Amplification of Quantum Entanglement

12 Hilbert space the quantum entanglement and superposition properties of the photon couples generated by parametric downconversion. The structure of the Wigner function and of the field’s correlation functions shows a decoherence-free multiphoton Schroedinger-cat behavior of the emitted field which is largely detectable against the squeezed-vacuum noise. [S0031-9007(98)07189-0]