EQUIVALENCE BETWEEN SQUEEZED-STATE AND TWIN-BEAM COMMUNICATION CHANNELS

We show the equivalence between two different communication schemes th at employ a couple of modes of the electromagnetic field. One scheme u ses unconventional heterodyne detection, with correlated signal and im age band modes in a twin-beam state from parametric downconversion. Th e other scheme is realized through a complex-number coding over quadra ture-squeezed states of two uncorrelated modes, each detected by ordin ary homodyning. This equivalence concerns all the stages of the commun ication channel: the encoded state, the optimal amplifier for the chan nel, the master equation modeling the loss, and the output measurement scheme. The unitary transformation that connects the two communicatio n schemes is realized by a frequency conversion device.