To take a (binary) decision you$rquot$d better use entanglement
G M D$rquot$Ariano, Matteo G. A. Paris, Paolo Perinotti · Journal of Optics B Quantum and Semiclassical Optics · 2002
We address two-mode quantum interferometry as binary measurements aimed at determining whether or not a phase perturbation has occurred. We show that optimized measurements achieve the best sensitivity when the input state is entangled . A concrete set-up based on parametric sources of entanglement and photodetection is also suggested and shown to approach ideal sensitivity.