Quantum theory predicts that two indistinguishable photons incident on a beam-splitter interferometer exit together (the pair emerges randomly from one port or the other). We use a special photon-number-resolving energy detector for a direct observation of this quantum-interference phenomenon. Simultaneous measurements from two such detectors, one at each beam-splitter-interferometer output port, confirm the absence of cross coincidences. Photon-number-resolving detectors are expected to find use in other quantum-optics and quantum-information-processing experiments.
Eight-port homodyne detection may be used to perform a joint measurement on a single-mode input to a beam splitter; the x quadrature is measured at one output port, and the p quadrature is measured at the other. This is possible even when the input mode contains only one photon. We show to what extent this "joint measurement of a single photon" may be reconciled with the semiclassical notion that the photon may only exit from one of the beam splitter output ports.
Truncated output states can be generated by the conditional measurement if the coherent state and arbitrary Fock state are regarded as the input states of beam splitters.The properties of this kind of truncated optical states are studied in this paper.The results have shown that the output states in one out port have stronger nonclassical properties of squeeze and sub-Poissonian distribution when zero photon is measured in the other out port,and the nonclassical properties can become stronger with the increase of input number state.When m(m＞0) photon is measured in one of the out ports,each output state after conditional measurement has the same property in optical field but also exhibits apparent nonclassical effects such as squeezing and sub-Poissonian distribution.It should be noted particularly that the number state corresponding to the measurement in output state after conditional measurement would be truncated if the single number state is input.