Entangled States in Interferometry

We show how some entangled quantum states can be used to improve interferometric measurements. We describe why Schrödinger-cat states are very sensitive to relative-phase shifts and why relative-phase states as described by A. Luis and L.L. Sánchez-Soto resolve the interval [0, 2π] well. We also describe how the quantum concept of well-defined relative-phase and the classical visibility of an interference pattern are related