Fidelity based unitary operation-induced quantum correlation for continuous-variable systems.

We propose a measure of nonclassical correlation $N_{\mathcal F}^{\mathcal G}$ in terms of local Gaussian unitary operations based on square of the fidelity $\mathcal F$ for bipartite continuous-variable systems. This quantity is easier to calculate or estimate and is a remedy for the local ancilla problem associated with the geometric measurement-induced nonlocality. A simple computation formula of $N_{\mathcal F}^{\mathcal G}$ for any $(1+1)$-mode Gaussian states is presented and an estimation of $N_{\mathcal F}^{\mathcal G}$ for any $(n+m)$-mode Gaussian states is given. For any $(1+1)$-mode Gaussian states, $N_{\mathcal F}^{\mathcal G}$ does not increase after performing a local Gaussian channel on the unmeasured subsystem. Comparing $N_{\mathcal F}^{\mathcal G}(\rho_{AB})$ in scale with other quantum correlations such as Gaussian geometric discord for two-mode symmetric squeezed thermal states reveals that $N_{\mathcal F}^{\mathcal G}$ is much better in detecting quantum correlations of Gaussian states.