QUASI-CONTINUOUS MEASUREMENTS OF PHOTON NUMBER

A quasicontinuous measurement incorporating lossless beam splitters and photodetectors is proposed. Here the measurement by photodetectors is assumed to obey the projection postulate. The photon statistics in the output state of the signal mode of a beam splitter is investigated. It is shown that under certain conditions the measurement yields results equivalent to those obtained by the continuous measurement of photon number described by the quantum Markov process. Furthermore, measurements using a nondegenerate parametric amplifier and four-wave mixer, instead of beam splitter, are considered. The relations to the continuous measurement of photon number with a quantum counter and the continuous quantum nondemolition measurement of photon number are discussed.