Phase estimation of phase shifts in two arms for an SU(1,1) interferometer with coherent and squeezed vacuum states

We theoretically study the quantum Fisher information (QFI) of the SU(1,1) interferometer with phase shifts in two arms by coherent ⊗squeezed vacuum state input, and give the comparison with the result of phase shift only in one arm. Different from the traditional MachZehnder interferometer, the QFI of single-arm case for an SU(1,1) interferometer can be slightly higher or lower than that of two-arm case, which depends on the intensities of the two arms of the interferometer. For coherent ⊗ squeezed vacuum state input with a fixed mean photon number, the optimal sensitivity is achieved with a squeezed vacuum input in one mode and the vacuum input in the other.