondemolition (QND) measurem ents are discussed. We review the use of meter squeezing; as a QND enhancem ent tool and present a method of QND enhancement using an electro-optic fee d-forward amplifier. By applying a linearized theory it is shown that these techniques work very well together. The combined effect of these enhanceme nt methods is modeled for two QND systems, a squeezed light beam splitter a nd an optical parametric amplifier. We also discuss the conflict between th e normal QND criteria and QND systems that involve noiseless amplification. We use an additional parameter to quantify the problem. A method for corre cting the effects of noiseless amplification is discussed and modeled. We a lso discuss a special case of QND that eliminates the optical interaction b etween the meter and signal input beams. This system is shown to be a very effective QND device. [S1050-2947(99)06411-2].