NUMBER-PHASE SQUEEZED STATES AND PHOTON FRACTIONING

The number-phase squeezing mechanisms related to the multiphoton and photon-fractioning procedures are analyzed. The main ingredients in these approaches are nonlinear multimode realizations of group-theoretical states and nonunitary subdynamics of the field modes. The states which are squeezed in the number of photons are suited to optical communications in local area networks; the states squeezed in the phase of the field optimize high-sensitive interferometry. Corresponding to the different kinds of squeezing and to the pertaining group-theoretical states one bas different types of amplifying devices with the same dynamical group of the states. In particular, two recently proposed devices - the photon-number amplifier (PNA) and the photon-number duplicator (PND) - attain both the multiphoton and photon-fractioning transformations. The PNA amplifies the field without degrading the direct-detection signal-to-noise ratio and thus can be used to produce number-squeezed states; the PND provides two copies of the same input number-state and, therefore, can connect two-mode states with one-mode states. Both the PNA and PND allow the realization of virtually lossless optical taps, which are essential in designing highly transparent local area networks. The PND can also be used in series with a conventional phase-insensitive amplifier to produce phase-squeezed states.