Quantum information via novel measurements

The state projection associated with the familiar (von Neumann) measurement of an observable does not describe the most general means of interrogating a quantum system. Two problems requiring a more general description are the discrimination between non–orthogonal quantum states and the simultaneous measurement of incompatible observables. We discuss both of these problems within the context of measurements of optical polarization. We illustrate the technique of field measurement by projection synthesis by describing a possible means for determining the optical phase probability distribution.