It is shown how the photon-number amplifier may be used to make, for either novel or conventional sources, an efficient direct-detection receiver and transceiver in a local-area network environment and how the parametric amplifier may be used similarly for a homodyne-detection receiver.
The number-phase squeezing mechanisms related to the multiphoton and photonfractioning 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 grouptheoretical states one has 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.
A self-homodyne detection scheme is proposed to perform two-mode tomography on a twin-beam state at the output of a nondegenerate optical parametric amplifier. This scheme has been devised to improve the matching between the local oscillator and the signal modes, which is the main limitation to the overall quantum efficiency in conventional homodyning. The feasibility of the measurement is analyzed on the basis of Monte Carlo simulations, studying the effect of nonunit quantum efficiency on detection of the correlation and the total photon-number oscillations of the twin-beam state.
A simple optical arrangement using polarization rotators and a single-pass parametric amplifier is being used to evade backaction noise in a measurement of a quadrature component of the light field.1 The transmitted field component is left in an eigenstate with an eigenvalue equal to the measured field value. The degree of precision for this eigenvalue can be made arbitrarily high as the optical losses are decreased and the parametric gain is increased. Measurement of the field is accomplished by a homodyne detection of a polarization component orthogonal to the incident and transmitted field. A pulse mode-locked Nd:YAG laser is used as a light source for the measured field and as a pump for the KTP parametric amplifier. If a direct detection measurement is made, instead of homodyne detection, the transmitted light is left in a state which has the properties of a Schrodinger cat,2 or more precisely, a Schrodinger kitten since the feasible experiments will only allow a small number of photons per cat. This catlike state can be transformed by a parametric amplifier into a state that is nearly the superposition of two coherent states. A homodyne measurement can demonstrate the quantum coherence of these two states.