  By performing two local displacement operations (LDOs) inside an SU(1,1)
interferometer, called as the displacement-assisted SU(1,1) [DSU(1,1)], both
the phase sensitivity based on homodyne detection and quantum Fisher
information (QFI) with and without photon losses are investigated in this
paper. In this DSU(1,1) interferometer, we focus our attention on the extent to
which the introduced LDO affects the phase sensitivity and the QFI, even in the
realistic scenario. Our analyses show that the estimation performance of
DSU(1,1) interferometer is always better than that of SU(1,1) interferometer
without the LDO, especially the phase precision of the former in the ideal
scenario gradually approaching to the Heisenberg limit via the increase of the
LDO strength. More significantly, different from the latter, the robustness of
the former can be enhanced markedly by regulating and controlling the LDO. Our
findings would open an useful view for quantum-improved phase estimation of
optical interferometers.
