Reshaping nonclassical properties and metrological performance of entangled coherent states via post-selected von Neumann measurements
In quantum metrology, measurements are usually treated as passive readout processes. Here we investigate whether post-selected von Neumann measurements (PVNMs) can be used as an active resource to reshape the nonclassical properties of a two-mode entangled coherent state (ECS). By analyzing the finite-coupling post-selected state, we show that PVNMs can enhance quadrature squeezing and sum squeezing, increase the Wigner-function negativity, and strengthen bipartite correlations, as witnessed by the Hillery-Zubairy criterion and linear entropy. We further evaluate the quantum Fisher information and the corresponding quantum Cramér-Rao bound for phase estimation, and discuss the trade-off between metrological gain and measurement-induced disturbance through the fidelity. Our scheme exhibits a phase-sensitivity advantage over standard ECS metrology for large average photon numbers. Our results suggest that PVNMs provide a tunable route for engineering nonclassical resources in continuous-variable sensing protocols.