Optical state measurement by information transfer

Mathematically, the simplest state of light containing phase information is a superposition of the vacuum and the one-photon state and, as we show in this paper, such a state is reasonably simple to measure. We investigate ho w the information contained in a more complicated pure state of light, in p articular the ratio of successive number-state coefficients, can be transfe rred selectively to fields in this two-state superposition for subsequent m easurement. By this means the number-state representation of the more compl icated state can be ascertained, provided there are no gaps in the number s tate distribution. We also discuss how to correct for the effect of non-uni t efficiencies of the photodetectors involved in the transferral process.