OPERATIONAL THEORY OF HOMODYNE DETECTION

We discuss a balanced homodyne detection scheme with imperfect detecto rs in the framework of the operational approach to quantum measurement . We show that a realistic homodyne measurement is described by a fami ly of operational observables that depends on the experimental setup, rather than a single field quadrature operator. We find an explicit fo rm of this family, which fully characterizes the experimental device a nd is independent of a specific state of the measured system. We also, derive operational homodyne observables for the setup with a random p hase, which has been recently applied in an ultrafast measurement of t he photon statistics of a pulsed diode laser. The operational formulat ion directly gives the relation between the detected noise and the int rinsic quantum fluctuations of the measured field. We demonstrate this with two examples: the operational uncertainty relation for the field quadratures, and the homodyne detection of suppressed fluctuations in photon statistics.