Phase-sensitivity enhancement based on a four-beam nonlinear interferometer

We propose a different type of nonlinear interferometer, namely, four-beam nonlinear interferometer, which can realize phase-sensitivity enhancement. We compare the phase sensitivity of the four-beam nonlinear interferometer and the corresponding shot-noise limit. Our results demonstrate that the four-beam nonlinear interferometer can achieve a phase-sensitivity enhancement compared with the corresponding shot-noise limit. Moreover, taking the losses into consideration, the phase sensitivity of the four-beam nonlinear interferometer can also beat the corresponding shot-noise limit. Our scheme may find potential applications in multiparameter quantum metrology.