Enhancing phase sensitivity by a nonlinear-feedback-assisted interferometer

Nonlinear feedback utilizing nonlinear elements usually provides better performance in preparation and manipulation of quantum states compared to linear feedback using linear elements. In this work, by employing nonlinear feedback, we propose a nonlinear-feedback-assisted interferometer for quantum metrology. We theoretically analyze the phase sensitivity via homodyne detection on both of output ports. It is found that this proposal can realize phase sensitivity enhancement by manipulating the nonlinear feedback strength. Furthermore, the phase sensitivity can saturate the classical and quantum Cramér-Rao bound, respectively. Moreover, we demonstrate that this proposal is superior to the linear-feedback-assisted interferometer.