TIME-RESOLVED QUANTUM MEASUREMENTS USING ACTIVE DETECTORS

Time-resolved quantum measurements using active detectors are analyzed . It is shown that the time-resolved observation of a quantum field le ads to a mode mismatch between observed field and detection device tha t unavoidably introduces vacuum modes into the measurement. When activ e detectors are used, this gives rise to considerable background noise . The same conclusion may be drawn when considering other highly resol ved quantum measurements of, e.g., energy, position, etc. Special emph asis is put on the analysis of time-resolved optical homodyne detectio n as an important example of an active detector. [S1050-2947(98)01002- 6].