Phase-sensitive nonclassical properties in quantum metrology with a displaced squeezed vacuum state.

We predict that the phase-dependent error distribution of locally unentangled quantum states directly affects quantum parameter estimation accuracy. Therefore, we employ the displaced squeezed vacuum (DSV) state as a probe state and investigate an interesting question of the phase-sensitive nonclassical properties in DSV's metrology. We found that the accuracy limit of parameter estimation is a function of the phase-sensitive parameter $\phi -\theta /2$ with a period $\pi $. We show that when $\phi -\theta /2$ $\in \left[ k\pi/2,3k\pi /4\right) \left( k\in \mathbb{Z}\right)$, we can obtain the accuracy of parameter estimation approaching the ultimate quantum limit through using the DSV state with the larger displacement and squeezing strength, whereas $\phi -\theta /2$ $\in \left(3k\pi /4,k\pi \right] \left( k\in \mathbb{Z}\right) $, the optimal estimation accuracy can be acquired only when the DSV state degenerates to a squeezed-vacuum state.