Unified treatment of heterodyne detection: the Shapiro-Wagner and Caves frameworks
Giulio Landolfi, G. Ruggeri, Giulio Soliani
Abstract
A comparative study is performed of two heterodyne systems of photon detectors expressed in terms of a signal annihilation operator and an image band creation operator, called Shapiro-Wagner and Caves' frame, respectively. This approach is based on the introduction of a convenient operator $\\hat \\psi$ which allows a unified formulation of both cases. For the Shapiro-Wagner scheme, where $[\\hat \\psi, \\hat \\psi^{\\dag}] =0$, quantum phase and amplitude are exactly defined in the context of relative number state (RNS) representation, while a procedure is devised to handle suitably and in a consistent way Caves' framework, characterized by $[\\hat \\psi, \\hat \\psi^{\\dag}] \\neq 0$, within the approximate simultaneous measurements of noncommuting variables. In such a case RNS phase and amplitude make sense only approximately.