High Quality Content by WIKIPEDIA articles! In functional analysis and quantum measurement theory, a positive-operator valued measure (POVM) is a measure whose elements are non-negative self-adjoint operators on a Hilbert space. It is the most general formulation of a measurement in the theory of quantum physics. The need for the POVM formalism arises from the fact that projective measurements on a larger system, described mathematically by a projection-valued measure (PVM), will act on a subsystem in ways that cannot be described by a PVM on the subsystem alone. They are used in the field of quantum information.