Feedback-assisted homodyne detection of phase shifts

The problem of noise from external feedback control is addressed for homodyne detection of optical phase shifts. Two different schemes are analyzed: the conventional single-homodyne detection, and a two-quadrature scheme, which involves couples of independent measurements of two conjugated quadratures. The effectiveness of the feedback mechanism in both schemes is studied versus the feedback coupling parameter and high-sensitive detection regimes are discussed. The effect of nonunit quantum efficiency of photodetectors is also considered. It is shown that nonunit quantum efficiency affects phase sensitivity in the single-quadrature scheme to a larger extent than in the double-quadrature one.