Two-photon spectral coherence matrix and characterization of multi-parameter entangled states

In this Letter we discuss how the classical coherence matrix can be generalized to describe the quantum properties of broadband two-photon entangled states. Procedures for experimental evaluation of two-photon matrix elements have been outlined. We illustrate how this formalism can be used for characterization of multi-parameter optical entanglement and discuss its possible applications in quantum optical measurement and quantum coherent control. (C) 2008 Elsevier B.V. All rights reserved.