FEEDBACK-ASSISTED HOMODYNE DETECTION OF PHASE-SHIFTS

The problem of noise from external feedback control is addressed for h omodyne detection of optical phase shifts. Two different schemes are a nalyzed: the conventional single-homodyne detection, and a two-quadrat ure 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 hi gh-sensitive detection regimes are discussed. The effect of nonunit qu antum efficiency of photodetectors is also considered. It is shown tha t nonunit quantum efficiency affects phase sensitivity in the single-q uadrature scheme to a larger extent than in the double-quadrature one.