QUANTUM PHASE SUPEROPERATOR

A unitary superoperator that represents a quantum phase is introduced by means of a density-matrix formalism of quantum mechanics. In this formalism, a quantum phase can be treated without using any of the additional techniques that are indispensable for defining a unitary phase operator when conventional phase operator methods are used. Furthermore, a phase-space distribution function for number and phase variables is introduced by means of the eigenoperator of the phase superoperator, and the basic properties of the distribution function are investigated. © 1995 The American Physical Society.