Squeezed states in direct and coherent detection

Abstract

With reference to squeezed states, we analyse the noise performances of the basic detection schemes in fibre telecommunications and interferometry. We have developed a semiclassical approach that allows us to translate the quantum mechanical formalism into synthetic expressions and rules only involving directly measurable physical quantities. As a result, we find that in the telecommunication field squeezed states do not allow significant improvements in system performances: in practice, the signal-to-noise ratio cannot be increased in standard detection schemes, both direct and coherent, by squeezing either the signal (because of propagation losses) or by the local oscillator. On the contrary, a significant improvement can be obtained in interferometric measurements if squeezed vacuum is coupled into the normally unused beamsplitter port.