Process positive-operator-valued measure: A mathematical framework for the description of process tomography experiments

We introduce a mathematical framework for the description of measurements of quantum processes. Using this framework, process estimation problems can be treated in a similar way as state estimation problems, only replacing the concept of positive-operator-valued measure (POVM) by the concept of process POVM (PPOVM). In particular, we will show that any measurement of qudit channels can be described by a collection of effects (positive operators) defined on a two-qudit system. However, the effects forming a PPOVM are not normalized in the usual sense. We will demonstrate the use of this formalism in discrimination problems by showing that perfect channel discrimination is equivalent to a specific unambiguous state discrimination.